Hollow honeycomb iron sulfide carbon composite negative electrode material and preparation method and application thereof

Abstract

The invention discloses a hollow honeycomb iron sulfide / carbon (FeS2 at C) composite negative electrode material as well as a preparation method and application of the hollow honeycomb iron sulfide / carbon (FeS2 at C) composite negative electrode material. According to the material, SiO2 nanospheres are taken as a template, and the hollow honeycomb FeS < 2 >-C composite material with a core-shell structure is constructed by combining spray drying with a carbon thermal reduction and vulcanization process. FeS2 nanoparticles in the material are uniformly embedded into a porous carbon skeleton, the thickness of a carbon layer is 2-5nm, the aperture is about 350nm, and the specific surface area is 150-300m < 2 > / g. The preparation method comprises the steps of template agent regulation and control, carbon source coating, high-temperature vulcanization and acid pickling and pore forming, and preferred growth of FeS2 crystals and uniform coating of a carbon layer are achieved by regulating and controlling the proportion of Fe (NO3) 3.9 H2O and chitosan and vulcanization conditions. The initial discharge capacity of the material under the current density of 0.5 A / g reaches 1700 mAh / g or above, the capacity retention rate is larger than or equal to 95% after circulation is conducted 100 times, the capacity is kept at 450 mAh / g or above after circulation is conducted 2000 times under the high rate of 10 A / g, and the reversible specific capacity is still kept at 300 mAh / g or above under the ultrahigh current density of 30 A / g. The performance advantage of the composite material is derived from the synergistic effect of a carbon layer conductive network, a porous buffer structure and sulfur vacancy active sites, and the composite material is suitable for a high-power sodium ion battery negative electrode.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, specifically to a method for preparing a hollow honeycomb iron sulfide / carbon composite material and its application in sodium-ion batteries. This material, with transition metal sulfide (FeS2) as the active core, utilizes a template method to construct a hierarchical porous carbon framework. This material, combined with sulfur vacancy regulation and heterogeneous interface optimization, effectively addresses bottleneck issues such as volume expansion, polysulfide dissolution, and poor conductivity during the charge and discharge processes of FeS2. The material is suitable for high-power, long-cycle sodium-ion battery energy storage systems. Background Art

[0002] Sodium-ion batteries have become an important alternative to lithium-ion batteries due to their abundant resources and cost advantages, but their negative electrode materials face problems such as low capacity and severe volume expansion. Iron-based sulfides have attracted much attention due to their high theoretical capacity (894 mAh / g), but their poor conductivity, polysulfide dissolution and volume expansion (~300%) lead to a sharp decline in cycle performance. In the existing technology: Carbon coating strategy: Zhang et al. prepared FeS 1-x @C carbon fiber composite material, the reversible specific capacity is 550 mAh / g at 0.1 A / g, but the capacity drops sharply to 240 mAh / g at 1 A / g (Journal of Alloys and Compounds, 2020, 842, 155642); Structural regulation: Li et al. increased the capacity to 731 mAh / g through a new structural design of single-walled carbon nanotube composite polyaniline wrapped iron sulfide, but the capacity dropped sharply to 315 mAh / g at high rate (5 A / g) (Journal of Materiomics, 2022, 8, 1278-1286); Defect engineering: Cao et al. introduced sulfur vacancies to achieve a capacity of 724 mAh / g, but the uniformity and density of sulfur vacancies are difficult to control.

[0003] The above method has the following bottlenecks: uneven carbon layer: traditional carbon coating cannot completely inhibit FeS2 agglomeration, resulting in obstruction of ion transmission path; poor structural stability: the hollow structure is prone to collapse during the cycle, and the capacity decays rapidly; uncontrollable interface reaction: the polysulfide shuttle effect leads to loss of active materials. The present invention constructs a hollow honeycomb carbon skeleton through a template method, combines sulfur vacancy control with heterogeneous interface optimization, and achieves a triple synergistic effect:

[0004] Porous buffer: The honeycomb channels formed by etching the SiO2 template provide buffer space for volume expansion; Conductive network: The nitrogen-doped carbon layer constructs a three-dimensional electron transmission path; Active site regulation: The dissolution of polysulfides is inhibited through the adsorption-catalysis dual mechanism. Summary of the Invention

[0005] Technical Solution

[0006] The present invention provides a hollow honeycomb iron sulfide / carbon composite negative electrode material and its preparation method. The material uses monodispersed SiO2 nanospheres as a hard template, and constructs a core-shell structure hollow honeycomb composite system through spray drying combined with carbon thermal reduction and sulfurization process. In the material, cubic FeS2 nanoparticles are uniformly embedded in a nitrogen-doped porous carbon skeleton. The preparation method includes the following key steps: (1) using Method: (1) a 300-400 nm monodisperse SiO2 template was synthesized by a novel method; (2) chitosan, Fe(NO3)3·9H2O and SiO2 were mixed and spray-dried (inlet air temperature 140°C) to form a Fe3O4@C / SiO2 precursor; (3) carbothermal reduction was achieved by calcination at 600°C for 3 h under an inert atmosphere; (4) FeS2 was generated by hydrothermal sulfurization at 160°C for 12 h using thioacetamide as a sulfur source; (5) the SiO2 template was removed by hydrofluoric acid etching to obtain a hollow honeycomb T-FeS2@C.

[0007] application

[0008] When used as the negative electrode of sodium-ion batteries, this composite material exhibits excellent sodium storage performance within the voltage window of 0.01-3.0V, making it particularly suitable for energy storage scenarios with high power and long cycle requirements. Specifically, it includes: (1) Power battery field: maintaining a capacity of more than 300mAh / g at an ultra-high current density of 30A / g, meeting the rapid charging and discharging requirements of electric vehicles; (2) Grid-level energy storage system: after 2000 cycles, the capacity retention rate is ≥90%, ensuring long-term operational stability; (3) Flexible electronic devices: The hollow honeycomb structure gives the material excellent mechanical toughness, and the capacity loss after 1000 bends is less than 5%. Its porous skeleton and carbon layer conductive network design can be further expanded to systems such as lithium-sulfur batteries and potassium-ion batteries.

[0009] Innovation

[0010] The core innovation of this invention lies in breaking through the technical bottleneck of FeS2 anode through the synergy of multi-scale structural design and chemical regulation:

[0011] Through the coordinated regulation of template method and carbon thermal reduction technology, a T-FeS2@C composite material with a core-shell honeycomb structure was constructed. Its core innovation is reflected in the deep integration of triple synergistic effects and multi-scale structural optimization: 1) SiO2 template is used to construct a hierarchical porous architecture to achieve Na +1) The three-dimensional interconnection of the transmission path and the significant reduction of ion migration resistance; 2) The flexible carbon layer formed by chitosan carbonization simultaneously achieves physical confinement of FeS2 nanoparticles, inhibits volume expansion, and efficiently constructs a conductive network; 3) The coordinated regulation of carbon layer defects and surface SO bonds breaks through the bottleneck of traditional interfacial reaction kinetics, dynamically activates active sites, and stabilizes SEI film formation. This material design breaks through the limitations of traditional single-component modification. Through the multi-scale synergy of nanoscale carbon layer conductive networks, mesoporous pore engineering, and atomic-level interface chemistry, it achieves simultaneous improvements in electron / ion transmission efficiency, structural stability, and interfacial reaction kinetics, providing a multi-dimensional regulatory paradigm for the development of sulfur-based anode materials.

[0012] Beneficial effects

[0013] Ultra-high specific capacity: The initial discharge capacity at 0.5A / g is over 1750mAh / g, which is 5 times the theoretical capacity of hard carbon. Long cycle life: The capacity remains over 450mAh / g after 2000 cycles at a high rate of 10A / g, with a decay rate of only 0.005% / cycle. Excellent rate performance: The reversible capacity is over 300mAh / g at a current density of 30A / g, and the ion diffusion coefficient is (2.5×10 -10 cm 2 / s) is 10 times that of traditional FeS2; high first efficiency and stability: initial coulombic efficiency ≥85%, dynamic optimization of the SEI film during the cycle continuously reduces the interfacial impedance; industrialization potential: raw material costs are reduced by 40%, batch capacity deviation is ≤3%, and kilogram-level pilot production has been achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 : Scanning electron microscope (SEM) image of T-FeS2@C composite material, showing the hollow honeycomb morphology and pore size distribution characteristics, and FeS2 nanoparticles are evenly embedded in the pore wall.

[0015] Figure 2 Transmission electron microscopy (TEM) and element distribution mapping (EDS mapping) show that FeS2 nanoparticles (black bright spots) are tightly coated by the nitrogen-doped carbon layer (gray substrate), and the Fe, S, and C elements are spatially uniformly distributed, verifying the construction of the core-shell structure.

[0016] Figure 3 : X-ray diffraction (XRD) pattern shows that the diffraction peaks of T-FeS2@C completely match those of cubic FeS2 standard card (PDF#00-42-1340) and there are no impurity peaks, proving that high-purity FeS2 crystals are generated.

[0017] Figure 4 :Raman spectrum, D band (1345cm -1 ) and G belt (1587cm-1 )Intensity ratio (I D / I G =1.06) indicates that the carbon layer is rich in defects, and the defect states induced by sulfur vacancies are between 500-800 cm -1 The interval shows a characteristic peak.

[0018] Figure 5 :Nitrogen adsorption-desorption isotherms and pore size distribution curves show that T-FeS2@C has type IV isotherm characteristics and mesopore-dominated pore size distribution (2-10nm), with a specific surface area of 280m 2 / g, pore volume 0.85cm 3 / g.

[0019] Figure 6 :Electrochemical cycle performance curve, showing T-FeS2@C at 1Ag -1 The initial capacity is 812 mAh / g, and after 100 cycles it reaches 880 mAh g -1 , ahead of other materials; capacity is 500mAh / g at a high rate of 10A / g.

[0020] Figure 7 a: Cyclic voltammetry (CV) curve analysis confirms the surface-dominated fast charge storage mechanism.

[0021] Figure 7 b, c: Electrochemical impedance spectroscopy (EIS) and ion diffusion coefficient calculation, high frequency region semicircle diameter (R ct =8Ω) and the low-frequency Warburg slope (σ=17.54Ω·s -1 / 2 ) indicates that the interfacial charge transfer and ion diffusion kinetics are significantly optimized.

[0022] Figure 7 d: The characteristic signal of the EPR curve at g = 2.003 confirms the existence of unpaired electrons in the material, which mainly come from sulfur vacancies or lattice defects.

[0023] Description of the associated drawings:

[0024] Figure 1-2 The hollow honeycomb structure and core-shell interface design are supported from the perspectives of morphology and element distribution;

[0025] Figure 3-6 Reveal the material composition and multi-scale synergistic mechanism through crystal structure, defect state and pore structure characterization;

[0026] Figure 7 The advantages of high capacity, long cycle and rate are verified from the perspective of electrochemical performance and kinetics, and a complete evidence chain of "structure-performance" association is constructed. DETAILED DESCRIPTION

[0027] Example 1: Using monodisperse SiO2 nanospheres (360 nm in diameter) as a hard template, 1 g of SiO2 was mixed with 1 g of chitosan and 1.11 g of Fe(NO3)3·9H2O, dissolved in 200 mL of a 1:9 acetic acid / water mixture, and stirred for 10 hours to form a homogeneous precursor. The precursor powder was prepared by spray drying (inlet air temperature 140°C, outlet air temperature 80°C). The precursor powder was then calcined at 600°C for 3 hours under a nitrogen atmosphere at a rate of 5°C / min to complete carbothermal reduction. The product was hydrothermally vulcanized with 3 g of thioacetamide at 160°C for 12 hours. Finally, the SiO2 template was removed by etching with 5% hydrofluoric acid, resulting in a hollow honeycomb T-FeS2@C composite material. This material exhibited an initial coulombic efficiency exceeding 86% as a negative electrode. The initial discharge capacity reaches 1755mAh / g at a current density of 0.5A / g, and the capacity retention rate is 91% after 2000 cycles. The reversible capacity is 500mAh / g at a high rate of 10A / g, and 350mAh / g at a high rate of 30A / g. The synergistic effect of its honeycomb pores and nitrogen-doped carbon layer effectively inhibits the volume expansion of FeS2. At the same time, sulfur vacancies anchor polysulfides through a chemical adsorption mechanism, reducing the loss of active materials. The hollow porous carbon matrix has a pore size of about 350nm and a specific surface area of 280m 2 / g, carbon layer thickness 3nm; FeS2 nanoparticles embedded in carbon matrix, particle size 20-30nm, crystal structure is cubic system; the sulfur vacancy density on the carbon matrix surface is 4.5×10 16 cm -2 (EPR characterization); the carbon content in the material is 38wt%, the FeS2 content is 58wt%. The carbon matrix is nitrogen-doped carbon with a nitrogen content of 7.5at%, of which pyridinic nitrogen accounts for 69%.

[0028] Example 2: SiO2, chitosan, and Fe(NO3)3·9H2O are mixed in a mass ratio of 1:2:0.8. The initial coulombic efficiency of this material as a negative electrode is over 87%. The initial discharge capacity is 1705mAh / g at a current density of 0.5A / g, the capacity retention rate is 92% after 2000 cycles, the reversible capacity is 455mAh / g at a high rate of 10A / g, and the reversible capacity is 305mAh / g at a high rate of 30A / g. The synergistic effect of its honeycomb pores and the nitrogen-doped carbon layer effectively inhibits the volume expansion of FeS2, while the sulfur vacancies anchor the polysulfide through a chemical adsorption mechanism to reduce the loss of active substances. The hollow porous carbon matrix has a pore size of about 350nm and a specific surface area of 295m 2 / g, carbon layer thickness 5nm; FeS2 nanoparticles embedded in carbon matrix, particle size 15-35nm, crystal structure is cubic system; the sulfur vacancy density on the carbon matrix surface is 1.5×10 16 cm -2(EPR characterization); the carbon content in the material is 48wt%, the FeS2 content is 51wt%. The carbon matrix is nitrogen-doped carbon with a nitrogen content of 6.5at%, of which pyridinic nitrogen accounts for 66%.

[0029] Example 3: SiO2, chitosan, and Fe(NO3)3·9H2O are mixed in a mass ratio of 1:1:1.3. The initial coulombic efficiency of the material as a negative electrode is over 85%. The material has an initial discharge capacity of 1805mAh / g at a current density of 0.5A / g, a capacity retention rate of 90% after 2000 cycles, a reversible capacity of 523mAh / g at a high rate of 10A / g, and a reversible capacity of 366mAh / g at a high rate of 30A / g. The synergistic effect of its honeycomb pores and the nitrogen-doped carbon layer effectively inhibits the volume expansion of FeS2, while the sulfur vacancies anchor polysulfides through a chemical adsorption mechanism to reduce the loss of active substances. The hollow porous carbon matrix has a pore size of about 350nm and a specific surface area of 180m 2 / g, carbon layer thickness 3.1nm; FeS2 nanoparticles embedded in carbon matrix, particle size 25-45nm, crystal structure is cubic system; the sulfur vacancy density on the carbon matrix surface is 3.5×10 15 cm -2 (EPR characterization); the carbon content in the material is 30.5wt%, the FeS2 content is 68.5wt%. The carbon matrix is nitrogen-doped carbon with a nitrogen content of 5.3at%, of which pyridinic nitrogen accounts for 69%.

[0030] Comparative Example 1 (no template method)

[0031] The SiO2 template was omitted and chitosan was directly mixed with Fe(NO3)3·9H2O. The resulting material was an irregular particle aggregate with a specific surface area of 50 m 2 / g, resulting in a disordered pore size distribution. Due to a lack of spatial confinement, FeS2 particles were severely agglomerated, resulting in an initial capacity of only 620 mAh / g at 0.5 A / g, which decayed to 45% after 100 cycles. This demonstrates that the template-based porous buffer structure is crucial for performance improvement.

[0032] Comparative Example 2 (no carbon coating)

[0033] By removing the chitosan carbon source and using only Fe(NO3)3 as the raw material, pure FeS2 was prepared. The FeS2 particles in the material were severely oxidized due to the lack of a carbon coating, and XRD revealed the presence of Fe3O4 as an impurity. Electrochemical testing revealed an initial capacity of only 480 mAh / g at 0.5 A / g, highlighting the crucial role of the carbon layer in preventing structural collapse.

[0034] Material characterization and electrochemical performance testing

[0035] 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.

[0036] 1. SEM analysis

[0037] from Figure 1 It can be observed that the sample presents a uniform porous honeycomb hollow structure, which provides structural guarantee for performance optimization. The rich pores are conducive to material transfer and exposure of active sites, forming a structure-performance correlation basis with optimal performance.

[0038] 2. TEM analysis

[0039] from Figure 2 The sample shows a clear boundary between the outer and inner layers of the T-FeS2@C sample, revealing fine microstructural details. EDS mapping reveals a highly consistent and concentrated distribution of Fe and S elements, confirming the presence of FeS2. C is evenly distributed throughout the entire region, indicating the formation of a unique honeycomb carbon-encapsulated FeS2 structure.

[0040] 3. XRD analysis

[0041] Figure 3 The XRD patterns of the comparative example and the example samples are shown in Table 1. Comparison of the patterns with the FeS2 (PDF no. 00-042-1340) standard card shows that the example 1 sample exhibits obvious FeS2 characteristic diffraction peaks, indicating that the product contains FeS2 phase.

[0042] 4. Raman analysis

[0043] Figure 4 Middle, D belt (1345cm -1 ) and G belt (1587cm -1 ) intensity ratio (I D / I G =1.06) reveals that under high temperature conditions, FeS2 nanoparticles have doping and etching effects on the carbon layer, while Fe 3+ Catalyze the decomposition and reorganization of carbon sources, prompting the carbon layer to form a special structure rich in defects.

[0044] 5. Analysis of nitrogen adsorption-desorption isotherms and pore size distribution curves

[0045] Figure 5 The adsorption behavior of the comparative example shows that the adsorption amount of Example 1 is significantly higher than that of the previous two, especially in the high-pressure region, the adsorption amount increases sharply, showing a typical IV type isotherm characteristic, accompanied by an obvious hysteresis loop, indicating that it is rich in mesoporous structure. The specific surface area and total pore volume of Example 1 far exceed those of the comparative example. This pore structure advantage is due to the FeS2 The synergistic effect with the carbon substrate—FeS2 nanoparticles act as a template to regulate the pyrolysis of the carbon source, forming a three-dimensional mesoporous network, while the carbon layer wrapping optimizes pore connectivity. Therefore, Example 1, with its more developed mesoporous system, has advantages in applications that rely on pore structure, such as adsorption and catalysis. Its high specific surface area and pore volume provide an ideal carrier for active site exposure and material transport, while the pore structure defects of the control sample limit the corresponding performance improvement.

[0046] 6. Cycle performance test

[0047] Figure 6 The medium cycle performance curve is the sample at 1Ag -1 Test results under current density. Taking the sample of Example 1 as an example, the comparative examples and other samples have better specific capacity during the cycle and stable coulombic efficiency. Comparing samples with different addition amounts (such as different amounts of ferric nitrate nine water additions (Figure b), different masses of SiO2 additions (Figure c)), T-FeS2@C has a slower specific capacity decay. This is because the structure of Example 1 effectively buffers volume changes during charge and discharge, improves stability, and improves electrochemical cycle performance. Other samples were tested using the same method, and their morphology, structure and performance results were consistent with the performance trend of Example 1, verifying the performance advantages and technical reliability of the material system.

[0048] 7. CV, impedance, and EPR analysis

[0049] Figure 7 a shows that in the voltage range of 0.01-3.0V, the CV curves of the first three cycles of Example 1 present a characteristic electrochemical reaction process. In the first cathode scan, the oxidation peak that appears is due to the formation of the SEI film on the electrode surface. The surface defects and active sites of the carbon layer provide stable nucleation sites for the SEI film, allowing it to grow uniformly. The reduction peak corresponds to Na + The reaction of embedding into FeS2 reflects the sodium storage function of FeS2. In the first anodic scan, the oxidation peak that appears is Na + The carbon layer physically confines the FeS2 to the electrolyte, suppressing its volume expansion during charge and discharge, reducing direct contact between the particles and the electrolyte, maintaining a stable electrode structure, and ensuring a consistently efficient electrochemical reaction.

[0050] Figure 7 b shows that its Warburg coefficient is 17.54ΩS -1 / 2 , which is smaller than the control sample, confirming that the D value is the largest and the ion transfer rate is faster, which is due to the Na + Low resistance diffusion channel and close contact between carbon layer and FeS2 optimize the interfacial ion transport kinetics. Figure 7c, R in the loop ct The increase first and then decrease, and the decrease of Rsf are related to the dynamic optimization of SEI film and electrode activation; the significant decrease of Warburg value is beneficial to Na + transfer, indicating that after electrode activation, the stable structure synergistically constructed by the carbon layer and FeS2 further optimizes the interfacial charge transfer and ion diffusion, profoundly explaining the intrinsic mechanism of the material's excellent cycle performance.

[0051] Figure 7 d, The characteristic signal in the EPR spectrum at g = 2.003 confirms the presence of unpaired electrons in the material, primarily originating from sulfur vacancies or lattice defects. From a formation mechanism perspective, the incompleteness of the high-temperature sulfurization reaction during the preparation process or the dynamic reconstruction of Fe-S bonds under thermal action may lead to the loss of sulfur atoms. These defect sites act as highly active centers, significantly altering the material's electron cloud density distribution and enhancing its adsorption and activation capacity for reactant molecules. For example, in catalytic reactions, sulfur vacancies can activate reactant molecules through an electron transfer mechanism, effectively lowering the reaction energy barrier and becoming a key factor in enhancing the material's redox activity.

[0052] 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 hollow honeycomb iron sulfide / carbon (T-FeS2@C) composite negative electrode material, characterized by comprising: Hollow porous carbon matrix, with a pore size of about 350nm and a specific surface area of 150-300m 2 / g, carbon layer thickness 2-5nm; FeS2 nanoparticles embedded in carbon matrix, particle size 10-50nm, cubic crystal structure (PDF#00-42-1340); carbon matrix surface sulfur vacancy density 1×10 15 -5×10 16 cm -2 ; The carbon content in the material is 30-50wt%, and the FeS2 content is 50-70wt%.

2. The material according to claim 1, characterized in that: The carbon matrix is nitrogen-doped carbon with a nitrogen content of 5-8 at%, wherein the pyridinic nitrogen accounts for ≥60%.

3. The material according to claim 1, wherein: The FeS2 nanoparticles form a heterogeneous interface with the carbon matrix, and the carbon layer evenly embeds the FeS2 in the honeycomb structure.

4. A method for preparing the material according to any one of claims 1 to 3, comprising the following steps: a. Preparation of SiO2 template: The method synthesizes monodisperse SiO2 nanospheres with a diameter of 300-400 nm; b. Precursor coating: SiO2, chitosan, and Fe(NO3)3·9H2O were mixed in a mass ratio of 1:(1-2):(0.8-1.5) and spray-dried to form a Fe3O4@C / SiO2 composite precursor; c. Carbothermal reduction: calcination at 600°C for 3 h under inert atmosphere, heating rate 5°C / min; d. Sulfurization treatment: using thioacetamide as the sulfur source, hydrothermal reaction at 160°C for 12 hours; e. Template removal: SiO2 was etched with 5% hydrofluoric acid to obtain hollow honeycomb-like T-FeS2@C.

5. The method according to claim 4, wherein: The inlet air temperature of the spray drying is 140°C, and the outlet air temperature is 85°C.

6. The method according to claim 4, wherein: During the calcination process, Fe 3+ Carbothermally reduced to Fe 2+ And react with sulfur source to generate FeS2.

7. A sodium ion battery, characterized in that: The material according to any one of claims 1 to 3 is used as the negative electrode.

8. The sodium ion battery according to claim 7, wherein: At a current density of 0.5-30A / g, the reversible capacity is ≥300mAh / g, and the capacity retention rate after 2000 cycles is ≥90%.

9. The sodium ion battery according to claim 7, wherein: The initial coulombic efficiency of the negative electrode is ≥85%.

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