Preparation method of bimetallic phosphide / hollow carbon sphere composite material for sodium-ion battery, preparation method of negative electrode for sodium-ion battery and sodium-ion battery
By preparing bimetallic phosphide/hollow carbon sphere composite materials, the problems of low capacity, poor kinetic performance and insufficient cycle stability of sodium-ion battery anode materials have been solved, achieving efficient charge transfer and structural stability under extreme operating conditions, thus promoting the commercialization of sodium-ion batteries.
Patent Information
- Application Number
- CN202511776744.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-03-03
AI Technical Summary
Existing sodium-ion battery anode materials suffer from low capacity, poor kinetic performance, and insufficient cycle stability. In particular, their performance degrades significantly under extreme conditions, and traditional improvement strategies cannot simultaneously address the issues of optimizing electronic conductivity and mitigating volume expansion.
Hollow carbon spheres were synthesized using a silica template method and coated with bimetallic oxides via a sol-gel method. Subsequently, they were subjected to high-temperature phosphating under an argon atmosphere to prepare a bimetallic phosphide/hollow carbon sphere composite material. This heterojunction structure was constructed to optimize the electronic structure and reduce the diffusion resistance of sodium ions.
It significantly improves the capacity and stability of sodium-ion batteries, especially exhibiting excellent electrochemical performance at high and low temperatures and high current densities, making it suitable for scenarios with stringent energy density and cycle life requirements, and reducing dependence on scarce lithium resources.
Smart Images
Figure CN121591179A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sodium-ion battery anode materials, specifically to a method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries, a method for preparing a negative electrode for sodium-ion batteries, and a sodium-ion battery. Background Technology
[0002] Driven by global energy transition and sustainable development, sodium-ion batteries, due to their abundant sodium resources and low cost, have become a key alternative to lithium-ion batteries in low-to-medium energy storage applications, showing great potential in portable electronic devices, smart grid peak shaving, and large-scale energy storage power stations. However, the commercialization of sodium-ion batteries is constrained by the performance of anode materials. Existing anode materials generally suffer from low capacity, poor kinetic performance, and insufficient cycle stability, especially under extreme conditions such as ultra-low temperatures and ultra-high current densities, where performance degradation is more significant.
[0003] Traditional carbon-based anodes (such as hard carbon) have low sodium storage capacity (typically less than 300 mAh g⁻¹). -1 The high capacity of tin-based and metal-compound-based anodes makes them difficult to match with high-capacity cathodes. While metal alloy-based and metal compound-based anodes have high theoretical capacities, their poor conductivity and severe volume expansion during charge and discharge (e.g., tin-based materials have a volume expansion rate exceeding 300%) lead to a sharp decline in cycle stability. Transition metal phosphides (such as CoP and Mn2P) are considered highly promising anode materials for sodium-ion batteries due to their high sodium storage capacity caused by multi-electron redox reactions. However, single-component transition metal phosphides suffer from low electronic conductivity (typically less than 10). -5 S cm -1 Its inherent defects, such as significant volume expansion (e.g., CoP expands by about 200% during sodiumification), limit its practical application.
[0004] Existing improvement strategies such as carbon coating and nanostructuring have made some progress, but still have shortcomings: single-metal phosphides cannot simultaneously solve the problems of optimizing electronic conductivity and mitigating volume expansion; the interfacial bonding between the carbon matrix and the active component is weak, and interfacial delamination easily occurs after long-term cycling, leading to performance degradation. Therefore, developing a sodium-ion battery anode material that combines high capacity, fast kinetics, and long-term cycling stability is of great significance.
[0005] In view of this, the inventor of this case conducted in-depth research, which led to the creation of this case. Summary of the Invention
[0006] The purpose of this invention is to provide a method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries, and to use the prepared bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries in the preparation of sodium-ion battery anodes and sodium-ion batteries. This method can reduce the diffusion resistance of sodium ions and accelerate charge transfer, thus solving the problems of insufficient cycle stability, poor kinetic performance, and weak adaptability to extreme conditions (high and low temperatures, high current) of existing sodium-ion battery anode materials (carbon-based materials have low sodium storage capacity, single metal phosphides have poor conductivity and significant volume expansion during sodiumification).
[0007] To achieve the above objectives, the solution of the present invention is: A method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries includes the following steps: Step 1, Preprocessing: Hollow carbon spheres were first synthesized using a silica template method, and then washed and dried sequentially. Step 2: Preparation of hollow carbon spheres coated with bimetallic oxides: Then, 0.3-0.5 g of pretreated hollow carbon spheres were dispersed in 30 mL of anhydrous ethanol and sonicated for 30 min until homogeneous to obtain a mixed solution of hollow carbon spheres. Then, manganese chloride tetrahydrate, cobalt nitrate hexahydrate and dopamine hydrochloride were weighed and dissolved in 30 mL of deionized water. The mixed solution of hollow carbon spheres was then added and stirred until completely dissolved. The pH was adjusted to 10 and stirred in a constant temperature water bath at 60℃ for 2 h. 0.2-0.3 g of ethylene glycol was added and stirring was continued until a viscous carbon sphere-bimetallic sol was formed. Then, the sol was vacuum dried at 60℃ for 24-28 h. Step 3: Preparation of bimetallic phosphide / hollow carbon sphere composite material: Finally, carbon spheres, bimetallic sol, and red phosphorus were placed in an argon atmosphere at a mass ratio of 1:3 for high-temperature phosphating treatment at 550~600 ℃ for 2~3 h. After cooling to room temperature, bimetallic phosphide / hollow carbon sphere composite material was obtained.
[0008] In step 1, the process of synthesizing hollow carbon spheres using the silica template method is as follows: 0.5 g of glucose powder is added to 50 mL of deionized water, sonicated for 30 min, then 0.1 g of SiO2 is added and sonicated for another 10 min. The sonicated solution is then poured into the lining of a 200 mL hydrothermal reactor and hydrothermally heated at 180 °C for 6 h. The resulting material is then placed in a forced-air drying oven and dried at 60 °C. The ceramic boat containing the sample is then placed in a tube furnace and subjected to high-temperature carbonization treatment under an argon atmosphere at 1000-1100 °C for 2-3 h. After cooling to room temperature, powder is obtained. The powder is then poured into 50 mL of 1 M NaOH solution, heated to 50 °C while stirring, and soaked for 6-8 h. The silica template is then removed to obtain hollow carbon spheres (denoted as HG).
[0009] In step 1, the heating rate of the high-temperature carbonization treatment is 3~5℃ / min.
[0010] In step 1, the cleaning process is as follows: the obtained hollow carbon spheres are sequentially immersed in deionized water and anhydrous ethanol for washing, and centrifuged and filtered at least twice using a centrifuge.
[0011] In step 1, the drying process is as follows: the cleaned hollow carbon balls are dried at 60°C for 12 hours.
[0012] In step 2, the mass ratio of manganese chloride tetrahydrate, cobalt nitrate hexahydrate, dopamine hydrochloride, and hollow carbon spheres is 8~10:8~10:3:1.
[0013] In step 3, the heating rate of the high-temperature phosphating treatment is 3~5℃ / min.
[0014] A method for preparing a negative electrode for sodium-ion batteries involves mixing the bimetallic phosphide / hollow carbon sphere composite material, a conductive agent, and a binder in a specific ratio to form a slurry. The slurry is then uniformly coated onto a copper foil and dried overnight to obtain the negative electrode for sodium-ion batteries.
[0015] The mass ratio of the bimetallic phosphide / hollow carbon sphere composite material, the conductive agent, and the binder is 6~8:3~1:1.
[0016] A sodium-ion battery includes a working electrode, a counter electrode, a separator, and an electrolyte. The working electrode is a negative electrode for sodium-ion batteries, the counter electrode is a sodium sheet, the separator is a glass fiber separator, and the electrolyte is sodium hexafluorophosphate electrolyte.
[0017] With the above technical solution, the present invention provides a method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries, and the synthesis schematic diagram is shown below. Figure 1As shown, hollow carbon spheres are first synthesized using a silica template method. Then, the carbon spheres are uniformly coated with manganese and cobalt sources using a sol-gel method. Finally, bimetallic phosphides (CoP and Mn2P) are synthesized and coated onto the hollow carbon spheres using a phosphating process. Simultaneously, dopamine hydrochloride molecules are added to introduce nitrogen to enhance reactive sites. This method can improve the low capacity problem of traditional carbon-based anodes due to limited sodium storage sites. By constructing a bimetallic phosphide heterojunction hollow carbon sphere composite material structure, the battery electrode process kinetics can be altered, and the electronic structure of the material can be optimized, reducing sodium ion diffusion resistance and accelerating charge transfer. This solves the problems of slow sodium ion diffusion and poor kinetic performance in electrode materials, as well as rapid capacity decay and short lifespan during sodium-ion battery cycling. When this bimetallic phosphide / hollow carbon sphere composite material is used as the anode electrode in sodium-ion batteries, the battery exhibits good stability and low resistance during charge and discharge, significantly improving the capacity of sodium-ion batteries.
[0018] Furthermore, the raw materials used in this invention are inexpensive, the formula is simple and easy to operate, which is conducive to mass production; and the composite material can be widely used in the anode of sodium-ion batteries, especially suitable for scenarios with stringent requirements for energy density and cycle life, such as integrated wind, solar and energy storage power stations and electric ships, which helps the commercialization of sodium-ion batteries, reduces dependence on scarce lithium resources, and has significant economic value and environmental benefits. Attached Figure Description
[0019] Figure 1 This is a schematic diagram illustrating the synthesis of a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries according to the present invention.
[0020] Figure 2 SEM image of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1; Figure 3 The image shows the EDS (energy dispersive spectroscopy) diagram of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1. Figure 4 The images are TEM images of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1, where (a) is a TEM image and (b) is an HRTEM image. Figure 5 The XRD pattern of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1; Figure 6 XPS images of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1 are shown, where (a) is the Co 2p spectrum, (b) is the Mn 2p spectrum, (c) is the P 2p spectrum, and (d) is the N 1s spectrum. Figure 7The charge-discharge curves of the DHC-CoP / Mn2P@HG anode material at a current density of 0.1 A / g are shown. Figure 8 Rate curves of DHC-CoP / Mn2P@HG anode material, DHC-CoP@HG anode material and DHC-Mn2P@HG anode material at different current densities at room temperature; Figure 9 The impedance test curves of DHC-CoP / Mn2P@HG anode material, DHC-CoP@HG anode material and DHC-Mn2P@HG anode material at different current densities at room temperature are shown. Figure 10 Long-cycle curves of DHC-CoP / Mn2P@HG anode materials, DHC-CoP@HG anode materials, and DHC-Mn2P@HG anode materials after 200 cycles at a current density of 1 A / g; Figure 11 The long-cycle curve of DHC-CoP / Mn2P@Ge anode material after 200 cycles at a current density of 1 A / g; Figure 12 The images show SEM images of the materials after long cycling, where (a) is the DHC-CoP / Mn2P@HG anode material, (b) is the DHC-CoP / Mn2P@Ge anode material, (c) is the DHC-CoP@HG anode material, and (d) is the DHC-Mn2P@HG anode material. Figure 13 Schematic diagram of the protection mechanism of bimetallic phosphide / hollow carbon sphere composite material, cobalt phosphide / hollow carbon sphere composite material, manganese phosphide / hollow carbon sphere composite material and bimetallic phosphide / carbon sphere composite material; Figure 14 The graphs show the charge-discharge performance of DHC-CoP / Mn2P@HG anode materials, DHC-CoP@HG anode materials, and DHC-Mn2P@HG anode materials at -30℃, where (a) is the rate performance graph and (b) is the long-cycle performance graph at a current density of 1A / g. Figure 15 The graphs show the charge-discharge performance of DHC-CoP / Mn2P@HG anode materials, DHC-CoP@HG anode materials, and DHC-Mn2P@HG anode materials at a high temperature of 50℃, where (a) is the rate performance graph and (b) is the long-cycle graph at a current density of 1A / g. Detailed Implementation
[0021] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.
[0022] I. Material Preparation Example 1 A method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries includes the following steps: Step 1, Preprocessing: First, 0.5 g of glucose powder was added to 50 mL of deionized water and sonicated for 30 min. Then, 0.1 g of SiO2 with a particle size of 20-40 nm was added and sonicated for another 10 min. The sonicated solution was then poured into the lining of a 200 mL hydrothermal reactor and hydrothermally heated at 180 °C for 6 h. The resulting material was then placed in a forced-air drying oven and dried at 60 °C. The ceramic boat containing the sample was then placed in a tube furnace and subjected to high-temperature carbonization under an argon atmosphere. The temperature was increased to 1000 °C at a rate of 3 °C / min and held for 2 h. After cooling to room temperature, powder was obtained. The powder was then poured into 50 mL of 1 M NaOH solution and heated to 50 °C while stirring. The mixture was soaked for 6 h to remove the silica template and obtain hollow carbon spheres. The hollow carbon spheres were then washed by soaking in deionized water and anhydrous ethanol, and centrifuged and filtered at least twice. Finally, the washed hollow carbon spheres were dried in a forced-air drying oven at 60 °C for 12 h. Step 2: Preparation of hollow carbon spheres coated with bimetallic oxides: Then, 0.3 g of pretreated hollow carbon spheres were dispersed in 30 mL of anhydrous ethanol and sonicated for 30 min until homogeneous to obtain a mixed solution of hollow carbon spheres. Then, 2.4 g of manganese chloride tetrahydrate, 2.4 g of cobalt nitrate hexahydrate and 0.9 g of dopamine hydrochloride were weighed and dissolved in 30 mL of deionized water. The mixed solution of hollow carbon spheres was then added and stirred until completely dissolved. The pH was adjusted to 10 and stirred in a constant temperature water bath at 60 °C for 2 h. 0.2 g of ethylene glycol was added and stirring was continued until a viscous carbon sphere-bimetallic sol was formed. Then, the sol was vacuum dried at 60 °C for 24 h. Step 3: Preparation of bimetallic phosphide / hollow carbon sphere composite material: Finally, carbon spheres-bimetallic sol and red phosphorus were placed in an argon atmosphere for high-temperature phosphating treatment at a mass ratio of 1:3. The temperature was increased to 550 °C at a rate of 3 °C / min, held for 2 h, and then cooled to room temperature to obtain a bimetallic phosphide / hollow carbon sphere composite material.
[0023] Example 2 A method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries includes the following steps: Step 1, Preprocessing: First, 0.5 g of glucose powder was added to 50 mL of deionized water and sonicated for 30 min. Then, 0.1 g of SiO2 with a particle size of 20-40 nm was added and sonicated for another 10 min. The sonicated solution was then poured into the lining of a 200 mL hydrothermal reactor and hydrothermally heated at 180 °C for 6 h. The resulting material was then placed in a forced-air drying oven and dried at 60 °C. The ceramic boat containing the sample was then placed in a tube furnace and subjected to high-temperature carbonization under an argon atmosphere. The temperature was increased to 1100 °C at a rate of 5 °C / min and held for 3 h. After cooling to room temperature, powder was obtained. The powder was then poured into 50 mL of 1 M NaOH solution and heated to 50 °C while stirring. The mixture was soaked for 8 h to remove the silica template and obtain hollow carbon spheres. The hollow carbon spheres were then washed by soaking in deionized water and anhydrous ethanol, and centrifuged and filtered at least twice. Finally, the washed hollow carbon spheres were dried in a forced-air drying oven at 60 °C for 12 h. Step 2: Preparation of hollow carbon spheres coated with bimetallic oxides: Then, 0.3 g of pretreated hollow carbon spheres were dispersed in 30 mL of anhydrous ethanol and sonicated for 30 min until homogeneous to obtain a mixed solution of hollow carbon spheres. Then, 3.0 g of manganese chloride tetrahydrate, 3.0 g of cobalt nitrate hexahydrate and 0.9 g of dopamine hydrochloride were weighed and dissolved in 30 mL of deionized water. The mixed solution of hollow carbon spheres was then added and stirred until completely dissolved. The pH was adjusted to 10 and stirred in a constant temperature water bath at 60 °C for 2 h. 0.3 g of ethylene glycol was added and stirring was continued until a viscous carbon sphere-bimetallic sol was formed. Then, the sol was vacuum dried at 60 °C for 28 h. Step 3: Preparation of bimetallic phosphide / hollow carbon sphere composite material: Finally, carbon spheres-bimetallic sol and red phosphorus were placed in an argon atmosphere for high-temperature phosphating treatment at a mass ratio of 1:3. The temperature was increased to 600 °C at a rate of 5 °C / min, held for 3 h, and then cooled to room temperature to obtain a bimetallic phosphide / hollow carbon sphere composite material.
[0024] Comparative Example 1 Unlike Example 1, in step 2, cobalt nitrate hexahydrate is not added, and the final product is a manganese phosphide / hollow carbon sphere composite material.
[0025] Comparative Example 2 Unlike Example 1, manganese chloride tetrahydrate was not added in step 2, and the final product was a cobalt phosphide / hollow carbon sphere composite material.
[0026] Comparative Example 3 Unlike embodiment 1, in step 1, NaOH solution is not added to remove the silica template, resulting in solid hard carbon spheres, and finally, a bimetallic phosphide / carbon sphere composite material is obtained.
[0027] II. Application of Materials Application Example 1 The bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1, the conductive agent Super P (conductive carbon black), and the binder PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 6:3:1 to form a slurry. The slurry was then uniformly coated onto a copper foil and dried overnight at 60°C to obtain a negative electrode for sodium-ion batteries, denoted as DHC-CoP / Mn2P@HG negative electrode material.
[0028] Application Example 2 The manganese phosphide / hollow carbon sphere composite material prepared in Comparative Example 1, the conductive agent Super P (conductive carbon black), and the binder PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 6:3:1 to form a slurry. The slurry was then uniformly coated onto copper foil and dried overnight at 60°C to obtain a negative electrode for sodium-ion batteries, denoted as DHC-Mn2P@HG negative electrode material.
[0029] Application Example 3 The cobalt phosphide / hollow carbon sphere composite material prepared in Comparative Example 2, the conductive agent Super P (conductive carbon black), and the binder PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 6:3:1 to form a slurry. The slurry was then uniformly coated onto copper foil and dried overnight at 60°C to obtain a negative electrode for sodium-ion batteries, denoted as DHC-CoP@HG negative electrode material.
[0030] Application Example 4 The bimetallic phosphide / hollow carbon sphere composite material prepared in Comparative Example 3, the conductive agent Super P (conductive carbon black), and the binder PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 6:3:1 to form a slurry. The slurry was then uniformly coated onto copper foil and dried overnight at 60°C to obtain a negative electrode for sodium-ion batteries, denoted as DHC-CoP / Mn2P@Ge negative electrode material.
[0031] Application Example 5 A 2016 coin cell sodium-ion half-cell was assembled using a sodium-ion battery negative electrode (DHC-CoP / Mn2P@HG negative electrode material, DHC-Mn2P@HG negative electrode material or DHC-CoP@HG negative electrode material) as the working electrode, a sodium sheet as the counter electrode, a glass fiber membrane as the separator, and sodium hexafluorophosphate electrolyte.
[0032] III. Material Characterization and Analysis 1. Figure 2The image shows a SEM image of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1. It indicates that the composite material has a uniform spherical structure with relatively uniform sphere size. This morphology is beneficial to increasing the contact area between the composite material and the electrolyte, which may increase the number of reactive sites during sodium ion storage.
[0033] 2. Figure 3 The image shows the EDS diagram of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1. Preliminary analysis indicates that the material contains carbon (C), cobalt (Co), phosphorus (P), and manganese (Mn), and the elements are relatively uniformly distributed. This preliminarily indicates that the bimetallic phosphides (CoP, Mn2P) are successfully and uniformly coated on the hollow carbon spheres. The uniform distribution of elements helps the material achieve a more stable and efficient electrochemical reaction during sodium ion storage, reducing problems such as excessive or insufficient local reactions caused by uneven element distribution. Combined with the uniform spherical morphology, this provides a good structural basis for the composite material to serve as a negative electrode for sodium-ion batteries in terms of electrochemical performance.
[0034] 3. Figure 4 The image shows a TEM image of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1, indicating that the composite material has a hollow structure. Figure 4 (b) also shows two continuous lattice fringes with different orientations, corresponding to lattice spacings of 0.172 nm and 0.249 nm, respectively, which correspond to CoP and Mn2P, further confirming the synthesis of bimetallic phosphides.
[0035] 4. Figure 5 The image shows the XRD pattern of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1. The figure displays the characteristic peaks of the CoP standard XRD pattern (ICDD#29-0497) and the Mn2P standard XRD pattern (ICDD#02-1027), indicating the successful preparation of the bimetallic phosphide. This is also consistent with... Figure 4 The HRTEM image in (b) corresponds to this.
[0036] 5. Figure 6 The image shows the XPS plot of the bimetallic phosphide / hollow carbon sphere composite material prepared in Example 1. Figure 6 (a) shows the fitted Co 2p spectrum of DHC-CoP / Mn2P@HG. Figure 6 The Co 2p spectrum in (a) contains two sets of spin-orbit double peaks and two distinct satellite peaks, located at 802.8 eV (Co 2p). 1 / 2 ) and 786.5 eV (Co 2p 3 / 2The two sets of spin orbital bimodals are located at 797.0 eV / 781.5 eV and 798.8 eV / 783.2 eV, respectively, corresponding to Co. 2+ With Co 3+ Co 2p 1 / 2 Co 2p 3 / 2 The characteristic peaks indicate that CoP has undergone partial oxidation, and at the same time confirm the existence of Co-P bonds, further confirming the successful preparation of the CoP phase. Figure 6 (b) The Mn 2p spectrum exhibits typical Mn 2p characteristics. 3 / 2 With Mn2p 1 / 2 The main peaks are located at 641.8 eV and 653.5 eV, respectively, and a distinct satellite peak appears on the high binding energy side of the main peak. The electronic configuration is completely consistent with that of the Mn2P standard spectrum, proving that the Mn2P phase has been successfully grown on the hard carbon surface. Figure 6 (c) The P 2p spectrum exhibits two sets of double peaks due to spin orbital splitting, with the peak at 129.5 eV (P 2p) being the most significant. 3 / 2 ) and 130.3 eV (P 2p 1 / 2 The P in CoP and Mn2P corresponds to... 2- The characteristic peak at 133.8 eV corresponds to a PC bond, indicating a chemical bonding between phosphorus and the carbon matrix. This interfacial bonding effectively enhances the bonding strength between the heterojunction and the carbon matrix, inhibiting the aggregation and shedding of active materials during charging and discharging. Figure 6 (d) N The 1S spectrum can be separated into pyridine. N (398.6 eV), pyrrole N (400.1 eV) and graphite N (401.0 eV) Three characteristic peaks, of which pyridine N With pyrrole N Graphite can enhance the electrochemical adsorption performance of materials by binding metal ions through coordination. N This can significantly improve the conductivity of the carbon matrix, and the three factors work synergistically to optimize the electrochemical performance of the composite material.
[0037] IV. Material Performance Testing 1. A 2016 coin-type sodium-ion half-cell was assembled using DHC-CoP / Mn2P@HG anode material as the working electrode. Charge-discharge tests were conducted, with a test voltage window of 0.01~3 V and a test current of 0.1 mA / g. Figure 7The charge-discharge curves of the DHC-CoP / Mn2P@HG anode material at a current density of 0.1 A / g show that the charge-discharge curves remain consistent, indicating that the DHC-CoP / Mn2P@HG anode material has good electrochemical reversibility.
[0038] 2. Using DHC-CoP / Mn2P@HG, DHC-Mn2P@HG, and DHC-CoP@HG anode materials as working electrodes, respectively, 2016 coin-type sodium-ion half-cells were assembled and subjected to charge-discharge tests. The test voltage window was 0.01~3V, and the test currents were 0.1A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, 5 A / g, and 10 A / g, respectively. Finally, the current was restored to 0.1 A / g, and the rate performance and electrochemical resistance of the battery were tested.
[0039] Figure 8 The figure shows the rate performance curves of DHC-CoP / Mn2P@HG anode materials at different current densities at room temperature. It can be seen that the DHC-CoP / Mn2P@HG anode material exhibits excellent rate performance at all current densities, which is better than the other two anode materials. At 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 and 10 A / g, the discharge capacities are 474.5, 426.3, 402.6, 375.8, 289.3 and 264.7 mAh / g, respectively. In addition, the specific capacity can be restored to 472.8 mAh / g after decreasing from 10 A / g to 5 A / g, 2 A / g, 1 A / g and 0.1 A / g.
[0040] Figure 9 The impedance test curves of DHC-CoP / Mn2P@HG anode materials at different current densities at room temperature are shown. It can be seen that the DHC-CoP / Mn2P@HG anode material has the lowest interfacial impedance, indicating the successful construction of a bimetallic phosphide heterojunction interface. This further activates the ion channels and heterojunction interface, significantly reducing the interfacial impedance and accelerating the Na+ ionization process. + The diffusion rate.
[0041] 3. Using DHC-CoP / Mn2P@HG, DHC-Mn2P@HG, DHC-CoP@HG, and DHC-CoP / Mn2P@Ge anode materials as working electrodes, 2016 coin-type sodium-ion half-cells were assembled and electrochemical tests were performed. The test voltage window was 0.01~3 V, the test current was 1 A / g, and the cycle was 200 times. After the test, the battery was removed, the internal electrodes were taken out, cleaned several times with ethanol, dried, and then characterized by SEM.
[0042] Figure 10 The long-cycle curves of DHC-CoP / Mn2P@HG anode materials, DHC-CoP@HG anode materials, and DHC-Mn2P@HG anode materials after 200 cycles at a current density of 1 A / g are shown. Figure 11 The image shows the long-cycle curve of the DHC-CoP / Mn2P@Ge anode material after 200 cycles at a current density of 1 A / g. Figure 12 This is the SEM morphology of the material after the corresponding cycle. For example... Figure 12 As shown in (a), no obvious cracks were observed in DHC-CoP / Mn2P@HG; in contrast, Figure 12 (c) DHC-CoP@HG and Figure 12 (d) DHC-Mn2P@HG exhibits relatively obvious cracks. This phenomenon is mainly attributed to the heterojunction formed by CoP and Mn2P—this structure can effectively disperse the stress caused by volume expansion. Without the bimetallic heterostructure, the electrode structures of DHC-CoP@HG and DHC-Mn2P@HG would be rapidly damaged due to severe volume expansion, leading to a significant reduction in cycle life. However, DHC-CoP / Mn2P@HG, with its bimetallic heterostructure, can effectively mitigate the structural damage caused by volume expansion, which is one of the reasons for its stable current output and suppressed rapid capacity decay.
[0043] To further verify the supporting role of hollow carbon spheres (HG) in improving material stability, this study also characterized the morphology of the DHC-CoP / Mn2P@Ge anode material after 200 cycles at a current density of 1 A / g using SEM. Figure 12 (b) Compared to DHC-CoP@HG and DHC-Mn2P@HG, DHC-CoP / Mn2P@Ge exhibits slightly less cracking. Nevertheless, at a current density of 1 A / g, the specific capacity of the DHC-CoP / Mn2P@Ge anode material begins to show an unstable decrease after 150 cycles. This result indicates that hollow carbon spheres provide superior protection, ensuring the electrode maintains structural integrity during charge and discharge, thereby significantly improving the material's cycle stability. The mechanism described above is as follows: Figure 13 As shown.
[0044] 4. Using DHC-CoP / Mn2P@HG, DHC-Mn2P@HG, and DHC-CoP@HG anode materials as working electrodes, respectively, 2016 coin-type sodium-ion half-cells were assembled. Electrochemical tests were conducted at -30℃, with a test voltage window of 0.01~3 V. The test currents were 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, 5 A / g, and 10 A / g, respectively. Finally, the current was restored to 0.1 A / g. The rate performance and long-cycle performance at a test current of 1 A / g were then tested.
[0045] Figure 14 (a) shows the rate performance test results of DHC-CoP / Mn2P@HG anode material, DHC-CoP@HG anode material and DHC-Mn2P@HG anode material at -30℃. At a current density of 0.1 A / g, the specific capacity of DHC-CoP / Mn2P@HG is about 440 mAh / g. Even when the current density is increased to 10 A / g, it can still maintain a certain capacity. However, the capacity of the two single metal materials drops sharply after the current density exceeds 2 A / g, and the performance deteriorates severely at high rates. This indicates that the heterojunction structure helps to alleviate the inhibition of ion transport at low temperature, so that the material has good capacity retention ability over a wide current range.
[0046] Figure 14 (b) shows the long-term cycling performance of DHC-CoP / Mn2P@HG anode material, DHC-CoP@HG anode material and DHC-Mn2P@HG anode material at -30℃ and a current density of 1 A / g. DHC-CoP / Mn2P@HG maintains stable capacity after 300 cycles, with an initial capacity of about 310 mAh / g and still reaching 300 mAh / g after cycling, with a capacity retention of 96%. In contrast, the initial capacity of DHC-CoP@HG anode material and DHC-Mn2P@HG anode material is lower and decays rapidly after multiple cycles. This indicates that the multi-level structure of the DHC-CoP / Mn2P@HG anode material can effectively buffer volume changes and maintain the integrity of the electrode structure at low temperatures.
[0047] 5. Using DHC-CoP / Mn2P@HG, DHC-Mn2P@HG, and DHC-CoP@HG anode materials as working electrodes, respectively, 2016 coin-type sodium-ion half-cells were assembled. Electrochemical tests were conducted at 50℃ with a test voltage window of 0.01~3 V and test currents of 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, 5 A / g, and 10 A / g, respectively. Finally, the current was restored to 0.1 A / g. The rate performance and long-cycle performance at a test current of 1 A / g were then tested.
[0048] Figure 15 (a) shows the rate performance test results of DHC-CoP / Mn2P@HG anode material, DHC-CoP@HG anode material and DHC-Mn2P@HG anode material at 50℃. As the current density gradually increases from 0.1 A / g to 10 A / g, the specific capacity of DHC-CoP / Mn2P@HG decreases the least, reaching close to 550 mAh / g at 0.1 A / g, and still maintains a high capacity even at a high rate of 10 A / g. The capacity decay of DHC-CoP@HG and DHC-Mn2P@HG is more significant, especially in the high current range above 5 A / g. Their performance is significantly worse than that of the bimetallic composite material. This indicates that the heterojunction structure helps to improve the rate stability of the material at 50℃ and the capacity retention ability at high current density, and significantly optimizes the electrochemical performance of the material. Figure 15 (b) Comparison of the long-cycle performance of DHC-CoP / Mn2P@HG anode materials at a high temperature of 50℃ and a current density of 1A / g. The specific capacity of DHC-CoP / Mn2P@HG is consistently higher than that of DHC-CoP@HG and DHC-Mn2P@HG, and its capacity decay is minimal after 500 cycles, demonstrating excellent cycle stability. In contrast, the two single-metal phosphide composite materials have lower initial capacities and show significant capacity decay during cycling, especially in the later stages. The results indicate that the synergistic effect of the CoP / Mn2P heterostructure and the hollow hard carbon spheres (HG) effectively suppresses the volume expansion and active material shedding at high temperatures, thereby improving structural stability.
[0049] The above embodiments and figures are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.
Claims
1. A method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries, characterized in that: Includes the following steps: Step 1, Preprocessing: Hollow carbon spheres were first synthesized using a silica template method, and then washed and dried sequentially. Step 2: Preparation of hollow carbon spheres coated with bimetallic oxides: Then, 0.3-0.5 g of pretreated hollow carbon spheres were dispersed in 30 mL of anhydrous ethanol and sonicated for 30 min until homogeneous to obtain a mixed solution of hollow carbon spheres. Then, manganese chloride tetrahydrate, cobalt nitrate hexahydrate and dopamine hydrochloride were weighed and dissolved in 30 mL of deionized water. The mixed solution of hollow carbon spheres was then added and stirred until completely dissolved. The pH was adjusted to 10 and stirred in a constant temperature water bath at 60℃ for 2 h. 0.2-0.3 g of ethylene glycol was added and stirring was continued until a viscous carbon sphere-bimetallic sol was formed. Then, the sol was vacuum dried at 60℃ for 24-28 h. Step 3: Preparation of bimetallic phosphide / hollow carbon sphere composite material: Finally, carbon spheres, bimetallic sol, and red phosphorus were placed in an argon atmosphere at a mass ratio of 1:3 for high-temperature phosphating treatment at 550~600 ℃ for 2~3 h. After cooling to room temperature, bimetallic phosphide / hollow carbon sphere composite material was obtained.
2. The method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries according to claim 1, characterized in that: In step 1, the process of synthesizing hollow carbon spheres using the silica template method is as follows: 0.5 g of glucose powder is added to 50 mL of deionized water, and sonicated for 30 min. Then, 0.1 g of SiO2 is added and sonicated for another 10 min. The sonicated solution is then poured into the lining of a 200 mL hydrothermal reactor and hydrothermally heated at 180°C for 6 h. The resulting material is then placed in a forced-air drying oven and dried at 60°C. The ceramic boat containing the sample is then placed in a tube furnace and subjected to high-temperature carbonization treatment under an argon atmosphere at 1000-1100°C for 2-3 h. After cooling to room temperature, powder is obtained. The powder is then poured into a 1 M NaOH solution and heated to 50°C while stirring. The solution is soaked for 6-8 h to remove the silica template and obtain hollow carbon spheres.
3. The method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries according to claim 2, characterized in that: In step 1, the heating rate of the high-temperature carbonization treatment is 3~5℃ / min.
4. The method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries according to claim 1, characterized in that: In step 1, the cleaning process is as follows: the obtained hollow carbon spheres are sequentially immersed in deionized water and anhydrous ethanol for washing, and centrifuged and filtered at least twice using a centrifuge.
5. The method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries according to claim 1, characterized in that: In step 1, the drying process is as follows: the cleaned hollow carbon balls are dried at 60°C for 12 hours.
6. The method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries according to claim 1, characterized in that: In step 2, the mass ratio of manganese chloride tetrahydrate, cobalt nitrate hexahydrate, dopamine hydrochloride, and hollow carbon spheres is 8~10:8~10:3:
1.
7. The method for preparing a bimetallic phosphide / hollow carbon sphere composite material for sodium-ion batteries according to claim 1, characterized in that: In step 3, the heating rate of the high-temperature phosphating treatment is 3~5℃ / min.
8. A method for preparing a negative electrode for a sodium-ion battery, characterized in that: The process involves preparing a slurry by mixing the bimetallic phosphide / hollow carbon sphere composite material as described in claim 1, a conductive agent, and a binder in a specific ratio. The prepared slurry is then uniformly coated onto a copper foil and dried overnight to obtain the negative electrode for the sodium-ion battery.
9. The method for preparing a negative electrode for a sodium-ion battery according to claim 8, characterized in that: The mass ratio of the bimetallic phosphide / hollow carbon sphere composite material, the conductive agent, and the binder is 6~8:3~1:
1.
10. A sodium-ion battery, comprising a working electrode, a counter electrode, a separator, and an electrolyte, characterized in that: The working electrode is the negative electrode for a sodium-ion battery as described in claim 8, the counter electrode is a sodium sheet, the separator is a glass fiber separator, and the electrolyte is sodium hexafluorophosphate electrolyte.