A silicon-carbon composite material embedded with FeS nanoclusters, a preparation method and application thereof

Abstract

This invention relates to the field of lithium-ion battery anode material technology, and more particularly to a silicon-carbon composite material embedded with FeS nanoclusters, its preparation method, and its application. The silicon-carbon composite material provided by this invention comprises nano-silicon and a carbon layer coating the surface of the nano-silicon; the carbon layer is a nitrogen-sulfur co-doped carbon layer; and FeS nanoclusters are embedded in the carbon layer. The carbon layer, acting as a soft buffer layer, can effectively alleviate the stress caused by the volume expansion of the silicon anode. Nitrogen and sulfur heteroatom doping can further improve the conductivity of the carbon material, thereby optimizing charge transport in the electrode. The introduction of FeS catalyzes the electrochemically inert Li... 15 The delithiation reaction of Si4 is characterized by a maximum 128-fold increase in Li-ion transport velocity within the delithiation potential range, and the Li-ion transport velocity increases after charging. 15 The Si4 residue is significantly reduced, which makes this material more suitable for Li 15 The lithium loss capacity caused by Si4 not being delithiated is significantly reduced, and the cycle performance is optimized.

Description

Technical Field

[0001] This invention relates to the field of lithium battery anode material technology, and in particular to a silicon-carbon composite material embedded with FeS nanoclusters, its preparation method and application. Background Technology

[0002] Lithium-ion batteries have evolved into a vast industrial chain serving grid-scale and mobile energy applications (such as electric vehicles and consumer electronics). With the rapid development of the industry, silicon materials are widely recognized as one of the most promising candidate materials for next-generation high-energy-density lithium-ion batteries. Silicon anodes have a theoretical specific capacity as high as 3590 mAh·g. -1 (Based on Li) 15 The silicon anode (Si4) has an ideal operating potential (0.4V). However, silicon anodes still face many challenges in practical applications. For example, with the cycling of lithium-ion batteries, the capacity of silicon anodes will decrease significantly.

[0003] One major reason for the capacity decay of silicon anodes is that, with the cycling of lithium-ion batteries, the main substance formed after lithium storage in the silicon anode material, Li, degrades. 15 Irreversible delithiation occurred in Si4. It is well known that silicon alloys can form various phases in the Li-Si system under different electrode potentials, including Li… 12 Si7, Li7Si3 and Li 15 Si4. It is worth noting that crystalline Li 15 The Si4 phase is the only electrochemically inert crystalline phase in the lithium-silicon system, exhibiting the most significant volume change (approximately 360%). This leads to the capture of a large amount of active lithium during cycling, thus significantly exacerbating capacity decay. Therefore, reducing the Li in the alloy product... 15 The lithium capture phenomenon caused by Si4 residue is crucial for improving the performance of silicon-carbon materials.

[0004] In current silicon anode materials, researchers often focus only on mitigating volume expansion or modulating the solid electrolyte interphase (SEI) film on the electrode surface to increase cycle stability, while Li... 15 The performance degradation caused by the residue of Si4 was ignored. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a silicon-carbon composite material embedded with FeS nanoclusters, its preparation method, and its applications. The silicon-carbon composite material provided by this invention not only alleviates volume expansion but also promotes Li... 15 The delithiation process of Si4 significantly reduces lithium loss capacity and optimizes cycle performance.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] The present invention provides a silicon-carbon composite material embedded with FeS nanoclusters, comprising nano-silicon and a carbon layer coating the surface of the nano-silicon; the carbon layer is a nitrogen-sulfur co-doped carbon layer; and FeS nanoclusters are embedded in the carbon layer.

[0008] Preferably, the size of the FeS nanoclusters is 5~10 nm.

[0009] Preferably, the silicon-carbon composite material contains 40-80 wt% Si, 7-10 at% N, 7-15 at% S, and 0.1-2 at% Fe.

[0010] Preferably, the particle size of the nano-silicon is 30~50nm.

[0011] This invention provides a method for preparing the silicon-carbon composite material described above, comprising the following steps:

[0012] By using cationic surfactants to positively charge nano-silicon, cationic surfactant-functionalized nano-silicon can be obtained.

[0013] The cationic surfactant-functionalized nano-silicon, water, and soluble ferrous salt are mixed, and then an alcohol solvent, dopamine, and ammonia are added to the resulting mixture to carry out a polymerization reaction. After solid-liquid separation, a silicon-carbon composite material precursor is obtained. The silicon-carbon composite material precursor includes nano-silicon and polydopamine coated on the surface of the nano-silicon. Ferrous salt is embedded in the polydopamine.

[0014] The silicon-carbon composite material precursor and sulfur source are calcined under a protective atmosphere to undergo sulfidation and carbonization, thereby obtaining the silicon-carbon composite material.

[0015] Preferably, the calcination temperature is 400~600℃, and the holding time is 2~4h.

[0016] Preferably, the volume ratio of the alcohol solvent to water is 6:(2~12).

[0017] Preferably, the mass ratio of the nano-silicon to the soluble ferrous salt is 1:(1~8).

[0018] Preferably, the soluble ferrous salt includes potassium ferrocyanide.

[0019] This invention provides the application of the silicon-carbon composite material described in the above-described scheme or the silicon-carbon composite material prepared by the above-described preparation method as a negative electrode material in lithium-ion batteries.

[0020] This invention provides a silicon-carbon composite material embedded with FeS nanoclusters, comprising nano-silicon and a carbon layer coating the surface of the nano-silicon; the carbon layer is a nitrogen-sulfur co-doped carbon layer; and FeS nanoclusters are embedded in the carbon layer. This invention specifically designs a silicon-carbon composite material with a core-shell structure in which FeS clusters are embedded in a nitrogen-sulfur co-doped carbon layer. The carbon layer, acting as a soft buffer layer, can effectively alleviate the stress caused by the volume expansion of the silicon anode. Nitrogen and sulfur heteroatom doping can further improve the conductivity of the carbon material, thereby optimizing charge transport in the electrode. The introduction of FeS catalyzes the electrochemically inert Li... 15 The delithiation reaction of Si4 is characterized by a maximum 128-fold increase in Li-ion transport velocity within the delithiation potential range, and the Li-ion transport velocity increases after charging. 15 The Si4 residue is significantly reduced, which makes this material more suitable for Li 15 The lithium loss capacity caused by Si4 not being delithiated is significantly reduced, and the cycle performance is optimized. Attached Figure Description

[0021] Figure 1 The XRD pattern of the silicon-carbon composite material prepared in Example 1;

[0022] Figure 2 TEM images of the silicon-carbon composite material prepared in Example 1 at different magnifications;

[0023] Figure 3 XPS spectrum of the silicon-carbon composite material prepared in Example 1;

[0024] Figure 4 The graph shows the cycle stability test results of the half-cells assembled in Example 1 and Comparative Example 1 after rate activation.

[0025] Figure 5 The graphs are dQ / dV curves of the half-cells assembled in Example 1 and Comparative Example 1, where (a) is Example 1 and (b) is Comparative Example 1.

[0026] Figure 6 The results are GITT test results for Example 1 and Comparative Example 1, where (a) is the lithiation process and (b) is the delithiation process;

[0027] Figure 7 The constant voltage charging curves are for Example 1 and Comparative Example 1, where (a) is Example 1 and (b) is Comparative Example 1.

[0028] Figure 8 The images show the non-in-situ Si 2p XPS diagrams of Example 1 and Comparative Example 1 after charging. Detailed Implementation

[0029] The present invention provides a silicon-carbon composite material, comprising nano-silicon and a carbon layer coated on the surface of the nano-silicon; the carbon layer is a nitrogen-sulfur co-doped carbon layer; and FeS nanoclusters are embedded in the carbon layer.

[0030] In this invention, the particle size of the nano-silicon is preferably 30-50 nm; the size of the FeS nanoclusters is preferably 5-10 nm.

[0031] In this invention, the silicon-carbon composite material contains 40-80 wt% Si, preferably 7-10 at% N, 7-15 at% S, and 0.1-2 at% Fe.

[0032] In specific embodiments of the present invention, the Si content in the silicon-carbon composite material can be 40wt%, 45wt%, 50wt%, 53wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, or 80wt%, the N content can be 7at%, 7.5at%, 8at%, 8.5at%, 9at%, 9.5at%, 9.8at%, or 10at%, the S content can be 7at%, 8at%, 8.6at%, 9at%, 10at%, 11at%, 12at%, 13at%, 14at%, or 15at%, and the Fe content can be 0.1at%, 0.3at%, 0.5at%, 0.8at%, 1.0at%, 1.2at%, 1.4at%, 1.6at%, 1.8at%, or 2at%.

[0033] In this invention, the carbon layer, acting as a soft buffer layer, effectively alleviates the stress caused by the volume expansion of the silicon anode. Nitrogen and sulfur heteroatoms doping further improves the conductivity of the carbon material, thereby optimizing charge transport in the electrode. The introduction of FeS catalyzes the chemically inert Li... 15 The delithiation reaction of Si4, after charging, Li 15 The Si4 residue is significantly reduced, which makes this material more suitable for Li 15 The lithium loss capacity caused by Si4 not being delithiated is significantly reduced, and the cycle performance is optimized.

[0034] This invention provides a method for preparing the silicon-carbon composite material described above, comprising the following steps:

[0035] By using cationic surfactants to positively charge nano-silicon, cationic surfactant-functionalized nano-silicon can be obtained.

[0036] The cationic surfactant-functionalized nano-silicon, water, and soluble ferrous salt are mixed, and then a second alcohol solvent, dopamine, and ammonia are added to the resulting mixture to carry out a polymerization reaction. After solid-liquid separation, a silicon-carbon composite material precursor is obtained. The silicon-carbon composite material precursor includes nano-silicon and polydopamine coated on the surface of the nano-silicon. Ferrous salt is embedded in the polydopamine.

[0037] The silicon-carbon composite material precursor and sulfur source are calcined under a protective atmosphere to undergo sulfidation and carbonization, thereby obtaining the silicon-carbon composite material.

[0038] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0039] This invention utilizes cationic surfactants to positively charge nano-silicon, thereby obtaining cationic surfactant-functionalized nano-silicon.

[0040] In this invention, the positive charge modification of nano-silicon using cationic surfactant preferably includes the following steps: dispersing nano-silicon in an alcohol solvent (i.e., the first alcohol solvent) to obtain a nano-silicon dispersion; mixing the nano-silicon dispersion with a cationic surfactant for adsorption, followed by solid-liquid separation to obtain cationic surfactant-functionalized nano-silicon.

[0041] In this invention, the first alcohol solvent is preferably methanol or ethanol, and in the embodiments of this invention, it is specifically anhydrous methanol. In this invention, the particle size of the nano-silicon is preferably 30-50 nm. In this invention, the dispersion is preferably ultrasonic dispersion; the conditions for ultrasonic dispersion are not particularly important, as long as the nano-silicon is dispersed uniformly. In this invention, the concentration of the nano-silicon dispersion is preferably 0.5-3 mg / mL, and in specific embodiments, it can be 0.5 mg / mL, 1.0 mg / mL, 1.5 mg / mL, 1.7 mg / mL, 2.0 mg / mL, 2.5 mg / mL, or 3 mg / mL.

[0042] In this invention, the cationic surfactant preferably comprises 3-aminopropyltriethoxysilane (APTES); the volume fraction of the cationic surfactant in the nano-silicon dispersion is preferably 0.5-2%, and in specific embodiments it can be 0.5%, 1%, 1.5%, or 2%. In this invention, the role of the cationic surfactant is to build charges on the silicon surface in preparation for the adsorption of ferrous ions in the next step (when the soluble ferrous salt is potassium ferrocyanide, it is the adsorption of ferrocyanide ions).

[0043] In this invention, the adsorption is preferably carried out under stirring conditions, and the adsorption time is preferably 4-12 hours, with 6 hours in a specific embodiment. This invention does not have special requirements for the solid-liquid separation conditions; any solid-liquid separation method well-known in the art can be used, such as centrifugation. After completing the solid-liquid separation, this invention preferably further includes washing the obtained solid with ethanol to remove excess cationic surfactant.

[0044] After obtaining cationic surfactant-functionalized nano-silicon, the present invention mixes the cationic surfactant-functionalized nano-silicon, water, and soluble ferrous salt to obtain a mixed liquid.

[0045] In this invention, it is preferable to first disperse cationic surfactant-functionalized nano-silicon into water, and then add soluble ferrous salt.

[0046] In this invention, the soluble ferrous salt preferably includes potassium ferrocyanide; the mass ratio of the nano-silicon to the soluble ferrous salt is preferably 1:(1~8), and in specific embodiments it can be 1:1, 1:2, 1:4, 1:6 or 1:8, with 1:4 being the most preferred. In this invention, the water is preferably deionized water. The function of the water is to disperse the nano-silicon adsorbing the cationic surfactant while dissolving the soluble ferrous salt. This invention does not impose a special limitation on the amount of water used, and it can be adjusted according to the amount of ferrous salt to be dissolved. In the embodiments of this invention, for 0.1~0.8g of soluble ferrous salt, the amount of water used is 40mL.

[0047] After adding a soluble ferrous salt, the present invention preferably involves ultrasonication to promote its dissolution. Taking potassium ferrocyanide as an example, after adding a soluble ferrous salt, the cationic surfactant-functionalized nano-silicon adsorbs ferrocyanide ions.

[0048] After obtaining the mixed liquid, the present invention adds an alcohol solvent (denoted as the second alcohol solvent), dopamine and ammonia to the obtained mixed liquid to carry out a polymerization reaction, and then separates the solid and liquid to obtain a silicon-carbon composite material precursor; the silicon-carbon composite material precursor includes nano-silicon and polydopamine coated on the surface of the nano-silicon; the polydopamine contains ferrous salt.

[0049] In this invention, the second alcohol solvent preferably includes ethanol or methanol; the volume ratio of the second alcohol solvent to water is preferably 6:(2~12), and in specific embodiments it can be 6:2, 6:3, 6:4, 6:5, 6:6, 6:7, 6:8, 6:9, 6:10, 6:11 or 6:12. In this invention, the function of the second alcohol solvent is to regulate the polymerization environment of dopamine and the concentration of ferrous salt, and the most preferred volume ratio of the second alcohol solvent to water is 6:4. In this invention, the dopamine serves as a carbon source and a nitrogen source; the mass ratio of the dopamine to the nano-silicon is preferably 2:(1~4), and most preferably 1:1. In this invention, the ammonia water serves as an initiator for dopamine polymerization; the mass concentration of the ammonia water is preferably 25%, and the amount of ammonia water used is preferably sufficient to maintain the pH value of the polymerization system at 8~9.

[0050] In this invention, it is preferable to first add a second alcohol solvent to the mixture and stir, then add dopamine and continue stirring, and finally add ammonia. Preferably, the ammonia is added slowly, specifically dropwise.

[0051] During the polymerization reaction, dopamine is polymerized into polydopamine under the action of ammonia water and coated on the surface of nano-silicon, while ferrous salt is embedded into polydopamine.

[0052] This invention does not have special requirements for the solid-liquid separation method; any solid-liquid separation method well-known in the art can be used, such as centrifugation. After solid-liquid separation, this invention preferably washes the obtained solid repeatedly with deionized water and ethanol to obtain the silicon-carbon composite material precursor.

[0053] After obtaining the silicon-carbon composite material precursor, the present invention calcines the silicon-carbon composite material precursor and a sulfur source under a protective atmosphere to induce sulfidation and carbonization, thereby obtaining the silicon-carbon composite material.

[0054] In this invention, the sulfur source preferably includes sulfur powder; the mass ratio of the sulfur source to the silicon-carbon composite material precursor is preferably 1:1. Preferably, the silicon-carbon composite material precursor and the sulfur source are placed separately at opposite ends of the same ceramic boat for calcination. In this invention, the protective atmosphere preferably includes an argon atmosphere; the calcination temperature is preferably 400~600℃, and in specific embodiments, it can be 400℃, 450℃, 500℃, 550℃, or 600℃; the calcination holding time is preferably 2~4 hours, and in specific embodiments, it can be 2 hours, 3 hours, or 4 hours; the rate of heating to the calcination temperature is preferably 2℃·min. -1 In the calcination process described in this invention, ferrous salt is sulfided into FeS, and polydopamine is carbonized into carbon at high temperature. Since it contains nitrogen, and potassium ferrocyanide contains nitrogen (when the ferrous salt is potassium ferrocyanide), a sulfur source is present during calcination, thus obtaining a nitrogen-sulfur co-doped carbon layer.

[0055] This invention provides the application of the silicon-carbon composite material described in the above-described scheme or the silicon-carbon composite material prepared by the above-described preparation method as a negative electrode material in lithium-ion batteries.

[0056] The following detailed description of the silicon-carbon composite material, its preparation method, and its application provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] 0.1g of Si powder was added to 60mL of methanol and subjected to high-energy sonication for 1 hour to ensure uniform dispersion of the silicon powder.

[0059] After homogenization by sonication, add 0.6 mL of APTES, stir continuously for 6 h, then centrifuge, wash the precipitate three times with ethanol to remove excess APTES;

[0060] The precipitate was evenly dispersed in 40 mL of deionized water, and 0.4 g of potassium ferrocyanide was added. The mixture was then sonicated to dissolve the precipitate. 60 mL of ethanol was added, and the mixture was transferred to a small beaker and stirred continuously for 1 h.

[0061] Add 0.1g of dopamine and stir continuously for 2 hours;

[0062] Slowly add 0.6 mL of ammonia solution (25% by mass) dropwise, and continue stirring for 12 hours;

[0063] The obtained precipitate was centrifuged and repeatedly washed with deionized water and ethanol to obtain the precursor.

[0064] The obtained precursor was placed in a tube furnace with argon as the protective gas and sulfur powder as the sulfur source. The mass ratio of sulfur source to precursor was 1:1. Calcination was carried out at 500℃ for 3 hours, with a heating rate of 2℃·min. -1 A silicon-carbon composite material, denoted as Si@FeS / C, was obtained. In this silicon-carbon composite material, the Si content was 53 wt% (measured by ICP), the N content was 9.8 at% (measured by XPS), the S content was 8.6 at% (measured by XPS), and the Fe content was 1.2 at% (measured by XPS).

[0065] Example 2

[0066] The only difference from Example 1 is that the amount of potassium ferrocyanide is changed to 0.1g, and the rest is the same as Example 1.

[0067] Example 3

[0068] The only difference from Example 1 is that the calcination temperature is 400°C; otherwise, it is the same as Example 1.

[0069] Comparative Example 1

[0070] Unmodified nano-silicon was used as the active material.

[0071] Comparative Example 2

[0072] Pure carbon layer coated Si:

[0073] 0.1 g of Si powder was ultrasonically dispersed in a mixture of 40 mL of deionized water and 60 mL of ethanol. Then, 0.1 g of dopamine was added and the mixture was stirred continuously for 12 h. Finally, 0.6 mL of ammonia water (25% by mass) was slowly added dropwise and the mixture was stirred continuously for 12 h.

[0074] The obtained precipitate was centrifuged and repeatedly washed with deionized water and ethanol to obtain the precursor.

[0075] The calcination process was carried out in a tube furnace at 500℃ for 3 hours with argon as the protective gas and a heating rate of 2℃·min. -1 .

[0076] Comparative Example 3

[0077] The difference from Example 1 is that no sulfur source is added during calcination; instead, Fe2O3 is introduced into the carbon coating layer. The specific steps are as follows:

[0078] The preparation of the precursor is the same as in Example 1;

[0079] The obtained precursor was placed in a tube furnace and calcined at 600℃ for 3 hours under argon as a protective gas, with a heating rate of 2℃·min. -1 A silicon-carbon composite material was obtained, in which Fe2O3 was embedded in the carbon coating layer.

[0080] Note: The calcination temperatures of Comparative Examples 3-7 are different from those of Example 1 because different phases have different suitable sintering temperatures.

[0081] Comparative Example 4

[0082] The difference from Example 1 is that the calcination is carried out under a reducing atmosphere, and Fe is introduced into the carbon coating layer. The specific steps are as follows:

[0083] The preparation of the precursor is the same as in Example 1;

[0084] The obtained precursor was placed in a tube furnace and reduced at 600°C with an argon-hydrogen mixture (hydrogen content 10%) as the protective gas. The calcination was carried out for 3 hours with a heating rate of 2°C / min. -1 A silicon-carbon composite material was obtained, in which Fe was embedded in the carbon coating layer.

[0085] Comparative Example 5

[0086] The difference from Example 1 is that MoS2 is introduced into the carbon coating layer. The specific steps are as follows:

[0087] Add 0.1g of Si powder to 60mL of methanol and sonicate at high energy for 1 hour to disperse the silicon powder evenly.

[0088] After homogenization by sonication, add 0.6 mL of APTES, stir continuously for 6 h, then centrifuge, wash the precipitate three times with ethanol to remove excess APTES;

[0089] The precipitate was evenly dispersed in 40 mL of deionized water, and 0.2 g of ammonium molybdate was added. The mixture was then sonicated to dissolve the precipitate. 40 mL of ethanol was added, and the mixture was transferred to a small beaker and stirred continuously for 1 h.

[0090] Add 0.1g of dopamine and stir continuously for 2 hours;

[0091] Slowly add 0.6 mL of ammonia solution and stir continuously for 12 hours;

[0092] The obtained precipitate was centrifuged and repeatedly washed with deionized water and ethanol to obtain the precursor.

[0093] The obtained precursor was placed in a tube furnace with argon as the protective gas and sulfur powder as the sulfur source. The mass ratio of sulfur source to precursor was 1:1. Calcination was carried out at 600℃ for 3 hours, with a heating rate of 2℃·min. -1 Silicon-carbon composite material was obtained.

[0094] Comparative Example 6

[0095] The difference from Example 1 is that Ni is introduced into the carbon coating layer. The specific steps are as follows:

[0096] 0.1g of Si powder was added to 60mL of methanol and subjected to high-energy sonication for 1 hour to ensure uniform dispersion of the silicon powder.

[0097] After homogenization by sonication, add 0.6 mL of APTES, stir continuously for 6 h, then centrifuge, wash the precipitate three times with ethanol to remove excess APTES;

[0098] The precipitate was evenly dispersed in 40 mL of deionized water, and 0.32 g of nickel nitrate hexahydrate was added. The mixture was then sonicated to dissolve the precipitate, and 40 mL of ethanol was added. The mixture was then transferred to a small beaker and stirred continuously for 1 h.

[0099] Add 0.1g of dopamine and stir continuously for 2 hours;

[0100] Slowly add 0.6 mL of ammonia solution and stir continuously for 12 hours;

[0101] The obtained precipitate was centrifuged and repeatedly washed with deionized water and ethanol to obtain the precursor.

[0102] The obtained precursor was placed in a tube furnace and subjected to reduction treatment at 600℃ with argon and hydrogen (hydrogen content 10%) as protective gases, followed by calcination for 3 hours at a heating rate of 2℃·min. -1 .

[0103] Comparative Example 7

[0104] The difference from Example 1 is that Co is introduced into the carbon coating layer. The specific steps are as follows:

[0105] 0.1g of Si powder was added to 60mL of methanol and subjected to high-energy sonication for 1 hour to ensure uniform dispersion of the silicon powder.

[0106] After homogenization by sonication, add 0.6 mL of APTES, stir continuously for 6 h, then centrifuge, wash the precipitate three times with ethanol to remove excess APTES;

[0107] The precipitate was evenly dispersed in 40 mL of deionized water, and 0.32 g of cobalt nitrate hexahydrate was added. The mixture was then sonicated to dissolve the precipitate, and 40 mL of ethanol was added. The mixture was then transferred to a small beaker and stirred continuously for 1 h.

[0108] Add 0.1g of dopamine and stir continuously for 2 hours;

[0109] Slowly add 0.6 mL of ammonia solution and stir continuously for 12 hours;

[0110] The obtained precipitate was centrifuged and repeatedly washed with deionized water and ethanol to obtain the precursor.

[0111] The obtained precursor was placed in a tube furnace and reduced at 600℃ under a protective atmosphere of argon and hydrogen (10% hydrogen content) for 3 hours, with a heating rate of 2℃·min. -1 .

[0112] Structural characterization and performance testing

[0113] The silicon-carbon composite material prepared in Example 1 was subjected to XRD testing, and the results are shown in the figure. Figure 1 .Depend on Figure 1 It can be seen that FeS and Si are present in silicon-carbon composite materials.

[0114] The silicon-carbon composite material prepared in Example 1 was observed by transmission electron microscopy (TEM), and the results are as follows: Figure 2 As shown, the three TEM images are progressively magnified from left to right. The first TEM image reveals that the silicon-carbon composite material has a coating structure, with silicon inside and a carbon coating layer outside. Upon further magnification, the second TEM image shows that the FeS crystal particles are approximately 5-10 nm in size, while the interplanar spacing measurement results in the third TEM image confirm that FeS is indeed embedded in the carbon coating layer.

[0115] XPS analysis was performed on the silicon-carbon composite material prepared in Example 1, and the results are shown in the figure. Figure 3 The presence of CN and CS bonds in the fine XPS spectrum of C1s indicates that the carbon layer exhibits N and S co-doping. The obvious CSC characteristic peaks in the S 2p spectrum and the obvious pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen characteristic peaks in the N 1s spectrum further confirm this phenomenon.

[0116] The materials prepared in each embodiment and comparative example were used as active materials and assembled into button half-cells for electrochemical performance testing. The specific steps are as follows: the active material, conductive carbon, and PAA (polyacrylic acid) were mixed in a mass ratio of 6:3:1, ground, and then coated onto copper foil. After vacuum drying, the loading capacity was 1.5 mg / cm³. 2 The electrode sheets were assembled into a button half-cell in an argon-filled glove box; lithium foil was used as the counter electrode, Celgard 2400 was used as the separator, and the electrolyte was a 1M LiPF6 electrolyte of ethylene carbonate, dimethyl carbonate and diethyl carbonate (molar ratio 1:1:1), with 5 vol% fluoroethylene carbonate added.

[0117] The button half-cells assembled in Example 1 (Si@FeS / C) and Comparative Example 1 (Si) were subjected to cycle performance tests at a current density of 0.2 A / g. The results are shown in [Figure 1]. Figure 4 .Depend on Figure 4 It can be seen that the silicon material with the special coating layer of this invention did not experience significant degradation and exhibited excellent cycle stability. In contrast, Comparative Example 1, which used pure silicon as the active material, showed poor cycle stability.

[0118] Figure 5 for Figure 4 Example 1 (Si@FeS / C, Figure 5 (a) and Comparative Example 1 (Si, Figure 5 (b) shows the differential capacity curves (dQ / dV) at different cycle numbers. As the number of cycle numbers increases, the dQ / dV curve of Comparative Example 1 exhibits significant polarization, indicating that the charge transport network inside its electrode gradually fails. However, Example 1 does not show significant polarization with increasing cycle number, indicating that the present invention constructs a stable charge transport network. Furthermore, in Comparative Example 1, Li... 15 The oxidation peak of Si4 (around 0.5V) gradually decreases with increasing cycle number, indicating that Li 15 The residual Si4 gradually increases, which is Figure 4 One of the reasons for capacity decay in Comparative Example 1. And in Example 1, Li 15 The stable oxidation peak of Si4 indicates that this invention achieves Li 15 Si4 reversible transformation.

[0119] The half-cells assembled in Example 1 and Comparative Example 1 were tested using galvanostatic intermittent titration (GITT) at an Arbin electrochemical workstation with a current density of 0.2 A·g. -1 The relaxation time is 2 hours. The test results are shown below. Figure 6 ,in, Figure 6 (a) shows the lithiation process of Example 1 (Si@FeS / C) and Comparative Example 1 (Si), and (b) shows the subsequent delithiation process. During the lithiation process, Si is successively lithilated into amorphous α-Li. x Si (0.3V in the figure) and crystalline c-Li 15 Si4 (0.1V in the figure). Figure 6 As shown in (a), in a-Li x Si and c-Li 15 During the Si4 alloying process, the lithium-ion diffusion coefficients of Example 1 were 6 times and 4.6 times that of Comparative Example 1, respectively, indicating that the design of the special coating layer of this invention optimizes lithium transport during the silicon-lithium alloying process. In the subsequent delithiation process, the amorphous Li-Si alloy exhibits higher electrochemical activity, thus displaying a superior lithiation reaction rate and a lower delithiation potential. Therefore, a-Li x Si and c-Li 15 The dealloying of Si4 is at 0.25V and 0.45V as shown in the figure. Figure 6 Figure (b) shows that in a-Li x Si and c-Li 15 During the dealloying process of Si4, the lithium-ion diffusion coefficients in Example 1 were 3.8 times and 128.2 times that of Comparative Example 1, respectively. Compared to the previous a-Li... x Si and c-Li 15 Alloying of Si4 and α-Li x The dealloying process of Si, c-Li 15 During the dealloying process of Si4, the lithium-ion diffusion in Example 1 was significantly increased, indicating that the special coating layer of the present invention promotes the alloying of silicon materials into Li. 15 Delithiation of Si4.

[0120] The half-cells assembled in Example 1 (Si@FeS / C) and Comparative Example 1 (Si) were subjected to constant voltage charging under test conditions of 0.2 A·g. -1 After 30 cycles, the battery was charged at a constant voltage of 3.0V. The test results are shown below. Figure 7 Since lithium ions captured by the SEI film exist stably in the form of lithium salts such as LiF, Li₂O, and Li₂CO₃ and cannot be released during constant voltage charging, the capacity obtained during constant voltage charging can be used to measure the capacity of the electrode due to the presence of lithium ions within it. 15 Lithium capture capacity due to Si4 residue. Figure 7 It can be seen that the lithium-ion capture capacity in Example 1 is 17.4 mAh·g. -1 This is far lower than that of Comparative Example 1 (lithium-ion capture capacity of 172.2 mAh·g). -1 This indicates that the special coating layer of the present invention promotes the alloying of silicon materials into Li... 15 Delithiation of Si4 inhibits lithium capture.

[0121] The results of the 3.0V constant voltage charging test on the button half-cells assembled in each embodiment and comparative example are summarized in Table 1.

[0122] Table 1. Performance comparison of different embodiments and comparative examples (unit: mAh·g) -1 )

[0123]

[0124] As shown in Table 1, compared to the embodiments of the present invention with special coating layers, the comparative examples with no coating layer (pure Si), pure carbon coating on Si, or special coating layers embedded with other metals have significantly higher lithium-ion capture capacities. This indicates that the special coating layer of the present invention has a significantly higher lithium-ion capture capacity for Li. 15 The reversible delithiation of Si4 exhibits a superior promoting effect. Furthermore, a comparison of Examples 1, 2, and 3 shows that excessively low iron content and low FeS formation temperature affect Li... 15 Si4 exhibits reversible delithiation, but its delithiation performance is still superior to other comparative examples.

[0125] After cycling the half-cells of Example 1 (Si@FeS / C) and Comparative Example 1 (Si) 30 times, they were disassembled in an argon-filled glove box and transferred to an X-ray photoelectron spectroscopy (XPS) instrument under inert gas protection to obtain the in-situ XPS pattern of the electrodes, specifically the Si 2p spectrum. Figure 8 As shown, Li-Si peaks still exist in Comparative Example 1 after charging is complete, indicating that the Li in Comparative Example 1... 15 Si4 cannot be completely delithiated. However, in Example 1, the Li-Si peak completely disappeared after charging, indicating that Example 1, with its special coating layer, promotes Li delithiation. 15 Si4 delithiation, this phenomenon is related to Figure 5 , Figure 6 , Figure 7 Consistent performance.

[0126] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material embedded with FeS nanoclusters, characterized by, Includes the following steps: APTES-functionalized silicon nanoparticles were obtained by positively modifying silicon nanoparticles with 3-aminopropyltriethoxysilane (APTES). The APTES-functionalized nano-silicon, water, and soluble ferrous salt are mixed, and then an alcohol solvent, dopamine, and ammonia are added to the resulting mixture to carry out a polymerization reaction. After solid-liquid separation, a silicon-carbon composite material precursor is obtained. The silicon-carbon composite material precursor includes nano-silicon and polydopamine coated on the surface of the nano-silicon. Ferrous salt is embedded in the polydopamine. The silicon-carbon composite material precursor and sulfur source are calcined under a protective atmosphere to undergo sulfidation and carbonization, thereby obtaining the silicon-carbon composite material. The silicon-carbon composite material comprises nano-silicon and a carbon layer coating the surface of the nano-silicon; the carbon layer is a nitrogen-sulfur co-doped carbon layer; and FeS nanoclusters are embedded in the carbon layer. The silicon-carbon composite material contains 40-80 wt% Si, 7-10 at% N, 7-15 at% S, and 0.1-2 at% Fe.

2. The production method according to claim 1, characterized by, The calcination temperature is 400~600℃, and the holding time is 2~4h.

3. The preparation method according to claim 1, characterized in that, The volume ratio of the alcohol solvent to water is 6:(2~12).

4. The method of claim 1, wherein, The mass ratio of the nano-silicon to the soluble ferrous salt is 1:(1~8).

5. The production method according to claim 1 or 4, characterized by, The soluble ferrous salt includes potassium ferrocyanide.

6. The method of claim 1, wherein, The FeS nanoclusters have a size of 5~10 nm.

7. The preparation method according to claim 1, characterized in that, The particle size of the nano-silicon is 30~50nm.

8. The application of the silicon-carbon composite material prepared by the preparation method according to any one of claims 1 to 7 as a negative electrode material in lithium-ion batteries.

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