Low-temperature carbon-MoS2 composite material as well as preparation method and application thereof

Abstract

The invention belongs to the field of negative electrode materials of ion batteries, and particularly discloses a low-temperature carbon-MoS2 composite material as well as a preparation method and application thereof. The preparation method comprises the following steps: cleaning, drying and carbonizing a biomass precursor to obtain a low-temperature carbon material; dissolving in deionized water, and ultrasonically stirring to obtain a dispersed solution; (NH4) 6Mo7O244H2O and C2H5NS are added, the mixture is stirred to be uniform, and a mixed solution is obtained; transferring into a high-pressure reaction kettle for reaction to obtain a black product, sequentially washing with deionized water and absolute ethyl alcohol, and drying to obtain the low-temperature carbon-MoS2 composite material. The composite material has excellent rate capability and long cycle stability, and has small interlayer acting force and excellent sodium ion diffusion kinetics in the charging and discharging process when being applied to a sodium battery negative electrode material.

Description

Technical Field

[0001] This invention belongs to the field of anode materials for ion batteries, specifically relating to a low-temperature carbon-MoS2 composite material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries have shown great potential to replace lithium-ion batteries in areas such as large-scale static energy storage and low-speed electric vehicles due to the abundance and low cost of sodium resources. However, the sodium ion radius (approximately 1.02 Å) is larger than that of lithium ions (approximately 0.76 Å), making it difficult to achieve efficient reversible sodium ion insertion / extraction in the interlayer spacing of traditional graphite anodes. Therefore, the development of high-performance anode materials has become the key to promoting the commercial application of sodium-ion batteries.

[0003] Hard carbon materials are currently recognized as one of the most promising anode materials for sodium-ion batteries. They are obtained through high-temperature (typically >900℃) pyrolysis of biomass or polymer precursors, possessing abundant nanopores, defects, and expanded carbon interlayer spacing, providing high reversible capacity. However, the high-temperature preparation process is energy-intensive and complex, and the structure of carbon materials at high temperatures (such as graphitization degree, pore distribution, and defect density) is difficult to precisely control, restricting their cost reduction and performance optimization. To reduce energy consumption, low-temperature carbon materials have emerged. Low-temperature carbonization processes are mild and cost-controllable, but the carbon materials prepared by this method typically have high structural disorder and poor crystallinity, resulting in insufficient sodium storage active sites and weak electron / ion conduction capabilities, exhibiting low reversible capacity and poor cycle stability, making it difficult to meet the application requirements of high-energy-density batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a low-temperature carbon-MoS2 composite material, its preparation method, and its application. This composite material has excellent rate performance and long-cycle stability. When applied to sodium battery anode materials, it exhibits small interlayer forces and excellent diffusion kinetics during charge and discharge.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a low-temperature carbon-MoS2 composite material includes the following steps: S1. The biomass precursor is washed, dried, and carbonized to obtain low-temperature carbon materials. S2. Dissolve the low-temperature carbon material in S1 in deionized water and stir ultrasonically to obtain a dispersion solution; S3, (NH4)6Mo7O is added to the dispersion solution in S2. 24 4H2O and C2H5NS, stir well to obtain a mixed solution; S4. The mixed solution obtained in S3 is transferred to a high-pressure reactor for reaction to obtain a black product. The product is washed with deionized water and anhydrous ethanol in sequence, and then dried to obtain a low-temperature carbon-MoS2 composite material.

[0006] Preferably, in S1, the biomass precursor includes one of the following: wood, cotton, hemp, bamboo, rice straw, wheat straw, and sugarcane bagasse.

[0007] Preferably, in S1, the drying temperature is 120-200℃ and the drying time is 2-20h, and the carbonization temperature is 500-800℃ and the time is 1-5h.

[0008] Preferably, in S2, the frequency of the ultrasound is 20-140 kHz, and the stirring time is 10-100 min.

[0009] Preferably, in S3, the (NH4)6Mo7O 24 The molar ratio of 4H2O to C2H5NS is 1:2-1:20.

[0010] Preferably, in step S4, the reaction temperature is 100-500℃ and the time is 1-5h.

[0011] Preferably, in step S4, the drying temperature is 70-150℃ and the drying time is 12-36h.

[0012] The present invention also provides a low-temperature carbon-MoS2 composite material prepared by the aforementioned preparation method.

[0013] The present invention also provides the application of the aforementioned low-temperature carbon-MoS2 composite material in the preparation of sodium-ion battery anode materials.

[0014] The present invention also provides a negative electrode material for sodium-ion batteries, wherein the negative electrode material contains the aforementioned low-temperature carbon-MoS2 composite material.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: This invention discloses a low-temperature carbon-MoS2 composite material, its preparation method, and its applications. The low-temperature carbon material prepared at 500-800℃ can be used as a negative electrode material for sodium-ion batteries. In this invention, a low-temperature carbon material is prepared by low-temperature carbonization of a biomass precursor material, and a small amount of MoS2 nanostructures are grown on its surface using a high-pressure ultrasonic hydrothermal method to construct a low-temperature carbon-based nanocomposite material. Structural characterization shows that this low-temperature carbon possesses abundant defect structures and amorphous features, not only providing a uniformly dispersed support for MoS2 nanosheets but also enhancing interfacial bonding through CS bonds, effectively suppressing the volume expansion and aggregation of MoS2. Electrochemical tests show that at 50 mA g… -1It still maintains 308mAh g after 100 cycles. -1 The capacity retention rate was 98.9%. Furthermore, during cycling, the capacity contribution rate in the ramp region gradually increased from 64.9% to 84.8%, indicating that the material exhibits continuous self-activation behavior, further enhancing its sodium storage performance. This invention achieves a balance between high capacity and high stability through the synergistic design of low-temperature carbon and MoS2, using a low-energy-consumption process, providing a new approach for developing low-cost, high-performance sodium-ion battery anode materials.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 The results are SEM images, where... Figure 1 In the image, 'a' represents the SEM image of the low-temperature carbon material in Example 2, with a scale bar of 10 μm. Figure 1 In the image, b represents the SEM image of CM in Comparative Example 2, with a scale bar of 10 μm. Figure 1 In this text, 'c' represents the SEM image of C / M-2 in Example 2, with a scale bar of 10 μm. Figure 1 In this context, d represents the SEM image of C / M-2 in Example 2, with a scale bar of 1 μm. Figure 2 The results are shown in the high-resolution transmission electron microscopy (HRTEM) images and elemental mapping diagrams. Figure 2 In this image, 'a' represents the TEM image result from Example 2, with a scale bar of 5 nm. Figure 2 In the image, b represents the HRTEM image with a scale bar of 5 nm. Figure 2 In the diagram, 'c' represents the distribution of carbon elements, with a scale bar of 100 nm. Figure 2 In the diagram, d represents the elemental distribution of C, Mo, and S, with a scale bar of 100 nm. Figure 2 In this diagram, 'e' represents the C elemental mapping, with a scale bar of 100 nm. Figure 2 In this diagram, f represents the elemental mapping of Mo, with a scale bar of 100 nm. Figure 2 In this context, g represents the S-element mapping diagram with a scale bar of 100 nm. Figure 3 The structural and compositional characterization results of the composite materials provided in Examples 1-3 are as follows: Figure 3 In the figure, 'a' represents the Raman spectral result (100-700 cm⁻¹). -1 ), Figure 3 In the figure, b represents the Raman spectral result (900-2000 cm⁻¹). -1 ), Figure 3 In this context, 'c' represents the XRD pattern result. Figure 3 In this context, d represents the C 1s result of the XPS spectrum. Figure 3 In this context, 'e' represents the Mo 3d result from XPS spectroscopy. Figure 3 In this context, f represents the S 2p result of the XPS spectrum; Figure 4 For the surface properties of different samples, among which, Figure 4 In the figure, 'a' represents the N2 adsorption-desorption isotherm of MoS2 and C / M-2. Figure 4 In the figure, b represents the N2 adsorption-desorption isotherm of carbon (C) at low temperature. Figure 4 In the figure, 'c' represents the corresponding pore size distribution curves for low-temperature carbon (C), MoS2, and C / M-2. Figure 4 In this context, d represents the thermogravimetric analysis curve; Figure 5 The electrochemical performance of sodium-ion batteries, among which, Figure 5 In this context, 'a' represents C / M⁻² at 0.2 mV s. -1 CV curves for the first five cycles at the scan rate. Figure 5 b in the figure represents C / M-2 at 50 mA g -1 Charge-discharge curves at current density Figure 5 In this context, 'c' represents the C / M ratio, CM, and the low-temperature carbon material at 200 mA g. -1 Up to 1000mA g -1 Rate performance at different current densities Figure 5 In this context, d represents C / M, CM, and the low-temperature carbon material at 50 mA g. -1 Cyclic performance at current density; Figure 6 The electrochemical performance of a half-cell assembled using a C / M-2 positive electrode and a metallic sodium negative electrode is shown. Figure 6 In the figure, 'a' represents the cyclic voltammetry curves at different scan rates. Figure 6 In the figure, b represents the double logarithmic plot of peak current versus scan rate and the b value associated with the main reduction and oxidation peaks. Figure 6 In this context, 'c' represents the voltage scan rate of 1.0 mV / s. -1 The contribution of pseudocapacitance to the current response. Figure 6 In the figure, d represents a comparative analysis of the contributions of capacitance and diffusion control to the current at different scan rates; Figure 7 The electrochemical performance of the C / M-2 electrode as the negative electrode in a sodium-ion battery is shown, among which, Figure 7 In this context, 'a' represents the C / M-2 electrode at 50 mA g. -1 Charge-discharge curves for the 1st, 5th, 10th, 50th, and 100th cycles at current density. Figure 7 In the figure, 'b' represents the ratio of the ramp capacity to the plateau capacity (in the charge / discharge curve). Figure 7 In this context, 'c' represents the EIS Nyquist plot of C / M-2 and C. Figure 7 In this context, d represents C / M⁻² and Z' and ω of low-temperature carbon. -1 / 2 Relationship diagram; Figure 8 The results are from the sodium ion storage kinetics analysis, where, Figure 8 In the figure, 'a' represents the voltage-specific capacity curve. Figure 8 In this context, b represents the GITT curve. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0020] Example 1 A method for preparing a low-temperature carbon-MoS2 composite material includes the following steps: S1. Pass bamboo powder through a 40-mesh sieve, wash with deionized water, dry at 150℃ for 15 hours, pre-treat at 300℃ for 2 hours in a muffle furnace, and then transfer it to a tube furnace for carbonization at 600℃ for 2 hours to obtain low-temperature carbon material. S2. Dissolve 0.5g of the low-temperature carbon material in S1 in 15mL of deionized water and stir ultrasonically at 40kHz for 30min to obtain a dispersion solution; S3, Add 0.25 mmol (NH4)6Mo7O to the dispersion solution in S2. 24 4H2O and 3.5mmol C2H5NS were stirred at 200rpm for 30min to obtain a mixed solution, in which the low-temperature carbon material in the dispersion solution reacted with ((NH4)6Mo7O 24 The mass ratio of 4H2O and C2H5NS is 1:1; S4. The mixed solution obtained in S3 is transferred to a high-pressure reactor with a capacity of 100 mL and lined with polytetrafluoroethylene. The reaction is carried out at 200 °C for 2.5 h to obtain a black product. The product is washed with deionized water and anhydrous ethanol in sequence and dried in an oven at 80 °C for 24 h to obtain the low-temperature carbon-MoS2 composite material C / M-1.

[0021] Example 2 The preparation method is the same as in Example 1, except that the low-temperature carbon material and ((NH4)6Mo7O 24 The mass ratio of 4H2O and C2H5NS) was 2:1 to obtain the low-temperature carbon-MoS2 composite material C / M-2.

[0022] Example 3 The preparation method is the same as in Example 1, except that the low-temperature carbon material and ((NH4)6Mo7O 24The mass ratio of 4H2O and C2H5NS) was 3:1 to obtain the low-temperature carbon-MoS2 composite material C / M-3.

[0023] Comparative Example 1 Molybdenum disulfide prepared separately 0.25 mmol (NH4)6Mo7O 24 4H2O and 3.5mmol C2H5NS were stirred at 200rpm for 30min to obtain a mixed solution, which was then transferred to a 100mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 200℃ for 2.5h to obtain molybdenum disulfide.

[0024] Comparative Example 2 Low-temperature carbon-MoS2 composite material synthesized by conventional hydrothermal synthesis method.

[0025] S1. Pass bamboo powder through a 40-mesh sieve, wash with deionized water, dry at 150℃ for 15 hours, pre-treat at 300℃ for 2 hours in a muffle furnace, and then transfer it to a tube furnace for carbonization at 600℃ for 2 hours to obtain low-temperature carbon material. S2, 0.25 mmol (NH4)6Mo7O 24 4H2O and 3.5mmol C2H5NS were stirred at 200rpm for 30min to obtain a mixed solution, which was then transferred to a 100mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 200℃ for 2.5h to obtain molybdenum disulfide. S3. The molybdenum disulfide obtained in S2 and the low-temperature carbon material prepared in S1 are mixed at a mass ratio of 1:2 and ground by ball milling for 2 hours. The rotation speed is 25 r / min, the ball-to-material ratio is 8:1, and the grinding ball size is 10 mm to obtain the composite material CM.

[0026] The effects of the low-temperature carbon-MoS2 composite materials C / M-1, C / M-2, and C / M-3 prepared in Examples 1-3 above were verified.

[0027] 1. Material Characterization: Scanning electron microscopy (SEM, SU8010, Japan), transmission electron microscopy (TEM, JEM-2100F, Japan), powder X-ray diffraction (XRD, D8 Advance, Germany), and Raman spectroscopy (Reman, DX, Thermo Fisher). X-ray photoelectron spectroscopy (XPS, ESCALAB Xi) + (Thermo Fisher Scientific). A thermogravimetric analyzer (TGA, Q600, USA) was used to determine the content of low-temperature carbon and MoS2 in the low-temperature carbon-MoS2 composite material. The pore size distribution and specific surface area of ​​the samples were determined using the N2 adsorption-desorption method.

[0028] 2. Electrochemical characterization: The electrochemical performance of the button cell was evaluated using a battery casing (CR2032).

[0029] First, the sample, conductive carbon black, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 7:2:1 and thoroughly ground in an agate mortar. Then, an appropriate amount of N-methylpyrrolidone was added to form a uniform slurry. Next, the slurry was evenly coated onto copper foil using an infrared drying coating machine and dried at 90°C for 35 minutes to obtain a dry electrode.

[0030] The compaction density of the electrode sheets is increased by rolling them using a roller press. The rolled electrodes are then cut into negative electrode sheets with a diameter of 14 mm. The CR2032 button cell is manufactured in a glove box filled with Ar, where the water and oxygen content are both below 0.01 ppm. Sodium metal is used as the counter electrode, and glass fiber (Whatman, 18 mm) is used as the separator. The electrolyte consists of a mixture of 1 M NaClO4 in DMC, EC = 1:1 V%, containing 5% fluoroethylene carbonate (FEC).

[0031] Within a voltage range of 3-0.01V, charge-discharge, rate, and GITT experiments were conducted at room temperature using a CT3001A eight-channel system manufactured by Wuhan Landian Co., Ltd., with different current densities and other electrochemical performance parameters set. Cyclic voltammetry (CV) was performed using an electrochemical workstation (Shanghai Chenhua CHI 660) within a voltage range of 0.01-3V, at a frequency of 0.2mV / s. -1 -1.0 mV s -1 The electrochemical impedance spectroscopy (EIS) measurements were performed on an electrochemical workstation (Shanghai Chenhua CHI660E) with an AC voltage amplitude of 5 mV and a frequency range of 10. -2 -10 5 Hz.

[0032] The results are as follows: Scanning electron microscopy (SEM) results are as follows Figure 1 As shown.

[0033] Depend on Figure 1 As shown in 'a', bamboo powder exhibits a large, sheet-like structure with striped texture, and its surface is covered with numerous fragmented particles of varying sizes. Simultaneously, the material itself possesses a certain degree of porosity, providing abundant active sites. From... Figure 1 As shown in b, the molybdenum disulfide particles in Comparative Example 2 are very loosely bonded to the carbon substrate, exhibiting obvious agglomeration, and there is no interfacial interaction between them and the carbon substrate. Figure 1As can be seen from c and d, the low-temperature carbon-MoS2 composite material of Example 2 of the present invention forms a tight bond with the carbon substrate through the nanoflower structure grown on the surface, realizing the interaction between the interfaces and ensuring the efficient transfer of electrons.

[0034] High-resolution transmission electron microscopy (HRTEM) image results as follows Figure 2 As shown.

[0035] Depend on Figure 2 As can be seen from 'a', C / M-2 nanosheets have fewer layers. Their inter-layer spacing is measured to be approximately 0.64 nm, which is 0.02 nm larger than that of MoS2 (0.62 nm). This is a perfect match for the characteristic spacing of the MoS2 (002) crystal plane, which directly confirms the crystal structure of MoS2.

[0036] Figure 2 The b HRTEM images clearly reveal the coating feature of MoS2 on the carbon phase through contrast differences, with the interface between the two clearly distinguishable. The carbon layer coated by molybdenum disulfide nanosheets exhibits an amorphous structure. This MoS2-coated carbon structure not only provides abundant active sites and ion transport channels based on the layered crystal structure of MoS2, but also optimizes electronic conduction efficiency and the cycling stability of the composite material by leveraging the high conductivity and structural stability of the carbon phase.

[0037] Depend on Figure 2 c- Figure 2 As can be seen from g, the nanosheet structure of MoS2 has been successfully grown on a carbon substrate, with a uniform distribution of Mo, S and C elements.

[0038] The results of structural and compositional characterization are as follows: Figure 3 As shown.

[0039] Depend on Figure 3 The Raman spectrum of a in the image confirms that the MoS2 synthesized in this invention consists of two phases: 1T and 2H. Generally, the phases are located at 148 (J1), 226 (J2), and 323 (J3) cm⁻¹. -1 The Raman signals are attributed to the phonon vibration modes specific to the metallic phase 1T-MoS2. (379 and 404 cm⁻¹) -1 At that point, the former is the E of 2H-MoS2. 2g 1 The vibrations are attributed to the in-plane vibrations of Mo and S atoms; the latter is A 1g The vibrations are attributed to the out-of-plane vibrations of the S atom at 379 and 404 cm⁻¹. -1 The peaks at these locations are E values ​​of 2H-MoS2. 2g 1 The vibrations are attributed to the in-plane vibrations of Mo and S atoms; and A 1gThe vibrations are attributed to the out-of-plane vibrations of S atoms. All of these peaks are present in the C / M sample, confirming that the MoS2 coating with low-temperature carbon retains the coexistence of the 1T and 2H phases. However, the broad peak widths and low intensities of all samples indicate that the hydrothermally synthesized material has low crystallinity and is amorphous.

[0040] Depend on Figure 3 As can be seen from b in the figure, the Raman spectrum is in the range of ~1340 cm⁻¹. -1 and ~1590cm -1 There are two broad peaks at ~1340cm. -1 The D peak at ~1590 cm⁻¹ corresponds to defects and disordered carbon structure. -1 The G peak at that location corresponds to carbon sp. 2 The hybrid in-plane stretching vibrations indicate that they are amorphous.

[0041] Figure 3 X-ray diffraction (XRD) results of c in the samples showed that both the low-temperature carbon and C / M-2 samples exhibited two broadened weak diffraction peaks at 24.8° and 43.1°, corresponding to the (002) and (100) crystal planes of carbon, respectively. For the C / M series samples, their XRD patterns simultaneously showed the characteristic peaks of MoS2 and the broadened peaks of carbon, confirming the successful coating of carbon by MoS2. The differences in the intensity and shape of the diffraction peaks among different C / M-2 samples reflected the control effect of the coating process on the crystallinity of MoS2 and the degree of graphitization of the carbon phase. In addition, the diffraction peaks of all samples were basically consistent with the standard structure of MoS2 crystal (JCPDS#37-1492), and no obvious impurity peaks were detected, indicating that the prepared hexagonal molybdenum disulfide has high purity. Calculations using the Bragg equation show that the interlayer spacing d of C / M-2 is 0.64 nm, which is larger than that of pure MoS2 (d = 0.62 nm). This result is consistent with TEM characterization. Figure 2 It is consistent with a) in.

[0042] To further investigate the structural characteristics of C / M-2, X-ray photoelectron spectroscopy (XPS) was used to analyze the surface composition and elemental valence states of its nanosheets. The results are as follows: Figure 3 d- Figure 3 As shown in f in the figure.

[0043] Figure 3 The 'e' in the figure represents the Mo 3d electron binding energy region between C / M-2 and pure MoS2 samples. The characteristic peaks of the C / M-2 nanosheets at 233.6 eV and 230.2 eV correspond to the 2H phase Mo, respectively. 4+ 3D 3 / 2 and 3D 5 / 2 Binding energy; the peaks at 232.3 eV and 229.1 eV correspond to the 1T phase Mo. 4+ 3D3 / 2 and 3D 5 / 2 Binding energy. The presence of the 2H and 1T two-phase peaks and their relationship with... Figure 3 The results correspond to the α Raman spectroscopy results. Furthermore, two weak peaks exist in the Mo 3d spectrum, corresponding to Mo... 6+ The characteristic signal of S 2s. Peak area analysis shows that Mo 4+ The dominant valence state is Mo. 6+ Its presence is mainly due to the fact that ammonium molybdate tetrahydrate did not fully participate in the reaction. Figure 3 In the figure, f represents the high-resolution S 2p spectra of C / M-2 and pure MoS2 samples, with characteristic peaks at 161.9 eV and 163.2 eV corresponding to S 2p values, respectively. 3 / 2 and 2p 1 / 2 The binding energy, and the broad S 2p peak detected at 164.0 eV, correspond to SO bonds resulting from unavoidable exposure to air. Figure 3 In the C 1s spectrum of d, the obvious peak at 284.8 eV is attributed to the C-C bond, and the peak at 285.9 eV corresponds to the CS bond, confirming that C successfully binds to the MoS2 bond through strong chemical bonds, while the broad peak in the 287~291 eV range may be due to the C=O on the material surface.

[0044] To further investigate the surface properties of C / M-2, its pore structure was analyzed using the N2 adsorption / desorption isotherm method. The nitrogen adsorption-desorption isotherms and pore size distribution curves of the synthesized sample are shown below. Figure 4 As shown.

[0045] Depend on Figure 4 a and Figure 4 As shown in b, all samples exhibited type IV isotherms, and a type H3 hysteresis loop appeared in the relative pressure (P / P0) range of 0.4-0.8. The type IV isotherm indicates that the samples prepared by the microwave hydrothermal method possess uniform microporous and mesoporous structures (pore sizes mainly distributed between 0 and 50 nm), while the type H3 hysteresis loop indicates the presence of slit-like pores or lamellar stacking pores in the material. From the specific surface area data, the specific surface areas of the low-temperature carbon material, MoS2, and C / M-2 were 581.45 m². 2 g -1 18.01m 2 g -1 10.97m 2 g -1The differences were significant. Specifically, the nitrogen adsorption capacity of the low-temperature carbon material and MoS2 was much higher than that of C / M-2, especially in the high relative pressure range (P / P0>0.8), where the adsorption capacity of both increased significantly, indicating the presence of numerous mesopores (2~50 nm) or macropores (>50 nm) within them. In contrast, the overall adsorption capacity of C / M-2 was lower, primarily because the MoS2 coating layer blocked the original open pores of the carbon material, thus reducing the total pore volume and specific surface area. Furthermore, the pore size distribution diagram (…) Figure 4 As shown in c), the pore size of C / M-2 is mainly concentrated in the range of 0~5nm, indicating that the sample is predominantly microporous, a structure that facilitates rapid sodium ion transport. Simultaneously, the BJH pore volume of C / M-2 decreases while the average pore size increases. This characteristic can reduce the loss of active material during the formation of the SEI (solid electrolyte interface) film, thereby contributing to improving the initial coulombic efficiency of the material.

[0046] Thermogravimetric analysis (TGA) was performed on the samples under atmospheric conditions to estimate the carbon content and MoS2 content in the material. For example... Figure 4 As shown in d, the weight loss from 0℃ to 400℃ represents the physical adsorption of water by the material. The weight loss from 400℃ to 500℃ is due to the oxidation of carbon to carbon dioxide and MoS2 to MoO3, and the presence of impurities is negligible. The calculation formula is as follows: ; Calculations show that the carbon content of the three carbon-containing samples is 53.66%, 74.71%, and 83.09%, respectively.

[0047] To explore the reaction mechanism of C / M-2 in the battery, cyclic voltammetry (CV) scans of the C / M-2 anode were performed as follows: Figure 5 As shown in 'a'.

[0048] Depend on Figure 5 As can be seen from 'a' in the data, in all CV scans, the first 5 cycles were recorded within the range of 0.01-3.0V, with a scan rate of 0.2mV / s. -1 During the initial cathode scan, the peak at 0.27 V is related to the solid electrolyte interphase (SEI) layer formed by electrolyte decomposition, while the reduction peak near 0.75 V is related to Na. + Through carbon layer insertion (MoS2+xNa) + +xe - →NaxMoS2). During the first charge, two oxidation peaks at 0.45V and 1.74V correspond to the decomposition reaction of NaxMoS2. As the CV scan continued, it could be seen that the discharge / charge curves of the 2nd to 5th cycles almost overlapped, indicating that Na storage in the C / M-2 composite material has high reversibility and cycle stability.

[0049] To further explore the kinetics of C / M-2, within a potential window of 0.01–3 V, at a ga of 50 mA... -1 The charge-discharge curves of the C / M-2 anode were measured using current density, as shown in the figure. Figure 5 As shown in b in Figure 1, the initial discharge curve shows a slope at 0.3-0.8V followed by a low-voltage plateau, corresponding to the irreversible formation of the SEI and the conversion reaction of molybdenum disulfide, which is consistent with the cv results. In the second cycle, the coulombic efficiency significantly increased to 90.04%, and the specific capacity loss in subsequent cycles was close to zero. The decrease in charge-discharge specific capacity was not significant, indicating that the composite structure based on low-temperature carbon materials effectively buffered the volume strain caused by the molybdenum disulfide conversion reaction and provided a stable conductive network. This enabled the composite material to achieve a highly reversible sodium insertion / deintercalation process after initial activation, exhibiting excellent cycle stability.

[0050] Figure 5 The value of 'c' in the figure represents the rate performance of all composite materials at different current densities. The results show that C / M-2 exhibits the best rate performance: as the current density increases from 50 mA g... -1 Increase to 100, 200 and 500 mg -1 At that time, C / M-2 had a discharge specific capacity of 338 mAh g. -1 Reduced to 310, 285 and 255 mAh g -1 When the current density reaches a very high 1000 mA g -1 At that time, it still had 232mAh g -1 The capacity.

[0051] from Figure 5 As can be seen from 'c', the material with the best rate capability is C / M-2. The performance of C / M-1 and C / M-3 is lower than that of C / M-2, indicating that the active material cannot provide Na when a small amount of MoS2 is present. + Sufficient storage space reduces the effective capacity; conversely, the presence of a large amount of MoS2 affects the stability of low-temperature carbon materials, leading to capacity decay. CM is a physically mixed material, and at a high current density of 1000 mA g... -1 At that time, it only had 122mAh g -1 The high specific capacity indicates that the microwave hydrothermal method used in this paper is beneficial for the synthesis of composite materials and improves their specific capacity. In addition to excellent rate performance, C / M-2 also exhibits good cycling performance. Figure 5 d in the figure shows the composite material and low-temperature carbon material at 50 mA g. -1 The long-cycle test results showed that all materials exhibited good cycling stability; in particular, C / M-2 still retained approximately 308 mAh g⁻¹ after 100 cycles. -1 The discharge capacity.

[0052] To investigate the mechanism of the charge-discharge reaction, a range of 0.2–1 mV s was used. -1 CV tests were performed at five different scan rates. Figure 6 As shown in Figure a, all CV curves have similar shapes at different scan rates, but the reduction / oxidation peaks change slightly with increasing scan rate, and the current response is stronger.

[0053] The formulas for calculating the scan rate (υ) and peak current (i) are shown below: ; in, Indicates the scan rate. and The value of is adjustable, where the value of b is related to the electrochemical behavior. When the value of b is close to 0.5, it is inferred that the process is diffusion-controlled, such as cation insertion. Furthermore, when the value of b is close to 1, it indicates that the electrochemical behavior is surface-controlled, such as surface adsorption.

[0054] like Figure 6 As shown in b, all b values ​​(1, 0.73, 0.82, and 0.93 for peaks 1, 2, 3, and 4, respectively) are close to 1, indicating that surface-induced pseudocapacitive behavior is dominant. This characteristic stems from the favorable active sites of the structure, which is consistent with the high-rate performance of C / M-2. To further confirm the capacitance contribution of the sample at a specific scan rate, the calculation formula is as follows: ; in, Indicates a specific scan speed. and The value is adjustable. From the above formula, we can derive: . This represents the contribution of capacitor control. This represents the contribution to diffusion control. (By...) Figure 6 From c in the equation, we can see that at 1.0 mV s -1 The pseudocapacitive contribution of C / M⁻² to the current response is 74.7%. This is within the range of 0.2–1 mVs. -1 Within the scan rate range, the capacitance contribution of the C / M-2 electrode increased from 56.3% to 74.7%. As expected, the pseudocapacitive contribution of the electrode tends to increase with increasing scan speed.

[0055] Depend on Figure 6As shown in d, the trend of the contribution ratio of surface capacitance behavior and bulk diffusion behavior to capacity in the electrode reaction changes with the scan rate. This indicates that in the sodium storage process of the prepared C / M-2 composite material, surface-driven pseudocapacitive behavior dominates, and its contribution rate increases significantly with increasing scan rate. The faster the scan rate (i.e., the faster the charge and discharge speed), the higher the proportion of capacitance contribution. This explains why the C / M-2 electrode can withstand extremely high current densities (1000 mA g / g). -1 Even at this level, it still maintains a high specific capacity (232 mAh g). -1 This is because at high rates, the rapid capacitive storage mechanism takes over most of the charge storage task. The amorphous structure of low-temperature carbon, defect sites, and the large specific surface area of ​​MoS2 nanosheets together provide a large number of surface active sites.

[0056] Therefore, pseudocapacitive behavior dominates in C / M-2. At all scan rates, the pure carbon control sample exhibits a lower pseudocapacitive contribution compared to the molybdenum disulfide-containing composite, consistent with its poor rate performance. The pseudocapacitive contribution directly affects the storage kinetics of Na. As the pseudocapacitive contribution increases, sodium ion transport is enhanced, as clearly observed in the rate performance tests discussed above. Furthermore, kinetic test results also demonstrate the significant performance of the C / M-2 half-cell.

[0057] Figure 7 In this context, 'a' represents the C / M-2 material at 50 mA g. -1 Charge-discharge curves for the 1st, 5th, 10th, 50th, and 100th cycles under the specified conditions are shown. The sample clearly exhibits a plateau region (voltage range 0–0.1 V) and a slope region (voltage range 0.1–3.0 V). During the 1st, 5th, and 10th discharge cycles, the sodium storage capacities of the C / M-2 electrode in the slope and plateau regions were 310.41 / 167.69, 257.17 / 54.38, and 267.65 / 55.25 mAh g, respectively. -1From the perspective of the slope region capacity contribution rate, the C / M-2 slope region contribution rate was 64.9% in the initial cycle; with the increase of the number of cycles, the slope region contribution rate increased to 82.4%, 82.9%, 83.2%, and 84.8% in cycles 5, 10, 50, and 100, respectively. This change indicates that as cycling progresses, the dispersion of MoS2 on the carbon surface gradually improves, the synergistic effect of carbon and MoS2 is fully activated, the overall utilization rate of sodium storage sites is significantly improved, and ultimately manifested as a continuous increase in slope region capacity. The storage of sodium ions in the C / M-2 electrode is similar to the storage of lithium ions in graphite, including surface adsorption and insertion between carbon layers in the pseudo-graphite structure. This is the main reason for the appearance of low-pressure plateau regions. The slope region with a voltage greater than 0.1V is related to the adsorption of Na ions at defect sites in C / M-2. This phenomenon indicates that the charge-discharge behavior of sodium ions in C / M-2 is "adsorption-intercalation". To further analyze the charge transfer kinetics of C / M-2, electrochemical impedance spectroscopy (EIS) was performed.

[0058] Depend on Figure 7 As can be seen from b, the capacity of the slope region mainly originates from surface-controlled processes, including Na. + Adsorption occurs at carbon defects and pore surfaces, as well as rapid pseudocapacitive reactions at active sites such as the edges of MoS2. These reactions exhibit fast kinetics and good rate performance. The plateau capacity corresponds to a bulk diffusion-controlled process, such as Na... + The intercalation between carbon layers or the conversion of MoS2 to Na2S and Mo are involved. This part of the reaction provides high capacity but has slow kinetics. As cycling progresses, the capacity contribution of the ramp region increases continuously from 64.9% to 84.8%, indicating that the sodium storage mechanism of the material gradually evolves from "intercalation / conversion-dominated" to "surface capacitance behavior-dominated". Figure 7 Figure c shows the Nyquist plot of C / M-2 versus C. The curves in the figure exhibit typical characteristics; the diameter of the semicircle in the high-frequency region reflects the magnitude of the charge transfer resistance (Rct) of the electrode, with a larger diameter indicating a larger charge transfer resistance. The charge transfer resistances of C / M-2 and C are 298 Ω and 595 Ω, respectively, indicating that Na... + The redox reaction occurs more rapidly on the C / M-2 surface. Therefore, C / M-2 can release a higher capacity under high current. Furthermore, the slope of the straight line in the low-frequency region reflects the Warburg impedance, and its relationship with Na... + The diffusion coefficient D in the electrode material is related. The equation is as follows: ; in, The gas constant is... The area of ​​the electrode sheet is... This represents the sodium ion concentration. For the number of transferred electrons, It is Faraday's constant. This is the Warburg coefficient.

[0059] Figure 7 In the equation, d is a linear fit between Z′ and ω⁻¹ / ², and the slopes σ for the C / M⁻² and pure carbon (C) electrodes are 55.16 and 149.76, respectively. The equation shows that the sodium ion diffusion coefficient of the C / M⁻² electrode is significantly higher than that of the pure carbon electrode, and the larger the diffusion coefficient, the faster the sodium ion diffusion rate.

[0060] The kinetics of C / M-2 in sodium storage were further investigated using GITT testing. The GITT testing conditions were: at 50 mA g... -1 Charge / discharge at a constant current for 10 minutes, then let stand for 30 minutes, until the charge / discharge reaches the cutoff voltage. From the voltage-specific capacity curve ( Figure 8 As shown in a), during the discharge phase, the voltage drop of the pure carbon (Pristine C) electrode is gradual, and the long plateau in the low-voltage region corresponds to the adsorption-type storage of sodium ions in carbon pores and defect sites. In contrast, the C / M-2 electrode exhibits a wide voltage plateau in the 0.5–1.0V range. This reflects the synergistic effect of the "adsorption / pore-filling" mechanism between molybdenum disulfide and carbon materials, indicating the introduction of a new sodium storage pathway. The reversible specific capacity also increases from 316 mAh·g for pure carbon. -1 Increased to 436mAh·g -1 This is consistent with the GCD test results.

[0061] Depend on Figure 8 As shown in the voltage-time curves, the C / M-2 electrode exhibits more pulses and longer charge / discharge times, reflecting both high capacity characteristics and excellent diffusion kinetics. Furthermore, the instantaneous voltage changes (charge jump, discharge drop) during current pulses are extremely small. This low polarization characteristic implies low sodium ion diffusion resistance within the electrode, contributing to its high capacity (20–1000 mA·g). -1 The key to maintaining high capacity under high current is... In summary, the GITT results fully demonstrate that C / M-2, through the synergistic effect of carbon and molybdenum disulfide components, significantly outperforms pure carbon electrodes in terms of sodium storage capacity, reaction reversibility, and kinetics, providing strong kinetic support for its application in sodium-ion batteries.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a low-temperature carbon-MoS2 composite material, characterized in that, Includes the following steps: S1. The biomass precursor is washed, dried, and carbonized to obtain low-temperature carbon materials. S2. Dissolve the low-temperature carbon material in S1 in deionized water and stir ultrasonically to obtain a dispersion solution; S3, (NH4)6Mo7O is added to the dispersion solution in S2. 24 4H2O and C2H5NS, stir well to obtain a mixed solution; S4. The mixed solution obtained in S3 is transferred to a high-pressure reactor for reaction to obtain a black product. The product is washed with deionized water and anhydrous ethanol in sequence, and then dried to obtain a low-temperature carbon-MoS2 composite material.

2. The preparation method according to claim 1, characterized in that, In S1, the biomass precursors include one of the following: wood, cotton, hemp, bamboo, rice straw, wheat straw, and sugarcane bagasse.

3. The preparation method according to claim 1, characterized in that, In S1, the drying temperature is 120-200℃ and the drying time is 2-20h, while the carbonization temperature is 500-800℃ and the time is 1-5h.

4. The preparation method according to claim 1, characterized in that, In S2, the frequency of the ultrasound is 20-140kHz, and the stirring time is 10-100min.

5. The preparation method according to claim 1, characterized in that, In S3, the (NH4)6Mo7O 24 The molar ratio of 4H2O to C2H5NS is 1:2-1:

20.

6. The preparation method according to claim 1, characterized in that, In S4, the reaction temperature is 100-500℃ and the time is 1-5h.

7. The preparation method according to claim 1, characterized in that, In step S4, the drying temperature is 70-150℃ and the drying time is 12-36h.

8. The low-temperature carbon-MoS2 composite material prepared by the preparation method according to any one of claims 1-7.

9. The application of the low-temperature carbon-MoS2 composite material as described in claim 8 in the preparation of sodium-ion battery anode materials.

10. A negative electrode material for sodium-ion batteries, characterized in that, The negative electrode material contains the low-temperature carbon-MoS2 composite material as described in claim 8.

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