Cobalt-doped SnS / SnS2 heterostructure / nitrogen-doped carbon core-shell nanotube composite negative electrode material and preparation method thereof

Abstract

The invention discloses a cobalt-doped SnS / SnS2 heterostructure / nitrogen-doped carbon core-shell nanotube composite negative electrode material and a preparation method of the cobalt-doped SnS / SnS2 heterostructure / nitrogen-doped carbon core-shell nanotube composite negative electrode material. According to the material, a nitrogen-doped carbon nanotube (CPPy-NT) is used as a skeleton, and a cobalt-doped SnS / SnS2 heterostructure is loaded, so that a core-shell nanotube composite system is formed. A SnS2 energy band structure is reconstructed through cobalt doping, a Co-S strong bond is formed, and volume expansion is inhibited; the nitrogen-doped carbon matrix provides a high conductive network (the conductivity is greater than 103S / cm) and rich mesopores (the aperture is 2-10nm), and accelerates Na < + > transmission (the diffusion coefficient is greater than 2.5 * 10 <-10 > cm < 2 > / s). The preparation method comprises template-assisted polymerization, calcination and hydrothermal vulcanization processes, and realizes accurate regulation and control of the material structure. The initial capacity of the obtained negative electrode is greater than 800mAh / g under 0.5 A / g, the capacity retention ratio is 98% or more after circulation for 100 times, the capacity retention ratio is 85% or more after circulation for 1500 times under 5A / g, and the rate capacity of 15A / g reaches 400mAh / g or more. The invention solves the problems of large volume expansion, poor conductivity and short cycle life of the tin sulfide-based material, and is suitable for high-performance sodium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the field of new energy materials and electrochemical energy storage technology, and specifically relates to a sodium ion battery negative electrode material and a preparation method thereof, in particular to a SnS / SnS2-based composite negative electrode material that achieves high capacity and long cycle stability through synergistic optimization of cobalt doping, heterostructure design and nitrogen-doped carbon matrix. Background Art

[0002] Sodium-ion batteries are considered an ideal alternative to large-scale energy storage systems due to their abundant sodium resources (2.3% abundance in the earth's crust), low cost (the price of sodium carbonate is less than 1 / 10 of that of lithium salts), and similar electrochemical mechanisms to lithium-ion batteries. Among the many negative electrode materials, layered tin sulfide (SnS2) can be a good alternative to sodium ions due to its high theoretical specific capacity (833mAh / g) and wide interlayer spacing (0.59nm). Providing a fast insertion / extraction channel has become a research hotspot. However, the practical application of SnS2-based materials still faces three major bottlenecks: (1) Poor cycle stability: SnS2 undergoes a dramatic volume change during the charge and discharge process (expansion rate > 250%), resulting in the pulverization of active material particles and the collapse of the electrode structure. After 50 cycles, the capacity usually decays to less than 50% of the initial value; (2) Insufficient intrinsic conductivity: SnS2 is a semiconductor material (conductivity < 10 -6 S / cm), the charge transfer kinetics are sluggish, and the capacity drops sharply at high rates (>5A / g);

[0003] (3) Polysulfide shuttle effect: The intermediate product soluble polysulfide (such as Na2S4) diffuses in the electrolyte, causing irreversible loss of active materials and capacity decay.

[0004] In response to the above problems, researchers have proposed a variety of modification strategies. For example, a conductive network is constructed and volume expansion is buffered by coating with carbon materials (such as graphene and carbon nanotubes), but traditional carbon coating materials are often unable to effectively inhibit the dissolution of polysulfides due to insufficient density or weak interface bonding. In addition, although single element doping (such as Fe, N) can partially improve conductivity, the doped atoms are prone to form local stress in the lattice, resulting in a decrease in structural stability. In recent years, heterostructure designs (such as SnS / SnS2, SnS2 / MoS2) have improved charge transfer through interface energy band engineering. However, the lattice mismatch between heterogeneous materials (such as the mismatch rate of SnS2 and MoS2 is 8%) can easily cause interface cracks, which in turn accelerates electrode failure. The core innovation of the present invention lies in proposing a "cobalt doping-heterostructure-core-shell confinement" collaborative optimization strategy: Cobalt doping regulates the electronic structure: Introducing Co 2+ / Co 3+Mixed valence, through d orbital hybridization to reduce the sodium ion diffusion barrier of SnS2 (from 0.8eV to 0.3eV), and form a strongly bonded Co-S interface (bond energy > 450kJ / mol), inhibiting volume expansion; SnS / SnS2 heterojunction accelerates charge separation: constructs a type II band alignment structure, realizes efficient separation of electron-hole pairs under the drive of the built-in electric field, and improves the interface reaction kinetics (charge transfer resistance is reduced by 60%); nitrogen-doped carbon core-shell nanotube confinement effect: with a high specific surface area (> 280m 2 / g) of nitrogen-doped carbon nanotubes as the skeleton, which anchors polysulfides through a dual mechanism of mesoporous confinement (pore size 2-10nm) and chemical adsorption of pyridinic nitrogen sites, while providing a continuous electron transport path (conductivity > 10 3 This multi-dimensional collaborative design breaks through the performance limitations of a single modification strategy and provides a new technical route for the development of high-stability and high-rate anode materials for sodium-ion batteries. Summary of the Invention

[0005] Material composition and structural design

[0006] Core-shell nanotube matrix: Nitrogen-doped carbon nanotubes (CPPy-NT) as core-shell skeleton, cobalt-doped SnS / SnS2 heterostructure loaded on the surface of carbon tubes, cobalt doping amount 3-5wt%, interface characteristics: Co 2+ / Co 3+ Mixed valence forms Co-S bonds with sulfur.

[0007] Preparation method

[0008] Step 1 (templated polymerization): methyl orange was used as the template, pyrrole was used as the carbon source, SnCl2·2H2O and CoCl2·6H2O were added, and ammonium persulfate was used to initiate the polymerization;

[0009] Step 2 (calcination loading): calcination at 600 °C for 3 h to form the Co-SnS@CPPy-NT intermediate;

[0010] Step 3 (hydrothermal vulcanization): Thioacetamide was used as the sulfur source, and the reaction was carried out at 160 °C for 12 h to obtain Co-SnS / SnS2@CPPy-NT.

[0011] application

[0012] Sodium-ion battery anode materials: Suitable for sodium-ion battery systems with high energy density (>300Wh / kg) and long cycle life (>1500 times) at high power density output, compatible with Prussian blue or layered oxide cathodes; Energy storage scenarios: including electric vehicles, grid-level energy storage, and portable electronic devices, with active material surface loading >3mg / cm 2 , electrode compaction density>1.8g / cm 3.

[0013] Innovation

[0014] Through the "solution reaction-high temperature sintering-hydrothermal sulfurization" multi-process collaborative preparation technology, a heterojunction composite structure of SnS / SnS2 wrapped with an N-doped carbon skeleton was successfully constructed, and the precise doping control of the Co element was achieved. This preparation strategy breaks through the limitations of a single process, allowing Co atoms to be evenly distributed at the SnS / SnS2 lattice interface, forming a unique Co-S bond anchoring structure, which effectively inhibits the agglomeration of active substances. In terms of material structure design, the N-doped carbon skeleton is coupled to the interface of SnS / SnS2 through CN bonds, and combined with the defect structure revealed by Raman spectroscopy and the active sites characterized by XPS, a sodium storage system of "defect regulation-interface optimization-active site collaboration" is constructed. In terms of performance optimization mechanism, it is revealed for the first time that Co doping reduces charge transfer resistance, improves electronic conductivity and Na + The triple synergistic effect of adsorption energy, in conjunction with the high conductivity and porous structure of the N-doped carbon skeleton, forms a dual optimization path of "element doping to optimize electron dynamics + multi-structure synergistic promotion of ion migration".

[0015] Beneficial effects

[0016] Electrochemical performance breakthroughs include: High capacity: Initial capacity greater than 800 mAh / g at 0.5 A / g, with capacity retention exceeding 98% after 100 cycles; Long cycle life: Capacity retention exceeding 85% after 1500 cycles at 5 A / g; Excellent rate capability: Reversible capacity exceeding 400 mAh / g at 15 A / g. Improved structural stability: Volume expansion suppression: Co-S bonds synergistically interact with the carbon skeleton, resulting in >95% structural integrity after electrode cycling; Polysulfide anchoring: Sulfur vacancies and pyridinic nitrogen sites exhibit >98% polysulfide adsorption efficiency. Industrial suitability: Scalable process: Single calcination output >1 kg / h, thioacetamide utilization >90%; Cost advantage: Cobalt doping requires only 3-5 wt%, reducing raw material costs by 30% compared to similar materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : Characterization of the core-shell nanotube structure of Example 1

[0018] (ab) SEM images: showing the tubular interwoven structure of nitrogen-doped carbon nanotubes (CPPy-NT) and the uniform loading morphology of SnS / SnS2 heterostructure.

[0019] (cd) TEM / HRTEM images: High-resolution images show the heterogeneous interface between SnS (interplanar spacing 0.28 nm) and SnS2 (interplanar spacing 0.32 nm), as well as the confinement effect of the carbon nanotube skeleton.

[0020] (e) EDS Mapping: Uniform distribution of Sn, S, Co, C, and N elements, verifying the successful construction of the multi-component composite structure.

[0021] Figure 2 :Material phase and chemical state analysis

[0022] XRD pattern: The characteristic peaks of SnS (orthorhombic phase, PDF#00-001-0984) and SnS2 (hexagonal phase, PDF#00-022-0951) coexist, confirming the formation of a heterogeneous structure.

[0023] Figure 3 : Electrochemical performance test results

[0024] (ad) Cycling performance curves: The capacity retention rate of Co-SnS / SnS2@CPPy-NT after 100 cycles at 1 A / g is 100.5%, which is significantly higher than that of the control group (SnS2@C retention rate <70%).

[0025] (e) Rate performance curve: When the current density increases from 0.5 A / g to 15 A / g, the reversible capacity decreases from 875 mAh / g to 479 mAh / g, and recovers to 840 mAh / g after returning to 0.5 A / g, reflecting excellent structural reversibility.

[0026] (f) Long-term cycle stability: After 500 cycles at 5 A / g, the capacity retention rate is 88%, and the electrode thickness expansion rate is less than 10%.

[0027] Figure 4 :Analysis of kinetic mechanism

[0028] (a) CV curve: At a scan rate of 0.2 mV / s, the redox peak symmetry of Co-SnS / SnS2@CPPy-NT is better than that of the control group, indicating that the reversibility of the interfacial reaction is improved.

[0029] (b) EIS spectrum: The semicircle diameter in the high-frequency region (corresponding to the charge transfer resistance Rct) decreases from 85Ω of pure SnS2 to 35Ω, and the slope in the low-frequency region (corresponding to Na + The diffusion coefficient) increased by 3 times.

[0030] (c) Capacitance contribution analysis: At a scan rate of 1.0 mV / s, the capacitance contribution accounts for 93.71%, indicating that the surface pseudocapacitance is the dominant fast energy storage mechanism.

[0031] (d) Adsorption curve

[0032] (e) Pore size distribution curve

[0033] (f) EPR spectrum

[0034] Description of the accompanying drawings

[0035] Figure 1 :From the perspectives of morphology, phase and chemical state, the successful construction of the core-shell structure, heterogeneous interface and doping characteristics of the material is explained;

[0036] Figure 2-4 : Through electrochemical performance and kinetic analysis, the mechanism of high capacity, long cycle and rapid sodium storage of the material is revealed;

[0037] The molar ratio of methyl orange to pyrrole is 0.02-0.05:1; the molar ratio of SnCl2·2H2O to pyrrole is 0.08-0.1:1; and the mass ratio of thioacetamide to the calcined SnS@CPPy-NT precursor during the sulfurization stage is 1.5-3:1. The amount of CoCl2·6H2O added is 3-7% of the mass of SnCl2·2H2O. DETAILED DESCRIPTION

[0038] Example 1:

[0039] Preparation process parameters include a molar ratio of methyl orange to pyrrole of 0.05:1; a molar ratio of SnCl2·2H2O to pyrrole of 0.088:1; an amount of ammonium persulfate equal to three times the molar amount of pyrrole monomer; and a mass ratio of thioacetamide to the calcined SnS@CPPy-NT precursor during the sulfurization step of 2:1. The cobalt doping level was 5% of the mass of the SnCl2·2H2O.

[0040] Specific protocol: 1.25 mmol methyl orange and 25 mmol pyrrole were dissolved in 100 mL deionized water. 2.2 mM MSnCl2·2H2O and 0.025 g CoCl2·6H2O were added. After mixing, 75 mM ammonium persulfate was added to initiate polymerization. After stirring for 10 hours, the mixture was filtered and dried. The product was calcined at 600°C under nitrogen for 3 hours to obtain the precursor. 0.2 g of the precursor was hydrothermally reacted with 0.4 g thioacetamide at 160°C for 12 hours. The product was washed with deionized water and dried in vacuo at 70°C to obtain Co-SnS / SnS2@CPPy-NT.

[0041] Technical effect: In the composite material, the actual cobalt doping amount is 4.3wt%, the molar ratio of SnS to SnS2 is 1:2, and the specific surface area of ​​the carbon matrix is ​​305m 2 / g, with a pore size distribution of 2-10nm. The nitrogen doping amount of nitrogen-doped carbon nanotubes is 5.6at%, of which pyridinic nitrogen accounts for 66%. The sulfur vacancy density of the SnS / SnS2 heterostructure is 3.5×10 16 cm -2The negative electrode had an initial capacity of 875 mAh / g at 0.5 A / g, and a capacity retention rate of 100% after 100 cycles. After 1500 cycles at a current density of 5 A / g, the capacity retention rate of the negative electrode was >85%. After 1500 cycles at 5 A / g, the capacity retention rate exceeded 86%, and the rate capacity at 15 A / g reached over 480 mAh / g.

[0042] Example 2:

[0043] Preparation process parameters: methyl orange to pyrrole molar ratio of 0.03:1; SnCl2·2H2O to pyrrole molar ratio of 0.09:1; ammonium persulfate dosage twice the pyrrole molar ratio; thioacetamide to precursor mass ratio of 1.5:1; and CoCl2·6H2O added in an amount of 3% by mass of SnCl2·2H2O. The detailed implementation plan is the same as in Example 1.

[0044] Technical effect: The actual cobalt doping amount is 2.1wt%, the SnS / SnS2 molar ratio is 1:1.5, and the carbon matrix specific surface area is 295m 2 / g, pore size distribution 2-10nm. Nitrogen doping amount 4.2at%, pyridinic nitrogen accounts for 63%, sulfur vacancy density 2.8×10 16 cm -2 The initial capacity at 0.5A / g is 820mAh / g, and the capacity retention rate after 100 cycles is 99%; the capacity retention rate after 500 cycles at 5A / g is 88%; the rate capacity at 15A / g is 450mAh / g.

[0045] Example 3

[0046] Preparation process parameters: methyl orange to pyrrole molar ratio of 0.04:1; SnCl2·2H2O to pyrrole molar ratio of 0.1:1 (range in claim 8: 0.08-0.1); ammonium persulfate dosage of 2.5 times the molar amount of pyrrole; thioacetamide to precursor mass ratio of 3:1; CoCl2·6H2O added in an amount of 7% by mass of SnCl2·2H2O. The detailed implementation plan is the same as in Example 1.

[0047] Technical effect: The actual cobalt doping amount is 4.8wt%, the SnS / SnS2 molar ratio is 1:2.8, and the carbon matrix specific surface area is 318m 2 / g, pore size distribution 2-10nm. Nitrogen doping amount 6.5at%, pyridinic nitrogen accounts for 68%, sulfur vacancy density 4.7×10 16 cm -2 The initial capacity at 0.5A / g is 905mAh / g, and the capacity retention rate after 100 cycles is 98.5%; the capacity retention rate after 500 cycles at 5A / g is 90%; the rate capacity at 15A / g is 510mAh / g.

[0048] Comparative Example 1

[0049] 0.025 mmol of methyl orange and 2.5 mmol of pyrrole were dissolved in 100 mL of deionized water. Subsequently, 7.5 mM ammonium persulfate was added, and an appropriate amount of deionized water was added. Stirring was continued for 10 hours. After the reaction was completed, the product was filtered and dried. The dried product was sintered in a tube furnace at 600°C for 3 hours. After the reaction was completed, the product was filtered, washed with deionized water, and dried in a vacuum drying oven at 70°C. The sample was named CPPy-NT.

[0050] Comparative Example 2

[0051] 0.025 mmol of methyl orange and 2.5 mmol of pyrrole were dissolved in 100 mL of deionized water. Subsequently, 0.5 g of SnCl2·2H2O was added as a tin source. Next, 7.5 mM ammonium persulfate was added, and an appropriate amount of deionized water was added, with stirring continued for 10 hours. After the reaction, the product was filtered and dried. The dried product was sintered in a tube furnace at 600°C for 3 hours. The sintered product was dispersed in 35 mL of deionized water at a rate of 0.2 g per portion, and 0.4 g of thioacetamide was added. After ultrasonic homogenization, the product was transferred to a reactor and hydrothermally treated at 160°C for 12 hours. After the reaction, the product was filtered, washed with deionized water, and dried in a vacuum drying oven at 70°C. The sample was named SnS@CPPy-NT.

[0052] Comparative Example 3

[0053] 0.025 mmol of methyl orange and 2.5 mmol of pyrrole were dissolved in 100 mL of deionized water, followed by the addition of 0.5 g of stannous chloride dihydrate. Subsequently, 7.5 mM of ammonium persulfate was added, and an appropriate amount of deionized water was added, with stirring continuing for 10 hours. After the reaction, the product was filtered and dried. The dried product was sintered in a tube furnace at 600°C for 3 hours. 0.2 g of the sintered product was dispersed in 35 mL of deionized water, 0.4 g of thioacetamide was added, and the mixture was ultrasonically homogenized before being transferred to a reactor for hydrothermal treatment at 160°C for 12 hours. After the reaction, the product was filtered, washed with deionized water, and dried in a vacuum drying oven at 70°C. The sample was named SnS / SnS2@CPPy-NT.

[0054] Comparative Example 4

[0055] 2.5 mmol of pyrrole was dissolved in 100 mL of deionized water, followed by the addition of 0.5 g of stannous chloride dihydrate and 5% CoCl2·6H2O as a doping tin source. Subsequently, 7.5 mM ammonium persulfate was added, and an appropriate amount of deionized water was added, and stirring was continued for 10 hours. After the reaction was completed, the product was filtered and dried. The dried product was sintered in a tube furnace at 600°C for 3 hours. The sintered product was dispersed in 35 mL of deionized water at a rate of 0.2 g per portion, 0.4 g of thioacetamide was added, and after ultrasonic homogenization, it was transferred to a reactor for hydrothermal treatment at 160°C for 12 hours. After the reaction was completed, the product was filtered, washed with deionized water, and dried in a vacuum drying oven at 70°C. The sample was named 0g methyl orange.

[0056] Material characterization and electrochemical performance testing

[0057] Next, the morphology and structure of the composite material are tested and characterized by phase testing, and the electrochemical performance of the composite material prepared by the present invention is tested and characterized by cycle performance testing.

[0058] 1. SEM and TEM analysis

[0059] from Figure 1 As can be seen in Figures (a-b), after the introduction of Co, the degree of structural interweaving of Example 1 is intensified, indicating that Co doping has a regulatory effect on the crystal growth dynamics and promotes the formation of heterogeneous structures. Figures (c-d) are samples of Example 1, and their structure shows that Co-SnS / SnS2 is uniformly loaded on CPPy-NT, forming a stable and regular composite structure. Figure (e) shows that Example 1 was analyzed by TEM-EDS mapping. The results show that Sn and S elements are evenly distributed in the carbon nanotube region composed of C and N, and there is no element segregation phenomenon.

[0060] 2. XRD analysis

[0061] Figure 2 The XRD patterns of the samples of Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1 are shown. As can be seen from the figure, the sample of Example 1 exhibits characteristic diffraction peaks of SnS and SnS2 (matching the SnS and SnS2 standard cards), indicating that the prepared product forms a SnS / SnS2 composite structure and is composited with CPPy-NT, confirming that each target sample achieves the expected phase composition.

[0062] 3. Cycle performance test

[0063] Figure 3 The mid-cycle performance curve shows that the samples of the present invention are -1Electrochemical performance under current density. Taking the sample of Example 1 as an example, comparing samples with different additive contents (such as 0, 0.05mmol of methyl orange, etc.), the target sample maintains better specific capacity during the cycle and the coulombic efficiency is stable. Further comparing samples with different Co content and Sn content, the specific capacity of the core sample of the present invention decays more slowly, indicating that its structure is more stable in cyclic charge and discharge, and effectively improves the electrochemical performance. The same method is used to detect the materials of other embodiments, and their morphology, structure and performance results are consistent with the core embodiment, verifying the stability of the material of the present invention and the reliability of the technical solution.

[0064] 4. CV, EIS, BET, EPR analysis

[0065] Figure 4 a, in the voltage range of 0.01-3.0 V, 0.2 mV s -1 At the scanning rate, the first three CV curves of Example 1 showed significant differences: the first reduction stage curve characteristics reflected Na + The complex reaction of active substances during the embedding process and the irreversible process of SEI film formation, the oxidation stage corresponds to Na + Deintercalation; The curves of the 2nd and 3rd cycles are highly overlapped, indicating that the electrode / electrolyte interface gradually stabilizes during the cycle, the SEI film tends to be perfect, and the reversibility of the electrochemical reaction is enhanced.

[0066] Figure 4 b shows, 1.0mV s -1 The contribution of capacitance is 93.71%.

[0067] Figure 4 c shows the EIS results after cycling. The charge transfer resistance increases first and then decreases, while the migration resistance continues to decrease, which is consistent with the formation of the SEI film and the activation of the material. The formation of the SEI film at the beginning of the cycle leads to an increase in resistance. As the cycle progresses, the Co-S bond anchors the active material, inhibits agglomeration, and the material is fully activated (after 50 cycles). The Warburg impedance decreases, promoting Na + transmission.

[0068] Figure 4 In Figure d, the adsorption curves for different samples show distinct trends. As relative pressure increases, the adsorption volume of Example 1 shows a clear upward trend, indicating that its adsorption capacity is particularly strong at certain pressure levels. This intuitively demonstrates how the adsorption capacity of gas molecules varies with pressure during the adsorption process for each material.

[0069] Figure 4In Figure 4, the peak positions and morphologies of the pore size distribution curves for different samples vary. For example, the peak of the curve for Comparative Example 1 reflects its primary pore size range. Compared with other samples, the concentration of the pore size distribution or the shift in the primary pore size range after doping or composite can be observed, clearly demonstrating the distribution of pore sizes within the material.

[0070] Figure 4 In f, the effect of Co doping (Example 1) on the signal near the g value is specifically reflected in the change of the intensity fluctuation characteristics, which accurately presents the difference in the electronic paramagnetic properties of the materials and can be used to deeply analyze the differences in the internal electronic structure of the materials.

[0071] The protection content of the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention and are protected by the appended claims.

Claims

1. A cobalt-doped SnS / SnS2 heterostructure / nitrogen-doped carbon core-shell nanotube composite negative electrode material, characterized by: The composite material comprises nitrogen-doped carbon nanotubes (CPPy-NTs) and a Co-SnS / SnS2 heterostructure uniformly loaded on the surface of the carbon nanotubes; the composite material comprises a cobalt doping amount of 1-5wt%, a molar ratio of SnS to SnS2 of 1:1-1:3, and a carbon matrix specific surface area of ​​280-320m 2 / g, pore size distribution 2-10nm.

2. The composite material according to claim 1, wherein: In the Co-SnS / SnS2 heterostructure, cobalt is in the form of Co 2+ / Co 3+ Mixed valence states exist and form Co-S bonds with sulfur.

3. The composite material according to claim 1, wherein: The nitrogen doping amount of the nitrogen-doped carbon nanotubes is 3-7 at %, wherein the proportion of pyridinic nitrogen is greater than 60%.

4. The composite material according to claim 1, wherein: The sulfur vacancy density of the SnS / SnS2 heterostructure is 1×10 15 -5×10 16 cm -2 .

5. A method for preparing the composite material according to any one of claims 1 to 4, comprising the following steps: a) Methyl orange and pyrrole were dissolved in deionized water, SnCl2·2H2O and CoCl2·6H2O were added, and finally ammonium persulfate was added to initiate polymerization, and the precursor SnS@CPPy-NT was obtained by calcination; b) Thioacetamide hydrothermal sulfurization to obtain Co-SnS / SnS2@CPPy-NT.

6. The method according to claim 5, wherein: In step b, the calcination temperature is 600° C., the heating rate is 5° C. / min, and the calcination time is 6 h.

7. The method according to claim 5, wherein: In step c, the vulcanization temperature is 160° C. and the vulcanization time is 12 h.

8. The method according to claim 5, wherein: The molar ratio of methyl orange to pyrrole is 0.02-0.05:1; the molar ratio of SnCl2·2H2O to pyrrole is 0.08-0.1:1; the amount of ammonium persulfate added is 2-3 times the molar amount of pyrrole monomer added; and the mass ratio of thioacetamide to the calcined SnS@CPPy-NT precursor during the sulfurization stage is 1.5-3:

1. The amount of CoCl2·6H2O added is 3-7% of the mass of SnCl2·2H2O.

9. A sodium ion battery negative electrode, comprising the composite material according to any one of claims 1 to 4, characterized in that: Negative electrode compaction density>1.8g / cm 3 , active material loading> 3mg / cm 2 .

10. The sodium ion battery negative electrode according to claim 9, wherein: The reversible capacity of the negative electrode is greater than 800 mAh / g at a current density of 0.5 A / g, and the capacity retention rate after 100 cycles is greater than 98%; the capacity retention rate of the negative electrode after 500 cycles at a current density of 5 A / g is greater than 85%.

Images