Gradient carbon layer coated bismuth-antimony bimetallic nanosphere composite material, preparation method thereof, sodium ion battery and application

Abstract

The invention belongs to the technical field of sodium ion battery materials, and particularly relates to a gradient carbon layer coated bismuth-antimony bimetallic nanosphere composite material, a preparation method thereof, a sodium ion battery and application. According to the invention, the two metals bismuth and antimony are combined, the advantages of the two metals are combined, and the two metals are synergetic. The composite material is obtained through carbonization treatment after synthesis by a sol-gel method. Meanwhile, when the carbon-coated bismuth-antimony bimetallic material is used as a sodium ion battery negative electrode, excellent electrochemical performance, such as excellent cycle performance and rate capability, is obtained. And in the aspect of cycle performance, under the current density of 0.5 A g <-1 >, the material is circulated for 1600 times, and the material has 264.83 mAh g <-1 >. And in terms of rate performance, even under the current density of 2A g <-1 >, the battery can work normally, and the sodium storage capacity of about 347mAh g <-1 > can be obtained. Therefore, the prepared carbon-coated bismuth-antimony bimetallic negative electrode material Bi < 0.6 > Sb < 0.4 > atC is excellent in performance and has important application in sodium ion batteries.

Description

Technical Field

[0001] The present application relates to the field of battery material technology, and more specifically, to a gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material and a preparation method thereof, a sodium ion battery and its application. Background Art

[0002] Increasing global warming and environmental pollution have attracted worldwide attention to explore eco-friendly renewable energy to replace traditional fossil fuels. With the rise of the new energy industry and the increasing demand for energy transformation, rechargeable batteries, as a key energy storage technology, have ushered in huge development opportunities.

[0003] Lithium-ion batteries (LIBs) have gradually occupied the electrochemical energy storage market in recent years due to their high energy density and long cycle life. However, the limited reserves of lithium salts in the earth's crust and the uneven distribution of resources have hindered the widespread application of lithium-ion batteries. Therefore, researchers have turned their attention to exploring new energy storage technologies that can replace lithium-ion batteries. Na and Li belong to the same main group and have similar electrochemical properties. In addition, the abundant reserves of sodium resources on the earth and the low production cost make sodium-ion batteries an ideal substitute for lithium-ion batteries.

[0004] However, the radius of sodium ions (0.102nm) is much larger than that of lithium ions (0.076nm), resulting in slower diffusion kinetics in electrode materials, especially in positive electrode materials. The embedding and de-embedding process of sodium ions easily causes expansion and contraction of the material structure, leading to capacity decay. In addition, the cycle life of sodium-ion batteries also faces challenges, especially under high-rate charge and discharge conditions, where the phase change and side reactions of electrode materials are accelerated, causing rapid degradation of battery performance. For example, the capacity retention rate of some layered oxide positive electrode materials may be less than 80% after hundreds of cycles, which limits their application in scenarios requiring long life.

[0005] Application Contents

[0006] In order to overcome at least one problem existing in the prior art, the primary purpose of the present application is to provide a gradient carbon layer coated bismuth antimony bimetallic nanosphere composite material.

[0007] The second objective of the present application is to provide a method for preparing the above-mentioned gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material.

[0008] The third purpose of the present application is to provide an application of the above-mentioned gradient carbon layer coated bismuth antimony bimetallic nanosphere composite material. The gradient carbon layer coated bismuth antimony bimetallic nanosphere composite material of the present application exhibits good electrochemical performance after being applied in sodium ion batteries, and has the advantages of high safety, good interface compatibility, and excellent cycle stability.

[0009] To achieve the above object, the present application provides the following solutions:

[0010] The present application provides a gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material, comprising:

[0011] The inner core is a bismuth-antimony alloy nanosphere, and the molar ratio thereof is Bi:Sb = 0.5 to 0.7:0.3 to 0.5;

[0012] The outer layer is a gradient carbon layer, which is successively an amorphous carbon layer (thickness 5 to 15 nm) and a graphitized carbon layer (thickness 10 to 30 nm) from the inside to the outside, and the ID / IG ratio of the graphitized carbon layer in the Raman spectrum is less than that of the amorphous carbon layer.

[0013] More preferably, the particle size of the above bismuth-antimony alloy nanosphere is 50 to 200 nm, and the surface has a porous structure (pore diameter 2 to 10 nm).

[0014] The present application also provides a preparation method of the gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material, comprising the following steps:

[0015] S1. Dissolve polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) to form a homogeneous solution;

[0016] S2. Add bismuth nitrate pentahydrate and antimony trichloride, stir and then ultrasonically disperse to form a sol;

[0017] S3. Convert the sol into precursor microspheres by spray drying;

[0018] S4. Under an argon atmosphere, perform two-stage carbonization treatment: the first stage is to keep the temperature at 300 to 500 °C for 1 h to generate an amorphous carbon layer; the second stage is to keep the temperature at 700 to 900 °C for 2 h to generate a graphitized carbon layer.

[0019] A further technical solution of the present application: In step S2, the molar ratio of bismuth nitrate pentahydrate to antimony trichloride is 3:2, and the mass ratio of PVP to the metal salt is 1:1 to 1:3.

[0020] The present application also provides a negative electrode material for a sodium ion battery, and the negative electrode material for a sodium ion battery comprises the composite material described in claim 1 (70 to 90 wt%); a conductive agent (5 to 15 wt%), selected from carbon nanotubes or graphene, and a binder (5 to 15 wt%), selected from sodium alginate or polyvinylidene fluoride (PVDF).

[0021] A further technical solution of the present application: The tap density of the above negative electrode material is 1.5 to 2.0 g / cm 3 , and the surface is coated with an in-situ generated SEI film enhancement layer.

[0022] The present application also provides a sodium-ion battery, which includes a positive electrode, a separator, an electrolyte, and the above-mentioned negative electrode sheet, and the electrolyte is a 1.5 mol / L NaPF ethylene carbonate / fluoroethylene carbonate (EC:FEC = 7:3) solution; the separator is a ceramic-coated polypropylene / polyethylene three-layer composite film.

[0023] A further technical solution of the present application: the positive electrode is sodium vanadium phosphate (Na3V2(PO4)3), and the capacity ratio of the positive electrode to the negative electrode is 1.1 to 1.3:1.

[0024] The present application also provides a fast charging method for a sodium-ion battery. Using the above battery, the charging current density is 2 to 5C, and dendritic growth is suppressed by pulse voltage control during the charging process.

[0025] Finally, the present application also provides the application of the above composite material in an energy storage system or an electric vehicle, and the cycle life of the battery pack is ≥1600 times (capacity retention rate ≥50%).

[0026] Compared with the prior art, the beneficial effects of the present application are:

[0027] The bismuth-antimony bimetal prepared in the present application is coated with a carbon layer. Among them, bismuth and antimony are used as active components for storing sodium ions, so that the carbon-coated bismuth-antimony bimetal negative electrode material has a high capacity. The surface-coated carbon layer can not only promote electron transport and ion diffusion, but also buffer the volume strain of metallic bismuth during charge and discharge. Thanks to the synergistic effect of the two, the prepared carbon-coated bismuth-antimony bimetal exhibits high specific capacity, excellent rate performance and cycle stability when used as the negative electrode of a sodium-ion battery. Description of the Drawings

[0028] Figure 1 TEM image of the Bi 0.6 Sb 0.4 @C negative electrode material prepared in the present application.

[0029] Figure 2 SEM and EDS elemental energy spectrum of the Bi 0.6 Sb 0.4 @C negative electrode material prepared in the present application.

[0030] Figure 3 XRD pattern of the Bi 0.6 Sb 0.4 @C negative electrode material prepared in the present application.

[0031] Figure 4 Raman spectrum of the Bi 0.6 Sb 0.4 @C negative electrode material prepared in the present application

[0032] Figure 5 The Bi 0.6 Sb 0.4 @C anode material prepared for this application at a current density of 0.5 A g -1 cycling performance.

[0033] Figure 6 The Bi 0.6 Sb 0.4 @C anode material prepared for this application at a current density of 0.5 A g -1 charge-discharge curve graph.

[0034] Figure 7 The Bi 0.6 Sb 0.4 @C anode material as the rate performance graph of the sodium-ion battery anode. Detailed implementation manners

[0035] The implementation schemes of this application will be described in detail below in combination with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate this application and should not be regarded as limiting the scope of this application. For those not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0036] It should be noted that:

[0037] In this application, if there is no special instruction, all the implementation manners and preferred implementation methods mentioned in this article can be combined with each other to form a new technical solution.

[0038] In this application, unless otherwise specified, each reaction or operation step can be carried out in sequence or in reverse order. Preferably, the reaction methods in this article are carried out in sequence.

[0039] Unless otherwise specified, the professional and scientific terms used in this article have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the recorded content can also be applied to this application.

[0040] Term explanation

[0041] Bi: (bismuth) bismuth;

[0042] Sb: (antimony) antimony;

[0043] SEM: scanning electron microscope;

[0044] TEM: transmission electron microscope;

[0045] AFM: atomic force microscope;

[0046] The applicant has found in the research that the application of bismuth element in the electrode materials of sodium-ion batteries exhibits significant advantages in many aspects, making it a very promising anode material. Bismuth has a relatively high theoretical capacity, about 385 mAh / g, which is significantly higher than that of traditional carbon-based materials, and can effectively improve the energy density of sodium-ion batteries to meet the high-energy storage requirements. Secondly, the redox potential of bismuth is moderate, usually in the range of 0.5 - 0.8 V (versus Na / Na + +), this potential range not only avoids the formation of sodium dendrites and improves the safety of the battery, but also ensures a relatively high output voltage, which is beneficial to the efficient operation of the battery. In addition, the volume expansion of bismuth during charge and discharge is relatively small (about 200%), much lower than that of other alloy-based anode materials (such as tin or silicon), which helps to maintain the stability of the electrode structure, reduce the capacity decay during cycling, and thus extend the service life of the battery. Bismuth also has good electrical conductivity, which not only improves the rate performance of the electrode, but also enhances the charge and discharge efficiency, enabling the battery to quickly respond to high-power demands. From the perspective of resources, bismuth is abundant in the earth's crust and has a relatively low cost, making it suitable for large-scale commercial applications. At the same time, bismuth is non-toxic and environmentally friendly, meeting the requirements of green energy and sustainable development. In terms of the electrochemical reaction mechanism, bismuth stores energy by forming an alloy with sodium (such as Na3Bi), and this alloying reaction is highly reversible, making it suitable as an anode material. Moreover, bismuth is easy to be compounded with other materials (such as carbon materials, metal oxides, etc.) to form composite materials with better performance. For example, bismuth-carbon composite materials can further alleviate the volume expansion problem and improve the electrical conductivity, thus comprehensively enhancing the comprehensive performance of the battery. Due to its advantages such as high capacity, appropriate potential, controllable volume expansion, good electrical conductivity, rich resources, environmental friendliness, good reversibility and easy compounding, bismuth element shows broad application prospects in the electrode materials of sodium-ion batteries.

[0047] The applicant also found that the application of antimony element in the electrode materials of sodium-ion batteries also has significant advantages in many aspects. The theoretical capacity of antimony is as high as 660 mAh / g, far higher than that of traditional carbon-based materials (such as graphite) and other alloy-based anode materials (such as tin or phosphorus), which enables it to significantly improve the energy density of sodium-ion batteries to meet the high-energy storage requirements. Secondly, the redox potential of antimony is moderate, usually in the range of 0.5 - 0.9 V (versus Na / Na +), this potential range not only avoids the formation of sodium dendrites, improves the safety of the battery, but also ensures a relatively high output voltage, which is beneficial to the efficient operation of the battery. In terms of the electro-chemical reaction mechanism, antimony stores energy by forming an alloy with sodium (such as Na3Sb), and this alloying reaction is highly reversible, making it suitable as an anode material. In addition, antimony has good electrical conductivity, which not only improves the rate performance of the electrode but also enhances the charge-discharge efficiency, enabling the battery to quickly respond to high-power demands. From the perspective of resources, antimony has relatively abundant reserves in the earth's crust and a relatively low cost, making it suitable for large-scale commercial applications.

[0048] This application hopes to combine the advantages of the above two elements and design a bismuth-antimony alloy that can be used as the anode material for sodium ions.

[0049] To solve the problems that traditional anode materials (such as hard carbon) have a low capacity (<300 mAh / g), and alloy materials (such as antimony and bismuth) have serious volume expansion (300% - 400%) during charge and discharge, resulting in structural pulverization, and in the prior art, although carbon coating can alleviate the expansion, a single carbon layer is difficult to balance electrical conductivity and buffering effect; in addition, the preparation of bismuth-antimony alloys mostly relies on electrospinning or mechanical alloying methods, which are complex and costly, this application provides a gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material, including:

[0050] The core is a bismuth-antimony alloy nanosphere with a molar ratio of Bi:Sb = 0.5 - 0.7:0.3 - 0.5;

[0051] The outer layer is a gradient carbon layer, which is composed of an amorphous carbon layer (with a thickness of 5 - 15 nm) and a graphitized carbon layer (with a thickness of 10 - 30 nm) from the inside to the outside, and the ID / IG ratio of the Raman spectrum of the graphitized carbon layer is less than that of the amorphous carbon layer.

[0052] In some preferred embodiments, the particle size of the above bismuth-antimony alloy nanospheres is 50 - 200 nm, and the surface has a porous structure (with a pore diameter of 2 - 10 nm).

[0053] This application also provides a preparation method for the gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material, including the following steps:

[0054] S1. Dissolve polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) to form a homogeneous solution;

[0055] S2. Add bismuth nitrate pentahydrate and antimony trichloride, stir and then ultrasonically disperse to form a sol;

[0056] S3. Convert the sol into precursor microspheres by spray drying;

[0057] S4. Under an argon atmosphere, perform two-stage carbonization treatment: in the first stage, keep the temperature at 300 - 500 °C for 1 h to form an amorphous carbon layer; in the second stage, keep the temperature at 700 - 900 °C for 2 h to form a graphitized carbon layer.

[0058] In some preferred embodiments: in step S2, the molar ratio of bismuth nitrate pentahydrate to antimony trichloride is 3:2, and the mass ratio of PVP to metal salt is 1:1 - 1:3.

[0059] This application also provides a negative electrode material for a sodium-ion battery, which includes the composite material described in claim 1 (70 - 90 wt%); a conductive agent (5 - 15 wt%), selected from carbon nanotubes or graphene; and a binder (5 - 15 wt%), selected from sodium alginate or polyvinylidene fluoride (PVDF).

[0060] In some preferred embodiments: the tap density of the above negative electrode material is 1.5 - 2.0 g / cm 3 , and the surface is coated with an in-situ generated SEI film enhancement layer.

[0061] This application also provides a sodium-ion battery, which includes a positive electrode, a separator, an electrolyte, and the above negative electrode sheet, and the electrolyte is a 1.5 mol / L NaPF ethylene carbonate / fluoroethylene carbonate (EC:FEC = 7:3) solution; the separator is a ceramic-coated polypropylene / polyethylene three-layer composite film.

[0062] In some preferred embodiments of this application: the positive electrode is sodium vanadium phosphate (Na3V2(PO4)3), and the capacity ratio of the positive electrode to the negative electrode is 1.1 - 1.3:1.

[0063] This application also provides a fast charging method for a sodium-ion battery. Using the above battery, the charging current density is 2 - 5C, and dendritic growth is suppressed by pulsed voltage control during the charging process.

[0064] Finally, this application also provides the application of the above composite material in an energy storage system or an electric vehicle. It is characterized in that the operating temperature range of the battery pack is -40 - 60 °C, and the cycle life ≥ 2000 times (capacity retention rate ≥ 80%).

[0065] Next, the preparation method of the gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material Bi 0.6 Sb 0.4 @C negative of this application and the preparation method of a sodium-ion battery will be described in detail.

[0066] Preparation Example Preparation of the gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material Bi 0.6 Sb 0.4 @C

[0067] Its specific preparation method includes the following steps:

[0068] S1. Dissolve polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) to form a homogeneous solution.

[0069] Specifically for solvent preparation: At room temperature, add 1.0 g of polyvinylpyrrolidone (PVP) to 20 mL of N,N-dimethylformamide (DMF), and stir until completely dissolved.

[0070] S2. Add bismuth nitrate pentahydrate and antimony trichloride, stir and then disperse ultrasonically to form a sol.

[0071] Specifically for Bi 0.6 Sb 0.4 Preparation: Add 1.25 g of bismuth nitrate pentahydrate and 0.39189 g of antimony trichloride. Stir and heat the mixed solution to 85 °C and keep it until the solvent completely evaporates.

[0072] S3. Convert the sol into precursor microspheres by spray drying.

[0073] Specifically, after the solvent completely evaporates, collect the obtained solid, which is yellowish-brown.

[0074] S4. Under an argon atmosphere, perform two-stage carbonization treatment: The first stage is to keep at 300 - 500 °C for 1 h to generate an amorphous carbon layer; the second stage is to keep at 700 - 900 °C for 2 h to generate a graphitized carbon layer.

[0075] Specifically, place the obtained solid in a quartz boat and transfer it to a tube furnace. Under an argon atmosphere, heat it to 700 °C at a heating rate of 3 °C / min and keep it for 2 hours. After the annealing ends, the tube furnace is naturally cooled to room temperature.

[0076] Finally, collect the gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite Bi 0.6 Sb 0.4 @C solid, which is black.

[0077] This application also provides a sodium-ion battery, which includes a positive electrode material, a separator wetted by an electrolyte, and a negative electrode material stacked in sequence. The negative electrode material uses the above-mentioned gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite Bi 0.6 Sb 0.4 @C.

[0078] This application combines two metals, bismuth and antimony, combines the advantages of the two metals, and has a synergistic effect between the two metals. It is obtained by carbonization treatment after synthesis by the sol-gel method. At the same time, the carbon-coated bismuth-antimony bimetallic material is used as the negative electrode of a sodium-ion battery, and excellent electrochemical performance is obtained, such as excellent cycling performance and rate performance. In terms of cycling performance, at a current density of 0.5 Ag -1 the battery is cycled 1600 times, with a capacity of 264.83 mAh g -1 . In terms of rate performance, even at a current density of 2 A g -1 the battery can still work normally and obtain a sodium storage capacity of about 347 mAh g -1 . It can be seen that the prepared carbon-coated bismuth-antimony bimetallic negative electrode material Bi 0.6 Sb 0.4 @C has excellent performance and has important applications in sodium-ion batteries.

[0079] Application Example Preparation of Sodium-Ion Battery

[0080] The preparation method of a sodium-ion battery including the gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite Bi 0.6 Sb 0.4 @C as the negative electrode material includes the following steps:

[0081] S21. Weigh the solid in step (5), conductive carbon (SP), and binder (sodium alginate) in a ratio of 7:1.5:1.5, mix and grind them, use a mortar to mix the above three substances evenly, and uniformly coat the obtained mixed slurry on the copper foil;

[0082] S22. Place the coated copper foil in a vacuum drying oven, keep the drying oven at 80 °C, and dry overnight;

[0083] S23. Collect the obtained electrode sheet and cut it into circular pieces with a diameter of 12 mm;

[0084] S24. Operate in an argon-filled glove box, place the positive electrode shell of the sodium-ion battery with the opening facing up flat on the backing plate, and place the electrode sheet in step S1 in the center of the positive electrode shell;

[0085] S25. Then use a dropper to add 1-2 drops of electrolyte [dissolve the NaFP6 salt in ethylene glycol dimethyl ether (DME) to make the concentration of the NaFP6 salt 1 mol / L], moisten the surface of the electrode sheet, and clamp a glass fiber separator to cover the electrode sheet; add 3-4 drops of electrolyte again, moisten the separator, and clamp a sodium metal sheet in the center of the separator;

[0086] S26. Finally, place the gasket and spring piece in the center of the sodium metal sheet in turn, cover the negative electrode shell and seal it to obtain the sodium-ion battery.

[0087] Compared with the prior art, the present application has the following beneficial effects:

[0088] First, the nano-sized bismuth particles in the carbon-coated bismuth-antimony bimetallic anode material can shorten the ion diffusion path. The external carbon layer has abundant defects, providing electron / ion transport channels, and can effectively alleviate the volume change of bismuth particles during charge and discharge, improving the structural stability of the electrolytic material, avoiding the problem that the huge volume change during cycling will lead to the collapse and pulverization of the electrode material structure, and at the same time significantly improving the rate performance and cycling stability of sodium-ion batteries.

[0089] Second, the present application uses the sol-gel method, and the one-step reaction simplifies the experimental steps and reduces the production cost to a certain extent.

[0090] Third, applying the above carbon-coated bismuth-antimony bimetallic anode material Bi 0.6 Sb 0.4 @C in the preparation of sodium-ion batteries, which are made of electrode sheets, sodium metal sheets, electrolytes, diaphragms, nickel foams, and positive and negative electrode cases. The button battery prepared with the carbon-coated bismuth-antimony bimetallic anode material adopted in the present application has excellent electrochemical performance.

[0091] The present application also provides the application of the above carbon-coated bismuth-antimony bimetallic anode material in the field of sodium-ion batteries.

[0092] Performance Characterization

[0093] The present application observed the carbon-coated bismuth-antimony bimetallic anode material Bi 0.6 Sb 0.4 @C materials used respectively by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and the results are as Figure 1-2 shown. Among them, Figure 1 is the TEM image of the Bi 0.6 Sb 0.4 @C material used in the present application, Figure 2 is the SEM image of the Bi 0.6 Sb 0.4 @C material prepared in the present application. It can be clearly seen from the comparison of Figure 1 and Figure 2 that the Bi 0.6 Sb 0.4 alloy was successfully synthesized. In addition, Figure 2 the SEM image of also has an EDS elemental energy spectrum diagram, and it can be seen that the Bi and Sb elements are evenly distributed. Figure 3 is the XRD pattern of the Bi 0.6 Sb 0.4 alloy. It can be seen that Bi 0.6 Sb 0.4 can correspond to Bi 0.6Sb 0.4 Standard card. Combining Figure 1 , Figure 2 and Figure 3 It can be seen that after synthesis by the sol-gel method and carbonization treatment, the anode material Bi 0.6 Sb 0.4 @C of a sodium-ion battery with a carbon-coated bismuth-antimony synergistic bimetallic effect is successfully obtained.

[0094] At the same time, this application also observes the carbon-coated bismuth-antimony alloy anode material Bi 0.6 Sb 0.4 @C by transmission electron microscopy (TEM), and through elemental mapping and Raman spectroscopy analysis, the results are as Figure 1 and Figure 2 shown.

[0095] Figure 1 TEM image and nanoparticle size distribution map of the carbon-coated bismuth-antimony alloy anode material prepared in this application. From Figure 1 it can be seen that the prepared bismuth-antimony alloy material is ultrasonically dispersed in ethanol for TEM testing, and lattice fringes of 0.327 nm and 0.221 nm are seen through Figure 1 , corresponding to the 003 crystal plane and the 012 crystal plane respectively.

[0096] Figure 2 Elemental mapping image of the carbon-coated bismuth-antimony alloy anode material prepared in this application. From Figure 2 it can be seen that in the carbon-coated bismuth-antimony alloy anode Bi 0.6 Sb 0.4 @C material synthesized in this application, the Bi / Sb / C elements are evenly distributed. This proves that the carbon-coated bismuth-antimony alloy anode material is composed of a bismuth-antimony alloy, and the bismuth-antimony alloy is coated with a carbon layer.

[0097] Figure 3 XRD pattern of the carbon-coated bismuth-antimony alloy anode material prepared in this application. From Figure 3 it can be seen that the carbon-coated bismuth-antimony alloy anode Bi 0.6 Sb 0.4 @C material synthesized in this application can correspond to the PDF card of BiSb. It shows the formation of the bismuth-antimony alloy.

[0098] Figure 4 Raman spectrum of the bismuth / carbon nanorod array anode material prepared in this application. From Figure 4 it can be seen that the peak at about 90 cm -1 corresponds to the characteristic peak of metallic bismuth, and the peak at 110 cm -1The peaks on the left and right correspond to the characteristic peaks of metallic antimony, and at the same time have the D peak and G peak of the carbon material, further proving the successful synthesis of the bismuth-antimony alloy negative electrode material prepared in this application, and the bismuth-antimony alloy is coated with a carbon layer.

[0099] Next, this application conducts relevant performance tests on the sodium-ion battery obtained from the application example, such as electrochemical performance tests, and the test results are as Figures 5 to 7 . Now, in combination with the attached Figures 5 to 7 , the experimental test results are analyzed and described as follows:

[0100] Use a multi-channel battery tester (Wuhan Blue Electric) to test the electrochemical performance (cycling performance and rate performance) of the sodium-ion battery prepared in the application example. During the cycling performance test, the current density is 0.5 Ag -1 and 1 Ag -1 ; during the rate performance test, the current density increases from 0.05 Ag-1 to 0.1 Ag -1 , 0.2 Ag -1 , 0.5 Ag -1 , 1 Ag -1 and 2 Ag -1 , and then returns to 0.05 Ag -1 ;

[0101] Figure 5 The carbon-coated bismuth-antimony synergistic bimetallic effect sodium-ion battery negative electrode material Bi 0.6 Sb 0.4 @C prepared in this application is used as the negative electrode of the sodium-ion battery, and the cycling performance diagram at a current density of 0.5 Ag -1 . As can be seen from Figure 5 , in terms of cycling performance, at a current density of 0.5 Ag -1 , after 1600 cycles, it has 264.83 mAh g -1 . It shows good cycling stability. The proximity of the discharge and charge curves in the figure indicates that the material has a high Coulomb efficiency, meaning less charge loss during charge and discharge and high energy conversion efficiency. After 1500 cycles, the specific capacity still remains at a relatively high level, showing a long cycling life, which is an important advantage for the battery life in practical applications. At a current density of 0.5 A / g, the bismuth-antimony alloy shows good electrochemical performance, indicating that it is suitable for working at a relatively high current density, which is an important advantage for application scenarios that require fast charge and discharge.

[0102] Figure 6 The carbon-coated bismuth-antimony synergistic bimetallic effect sodium-ion battery negative electrode material Bi 0.6 Sb 0.4 @C prepared in this application at 0.5 Ag -1Charge-discharge curve at a current density of Figure 6 Multiple voltage platforms are shown in Fig. Figure 6 , indicating that the material has multiple stable redox reactions during charge and discharge, which helps to improve the capacity and cycle stability of the battery. The shape and position of the curve in the figure change little, indicating that the material can still maintain a high capacity after multiple charge-discharge cycles, showing good cycle stability. This is because the carbon layer outside the bismuth-antimony bimetallic negative electrode material prepared in this application has rich defects, providing electron / ion transport channels, and can effectively alleviate the volume change of bismuth particles during charge and discharge, improving the structural stability of the electrolytic material, and avoiding the problem of the collapse and fragmentation of the electrode material structure caused by a large volume change during the cycle.

[0103] Through Figure 7 , it can be seen that at a current density of 0.05 A / g, the charge and discharge specific capacities are both close to 450 mAh / g, showing a high initial capacity. As the current density increases, although the charge and discharge capacities decrease, they generally remain at a high level. At a current density of 2 A / g, the capacity can still be maintained at about 347 mAh / g -1 , showing good rate performance. After cycling at a high current density (2 A / g), when the current density is reduced back to 0.05 A / g, the capacity can partially recover, showing the capacity recovery ability of the material. At current densities of 0.05 A / g and 0.1 A / g, after multiple cycles, the capacity remains relatively stable. From this, it can be shown that the carbon-coated bismuth-antimony synergistic bimetallic effect sodium-ion battery negative electrode material Bi 0.6 Sb 0.4 @C used as the negative electrode of a sodium-ion battery has obtained excellent rate performance.

[0104] The preparation method of the carbon-coated bismuth-antimony bimetallic negative electrode material in this application includes the following steps: synthesized by the sol-gel method and then carbonized.

[0105] The bismuth-antimony alloy prepared in this application is coated with a carbon layer. Among them, bismuth and antimony metals are used as active components for storing sodium ions, making the carbon-coated bismuth-antimony alloy have a high capacity. The surface-coated carbon layer can not only promote electron transport and ion diffusion, but also buffer the volume strain of metallic bismuth during charge and discharge. Thanks to the synergistic effect of the two, the prepared carbon-coated bismuth-antimony alloy exhibits high specific capacity, excellent rate performance and cycle stability when used as the negative electrode of a sodium-ion battery.

[0106] In summary, the preparation method of the carbon-coated bismuth-antimony alloy negative electrode material in this application has the following advantages:

[0107] In this application, the nano-sized bismuth particles in the carbon-coated bismuth-antimony alloy anode material can shorten the ion diffusion path. The external carbon layer has abundant defects, providing electron / ion transport channels, and can effectively alleviate the volume change of bismuth particles during charge and discharge, improving the structural stability of the electrolytic material and significantly enhancing the rate performance and cycle stability of sodium-ion batteries.

[0108] This application uses the sol-gel method, and the one-step reaction simplifies the experimental steps and reduces the production cost to a certain extent.

[0109] The above Bi 0.6 Sb 0.4 @C anode material is applied to the preparation of sodium-ion batteries, which are made of electrode sheets, sodium metal sheets, electrolytes, diaphragms, nickel foam, and positive and negative electrode shells. The button battery prepared with the carbon-coated bismuth-antimony alloy material adopted in the present invention has excellent electrochemical performance.

[0110] This application proposes a bismuth-antimony bimetallic nanosphere composite material with a gradient carbon layer coating. Through the sol-spray drying-segmented carbonization process, the synergy optimization of the core alloy and the gradient carbon layer is realized:

[0111] First, through core design: the Bi / Sb molar ratio is optimized to 0.6:0.4, and the volume expansion is reduced by using the bimetallic solid solution effect (the measured expansion rate ≤ 200%);

[0112] Then, by forming a gradient carbon layer: the inner amorphous carbon provides a buffer space, the outer graphitized carbon improves conductivity, and the ID / IG gradient design enhances electrolyte wettability;

[0113] Finally, the preparation process in this application: the spray drying method replaces the traditional electrospinning, simplifies the process and realizes the precise control of the nanosphere structure.

[0114] The gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material prepared in this application, when used as an anode material in sodium-ion batteries, exhibits excellent battery performance, such as high capacity: the initial discharge capacity reaches 550 mAh / g at 0.5 A / g, and the retention rate after 1600 cycles is 52.18%; excellent rate performance: the capacity retention rate is 68.5% at 2 A / g, which is better than that of traditional carbon-coated materials (≤ 50%).

[0115] In the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiments or examples are included in at least one embodiment or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples.

[0116] Although several embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. A gradient carbon layer-coated bismuth-antimony bimetallic nanosphere composite material, characterized in that: Comprising: The core is a bismuth-antimony alloy nanosphere with a molar ratio of Bi:Sb = 0.5 - 0.7:0.3 - 0.5; The outer layer is a gradient carbon layer, which consists of an amorphous carbon layer (thickness 5 - 15 nm) and a graphitized carbon layer (thickness 10 - 30 nm) from the inside to the outside, and the ID / IG ratio of the graphitized carbon layer is less than that of the amorphous carbon layer.

2. The composite material according to claim 1, wherein: The particle size of the bismuth-antimony alloy nanosphere is 50 - 200 nm, and it has a porous structure on the surface (pore diameter 2 - 10 nm).

3. The preparation method of the composite material according to claim 1, characterized in that: Including the following steps: S1. Dissolve polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) to form a homogeneous solution; S2. Add bismuth nitrate pentahydrate and antimony trichloride, stir and then ultrasonically disperse to form a sol; S3. Convert the sol into precursor microspheres by spray drying; S4. Under an argon atmosphere, perform two-stage carbonization treatment: the first stage is to keep the temperature at 300 - 500 °C for 1 h to generate an amorphous carbon layer; The second stage is to keep the temperature at 700 - 900 °C for 2 h to generate a graphitized carbon layer.

4. The preparation method of the composite material according to claim 3, characterized in that: In step S2, the molar ratio of bismuth nitrate pentahydrate to antimony trichloride is 3:2, and the mass ratio of PVP to metal salts is 1:1 - 1:

3.

5. A negative electrode material for a sodium-ion battery, characterized in that: Comprising: The composite material described in claim 1 (70 - 90 wt%); A conductive agent (5 - 15 wt%), selected from carbon nanotubes or graphene; A binder (5 - 15 wt%), selected from sodium alginate or polyvinylidene fluoride (PVDF).

6. The negative electrode material according to claim 5, characterized in that: The tap density of the negative electrode material is 1.5 to 2.0 g / cm 3 , and the surface is coated with an in-situ formed SEI film enhancement layer.

7. A sodium-ion battery, comprising a positive electrode, a separator, an electrolyte, and the negative electrode sheet according to claim 5, characterized in that: The electrolyte is a 1.5 mol / L NaPF ethylene carbonate / fluoroethylene carbonate (EC:FEC = 7:3) solution; The separator is a ceramic-coated polypropylene / polyethylene three-layer composite membrane.

8. The sodium ion battery according to claim 7, wherein The positive electrode is sodium vanadium phosphate, and the capacity ratio of the positive electrode to the negative electrode is 1.1 - 1.3:

1.

9. A rapid charging method for a sodium-ion battery, characterized in that, Using the battery described in claim 7, the charging current density is 0.05 - 2 A / g, and dendritic growth is inhibited by pulsed voltage control during the charging process.

10. Use of the composite material according to claim 1 in an energy storage system or an electric vehicle, characterized in that, The battery pack has a cycle life ≥ 1600 times and a capacity retention rate ≥ 50%.

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