An inner-outer double-doped modified carbon-coated porous silicon material, a preparation method thereof and application thereof

Abstract

The present application relates to the field of porous silicon material, more particularly to a kind of inside and outside double-doped modified carbon-coated porous silicon material and its preparation method and application.The material includes core layer and wrapping layer: core layer includes lithium inert metal doped silicon matrix, and the lithium inert metal does not carry out deintercalation lithium reaction in charge-discharge process;The wrapping layer is coated outside the core layer, and it is heteroatom doped amorphous carbon layer.The material enhances conductivity and structural strength by internal metal doping, improves ionic conductivity by external heteroatom doping, and uses porous structure to accommodate volume expansion, thereby improving the cycle stability and rate performance of lithium ion battery silicon-based negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of porous silicon materials, and more specifically, to a carbon-coated porous silicon material with internal and external dual doping, its preparation method, and its application. Background Technology

[0002] In the field of lithium-ion battery materials technology, developing novel anode materials with high specific capacity has become an important research direction in order to meet the continuous demand for higher energy density in fields such as electric vehicles. Silicon is regarded as a strong candidate for the next generation of anode materials due to its theoretical specific capacity, which is much higher than that of traditional graphite. However, the huge volume expansion that occurs during charging and discharging is a fundamental challenge that restricts its practical application.

[0003] To buffer the volume expansion of silicon and improve its conductivity, related technologies typically address both material structure design and surface modification. On one hand, constructing porous or quasi-porous silicon structures aims to provide internal space for volume expansion, thereby alleviating structural stress. On the other hand, coating silicon particles with carbon materials is a common strategy. Core-shell structures directly encapsulate silicon particles with carbon layers to limit expansion and improve electronic conductivity. Based on this, yolk-shell structures, by reserving gaps between the silicon core and carbon shell, can more effectively adapt to volume changes and reduce the area of ​​side reactions with the electrolyte. However, these existing solutions still have inherent limitations: the structural strength and electronic conductivity of the porous silicon matrix itself are still insufficient, facing the risk of pulverization and conductive network degradation during long-term cycling; and the ionic conductivity of conventional carbon coatings (whether core-shell or yolk-shell structures) is relatively limited, which restricts the rapid transport of lithium ions and affects the material's charge-discharge performance at high rates.

[0004] Therefore, how to solve the structural stability problem caused by volume expansion of silicon-based anode materials, and the rate performance problem caused by slow ion transport at the interface, that is, to achieve an effective balance between cycle life and rate performance, remains a technical bottleneck that needs to be overcome in this field. Summary of the Invention

[0005] In view of this, the purpose of this invention is to at least partially solve one of the technical problems in the related art. To this end, this invention provides a dual-doped modified carbon-coated porous silicon material consisting of an N / P / S doped carbon layer and a lithium inert metal (which does not undergo lithium insertion / extraction reaction during charging and discharging) M (Zn / Ni / Ti / Co / Cu / Fe) doped porous silicon. This solves the problems of insufficient conductivity and structural pulverization caused by expansion in the porous silicon matrix, and improves the ionic conductivity of the yolk-shell carbon layer. Its preparation process is simple, has a short cycle time, and low energy consumption, making it suitable for large-scale production.

[0006] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0007] According to one aspect of the present invention, a carbon-coated porous silicon-like material with internal and external dual doping is provided, comprising:

[0008] The core layer comprises a silicon substrate doped with a lithium inert metal; the lithium inert metal includes metals that do not undergo lithium insertion / extraction reactions during charging and discharging.

[0009] An encapsulation layer, covering the outside of the core layer, comprising a heteroatom-doped amorphous carbon layer.

[0010] In some of these embodiments, the lithium inert metal includes at least one selected from zinc, nickel, titanium, cobalt, copper, and iron.

[0011] In some of these embodiments, the heteroatom includes at least one of N, P, and S.

[0012] In some embodiments, the core layer is a silicide phase of the lithium inert metal.

[0013] In some of these embodiments, the mass ratio of the silicon substrate to the lithium inert metal is (80:20) to (99:1).

[0014] In some embodiments, the thickness of the outer wrapping layer is 20 μm to 30 μm.

[0015] According to another aspect of the present invention, the present invention provides a method for preparing the above-mentioned internally and externally doped modified carbon-coated porous silicon material, comprising the following steps:

[0016] S1: Silicon powder is mixed with lithium inert metal and alloyed to obtain the first precursor;

[0017] S2: Mix the first precursor with magnesium powder and alloy it in a second time to obtain a magnesium-containing intermediate;

[0018] S3: The magnesium-containing intermediate is subjected to nitriding treatment in a nitrogen-containing atmosphere to obtain a template-containing intermediate;

[0019] S4: In an atmosphere containing carbon source gas and doped gas containing heteroatoms, the template intermediate is subjected to chemical vapor deposition to form an intermediate product coated with a doped carbon layer.

[0020] S5: The intermediate product is etched with an acid solution to remove the template and obtain the internal and external doped modified carbon-coated porous silicon material.

[0021] Step S1 achieves initial uniform doping of metal in the silicon substrate; step S2 introduces magnesium as a pore-forming agent precursor; step S3 converts magnesium into a magnesium nitride template that can be removed by subsequent acid etching through nitriding, thereby forming a porous structure inside the material; step S4 directly deposits a doped carbon layer on the template-containing intermediate, achieving tight and complete encapsulation of the framework structure by the carbon layer and heteroatom doping; finally, step S5 removes the template to form the yolk-shell cavity. This allows for the precise, reliable, and repeatable fabrication of a yolk-shell structure with an internal metal-doped silicon framework, an external heteroatom-doped carbon shell, and a reserved expansion space between the two.

[0022] In some of these embodiments, in step S1, the mass ratio of silicon powder to lithium inert metal is (80:20) to (99:1).

[0023] In some of these embodiments, the particle size range of the silicon powder and lithium inert metal in step S1 is 1~5 μm;

[0024] In some of these embodiments, the particle size of the magnesium powder in step S2 ranges from 1 to 5 μm;

[0025] In some embodiments, the alloying temperature is 450°C to 750°C, and the holding time is 3h to 15h; preferably, the alloying heating rate is 1°C / min to 30°C / min.

[0026] In some embodiments, in step S2, the mass ratio of the first precursor to magnesium powder is (1:1.7) to (1:2.5).

[0027] In some embodiments, the conditions for secondary alloying in step S2 include: a temperature of 500℃~750℃ and a holding time of 5 h~20 h; preferably, the heating rate is 1~20℃ / min.

[0028] In some embodiments, in step S3, the nitrogen-containing atmosphere is at least one of ammonia, nitrogen, nitric oxide, and nitrogen dioxide, and the flow rate is 100 L / min to 200 L / min.

[0029] In some embodiments, the nitriding treatment conditions in step S3 include: a temperature of 600℃~900℃ and a holding time of 5~20h.

[0030] In some embodiments, the carbon-containing atmosphere in step S4 includes at least one of methane, acetylene, and propylene, and the flow rate is 10 L / min to 100 L / min.

[0031] In some embodiments, the doping atmosphere in step S4 includes at least one of ammonia, phosphine, and hydrogen sulfide, and the flow rate is 1 L / min to 10 L / min.

[0032] In some embodiments, in step S4, the temperature of chemical vapor deposition is 700°C to 1000°C, and the holding time is 10 min to 120 min.

[0033] In some of these embodiments, the heating rate of chemical vapor deposition is 0.1°C / min to 20°C / min.

[0034] In some embodiments, the acid solution in step S5 is hydrochloric acid, sulfuric acid, or nitric acid.

[0035] In some embodiments, the etching temperature in step S5 is 40°C to 80°C, and the etching time is 2 h to 8 h.

[0036] According to another aspect of the present invention, the present invention provides the application of the above-described internally and externally doped modified carbon-coated porous silicon material or the internally and externally doped modified carbon-coated porous silicon material prepared by the above-described preparation method in battery anode materials.

[0037] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises the aforementioned battery negative electrode material.

[0038] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0039] The present invention provides a carbon-coated porous silicon material with internal and external dual doping. By employing a composite structure consisting of a lithium-doped silicon substrate as the core layer and a heteroatom-doped amorphous carbon layer as the outer coating, it effectively balances cycle life and rate performance of silicon-based materials. Specifically, the lithium-doped inert metal in the core layer enhances the overall electronic conductivity and mechanical strength of the material, helping to buffer volume expansion and maintain structural integrity. Simultaneously, the heteroatom-doped carbon layer on the outside improves the lithium-ion transport rate (ionic conductivity) and helps form a stable solid electrolyte interface film. This synergistic effect of the composite structure allows the material to better adapt to volume changes in silicon during charging and discharging, maintaining excellent electrical contact, thereby significantly improving both the cycle stability and rapid charge / discharge capability (rate performance) of lithium-ion batteries.

[0040] More specifically:

[0041] 1. By incorporating lithium inert metal into the silicon matrix, the mechanical strength of the core framework and the stability of the electronic conductivity network are effectively enhanced, thereby significantly suppressing the pulverization problem caused by the huge volume expansion of silicon during charging and discharging, and improving the cycle stability of the material. Simultaneously, doping the outer carbon layer with heteroatoms introduces defects that facilitate lithium-ion transport or forms a fast-ion conductor phase, effectively increasing the diffusion rate of lithium ions at the electrode / electrolyte interface and improving the high-rate charge-discharge performance of the material. The synergistic effect of internal structural reinforcement and external interface optimization allows the material to achieve both high cycle life and high power output, resolving the contradiction of balancing the performance of traditional silicon-carbon anodes.

[0042] 2. Lithium, an inert metal element, ensures that it can effectively form a reinforcing phase (such as silicide) in the silicon matrix. While improving conductivity, it does not participate in or participates in the lithiation reaction with minimal involvement, thus avoiding the negative impacts of volume changes and capacity loss caused by additional lithium intercalation. By limiting N, P, and S to external doping elements, it ensures that these heteroatoms can be effectively integrated into the carbon layer lattice. By introducing defects, changing electron cloud density, or forming specific functional groups, it significantly enhances the ionic conductivity and interfacial compatibility of the carbon layer. At the same time, it avoids the introduction of other impurity elements that may damage the carbon layer structure or cause side reactions with the electrolyte, thereby improving rate performance while ensuring the electrochemical stability and compatibility of the material system.

[0043] 3. Applying the silicon-carbon composite material, which possesses both high structural stability (derived from internal metal doping and yolk-shell structure) and high interfacial ion transport capability (derived from external heteroatom-doped carbon layers), to the anode of lithium-ion batteries can directly improve the cycle life and fast charge / discharge capability of the anode. Complete lithium-ion batteries assembled based on this anode simultaneously achieve high cycle capacity retention and excellent rate performance, overcoming the shortcomings of traditional silicon-based anode batteries, such as rapid capacity decay and difficulty in achieving high power output.

[0044] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0045] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0046] Figure 1 This is a scanning electron microscope (SEM) image of the (p-ZnSi2-Si@NC) dual-doped modified carbon-coated porous silicon material prepared in Example 1 of this invention.

[0047] Figure 2These are overall transmission electron microscope (TEM) images and partial high-resolution TEM images of the (p-ZnSi2-Si@NC) dual-doped modified carbon-coated porous silicon material prepared in Example 1 of this invention.

[0048] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0049] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0050] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0051] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0052] In this application, "lithium inert metal" refers to a metal element that does not participate in or participates very little in the lithium-ion deintercalation and insertion reaction during the charging and discharging process of lithium-ion batteries. Its introduction aims to improve the electronic conductivity and structural mechanical strength of the matrix without significantly sacrificing the specific capacity of the material.

[0053] For example, it may include, but is not limited to, at least one of zinc, nickel, titanium, cobalt, copper, and iron, which may exist in the silicon matrix as elements, alloys, or silicides (such as MSi2).

[0054] Specifically, the mass ratio of the “lithium inert metal” to silicon ranges from (80:20) to (99:1); its characteristic of “not participating in lithium insertion / extraction reactions” means that within an electrochemical window of 0.005V to 1.5V (vs. Li / Li+), the metal component typically contributes no or less than 5% to the capacity of the full cell.

[0055] In this application, "heteroatom-doped amorphous carbon layer" refers to a functional layer in which non-carbon elements are introduced into a coating layer mainly composed of amorphous carbon through chemical methods to change its electronic structure, improve ionic conductivity and promote the formation of a stable solid electrolyte interface (SEI) film.

[0056] For example, the heteroatom may include, but is not limited to, at least one of nitrogen, phosphorus, and sulfur; the carbon layer may be formed by chemical vapor deposition in a mixed atmosphere containing a carbon source gas and a dopant gas containing the heteroatom.

[0057] In this application, "yolk-shell structure" refers to a core-shell-cavity composite microstructure in which the encapsulated core particle ("yolk") and the outer complete encapsulation layer ("eggshell") are physically separated by a reserved or formed internal cavity, which is used to accommodate the volume expansion of the core material under specific conditions.

[0058] For example, the core can be a metal-doped porous silicon substrate, the cladding layer can be a heteroatom-doped amorphous carbon layer, and the cavity can be obtained by removing a pre-formed soluble template (such as Mg3N2).

[0059] Specifically, in lithium-ion battery anode applications, the electrode expansion rate of materials with this structure can be less than 100% in the fully charged state (100% SOC); the average distance between the core particle and the coating layer (i.e., cavity size) is about 10%-50% of the original size of the core particle.

[0060] In this application, "quasi-porous silicon matrix" refers to a porous structure obtained by reacting silicon powder and magnesium powder to form magnesium silicide, then introducing nitrogen gas to form a molten magnesium nitride template intermediate using the nitrogen-loving properties of magnesium atoms, and then removing the template by acid washing. That is, a silicon host material with an internal interconnected pore network or a large number of isolated pores is obtained. Its porous structure provides a buffer space for the volume expansion of the active material silicon during the lithium intercalation process, thereby relieving the stress of the overall structure.

[0061] For example, the pores can be obtained by reacting with a pore-forming agent (such as magnesium) to form an intermediate phase, and then removing the template through subsequent steps (such as nitriding to form an acid-soluble template and etching); its silicon framework can be doped with lithium inert metal to enhance conductivity and strength.

[0062] Specifically, the tap density of the porous silicon substrate is in the range of 0.7 g / cm³. 3 ~0.9 g / cm 3 Specific surface area ranges from 3 m² 2 / g~7 m 2 / g; the size of the pores is distributed on the nanometer to submicron scale.

[0063] In this application, "internal and external doping" refers to the doping modification of the internal core and external coating layer of a composite material with different types of elements. The aim is to improve the electronic conductivity and structural stability of the core through internal doping and improve the ion transport dynamics of the coating layer through external doping, thereby synergistically improving the overall electrochemical performance of the material.

[0064] For example, in the eggshell-structured silicon-carbon composite material, internal doping refers to the incorporation of lithium inert metal elements into the silicon matrix, while external doping refers to the incorporation of heteroatoms such as nitrogen, phosphorus, and sulfur into the amorphous carbon coating layer.

[0065] Specifically, the “dual doping” strategy enables the material to retain more than 85% of its capacity after 500 cycles at 1C, while maintaining a constant current ratio of more than 87% under 4C high-rate discharge conditions, thus achieving simultaneous optimization of cycle stability and rate performance.

[0066] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0067] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0068] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0069] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0070] Currently, in the field of silicon-based anode materials for lithium-ion batteries, a widely adopted technical solution to address the significant volume expansion of silicon during charging and discharging and to improve cycle stability is the construction of an eggshell structure. This is achieved by coating a silicon substrate with a complete carbon shell, leaving a cavity between the silicon substrate and the carbon shell. The basic working principle is that the internal cavity provides buffer space for the volume expansion of silicon during lithium intercalation, thereby alleviating mechanical stress; simultaneously, the continuous external carbon layer restricts direct contact between the electrolyte and silicon, forming a relatively stable solid electrolyte interface film.

[0071] However, this approach faces performance bottlenecks when applied to high-power scenarios with stringent charge / discharge rate requirements. A fundamental contradiction lies in the fact that the dense carbon coating designed to optimize structural stability and electronic conductivity inevitably impairs the lithium-ion transport kinetics at the interface due to its inherent physicochemical properties. Specifically, under conditions requiring rapid charge / discharge, the low ionic conductivity of the traditional amorphous carbon shell becomes a limiting factor, hindering lithium-ion migration at the carbon layer / electrolyte interface and leading to increased electrode polarization and decreased rate performance.

[0072] Through in-depth analysis, the inventors discovered that the root causes of the aforementioned contradictions are multifaceted. From a materials perspective, in the unmodified amorphous carbon layer, the diffusion path of lithium ions is tortuous, resulting in a low intrinsic diffusion coefficient, making it difficult to meet the ion flux requirements at high rates. From a structural perspective, while the yolk-shell structure itself buffers volume expansion, it also objectively increases the diffusion path length of lithium ions from the electrolyte to the internal silicon active material. Furthermore, from an interfacial electrochemistry perspective, the ion transport characteristics of the interfacial phase formed between the carbon layer surface and the electrolyte directly affect the overall reaction rate. These factors collectively limit the upper limit of the ability of traditional yolk-shell structured silicon-carbon materials to achieve high rate performance while pursuing high cycle stability.

[0073] To overcome the aforementioned contradictions, this invention proposes a technical approach of synergistic internal and external modification. Its core concept lies in: introducing metal elements that do not participate in the lithium reaction during charging and discharging into the internal silicon matrix to construct a reinforcing phase and conductive network; and simultaneously introducing heteroatoms into the external carbon coating layer to optimize its lattice structure and interface characteristics, thus performing targeted functionalization design on both the internal and external parts of the material. This effectively improves the overall electronic conductivity and ion transport rate of the material without significantly sacrificing the volume expansion buffering capacity and structural integrity provided by the yolk-shell structure. In other words, it provides a yolk-shell structure silicon-carbon material with dual internal and external doping modification to solve the problem in related technologies where yolk-shell structure silicon-carbon anode materials struggle to simultaneously achieve high cycle stability and high rate performance, achieving the technical effect of maintaining high capacity retention during long cycles while also realizing rapid charge and discharge.

[0074] This invention effectively overcomes the aforementioned defects by employing a composite structure consisting of a silicon substrate doped with lithium inert metal as the core layer and an amorphous carbon layer doped with heteroatoms as the outer coating layer. Specifically, the lithium inert metal doping in the core layer enhances the overall electronic conductivity and mechanical strength of the material, helping to buffer volume expansion and maintain structural integrity; simultaneously, the heteroatom-doped carbon layer on the outside improves the lithium-ion transport rate (ionic conductivity) and helps to form a stable solid electrolyte interface film. This synergistic effect of the composite structure allows the material to better adapt to the volume changes of silicon during charging and discharging, maintaining excellent electrical contact, thereby significantly improving both the cycle stability and rapid charge / discharge capability (rate performance) of the lithium-ion battery.

[0075] Specifically, the present invention adopts the following technical solution:

[0076] According to one aspect of the present invention, a carbon-coated porous silicon-like material with internal and external dual doping is provided, comprising:

[0077] The core layer comprises a silicon substrate doped with a lithium inert metal; the lithium inert metal includes metals that do not undergo lithium insertion / extraction reactions during charging and discharging.

[0078] An encapsulation layer, covering the outside of the core layer, comprising a heteroatom-doped amorphous carbon layer.

[0079] In some of these embodiments, the lithium inert metal includes at least one selected from zinc, nickel, titanium, cobalt, copper, and iron.

[0080] In some of these embodiments, the heteroatom includes at least one of N, P, and S.

[0081] In some embodiments, the core layer is a silicide phase of the lithium inert metal.

[0082] In some of these embodiments, the mass ratio of the silicon substrate to the lithium inert metal is (80:20) to (99:1).

[0083] In some embodiments, the thickness of the outer wrapping layer is 20 μm to 30 μm.

[0084] According to another aspect of the present invention, the present invention provides a method for preparing the above-mentioned internally and externally doped modified carbon-coated porous silicon material, comprising the following steps:

[0085] S1: Silicon powder is mixed with lithium inert metal M and alloyed to obtain the first precursor;

[0086] S2: Mix the first precursor with magnesium powder and alloy it in a second time to obtain a magnesium-containing intermediate;

[0087] S3: The magnesium-containing intermediate is subjected to nitriding treatment in a nitrogen-containing atmosphere to obtain a template-containing intermediate;

[0088] S4: In an atmosphere containing carbon source gas and doped gas containing heteroatoms, the template intermediate is subjected to chemical vapor deposition to form an intermediate product coated with a doped carbon layer.

[0089] S5: The intermediate product is etched with an acid solution to remove the template and obtain the internal and external doped modified carbon-coated porous silicon material.

[0090] The reactions involved in the above process are as follows:

[0091] S1:2 (Si excess);

[0092] S2: (Mg is in excess; the excess Mg evaporates after the reaction).

[0093] S3: (N2 excess).

[0094] In step S1, the amount of lithium inert metal doping is controlled by changing the mass ratio of silicon powder to lithium inert metal powder. If the amount added is too small, it will not effectively improve conductivity, nor will it be sufficient to strengthen the silicon substrate by utilizing the doping effect; if the amount added is too large, since lithium inert metal itself does not intercalate lithium, it will greatly reduce the energy density of the material and will not be able to exert optimal electrochemical performance.

[0095] In some of these embodiments, in step S1, the mass ratio of silicon powder to lithium inert metal is (80:20) to (99:1), preferably (90:10) to (97:3), and most preferably 95:5.

[0096] In some embodiments, the particle size range of silicon powder, lithium inert metal in step S1, and magnesium powder in step S2 is 1 μm to 5 μm.

[0097] In some embodiments, the alloying temperature is 450℃~750℃, and the holding time is 3h~15h; the holding temperature is preferably 500℃~700℃, more preferably 550℃~650℃; the holding time is preferably 5h~10h, more preferably 6h~8h.

[0098] In some of these embodiments, the alloying heating rate is 1°C / min to 30°C / min, more preferably 1°C / min to 20°C / min, and even more preferably 5°C / min to 10°C / min.

[0099] In some embodiments, in step S2, the mass ratio of the first precursor to magnesium powder is (1:1.7) to (1:2.5), preferably (1:1.7) to (1:2), and most preferably 1:1.8.

[0100] In some embodiments, the inert atmosphere in S2 is preferably argon.

[0101] In some embodiments, the conditions for secondary alloying in step S2 include: a temperature of 500℃~750℃ and a holding time of 5 h~20 h; preferably, a heating rate of 1℃ / min~20℃ / min; wherein the heating rate is preferably 5℃ / min~15℃ / min, more preferably 5℃ / min~10℃ / min; the holding temperature is preferably 550℃~700℃, more preferably 550℃~600℃; and the holding time is preferably 5 h~15 h, more preferably 6 h~10 h.

[0102] In this invention, the selection of the alloying reaction temperature and holding time in steps S1 and S2 is crucial. When the reaction temperature is too low or the holding time is too short, the alloying reaction will be insufficient or even impossible, resulting in an alloyed product powder with uneven composition. When the reaction temperature is too high or the holding time is too long, energy will be wasted in S1, and in S2, in addition to increased cost, the volatility of magnesium powder at high temperatures will result in excess silicon that cannot undergo the alloying reaction, leading to uneven material composition distribution.

[0103] In some embodiments, in step S3, the nitrogen-containing atmosphere is one of ammonia, nitrogen, oxygen, nitric oxide, and nitrogen dioxide, and the flow rate is 100 L / min to 200 L / min; preferably 100 L / min to 150 L / min.

[0104] In some embodiments, the nitriding treatment conditions in step S3 include: a temperature of 600℃~900℃ and a holding time of 5h~20h; wherein the heating rate is 0.1℃ / min~10℃ / min, preferably 1℃ / min~8℃ / min, more preferably 3℃ / min~5℃ / min; the holding temperature is preferably 650~800℃, more preferably 700℃~780℃, and most preferably 750℃~780℃; and the holding time is preferably 5h~12h, more preferably 6h~8h.

[0105] In step S3, due to the difference in reactivity between silicon atoms, magnesium atoms, and lithium inert metal atoms and nitrogen atoms, nitrogen atoms will combine with magnesium atoms to form Mg3N2. Mg3N2 is used as a pore-forming template and is subsequently removed by acid washing. Lithium inert metal atoms do not react with nitrogen atoms, but are dispersed in the silicon substrate.

[0106] In this invention, the selection of the heating rate, reaction temperature, and holding time in step S3 of the nitriding reaction is crucial in determining the porous structure of the material. If the heating rate is too fast or the holding time is too short, the reaction will be incomplete, and may even affect the smooth conversion of MgSi2 to Mg3N2. If the reaction temperature is too low, the nitrogen-containing substances in the atmosphere will not be able to decompose smoothly and participate in the reaction. If the heating rate is too slow, the reaction temperature is too high, or the holding time is too long, it will lead to meaningless energy consumption, waste of nitrogen-containing atmosphere, and increased cost.

[0107] In some embodiments, the carbon-containing atmosphere in step S4 includes one of methane, acetylene, and propylene, and the flow rate is 10 L / min to 100 L / min, preferably 20 L / min to 80 L / min, and more preferably 40 L / min to 60 L / min.

[0108] In some embodiments, the doping atmosphere in step S4 includes at least one of ammonia, phosphine, and hydrogen sulfide, with ammonia being the most preferred; the flow rate is 1 L / min to 10 L / min, preferably 2 L / min to 8 L / min, and more preferably 4 L / min to 6 L / min.

[0109] In step S4, the thickness of the carbon coating and the doping amounts of nitrogen, phosphorus, and sulfur are controlled by changing the flow rate of the atmosphere. If the atmosphere flow rate is too low, the carbon coating will be too thin, failing to guarantee the structural stability of the internal silicon material, which will still be eroded by the electrolyte, affecting cycle stability and safety. Insufficient nitrogen, phosphorus, and sulfur doping amounts will also result in insufficient improvement in the ionic conductivity of the carbon layer, failing to achieve better results. If the atmosphere flow rate is too high, the formation of an excessively thick carbon layer will increase the diffusion distance of lithium ions, affecting rate performance and charge / discharge efficiency. Excessive flow rates of nitrogen, phosphorus, and sulfur-containing atmospheres will lead to uneven distribution of dopants in the carbon layer, resulting in meaningless consumption.

[0110] In some embodiments, in step S4, the temperature of chemical vapor deposition is 700℃~1000℃, and the holding time is 10min~120min; preferably, the heating rate of chemical vapor deposition is 0.1℃ / min~20℃ / min.

[0111] In step S4, controlling the holding temperature and holding time during the CVD process is crucial. If the holding temperature is too low or the holding time is too short, the decomposition and deposition of carbon elements will not be sufficient, resulting in an incomplete carbon layer coating and the risk of the internal silicon material still reacting with the electrolyte. If the holding temperature is too high or the holding time is too long, the thickness of the surface-coated carbon layer will become uncontrollable, affecting material performance and wasting energy.

[0112] In some embodiments, the acid solution in step S5 is hydrochloric acid, sulfuric acid, or nitric acid.

[0113] In some embodiments, the etching temperature in step S5 is 40°C to 80°C, most preferably 60°C; the etching time is 2h to 8h, preferably 4h to 6h.

[0114] In step S5 of this invention, the control of the acid etching temperature and time determines the purity of the final product. If the acid etching temperature is too low or the time is insufficient, Mg3N2 cannot be completely removed, and non-lithium-intercalated Mg3N2 will still exist between the pores, not only occupying the space reserved for silicon expansion but also affecting the electrical properties of the material. If the acid etching temperature is too high or the time is too long, it may affect the overall structure of the final product and destroy its integrity.

[0115] This invention obtains a dual-doped modified carbon-coated porous silicon material by strictly controlling the reaction conditions. The internal silicon has a porous structure, which alleviates volume expansion. The lithium inert metal doping improves its conductivity and enhances its structural strength. The external carbon layer has a complete structure, which stabilizes the SEI layer. The nitrogen / phosphorus / sulfur doping effectively improves its ionic conductivity.

[0116] This invention achieves continuous nitriding and CVD carbon coating at low temperatures (below 1000°C) through two alloying processes, using a rotary kiln or fluidized bed with only one filling and one atmosphere switch. A subsequent acid etching process yields a double-doped, carbon-coated porous silicon material for lithium-ion battery anodes, significantly improving the cycle performance of silicon materials. The process is simple, continuous, and time-saving; the raw materials are inexpensive and readily available, resulting in low costs and facilitating large-scale commercial production.

[0117] According to another aspect of the present invention, the present invention provides the application of the above-described internally and externally doped modified carbon-coated porous silicon material or the internally and externally doped modified carbon-coated porous silicon material prepared by the above-described preparation method in battery anode materials.

[0118] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises the aforementioned battery negative electrode material.

[0119] The present invention does not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape, and those skilled in the art can choose according to specific practical needs.

[0120] According to another aspect of the present invention, a battery is provided comprising the negative electrode material described in the above-described technical solution. Thus, the battery possesses all the features and advantages of the negative electrode material described in the above-described technical solution, which will not be repeated here.

[0121] In a specific embodiment of the present invention, the battery can be a battery module assembled from individual battery cells. The battery module can contain one or more battery cells, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In the battery module, the multiple battery cells can be arranged sequentially along the length of the battery module; of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells can be fixed using fasteners. The battery module may also include a housing with a receiving space, in which the multiple battery cells are received.

[0122] In the description of this invention, "a plurality of" means two or more.

[0123] In a specific embodiment of the present invention, the battery can also be a battery pack assembled from the aforementioned battery modules. The battery pack may contain one or more battery modules, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack. Specifically, the battery pack may include a battery box and multiple battery modules disposed within the battery box; the battery box includes an upper box and a lower box, the upper box covering the lower box and forming a closed space for accommodating the battery modules. The multiple battery modules can be arranged in the battery box in any manner.

[0124] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0125] Example 1

[0126] A method for preparing a carbon-coated porous silicon material with internal and external dual doping includes the following steps:

[0127] S1: Silicon powder with an average particle size of 3μm~5μm and zinc powder are mixed evenly at a mass ratio of 95:5, placed in a tube furnace, heated to 650℃ at a heating rate of 10℃ / min under an argon atmosphere, held at the temperature for 6h, and then cooled with the furnace to obtain the first precursor powder composed of Si and ZnSi2.

[0128] S2: The first precursor powder and magnesium powder with an average particle size of 3μm~5μm are mixed evenly at a mass ratio of 1:1.8, and placed in another tube furnace. The mixture is heated to 580℃ at 10℃ / min under an argon atmosphere, held for 6 hours, and then cooled to obtain a magnesium-containing intermediate.

[0129] S3: The magnesium-containing intermediate obtained in S2 was transferred to a fluidized bed reactor and heated to 780°C at a rate of 5°C / min under an ammonia atmosphere with a flow rate of 100 L / min. After holding at this temperature for 8 hours, the mixture was cooled to obtain intermediate powder containing Mg3N2 template.

[0130] S4: Maintain the reactor temperature program, adjust the ammonia gas flow rate to 5 L / min, and simultaneously introduce acetylene gas at a flow rate of 50 L / min. Heat the system to 900℃ at a rate of 5℃ / min and hold at this temperature for 30 min for chemical vapor deposition. After deposition, cool to obtain an intermediate product coated with a nitrogen-doped carbon layer.

[0131] S5: The intermediate product obtained in S4 was immersed in a 1 mol / L hydrochloric acid solution and etched by stirring in a 60℃ constant temperature water bath for 6 hours. After the reaction was completed, the mixture was filtered and the filter cake was repeatedly washed with deionized water until the filtrate was neutral. Finally, the filter cake was dried in an 80℃ vacuum oven for 12 hours to obtain the final product, denoted as p-ZnSi2-Si@NC-1.

[0132] The material was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM image of the p-ZnSi2-Si@NC prepared in this embodiment is shown below. Figure 1 As shown in the SEM images, the material particles are spherical with smooth surfaces, a particle size of 3-4 μm, and an intact carbon coating. The overall transmission electron microscope (TEM) image and local high-resolution TEM images of the p-ZnSi2-Si@NC prepared in this embodiment are shown below. Figure 2 As shown, the TEM images clearly reveal a typical yolk shell structure: an internal porous silicon framework (with visible continuous framework and pores), and an external uniform amorphous carbon layer, with a distinct cavity between the shell and the core. High-resolution TEM measurements indicate that the thickness of the external carbon layer is approximately 25 nm, and elemental distribution analysis confirms that nitrogen is uniformly distributed within the carbon layer.

[0133] Example 2

[0134] The only difference between this embodiment and Embodiment 1 is that the mass ratio of silicon powder to zinc powder is adjusted to 80:20 in step S1. The final material is denoted as p-ZnSi2-Si@NC-2.

[0135] Example 3

[0136] The difference between this embodiment and Embodiment 1 lies only in the alloying conditions of steps S1 and S2: the alloying temperature of S1 is 450℃, and the holding time is 3 hours; the secondary alloying temperature of S2 is 500℃, and the holding time is 5 hours. The other steps are the same as in Embodiment 1. The final material is denoted as p-ZnSi2-Si@NC-3.

[0137] Example 4

[0138] The only difference between this embodiment and Example 1 is the change in the nitriding conditions in step S3: the nitriding reaction temperature is increased to 900℃, and the holding time is extended to 20 hours. The other steps are the same as in Example 1. The final material is denoted as p-ZnSi2-Si@NC-4.

[0139] Example 5

[0140] The only difference between this embodiment and Example 1 is the change in the chemical vapor deposition conditions in step S4: the acetylene gas flow rate is increased to 100 L / min, while other conditions remain unchanged. The final material is denoted as p-ZnSi2-Si@NC-5.

[0141] Example 6

[0142] The only difference between this embodiment and Embodiment 1 is the change in the chemical vapor deposition conditions in step S4: the deposition temperature is reduced to 700℃, and the holding time is shortened to 10 min. The other steps are the same as in Embodiment 1. The final material is denoted as p-ZnSi2-Si@NC-6.

[0143] Example 7

[0144] The only difference between this embodiment and Embodiment 1 is the change in the acid etching conditions in step S5: the etching temperature is reduced to 40°C, and the etching time is shortened to 2 hours. The other steps are the same as in Embodiment 1. The final material is denoted as p-ZnSi2-Si@NC-7.

[0145] Example 8

[0146] This embodiment provides a variant material with phosphorus doped carbon coating. Its preparation method is basically the same as in Example 1, except for step S4: In S4, instead of ammonia, a mixture of phosphine (PH3, diluted to a safe concentration with argon) and acetylene at a flow rate of 5 L / min is introduced, and deposition is carried out at 900°C for 30 min. The final material is denoted as p-ZnSi2-Si@PC.

[0147] This embodiment demonstrates the feasibility of using phosphine as a dopant source to achieve phosphorus-doped carbon coating. Those skilled in the art will understand that hydrogen sulfide (H2S) can be used to achieve sulfur doping, while a mixture of ammonia and phosphine or hydrogen sulfide can be used to achieve nitrogen-phosphorus or nitrogen-sulfur co-doping; the composition of the co-doped material can be controlled by adjusting the mixing ratio.

[0148] Comparative Example 1

[0149] This comparative example provides a comparative material without internal metal doping. Its preparation method is as follows: step S1 in Example 1 is omitted; silicon powder and magnesium powder are directly mixed at a mass ratio of 1:1.8 for step S2 (corresponding to alloying). Subsequent steps S3 to S5 are exactly the same as in Example 1. The final material obtained is an undoped metal-like porous silicon@nitrogen-doped carbon material, denoted as p-Si@NC.

[0150] Comparative Example 2

[0151] This comparative example provides a comparative material without external carbon layer heteroatom doping. Its preparation method is basically the same as in Example 1, except for step S4: in S4, only acetylene gas at a flow rate of 50 L / min is introduced, without any doping gas (such as ammonia), and deposition is carried out at 900°C for 30 min. The final material is a zinc-doped porous silicon@pure carbon coated material, denoted as p-ZnSi2-Si@C.

[0152] Experimental Examples and Data Validation

[0153] The materials obtained in Examples 1-8 and Comparative Examples 1-2 were subjected to physical characterization and electrochemical performance testing to verify the technical effects of the present invention.

[0154] 1. Material physicochemical properties and coin cell first-efficiency test

[0155] The silicon-carbon anode materials obtained in the examples and comparative examples were tested for carbon content, tap density and specific surface area, and then assembled into coin cells for testing of initial discharge capacity and initial coulombic efficiency.

[0156] Fabrication of button cells:

[0157] The silicon-carbon anode materials obtained in the examples and comparative examples were mixed with binder, conductive agent, and solvent to form a slurry, which was then uniformly coated onto copper foil. After drying and rolling, the anode sheet was obtained. The binder used was PAA Li (main component is lithium polyacrylate), the conductive agent was SP (conductive carbon black), and the solvent was deionized water. The silicon-carbon anode material ratio was SP:PAA Li:deionized water = 95g:1g:4g:220mL. LB046 (solvent: ethylene carbonate EC: dimethyl carbonate DEC = 1:1, lithium hexafluorophosphate LiPF6) was used as the electrolyte, a polypropylene (PP) membrane as the separator, and a lithium metal sheet as the counter electrode. These components were then assembled together with the anode sheet to form a coin cell.

[0158] Each button cell was assembled in a glove box under an Ar atmosphere. After stabilization, performance tests were performed using a Landon CT2001A electrochemical workstation. The charge / discharge rate was 0.1C, and the charge / discharge voltage range was 0.005-1.5V. The test results are shown in Table 1 below.

[0159] Table 1: Comparison of the physicochemical properties and button cell performance of each embodiment and comparative example

[0160]

[0161] As can be seen from Table 1 above, the first discharge specific capacity and coulombic efficiency of Example 1 of the present invention are better than those of the comparative example. This is because the appropriate proportion of lithium inert metal doped in the example can improve conductivity, and the appropriate proportion of nitrogen doped can increase the lithium ion diffusion rate and improve the charge and discharge efficiency.

[0162] 2. Performance testing of pouch batteries:

[0163] The silicon-carbon anode material obtained in the examples and comparative examples was mixed evenly with 90 wt.% graphite material to prepare a negative electrode sheet, and NCM811 was used to prepare a positive electrode sheet. LB046 (solvent: ethylene carbonate EC: dimethyl carbonate DEC = 1:1, lithium salt: lithium hexafluorophosphate LiPF6) was used as the electrolyte, and a polypropylene (PP) membrane was used as the separator to prepare a soft-pack battery.

[0164] The following performance tests were performed on the pouch battery:

[0165] ① Electrode Full-Charge Expansion Test: The thickness L1 of each electrode after rolling is measured. Then, the soft-pack battery is fully charged to 100% SOC and disassembled. The full-charge thickness L2 of the electrode is measured. Full-charge expansion rate = (L2-L1) / L1 100%.

[0166] ② Cyclic performance test: Each pouch battery was subjected to a cyclic performance test at 25°C, with a charge / discharge rate of 1C and a charge / discharge voltage range of 2.5-4.2V. After 500 cycles, the capacity retention rate was recorded.

[0167] ③ Rate performance test: Under the same temperature and charging voltage range conditions as the cycle test, the constant current ratio of each pouch battery under 2C and 4C conditions is tested. Constant current ratio = constant current capacity / (constant current capacity + 0.1C constant voltage capacity).

[0168] The test results are shown in Table 2 below.

[0169] Table 2: Performance Comparison of Pouch Batteries in Each Example and Comparative Example

[0170]

[0171] As can be seen from Table 2 above, the cycle performance of the pouch cells obtained using the silicon-carbon composite materials of Examples 1-7 is...

[0172] The expansion rate of the pouch cells in Examples 1-7 is significantly better than that of the pouch cells obtained using the negative electrode material of Comparative Example 1. This is because the lithium inert metal is doped into the porous silicon matrix in an appropriate proportion, which suppresses the expansion and pulverization of the material, further alleviates the expansion, and improves the cycle performance. At the same time, the 2C / 4C constant current ratios of the pouch cells in Examples 1-7 are better than those of the pouch cells in Comparative Example 2. This is because the doped nitrogen element forms fast ion conductor lithium nitride during the charging and discharging process, which promotes the diffusion and transport of lithium ions and improves the rate performance.

[0173] Experimental data fully demonstrate that the yolk-shell structured silicon-carbon material provided by this invention, which is synergistically constructed by internal lithium inert metal (such as Zn) doping and external heteroatom (such as N or P) doped carbon layers, can simultaneously achieve high cycle capacity retention, low volume expansion, and excellent rate-charging performance, resolving the contradiction between cycle stability and rate performance that traditional silicon-carbon materials struggle to balance. Those skilled in the art can combine the features of the above embodiments, for example, combining the metal ratio of Example 1 with the phosphorus doping process of Example 8, or using other listed metal elements such as nickel and cobalt for internal doping. These variations and combinations based on the concept of this invention can achieve similar technical effects and should fall within the protection scope of this invention.

[0174] The preparation method and application of a dual-doped modified carbon-coated porous silicon material provided in this application have been described in detail above, including the process equipment and process flow. However, this does not mean that this invention can only be realized by relying on the above-mentioned equipment and process. The description of the above embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​this invention. Those skilled in the art should understand that equivalent substitutions of raw materials and additions of auxiliary components, as well as the selection of specific methods, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0175] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0176] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0177] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carbon-coated porous silicon material with internal and external dual doping, characterized in that, include: The core layer comprises a silicon substrate doped with a lithium inert metal; the lithium inert metal includes metals that do not undergo lithium insertion / extraction reactions during charging and discharging. A wrapping layer, covering the outside of the core layer, the wrapping layer comprising a heteroatom-doped amorphous carbon layer; The lithium inert metal includes at least one of zinc, nickel, titanium, cobalt, copper, and iron; The heteroatom includes at least one of N, P and S; The core layer is a silicide phase of the lithium inert metal; The internally and externally doped modified carbon-coated porous silicon material has an egg yolk shell structure, with a clear cavity between the coating layer and the core layer.

2. The carbon-coated porous silicon material with internal and external dual doping according to claim 1, characterized in that, The mass ratio of the silicon substrate to the lithium inert metal is (80:20) to (99:1); And / or, the thickness of the outer wrapping layer is 20μm~30μm.

3. A method for preparing the internally and externally doped modified carbon-coated porous silicon material according to claim 1 or 2, characterized in that, Includes the following steps: S1: Silicon powder is mixed with lithium inert metal and alloyed to obtain the first precursor; S2: Mix the first precursor with magnesium powder and alloy it in a second time to obtain a magnesium-containing intermediate; S3: The magnesium-containing intermediate is subjected to nitriding treatment in a nitrogen-containing atmosphere to obtain a template-containing intermediate; S4: In an atmosphere containing carbon source gas and doped gas containing heteroatoms, the template intermediate is subjected to chemical vapor deposition to form an intermediate product coated with a doped carbon layer. S5: The intermediate product is etched with an acid solution to remove the template and obtain the internal and external doped modified carbon-coated porous silicon material.

4. The preparation method according to claim 3, characterized in that, In step S1, the mass ratio of silicon powder to lithium inert metal is (80:20) to (99:1). And / or, the particle size range of the silicon powder and lithium inert metal in step S1 is 1 μm to 5 μm; And / or, the particle size range of the magnesium powder in step S2 is 1 μm to 5 μm; And / or, the alloying temperature is 450℃~750℃, and the holding time is 3h~15h.

5. The preparation method according to claim 3, characterized in that, In step S2, the mass ratio of the first precursor to magnesium powder is (1:1.7) to (1:2.5). And / or, the conditions for secondary alloying in step S2 include: a temperature of 500℃~750℃ and a holding time of 5h~20h.

6. The preparation method according to claim 3, characterized in that, In step S3, the nitrogen-containing atmosphere includes at least one of ammonia, nitrogen, nitric oxide and nitrogen dioxide, and the flow rate is 100 L / min to 200 L / min. And / or, in step S3, the nitriding treatment conditions include: a temperature of 600℃~900℃ and a holding time of 5h~20h.

7. The preparation method according to claim 3, characterized in that, In step S4, the carbon source gas includes at least one of methane, acetylene, and propylene, and the flow rate is 10 L / min to 100 L / min. And / or, the doping gas in step S4 includes at least one of ammonia, phosphine, and hydrogen sulfide, with a flow rate of 1 L / min to 10 L / min; And / or, in step S4, the temperature of chemical vapor deposition is 700℃~1000℃, and the holding time is 10min~120min; And / or, the acid solution in step S5 is hydrochloric acid, sulfuric acid, or nitric acid; And / or, in step S5, the etching temperature is 40℃~80℃ and the etching time is 2h~8h.

8. A battery negative electrode material, characterized in that, The material includes the internally and externally doped modified carbon-coated porous silicon material as described in claim 1 or 2, or the internally and externally doped modified carbon-coated porous silicon material prepared by the preparation method described in any one of claims 3 to 7.

9. A lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The negative electrode comprises the battery negative electrode material as described in claim 8.

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