A bulk-sulfur-doped silicon-carbon composite negative electrode material, a preparation method and application thereof

Abstract

The embodiment of the present application relates to a kind of body phase sulfur doped silicon-carbon composite negative electrode material and its preparation method and application, the silicon-carbon composite negative electrode material described includes nano silicon particles dispersed in the pore of porous carbon matrix, the body phase of nano silicon particles contains sulfur element in the form of Si-S bonding, and the content of sulfur element in the body phase region of nano silicon particles is higher than the content in surface region.The silicon-carbon composite negative electrode material of body phase doping provided by the present application, Si-S bonding in the body phase of nano silicon particles makes sulfur element stable solid solution in silicon lattice, effectively alleviates the volume expansion stress in the process of lithiation / delithiation, and the distribution gradient that sulfur element is rich in body phase, surface is relatively poor, both form buffer layer in particle interior, and reduce surface side reaction, so as to inhibit the excessive growth of solid electrolyte interface film.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to a bulk sulfur-doped silicon-carbon composite anode material, its preparation method, and its application. Background Technology

[0002] With the increasing demand for high-energy-density lithium-ion batteries from electric vehicles and energy storage systems, silicon (Si)-based anode materials are considered the most promising next-generation anode materials due to their extremely high theoretical specific capacity and low delithiation potential.

[0003] However, silicon undergoes a dramatic volume change of over 300% during lithiation / delithiation, which not only leads to the pulverization of active materials and the collapse of electrode structures, but also triggers repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, resulting in irreversible consumption of active lithium and electrolyte, ultimately manifesting as a sharp decline in battery cycle life. Furthermore, silicon's inherently low electronic / ionic conductivity severely limits its rate performance.

[0004] To alleviate these problems, a common strategy is to coat silicon particles with carbon materials (such as amorphous carbon and graphene), using the flexibility and high conductivity of carbon materials to buffer volume expansion and improve conductivity. However, conventional Si / C composites still face serious challenges: First, silicon and carbon components are usually bonded only by physical contact or weak van der Waals forces, and under repeated stress impacts, the interface is prone to delamination and loss of electrical contact; second, the heterogeneous interface itself constitutes a barrier to lithium-ion diffusion, affecting reaction kinetics; finally, the continuous growth of an unstable SEI film results in low initial coulombic efficiency and poor cycle stability.

[0005] To optimize the performance of carbon matrices, elemental doping (such as nitrogen and boron) has been extensively studied. While nitrogen doping improves conductivity, its contribution to enhancing structural stability is limited; boron doping primarily strengthens the framework strength, with insufficient improvement in conductivity. In recent years, sulfur (S) doping has attracted attention as an emerging technique. However, in existing technologies, the application of sulfur is limited to surface modification of silicon particles or as a crosslinking agent; sulfur cannot effectively penetrate the bulk phase of silicon. This superficial modification method cannot fundamentally and synergistically improve the bulk conductivity, mechanical strength, and interfacial stability of silicon materials.

[0006] In summary, existing technologies have not yet effectively solved the problem of synergistic optimization among bulk conductivity, structural stability, and interfacial dynamics in silicon-carbon composite materials. In particular, how to construct an "integrated" structure within the material simultaneously possessing high conductivity, strong mechanical binding force, and a stable electrochemical interface through a bulk-scale atomic-level doping strategy remains a critical technical challenge that needs to be overcome in this field.

[0007] Therefore, developing a novel bulk doping technology and material structure that can fundamentally and synergistically improve the overall electrochemical performance of silicon-carbon composite materials has significant theoretical importance and enormous application value. Summary of the Invention

[0008] The purpose of this invention is to address the deficiencies of existing technologies by providing a bulk sulfur-doped silicon-carbon composite anode material, its preparation method, and its application. The bulk sulfur-doped silicon-carbon composite anode material provided by this invention achieves synergistic regulation of volume expansion and interface stability from the inside to the outside, significantly improving the material's cycle stability and rate performance.

[0009] To achieve the above objectives, in a first aspect, the present invention provides a bulk sulfur-doped silicon-carbon composite anode material, characterized in that the silicon-carbon composite anode material comprises nano-silicon particles dispersed in the pores of a porous carbon matrix, wherein the bulk phase of the nano-silicon particles contains sulfur elements existing in the form of Si-S bonds, and the content of sulfur elements in the bulk phase region of the nano-silicon particles is higher than that in the surface region.

[0010] Preferably, the porous carbon matrix contains sulfur in the form of CSC and / or SS bonds.

[0011] Preferably, the specific surface area of ​​the porous carbon matrix is ​​1000 m². 2 / g-2000m 2 / g, wherein the pore size of the porous carbon matrix is ​​0.5nm-5nm.

[0012] Preferably, the silicon-carbon composite anode material has a core-shell-shell structure, comprising, from the inside out: The core composite includes the porous carbon matrix and the nano-silicon particles; An intermediate passivation layer covers the outer surface of the core composite. A carbon coating layer is applied to the outer surface of the intermediate passivation layer.

[0013] Preferably, when the intermediate passivation layer is a carbon material layer, the thickness of the intermediate passivation layer is 0.5 nm to 5 nm; When the intermediate passivation layer is a metal oxide layer or a metal passivation layer, the thickness of the intermediate passivation layer is 0.5 nm to 3 nm; The thickness of the carbon coating layer is 2nm-20nm.

[0014] In a second aspect, the present invention provides a method for preparing the silicon-carbon composite anode material described in the first aspect above, the method comprising the following steps: The porous carbon matrix was placed in a chemical vapor deposition reactor and heated under a protective atmosphere; A mixed gas containing silicon source gas and sulfur source gas is introduced into the reactor, causing the silicon source gas and the sulfur source gas to undergo a co-deposition reaction in the pores of the porous carbon matrix, forming bulk sulfur-doped nano-silicon particles in situ. The sulfur element in the sulfur source gas is doped into the bulk interior of the nano-silicon particles to form Si-S bonds, and the sulfur content in the bulk region is higher than that in the surface region, resulting in a bulk sulfur-doped core composite.

[0015] Preferably, the sulfur element in the sulfur source gas reacts with the carbon in the porous carbon matrix to form CSC and / or SS bonds.

[0016] Preferably, the temperature of the co-deposition reaction is 450℃-700℃, and the time of the co-deposition reaction is 1h-6h.

[0017] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the carbon composite negative electrode material described in the first aspect, or comprising the silicon-carbon composite negative electrode material prepared by the preparation method described in the second aspect.

[0018] Fourthly, the present invention provides an energy storage device, the energy storage device comprising a lithium-ion battery or a lithium-ion capacitor; The energy storage device comprises the silicon-carbon composite negative electrode material described in the first aspect above, or comprises the silicon-carbon composite negative electrode material prepared by the preparation method described in the second aspect above, or comprises the negative electrode sheet described in the third aspect above.

[0019] The bulk sulfur-doped silicon-carbon composite anode material provided by this invention significantly improves the key performance bottlenecks of silicon-carbon composite anode materials through the synergistic design of bulk chemical modification and coating, resulting in a significant improvement in overall electrochemical performance, mainly reflected in the following aspects: First, on the one hand, the bulk phase of the nano-silicon particles contains sulfur in the form of Si-S bonds, and the content of sulfur in the bulk region is higher than that in the surface region (exhibiting a distribution gradient of bulk enrichment and surface depletion). This structure not only stabilizes sulfur in the silicon lattice through Si-S bonding, effectively alleviating the volume expansion stress during lithiation / delithiation, but its gradient distribution can also form a buffer layer inside the particles and reduce surface side reactions, thereby inhibiting the excessive growth of the solid electrolyte interphase (SEI) film. At the same time, the Si-S bonds in the bulk phase of the nano-silicon particles significantly improve the intrinsic electronic conductivity of silicon by regulating its electronic structure.

[0020] On the other hand, the porous carbon matrix, as a conductive support framework, contains sulfur elements in the form of CSC and / or SS bonds. These chemical bonds act as "flexible hinges," which not only enhance the structural toughness of the conductive support framework to adapt to the volume changes of silicon, but also significantly improve the electronic conductivity of the three-dimensional conductive network and help maintain the stability of the electrode interface. This indirectly promotes the formation of a denser and more stable SEI film, further improving the cycling stability of the material.

[0021] Second, the bulk sulfur-doped silicon-carbon composite anode material provided by this invention has a core-shell-shell structure, wherein the core acts as an internal buffer through Si-S bonds; the intermediate passivation layer effectively isolates the silicon from direct contact with the electrolyte, stabilizing the electrode / electrolyte interface; and the carbon coating layer provides mechanical constraint and constructs an efficient electron transport channel. The synergistic effect of these three elements significantly improves the structural integrity of the material during long-term cycling.

[0022] Through the synergistic design of the above-mentioned bulk sulfur doping, gradient distribution, porous carbon matrix bonding and multi-level coating structure, the silicon-carbon composite anode material of the present invention exhibits high specific capacity, excellent cycle life and good rate performance, effectively overcoming the key bottlenecks of traditional silicon-based anode materials such as rapid capacity decay and poor cycle performance caused by large volume expansion, unstable interface and poor conductivity. Attached Figure Description

[0023] Figure 1 This is one of the process flow diagrams for preparing bulk sulfur-doped silicon-carbon composite anode materials provided in this embodiment of the invention; Figure 2 The second flowchart illustrates the preparation process of the bulk sulfur-doped silicon-carbon composite anode material provided in this embodiment of the invention. Figure 3 EDS surface distribution diagram of Si element in the bulk sulfur-doped silicon-carbon composite anode material provided in Embodiment 3 of the present invention; Figure 4 EDS surface distribution diagram of O element in the bulk sulfur-doped silicon-carbon composite anode material provided in Embodiment 3 of the present invention; Figure 5 EDS surface distribution diagram of S element in the bulk sulfur-doped silicon-carbon composite anode material provided in Embodiment 3 of the present invention; Figure 6 The electrochemical curve of the bulk sulfur-doped silicon-carbon composite anode material provided in Example 3 of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] The reagents and materials used in the following examples and comparative examples are all commercially available conventional reagent products, or can be prepared by conventional methods. Where specific experimental steps or conditions are not specified in the examples, they were performed according to conventional experimental steps and conditions in the art. Unless otherwise specified, all equipment used is conventional equipment currently available in the art.

[0026] It should be noted that the pore size of the porous carbon matrix in this invention refers to the average diameter of the internal pores in the porous carbon matrix. The pore size of the porous carbon matrix in the embodiments of this invention can be determined by instruments and conventional methods known in the art. Specifically, the Brunauer-Emmet-Teller (BET) gas adsorption method can be used, and the measuring instrument is a Micromeritics ASAP2460 specific surface area and pore size analyzer from McMuritics (Shanghai) Instruments Co., Ltd., USA.

[0027] This invention provides a bulk sulfur-doped silicon-carbon composite anode material, which includes nano-silicon particles dispersed in the pores of a porous carbon matrix. The bulk phase of the nano-silicon particles contains sulfur elements in the form of Si-S bonds, and the content of sulfur elements in the bulk phase region of the nano-silicon particles is higher than that in the surface region.

[0028] Sulfur is introduced in situ into the bulk phase of nano-silicon particles, forming Si-S bonds with silicon and achieving a gradient distribution of sulfur enriched in the bulk phase and relatively exposed on the surface. The Si-S bonding and distribution design is beneficial because the large radius and moderate electronegativity of sulfur atoms can introduce a certain degree of flexibility into the silicon lattice, thereby alleviating buffer stress. It can also significantly improve the intrinsic electronic conductivity of nano-silicon and induce the formation of a more stable solid electrolyte interface film with better ionic conductivity.

[0029] In nano-silicon particles, the sulfur content is higher in the bulk region than in the surface region, forming a sulfur distribution gradient. Preferably, the sulfur content in the bulk region of the nano-silicon particles does not exceed five times the sulfur content in the surface region.

[0030] Furthermore, the porous carbon matrix, serving as a conductive support framework, provides physical space for the uniform distribution and volume changes of nano-silicon particles through its nanoscale pores, allowing the particles to be uniformly dispersed on the conductive support framework. Additionally, the porous carbon matrix contains sulfur, present in the form of CSC and / or SS bonds. These bonds form localized flexible connection points within the conductive support framework. During silicon expansion or contraction, these bonds can absorb stress through bond angle adjustment, slight rotation, or reversible breakage, while maintaining the continuity of the conductive network. Thus, the CSC and / or SS bonds in the porous carbon matrix further enhance the structure's toughness and conductivity.

[0031] The sulfur content in the silicon-carbon composite anode material accounts for 0.1wt%-5wt% of the total mass of the silicon-carbon composite anode material.

[0032] Porous carbon matrix includes one or more of the following: porous carbon, covalent organic framework material (COF), carbon fiber, graphene, graphene oxide, graphene-like material with porous structure, or expanded graphite.

[0033] The specific surface area of ​​the porous carbon matrix is ​​1000 m². 2 / g-2000m 2 / g, the porous carbon matrix has a pore size of 0.5nm-5nm and a pore volume of 0.5cm³. 3 / g-1.7cm 3 / g, ash content less than 0.1wt%.

[0034] Furthermore, this application also has a multi-level core-shell-shell structure. Specifically, the bulk sulfur-doped silicon-carbon composite anode material provided in this application has a core-shell-shell structure, which includes, from the inside out: The core composite includes the porous carbon matrix and the nano-silicon particles; An intermediate passivation layer covers the outer surface of the core composite. A carbon coating layer is applied to the outer surface of the intermediate passivation layer.

[0035] The intermediate passivation layer, located outside the core complex, effectively isolates the active material from direct contact with the electrolyte, suppresses side reactions, and serves as a stress buffer. The outermost carbon coating layer provides strong mechanical confinement and a highly efficient electronic conduction network.

[0036] The intermediate passivation layer comprises any one of a carbon material layer, a metal oxide layer, or a metal nitride layer. When the intermediate passivation layer is a carbon material layer, its thickness is 1 nm-5 nm; when it is a metal oxide layer or a metal nitride layer, its thickness is 0.5 nm-3 nm. The metal oxide is selected from one or more of aluminum oxide, titanium oxide, or magnesium oxide; the metal nitride is selected from one or more of titanium nitride or silicon nitride.

[0037] The thickness of the carbon coating layer is 2 nm-20 nm, and the carbon coating layer is amorphous carbon, graphitized carbon, or organic carbon pyrolysis carbon layer.

[0038] Compared with the prior art, the present invention has the following beneficial effects: The bulk sulfur-doped silicon-carbon composite material provided by this invention significantly improves the key performance bottlenecks of silicon-carbon composite anode materials through the synergistic design of bulk chemical modification and coating, resulting in a significant improvement in overall electrochemical performance, mainly reflected in the following aspects: First, on the one hand, the bulk phase of the nano-silicon particles contains sulfur in the form of Si-S bonds, and the content of sulfur in the bulk region is higher than that in the surface region (exhibiting a distribution gradient of bulk enrichment and surface depletion). This structure not only stabilizes sulfur in the silicon lattice through Si-S bonding, effectively alleviating the volume expansion stress during lithiation / delithiation, but its gradient distribution can also form a buffer layer inside the particles and reduce surface side reactions, thereby inhibiting the excessive growth of the solid electrolyte interphase (SEI) film. At the same time, the Si-S bonds in the bulk phase of the nano-silicon particles significantly improve the intrinsic electronic conductivity of silicon by regulating its electronic structure.

[0039] On the other hand, the porous carbon matrix, as a conductive support framework, contains sulfur elements in the form of CSC and / or SS bonds. These chemical bonds act as "flexible hinges," which not only enhance the structural toughness of the conductive support framework to adapt to the volume changes of silicon, but also significantly improve the electronic conductivity of the three-dimensional conductive network and help maintain the stability of the electrode interface. This indirectly promotes the formation of a denser and more stable SEI film, further improving the cycling stability of the material.

[0040] Second, the bulk sulfur-doped silicon-carbon composite anode material provided by this invention has a core-shell-shell structure, wherein the core acts as an internal buffer through Si-S bonds; the intermediate passivation layer effectively isolates the silicon from direct contact with the electrolyte, stabilizing the electrode / electrolyte interface; and the carbon coating layer provides mechanical constraint and constructs an efficient electron transport channel. The synergistic effect of these three elements significantly improves the structural integrity of the material during long-term cycling.

[0041] The aforementioned multiple mechanisms work synergistically from the inside out, enabling the silicon-carbon composite anode material of the present invention to possess high specific capacity, excellent cycle stability, and outstanding rate performance in practical applications, fundamentally overcoming the problem of rapid capacity decay caused by large volume expansion, unstable interface, and poor conductivity of traditional silicon anodes.

[0042] In addition, embodiments of the present invention also provide a method for preparing the above-mentioned bulk sulfur-doped silicon-carbon composite anode material, such as... Figure 1 As shown, it includes the following steps: Step 110: Place the porous carbon matrix in a chemical vapor deposition reactor and heat it under a protective atmosphere.

[0043] Specifically, the porous carbon matrix can be placed in a chemical vapor deposition (CVD) apparatus (fluidized bed or rotary furnace) and heated to the vapor deposition temperature of 450℃-700℃ at a heating rate of 3℃ / min-10℃ / min under a protective atmosphere.

[0044] Among them, porous carbon matrix includes one or more of porous carbon, covalent organic framework material COF, carbon fiber, graphene, graphene oxide, graphene-like material with porous structure, or expanded graphite.

[0045] The protective atmosphere includes one or more of argon, nitrogen, or helium; wherein the oxygen content in the nitrogen is less than 5 ppm.

[0046] Step 120: A mixed gas containing silicon source gas and sulfur source gas is introduced into the reactor, so that the silicon source gas and sulfur source gas undergo a co-deposition reaction in the pores of the porous carbon matrix, forming bulk sulfur-doped nano-silicon particles in situ. The sulfur element in the sulfur source gas is doped into the bulk interior of the nano-silicon particles to form Si-S bonds, and the content of sulfur element in the bulk region is higher than that in the surface region, thus obtaining a bulk sulfur-doped core composite.

[0047] Specifically, under a protective atmosphere, a mixed gas containing silicon source gas and sulfur source gas is introduced into the reactor, causing the silicon source gas and sulfur source gas to co-deposit within the pores of the porous carbon matrix. Preferably, the co-deposit reaction time is 1-6 hours. The silicon source gas includes one or more of silane, dichlorosilane, or dichlorosilane; the sulfur source gas includes one or more of hydrogen sulfide, carbon disulfide, thiophene, or dimethyl sulfide. The volumetric flow rate ratio of the protective atmosphere, carbon source gas, and sulfur source gas is (0-7):(0-5):(0-2).

[0048] This invention utilizes chemical vapor deposition to in-situ dope sulfur into the bulk phase of nano-silicon particles, forming Si-S bonds. The sulfur distribution gradient, characterized by its enrichment in the bulk phase and relative depletion on the surface, facilitates the formation of a buffer layer internally and reduces side reactions on the surface, thereby suppressing excessive growth of the solid electrolyte interphase (SEI) film. Simultaneously, the Si-S bonds within the nano-silicon particle bulk phase significantly enhance the intrinsic electronic conductivity of silicon by modulating its electronic structure. Furthermore, the porous carbon matrix, serving as a conductive support framework, contains sulfur in the form of CSC and / or SS bonds. These chemical bonds act as "flexible hinges," not only enhancing the structural toughness of the conductive support framework to accommodate silicon volume changes but also significantly improving the electronic conductivity of the three-dimensional conductive network and contributing to the stability of the electrode interface. This indirectly promotes the formation of a denser and more stable SEI film, further improving the material's cycling stability.

[0049] Furthermore, such as Figure 2 As shown, the preparation method includes the following steps: Step 130: The bulk-doped core composite is purged with a protective gas and heated to the passivation temperature. Then, a passivation gas is introduced to form an intermediate passivation layer on the outer surface of the bulk-doped core composite, thus obtaining a core composite with an intermediate passivation layer.

[0050] In order to effectively isolate the active material from direct contact with the electrolyte, suppress side reactions, and act as a stress buffer, an intermediate passivation layer is prepared on the outer surface of the bulk-doped core composite. Specifically, the temperature is increased to the passivation temperature at a heating rate of 3℃ / min-10℃ / min under a protective atmosphere, which includes one or more of argon, nitrogen, or helium; wherein the oxygen content in the nitrogen is less than 5 ppm.

[0051] The intermediate passivation layer comprises any one of a carbon material layer, a metal oxide layer, or a metal nitride layer. When the intermediate passivation layer is a carbon material layer, its thickness is 1 nm–5 nm; when it is a metal oxide layer or a metal nitride layer, its thickness is 0.5 nm–3 nm. The metal oxide is selected from one or more of aluminum oxide, titanium oxide, or magnesium oxide; the metal nitride is selected from one or more of titanium nitride or silicon nitride.

[0052] In this step, the passivation gas is selected based on the target intermediate passivation layer: When the intermediate passivation layer is a carbon material layer, the passivation temperature is 500℃-700℃, and the passivation time is 0.5h-2h. The passivation gas includes one or more of methane, acetylene, or propylene.

[0053] When the intermediate passivation layer is a metal oxide passivation layer, the passivation temperature is 100℃-300℃, and the passivation time is 3h-10h. The passivation gas is a corresponding organometallic precursor, or an alternating pulsed gas mixture of a corresponding organometallic precursor and an oxidizing gas. For example, when the intermediate passivation layer is aluminum oxide, the passivation gas is aluminum isopropoxide; when the intermediate passivation layer is titanium oxide, the passivation gas is an alternating pulsed gas mixture of titanium tetrachloride and an oxidizing gas or tetraisopropyl titanate and an oxidizing gas; when the intermediate passivation layer is magnesium oxide, the passivation gas is an alternating pulsed gas mixture of magnesia and an oxidizing gas. The oxidizing gas includes one or more of carbon dioxide, carbon monoxide, or water vapor.

[0054] When the intermediate passivation layer is a metal nitride passivation layer, the passivation temperature is 300℃-500℃, the passivation time is 1h-5h, and the passivation gas is a mixture of the corresponding metal precursor and nitrogen. For example, when the intermediate passivation layer is titanium nitride, the metal precursor is titanium tetrachloride or tetra(dimethylamino)titanium; when the intermediate passivation layer is silicon nitride, the metal precursor is dichlorosilane or silane.

[0055] Step 140: Carbon coating treatment is performed on the outer surface of the core composite with intermediate passivation layer to form a carbon coating layer, thereby obtaining a bulk sulfur-doped silicon-carbon composite anode material.

[0056] The purpose of this step is to provide the material with strong mechanical constraints and an efficient electronic conduction network by carbon coating the outer surface of the core composite with an intermediate passivation layer, thereby forming a carbon coating layer on the outer surface of the core composite with an intermediate passivation layer.

[0057] The carbon coating treatment in this invention can be selected according to actual needs, for example: The core composite with an intermediate passivation layer is placed in a reactor and heated to the vapor deposition temperature under a protective atmosphere. Then, a mixed gas consisting of carbon source gas and inert carrier gas is introduced for chemical vapor deposition.

[0058] The protective atmosphere includes one or more of argon, nitrogen, or helium, with the oxygen content in the nitrogen being less than 5 ppm. The carbon source gas includes one or more of methane, acetylene, or propylene. The heating rate is 3℃ / min–10℃ / min.

[0059] The carbon coating treatment methods described above are merely examples and are not intended to limit the carbon coating treatment methods in this invention. Those skilled in the art can select the corresponding carbon coating treatment method according to actual needs.

[0060] The bulk sulfur-doped silicon-carbon composite anode material prepared using the method of this invention exhibits a multi-level synergistic protection effect from the inside out, enabling the material to simultaneously maintain structural integrity, interface stability, and rapid charge transport capability during long-term cycling. When the bulk sulfur-doped silicon-carbon composite anode material prepared by this invention is applied to lithium-ion batteries or lithium-ion capacitors, it can achieve a balance between high specific capacity, excellent cycle life, and outstanding rate performance.

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0062] Example 1 In this embodiment 1, the intermediate passivation layer is a carbon material passivation layer.

[0063] 1. Weigh 500g of commercially available coconut shell-based porous carbon and fill it into a fluidized bed reactor. Under nitrogen protection (oxygen content <5ppm, flow rate 10L / min), heat to 500℃ at a heating rate of 5℃ / min.

[0064] 2. Subsequently, a mixed gas mixture of nitrogen 2.5 L / min, silane 2.5 L / min, and hydrogen sulfide 0.5 L / min was introduced, and the reaction was carried out for 3 hours to obtain a bulk sulfur-doped core complex.

[0065] 3. Purge with nitrogen and heat to 550℃, then introduce acetylene gas (nitrogen to acetylene flow rate ratio of 1:1, both 3L / min), react for 1.5 h to form a carbon material passivation layer with a thickness of about 3nm, thus obtaining a core composite with a carbon material passivation layer.

[0066] 4. The core composite with the intermediate passivation layer is placed in a rotary kiln and heated to 580℃ at a rate of 10℃ / min under nitrogen protection. Then, acetylene gas (nitrogen to acetylene flow rate ratio of 2:1, acetylene flow rate of 3L / min) is introduced for carbon coating over 2 hours. After coating, it is naturally cooled to room temperature to obtain the final silicon-carbon composite anode material.

[0067] The prepared sample materials were characterized and tested: Composition and structure analysis: Carbon content was measured using a carbon-sulfur analyzer (CS-2800G); Silicon content was calculated using X-ray fluorescence spectroscopy (XRF) analysis. Oxygen content is detected using a carbon, nitrogen, and hydrogen analyzer; Sulfur content was measured using an inductively coupled plasma spectrometer.

[0068] Tests showed that the material contained 51.54 wt% carbon, 46.79 wt% silicon, 0.49 wt% oxygen, and 12,257 ppm sulfur.

[0069] Example 2: In this embodiment 2, the intermediate passivation layer is an aluminum oxide passivation layer.

[0070] The difference between Example 2 and Example 1 is that the passivation temperature is maintained at 500°C, aluminum isopropoxide is used as the passivation gas, and nitrogen is used as the carrier gas to carry the aluminum isopropoxide into the deposition furnace to form an aluminum oxide passivation layer with a thickness of about 2 nm.

[0071] Tests showed that the material contained 50.04 wt% carbon, 46.61 wt% silicon, 1.72 wt% oxygen, and 10,582 ppm sulfur.

[0072] Example 3 In this embodiment 3, the intermediate passivation layer is a titanium nitride passivation layer.

[0073] The difference between Example 2 and Example 1 is that the temperature is lowered to 400°C, a mixture of titanium tetrachloride and nitrogen is introduced, and the reaction is carried out for 1.5 h to form a titanium nitride passivation layer with a thickness of about 2.5 nm. The oxygen content is 0.62 wt%, and the sulfur content is 11382 ppm.

[0074] Figures 3-5 The EDS elemental distribution diagrams of the silicon-carbon composite anode material prepared in Example 3 are shown below. Figure 3 , Figure 4 and Figure 5 Corresponding to the distribution of Si, O, and S elements respectively, through Figures 3-5 The EDS elemental distribution map shows that in Example 3, the nano-silicon particles (Si-enriched regions) are uniformly dispersed in the porous carbon matrix. Sulfur is enriched inside the nano-silicon particles while being relatively depleted on the surface. Furthermore, the oxygen content is low and uniformly distributed, confirming that the material possesses a bulk sulfur-doped gradient distribution structure and high purity. It should be noted that because the titanium nitride passivation layer is thin and has a low titanium content (approximately 0.49 wt%), its signal is weak in the EDS mapping and therefore it is not shown; the presence of titanium was confirmed by testing its content.

[0075] Figure 6 The electrochemical curve of the bulk sulfur-doped silicon-carbon composite anode material provided in Example 3 of this invention is shown. Figure 6 The electrochemical test results show that the material prepared in Example 3 retains 93.8% of its capacity after 100 cycles at a current density of 0.5 A / g, and has an initial coulombic efficiency of 83.12%, demonstrating excellent structural stability and interfacial compatibility.

[0076] Example 4 In this embodiment 4, the intermediate passivation layer is a titanium nitride passivation layer.

[0077] The difference between Example 4 and Example 3 is that the hydrogen sulfide flow rate is controlled at 0.2 L / min.

[0078] Tests showed that the material contained 50.81 wt% carbon, 47.77 wt% silicon, 0.52 wt% oxygen, and 5372 ppm sulfur.

[0079] Example 5 In this embodiment 5, the intermediate passivation layer is a titanium nitride passivation layer.

[0080] The difference between Example 5 and Example 3 is that the hydrogen sulfide flow rate is controlled at 1.0 L / min.

[0081] Tests showed that the material contained 49.75 wt% carbon, 46.26 wt% silicon, 0.53 wt% oxygen, and 24,719 ppm sulfur.

[0082] Example 6 In this embodiment 6, the intermediate passivation layer is a titanium nitride passivation layer.

[0083] The difference between Example 6 and Example 3 is that the hydrogen sulfide flow rate is controlled at 1.8 L / min.

[0084] Tests showed that the material contained 48.98 wt% carbon, 45.42 wt% silicon, 0.42 wt% oxygen, and 41,724 ppm sulfur.

[0085] Comparative Example 1 Comparative Example 1 uses a conventional method to prepare a silicon-carbon composite material without sulfur doping.

[0086] Preparation steps: Using the same porous carbon matrix, only silane is introduced to deposit nano-silicon particles, without a sulfur source.

[0087] The subsequent steps are the same as in Example 3.

[0088] Tests showed that the material contained 51.03 wt% carbon, 47.93 wt% silicon, 0.63 wt% oxygen, and 284 ppm sulfur.

[0089] Various performance tests were conducted on the silicon-carbon anode materials of the above embodiments and comparative examples, and the test results are recorded in Table 1.

[0090] Inductively coupled plasma spectrometry was used to calculate the content of Ti and Al elements, respectively.

[0091] The specific surface area was measured using a specific surface area analyzer (model: BSD-660S) via nitrogen adsorption-desorption method.

[0092] Electrochemical performance testing: The material was made into a negative electrode sheet, and then assembled into a coin cell using metallic lithium as the counter electrode for testing.

[0093] Silicon-carbon composite anode material, conductive additive carbon black, and binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1) were weighed at a mass ratio of 95:2:3 and placed in a pulping machine at room temperature to prepare a slurry. The prepared slurry was evenly coated onto copper foil and dried in a forced-air drying oven at 50°C for 2 hours. Then, it was cut into 8×8mm electrode sheets and placed in a vacuum drying oven at 100°C for 10 hours. The dried electrode sheets were then transferred to a glove box for later use in battery assembly.

[0094] The assembly of the button cell is as follows: The assembly of the simulated battery is carried out in a glove box containing a high-purity Ar atmosphere. Lithium metal is used as the counter electrode, and a solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v=1:1) containing 1 mol / L LiPF6 is used as the electrolyte. Polyethylene is used as the separator to assemble the battery.

[0095] The testing process for the assembled coin cell half-cells involved constant current charge-discharge testing using a charge-discharge apparatus. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Routine charge-discharge tests were conducted at a current density of C / 10. Detailed test data for the initial coulombic efficiency, discharge specific capacity, charge specific capacity, and capacity retention (cycle life) after 100 cycles of the coin cell half-cells are shown in Table 1. The discharge process described above represents lithium insertion, corresponding to charging in a full cell; the charging process represents lithium delithiation, corresponding to discharging in a full cell.

[0096] The initial expansion rate of the negative electrode in a coin cell was tested using the following method: At room temperature, the prepared negative electrode sheet was ion-beam cut, and the cross-section was photographed using a scanning electron microscope (SEM). The thickness of the negative electrode sheet before assembly into the coin cell was recorded as T1; the thickness of the copper foil current collector substrate was recorded as T2. The coin cell was fully charged at a current density of 0.1C and a charging cutoff voltage of 2V. The cell was then disassembled in a glove box, the negative electrode sheet was removed, and after ion-beam cutting, the cross-section was photographed using an SEM, and the thickness of the negative electrode sheet at this point was measured and recorded as T3. The coin cell expansion rate was then calculated using the formula: coin cell expansion rate = (T3 - T1) / (T1 - T2) × 100%.

[0097] Table 1 According to a comparison of data from Examples 1 to 6 and Comparative Example 1 of the present invention, the bulk sulfur-doped silicon-carbon composite anode material provided by the present invention comprises sulfur-doped silicon nanoparticles dispersed in a porous carbon matrix, a porous carbon matrix containing CSC / SS bonds, and sequentially coated intermediate passivation layers and carbon coating layers. This design achieves comprehensive structural control from bulk bonding modification to external synergistic constraints, significantly improving the structural stability and electrochemical performance of the material.

[0098] As shown in Table 1, the coin cell expansion rates (88.5%-99.5%) of Examples 1-6 were significantly lower than those of Comparative Example 1 (121.6%), verifying the synergistic effect of bulk sulfur doping and multilayer coating structure in suppressing silicon volume expansion. Among them, Example 3 (sulfur doping amount of approximately 1.2 wt%, titanium nitride passivation layer) exhibited the best overall performance: the lowest coin cell expansion rate (88.5%), an initial coulombic efficiency of 83.12% at 0.8V, and a capacity retention rate of 93.8% after 100 cycles.

[0099] Experiments on sulfur doping control (Examples 4, 3, 5, and 6) showed that when the sulfur content was in the range of approximately 0.5 wt% to 2.5 wt%, the materials exhibited good cycling stability (capacity retention ≥ 89.7%). Example 3, with a sulfur content of approximately 1.1 wt%, demonstrated the best overall performance (capacity retention 93.8% and coin cell expansion 88.5%). Further increasing the sulfur content to 4.17 wt% (Example 6) resulted in a decrease in cycling stability, indicating that excessive sulfur doping may adversely affect the stability of the silicon lattice. Therefore, the sulfur doping content is preferably controlled within the range of 0.5 wt% to 2.5 wt%, especially 1.0 wt% to 1.5 wt%.

[0100] A comparison of different passivation layers (Examples 1-3) shows that, under the same sulfur doping conditions, Example 3, which uses titanium nitride as the intermediate passivation layer, performs best. The Ti content is approximately 4930 ppm, indicating that the titanium nitride passivation layer has been successfully introduced and effectively coated, significantly improving interface stability. It should be noted that "ash content less than 0.1%" refers to the porous carbon matrix before coating; the titanium nitride passivation layer is a subsequently deposited functional layer and its ash content is not included in the original carbon matrix.

[0101] Compared with the sulfur-free Comparative Example 1 (initial coulombic efficiency 78.47%, capacity retention after 100 cycles 78.4%), the initial coulombic efficiency (≥80.68%) and capacity retention after 100 cycles (≥89.7%) of all sulfur-doped examples were significantly improved, which, in turn, confirms the key role of bulk sulfur doping in constructing the "core buffer-interface stability-conductive network synergy" system.

[0102] In summary, this invention, through the synergistic design of bulk sulfur doping, gradient distribution, porous carbon matrix bonding, and multi-level coating structure, achieves high initial coulombic efficiency and excellent cycle stability while maintaining high discharge specific capacity (≥1930.80 mAh / g), providing a high-performance anode material solution for high energy density lithium-ion batteries.

[0103] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A bulk sulfur-doped silicon-carbon composite anode material, characterized in that, The silicon-carbon composite anode material includes nano-silicon particles dispersed in the pores of a porous carbon matrix. The bulk phase of the nano-silicon particles contains sulfur elements in the form of Si-S bonds, and the content of sulfur elements in the bulk phase region of the nano-silicon particles is higher than that in the surface region.

2. The silicon-carbon composite anode material according to claim 1, characterized in that, The porous carbon matrix contains sulfur in the form of CSC and / or SS bonds.

3. The silicon-carbon composite anode material according to claim 1, characterized in that, The specific surface area of ​​the porous carbon matrix is ​​1000 m². 2 / g-2000m 2 / g, wherein the pore size of the porous carbon matrix is ​​0.5nm-5nm.

4. The silicon-carbon composite anode material according to any one of claims 1-3, characterized in that, The silicon-carbon composite anode material has a core-shell-shell structure, comprising, from the inside out: The core composite includes the porous carbon matrix and the nano-silicon particles; An intermediate passivation layer covers the outer surface of the core composite. A carbon coating layer is applied to the outer surface of the intermediate passivation layer.

5. The silicon-carbon composite anode material according to claim 4, characterized in that, When the intermediate passivation layer is a carbon material layer, the thickness of the intermediate passivation layer is 0.5 nm-5 nm; When the intermediate passivation layer is a metal oxide layer or a metal passivation layer, the thickness of the intermediate passivation layer is 0.5 nm to 3 nm; The thickness of the carbon coating layer is 2nm-20nm.

6. A method for preparing the silicon-carbon composite anode material according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: The porous carbon matrix was placed in a chemical vapor deposition reactor and heated under a protective atmosphere; A mixed gas containing silicon source gas and sulfur source gas is introduced into the reactor, causing the silicon source gas and the sulfur source gas to undergo a co-deposition reaction in the pores of the porous carbon matrix, forming bulk sulfur-doped nano-silicon particles in situ. The sulfur element in the sulfur source gas is doped into the bulk interior of the nano-silicon particles to form Si-S bonds, and the sulfur content in the bulk region is higher than that in the surface region, resulting in a bulk sulfur-doped core composite.

7. The preparation method according to claim 6, characterized in that, The sulfur element in the sulfur source gas reacts with the carbon in the porous carbon matrix to form CSC and / or SS bonds.

8. The preparation method according to claim 6, characterized in that, The temperature of the co-deposition reaction is 450℃-700℃, and the time of the co-deposition reaction is 1h-6h.

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes the silicon-carbon composite negative electrode material according to any one of claims 1-5, or the silicon-carbon composite negative electrode material prepared by any one of claims 6-8.

10. An energy storage device, characterized in that, The energy storage device includes a lithium-ion battery or a lithium-ion capacitor. The energy storage device comprises the silicon-carbon composite negative electrode material according to any one of claims 1-5, or comprises the silicon-carbon composite negative electrode material prepared by any one of claims 6-8, or comprises the negative electrode sheet according to claim 9.

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