Preparation method of uniformly distributed bismuth nanoparticle / carbon nanorod composite and application thereof

Abstract

This invention relates to a method for preparing a uniformly distributed bismuth nanoparticle / carbon nanorod composite material (Bi / CNRs) and its application as a negative electrode material for low-temperature fast-charging sodium-ion batteries. The preparation steps of this composite material are as follows: a) preparing bismuth iodide nanosheets (BiOI NSs); b) dispersing BiOI NSs and trimesic acid in a mixed solution of N,N-dimethylformamide and methanol, followed by hydrothermal reaction to obtain metal-organic framework materials (Bi-MOFs); c) thermally shocking the Bi-MOFs in an Ar atmosphere to obtain the Bi / CNRs composite material. As a negative electrode material for sodium-ion batteries, Bi / CNRs exhibits outstanding low-temperature electrochemical performance, reaching -40℃ and 5Ag. ‑1 The capacity at current density is 261 mAh g. ‑1 ;1A g ‑1 The capacity after 2400 cycles is 240mAh g. ‑1 This invention provides a new approach for developing low-temperature sodium-ion battery anode materials with excellent overall performance.

Description

Technical fields:

[0001] This invention relates to a method for preparing a uniformly distributed bismuth nanoparticle / carbon nanorod composite material and its application as a negative electrode material for low-temperature sodium-ion batteries. Background technology:

[0002] Lithium-ion batteries, with their high energy and power density, are widely used in various energy storage devices. However, lithium resources are limited and unevenly distributed, failing to meet the enormous demands of large-scale energy storage. Furthermore, the severe capacity decay of lithium-ion batteries at low temperatures significantly restricts their application in extreme environments such as high latitudes, high altitudes, polar regions, deep seas, and space. Sodium-ion batteries, due to abundant sodium resources and a similar energy storage mechanism to lithium-ion batteries, have attracted widespread attention. Moreover, compared to lithium-ion batteries... + In comparison, Na + Sodium-ion batteries exhibit weak solvation shell binding energy and low desolvation energy, giving them a significant advantage in low-temperature and rate performance. However, at low temperatures, the increased electrolyte viscosity leads to lower ionic conductivity, and slow ion diffusion within the electrodes intensifies battery polarization and degrades performance. To address this, scientists both domestically and internationally have conducted extensive research, primarily focusing on electrolytes, with relatively slower progress in anode materials. Therefore, finding anode materials for sodium-ion batteries with excellent low-temperature fast-charging performance remains a significant challenge.

[0003] Recently, researchers have studied several promising low-temperature sodium-ion battery anode materials, such as hard carbon, metals (Sn, Sb, Bi, etc.), and transition metal chalcogenides (SnS2, MoS2, MoSe2, etc.). Among them, metallic Bi has attracted widespread attention due to its large interlayer spacing, high theoretical capacity, and good rate performance. However, its performance at low temperatures still needs further improvement. This invention aims to prepare Bi-based sodium-ion battery anode materials with excellent fast-charging performance and cycle stability at low temperatures through a simple operating method. Summary of the Invention:

[0004] To address the aforementioned issues, this invention prepares a uniformly distributed bismuth nanoparticle / carbon nanorod composite material (Bi / CNRs) and uses it as a negative electrode material for low-temperature sodium-ion batteries.

[0005] The Bi / CNRs composite material consists of uniformly sized bismuth nanoparticles uniformly loaded onto carbon nanorods. This composite material offers the following advantages: First, the organic ligand-derived carbon framework not only possesses high conductivity and structural stability but also effectively mitigates Na+ degradation. +First, the volume expansion during the insertion / extraction process; second, the uniform loading of bismuth nanoparticles generated in situ by thermal shock onto carbon nanorods increases the specific surface area, providing more active sites, and the hierarchical pore structure of micropores / mesopores also provides effective diffusion channels for the electrolyte; third, the extreme heat generated under high-temperature shock can effectively remove impurity elements, thus forming abundant defects, enhancing the resistance to Na+. + Fourth, the adsorption capacity of Na increases its storage capacity; + Bi / CNRs can directly alloy with Bi without requiring a solvation process, greatly improving the low-temperature reaction kinetics. Therefore, as a negative electrode material for sodium-ion batteries, Bi / CNRs exhibit excellent low-temperature electrochemical performance.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a uniformly distributed bismuth nanoparticle / carbon nanorod composite material includes the following steps:

[0008] a. Preparation of bismuth iodide nanosheets (BiOI NSs): Dissolve 0.05–0.6 g of bismuth trichloride (BiCl3) in 20–100 ml of 1.0–1.5 M acetic acid solution, and dissolve 0.04–0.5 g of potassium iodide (KI) in 10–50 ml of ultrapure water. Stir well, then pour the KI aqueous solution into the BiCl3 acetic acid solution, adjust the pH to 4–7, continue stirring for 30–60 min, and then place the solution in a reaction vessel and react at 100–180 °C for 2–12 h. After centrifugation and washing, freeze dry for 10–20 h.

[0009] b. Preparation of metal-organic framework materials Bi-MOFs: Dissolve 0.2-1.5g BiOI NSs and 0.3-1.7g trimesic acid (H3BTC) in a mixed solution of 10-80ml N,N-dimethylformamide and methanol. After stirring evenly, place the solution in a reaction vessel and react at 100-180℃ for 2-12h. After centrifugation and washing, vacuum dry for 10-20h.

[0010] c. The prepared Bi-MOFs are subjected to ultrafast thermal shock treatment in an Ar atmosphere with a current pulse of 10-100A and a time of 5-120s, finally obtaining a uniformly distributed bismuth nanoparticle / carbon nanorod composite material, namely Bi / CNRs.

[0011] Furthermore, in step a, the size of BiOI can be controlled by adjusting the concentrations of BiCl3 and KI, as well as the reaction time.

[0012] In step b, the morphology of Bi-MOFs can be controlled by adjusting the ratio of ligand H3BTC to precursor BiOI NSs.

[0013] In step c, the size of bismuth nanoparticles and the Bi content in the final composite material can be controlled by adjusting the Joule heating pulse parameters.

[0014] In step c, the distribution of bismuth nanoparticles in carbon nanorods in the final composite material can be controlled by adjusting the thermal shock time.

[0015] The uniformly distributed bismuth nanoparticle / carbon nanorod composite material obtained by the above preparation method was used as a negative electrode material for sodium-ion batteries for electrochemical performance testing, including the following steps:

[0016] a. Preparation of working electrode: First, the active material, namely Bi / CNRs, is mixed evenly with conductive carbon black and binder sodium carboxymethyl cellulose in deionized water at a ratio of 7:2:1 and then coated onto copper foil. After vacuum drying at 70-100℃ for 10-12h, it is then cut into circular electrode sheets with a diameter of 11-12mm.

[0017] b. Sodium-ion battery assembly: The active material is used as the working electrode, the sodium metal sheet is used as the counter electrode / reference electrode, the separator is made of Whatman glass fiber, and the electrolyte is 1M NaPF6 dissolved in ethylene glycol dimethyl ether. The CR2025 button battery is assembled in an argon-filled glove box. The water oxygen value in the glove box is controlled at [H2O] < 1ppm and [O2] < 1ppm respectively.

[0018] c. Cyclic voltammetry tests were performed using an Ivium-n-Stat electrochemical workstation at a scan rate of 0.1–1.0 mV / s. -1 The voltage range is 0.01 to 1.5V;

[0019] d. Electrochemical impedance spectroscopy was performed at room temperature using an Ivium-n-Stat electrochemical workstation, with the frequency range set from 100 kHz to 10 mHz.

[0020] e. Battery room temperature test: The LAND-CT2001A battery test system was used to perform constant current charge and discharge tests at room temperature, with a voltage range of 0.01 to 1.5V;

[0021] f. Low temperature test of battery: Place the battery in a BPH-060B high and low temperature test chamber and use the LAND-CT2001A battery test system to perform constant current charge and discharge test at low temperature, with a voltage range of 0.01~1.5V.

[0022] g. Disassembly and characterization of the battery: The button battery after charge and discharge test was disassembled in the glove box, the electrode plates were removed, and the battery was soaked in ethylene glycol dimethyl ether solution for 20-24 hours. Then it was washed with ethanol 3-6 times. After drying, it was characterized by in-situ transmission electron microscopy (TEM). The water oxygen value in the glove box was controlled at [H2O] < 1 ppm and [O2] < 1 ppm, respectively.

[0023] h. In-situ XRD characterization of the battery: The in-situ XRD cell used beryllium metal as the window to transmit X-rays, aluminum foil as the current collector, and 1M NaPF6 dissolved in diethylene glycol dimethyl ether as the electrolyte. The separator was the same as that used in coin cells. (0.1Ag) -1 Constant current charge-discharge was performed at a current density, and XRD data were collected every 4 minutes, within the range of 10° to 90° at 10°min intervals. -1 The scan speed was tested.

[0024] The technical effects of this invention are:

[0025] This invention prepares uniformly distributed bismuth nanoparticle / carbon nanorod composites (Bi / CNRs) via an ultrafast thermal shock method. These composites exhibit high conductivity and electrochemical reaction rates, and can effectively mitigate the volume expansion of Bi during cycling. As a negative electrode material for sodium-ion batteries, Bi / CNRs demonstrate outstanding low-temperature performance (-40℃, 5Ag)... -1 The capacity at current density is 261 mAh g. -1 1Ag -1 The capacity after 2400 cycles is 240mAh g. -1 This invention provides a new approach for developing low-temperature sodium-ion battery anode materials with excellent overall performance. Attached image description:

[0026] Figure 1 The rate performance curve of the Bi / CNRs composite material as a sodium-ion battery anode material in Example 1 of this invention at -40℃.

[0027] Figure 2 XRD pattern of Bi / CNRs composite material in Example 1 of this invention.

[0028] Figure 3 Raman spectrum of Bi / CNRs composite material in Example 1 of this invention.

[0029] Figure 4 EPR spectrum of the Bi / CNRs composite material in Example 1 of this invention.

[0030] Figure 5 TGA curve of Bi / CNRs composite material in Example 1 of this invention.

[0031] Figure 6 The N2 adsorption-desorption curves and pore size distribution diagram of the Bi / CNRs composite material in Example 1 of this invention (illustrated).

[0032] Figure 7 XPS full spectrum of Bi / CNRs composite material in Example 1 of this invention.

[0033] Figure 8 The high-resolution Bi 4f XPS spectrum of the Bi / CNRs composite material in Example 1 of this invention.

[0034] Figure 9 The C1s XPS high-resolution spectrum of the Bi / CNRs composite material in Example 1 of this invention.

[0035] Figure 10 O1s XPS high-resolution spectrum of Bi / CNRs composite material in Example 1 of this invention.

[0036] Figure 11 FESEM image of the Bi / CNRs composite material in Example 1 of this invention.

[0037] Figure 12 TEM image of the Bi / CNRs composite material in Example 1 of this invention.

[0038] Figure 13 HRTEM image of the Bi / CNRs composite material in Example 1 of this invention.

[0039] Figure 14 SAED photograph of the Bi / CNRs composite material in Example 1 of this invention.

[0040] Figure 15 The cyclic voltammogram of the Bi / CNRs composite electrode in a sodium-ion battery in Example 1 of this invention at room temperature, scanned at a rate of 0.1 mV / s. -1 .

[0041] Figure 16 Cyclic performance curves of the Bi / CNRs composite electrode at different temperatures in Example 1 of this invention.

[0042] Figure 17 In Example 1 of this invention, the Bi / CNRs composite electrode was used in a sodium-ion battery with a content of 0.1 Ag. -1 Cyclic performance and coulombic efficiency curves at current density at -40℃.

[0043] Figure 18 The charge-discharge curves of the Bi / CNRs composite electrode in Example 1 of this invention at -40°C under different current densities in a sodium-ion battery.

[0044] Figure 19 In Example 1 of this invention, the Bi / CNRs composite electrode was used in a sodium-ion battery with a capacity of 1Ag. -1 Cyclic performance and coulombic efficiency curves at current density and -40℃.

[0045] Figure 20 EIS impedance spectra and equivalent circuit diagrams (illustrated figures) of the Bi / CNRs composite electrode in a sodium-ion battery at the initial stage and after different cycle numbers in Example 1 of this invention.

[0046] Figure 21 A comparative bar graph showing the impedance values ​​obtained by fitting the Bi / CNRs composite electrode in a sodium-ion battery in Example 1 of this invention.

[0047] Figure 22 The Bi / CNRs composite electrode in Example 1 of this invention was tested in a sodium-ion battery at different scan rates (0.2–1.0 mV / s). -1 Cyclic volt-ampere curves under ( ).

[0048] Figure 23 The linear relationship between logi and logv of the Bi / CNRs composite electrode in sodium-ion battery under different redox states in Example 1 of this invention.

[0049] Figure 24 In Example 1 of this invention, the Bi / CNRs composite electrode was scanned at a rate of 1.0 mV / s in a sodium-ion battery. -1 The contribution diagram of pseudocapacitive storage process and diffusion storage process at that time.

[0050] Figure 25 The contribution rate of pseudocapacitance and diffusion storage to capacity normalization of the Bi / CNRs composite electrode in sodium-ion battery at different scan rates in Example 1 of this invention.

[0051] Figure 26 In-situ XRD pattern of the Bi / CNRs composite electrode in Example 1 of this invention during the charge and discharge process of a sodium-ion battery.

[0052] Figure 27 TEM image of the Bi / CNRs composite material in Example 2 of this invention.

[0053] Figure 28 TEM image of the Bi / CNRs composite material in Example 3 of this invention. Detailed Implementation

[0054] The specific content and implementation methods of the present invention will now be further described with reference to the embodiments. However, the embodiments are merely illustrative and should not be construed as limiting the technical solution of the present invention. The following is a detailed description of Embodiment 1. Embodiments 2 and 3 of the present invention are similar in content to Embodiment 1.

[0055] The embodiments of the present invention are now described below:

[0056] Example 1

[0057] The preparation process and steps in this embodiment are as follows:

[0058] (1) Dissolve 0.158g BiCl3 in 50ml of 1.2M acetic acid solution, dissolve 0.083g KI in 12.5ml of ultrapure water, stir evenly, then pour the KI aqueous solution into the BiCl3 acetic acid solution, adjust the pH to 6, continue stirring for 30min, then place the solution in a reaction vessel and react at 160℃ for 2h. After centrifugation and washing, freeze dry for 12h to obtain BiOINSs;

[0059] (2) Dissolve 0.339g BiOI NSs and 0.6g trimesic acid in a mixed solution of 20ml N,N-dimethylformamide and methanol. After stirring evenly, place the solution in a reaction vessel and react at 120℃ for 3h. After centrifugation and washing, vacuum dry for 12h to obtain Bi-MOFs.

[0060] (3) Bi-MOFs were subjected to ultrafast thermal shock treatment in Ar atmosphere with a current pulse of 10A and a time of 15s to finally obtain Bi / CNRs composite material.

[0061] The Bi / CNRs composite material obtained by the above preparation method was used as a negative electrode material for sodium-ion batteries for electrochemical performance testing, including the following steps:

[0062] a. Preparation of working electrode: First, the active material, namely Bi / CNRs, is mixed evenly with conductive carbon black and binder sodium carboxymethyl cellulose in deionized water at a ratio of 7:2:1 and then coated onto copper foil. After vacuum drying at 70-100℃ for 10-12h, it is then cut into circular electrode sheets with a diameter of 11-12mm.

[0063] b. Sodium-ion battery assembly: The active material is used as the working electrode, the sodium metal sheet is used as the counter electrode / reference electrode, the separator is made of Whatman glass fiber, and the electrolyte is 1M NaPF6 dissolved in ethylene glycol dimethyl ether. The CR2025 button battery is assembled in an argon-filled glove box. The water oxygen value in the glove box is controlled at [H2O] < 1ppm and [O2] < 1ppm respectively.

[0064] c. Cyclic voltammetry tests were performed using an Ivium-n-Stat electrochemical workstation at a scan rate of 0.1–1.0 mV / s. -1 The voltage range is 0.01 to 1.5V;

[0065] d. Electrochemical impedance spectroscopy was performed at room temperature using an Ivium-n-Stat electrochemical workstation, with the frequency range set from 100 kHz to 10 mHz.

[0066] e. Battery room temperature test: The LAND-CT2001A battery test system was used to perform constant current charge and discharge tests at room temperature, with a voltage range of 0.01 to 1.5V;

[0067] f. Low temperature test of battery: Place the battery in a BPH-060B high and low temperature test chamber and use the LAND-CT2001A battery test system to perform constant current charge and discharge test at low temperature, with a voltage range of 0.01~1.5V.

[0068] g. Disassembly and characterization of the battery: The button battery after charge and discharge test was disassembled in the glove box, the electrode plates were removed, and the battery was soaked in ethylene glycol dimethyl ether solution for 20-24 hours. Then it was washed with ethanol 3-6 times. After drying, it was characterized by in-situ transmission electron microscopy (TEM). The water oxygen value in the glove box was controlled at [H2O] < 1 ppm and [O2] < 1 ppm, respectively.

[0069] h. In-situ XRD characterization of the battery: The in-situ XRD cell used beryllium metal as the window to transmit X-rays, aluminum foil as the current collector, and 1M NaPF6 dissolved in diethylene glycol dimethyl ether as the electrolyte. The separator was the same as that used in coin cells. (0.1Ag) -1 Constant current charge-discharge was performed at a current density, and XRD data were collected every 4 minutes, within the range of 10° to 90° at 10°min intervals. -1 The scan speed was tested.

[0070] Morphology and structural characterization of uniformly distributed bismuth nanoparticle / carbon nanorod composites (Bi / CNRs):

[0071] We characterized the structure and morphology of the Bi / CNRs composite material by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Figure 2 The image shows the XRD pattern of the Bi / CNRs composite material. It can be seen that the composite material has good crystallinity, and its diffraction peaks correspond to the orthorhombic Bi phase (JCPDS No. 85-1329). Figure 3 The Raman spectrum of the Bi / CNRs composite material clearly shows the position at 1340 cm⁻¹. -1 and 1590cm-1 Characteristic peaks of carbon. Further, they can be divided into four smaller peaks, namely the D2 band (located at 1183 cm⁻¹). -1 (caused by out-of-plane carbon atoms), D1 band (located at 1345 cm⁻¹) -1 (corresponding to defects and disorder in the carbon lattice), D3 band (located at 1497 cm⁻¹). -1 (related to amorphous sp3 carbon) and the typical G-band (located at 1596 cm⁻¹) -1 (This corresponds to the in-plane vibration of sp2 hybridized crystalline carbon). The I value is determined by calculating the integral areas of the D1 and G bands. D1 / I G The ratio of 1.86 indicates that there are many defects in the carbon nanorods, which is beneficial to Na + Storage. To further verify this, we performed electron paramagnetic resonance (EPR) tests. For example... Figure 4 As shown, a strong EPR signal is present at g = 2.0034, confirming the presence of numerous carbon vacancies in the Bi / CNRs composite material. Figure 5 Thermogravimetric analysis (TGA) revealed that the content of metallic Bi in the composite material was approximately 86.8%. Figure 6 The N2 adsorption-desorption curves and Barrett-Joyer-Halenda pore size distribution diagram (inset) of the Bi / CNRs composite material show that the specific surface area of ​​the composite material is 48.1 m². 2 g -1 Furthermore, it possesses a hierarchical pore structure of micropores / mesopores. The abundant pores and large specific surface area not only facilitate the diffusion of the electrolyte but also provide a suitable environment for Na+. + The embedding provides more effective active sites. We further investigated the surface chemical composition of the Bi / CNRs composite material using X-ray photoelectron spectroscopy (XPS). Figure 7 The XPS full spectrum shown can be seen as peaks for Bi, C, and O. Figure 8 The XPS high-resolution spectrum of Bi₄f shows characteristic peaks at 157.3 and 162.7 eV corresponding to metallic Bi, and characteristic peaks at 159.2 and 164.6 eV corresponding to Bi₂. 3+ This indicates that the surface portion of the Bi nanoparticles is oxidized. Figure 9 The XPS high-resolution spectrum of C1s shows the main peak at 284.8 eV corresponding to CC / C=C, while the peaks at 285.7 and 289.2 eV correspond to CO and C=O, respectively. Figure 10 The XPS high-resolution spectrum of O1s shows that the peaks at binding energies of 530.3, 532.4, and 533.9 eV correspond to Bi-O, CO-Bi, and CO, respectively. Figure 11 and 12The images show FESEM and TEM images of the Bi / CNRs composite material. As can be seen, after ultrafast thermal shock, Bi-MOFs form carbon nanorods in situ, with bismuth nanoparticles uniformly loaded on the carbon nanorods. The organic ligand-derived carbon framework not only buffers the volume expansion during charge and discharge but also possesses high conductivity, facilitating rapid electron transport. The ultrafast heating and cooling rates of the thermal shock promote the formation of uniformly sized and well-dispersed bismuth nanoparticles. This small particle size (approximately 26.5 nm) effectively shortens the Na... + The diffusion distance in the active material reduces the diffusion resistance, which is crucial for the low-temperature fast-charging performance of the composite material. Figure 13 The image shows a high-resolution transmission electron microscope (HRTEM) image of the Bi / CNRs composite material, where the interplanar spacings of 0.326 nm and 0.234 nm correspond to the (012) and (104) crystal planes of Bi, respectively. Figure 14 The selected area electron diffraction (SAED) pattern of the Bi / CNRs composite material shows that the composite material has good crystallinity, which is consistent with the XRD results.

[0072] To investigate the electrochemical performance of Bi / CNRs composite materials as anode materials in sodium-ion batteries, we assembled samples into half-cells for testing. First, we obtained the cyclic voltammograms of the Bi / CNRs composite electrode in a sodium-ion battery for the first five cycles at room temperature, as shown below. Figure 15 As shown, the scan rate is 0.1 mV / s. -1 The potential range is 0.01-1.5V (vs. Na / Na). + During the cathode scan, the peaks at 0.70 V and 0.49 V correspond to the formation of NaBi and Na3Bi, respectively. For the anodic scan, the peaks at 0.60 V and 0.75 V correspond to the dealloying reactions that gradually form NaBi and Bi from Na3Bi, respectively. Furthermore, the strong and sharp redox peaks and highly overlapping CV curves indicate that the Bi / CNRs composite electrode possesses excellent reversibility. To investigate the low-temperature electrochemical performance of the Bi / CNRs composite electrode, we conducted cycling performance tests at different temperatures. Figure 16 As shown, in 1Ag -1 At current density, the capacity of the Bi / CNRs composite material decreases as the temperature decreases, but recovers when the temperature rises back to 0℃, demonstrating that the composite material has excellent low-temperature resistance. Figure 17 The Bi / CNRs composite electrode was demonstrated in 0.1Ag. -1 Cycling performance test results at -40℃ under current density. The reversible capacity of this composite electrode after 100 cycles is 370 mAh g. -1 It exhibits good low-temperature cycling stability. Figure 1 Rate performance of the Bi / CNRs composite electrode at -40℃. Current densities of 0.1, 0.2, 0.5, 1, 2, and 5 Ag are also presented. -1 At that time, the average discharge capacities of the composite material electrode were 410, 394, 382, ​​371, 354 and 261 mAh g, respectively. -1 When the current density jumps back to 0.1 Ag -1 When the electrode capacity is restored, it gradually stabilizes in subsequent charge-discharge cycles. Figure 18 The charge-discharge curves of the Bi / CNRs composite electrode at different current densities at -40℃ are shown. Notably, at a high current density of 5Ag... -1 There is still a clear charge-discharge plateau, which means that the Bi / CNRs composite electrode has excellent low-temperature fast-charging performance. Figure 19 Bi / CNRs composite electrode in 1Ag -1 Cycling performance test results at -40℃ under current density. After 2400 cycles, the discharge capacity of the Bi / CNRs composite electrode still remains at 240 mAh g⁻¹. -1 The capacity retention rate was 67.3%, further confirming its excellent cycling stability at low temperatures.

[0073] Figure 20 and 21 The figures show the electrochemical impedance spectroscopy (EIS) of the Bi / CNRs composite electrode in its initial state and after different cycling numbers, as well as a comparison bar graph of the fitted impedance values. The Bi / CNRs composite electrode exhibits a relatively small charge transfer resistance (Ro). ct ) and contact resistance (R el The RΩ values ​​are 5.89Ω and 1.48Ω, respectively. It is noteworthy that the RΩ of this composite electrode decreases with continued cycling. ct The R value gradually decreases and stabilizes after 50 laps. ct The value is only 1.19 Ω. This indicates that the Bi / CNRs composite electrode has fast ion / electron diffusion kinetics.

[0074] To better understand the storage mechanism of Bi / CNRs composite electrodes, we conducted scans at different scan rates (0.2–1.0 mV / s). -1 A cyclic voltammetry test was performed on it, and the results are as follows: Figure 22 As shown. Typically, the scan rate (v) and peak current (i) have the following relationship:

[0075] i = av b (1)

[0076] Where a and b are adjustable parameters. Equation 1 can also be expressed in the following form:

[0077] log(i) = blog(v) + log(a) (2)

[0078] Here, b is the slope of the linear relationship between logi and logv, and its magnitude can qualitatively determine Na. + Storage mechanism. b = 0.5 indicates that the electrochemical reaction at the electrode is Na. + Intercalation / extraction reactions are diffusion-controlled processes; b = 1 indicates that the electrochemical reaction at the electrode is controlled by surface reactions, i.e., pseudocapacitive processes. Through... Figure 23 The logi-logv relationship was calculated, with slopes b of 0.86 (R1), 0.59 (R2), 0.80 (O2), and 0.63 (O1), indicating that the kinetics of the Bi / CNRs composite electrode are simultaneously controlled by diffusion and pseudocapacitive behavior. Furthermore, at a fixed potential, the pseudocapacitive behavior (k1v) and diffusion behavior (k2v)... 1 / 2 The relative contribution of ) can be obtained from the following equation:

[0079] i(V) = k1v + k2v 1 / 2 (3)

[0080] Where k1 and k2 are adjustable parameters. Equation 3 can also be expressed in the following form:

[0081] i(V) / v 1 / 2 = k1v 1 / 2 + k2 (4)

[0082] By calculating i(V) / v 1 / 2 With v 1 / 2 The slope of the linear relationship yields k1, which in turn determines the specific proportion of pseudocapacitance stored throughout the entire electrochemical process. For example... Figure 24 and 25 As shown, with the increase of scan rate, the proportion of capacitance contributed by pseudocapacitance also gradually increases, at a scan rate of 1.0 mV / s. -1 At that time, the contribution of the Bi / CNRs composite electrode to the capacitance control process was 92.8%. These results indicate that the electrochemical process in the Bi / CNRs composite electrode is mostly a capacitance storage process. This is attributed to the fact that the large specific surface area of ​​the carbon nanorods provides an effective pathway for electrolyte transport, while simultaneously providing a suitable environment for Na+ storage. + The embedding provides effective active sites. Furthermore, the composite material contains a large number of carbon vacancies, which can induce the generation of additional Na+. + Adsorption of active sites promotes the generation of pseudocapacitance.

[0083] To elucidate the reaction mechanism of the Bi / CNRs composite electrode during charge / discharge, we performed in-situ XRD characterization. Figure 26 We can see that as the discharge process proceeds, the characteristic peaks of the metallic Bi phase at 26.9°, 37.7°, and 39.4° gradually disappear due to the alloying reaction, while characteristic peaks of NaBi appear at 25.4°, 31.6°, and 36.5°. Subsequently, during deeper discharge, the NaBi peak intensity decreases while the Na3Bi intensity increases, until the NaBi peak completely disappears, indicating that NaBi has been completely converted to Na3Bi. During the subsequent charging process, the Na3Bi diffraction peak gradually weakens until it disappears, accompanied by the formation of NaBi. As the charging process continues, the characteristic peaks of metallic Bi gradually appear until the charging is completed, at which point NaBi is completely converted to metallic Bi. These results demonstrate that the Bi / CNRs composite electrode undergoes a multi-step reaction during charge and discharge and exhibits good reversibility. Based on the in-situ XRD characterization results, the stepwise alloying / dealloying reaction of the Bi / CNRs composite electrode can be described as follows:

[0084] Discharge process:

[0085] Bi + Na + + e - → NaBi (5)

[0086] NaBi + 2Na + + 2e - → Na3Bi (6)

[0087] Charging process:

[0088] Na3Bi → NaBi + 2Na + + 2e - (7)

[0089] NaBi → Bi + Na + + e - (8)

[0090] In summary, we designed and prepared bismuth nanoparticle / carbon nanorod composites (Bi / CNRs) using a novel and simple method. In this composite, the uniformly sized and distributed bismuth nanoparticles synthesized by ultrafast thermal shock can shorten the electron and ion transport paths, reduce polarization resistance, and improve low-temperature fast-charging performance; carbon vacancies enhance the Na+... +The adsorption capacity of the organic ligand-derived carbon nanorods enhances the sodium storage capacity; the organic ligand-derived carbon nanorods act as a buffer, reducing strain caused by volume changes and enhancing structural stability. Therefore, as a negative electrode material for sodium-ion batteries, the Bi / CNRs composite material exhibits outstanding low-temperature performance, reaching -40℃ and 5Ag. -1 The capacity at current density is 261 mAh g. -1 1Ag -1 The capacity after 2400 cycles is 240mAh g. -1 This work provides new insights for developing efficient and low-cost anode materials for low-temperature sodium-ion batteries.

[0091] Example 2

[0092] The preparation process and steps in this embodiment are as follows:

[0093] (1) Dissolve 0.14g BiCl3 in 50ml of 1.2M acetic acid solution, dissolve 0.09g KI in 12.5ml of ultrapure water, stir evenly, then pour the KI aqueous solution into the BiCl3 acetic acid solution, adjust the pH to 6, continue stirring for 30min, then place the solution in a reaction vessel and react at 160℃ for 2h. After centrifugation and washing, freeze dry for 12h to obtain BiOI NSs;

[0094] (2) Dissolve 0.3g BiOI NSs and 0.5g pyromellitic acid in a mixed solution of 20ml N,N-dimethylformamide and methanol. After stirring evenly, place the solution in a reaction vessel and react at 120℃ for 3h. After centrifugation and washing, vacuum dry for 12h to obtain Bi-MOFs.

[0095] (3) Bi-MOFs were subjected to ultrafast thermal shock treatment in Ar atmosphere with a current pulse of 10A and a time of 10s to finally obtain Bi / CNRs composite material.

[0096] The Bi / CNRs composite material obtained by the above preparation method was used as a negative electrode material for sodium-ion batteries for electrochemical performance testing, including the following steps:

[0097] a. Preparation of working electrode: First, the active material, namely Bi / CNRs, is mixed evenly with conductive carbon black and binder sodium carboxymethyl cellulose in water at a ratio of 7:2:1 and then coated onto copper foil. After vacuum drying at 70-100℃ for 10-12h, it is cut into circular electrode sheets with a diameter of 11-12mm.

[0098] b. Sodium-ion battery assembly: The active material is used as the working electrode, the sodium sheet is used as the counter electrode / reference electrode, the separator is Whatman glass fiber, and the electrolyte is 1M NaPF6 dissolved in ethylene glycol dimethyl ether. The CR2025 button battery is assembled in an argon-filled glove box. The water oxygen value of the glove box is [O2]<1ppm, [H2O]<1ppm.

[0099] c. Cyclic voltammetry tests were performed using an Ivium-n-Stat electrochemical workstation at a scan rate of 0.1–1.0 mV / s. -1 The voltage range is 0.01 to 1.5V;

[0100] d. Electrochemical impedance spectroscopy was performed at room temperature using an Ivium-n-Stat electrochemical workstation, with the frequency range set from 100 kHz to 10 mHz.

[0101] e. Battery room temperature test: The LAND-CT2001A battery test system was used to perform constant current charge and discharge tests at room temperature, with a voltage range of 0.01 to 1.5V;

[0102] f. Low temperature test of battery: Place the battery in a BPH-060B high and low temperature test chamber and use the LAND-CT2001A battery test system to perform constant current charge and discharge test at low temperature, with a voltage range of 0.01~1.5V.

[0103] g. Disassembly and characterization of the battery: The button battery after charge and discharge test was disassembled in the glove box, the electrode plates were removed, and the battery was soaked in ethylene glycol dimethyl ether solution for 20-24 hours. Then it was washed with ethanol 3-6 times. After drying, it was characterized by in-situ transmission electron microscopy (TEM). The water oxygen value in the glove box was controlled at [H2O] < 1 ppm and [O2] < 1 ppm, respectively.

[0104] h. In-situ XRD characterization of the battery: The in-situ XRD cell used beryllium metal as the window to transmit X-rays, aluminum foil as the current collector, and 1M NaPF6 dissolved in diethylene glycol dimethyl ether as the electrolyte. The separator was the same as that used in coin cells. (0.1Ag) -1 Constant current charge-discharge was performed at a current density, and XRD data were collected every 4 minutes, within the range of 10° to 90° at 10°min intervals. -1 The scan speed was tested.

[0105] The TEM image of the Bi / CNRs composite material prepared in this embodiment is as follows. Figure 27 As shown in the figure, the composite material prepared in this embodiment has a similar morphology to the material prepared in Example 1, with bismuth nanoparticles uniformly loaded on carbon nanorods.

[0106] Example 3

[0107] The preparation process and steps in this embodiment are as follows:

[0108] (1) Dissolve 0.16g BiCl3 in 50ml of 1.2M acetic acid solution, dissolve 0.08g KI in 12.5ml of ultrapure water, stir evenly, then pour the KI aqueous solution into the BiCl3 acetic acid solution, adjust the pH to 6, continue stirring for 30min, then place the solution in a reaction vessel and react at 160℃ for 2h. After centrifugation and washing, freeze dry for 12h to obtain BiOI NSs;

[0109] (2) Dissolve 0.4g BiOI NSs and 0.7g pyromellitic acid in a mixed solution of 20ml N,N-dimethylformamide and methanol. After stirring evenly, place the solution in a reaction vessel and react at 120℃ for 3h. After centrifugation and washing, vacuum dry for 12h to obtain Bi-MOFs.

[0110] (3) Bi-MOFs were subjected to ultrafast thermal shock treatment in Ar atmosphere with a current pulse of 10A and a time of 30s to finally obtain Bi / CNRs composite material.

[0111] The Bi / CNRs composite material obtained by the above preparation method was used as a negative electrode material for sodium-ion batteries for electrochemical performance testing, including the following steps:

[0112] a. Preparation of working electrode: First, the active material, namely Bi / CNRs, is mixed evenly with conductive carbon black and binder sodium carboxymethyl cellulose in water at a ratio of 7:2:1 and then coated onto copper foil. After vacuum drying at 70-100℃ for 10-12h, it is cut into circular electrode sheets with a diameter of 11-12mm.

[0113] b. Sodium-ion battery assembly: The active material is used as the working electrode, the sodium sheet is used as the counter electrode / reference electrode, the separator is Whatman glass fiber, and the electrolyte is 1M NaPF6 dissolved in ethylene glycol dimethyl ether. The CR2025 button battery is assembled in an argon-filled glove box. The water oxygen value of the glove box is [O2]<1ppm, [H2O]<1ppm.

[0114] c. Cyclic voltammetry tests were performed using an Ivium-n-Stat electrochemical workstation at a scan rate of 0.1–1.0 mV / s. -1 The voltage range is 0.01 to 1.5V;

[0115] d. Electrochemical impedance spectroscopy was performed at room temperature using an Ivium-n-Stat electrochemical workstation, with the frequency range set from 100 kHz to 10 mHz.

[0116] e. Battery room temperature test: The LAND-CT2001A battery test system was used to perform constant current charge and discharge tests at room temperature, with a voltage range of 0.01 to 1.5V;

[0117] f. Low temperature test of battery: Place the battery in a BPH-060B high and low temperature test chamber and use the LAND-CT2001A battery test system to perform constant current charge and discharge test at low temperature, with a voltage range of 0.01~1.5V.

[0118] g. Disassembly and characterization of the battery: The button battery after charge and discharge test was disassembled in the glove box, the electrode plates were removed, and the battery was soaked in ethylene glycol dimethyl ether solution for 20-24 hours. Then it was washed with ethanol 3-6 times. After drying, it was characterized by in-situ transmission electron microscopy (TEM). The water oxygen value in the glove box was controlled at [H2O] < 1 ppm and [O2] < 1 ppm, respectively.

[0119] h. In-situ XRD characterization of the battery: The in-situ XRD cell used beryllium metal as the window to transmit X-rays, aluminum foil as the current collector, and 1M NaPF6 dissolved in diethylene glycol dimethyl ether as the electrolyte. The separator was the same as that used in coin cells. (0.1Ag) -1 Constant current charge-discharge was performed at a current density, and XRD data were collected every 4 minutes, within the range of 10° to 90° at 10°min intervals. -1 The scan speed was tested.

[0120] The TEM image of the Bi / CNRs composite material prepared in this embodiment is as follows. Figure 28 As shown in the figure, the composite material prepared in this embodiment has a similar morphology to the material prepared in Example 1, with bismuth nanoparticles uniformly distributed, but exhibiting small-scale agglomeration.

[0121] The above embodiments are merely a few implementations of the present invention, and not all of them. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a bismuth nanoparticle / carbon nanorod composite material with uniform distribution, comprising the following steps: a. preparing bismuth oxyiodide nanosheets (BiOI NSs) : dissolving bismuth trichloride (BiCl3) in an acetic acid solution, dissolving potassium iodide (KI) in ultrapure water, stirring uniformly, pouring the KI aqueous solution into the BiCl3 acetic acid solution, adjusting the pH value, continuing to stir, and then placing the solution in a reaction kettle for reaction, followed by centrifugation and washing, and freeze-drying; b. preparing metal organic framework materials (Bi-MOFs) : dissolving BiOI NSs and trimesic acid (H3BTC) in a mixed solution of N, N-dimethylformamide and methanol, stirring uniformly, and then placing the solution in a reaction kettle for reaction, followed by centrifugation and washing, and vacuum drying; c. subjecting the prepared Bi-MOFs to ultrafast thermal shock treatment in an Ar atmosphere, adjusting the joule heat pulse parameters to control the size of bismuth nanoparticles and the content of Bi in the final composite material, and adjusting the thermal shock time to control the distribution of bismuth nanoparticles in the carbon nanorods in the final composite material, specifically as follows: subjecting the prepared Bi-MOFs to ultrafast thermal shock treatment in an Ar atmosphere, the current pulse is 10-100 A, and the time is 5-120 s, to obtain a bismuth nanoparticle / carbon nanorod composite material with uniform distribution, namely Bi / CNRs.

2. The method of claim 1, wherein the bismuth nanoparticle / carbon nanorod composite material is uniformly distributed. In step a, the size of BiOI is controlled by adjusting the concentration of BiCl3 and KI and the reaction time, specifically as follows: dissolving 0.05-0.6 g of bismuth trichloride (BiCl3) in 20-100 ml of 1.0-1.5 M acetic acid solution, dissolving 0.04-0.5 g of potassium iodide (KI) in 10-50 ml of ultrapure water, stirring uniformly, pouring the KI aqueous solution into the BiCl3 acetic acid solution, adjusting the pH value to 4-7, continuing to stir for 30-60 min, and then placing the solution in a reaction kettle for reaction at 100-180 °C for 2-12 h, followed by centrifugation and washing, and freeze-drying for 10-20 h.

3. The method of claim 1, wherein the bismuth nanoparticle / carbon nanorod composite material is uniformly distributed. In step b, the morphology of Bi-MOFs is controlled by adjusting the ratio of ligand H3BTC to precursor BiOI NSs, specifically as follows: dissolving 0.2-1.5 g of BiOI NSs and 0.3-1.7 g of trimesic acid (H3BTC) in 10-80 ml of a mixed solution of N, N-dimethylformamide and methanol, stirring uniformly, and then placing the solution in a reaction kettle for reaction at 100-180 °C for 2-12 h, followed by centrifugation and washing, and vacuum drying for 10-20 h.

4. The bismuth nanoparticle / carbon nanorod composite material with uniform distribution obtained by the preparation method according to any one of claims 1-3.

5. The application of the bismuth nanoparticle / carbon nanorod composite material with uniform distribution according to claim 4 in electrochemical performance testing as a sodium ion battery negative electrode material, comprising the following steps: a. Working electrode preparation: The active material, i.e. Bi / CNRs, was mixed with conductive carbon black and binder sodium carboxymethyl cellulose in a ratio of 7:2:1 in deionized water, then coated on a copper foil, vacuum dried at 70-100 °C for 10-12 h, and then cut into a circular electrode sheet with a diameter of 11-12 mm; b. Sodium-ion battery assembly: The active material was used as the working electrode, a metal sodium sheet as the counter electrode / reference electrode, a Whatman glass fiber was used as the separator, and 1 M NaPF6 dissolved in ethylene glycol dimethyl ether was selected as the electrolyte. The CR2025 type button cell was assembled in an argon-filled glove box, and the water and oxygen values of the glove box were controlled at [H2O] < 1 ppm, [O2] < 1 ppm, respectively; c. Cyclic voltammetry tests were performed using an Ivium-n-Stat electrochemical workstation with a scan rate of 0.1-1.0 mV s -1 and a voltage range of 0.01-1.5 V. d. Electrochemical impedance test was performed at room temperature using Ivium-n-Stat electrochemical workstation, and the frequency range was set to 100 kHz to 10 mHz; e. Normal temperature test of the battery: Constant current charge-discharge test was performed at room temperature using LAND-CT2001A battery test system, and the voltage range was 0.01-1.5 V; f. Low temperature test of the battery: The battery was placed in a BPH-060B type high-low temperature test box, and constant current charge-discharge test was performed at low temperature using LAND-CT2001A battery test system, and the voltage range was 0.01-1.5 V; g. Disassembly characterization of the battery: The button cell after charge-discharge test was disassembled in the glove box, the electrode sheet was taken out, soaked in ethylene glycol dimethyl ether solution for 20-24 h, washed with ethanol for 3-6 times, and then dried for in-situ transmission electron microscopy (TEM) characterization. The water and oxygen values in the glove box were controlled at [H2O] < 1 ppm, [O2] < 1 ppm, respectively. h. In-situ XRD characterization of the battery: The in-situ XRD cell was operated with a metal as the window to transmit X-rays, aluminum foil as the current collector, electrolyte was 1 M NaPF6dissolved in diethylene glycol dimethyl ether, the separator was the same as in the coin cell, and the galvanostatic charge-discharge was performed at 0.1 A g -1 The XRD data were collected every 4 min interval, and the test was performed at a scan rate of 10° min -1 -1 in the range of 10°~90°.

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