Negative electrode material, preparation method therefor, and application thereof

Abstract

The embodiments of the present invention relate to a negative electrode material, a preparation method therefor, and an application thereof. The preparation method comprises: in an inert atmosphere, introducing a mixed gas of a first silicon source gas, a nitrogen source gas, and a first protective gas into a chemical vapor deposition furnace, so that the first silicon source gas and the nitrogen source gas are subjected to chemical vapor deposition in a porous carbon matrix so as to obtain a first nitrogen-doped silicon-carbon composite material; introducing a mixed gas of a second silicon source gas and a second protective gas into a chemical vapor deposition furnace, so that the second silicon source gas is deposited in the first nitrogen-doped silicon-carbon composite material so as to obtain a second nitrogen-doped silicon-carbon composite material; repeating the above steps multiple times; in an inert atmosphere, introducing a mixed gas of a third protective gas and a carbon source gas into a chemical vapor deposition furnace, and performing passivation treatment on the second nitrogen-doped silicon-carbon composite material so as to obtain a passivated silicon-carbon composite material; and performing nitrogen-containing carbon coating on the passivated silicon-carbon composite material to form a nitrogen-doped carbon coating layer so as to obtain a negative electrode material.

Description

A negative electrode material, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202411471377.5, filed on October 22, 2024, entitled "An Anode Material and Its Preparation Method and Application". Technical Field

[0002] This invention relates to the field of materials technology, and in particular to a negative electrode material, its preparation method, and its application. Background Technology

[0003] Currently, graphite is the most common anode material for lithium-ion batteries. However, its relatively low theoretical capacity limit (372 mAh / g) makes it unsuitable for current applications. Silicon, with its high theoretical specific capacity of 4200 mAh / g, low lithium intercalation potential, and low cost, holds promise as a next-generation anode material for lithium-ion batteries. However, silicon also presents several challenges as an anode material: First, severe volume expansion during lithium intercalation and deintercalation leads to easy pulverization and detachment from the current collector, resulting in loss of electrochemical performance. Second, an unstable solid electrolyte interface (SEI) layer easily forms on the silicon surface, causing irreversible capacity decay. Third, silicon has poor conductivity, preventing effective capacity release at high rates. These issues severely limit the application of silicon anode materials in lithium-ion batteries.

[0004] Currently, the main methods to reduce the expansion of silicon anode materials are silicon particle nano-sizing and carbon layer coating. However, silicon itself has poor conductivity, and the carbon coating layer is difficult to maintain structural stability over a long period of time under the huge volume changes of silicon-based materials.

[0005] The first patent, titled "A Nanoscale Silicon-Carbon Composite Material and Its Preparation Method and Application," published in CN109167031A, discloses a nanoscale silicon-carbon composite material with a multi-level structure. It uses silicon nanoparticles as the core, amorphous carbon as the intermediate coating layer, and fluorinated carbon as the outer shell. This structure effectively improves the electrochemical performance of the material, but the process uses fluorine-containing substances, making the production process unsafe. The second patent, titled "A High-Conductivity Silicon-Carbon Anode Material and Its Preparation Method," published in CN117894951A, discloses a method of depositing a soft carbon layer on the pore walls of a porous hard carbon framework, depositing nanoscale silicon within the soft carbon layer, and then coating it with a carbon coating layer to obtain a silicon-carbon anode material powder containing a carbon layer. While this material improves the conductivity and rate performance of silicon-carbon materials to some extent, controlling the soft carbon layer during preparation is difficult, and its stability is poor during long-term cycling.

[0006] Therefore, there is an urgent need to develop a new type of silicon-carbon composite material to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a negative electrode material, its preparation method, and its application. This preparation method involves forming Si-N bonds in a porous carbon matrix through silicon-nitrogen co-deposition, which improves the conductivity of the silicon-carbon composite material and suppresses silicon volume expansion, thereby enhancing the material's stability. Subsequently, carbon coating is performed in a nitrogen-containing atmosphere to obtain a nitrogen-doped carbon coating layer, effectively constructing a conductive network. This results in a negative electrode material with superior conductivity, effectively increasing the electron transport speed of silicon and overcoming the problem of low silicon conductivity.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a negative electrode material, the method comprising:

[0009] Step 1: In an inert atmosphere, a mixture of a first silicon source gas, a nitrogen source gas, and a first protective gas is introduced into a vapor deposition furnace, so that the first silicon source gas and the nitrogen source gas are vapor deposited in a porous carbon matrix to obtain a first nitrogen-doped silicon-carbon composite material.

[0010] Step 2: The mixture of the second silicon source gas and the second protective gas is introduced into the vapor deposition furnace, so that the second silicon source gas is deposited in the first nitrogen-doped silicon-carbon composite material to obtain the second nitrogen-doped silicon-carbon composite material.

[0011] Step 3: Repeat steps 1 and 2 several times;

[0012] Step 4: Under an inert atmosphere, a mixture of the third protective gas and the carbon source gas is introduced into the vapor deposition furnace to passivate the second nitrogen-doped silicon-carbon composite material, thereby obtaining a passivated silicon-carbon composite material.

[0013] Step 5: The passivated silicon-carbon composite material is coated with nitrogen-containing carbon to form a nitrogen-doped carbon coating layer, thereby obtaining the negative electrode material; in the negative electrode material, a conductive network is constructed through the interconnection of nitrogen in the carbon coating layer and nitrogen in the silicon-carbon composite material inside the carbon coating layer.

[0014] Preferably, the nitrogen-containing carbon coating of the passivated silicon-carbon composite material specifically includes:

[0015] Under a nitrogen-containing atmosphere, a carbon source gas is introduced into the vapor deposition furnace to perform vapor deposition on the passivated silicon-carbon composite material surface;

[0016] Alternatively, the passivated silicon-carbon composite material is mixed evenly with a solid carbon source in an organic solvent, and then spray-dried to obtain powder. The powder is then placed in a carbonization furnace and carbonized under a nitrogen-containing atmosphere.

[0017] The carbon source gas includes one or more of acetylene, ethylene, propylene, methane, and carbon dioxide; the solid carbon source includes one or more of phenolic resin, epoxy resin, and melamine resin; the carbonization treatment conditions are: temperature 400℃-1000℃, time 2 hours-10 hours; the nitrogen-containing atmosphere includes one or more of ammonia, nitric oxide, nitrogen dioxide, and dinitrogen tetroxide.

[0018] Preferably, the porous carbon matrix has a particle size D50 of 3μm-20μm, a pore size of 1nm-4nm, and a micropore ratio of 10%-100%.

[0019] Preferably, the first silicon source gas includes one or more of the following: silane, silane, chlorosilane, trichlorosilane, and silicon tetrachloride; the nitrogen source gas is one or more of ammonia, nitric oxide, nitrogen dioxide, and dinitrogen tetroxide; and the flow rate ratio of the first silicon source gas, the nitrogen source gas, and the first protective gas is 33:[2-8]:35.

[0020] Preferably, in step 1, the conditions for vapor deposition are: temperature 300℃-700℃, time 10min-160min.

[0021] Preferably, the second silicon source gas includes one or more of the following: silane, silane, chlorosilane, trichlorosilane, and silicon tetrachloride; the flow rate ratio of the second silicon source gas to the second protective gas is [2-33]:35.

[0022] Preferably, in step 4, the carbon source gas includes one or more of acetylene, methane, and propylene.

[0023] Preferably, in step 2, the deposition conditions are: temperature 300℃-700℃, time 10min-160min; in step 4, the passivation conditions are: temperature 300℃-700℃, time 1 hour-3 hours.

[0024] In a second aspect, the present invention provides a negative electrode material, which is prepared by any of the preparation methods described in the first aspect above.

[0025] Thirdly, the present invention provides a negative electrode material having a core-shell structure, comprising a core and a shell;

[0026] The core is a passivated silicon-carbon composite material, which is nitrogen-doped.

[0027] The outer shell is a carbon coating layer doped with nitrogen.

[0028] In the negative electrode material, the nitrogen-doped structure in the outer shell and the nitrogen-containing structure in the core form an electronic coupling to construct a conductive network; preferably, the conductive network is a three-dimensional conductive network.

[0029] Preferably, the particle size D50 of the porous carbon matrix in the negative electrode material is 3μm-20μm, the pore size is 1nm-4nm, and the proportion of micropores in the porous carbon matrix is ​​between 10% and 100%.

[0030] Fourthly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material described in either the second or third aspect.

[0031] Fifthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described in the fourth aspect.

[0032] This invention provides a method for preparing an anode material. First, Si-N bonds are generated in a porous carbon matrix through silicon-nitrogen co-deposition. The formation of Si-N bonds enhances the conductivity of the silicon-carbon composite material and suppresses the volume expansion of silicon, thereby improving the stability of the material. Nitrogen doping provides more free electrons, as nitrogen can act as an electron donor or acceptor, improving the conductivity of the silicon-carbon composite material. Nitrogen doping also provides more active sites for subsequent silicon deposition. Second, further silicon deposition increases the capacity of the silicon-carbon composite material. Finally, by forming a nitrogen-containing carbon coating layer, the mechanical strength of the carbon coating layer is increased, which can more effectively buffer the pressure generated by the internal silicon expansion. Furthermore, the nitrogen in the carbon coating layer and the nitrogen in the silicon-carbon composite material inside the carbon coating layer strengthen the connection between the core layer and the outside of the anode material, effectively constructing a conductive network. This results in a cathode material with better conductivity, effectively improving the electron transport speed of silicon and overcoming the problem of low silicon conductivity. Attached Figure Description

[0033] Figure 1 is a flowchart of a method for preparing a negative electrode material according to an embodiment of the present invention;

[0034] Figure 2 is a schematic diagram of the structure of a negative electrode material provided in an embodiment of the present invention. Detailed Implementation

[0035] 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.

[0036] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] This invention provides a method for preparing a negative electrode material, the process of which is shown in Figure 1 and includes the following steps:

[0038] Step 1: In an inert atmosphere, a mixture of the first silicon source gas, nitrogen source gas, and first protective gas is introduced into a vapor deposition furnace, so that the first silicon source gas and nitrogen source gas are vapor deposited in a porous carbon matrix to obtain the first nitrogen-doped silicon-carbon composite material.

[0039] Specifically, under an inert atmosphere, the porous carbon matrix is ​​first placed in a vapor deposition furnace, and then the vapor deposition furnace is heated. The inert atmosphere can be nitrogen and / or argon. The first silicon source gas can specifically include one or more of silane, disilane, chlorosilane, trichlorosilane, and silicon tetrachloride. The nitrogen source gas can be one or more of ammonia, nitric oxide, nitrogen dioxide, and dinitrogen tetroxide. The first protective gas can be one or more of nitrogen, argon, and helium. The flow rate ratio of the first silicon source gas, nitrogen source gas, and first protective gas can be 33:[2-8]:35, preferably 33:[4-6]:35. The particle size D50 of the porous carbon matrix is ​​specifically 3μm-20μm, the pore size is specifically 1nm-4nm, and the micropore ratio in the porous carbon matrix is ​​specifically 10%-100%. In this application, the conditions for vapor deposition are all within the same range: the temperature can be 300℃-700℃, preferably 400℃-600℃, and the time can be 10min-160min, preferably 90min-150min.

[0040] This step employs co-deposition of silicon and nitrogen sources. Nitrogen doping provides more free electrons, as nitrogen can act as both an electron donor and acceptor, thus improving the conductivity of the silicon-carbon composite material. Nitrogen doping also provides more active sites, offering opportunities for subsequent silicon deposition. When this silicon-carbon composite material is used in lithium-ion batteries, it can increase the battery's capacity.

[0041] In this invention, the particle size D50 of the porous carbon matrix refers to the volume median particle size of the porous carbon matrix, representing the particle size corresponding to 50% of the volume distribution of the porous carbon matrix, a meaning known in the art. The particle size D50 of the porous carbon matrix provided in this embodiment can be determined using instruments and conventional methods known in the art. Specifically, the particle size D50 can be determined using a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0042] In this invention, the pore size of the porous carbon matrix refers to the diameter of the internal pores within the porous carbon matrix, a meaning known in the art. The pore size of the porous carbon matrix provided in the embodiments of this invention can be determined using instruments and conventional methods known in the art. Specifically, a gas adsorption method (Brunauer-Emmet-Teller, BET) can be used. The measuring instrument is a Micromeritics ASAP2460 specific surface area and pore size analyzer from McMuritics (Shanghai) Instruments Co., Ltd., USA, and the adsorbate is nitrogen gas.

[0043] In this invention, micropores in the porous carbon matrix refer to pores with a diameter of less than 2 nm, a meaning known in the art. The proportion of micropores in the porous carbon matrix provided in the embodiments of this invention can be determined using instruments and conventional methods known in the art. Specifically, a gas adsorption method (Brunauer-Emmet-Teller, BET) can be used. The measuring instrument is a Micromeritics ASAP2460 specific surface area and pore size analyzer from McMuritics (Shanghai) Instruments Co., Ltd., USA, and nitrogen is used as the adsorbate.

[0044] Step 2: The mixture of the second silicon source gas and the second protective gas is introduced into the vapor deposition furnace, so that the second silicon source gas is deposited in the first nitrogen-doped silicon-carbon composite material to obtain the second nitrogen-doped silicon-carbon composite material.

[0045] Specifically, the second silicon source gas may include one or more of the following: silane, disilane, chlorosilane, trichlorosilane, and silicon tetrachloride. The second protective gas may be one or more of the following: nitrogen, argon, and helium. The flow ratio of the second silicon source gas to the second protective gas may be [2-33]:35, preferably [10-33]:35.

[0046] This step primarily involves silicon deposition, which can improve the capacity of the second nitrogen-doped silicon-carbon composite material.

[0047] The silicon deposition in this step also uses vapor deposition technology, and the specific conditions are the same as those specified in step 1: the temperature is 300℃-700℃, preferably 400℃-600℃, and the time is 10min-160min, preferably 90min-150min.

[0048] Step 3: Repeat steps 1 and 2 several times.

[0049] Specifically, the purpose of repeating this process several times is to ensure that silicon and nitrogen are fully deposited in the porous carbon matrix. This "several times" can be 2-6 times.

[0050] In a specific example, if step 3 states that steps 1 and 2 are executed four times in a loop, then the total number of times steps 1 and 2 are executed is 5.

[0051] Step 4: Under an inert atmosphere, a mixture of the third protective gas and the carbon source gas is introduced into a vapor deposition furnace to passivate the second nitrogen-doped silicon-carbon composite material, thereby obtaining a passivated silicon-carbon composite material.

[0052] Passivation treatment refers to the process of passing a mixture of a third protective gas and a carbon source gas into a vapor deposition furnace under an inert atmosphere to perform vapor deposition on a second nitrogen-doped silicon-carbon composite material.

[0053] Specifically, the inert atmosphere can be one or more of nitrogen, argon, and helium. The carbon source gas can specifically include one or more of acetylene, methane, and propylene. The third protective gas can be one or more of nitrogen, argon, and helium. The flow ratio of the third protective gas to the carbon source gas can be 35:[2-6], preferably 35:[4-5]. The passivation treatment time can be 1 hour to 3 hours, preferably 100 min to 2 hours. After passivation treatment, a carbon layer will be formed on the surface of the second nitrogen-doped silicon-carbon composite material. The carbon layer can protect the material inside and improve the stability of the material.

[0054] It should be noted that the passivation treatment in this step also adopts the vapor deposition method, and the temperature conditions are the same as those specified in step 1, with a temperature of 300℃-700℃, preferably 400℃-600℃.

[0055] Step 5: The passivated silicon-carbon composite material is coated with nitrogen-containing carbon to form a nitrogen-doped carbon coating layer, thereby obtaining the anode material.

[0056] In the negative electrode material, a conductive network is constructed by connecting nitrogen in the carbon coating layer and nitrogen in the silicon-carbon composite material inside the carbon coating layer.

[0057] In this application, carbon coating containing nitrogen elements is performed using the following two methods.

[0058] The first method involves introducing a carbon source gas into a vapor deposition furnace under a nitrogen-containing atmosphere to perform vapor deposition on the passivated silicon-carbon composite material surface. The nitrogen-containing atmosphere can be understood as a highly reactive nitrogen-containing compound gas. Specifically, the nitrogen-containing atmosphere may include one or more of ammonia, nitric oxide, nitrogen dioxide, and dinitrogen tetroxide. The carbon source gas may include one or more of acetylene, ethylene, propylene, methane, and carbon dioxide. The flow rate ratio of the carbon source gas to the nitrogen-containing compound gas can be 10:(1-3), wherein the flow rate of the carbon source gas can be 1 L / min-50 L / min, preferably 20 L / min-40 L / min. The vapor deposition temperature can be 300℃-700℃, preferably 400℃-600℃, and the time can be 10 min-160 min, preferably 90 min-150 min.

[0059] The second method of carbon coating specifically involves uniformly mixing a passivated silicon-carbon composite material with a solid carbon source in an organic solvent, followed by spray drying to obtain a powder, and then carbonizing the powder under a nitrogen-containing atmosphere. The solid carbon source can specifically include one or more of phenolic resin, epoxy resin, and melamine resin. The carbonization conditions can be: temperature 400℃-1000℃, preferably 500℃-800℃, time 2 hours-10 hours, preferably 4 hours-8 hours. The organic solvent can specifically include one or more of anhydrous ethanol, methanol, ethylene glycol, and acetone. The spray drying conditions are: outlet temperature 130℃-200℃, preferably 150℃-180℃, pressure 3MPa-4MPa. The mass ratio of the passivated silicon-carbon composite material to the solid carbon source can be 10:[1-10], preferably 10:[1-5]. The mixing time can be 2 hours-24 hours, preferably 4 hours-20 hours.

[0060] In this invention, the organic solvent acts as a dispersant, helping to uniformly mix the passivated silicon-carbon composite material with the solid carbon source, preventing agglomeration, and is completely volatilized and removed during spray drying—a technique well-known in the art. In this embodiment, the mass fraction of the passivated silicon-carbon composite material and the solid carbon source in the organic solvent is 10%-50%.

[0061] Spray drying refers to a continuous process technology that disperses liquid materials (solutions, suspensions, or slurries) into tiny droplets through an atomizer and rapidly dries them with hot air (or gas) to form a solid powder; this is a well-known concept in the art. The spray drying in this embodiment of the invention can be achieved using a spray drying tower known in the art.

[0062] The carbonization process can be carried out in a carbonization furnace known in the art, and the heating rate of the carbonization furnace can be 5°C / min.

[0063] The nitrogen-containing atmosphere is as specified in the first method.

[0064] The structure of the anode material prepared by the above preparation method of the present invention is shown in Figure 2. It can be seen that the interior of the anode material is a porous carbon matrix and nano-silicon particles and nitrogen-doped nano-silicon particles deposited in the pores of the porous carbon matrix, and the exterior is a nitrogen-doped carbon coating layer.

[0065] This invention also provides a negative electrode material with a core-shell structure, comprising a core and an outer shell. The core is a passivated silicon-carbon composite material, in which nitrogen is doped, the nitrogen originating from the nitrogen source gas mentioned in the above preparation method. The outer shell is a nitrogen-doped carbon coating layer. In this negative electrode material, the nitrogen-doped structure in the outer shell and the nitrogen-containing structure in the core form electronic coupling, constructing a conductive network, specifically a three-dimensional conductive network.

[0066] Electronic coupling refers to the synergy or extension of electronic structures between different materials or structures, enabling electrons or charges to propagate across the interface (i.e., forming a conductive path).

[0067] In this anode material, the particle size D50 of the porous carbon matrix is ​​3μm-20μm, the pore size is 1nm-4nm, and the proportion of micropores in the porous carbon matrix is ​​between 10% and 100%.

[0068] This invention involves carbon coating of silicon-carbon composite materials with nitrogen-containing elements. The introduction of nitrogen doping gives the carbon coating layer the following advantages:

[0069] First, nitrogen doping can alter the surface chemical properties of carbon materials, increasing their chemical stability. Nitrogen can form strong covalent bonds, which helps improve the durability of the material in electrochemical reactions. Second, nitrogen-doped carbon coatings can improve the electrochemical stability of anode materials. Nitrogen can act as an electron donor or acceptor, helping to stabilize the charge state on the surface of the anode material and reducing structural degradation during charge and discharge processes. Third, nitrogen doping can increase the mechanical strength of the carbon coating, making it more able to withstand the stress caused by volume expansion and contraction during electrochemical reactions. Fourth, nitrogen-doped carbon coatings can improve the interfacial stability between the anode material and the electrolyte, reducing interfacial reactions. Therefore, the carbon coating of this application can more effectively buffer the pressure generated by the expansion of internal silicon, and even if it expands, it can return to its original state, effectively solving various problems caused by the volume expansion of silicon as an anode material.

[0070] Furthermore, for the overall anode material system, nitrogen doping in both the carbon coating layer and the internal silicon-carbon composite material can enhance electronic conductivity and improve the electron transport capability of the silicon-carbon composite material. Since there are pathways between the nitrogen in the carbon coating layer and the nitrogen in the silicon-carbon composite material, a more efficient conductive network can be formed. This alters the electrical properties of the porous carbon material, making the conductive path more continuous and reducing electron transport impedance. This interconnected conductive network can significantly improve the overall electron transport efficiency of the material, facilitating faster charge and discharge processes.

[0071] In summary, the method for preparing an anode material provided by this invention firstly generates Si-N bonds through silicon-nitrogen co-deposition. The formation of Si-N bonds enhances the conductivity of the silicon-carbon composite material and suppresses the volume expansion of silicon, thereby improving the stability of the material. Nitrogen doping provides more free electrons because nitrogen can act as an electron donor or acceptor, improving the conductivity of the silicon-carbon composite material. Nitrogen doping also provides more active sites, providing sites for subsequent silicon deposition. Secondly, further silicon deposition improves the capacity of the second nitrogen-doped silicon-carbon composite material. Finally, by coating the silicon-carbon material with nitrogen-containing carbon, a nitrogen-doped carbon coating layer is obtained. On the one hand, this increases the mechanical strength of the carbon coating layer, which can more effectively buffer the pressure generated by the internal silicon expansion; on the other hand, the nitrogen in the carbon coating layer and the nitrogen in the silicon-carbon composite material inside the carbon coating layer strengthen the connection between the core layer and the outside of the anode material, effectively constructing a conductive network, giving the anode material better conductivity, effectively improving the electron transport speed of silicon, and overcoming the problem of low silicon conductivity.

[0072] The negative electrode material provided by this invention can be used in the electrode materials of lithium-ion batteries.

[0073] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the specific process of preparing anode materials using the method provided in the above embodiments of the present invention, as well as the electrochemical characteristics of the prepared anode materials.

[0074] Example 1

[0075] The first step involves placing 5 kg of porous carbon matrix in a vapor deposition furnace under a nitrogen atmosphere and heating the furnace to 500°C. Then, a mixture of silane, ammonia, and nitrogen is introduced into the vapor deposition furnace at a flow rate ratio of 33:2:35 and the gas is continuously introduced for 20 minutes, allowing silane and ammonia to be deposited in the porous carbon matrix to obtain the first nitrogen-doped silicon-carbon composite material.

[0076] The second step involves introducing a mixture of silane and nitrogen at a flow rate ratio of 33:35 into a vapor deposition furnace at 500°C for 20 minutes, allowing silane to be deposited in the first nitrogen-doped silicon-carbon composite material to obtain the second nitrogen-doped silicon-carbon composite material.

[0077] The third step is to repeat the first and second steps twice.

[0078] The fourth step involves passing through a nitrogen-doped silicon-carbon composite material in a nitrogen atmosphere for 100 minutes, using a mixture of nitrogen and acetylene. The nitrogen to acetylene flow rate ratio is 35:4.

[0079] The fifth step involves stirring the passivated silicon-carbon composite material and phenolic resin in anhydrous ethanol at a mass ratio of 10:1 for 4 hours to ensure thorough mixing and obtain a mixture.

[0080] The sixth step is to spray-dry the mixture to obtain powder. The spray-drying conditions are a temperature of 150℃ and a pressure of 3MPa.

[0081] Step 7: In an ammonia atmosphere, 1 kg of powder is placed in a carbonization furnace, and the furnace is heated to 550°C at a heating rate of 5°C / min and held for 4 hours to obtain the negative electrode material. The ammonia flow rate is 5 L / min.

[0082] First, the conductivity of the negative electrode material was tested: 0.5g of the negative electrode material was weighed and placed in a powder resistivity tester, and the conductivity was tested under a pressure of 20MPa.

[0083] Next, the prepared negative electrode material was used to fabricate a lithium-ion battery electrode, and the electrode was used to assemble a coin cell for testing, as detailed below:

[0084] First, the negative electrode material, acetylene black, and carboxymethyl cellulose (CMC) are added to deionized water in a mass ratio of 90:5:5 and mixed evenly. The mixture is then prepared into a slurry using a pulping machine and coated onto a copper foil current collector to obtain an electrode sheet. The electrode sheet is then dried in a vacuum drying oven at 85°C for 10 hours.

[0085] Next, cut the dried electrode into 14mm round pieces.

[0086] Then, the above-mentioned electrodes were assembled into a CR2032 coin cell in an argon-filled glove box. The electrolyte of the CR2032 coin cell was 1 mol / L lithium hexafluorophosphate (LiPF6), and the solvents were ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), with a volume ratio of EC, DMC, and DEC of 1:1:1. The counter electrode was a lithium sheet.

[0087] Finally, the CR2032 button cell was left to stand for 8 hours at room temperature, and then charge and discharge tests were conducted on the Blue Battery Testing System (CT2001A), as follows:

[0088] 1. Testing the initial expansion rate of the electrode: At room temperature, the prepared electrode is cut by ion beam, and the cross-section is photographed using a scanning electron microscope. The thickness of the electrode is recorded as T1, and the thickness of the copper foil current collector substrate is also measured and recorded as T2. Under a current density of 0.1C and a charging cutoff voltage of 2V, the coin cell is fully charged. The battery is then disassembled in a glove box, the electrode is removed, and after ion beam cutting, the cross-section is photographed again, and the thickness of the electrode at this point is measured and recorded as T3. The initial expansion rate is then calculated using the following formula:

[0089] First-cycle expansion rate = (T3-T1) / (T1-T2)×100%.

[0090] 2. Test the cycle capacity retention rate: The voltage window is 0.01V-2V, the discharge rate is 0.1C, the lower limit of the discharge voltage window is 0.01V, and the number of cycles is 200.

[0091] Example 2

[0092] The first step involves placing 5 kg of porous carbon matrix in a vapor deposition furnace under a nitrogen atmosphere and heating the furnace to 500°C. Then, a mixture of silane, ammonia, and nitrogen is introduced into the vapor deposition furnace at a flow rate ratio of 33:5:35 and the gas is continuously introduced for 20 minutes, allowing silane and ammonia to be deposited in the porous carbon matrix to obtain the first nitrogen-doped silicon-carbon composite material.

[0093] The remaining steps and testing process are the same as in Example 1.

[0094] Example 3

[0095] The first and second steps are the same as in Example 1.

[0096] The third step is to repeat the first and second steps four times.

[0097] The remaining steps and testing process are the same as in Example 1.

[0098] Example 4

[0099] Steps one through six are the same as in Example 1.

[0100] Step 7: In an ammonia atmosphere, 1 kg of powder is placed in a carbonization furnace, and the furnace is heated to 600°C at a heating rate of 5°C / min and held for 4 hours to obtain the negative electrode material. The ammonia flow rate is 5 L / min.

[0101] The testing process is the same as in Example 1.

[0102] Example 5

[0103] Steps one through four are the same as in Example 1.

[0104] The fifth step involves introducing acetylene into a vapor deposition furnace under an ammonia atmosphere. 1 kg of passivated silicon-carbon composite material is held at 500°C for 100 min to perform vapor deposition, forming a nitrogen-doped carbon coating layer on the surface of the passivated silicon-carbon composite material, thereby obtaining the negative electrode material. The flow rate of acetylene is 20 L / min, and the flow rate of ammonia is 2 L / min.

[0105] The testing process is the same as in Example 1.

[0106] Example 6

[0107] The first and second steps are the same as in Example 1.

[0108] The third step is to repeat steps one and two three times.

[0109] The remaining steps and testing process are the same as in Example 1.

[0110] Example 7

[0111] The first step involves placing 5 kg of porous carbon matrix in a vapor deposition furnace under an argon atmosphere and heating the furnace to 400°C. Then, a mixture of silane, nitric oxide, and argon is introduced into the vapor deposition furnace at a flow rate ratio of 33:8:35 and the gas is continuously introduced for 10 minutes, allowing silane and nitric oxide to deposit in the porous carbon matrix, thus obtaining the first nitrogen-doped silicon-carbon composite material.

[0112] The second step involves introducing a mixture of silane and argon at a flow rate ratio of 2:35 into a vapor deposition furnace at 600°C for 100 minutes, allowing silane to be deposited in the first nitrogen-doped silicon-carbon composite material to obtain the second nitrogen-doped silicon-carbon composite material.

[0113] The third step is to repeat the first and second steps six times.

[0114] The fourth step involves passing through a vapor deposition furnace under an argon atmosphere with a mixture of argon and methane for 2 hours to passivate the second nitrogen-doped silicon-carbon composite material, resulting in a passivated silicon-carbon composite material. The flow ratio of argon to methane is 35:2.

[0115] The fifth step involves stirring the passivated silicon-carbon composite material and epoxy resin in acetone at a mass ratio of 10:5 for 20 hours to ensure thorough mixing and obtain a mixture.

[0116] The sixth step is to spray-dry the mixture to obtain powder. The spray-drying conditions are: temperature 180℃ and pressure 4MPa.

[0117] Step 7: Under a nitric oxide atmosphere, 2 kg of powder is placed in a carbonization furnace, and the furnace is heated to 400°C at a heating rate of 5°C / min and held for 8 hours to obtain the negative electrode material. The flow rate of nitric oxide is 10 L / min.

[0118] Example 8

[0119] In the first step, 5 kg of porous carbon matrix was placed in a vapor deposition furnace under an argon atmosphere, and the vapor deposition furnace was heated to 600°C. Then, a mixed gas of chlorosilane, nitrogen dioxide and argon was introduced into the vapor deposition furnace at a flow ratio of 33:4:35 and the gas was continuously introduced for 90 min, so that chlorosilane and nitrogen dioxide were deposited in the porous carbon matrix to obtain the first nitrogen-doped silicon-carbon composite material.

[0120] The second step involves introducing a mixture of chlorosilane and argon at a flow rate ratio of 18:35 into a vapor deposition furnace at 600°C for 160 minutes, allowing chlorosilane to be deposited in the first nitrogen-doped silicon-carbon composite material to obtain the second nitrogen-doped silicon-carbon composite material.

[0121] The third step is to repeat steps one and two three times.

[0122] The fourth step involves passing through a vapor deposition furnace under an argon atmosphere, where a mixture of argon and propylene is continuously introduced for 1 hour to passivate the second nitrogen-doped silicon-carbon composite material, resulting in a passivated silicon-carbon composite material. The flow ratio of argon to propylene is 35:6.

[0123] The fifth step involves stirring the passivated silicon-carbon composite material and epoxy resin in methanol at a mass ratio of 10:10 for 2 hours to ensure thorough mixing and obtain a mixture.

[0124] The sixth step is to spray-dry the mixture to obtain powder. The spray-drying conditions are: temperature 130℃ and pressure 4MPa.

[0125] Step 7: Under a nitrogen dioxide atmosphere, 2 kg of powder is placed in a carbonization furnace, and the furnace is heated to 1000°C at a heating rate of 5°C / min and held for 2 hours to obtain the negative electrode material. The flow rate of nitrogen dioxide is 10 L / min.

[0126] Example 9

[0127] The first step involves placing 5 kg of porous carbon matrix in a vapor deposition furnace under a helium atmosphere and heating the furnace to 550°C. Then, a mixture of trichlorosilane gas, nitrogen tetroxide, and helium is introduced into the vapor deposition furnace at a flow rate ratio of 33:6:35 and the gas is continuously introduced for 50 minutes, allowing the trichlorosilane gas and nitrogen tetroxide to deposit in the porous carbon matrix, thus obtaining the first nitrogen-doped silicon-carbon composite material.

[0128] The second step involves introducing a mixture of trichlorosilane gas and helium gas with a flow rate ratio of 24:35 into a vapor deposition furnace at 600°C for 150 minutes. This allows the trichlorosilane gas to deposit in the first nitrogen-doped silicon-carbon composite material, resulting in the second nitrogen-doped silicon-carbon composite material.

[0129] The third step is to repeat the first and second steps five times.

[0130] The fourth step involves passing through a helium and acetylene mixture into a vapor deposition furnace under a helium atmosphere for 3 hours to passivate the second nitrogen-doped silicon-carbon composite material, resulting in a passivated silicon-carbon composite material. The flow ratio of helium to acetylene is 35:4.

[0131] In the fifth step, under a nitrogen tetroxide atmosphere, acetylene is introduced into a vapor deposition furnace, and 1 kg of passivated silicon-carbon composite material is subjected to vapor deposition at 600°C for 120 min to form a nitrogen-doped carbon coating layer on the surface of the passivated silicon-carbon composite material, thereby obtaining the negative electrode material. The flow rate of acetylene is 40 L / min, and the flow rate of nitrogen tetroxide is 8 L / min.

[0132] Example 10

[0133] The first step involves placing 5 kg of porous carbon matrix in a vapor deposition furnace under a nitrogen atmosphere and heating the furnace to 450°C. Then, a mixture of silicon tetrachloride gas, ammonia gas, and nitrogen gas is introduced into the vapor deposition furnace at a flow rate ratio of 33:5:35 and the gas is continuously introduced for 80 minutes, allowing the silicon tetrachloride gas and ammonia gas to deposit in the porous carbon matrix, thus obtaining the first nitrogen-doped silicon-carbon composite material.

[0134] The second step involves introducing a mixture of silicon tetrachloride gas and nitrogen gas with a flow ratio of 10:35 into a vapor deposition furnace at 450°C for 80 minutes. This allows the silicon tetrachloride gas to deposit in the first nitrogen-doped silicon-carbon composite material, resulting in the second nitrogen-doped silicon-carbon composite material.

[0135] The third step is to repeat the first and second steps four times.

[0136] The fourth step involves passing through a nitrogen-doped silicon-carbon composite material in a nitrogen atmosphere for 1.5 hours, using a mixture of nitrogen and methane. The nitrogen to methane flow ratio is 35:5.

[0137] The fifth step involves introducing methane into a vapor deposition furnace under an ammonia atmosphere and performing vapor deposition on 1 kg of passivated silicon-carbon composite material at 400°C for 160 min. This process forms a nitrogen-doped carbon coating layer on the surface of the passivated silicon-carbon composite material, thereby obtaining the negative electrode material. The flow rate of methane is 50 L / min, and the flow rate of ammonia is 15 L / min.

[0138] Comparative Example 1

[0139] The first step involves placing 5 kg of porous carbon matrix in a vapor deposition furnace under a nitrogen atmosphere and heating the furnace to 500°C. Then, a mixture of silane and nitrogen is introduced into the vapor deposition furnace at a flow rate ratio of 33:35 and the gas is continuously introduced for 20 minutes, allowing silane to be deposited in the porous carbon matrix, thus obtaining the first nitrogen-free silicon-carbon composite material.

[0140] The second step involves introducing a mixture of silane and nitrogen at a flow rate ratio of 33:35 into a vapor deposition furnace at 500°C for 20 minutes, allowing silane to be deposited in the first nitrogen-free silicon-carbon composite material to obtain the second nitrogen-free silicon-carbon composite material.

[0141] The third step is to repeat the first and second steps twice.

[0142] The fourth step involves passing through a nitrogen- and acetylene mixture in a nitrogen atmosphere into a vapor deposition furnace for 100 minutes to passivate the second nitrogen-free silicon-carbon composite material, resulting in a passivated silicon-carbon composite material. The flow ratio of nitrogen to acetylene is 35:4.

[0143] The remaining steps and testing process are the same as in Example 1.

[0144] Comparative Example 2

[0145] Steps one through six are the same as in Example 1.

[0146] Step 7: Place 1 kg of powder in a carbonization furnace, heat the furnace to 550°C at a heating rate of 5°C / min, and hold for 4 hours to obtain the negative electrode material.

[0147] The testing process is the same as in Example 1.

[0148] Comparative Example 3

[0149] The first step involves placing 5 kg of porous carbon matrix in a vapor deposition furnace under a nitrogen atmosphere and heating the furnace to 500°C. Then, a mixture of silane and nitrogen is introduced into the vapor deposition furnace at a flow rate ratio of 33:35 and the gas is continuously introduced for 20 minutes, allowing silane to be deposited in the porous carbon matrix, thus obtaining the first nitrogen-free silicon-carbon composite material.

[0150] The second step involves introducing a mixture of silane and nitrogen at a flow rate ratio of 33:35 into a vapor deposition furnace at 500°C for 20 minutes, allowing silane to be deposited in the first nitrogen-free silicon-carbon composite material to obtain the second nitrogen-free silicon-carbon composite material.

[0151] The third step is to repeat the first and second steps twice.

[0152] The fourth step involves passing through a nitrogen-doped silicon-carbon composite material in a nitrogen atmosphere for 100 minutes, using a mixture of nitrogen and acetylene. The nitrogen to acetylene flow rate ratio is 35:4.

[0153] The fifth step involves stirring the passivated silicon-carbon composite material and phenolic resin in anhydrous ethanol at a mass ratio of 10:1 for 4 hours to ensure thorough mixing and obtain a mixture.

[0154] The sixth step is to spray-dry the mixture to obtain powder. The spray-drying conditions are: temperature 150℃ and pressure 3MPa.

[0155] Step 7: Place 1 kg of powder in a carbonization furnace, heat the furnace to 550°C at a heating rate of 5°C / min, and hold for 4 hours to obtain the negative electrode material.

[0156] The testing process is the same as in Example 1.

[0157] Comparative Example 4

[0158] The first and second steps are the same as in Example 1.

[0159] The third step involves passing through a nitrogen- and acetylene mixture in a nitrogen atmosphere into a vapor deposition furnace for 100 minutes to passivate the second nitrogen-doped silicon-carbon composite material, resulting in a passivated silicon-carbon composite material. The flow ratio of nitrogen to acetylene is 35:4.

[0160] The fourth step involves stirring the passivated silicon-carbon composite material and phenolic resin in anhydrous ethanol at a mass ratio of 10:1 for 4 hours to ensure thorough mixing and obtain a mixture.

[0161] The fifth step is to spray dry the mixture to obtain powder. The spray drying conditions are a temperature of 150℃ and a pressure of 3MPa.

[0162] Step 6: In an ammonia atmosphere, 1 kg of powder is placed in a carbonization furnace, and the furnace is heated to 550°C at a heating rate of 5°C / min and held for 4 hours to obtain the negative electrode material. The ammonia flow rate is 5 L / min.

[0163] The testing process is the same as in Example 1.

[0164] Table 1 shows the electrochemical test results of the negative electrode materials of Examples 1-6 and Comparative Examples 1-4.

[0165] Table 1

[0166] As can be seen from the data in Table 1, the coin cell assembled with the negative electrode material prepared by the method of this invention exhibits significantly better cycle capacity retention, first-cycle expansion rate, and conductivity after 200 cycles compared to Comparative Examples 1-4. This is because the first nitrogen-doped silicon-carbon composite material formed by the co-deposition of silicon and nitrogen sources contains Si-N bonds. The formation of Si-N bonds enhances the conductivity of the silicon-carbon composite material, suppresses silicon volume expansion, and thus improves the material's stability. Therefore, this negative electrode material has a higher cycle capacity retention rate. Furthermore, nitrogen doping maintains the electrochemical performance of the silicon-carbon composite material while improving its conductivity. The nitrogen in the nitrogen-doped carbon coating layer and the nitrogen in the internal Si-N bonds strengthen the connection between the core layer and the outside, effectively constructing a conductive network, resulting in better conductivity of the negative electrode material and effectively improving the electron transport speed of silicon. The nitrogen-doped carbon coating layer can effectively buffer the pressure generated by the internal silicon expansion and can recover to its original shape, effectively solving the problem of high silicon material expansion. Therefore, the first-cycle expansion rate of the negative electrode material of this application is relatively low. Furthermore, by repeating steps one and two multiple times, the Si-N bond content can be adjusted. While enhancing conductivity, the Si-N bonds can also isolate silicon particles, reduce the first-cycle expansion rate, and give it better cycle stability.

[0167] Using the Unicube elemental analyzer in CHNS analysis mode, 3 mg of the negative electrode material samples prepared in Example 1 and Comparative Examples 1-3 were taken to analyze the nitrogen content. The specific conditions were as follows: the pressure of helium and oxygen (gas purity greater than 99.99%) was 1200 mbar, the combustion tube temperature was set to 1150℃, the reduction tube temperature was set to 850℃, the helium flow rate was 200 mL / min, the oxygen flow rate was 15 mL / min, a thermal conductivity detector (TCD) was used, the detector temperature was 65℃, and after the detector was turned on, it was stabilized for 45-60 min. After the baseline stabilized (when there was no sample input, the analyzer reading or signal reached a stable and repeatable state), the test could begin.

[0168] Test Results: The nitrogen content of the negative electrode material in Example 1 was 2.33%. The nitrogen content of the negative electrode material in Comparative Example 1 was 0.83%, in Comparative Example 2 it was 1.34%, and in Comparative Example 3 it was 0.01%. Therefore, nitrogen doping was successfully performed in the carbon coating layer of Example 1 of this application. It should be noted that although nitrogen doping was not performed throughout the entire process in Comparative Example 3, there may be a small amount of nitrogen impurities in the porous carbon matrix or errors during the testing process, resulting in the detection of trace amounts of nitrogen.

[0169] 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 method for preparing a negative electrode material, characterized in that, The preparation method includes: Step 1: In an inert atmosphere, a mixture of a first silicon source gas, a nitrogen source gas, and a first protective gas is introduced into a vapor deposition furnace, so that the first silicon source gas and the nitrogen source gas are vapor deposited in a porous carbon matrix to obtain a first nitrogen-doped silicon-carbon composite material. Step 2: The mixture of the second silicon source gas and the second protective gas is introduced into the vapor deposition furnace, so that the second silicon source gas is deposited in the first nitrogen-doped silicon-carbon composite material to obtain the second nitrogen-doped silicon-carbon composite material. Step 3: Repeat steps 1 and 2 several times; Step 4: Under an inert atmosphere, a mixture of the third protective gas and the carbon source gas is introduced into the vapor deposition furnace to passivate the second nitrogen-doped silicon-carbon composite material, thereby obtaining a passivated silicon-carbon composite material. Step 5: The passivated silicon-carbon composite material is coated with nitrogen-containing carbon to form a nitrogen-doped carbon coating layer, thereby obtaining the negative electrode material; in the negative electrode material, a conductive network is constructed through the interconnection of nitrogen in the carbon coating layer and nitrogen in the silicon-carbon composite material inside the carbon coating layer.

2. The preparation method according to claim 1, characterized in that, The process of applying nitrogen-containing carbon coating to the passivated silicon-carbon composite material specifically includes: Under a nitrogen-containing atmosphere, a carbon source gas is introduced into the vapor deposition furnace to perform vapor deposition on the passivated silicon-carbon composite material surface; Alternatively, the passivated silicon-carbon composite material is mixed evenly with a solid carbon source in an organic solvent, and then spray-dried to obtain powder. The powder is then placed in a carbonization furnace and carbonized under a nitrogen-containing atmosphere. The carbon source gas includes one or more of acetylene, ethylene, propylene, methane, and carbon dioxide; the solid carbon source includes one or more of phenolic resin, epoxy resin, and melamine resin; the carbonization treatment conditions are: temperature 400℃-1000℃, time 2 hours-10 hours; the nitrogen-containing atmosphere includes one or more of ammonia, nitric oxide, nitrogen dioxide, and dinitrogen tetroxide.

3. The preparation method according to claim 1, characterized in that, The porous carbon matrix has a particle size D50 of 3μm-20μm, a pore size of 1nm-4nm, and a micropore ratio of 10%-100%.

4. The preparation method according to claim 1, characterized in that, The first silicon source gas includes one or more of the following: silane, silane, chlorosilane, trichlorosilane, and silicon tetrachloride; the nitrogen source gas is one or more of ammonia, nitric oxide, nitrogen dioxide, and dinitrogen tetroxide; the flow rate ratio of the first silicon source gas, the nitrogen source gas, and the first protective gas is 33:[2-8]:

35.

5. The preparation method according to claim 1, characterized in that, In step 1, the conditions for vapor deposition are: temperature 300℃-700℃, time 10min-160min.

6. The preparation method according to claim 1, characterized in that, The second silicon source gas includes one or more of the following: silane, silane, chlorosilane, trichlorosilane, and silicon tetrachloride; the flow rate ratio of the second silicon source gas to the second protective gas is [2-33]:

35.

7. The preparation method according to claim 1, characterized in that, In step 4, the carbon source gas includes one or more of acetylene, methane, and propylene.

8. The preparation method according to claim 1, characterized in that, In step 2, the deposition conditions are: temperature 300℃-700℃, time 10min-160min; in step 4, the passivation conditions are: temperature 300℃-700℃, time 1 hour-3 hours.

9. A negative electrode material, characterized in that, The negative electrode material is prepared by any one of the preparation methods described in claims 1-8.

10. A negative electrode material, characterized in that, The negative electrode material has a core-shell structure, including a core and an outer shell; The core is a passivated silicon-carbon composite material, which is nitrogen-doped. The outer shell is a carbon coating layer doped with nitrogen. In the negative electrode material, the nitrogen-doped structure in the outer shell and the nitrogen-containing structure in the core form an electronic coupling to construct a conductive network; preferably, the conductive network is a three-dimensional conductive network.

11. The negative electrode material according to claim 10, characterized in that, The porous carbon matrix in the negative electrode material has a particle size D50 of 3μm-20μm and a pore size of 1nm-4nm, and the proportion of micropores in the porous carbon matrix is ​​between 10% and 100%.

12. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode material as described in claim 9 or any one of claims 10-11.

13. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 12.

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