Lithium-ion battery negative electrode material and preparation method therefor

Abstract

The present application relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery negative electrode material and a preparation method therefor. The negative electrode material comprises, from inside to outside, a porous substrate, a conductive carbon material, and a coating layer. The porous substrate is made of silicon, a silicon alloy, or a silicon oxide. The porous substrate comprises a plurality of pores, and at least some of the pores are opened on the surface of the porous substrate. A portion of the conductive carbon material is located on the surface of the porous substrate, and the other portion of the conductive carbon material is located in the pores of the porous substrate. The coating layer has ionic conductivity and / or electronic conductivity, and encapsulates an entirety composed of the porous substrate and the conductive carbon material. On the basis of the lithium-ion battery negative electrode material provided in the present application, when a silicon material, a silicon alloy material and a silicon-oxygen material are used as negative electrode materials, damage to the material caused by volume expansion of silicon can be reduced, and the conductivity of the negative electrode material can also be improved, thereby improving the electrochemical performance of the silicon-based negative electrode material.

Description

A negative electrode material for lithium-ion batteries and its preparation method

[0001] This application claims priority to Chinese Patent Application No. 202411686703.4, filed on November 22, 2024, entitled "A negative electrode material for a lithium-ion battery and a method for preparing the same," the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium-ion battery technology, and in particular to a negative electrode material for lithium-ion batteries and a method for preparing the same. Background Technology

[0003] With the rapid development of society, new energy vehicles, power tools, and electronic products require lithium-ion batteries to have higher energy density. The capacity of traditional graphite anode materials has approached the theoretical capacity and is difficult to meet the high energy density requirements. Silicon anode materials have a theoretical capacity of up to 4200 mAh / g and have advantages such as abundant reserves and a discharge platform similar to graphite. They are considered to be the next generation of lithium-ion battery anode materials with great development potential.

[0004] However, during charging and discharging, silicon exhibits a volume expansion of >300%. This enormous stress not only causes material particles to break and accelerates lithium-ion consumption due to SEI film reconstruction, but also leads to material pulverization, severely affecting its capacity and electrochemical performance. Furthermore, silicon anode materials suffer from low conductivity, which limits the practical application of silicon as anode material for lithium-ion batteries. Summary of the Invention

[0005] This application provides a negative electrode material for lithium-ion batteries and a method for preparing the same, in order to improve the technical problems of volume expansion and poor conductivity of silicon-based negative electrode materials, thereby improving the electrochemical performance of lithium-ion batteries.

[0006] The technical solution of this application is as follows:

[0007] In a first aspect, this application provides a negative electrode material for a lithium-ion battery, the negative electrode material comprising, from the inside out, a porous matrix, a conductive carbon material, and a coating layer.

[0008] The porous matrix is ​​made of silicon, silicon alloy, or silicon oxide. The porous matrix comprises multiple pores, at least some of which open onto the surface of the porous matrix.

[0009] Some conductive carbon material is located on the surface of the porous matrix, while some conductive carbon material is located within the pores of the porous matrix.

[0010] The coating layer has ionic and / or electronic conductivity and encapsulates the porous matrix and conductive carbon material as a whole.

[0011] Based on the lithium-ion battery anode material provided in the first aspect, the pores of the porous matrix provide space for the volume expansion of silicon during charging and discharging. The conductive carbon material embedded in the pores and coated on the surface of the porous matrix enhances the conductivity inside and outside the silicon particles. The conductive carbon material layer on the surface also plays a role in buffering the volume expansion of silicon to a certain extent. The outermost layer of the anode material can trap the conductive carbon material on the surface of the porous matrix, effectively preventing the conductive carbon material from falling off, further suppressing the volume expansion of silicon, and improving its electrochemical performance.

[0012] Therefore, the lithium-ion battery anode material provided in this application can reduce the damage caused by silicon volume expansion when silicon, silicon alloy, or silicon-oxygen materials are used as anode materials, and can also improve the conductivity of the anode material, thereby improving the electrochemical performance of silicon-based anode materials.

[0013] In one possible design, the coating layer is in the form of a membrane or a mesh.

[0014] Based on the negative electrode material of the lithium-ion battery provided by this embodiment, when the coating layer is in the form of a film or a mesh, the coating layer has a relatively good coating force, thus playing a better role in preventing the conductive material from falling off.

[0015] In one possible design, the coating layer is in the form of a film, and the material of the coating layer is cyclized polyacrylonitrile. Cyclic polyacrylonitrile has good electrical conductivity, which can both prevent the conductive carbon material from falling off and enhance the conductivity of the negative electrode material.

[0016] In one possible design, the porous matrix is ​​in the micrometer range, the pore diameter is greater than 100 nanometers and less than 300 nanometers, and the diameter of the conductive carbon material is less than 100 nanometers.

[0017] The negative electrode material for lithium-ion batteries provided by this embodiment has a porous substrate with micron-level dimensions, pore diameters greater than 100 nanometers and less than 300 nanometers, and a conductive carbon material diameter less than 100 nanometers. This allows the porous substrate to possess a certain degree of structural stability, while also enabling the insertion of conductive carbon material into the pores, thereby improving the conductivity of the porous substrate from within. Furthermore, the gaps between the pores and the conductive carbon material not only mitigate the volume expansion of silicon but also facilitate the wetting of the porous substrate by the electrolyte.

[0018] In one possible design, the conductive carbon material is carbon nanospheres.

[0019] Based on the negative electrode material of the lithium-ion battery provided by this embodiment, carbon nanospheres have the characteristics of good conductivity, easy availability of raw materials, and low calcination temperature. Thus, it is easy to improve the conductivity of the negative electrode material and the cost is low.

[0020] Secondly, based on the same inventive concept, this application also provides a method for preparing a lithium-ion battery negative electrode material, comprising the following steps:

[0021] A porous matrix is ​​provided. The porous matrix includes a plurality of pores, at least some of which open onto the surface of the porous matrix.

[0022] Conductive carbon material is formed on the surface and in the pores of a porous matrix.

[0023] A coating layer is wrapped around the surface of the integral structure formed by the porous matrix and the conductive carbon material, and the coating layer has ionic conductivity and / or electronic conductivity.

[0024] The lithium-ion battery anode material prepared by the method provided in the second aspect can be used to produce the lithium-ion battery anode material of the first aspect, thus possessing the beneficial effects of the lithium-ion battery anode material provided in the first aspect, which will not be elaborated here.

[0025] In one possible design, the preparation of the conductive carbon material includes the following steps:

[0026] The carbon source, structure directing agent, and dispersant are dissolved to form a solution.

[0027] A porous matrix is ​​added to the solution, and the solution is distributed in the pores and surface of the porous matrix.

[0028] The carbon source in the solution undergoes a carbonization reaction under the action of a structure-directing agent, generating monodisperse carbon spheres.

[0029] By controlling the calcination conditions, carbon balls are carbonized to form conductive carbon materials.

[0030] Based on the method for preparing lithium-ion battery anode materials provided in this embodiment, during the preparation of conductive carbon materials, due to the fluidity of the solution, the solution can easily penetrate deep into the pores of the porous matrix. In this way, conductive carbon materials can be formed deep into the pores of the porous matrix, thereby helping to improve the conductivity of the porous matrix from the inside out.

[0031] In one possible design, the carbon source is one of glucose, maltose, sucrose, and soluble starch.

[0032] The structure directing agent is one of polyquaternary ammonium salt, polymethacrylamide propyltrimethylammonium chloride, and polydiallyl dimethylammonium chloride.

[0033] In one possible design, the porous substrate is a porous silicon substrate, and the formation of the porous silicon substrate includes the following steps:

[0034] Micron-sized silicon powder was treated with a mixed solution of AgNO3 and HF to obtain silver-deposited silicon particles.

[0035] A porous silicon matrix was obtained by treating silicon particles with Ag particles on their surface with a mixed solution of H2O2 and HF.

[0036] Based on the method for preparing lithium-ion battery anode materials provided in this embodiment, pores are created on silicon powder using AgNO3, HF, and H2O2. This method is simple and easy to implement.

[0037] In one possible design, the coating layer is cyclized polyacrylonitrile. The preparation of the coating layer includes the following steps:

[0038] Polyacrylonitrile and a porous matrix containing conductive carbon material are placed in N,N-dimethylformamide solvent, heated and stirred to ensure uniform mixing of polyacrylonitrile and conductive carbon material in the solvent.

[0039] Subsequently, the mixed solution is post-processed to obtain a mixed powder. Under the protection of an inert gas, the mixed powder is calcined to cause polyacrylonitrile to cyclize, thereby encapsulating the integral structure formed by the conductive carbon material and the porous matrix.

[0040] Based on the method for preparing lithium-ion battery anode material provided in this embodiment, the polyacrylonitrile prepared by the above steps is distributed relatively evenly on the surface of the integral structure formed by porous silicon and conductive carbon material, thus effectively preventing the conductive carbon material from falling off.

[0041] The above description is merely an overview of the technical solutions of the embodiments of this application. In order to better understand the technical means of the embodiments of this application and to implement them in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the embodiments of this application more obvious and understandable, specific implementation methods of this application are described below. Attached Figure Description

[0042] Figure 1 is a comparison of the capacity retention of the negative electrode material prepared in Example 1 and the negative electrode material prepared in Comparative Example 1 when they are assembled into CR2025 type coin cells after 50 cycles.

[0043] Figure 2 shows the EIS comparison diagram of the negative electrode material prepared in Example 1 and the negative electrode material prepared in Comparative Example 1 after being assembled into CR2025 type coin cells and charged and discharged for 2 weeks. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0045] The embodiments given in this application can be combined with each other without contradiction. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0046] There are no particular restrictions on the source of any raw materials used in this application; they may be purchased from the market or prepared in accordance with conventional methods known to those skilled in the art.

[0047] All raw materials used in this application, unless otherwise specified in their parameters, are commonly used in the art and can be purchased from commercial sources or prepared by conventional methods by those skilled in the art based on the name of the raw material and its corresponding use.

[0048] The processes used in this application are all commonly used abbreviations in the field. The specific steps and conventional parameters of each abbreviation are clear and unambiguous in their respective fields, and those skilled in the art can implement them using conventional methods based on the abbreviations.

[0049] Unless otherwise defined, all terms used herein have the meanings commonly understood by those skilled in the art, unless otherwise specified.

[0050] The following provides a detailed description of this application.

[0051] As mentioned in the background art, silicon suffers from volume expansion and poor conductivity during the charging and discharging process of lithium-ion batteries, which affects the electrochemical performance of silicon.

[0052] Based on this, this application provides a negative electrode material for a lithium-ion battery, which includes, from the inside out, a porous matrix, a conductive carbon material, and a coating layer.

[0053] The porous matrix is ​​made of silicon, silicon alloy, or silicon oxide. The porous matrix comprises multiple pores, at least some of which open onto the surface of the porous matrix.

[0054] Part of the conductive carbon material is located on the surface of the porous matrix, and another part is located in the pores of the porous matrix.

[0055] The coating layer has ionic and / or electronic conductivity and encapsulates the porous matrix and conductive carbon material as a whole.

[0056] The silicon, silicon alloys, and silicon oxides mentioned in this application are all used in the negative electrode field of lithium-ion batteries. Silicon alloys are composite materials formed by alloying silicon with one or more metallic elements (such as tin, aluminum, nickel, cobalt, etc.). Silicon oxide (SiOx) refers to compounds formed by silicon and oxygen in different proportions, where the value of x is typically between 1 and 2. Common silicon-oxygen materials include SiO and SiO2. Among these, silicon exhibits the greatest volume expansion during charge and discharge, while silicon alloys or silicon oxides show relatively smaller volume expansion during the same process.

[0057] In some embodiments of this application, the pores include pores opening onto the surface of the porous matrix. In other embodiments of this application, the pores of the porous matrix also include pores within the porous matrix.

[0058] The negative electrode material provided in this application includes a porous matrix. The pores of the porous matrix provide a buffer space for the volume expansion of the negative electrode material during charging and discharging, which can reduce the stress caused by volume expansion and improve the structural stability of the negative electrode material.

[0059] The negative electrode material of this application also includes conductive carbon material, with some conductive carbon material located inside the pores and another part located on the surface of the porous matrix. Thus, the conductive carbon material not only exists on the surface of the porous matrix but also penetrates deep into the interior of the porous matrix. This structure helps to improve the conductivity of the negative electrode material from the inside out.

[0060] The negative electrode material of this application also includes a coating layer, which encapsulates the porous matrix and conductive carbon material to prevent the conductive carbon material from detaching during charging and discharging. Furthermore, the coating layer possesses ionic and / or electronic conductivity, and to a certain extent, can form a conductive network on the surface of the integrated structure composed of the porous matrix and conductive carbon material, further improving the conductivity of the negative electrode material.

[0061] As can be seen from the above, the lithium-ion battery anode material provided in this application can reduce the damage caused by silicon volume expansion when silicon, silicon alloy, or silicon-oxygen materials are used as anode materials, and can also improve the conductivity of the anode material, thereby improving the electrochemical performance of silicon-based anode materials.

[0062] In some embodiments of this application, the coating layer is in the form of a film or a mesh. Specifically, a major function of the coating layer in this application is to prevent the conductive carbon material from falling off. When the coating layer is in the form of a film or a mesh, it has better coating force, thus effectively preventing the conductive material from falling off.

[0063] It should be noted that the thickness of the coating layer in the application must be appropriate. Generally speaking, if the coating layer is too thin, it will lead to incomplete coating and will not effectively prevent the detachment of conductive carbon material particles. However, if the coating layer is too thick, it will lead to a longer ion transport path and increased impedance. Therefore, the coating amount needs to be controlled during the preparation of the negative electrode material.

[0064] In some embodiments of this application, the coating layer is in the form of a film, and the material of the coating layer is cyclized polyacrylonitrile. Cyclic polyacrylonitrile has good electrical conductivity, which can both prevent the conductive carbon material from falling off and enhance the electrical conductivity of the negative electrode material.

[0065] It should be noted that using cyclized polyacrylonitrile as the coating material is only one embodiment of this application. In other embodiments of this application, other materials may also be selected, such as graphene or carbon nanotubes.

[0066] In some embodiments of this application, the porous matrix has a size in the micrometer range, the pore diameter is greater than 100 nanometers and less than 300 nanometers, and the diameter of the conductive carbon material is less than 100 nanometers.

[0067] Specifically, the size of the porous substrate cannot be too large or too small. If the size of the porous substrate is too small, it is not convenient to create pores in the porous substrate based on existing processes. Or, after creating pores in the porous substrate, the structure of the porous substrate itself is prone to collapse. If the size of the porous substrate is too large, it will also affect the preparation of the negative electrode sheet. Taking all factors into consideration, the size of the porous substrate in this application is at the micrometer level.

[0068] For reasons similar to those mentioned above, the size of the pores must not affect the structural stability of the porous matrix, and must be able to accommodate conductive carbon materials. Therefore, taking all factors into consideration, the pore size of this application is greater than 100 nanometers and less than 300 nanometers.

[0069] In this application, the diameter of the conductive carbon material is less than 100 nanometers, thus creating a certain gap between the conductive carbon material and the pores. This gap serves two purposes:

[0070] Firstly, during the charging and discharging process of lithium-ion batteries, the space between the conductive carbon material and the pores can provide a buffer space for the volume expansion of silicon, reducing stress in the negative electrode material and preventing SEI film tearing and negative electrode material pulverization. Secondly, the gaps can serve as channels for the lithium-ion battery electrolyte, facilitating the wetting of the porous substrate by the electrolyte.

[0071] In some embodiments of this application, the conductive carbon material is carbon nanospheres. Carbon nanospheres were chosen because they possess excellent conductivity, are readily available from raw materials, and require a relatively low calcination temperature. It should be noted that using carbon nanospheres as the conductive material is only one embodiment of this application; in other embodiments, graphene nanospheres or carbon nanotube nanospheres that meet the particle size requirements may also be used as the conductive carbon material.

[0072] Based on the same inventive concept, the present invention also provides a method for preparing a lithium-ion battery anode material, comprising the following steps:

[0073] A porous matrix is ​​provided. The porous matrix includes a plurality of pores, at least some of which open onto the surface of the porous matrix.

[0074] Conductive carbon material is formed on the surface and in the pores of a porous matrix.

[0075] A coating layer is wrapped around the surface of the integral structure formed by the porous matrix and the conductive carbon material, and the coating layer has ionic conductivity and / or electronic conductivity.

[0076] The method for preparing lithium-ion battery anode materials provided herein can produce lithium-ion battery anode materials in the first aspect, thus possessing the beneficial effects of lithium-ion battery anode materials, which will not be elaborated here.

[0077] In some embodiments of this application, the preparation of the conductive carbon material includes the following steps:

[0078] S1) Dissolve the carbon source, structure directing agent, and dispersant to form a solution.

[0079] S2) A porous matrix is ​​added to the solution, and the solution is distributed in the pores and surface of the porous matrix.

[0080] S3) causes the carbon source in the solution to undergo a carbonization reaction under the action of the structure directing agent, generating monodisperse carbon spheres.

[0081] S4) Control the calcination conditions to carbonize the carbon balls and form conductive carbon materials.

[0082] As can be seen from step S1), in preparing the conductive carbon material, this application first dissolves the reactants, structure-directing agent, and dispersant to form a solution. The role of the dispersant and structure-directing agent is to guide and control the formation of uniform and size-controllable carbon spheres from the reactants during subsequent reactions. In some embodiments of this application, the structure-directing agent and the dispersant can be the same substance.

[0083] In step S2), a porous matrix is ​​added to the solution. Due to the fluidity of the solution, it can enter the pores of the porous matrix, thus creating a solution of the same concentration in both the pores and on the surface of the porous matrix.

[0084] As can be seen from the above steps, during the preparation of conductive carbon materials, due to the fluidity of the solution, the solution can easily penetrate deep into the pores of the porous matrix. In this way, conductive carbon materials can be formed deep into the pores of the porous matrix, which in turn helps to improve the conductivity of the porous matrix from the inside out.

[0085] It should be noted that, in this application, the size of the conductive carbon material can be controlled by the amount of structure-directing agent added and the calcination conditions.

[0086] In some embodiments of this application, the carbon source is one of glucose, maltose, sucrose, and soluble starch.

[0087] The structure directing agent is one of polyquaternary ammonium salt, polymethacrylamide propyltrimethylammonium chloride, and polydiallyl dimethylammonium chloride.

[0088] In some embodiments of this application, the porous substrate is a porous silicon substrate, and the formation of the porous silicon substrate includes the following steps:

[0089] Micron-sized silicon powder was treated with a mixed solution of AgNO3 and HF to obtain silver-deposited silicon particles.

[0090] A porous silicon matrix was obtained by treating silicon particles with Ag particles on their surface with a mixed solution of H2O2 and HF.

[0091] The chemical reactions that occur during the process of obtaining silver-deposited silicon particles are as follows:

[0092] Si(s)+4AgNO3+6HF→H2SiF6+4Ag+4HNO3.

[0093] The chemical reactions that occur between H2O2 and HF and silicon particles are as follows:

[0094] Si+n / 2H2O2+6HF→nH2O+H2SiF6+(4-n) / 2H2↑.

[0095] During the formation of pores on the surface of micron-sized silicon powder, Ag mainly plays a catalytic and positioning role. That is, at the locations where Ag particles are attached to the surface of silicon particles, silicon easily reacts with H2O2, and the resulting product reacts with HF to generate soluble H2SiF6, thus creating corresponding pores in the silicon powder and obtaining a porous silicon matrix.

[0096] It should be noted that when forming a porous silicon substrate using the above method, the size of Ag particle aggregation can be controlled by adjusting the concentration of AgNO3, and the C concentration can be adjusted accordingly. HF / (C H2O2 +C HF The molar concentration ratio controls the reaction rate and etching direction, and the pore size is controlled by adjusting these two factors.

[0097] It should be noted that the porous silicon substrate preparation method provided in this application is only one method for preparing porous silicon. The porous silicon substrate mentioned in this application can also be prepared by other existing methods, such as anodic oxidation, laser etching, and photolithography. The porous silicon substrate of this application can also be obtained by purchase.

[0098] In one embodiment of this application, the coating layer is cyclized polyacrylonitrile. The preparation of the coating layer includes the following steps:

[0099] Polyacrylonitrile and a porous matrix containing conductive carbon material are placed in N,N-dimethylformamide solvent, heated and stirred to ensure uniform mixing of polyacrylonitrile and conductive carbon material in the solvent.

[0100] Subsequently, the mixed solution is post-treated to obtain a mixed powder. Under the protection of an inert gas, the mixed powder is calcined to cause polyacrylonitrile to cyclize and coat the surface of the integral structure formed by the conductive carbon material and the porous matrix.

[0101] The polyacrylonitrile prepared through the above steps is evenly distributed on the surface of the integral structure formed by porous silicon and conductive carbon material, thus effectively preventing the conductive carbon material from falling off.

[0102] It should be noted that this application provides a specific method for preparing the coating layer. Based on the core idea of ​​this application, other materials can also be selected for the coating layer, and different materials will result in different coating methods. After understanding the function of the coating layer in this application, those skilled in the art are able to select suitable coating materials and appropriate coating methods. Therefore, the cyclized polyacrylonitrile mentioned in this application is merely an example and is not intended to limit this application.

[0103] For example, as mentioned before, in addition to cyclized polyacrylonitrile, the coating material can also be other film-like or mesh-like materials, such as graphene or carbon nanotubes.

[0104] For carbon nanotubes, since they are tubular materials, multiple carbon nanotubes coming into contact with each other will form a network structure. Therefore, when using carbon nanotubes as a coating material, it is only necessary to perform a simple physical mixing of the carbon nanotubes with porous silicon containing conductive carbon material.

[0105] For graphene, a uniformly dispersed graphene oxide solution is ultrasonically mixed with a porous silicon matrix containing conductive carbon material, and then dried and sintered at high temperature to obtain a graphene-coated anode material.

[0106] The foregoing has provided a detailed description of the negative electrode material for the lithium-ion battery and a detailed description of the preparation method for the lithium-ion battery. The following specific embodiments verify the effectiveness of this application.

[0107] Example 1:

[0108] 1) Preparation of porous silicon substrate

[0109] 1.1) The micron-sized silicon powder raw material is subjected to ultrasonic and centrifugal cleaning with deionized water and anhydrous ethanol, and then vacuum dried to remove impurities from the silicon powder.

[0110] 1.2) Prepare 200 mL of a mixed solution containing 0.02 mol / L AgNO3 and 2 mol / L HF. Take 2 g of silicon powder treated in step 1.1) and add it to the mixed solution. React for 3 min under rapid stirring. Then wash with deionized water and vacuum dry to obtain Ag-deposited silicon particles.

[0111] 1.3) Prepare 200 mL of a mixed solution containing 0.05 mol / L H2O2 and 0.15 mol / L HF. Add silicon particles with Ag particles on their surface to the above mixed solution, react for 30 min, wash with deionized water, and vacuum dry to obtain a porous silicon matrix, denoted as Si.

[0112] 2) Formation of carbon nanospheres on the surface and in the pores of a porous silicon substrate.

[0113] 2.1) Weigh 10g of glucose and 0.16g of polyquaternium-11 and add them to 50mL of deionized water. Stir and dissolve at room temperature for 30min. Then add 1g of the porous silica matrix prepared in step 1) and continue stirring at room temperature for 2h.

[0114] 2.2) Transfer the mixture obtained in step 2.1) to a Teflon-lined stainless steel reactor (100 ml), hydrothermally treat it at 170 °C for 12 h, and then allow it to cool naturally to room temperature.

[0115] 2.3) The solution after the initial reaction was centrifuged at 11000 rpm / min for 2 h, then washed with deionized water and anhydrous ethanol and dried. Finally, the dried product was carbonized at 700℃ for 30 min under nitrogen protection to obtain a porous silicon sample with pore embedding and surface coating of carbon nanospheres, denoted as Si@C.

[0116] 3) Formation of cyclized polyacrylonitrile coating

[0117] Polyacrylonitrile and Si@C were weighed at a mass ratio of 5:95 and placed in N,N-dimethylformamide solvent. The mixture was then stirred in an oil bath at 80°C for 2 hours. The stirred mixture was then subjected to vacuum drying and grinding. Finally, the powdered mixture was placed in a tube furnace purged with argon gas and calcined at 280°C for 1 hour to obtain a porous Si@C sample coated with cyclized polyacrylonitrile, denoted as Si@C-cPAN.

[0118] Comparative Example 1:

[0119] 1) Preparation of porous silicon substrate

[0120] 1.1) The micron-sized silicon powder raw material is subjected to ultrasonic and centrifugal cleaning with deionized water and anhydrous ethanol, and then vacuum dried to remove impurities from the silicon powder.

[0121] 1.2) Prepare 200 mL of a mixed solution containing 0.02 mol / L AgNO3 and 2 mol / L HF. Take 2 g of silicon powder treated in step 1.1) and add it to the mixed solution. React for 3 min under rapid stirring. Then wash with deionized water and vacuum dry to obtain Ag-deposited silicon particles.

[0122] 1.3) Prepare 200 mL of a mixed solution containing 0.05 mol / L H2O2 and 0.15 mol / L HF. Add silicon particles with Ag particles on their surface to the above mixed solution, react for 30 min, wash with deionized water, and vacuum dry to obtain a porous silicon matrix, denoted as Si.

[0123] Comparative Example 2:

[0124] 1) Preparation of porous silicon substrate

[0125] 1.1) The micron-sized silicon powder raw material is subjected to ultrasonic and centrifugal cleaning with deionized water and anhydrous ethanol, and then vacuum dried to remove impurities from the silicon powder.

[0126] 1.2) Prepare 200 mL of a mixed solution containing 0.02 mol / L AgNO3 and 2 mol / L HF. Take 2 g of silicon powder treated in step 1.1) and add it to the mixed solution. React for 3 min under rapid stirring. Then wash with deionized water and vacuum dry to obtain Ag-deposited silicon particles.

[0127] 1.3) Prepare 200 mL of a mixed solution containing 0.05 mol / L H2O2 and 0.15 mol / L HF. Add silicon particles with Ag particles on their surface to the above mixed solution, react for 30 min, wash with deionized water, and vacuum dry to obtain a porous silicon matrix, denoted as Si.

[0128] 2) Formation of carbon nanospheres on the surface and in the pores of a porous silicon substrate.

[0129] 2.1) Weigh 10g of glucose and 0.16g of polyquaternium-11 and add them to 50mL of deionized water. Stir and dissolve at room temperature for 30min. Then add 1g of the porous silica matrix prepared in step 1) and continue stirring at room temperature for 2h.

[0130] 2.2) Transfer the mixture obtained in step 2.1) to a Teflon-lined stainless steel reactor (100 ml), hydrothermally treat it at 170 °C for 12 h, and then allow it to cool naturally to room temperature.

[0131] 2.3) The solution after the initial reaction was centrifuged at 11000 rpm / min for 2 h, then washed with deionized water and anhydrous ethanol and dried. Finally, the dried product was carbonized at 700℃ for 30 min under nitrogen protection to obtain a porous silicon sample with pore embedding and surface coating of carbon nanospheres, denoted as Si@C.

[0132] Comparative Example 3:

[0133] 1) Preparation of porous silicon substrate

[0134] 1.1) The micron-sized silicon powder raw material is subjected to ultrasonic and centrifugal cleaning with deionized water and anhydrous ethanol, and then vacuum dried to remove impurities from the silicon powder.

[0135] 1.2) Prepare 200 mL of a mixed solution containing 0.02 mol / L AgNO3 and 2 mol / L HF. Take 2 g of silicon powder treated in step 1.1) and add it to the mixed solution. React for 3 min under rapid stirring. Then wash with deionized water and vacuum dry to obtain Ag-deposited silicon particles.

[0136] 1.3) Prepare 200 mL of a mixed solution containing 0.05 mol / L H2O2 and 0.15 mol / L HF. Add silicon particles with Ag particles on their surface to the above mixed solution, react for 30 min, wash with deionized water, and vacuum dry to obtain a porous silicon matrix, denoted as Si.

[0137] 2) Formation of cyclized polyacrylonitrile coating

[0138] Polyacrylonitrile and the porous silicon matrix prepared in step 1) were weighed at a mass ratio of 5:95 and placed in N,N-dimethylformamide solvent. The mixture was then stirred in an oil bath at 80°C for 2 hours. The stirred mixture was then subjected to vacuum drying, grinding and other processes. Finally, the mixture powder was placed in a tube furnace with argon gas and calcined at 280°C for 1 hour to obtain cyclized polyacrylonitrile-coated porous silicon, denoted as Si@cPAN.

[0139] Performance testing: The negative electrode materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were used in conjunction with LiNi. 0.9 Co 0.06 Mn 0.04 The O2 cathode material was assembled into CR2025 type coin cells, and cycle performance and internal resistance tests were conducted. The cycle performance test was carried out under the conditions of 2.8-4.2V, 1C, and 25℃. In the internal resistance test, the EIS test frequency was 0.01-100000Hz, the battery SOC was 100%, and the voltage disturbance was 10mV.

[0140] Test Result Analysis:

[0141] Table 1 is a summary chart of the test data for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0142] Table 1 Summary of Electrochemical Data

[0143] Please refer to Table 1. In the cycle performance test and internal resistance test, Example 1 performed the best, while Comparative Example 1 performed the worst. This shows that setting conductive carbon material and coating layer in the pores and surface of the porous silicon substrate significantly improves the electrochemical performance of the negative electrode material.

[0144] In the cycle performance test and internal resistance test, the effect of Comparative Example 2 was better than that of Comparative Example 1, but not as good as that of Example 1. This shows that although setting conductive carbon material only in the pores and surface of the porous silicon substrate can improve the electrochemical performance of the negative electrode material, the effect will be better after setting the coating layer.

[0145] In the cycle performance test and internal resistance test, the effect of Comparative Example 3 was better than that of Comparative Example 1, but not as good as that of Example 1. This shows that simply setting a coating layer on the surface of the porous silicon substrate can improve the electrochemical performance of the negative electrode material. However, the effect will be better after setting conductive carbon material in the pores and surface of the porous silicon substrate.

[0146] Figure 1 shows a comparison of the capacity retention after 50 cycles of the CR2025 coin cells assembled from the negative electrode materials prepared in Example 1 and Comparative Example 1. The comparison of cycle capacity retention in Figure 1 shows that the lithium-ion battery using the negative electrode material prepared in Example 1 exhibits better cycle performance, maintaining a capacity retention of 89.70% after 50 cycles. In contrast, the lithium-ion battery using the negative electrode material prepared in Comparative Example 1 shows a rapid decline in cycle performance, with a capacity retention of only 56.93% after 50 cycles.

[0147] Figure 2 shows a comparison of the EIS (Electronic Information Performance Index) of the negative electrode materials prepared in Example 1 and Comparative Example 1 after being assembled into CR2025 coin cells and charged and discharged for 2 weeks. The test frequency was 0.01Hz-100000Hz, the voltage was 4.2V, and the voltage perturbation was 10mV. As can be seen from the figure, the second semicircle of Example 1 is significantly smaller than that of Comparative Example 1, indicating that the charge transfer impedance of Example 1 is lower. This shows that the electronic conductivity of the porous silicon substrate is enhanced after the conductive material modification treatment, thereby reducing the lithium-ion transfer impedance of the material.

Claims

1. A negative electrode material for a lithium-ion battery, characterized in that, The negative electrode material, from the inside out, includes a porous matrix, a conductive carbon material, and a coating layer; The porous substrate is made of silicon, silicon alloy, or silicon oxide; the porous substrate includes a plurality of pores, at least some of which open onto the surface of the porous substrate; Some of the conductive carbon material is located on the surface of the porous matrix, and some of the conductive carbon material is located within the pores of the porous matrix; The coating layer has ionic and / or electronic conductivity and encapsulates the porous matrix and the conductive carbon material as a whole.

2. The anode material for a lithium-ion battery according to claim 1, wherein, The coating layer is in the form of a membrane or a mesh.

3. The anode material for lithium ion batteries according to claim 2, characterized in that, The coating layer is in the form of a film, and the material of the coating layer is cyclized polyacrylonitrile.

4. The anode material for lithium ion batteries according to any one of claims 1 to 3, characterized in that, The porous matrix has a size in the micrometer range, the pore diameter is greater than 100 nanometers and less than 300 nanometers, and the diameter of the conductive carbon material is less than 100 nanometers.

5. The anode material for lithium-ion batteries according to claim 4, characterized in that, The conductive carbon material is carbon nanospheres.

6. A method for preparing a lithium ion battery anode material, characterized in that, Includes the following steps: The porous matrix is ​​provided; the porous matrix includes a plurality of pores, at least some of which open onto the surface of the porous matrix. The conductive carbon material is formed on the surface and in the pores of the porous matrix; The coating layer is wrapped around the surface of the integral structure formed by the porous matrix and the conductive carbon material, and the coating layer has ionic conductivity and / or electronic conductivity.

7. The method for preparing the lithium-ion battery negative electrode material according to claim 6, characterized in that, The preparation of the conductive carbon material includes the following steps: The carbon source, structure directing agent, and dispersant are dissolved to form a solution; A porous matrix is ​​added to the solution, and the solution is distributed in the pores and surface of the porous matrix; The carbon source in the solution undergoes a carbonization reaction under the action of a structure-directing agent to generate monodisperse carbon spheres; The carbon balls are carbonized by controlling the calcination conditions to form the conductive carbon material.

8. The method for preparing the lithium-ion battery anode material according to claim 7, characterized in that, The carbon source is one of glucose, maltose, sucrose, and soluble starch; The structure-directing agent is one of polyquaternary ammonium salt, polymethacrylamide propyltrimethylammonium chloride, and polydiallyl dimethylammonium chloride.

9. The method for preparing the lithium-ion battery anode material according to claim 6, characterized in that, The porous substrate is a porous silicon substrate, and the formation of the porous silicon substrate includes the following steps: Micron-sized silicon powder was treated with a mixed solution of AgNO3 and HF to obtain silver-deposited silicon particles. The porous silicon matrix is ​​obtained by treating silicon particles with Ag particles on their surface with a mixed solution of H2O2 and HF.

10. The method for preparing the lithium-ion battery anode material according to claim 7, characterized in that, The coating layer is cyclized polyacrylonitrile; the preparation of the coating layer includes the following steps: Polyacrylonitrile and a porous matrix containing the conductive carbon material are placed in an N,N-dimethylformamide solvent, heated and stirred to ensure that the polyacrylonitrile and the conductive carbon material are mixed evenly in the solvent. Subsequently, the mixed solution is post-processed to obtain a mixed powder. Under the protection of an inert gas, the mixed powder is calcined to cause polyacrylonitrile to cyclize, thereby encapsulating the integral structure formed by the conductive carbon material and the porous matrix.

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