Double-carbon-coated silicon negative electrode material based on coordination template method, preparation method, lithium ion battery negative electrode and lithium ion battery

Abstract

The invention belongs to the field of lithium ion battery materials, and particularly relates to a dual-carbon-coated silicon negative electrode material based on a coordination template method, a preparation method, a lithium ion battery negative electrode and a lithium ion battery, and the preparation method comprises the following steps: S1, uniformly dispersing an iron source, a conductive polymer monomer and nano silicon powder in deionized water under the ice bath condition of 0-5 DEG C, then adding graphene oxide, and uniformly stirring to obtain a precursor solution; performing ultrasonic treatment for 30 to 60 minutes; s2, preparing a sulfur-containing solution, and dropwise adding the sulfur-containing solution into the mixed solution obtained in the step S1 for reaction; s3, after the reaction is finished, adding an initiator, and carrying out polymerization reaction under an ice bath condition; and S4, performing calcination in an inert atmosphere, and then performing acid pickling to obtain the double-carbon-coated silicon negative electrode material. The silicon-based negative electrode material with the graphene-porous carbon double-coated structure is constructed through a coordination chemical strategy, and is particularly suitable for high energy density and high working condition stability demand scenes.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion battery materials, and particularly relates to a double-carbon-coated silicon negative electrode material based on a coordination template method, a preparation method, a lithium ion battery negative electrode, and a lithium ion battery. BACKGROUND

[0002] As a core device of modern energy storage, the energy density bottleneck of lithium ion batteries has become a key obstacle to the breakthrough of electric vehicle endurance and the performance leap of portable electronic devices. The traditional graphite negative electrode is limited by the theoretical capacity ceiling of 372 mAh / g, and even if it is matched with high-nickel ternary positive electrode materials (such as NCM811), the energy density of the battery monomer is still locked below 300 Wh / kg - this is a generational gap with the industry's goal of 500 Wh / kg in 2030. Silicon-based negative electrodes are considered to be the hope of breaking through the bottleneck with their ultra-high theoretical capacity of 3579 mAh / g (Li 15 Si4 phase) and suitable lithium intercalation potential of 0.4 V (vs. Li + / Li). However, silicon materials undergo a volume expansion of up to 300% (the expansion rate is 12 times larger than that of graphite materials) during lithium extraction and intercalation, triggering a triple chain disaster: first, the mechanical stress generated by repeated expansion and contraction exceeds the fracture strength of silicon (>1 GPa), leading to particle pulverization and detachment from the current collector. Scanning electron microscopy analysis in the prior art (Electrochim. Acta, vol. 269, pp. 1-10, 2018) confirms that the particle size fragmentation rate of pure silicon negative electrodes exceeds 90% after 100 cycles, and the effective contact area of active materials is significantly reduced; second, the newly generated silicon surface continuously reacts with the electrolyte to form an unstable SEI film, with a thickness of more than 50 nm (the conventional graphite SEI is only 5-10 nm), which not only consumes a large amount of active lithium ions, making the initial coulombic efficiency drop to below 75%, but also causes the electrolyte inventory to be rapidly depleted due to repeated rupture and regeneration during cycling; third, the severe volume change destroys the internal conductive network of the electrode, and the charge transfer resistance increases by 300%-500% after 100 cycles, causing the rate capability to drop sharply. These defects collectively form the "death triangle" of silicon negative electrodes for commercialization - high capacity, long life, and fast charging capability are difficult to achieve simultaneously, becoming a formidable obstacle in the path of industrial upgrading.

[0003] To tame the persistent expansion problem of silicon, researchers worldwide have been working on it for over a decade, mainly developing two technical routes, both of which have reached a dilemma of trade-offs. The nanostructuring strategy, through the fabrication of silicon nanowires (e.g., CN201410682515.4) or etching porous silicon (e.g., CN201910804216.6), shortens the ion diffusion path to the nanoscale to alleviate mechanical stress. However, this approach introduces new challenges: the enormous specific surface area of ​​nanomaterials (>100 m² / g) amplifies the electrode / electrolyte side reaction interface, further collapsing the initial coulombic efficiency to 65%–70%; more seriously, the tap density of nano-silicon is less than 0.8 g / cm³. 3 (Micron-sized silicon > 1.5 g / cm³) 3 This results in a volumetric energy density loss of over 30%, and the cost of preparing nanowires by vapor deposition is as high as $1000 / kg, making the industrialization prospects bleak. The carbon composite coating route attempts to construct a "rigid and flexible" protection system: single-layer carbon coating (such as CN201810798105.4 using pyrolytic carbon) partially improves conductivity, but the expansion stress still causes the carbon layer to crack at a rate of 80% after 20 cycles; the graphene composite scheme (such as Liu et al. preparing self-supporting nano-silicon / graphene composite paper flexible electrode, Materials Reports, 2016, 30(18):5.) establishes a three-dimensional conductive framework, but because silicon and graphene are only bonded by van der Waals forces, the silicon particles are severely displaced after cycling, eventually leading to interface peeling failure; the traditional double carbon coating method (such as CVD deposition of carbon layer + solution coating of graphene) enhances the synergistic effect, but the process complexity increases sharply - the high-temperature CVD process (>800℃) triggers the oxidation of silicon surface to generate insulating SiO. x Furthermore, the multi-step processing increases production costs by 250%. What is particularly regrettable is that when researchers attempted to enhance interfacial stability through fluorine doping (Su Nan et al., Journal of Inorganic Materials, 2023), the strong electronegativity of fluorine atoms hindered lithium-ion diffusion, causing the capacity to plummet to 500 mAh / g at a current density of 5 A / g (approximately 5 C), exposing the inherent limitations of a single modification method.

[0004] Current silicon-carbon anode technology has entered a critical phase: the nanoscale approach is hampered by cost and volumetric energy density, while carbon composite solutions are caught in a triangular contradiction between interfacial bonding strength, process complexity, and coating uniformity. An ideal solution must simultaneously meet four stringent requirements: First, achieve strong bonding between silicon and the carbon matrix at the molecular scale, enabling interfacial bonding energy to exceed 2 J / m. 2 (Traditional physical mixing <0.5J / m) 2 Second, construct a coating structure that combines electron / ion channels to encapsulate Li. + The diffusion coefficient was increased to 10~12 cm. 2 / s scale (pure silicon material is only 10~14cm) 2Third, develop a simple low-temperature process (<600℃) to avoid material degradation caused by high temperatures; fourth, control the raw material cost to below $15 / kg (commercial nano-silicon powder >$50 / kg). Among existing technologies, the "double carbon coating" structure is particularly promising—the synergy between the in-plane conductive network of graphene and the volume buffering function of the carbon layer is highly anticipated by the academic community. However, how to achieve precise bonding between silicon particles and double carbon components at the nanoscale, how to balance the density and ion permeability of the coating layer, and how to avoid structural defects caused by multi-step processing have become three major barriers between ideal and reality. This urgently requires a revolutionary material design philosophy to reconstruct the silicon-carbon interaction mechanism at the atomic level, thereby giving birth to a next-generation solution that integrates "molecular-level coupling, intrinsic conductivity, and self-assembly process". Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a silicon-based anode material with dual carbon coating based on coordination template method, a preparation method, a lithium-ion battery anode, and a lithium-ion battery. The silicon-based anode material with a graphene-porous carbon dual coating structure is constructed through a coordination chemistry strategy, which is suitable for scenarios requiring high energy density and high operating stability, such as electric vehicle power batteries, energy storage in special extreme environments, and high-power consumer electronics (drones, power tools, etc.).

[0006] The specific technical solution is as follows: The preparation method of double carbon-coated silicon anode material based on coordination template method includes the following steps: S1 Under ice bath conditions of 0~5℃, iron source, conductive polymer monomer and nano silicon powder are uniformly dispersed in deionized water, then graphene oxide is added and ultrasonicated for 30~60 minutes. S2 Prepare a sulfur-containing solution and add it dropwise to the mixed solution obtained in step S1 to carry out the reaction; After the S3 reaction is completed, an initiator is added and polymerization is carried out under ice bath conditions; S4 is calcined in an inert atmosphere, followed by acid washing to obtain the double carbon-coated silicon anode material.

[0007] The mechanism of this invention is as follows: A strong silicon-carbon interface is constructed at the molecular scale using a coordination template method: First, iron ions (Fe...) are used in an ice bath... 3+ A bridging structure is created between nano-silicon and graphene oxide (GO), achieving "molecular anchoring" between silicon particles and GO through a sulfur coordination reaction. Subsequently, in-situ polymerization forms a polypyrrole coating layer. After low-temperature carbonization and acid etching of the sacrificial template, a synergistic coating structure of a conductive graphene oxide layer and a porous carbon layer is obtained. In this dual-carbon architecture, the porous carbon layer effectively buffers the volume expansion of silicon, while the graphene oxide constructs a fast electron channel, synergistically enhancing the ion diffusion coefficient and electrochemical performance.

[0008] In step S1, under ice bath conditions (0~5℃), the iron source (such as ferric ammonium oxalate) dissociates into Fe. 3+ The N atoms of the conductive polymer monomer (pyrrole) form hydrogen bonds (Si-OH···N) with the Si-OH on the surface of the nano-silicon powder, while the oxygen-containing functional groups (-COOH, -OH) of graphene oxide (GO) adsorb Fe through hydrogen bonds. 3+ And silicon particles, to achieve nano-silicon, Fe 3+ The uniform dispersion of pyrrole monomers on the GO surface forms a "silicon-pyrrole-Fe" structure. 3+ -GO" pre-assembled components.

[0009] Preferably, in step S1, the iron source is ferric ammonium oxalate or ferric ammonium citrate; the conductive polymer monomer is pyrrole; and the particle size of the nano-silicon powder is 50~200nm.

[0010] Furthermore, in step S1, the mixing ratio of the iron source, conductive polymer monomer, nano-silicon powder, and graphene oxide is 1 mol:(2.5~3.0) mol:(150~200) g:(85~100) g. Deionized water provides a homogeneous environment for the reaction, and its amount can be adjusted according to the degree of dissolution and dispersion of the reaction raw materials. Preferably, in step S1, the mixing ratio of the iron source, conductive polymer monomer, nano-silicon powder, graphene oxide, and deionized water is 1 mol:(2.5~3.0) mol:(150~200) g:(85~100) g:(200~250) L.

[0011] In step S2, during the process of adding the sulfur-containing reagent dropwise into the mixed solution, Fe... 3+ / S 2- In-situ formation of Fe by coordination reaction 3+ Complexes anchor silicon particles to the GO surface. Iron ions (Fe) 3+ The Fe group first adsorbs onto the surface of the nano-silicon particles, forming initial binding sites; subsequently, sulfur-containing ligands (such as diethyldithiocarbamate) are introduced and bind to Fe. 3+ Efficient coordination occurs, generating a metal complex with a specific geometry. This complex acts as a "molecular bridge," with its hydrophobic ends firmly bonded to graphene oxide (GO) sheets through multiple chemical interactions (including covalent bonds, π-π stacking, and hydrogen bonds), thereby achieving precise bonding between silicon particles and the GO substrate at the atomic scale. This "three-point anchoring" strategy (silicon-metal-ligand-GO) forms a rigid interconnect network, effectively suppressing the displacement and shedding of silicon particles during cycling.

[0012] Furthermore, in step S2, the sulfur-containing solution is an aqueous solution of sodium diethyldithiocarbamate, and the molar ratio of the total amount of Fe in the iron source to the total amount of S in the sulfur-containing solution is 1:(2.6~4.0); the reaction temperature is 0~5℃, and the reaction time is 1~3h.

[0013] Preferably, in step S2, the concentration of the sulfur-containing solution is 0.4~0.6 mol / L.

[0014] In step S3, the initiator initiates the formation of a polymer (such as polypyrrole) coating layer on the surface of the nano-silicon powder by the conductive polymer monomer.

[0015] Furthermore, in step S3, the initiator is preferably ammonium persulfate; the molar ratio of the conductive polymer monomer to the initiator is 1:(0.85~1.05); the polymerization reaction temperature is 0~5℃, and the reaction time is 11~13h.

[0016] In step S4, during the calcination process, the polymer coating layer is transformed into a porous amorphous carbon layer, and correspondingly, Fe... 3+ The complex is converted to Fe 1-x S-carbon composite phase; Fe is removed during acid washing by etching. 1-x S forms through-holes (pore size 2~50nm), ultimately forming a double-coated structure of Si@C@GO consisting of graphene oxide support and porous carbon connecting layer.

[0017] Furthermore, the calcination temperature is 500~600℃, the calcination time is 1.5~3h, and the heating rate is ≤5℃ / min; the pickling time is 10~14h, and the pickling solution is preferably 0.5-3M hydrochloric acid solution.

[0018] A second aspect of the present invention provides a double-carbon-coated silicon anode material obtained according to the above preparation method, having a specific surface area of ​​38-42 m². 2 / g, porosity 40~43%, double carbon coating thickness 12±2nm, Raman spectrum I D / I G =0.97~1.03.

[0019] A third aspect of the present invention provides a lithium-ion battery anode, the lithium-ion battery anode comprising the double carbon-coated silicon anode material, a conductive agent and a binder; preferably, the conductive agent is carbon black and the binder is sodium carboxymethyl cellulose; the mass ratio of the double carbon-coated silicon anode material, carbon black and sodium carboxymethyl cellulose is preferably (60±2):(15±1):(25±1).

[0020] A fourth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising the aforementioned lithium-ion battery negative electrode. The lithium-ion battery exhibits an initial discharge specific capacity of ≥1550 mAh / g at 0.1 A / g, a capacity retention rate of ≥85% after 100 cycles at 1000 mAh / g, and an electrode expansion rate of ≤20% after 200 cycles at 5 A / g; furthermore, at a low temperature of -30℃, the capacity retention rate at 0.2C discharge is ≥80%.

[0021] Compared with the prior art, the present invention has the following advantages: (1) This invention pioneers the "coordination-etching" template method, utilizing Fe 1-x The S sacrificial layer guides the formation of a through-pore carbon structure, which, unlike traditional processes such as physical mixing or CVD deposition, solves the industry pain points of uneven coating thickness (fluctuating within the range of 5~50nm) and weak interfacial bonding; at the same time, through Fe... 3+ / pyrrole / S 2- Coordination reactions achieve silicon-carbon interfacial bonding at the molecular scale (XPS detected CS covalent bonds with a binding energy of 285.6 eV), combining the two-dimensional extensibility of graphene with the one-dimensional anchoring function of porous carbon to form a two-dimensional confined protection network; the entire process temperature is ≤550℃ (traditional CVD requires >800℃), ice bath polymerization inhibits GO reduction, and dilute hydrochloric acid etching simultaneously achieves pore formation and purification, thereby increasing the utilization rate of nano-silicon by 40%.

[0022] (2) Compared with traditional silicon-carbon composite materials, the double carbon coated silicon anode material of the present invention has an expansion suppression effect: the porous carbon layer (porosity 40~43%) forms a “surface support-line anchoring” synergistic structure with graphene, which compresses the electrode cyclic expansion rate to <20% (traditional silicon-carbon >80%), and the silicon particles do not pulverize after 100 cycles (SEM confirmed).

[0023] (3) The double carbon-coated silicon anode material of the present invention has uniform carbon coating to promote the formation of a stable SEI film, with an initial coulombic efficiency of 85.4% and a 40% reduction in active lithium loss; the electron channels constructed by graphene and the ion diffusion channels of the porous carbon layer work synergistically to maintain a capacity of 310 mAh / g at an ultra-high rate of 15 A / g (3 times that of commercial silicon-carbon materials); when cycled at a constant capacity of 1000 mAh / g, the capacity retention rate reaches 85.4% after 100 cycles (<70% of the traditional scheme), and EIS test shows that the charge transfer impedance drops to 42 Ω (only 28% of the comparative sample).

[0024] (4) The double carbon-coated silicon anode material of the present invention is particularly suitable for scenarios requiring high energy density and high working stability; electric vehicle power battery: when matched with ternary lithium-rich cathode, the full battery energy density can be achieved >400Wh / kg, and it supports 10C fast charging (5A / g cycle 200 times capacity decay <10%); special extreme environment energy storage: the porous carbon layer buffer mechanism ensures that the capacity retention rate is >80% in the -30℃ low temperature environment, meeting the needs of polar scientific research equipment; high power consumer electronics: the 15A / g discharge capacity is suitable for pulse high current applications such as drones and power tools, and the cycle life exceeds 1000 times. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of the double carbon-coated silicon anode material of the present invention; Figure 2a is the XRD pattern of the materials prepared in Example 1 and Comparative Examples 1-3; Figure 2 bd represents the Raman spectrum, nitrogen adsorption-desorption isotherm, and thermogravimetric analysis diagram of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 3, respectively. Figure 3 a and b are SEM, TEM (200nm), TEM (100nm), and TEM (10nm) images of the materials prepared in Example 1, respectively. Figure 4 a is a cycle performance diagram of the materials prepared in Examples 1 and 4-7; Figure 4 b is a rate performance graph of the materials prepared in Example 1, Comparative Example 1, and Example 7; Figure 4 c is the AC impedance diagram of the materials prepared in Example 1 and Comparative Examples 1-3; Figure 4 d represents the AC impedance diagram of the material prepared in Example 1 after different number of cycles; Figure 5 The graphs a and b represent the peak current-scan rate logarithmic relationship curve, capacitance contribution graph, and Na content during the sodiumization process of the material prepared in Example 1, respectively. + Diffusion coefficient diagram, Na in the desodiumization process + Diffusion coefficient diagram. Detailed Implementation

[0026] To better understand the purpose, structure, and function of this invention, the invention will be described in detail below with reference to the accompanying drawings. Figure 1 This is a schematic diagram of the preparation process of the double carbon-coated silicon anode material of the present invention.

[0027] Example 1 The preparation method of double carbon-coated silicon anode material based on coordination template method includes the following steps: S1 under 0℃ ice bath conditions, 225mg of ferric ammonium oxalate C6H 12 FeN3O 12 0.1 mL of pyrrole monomer (approximately 96.6 mg, 1.44 mmol) and 100 mg of 80 nm nano-silica powder were dispersed in 120 mL of deionized water and sonicated for 10 min to achieve uniform dispersion; then 50 mg of graphene oxide was added and sonicated for 30 min. S2 Prepare a 0.5 mol / L sodium diethyldithiocarbamate aqueous solution and add it dropwise to the mixed solution obtained in step S1 at a rate of 1 mL / min. Stir for 60 min under 0℃ ice bath conditions to complete the coordination reaction; wherein the molar ratio of the total Fe in ferric ammonium oxalate to the total S in the sodium diethyldithiocarbamate solution is 1:3.33. After the S3 reaction was completed, 300 mg of ammonium persulfate (1.31 mmol) was added to initiate polymerization, and the reaction was carried out in an ice bath at 0°C for 12 h. S4 was washed with water and alcohol, dried under vacuum at 70℃, and then calcined and carbonized at 550℃ for 2 hours in an argon atmosphere at a rate of 5℃ / min. It was then acid-washed with 1M HCl for 12 hours to remove Fe. 1-x The sacrificial template S is washed with deionized water until neutral and then vacuum dried at 60°C to obtain Si@GO@C material, denoted as Si@GO@C or Si@GO@C (after acid washing).

[0028] Example 2 Referring to Example 1, the difference is that in step S2, the molar ratio of the total amount of Fe in ferric ammonium oxalate to the total amount of S in sodium diethyldithiocarbamate solution is 1:2.66.

[0029] Example 3 Referring to Example 1, the difference is that in step S2, the molar ratio of the total amount of Fe in ferric ammonium oxalate to the total amount of S in sodium diethyldithiocarbamate solution is 1:4.00.

[0030] Example 4 Referring to Example 1, the difference is that in step S1, the amount of nano-silicon powder added is 50 mg, denoted as 0.01Si.

[0031] Example 5 Referring to Example 1, the difference is that in step S1, the amount of nano-silicon powder added is 150mg, denoted as 0.03Si.

[0032] Example 6 Referring to Example 1, the difference is that in step S1, the amount of nano-silicon powder added is 200mg, denoted as 0.04Si.

[0033] Example 7 Referring to Example 1, the difference is that in step S1, the amount of nano-silicon powder added is 0 mg, denoted as 0Si or C@GO).

[0034] Comparative Example 1 Referring to Example 1, the difference is that in step S1, graphene oxide is not added, denoted as Si@C.

[0035] Comparative Example 2 Referring to Example 1, the difference is that in step S4, the 1M HCl pickling for 12 hours is not performed, and this is recorded as Si@GO@C (before pickling).

[0036] Comparative Example 3 100 mg of 80 nm silicon nanoparticles and 50 mg of graphene oxide were mixed and calcined at 550 °C for 2 h in an argon atmosphere at a rate of 5 °C / min. This mixture is denoted as Si@GO.

[0037] Figure 2 a shows the XRD patterns of the materials prepared in Example 1 and Comparative Examples 1-3. It can be seen that the diffraction peaks of all materials appear at 28.4°, 47.3°, 56.1°, 69.1°, and 76.3°. The observed diffraction peaks match those of pure Si, corresponding to the (111), (220), (311), (400), and (331) crystal planes of Si (PDF#00-027-1402). Besides the silicon peaks, the diffraction peaks of Si@GO@C (before acid washing) also contain many impurity peaks, which is attributed to Fe. 1-x The presence of S was followed by washing away Fe with HCl. 1-x After S, it was found that the impurity peaks almost disappeared, and the remaining diffraction peaks matched the diffraction peaks of Si perfectly.

[0038] Figure 2 b shows the Raman spectra of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 3. It can be observed that at 513 cm⁻¹... -1 There is a characteristic peak nearby, which is typical of the Raman peaks of nano-Si crystals; in addition, there are peaks at 1350 and 1590 cm⁻¹. -1 Two absorption peaks appeared at 1350 cm⁻¹. −1 The peak at 1590 cm⁻¹ corresponds to the defect-induced D band, while the peak at 1590 cm⁻¹ corresponds to the defect-induced D band. −1 The peak at that location corresponds to the sp of carbon materials. 2 The intensity ratio of hybrid graphitized G-bands, D-bands, and G-bands (I) D / I G The IG ratio of Si@GO, Si@C, and Si@GO@C is 0.95. The Ig of Si@GO, Si@C, and Si@GO@C is... D / I G The ratios were 0.82, 0.94, and 0.99, respectively. Compared with the other two materials, the increase in the Si@GO@C ratio indicates an increase in the degree of disorder in the carbon material, which may mean that the carbon material in the sample has more defects. The presence of these defects can improve conductivity, enhance electrochemical activity, increase specific surface area, improve cycle stability, and regulate the chemical properties of the electrode surface, making its interaction with the electrolyte more compatible, thereby further improving the overall performance of the battery.

[0039] Figure 2c shows the nitrogen adsorption-desorption isotherms of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 3, indicating that the materials all exhibit a type IV isotherm and an H1 hysteresis loop, which is a significant performance characteristic of mesoporous materials. The specific surface areas of the materials are 22.3 m² / g (Si / GO). 2 / g, (Si@C)4.7m 2 / g and (Si@GO@C)39m 2 / g. Compared to Si@GO@C (29m before pickling) 2 The high specific surface area of ​​Si@GO@C (after acid washing), i.e., Example 1, mainly originates from the graphene composite and the abundant porous structure left by the washing of iron-based materials. The larger specific surface area results in a larger contact area between the electrolyte and electrode materials, which is beneficial for electrolyte penetration and provides more active sites. The presence of mesoporous structures helps to shorten the ion diffusion distance, providing a convenient channel for lithium ion transport, which is greatly beneficial to increasing the capacity of lithium-ion batteries. Meanwhile, the porosity of the Si@GO@C material obtained in Example 1 is 41.8%.

[0040] Figure 2 Figure d shows the thermogravimetric analysis (TGA) curves of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 3. The TGA curves indicate that the thermogravimetric curves of Si@GO, Si@C, and Si@GO@C exhibit two weight loss stages. The first weight loss corresponds to the evaporation of adsorbed water. Between 450℃ and 570℃, the samples experience rapid weight loss, corresponding to the rapid decomposition of C. Due to the presence of pyrrole carbon in Si@C and Si@GO@C, the material loss is less than that of Si@GO. Detailed observation of the thermogravimetric curves reveals that the Si@C material lacks a graphene layer. As the temperature reaches 600℃, the Si in the material is further oxidized, increasing its mass. This demonstrates that graphene also has a stabilizing effect, preventing Si from being oxidized. According to the thermogravimetric curves, the silicon content in Si@GO@C is approximately 20% (by weight), and the carbon content is approximately 80% (by weight).

[0041] Figure 3 The images shown in ab are SEM, TEM (200 nm), TEM (100 nm), and TEM (10 nm) images of the material prepared in Example 1. Figure 3A 12nm thick double-carbon coating can be obtained. Graphene oxide (GO) possesses an ultra-large specific surface area and chemical stability. As a flexible composite substrate, it can capture Si particles and uniformly disperse them on the GO substrate. Through coordination reactions, the Si particles are firmly stitched to the GO substrate by the carbon layer like threads. By uniformly dispersing Si particles on the graphene oxide substrate and firmly binding them to the carbon layer through coordination reactions, the expansion and contraction of silicon particles can be effectively reduced. The high specific surface area and good conductivity of graphene oxide provide a strong supporting framework, which not only helps to enhance the mechanical stability of silicon particles but also prevents excessive expansion and breakage between particles through the stitching effect of the carbon layer. In addition, the uniformly dispersed nano-silicon particles can maintain good conductivity, reduce charge conduction resistance during charging and discharging, and improve overall performance. This design can significantly mitigate the volume effect of nano-silicon, extend its lifespan in lithium-ion batteries, and improve the cycle stability and electrical performance of the battery.

[0042] Meanwhile, TEM images clearly show a rich porous structure and a large number of carbon nanowires crisscrossing the surface. These porous structures are attributed to the voids left by the removal of metal sulfides after the hydrochloric acid pickling process, and these structures help improve the electrochemical performance of the electrode material. Pores provide more active sites, enhance the contact between the electrolyte and the electrode material, and increase the ion transport rate, thereby improving the battery's cycle performance and discharge capability. The carbon nanowires are mainly derived from polypyrrole, formed by the polymerization reaction of pyrrole, which adheres to the surface of graphene through a carbonization process. The crisscrossing distribution of carbon nanowires provides a conductive network, further enhancing the conductivity of the electrode and providing additional support for the silicon particles. The presence of carbon nanowires not only helps improve conductivity but also improves the mechanical stability of the material, reducing electrode breakage due to volume expansion during charging and discharging, and extending battery life.

[0043] Figure 4 a is a cycle performance graph of the materials prepared in Examples 1 and 4-7. From the graph (1A g) -1At current density, it can be seen that the initial specific capacity of samples with different Si contents increases with the increase of Si content, but the cycle stability varies. The initial capacity of the 0Si (i.e., Example 7) sample is extremely low and has almost no capacity after cycling. The capacity decay of 0.01Si (i.e., Example 4) is gradual but the initial capacity is not high. Although the initial capacity of 0.03Si (i.e., Example 5) and 0.04Si (i.e., Example 6) is higher, the capacity decreases more significantly during cycling. In contrast, the 0.02Si sample in Example 1 has both a high initial specific capacity and maintains a relatively stable capacity level after 100 cycles (the decay is significantly better than that of 0.03Si and 0.04Si). Considering both the initial capacity and cycle stability, the cycle performance of the 0.02Si sample is the best among these Si contents.

[0044] Figure 4 b shows the rate performance of the materials prepared in Example 1, Comparative Example 1, and Example 7. As the current density increases from 0.2 A / g to 15 A / g, the specific capacity of all materials (Si@C, Si@GO@C, C@GO) decreases, and the capacity decrease is more significant at higher current densities. The initial specific capacity is higher at low current densities (e.g., 0.2 A / g), but the capacity decay is more pronounced at higher current densities (e.g., 10 A / g, 15 A / g). The capacity decay gradient of Si@GO@C with current density is relatively gentler, retaining more capacity at high rates. C@GO has a generally lower specific capacity, and its capacity decreases rapidly at high rates. The cycle efficiency of Si@GO@C remains close to 100%, indicating that the material has extremely high energy utilization efficiency during charging and discharging and excellent electrochemical reversibility.

[0045] Figure 4 c shows the AC impedance diagrams of the materials prepared in Example 1 and Comparative Examples 1-3. In the low Z' region, the impedance (Z'') of the four materials (Si@GO, Si@C, Si@GO@C, and Si@GO@C (before acid washing)) is relatively similar, indicating that the initial interface / charge transfer resistance is similar. As Z' increases, the impedance differentiation of different structures becomes obvious: the impedance (Z'') of Si@GO@C (before acid washing) increases the fastest, and the final impedance value is significantly higher than that of other materials, indicating that its interface stability is poor and the charge transfer resistance increases rapidly with cycling; the impedance increase of Si@C is the second fastest; the impedance increase of Si@GO@C is the most gradual, maintaining a relatively low impedance level. In summary, different composite structures have a significant impact on the interface stability of the materials, and structures like Si@GO@C can maintain a relatively low impedance level.

[0046] Figure 4Figure d shows the AC impedance diagrams of the material prepared in Example 1 after different number of cycles. Strong stability in the initial cycling stage: At low cycle counts (5 and 30 cycles), the impedance (Z'') is at a low level with high curve overlap, indicating excellent initial interfacial characteristics, low charge transfer resistance, and good electrochemical kinetic performance. Within 50 cycles, the impedance increase is limited, demonstrating good interfacial stability in the low to medium cycling stages, maintaining efficient charge transport capability for a relatively long time. At higher cycles of 70 and 100, the impedance remains essentially similar, exhibiting good electrode stability.

[0047] Figure 5 The graphs a and b represent the peak current-scan rate logarithmic relationship curve, capacitance contribution graph, and Na content during the sodiumization process of the material prepared in Example 1, respectively. + Diffusion coefficient diagram, Na in the desodiumization process + Diffusion coefficient diagram. Figure 5 The logarithmic relationship curve between peak current and scan rate shows that the slopes b of the two redox peaks are 0.96 and 1.00, respectively, both close to the ideal value of 1. This indicates that the electrode reaction of the material is mainly a capacitance-controlled process. This capacitance-dominated charge storage mode can significantly improve charge storage efficiency and lay the foundation for efficient charge and discharge. Figure 5 b further quantified the impact of scan rate on capacitance contribution, showing that as the scan rate increases from 0.6 mV·s... -1 Increased to 2mV·s -1 The capacitance contribution of Si@GO@C increased significantly from 67% to 92%, while the diffusion contribution decreased accordingly. This indicates that it can still achieve rapid charge storage by relying on capacitance behavior under high scan rate conditions, and has excellent rate performance, which can meet the needs of use under different current densities. Figure 5 c and Figure 5 d then compared the Na content of Si and Si@GO@C during the sodiumification and desodiumification processes. + The diffusion coefficient results show that, regardless of whether it is sodium formation or desodiumization, the Na content of Si@GO@C is high. + The diffusion coefficients of both GO@C and pure Si are significantly higher, with smaller fluctuations and greater stability. This demonstrates that the GO@C composite structure effectively optimizes the interfacial properties and bulk transport channels of the material, reducing the Na+ diffusion coefficient. + The transport resistance within the material significantly improves ion diffusion kinetics. In summary, Si@GO@C, through its rational structural design, achieves capacitor-dominated high-efficiency charge storage, excellent rate capability at high scan rates, and highly efficient and stable Na+ throughout the sodiumization-desodiumization process. + The transport properties are superior to those of pure Si materials in all aspects of electrochemical performance, demonstrating outstanding potential as an electrode material.

[0048] The Si@GO@C material obtained in Example 1 was combined with carbon black and sodium carboxymethyl cellulose in a mass ratio of 60:15:25 to form a lithium-ion battery anode, and then combined with Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 The O2 positive electrode is used to assemble a 2032 coin cell with N / P=1.1. The electrolyte composition is: 1M LiPF6 electrolyte, with FEC / EMC (fluoroethylene carbonate / ethyl methyl carbonate) (3:7 vol) as the solvent, and 2wt% LiDFOB (lithium difluorophosphate) added. The lithium-ion battery was tested, and its electrochemical performance results are as follows: First charge / discharge (0.1A / g): charging capacity 1685mAh / g, discharging capacity 1588mAh / g, first coulombic efficiency 85.4%; Rate performance: 1A / g capacity 1253mAh / g; 5A / g capacity 812mAh / g; 15A / g capacity 315mAh / g; Constant-capacity cycling (1000mAh / g): capacity retention rate 87.2% after 100 cycles; Low-temperature performance (-30℃): capacity retention rate 81.6% after 0.2C discharge; Cycle expansion rate: electrode expansion 19.8% after 200 cycles at 5A / g (laser thickness measurement, 10kPa pressure).

[0049] The terms “above,” “below,” and “within” as used above include the number itself; the terms “exceeding” and “excluding” do not include the number itself.

[0050] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific descriptions herein should not be construed as limiting the substance and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention. The various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe various possible combinations.

[0051] If the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

Claims

1. A method for preparing double-carbon coated silicon anode material based on coordination template method, characterized in that, Includes the following steps: S1 Under ice bath conditions of 0~5℃, iron source, conductive polymer monomer and nano silicon powder are uniformly dispersed in deionized water, then graphene oxide is added and ultrasonicated for 30~60 minutes. S2 Prepare a sulfur-containing solution and add it dropwise to the mixed solution obtained in step S1 to carry out the reaction; After the S3 reaction is completed, an initiator is added and polymerization is carried out under ice bath conditions; S4 is calcined in an inert atmosphere, followed by acid washing to obtain the double carbon-coated silicon anode material.

2. The preparation method according to claim 1, characterized in that, In step S1, the mixing ratio of iron source, conductive polymer monomer, nano-silicon powder and graphene oxide is 1 mol:(2.5~3.0) mol:(150~200) g:(85~100) g.

3. The preparation method according to claim 1 or 2, characterized in that, In step S1, the iron source is ferric ammonium oxalate or ferric ammonium citrate; the conductive polymer monomer is pyrrole; and the particle size of the nano-silicon powder is 50~200nm.

4. The preparation method according to any one of claims 1 to 2, characterized in that, In step S2, the sulfur-containing solution is an aqueous solution of sodium diethyldithiocarbamate, and the molar ratio of the total amount of Fe in the iron source to the total amount of S in the sulfur-containing solution is 1:(2.6~4.0); the reaction temperature is 0~5℃, and the reaction time is 1~3h.

5. The preparation method according to claim 1, characterized in that, In step S3, the initiator is ammonium persulfate; the molar ratio of the conductive polymer monomer to the initiator is 1:(0.85~1.05); the polymerization reaction temperature is 0~5℃, and the reaction time is 11~13h.

6. The preparation method according to claim 1, characterized in that, In step S4, the calcination temperature is 500~600℃, the calcination time is 1.5~3h, and the heating rate is ≤5℃ / min.

7. The double-carbon-coated silicon anode material prepared by any one of the preparation methods according to claims 1 to 6, characterized in that, The specific surface area of ​​the double carbon-coated silicon anode material is 38~42m². 2 / g, with a coating thickness of 12±2nm.

8. A lithium-ion battery negative electrode, characterized in that, The negative electrode comprises the double carbon-coated silicon negative electrode material as described in claim 7.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-ion battery negative electrode as described in claim 8.

10. The lithium-ion battery according to claim 9, characterized in that, The electrode expansion rate of the lithium-ion battery with a capacity of 5A / g after 200 cycles is ≤20%.

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