Hollow cage-shaped silicon-carbon composite negative electrode material and preparation method thereof

Abstract

This application discloses a hollow cage-like silicon-carbon composite anode material and its preparation method. The hollow cage-like silicon-carbon composite anode material has an internally hollow cage-like structure. The cage-like structure is formed by the self-assembly of a 3D network structure, which includes a framework and multiple carbon spheres. The framework includes silicon material, specifically one-dimensional linear silicon material, and the multiple carbon spheres are attached to the silicon material. Compared to existing porous carbon frameworks, the hollow cage-like silicon-carbon composite anode material disclosed in this application not only has higher capacity and conductivity but also possesses the flexibility lacking in porous carbon. When other anode materials, especially silicon-based anode materials, are loaded into the hollow structure, the cage-like structure can provide more expansion space for the internal anode material, thereby more effectively improving the cycle stability of the anode material.

Description

Technical Field

[0001] This application relates to the field of anode material technology, and in particular to a hollow cage-like silicon-carbon composite anode material and its preparation method. Background Technology

[0002] Porous carbon exhibits good electrical conductivity, but its theoretical specific capacity needs further improvement. Commonly used methods for preparing porous carbon include physical methods, chemical methods, and template methods.

[0003] Generally, in the preparation of porous carbon using physical and chemical methods, micropores (pore size less than 2 nm) are the most common, followed by mesopores (pore size 2 nm-50 nm), and macropores (pore size greater than 50 nm) are the least common. Physical methods typically use gases such as CO2 and water vapor as activators, which interact with the porous carbon precursor at high temperatures to achieve pore formation. This method has the advantages of being green, environmentally friendly, and highly sustainable. However, the pore-forming efficiency of physical methods is generally low, which limits its application. Chemical methods typically use alkaline activators such as KOH and K2CO3, or acidic activators such as ZnCl2 and H3PO4. During high-temperature carbonization, alkaline activators have a strong etching effect on the carbon material, causing the carbon source to vaporize into carbon dioxide or carbon monoxide, promoting the formation of a porous structure in the carbon material, usually containing abundant micropores and defects. When this type of porous carbon material is used in silicon-carbon anodes, it exhibits a low initial coulombic efficiency. Similarly, acidic activators promote the dehydration of the precursor, achieving the effect of pore formation. In addition, alkaline activators have a strong corrosive effect on production equipment, requiring high-quality equipment and limiting their application; acidic activators not only have low pore-forming efficiency, limiting their application, but also ZnCl2 has a polluting and damaging effect on the environment, making them unsuitable for mass production.

[0004] The template method is commonly used to fabricate porous carbon materials with ultra-large pore sizes, where the size of the template determines the macropore diameter of the porous carbon. Combined with physical or chemical activation, the template method can prepare hierarchical porous structures. However, the template method requires etching the template out of the carbon material, which is not only complex but also requires template consumables. The high cost of both raw materials and processing significantly limits its application.

[0005] In summary, commonly used methods for preparing porous carbon generally involve etching and pore formation. Etching inevitably introduces defects into carbon materials, especially porous carbon materials rich in micropores. When defective microporous carbon materials are used as anodes in lithium-ion batteries, the defects and the inner surfaces of the micropores consume a large amount of active lithium, forming a solid-liquid interface (SEI) film, leading to a decrease in initial coulombic efficiency.

[0006] Meanwhile, the theoretical specific capacity of silicon-based anodes is 4200 mAh / g, ten times that of traditional graphite anodes, significantly improving the energy density and battery life of lithium batteries. However, the commercial application of silicon-based anodes faces many challenges. For example, during charging and discharging, rapid volume expansion and contraction can cause electrode cracking, pulverization, and even detachment, leading to battery failure. Furthermore, silicon has poor conductivity. These shortcomings limit the use of silicon-based anodes.

[0007] Therefore, there is an urgent need for a silicon-carbon composite material and its preparation method to overcome the defects of traditional porous carbon materials and silicon-based anode materials, so as to enable them to have good electrochemical performance. Summary of the Invention

[0008] In view of this, one objective of this application is to provide a hollow cage-like silicon-carbon composite anode material, which uses a 3D network formed by a one-dimensional linear silicon material with multiple carbon spheres attached to its surface as a framework to form an internal hollow cage-like structure. Compared with porous carbon framework structures, this structure has higher capacity and lower specific surface area, which can better improve the first-efficiency and cycle performance of the anode material. At the same time, the microcrystalline carbon (i.e., carbon sphere) conductive network constructed by the 3D network structure can more effectively conduct lithium ions, thereby improving the first-efficiency and cycle performance of the anode material.

[0009] Another objective of this application is to provide a method for preparing a hollow cage-like silicon-carbon composite anode material.

[0010] To achieve the above objectives, the first aspect of this application proposes a hollow cage-like silicon-carbon composite anode material, wherein the hollow cage-like silicon-carbon composite anode material has an internally hollow cage-like structure; the cage-like structure is formed by self-assembly and connection of a 3D network structure, and the 3D network structure includes a framework and a plurality of carbon spheres, the framework includes silicon material, the silicon material includes one-dimensional linear silicon material, and the plurality of carbon spheres are attached to the silicon material.

[0011] The hollow cage-like silicon-carbon composite anode material described in this application can bring at least the following beneficial effects:

[0012] A 3D network formed by using one-dimensional linear silicon material with multiple carbon spheres on its surface as a framework constitutes a hollow cage-like structure. Compared with porous carbon framework structures, it has higher capacity and lower specific surface area, which can better improve the first-efficiency and cycle performance of the anode material. At the same time, the microcrystalline carbon conductive network constructed by the 3D mesh structure can more effectively conduct lithium ions, improving the first-efficiency and cycle performance of the anode material.

[0013] In some embodiments, the plurality of carbon spheres are connected in series or coated on the silicon material.

[0014] In some embodiments, the one-dimensional linear silicon material includes at least one of silicon nanowires and silicon nanotubes.

[0015] In some embodiments, the cage-like structure is loaded with other types of anode materials; these other types of anode materials include at least one of silicon nanowires, silicon nanoparticles, silicon micron-sized particles, silicon suboxide, elemental tin, and tin oxide. The present application's 3D mesh structure exhibits good toughness. Loading other types of anode materials, particularly silicon-based anode materials, within the cage-like structure provides a buffer and constraint for expansion, mitigating the macroscopic volume expansion of the electrode caused by silicon expansion, maintaining its structural stability, and improving cycle performance.

[0016] The second aspect of this application provides a method for preparing a hollow cage-like silicon-carbon composite anode material, comprising:

[0017] A carbon source and a silicon material are mixed to obtain a silicon material with a carbon source adsorbed on its surface; the silicon material includes a one-dimensional linear silicon material.

[0018] The silicon material with carbon source adsorbed on its surface and the crosslinking agent are subjected to hydrothermal reaction or wet ball milling in a reaction solvent, followed by filtration to obtain a 3D network structure.

[0019] The 3D network structure is fully wetted with a chelating agent, then dried and carbonized to obtain the hollow cage-like silicon-carbon composite anode material.

[0020] In some embodiments, the carbon source includes biomass carbon, preferably lignin.

[0021] In some embodiments, the one-dimensional linear silicon material includes at least one of silicon nanowires and silicon nanotubes.

[0022] Preferably, the silicon material is silicon nanowires.

[0023] In some embodiments, the crosslinking agent includes, but is not limited to, at least one of hexamethylenediamine, glutaraldehyde, polyvinyl alcohol, etc., preferably hexamethylenediamine.

[0024] In some embodiments, the chelating agent includes at least one of phosphoric acid, ethylenediaminetetraacetic acid, and aminotrimethylenephosphonic acid, preferably phosphoric acid, and more preferably concentrated phosphoric acid.

[0025] In some embodiments, the reaction solvent includes, but is not limited to, water, preferably deionized water.

[0026] In some embodiments, the mass ratio of the carbon source, the silicon material, the crosslinking agent, the chelating agent, and the reaction solvent is 1:(0.1-1):(0.5-2.0):(0.1-3):(100-150).

[0027] In some embodiments, the temperature of the hydrothermal reaction is 160-220°C.

[0028] In some embodiments, the hydrothermal reaction takes 8-18 hours.

[0029] In some embodiments, the carbonization temperature is 300-1100°C.

[0030] In some embodiments, the carbonization time is 0.5-2 hours.

[0031] In some embodiments, the heating rate of the carbonization is 1-10 °C / min.

[0032] In some embodiments, the cooling method after carbonization is natural cooling.

[0033] In some embodiments, the carbonization atmosphere is an inert gas atmosphere or a mixed gas atmosphere, wherein the mixed gas is a mixture of inert gas and hydrogen, and the volume ratio of inert gas to hydrogen in the mixed gas is (90-97):(3-10).

[0034] In some embodiments, the method of mixing the carbon source and silicon material includes at least one of grinding, ultrasonic dispersion, mechanical stirring and magnetic stirring.

[0035] In some embodiments, the filtration method includes at least one of centrifugal separation and vacuum filtration.

[0036] In some embodiments, the method for preparing the hollow cage-like silicon-carbon composite anode material further includes the step of loading other types of anode materials inside the hollow cage-like structure of the hollow cage-like silicon-carbon composite anode material after carbonization. The other types of anode materials include at least one of silicon nanowires, silicon nanoparticles, silicon micron particles, silicon suboxide, elemental tin, and tin oxide.

[0037] The method for preparing the hollow cage-like silicon-carbon composite anode material described in this application can bring at least the following technical effects:

[0038] Using one-dimensional linear silicon materials (e.g., silicon nanowires) as a framework, a 3D network structure is formed through cross-linking with organic carbon sources. This network structure is then further processed through chelation and carbonization to create a hollow cage-like structure (i.e., a cage-like structure with a hollow interior). This cage-like structure exhibits significantly superior performance. Specifically:

[0039] 1. By using one-dimensional linear silicon materials (e.g., silicon nanowires) as a framework and constructing a hollow cage-like structure through complexing agents and self-assembly processes, the microcrystalline carbon and one-dimensional linear silicon materials (e.g., silicon nanowires) contained in the structure have higher capacity compared to porous carbon framework structures, which can improve the capacity of anode materials.

[0040] 2. Its 3D mesh structure constructs a microcrystalline carbon conductive network that can more effectively conduct lithium ions, improving the first-efficiency and cycle performance of the anode material.

[0041] 3. The hollow cage-like structure formed by stacking spherical carbon has a lower specific surface area than porous carbon, which can better improve the first efficiency and cycle performance of the anode material.

[0042] 4. The formed negative electrode material has a 3D network structure and good toughness. After loading other types of negative electrode materials, especially silicon-based negative electrode materials, inside the cage structure, it can provide a certain buffer and restraint capacity for their expansion, alleviate the macroscopic volume expansion of the electrode caused by silicon expansion, maintain its structural stability, and improve cycle performance.

[0043] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0044] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0045] in:

[0046] Figure 1 This is a flowchart illustrating a method for preparing a hollow cage-like silicon-carbon composite anode material, which is an exemplary embodiment of this application.

[0047] Figure 2 The flowchart illustrates a method for preparing a hollow cage-like silicon-carbon composite anode material, which is another exemplary embodiment of this application.

[0048] Figure 3 The image shows a scanning electron microscope (SEM) image of the hollow cage-like silicon-carbon composite anode material prepared in Example 1.

[0049] Figure 4 The image shows a scanning electron microscope (SEM) image of the silicon-carbon composite material prepared in Comparative Example 3. Detailed Implementation

[0050] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0051] In this application, the disclosure of numerical ranges includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0052] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0053] When the term “and / or” is used in a list containing two or more items, it means that any of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression “A and / or B” is intended to mean A or B or A and B, that is, A only, B only, or a combination of A and B.

[0054] Hollow Cage-like Silicon-Carbon Composite Anode Material

[0055] The hollow cage-like silicon-carbon composite anode material of this application embodiment is a cage-like structure with a hollow interior. The cage-like structure is formed by self-assembly and connection of a 3D network structure, and the 3D network structure includes a skeleton and a plurality of carbon spheres. The skeleton includes silicon material, and the silicon material includes one-dimensional linear silicon material. The plurality of carbon spheres are attached to the silicon material.

[0056] The hollow cage-like silicon-carbon composite anode material described in this application uses a 3D network formed by a one-dimensional linear silicon material with multiple carbon spheres attached to its surface as a framework to create an internally hollow cage-like structure. Compared with porous carbon framework structures, this structure has higher capacity and lower specific surface area, which can better improve the first-efficiency and cycle performance of the anode material. At the same time, the microcrystalline carbon (i.e., carbon sphere) conductive network constructed by the 3D network structure can more effectively conduct lithium ions, improving the first-efficiency and cycle performance of the anode material.

[0057] In some embodiments, the plurality of carbon spheres are connected in series on the silicon material.

[0058] In other embodiments, the plurality of carbon spheres are coated on the silicon material.

[0059] In some embodiments, the one-dimensional linear silicon material includes, but is not limited to, at least one of silicon nanowires, silicon nanotubes, etc.

[0060] As an optional example, the 3D network structure consists of the framework and a plurality of carbon spheres, wherein the framework is made of silicon material, and the silicon material is at least one of silicon nanowires, silicon nanotubes, etc.

[0061] In some embodiments, the cage structure is loaded with other types of negative electrode materials.

[0062] For example, the other types of anode materials include, but are not limited to, at least one of silicon nanowires, silicon nanoparticles, silicon micron particles, silicon suboxide, elemental tin, tin oxide, etc.

[0063] For example, when the cage structure is loaded with other types of negative electrode materials, the mass of the other types of negative electrode materials is 20-80% of the total mass of the hollow cage silicon-carbon composite negative electrode material loaded with other types of negative electrode materials (the sum of the mass of the other types of negative electrode materials and the mass of the hollow cage silicon-carbon composite negative electrode material before loading other types of negative electrode materials), including but not limited to 30%, 40%, 50%, 60% or 70%, etc.

[0064] The present application has a 3D mesh structure with good toughness. After loading other types of anode materials, especially silicon-based anode materials, inside the cage structure, it can provide a certain buffer and restraint for their expansion, alleviate the macroscopic volume expansion of the electrode caused by silicon expansion, maintain its structural stability, and improve cycle performance.

[0065] <Preparation Method of Hollow Cage Silicon-Carbon Composite Anode Material>

[0066] The method for preparing the hollow cage-like silicon-carbon composite anode material in this application embodiment can be used to prepare the hollow cage-like silicon-carbon composite anode material in this application embodiment.

[0067] Figure 1 This is a flowchart illustrating a method for preparing a hollow cage-like silicon-carbon composite anode material, which is an exemplary embodiment of this application.

[0068] like Figure 1 As shown, the preparation method of the hollow cage-like silicon-carbon composite anode material in this application includes the following steps:

[0069] S101. Mix carbon source and silicon material to obtain silicon material with carbon source adsorbed on the surface; the silicon material includes one-dimensional linear silicon material.

[0070] S102. The silicon material with carbon source adsorbed on the surface obtained in step S101 and the crosslinking agent are subjected to a hydrothermal reaction in a reaction solvent, followed by filtration to obtain a 3D network structure.

[0071] S103. The 3D network structure obtained in step S102 is fully wetted with a chelating agent, then dried and carbonized to obtain the hollow cage-like silicon-carbon composite anode material.

[0072] In some embodiments, the method of mixing the carbon source and silicon material includes, but is not limited to, at least one of grinding, ultrasonic dispersion, mechanical stirring and magnetic stirring, with grinding being preferred.

[0073] In some embodiments, the one-dimensional linear silicon material includes, but is not limited to, at least one of silicon nanowires, silicon nanotubes, etc.

[0074] As a preferred example, the silicon material is silicon nanowires.

[0075] In some embodiments, the carbon source includes, but is not limited to, biomass carbon.

[0076] For example, biomass carbon includes, but is not limited to, at least one of lignin, pine cones, corn cobs, and coconut shells, preferably lignin. Lignin is a major component of waste from the paper industry (commonly known as "black pulp"). It has traditionally been used as fuel for power generation, resulting in resource waste and poor sustainability. From a sustainable development perspective, this application aims to develop and utilize this environmentally polluting industrial waste, transforming it into a useful industrial raw material for manufacturing silicon-carbon composite materials for use as the negative electrode in secondary batteries such as lithium-ion batteries. At the same carbonization temperature, the carbon yield of lignin is higher than that of biomass-based and polymer resins. Lignin raw materials have a significant advantage in cost.

[0077] In some embodiments, the crosslinking agent includes, but is not limited to, at least one of hexamethylenediamine, glutaraldehyde, polyvinyl alcohol, etc., preferably hexamethylenediamine.

[0078] In some embodiments, the chelating agent includes, but is not limited to, at least one of phosphoric acid, ethylenediaminetetraacetic acid (EDTA), aminotrimethylenephosphonic acid (ATMP), etc., preferably phosphoric acid, more preferably concentrated phosphoric acid.

[0079] In some embodiments, the reaction solvent includes, but is not limited to, water, preferably water, and more preferably deionized water.

[0080] In some embodiments, the mass ratio of the carbon source, the silicon material, the crosslinking agent, the chelating agent, and the reaction solvent (carbon source: silicon source: crosslinking agent: chelating agent: reaction solvent) is 1:(0.1-1):(0.5-2):(0.1-3):(100-150), including but not limited to 1:0.5:0.5:0.1:100, 1:0.5:2:0.1:100, 1 The following ratios are preferred: 0.5:1.25:0.1:100, 1:1:1.25:1:120, 1:0.01:1.25:2:150, 1:0.25:0.5:1.5:125, 1:0.25:2:1.5:100, 1:0.75:1.8:2:110, or 1:0.75:0.8:0.1:100, with 1:0.3:1:1.5:125 being the most preferred.

[0081] In some embodiments, the temperature of the hydrothermal reaction is 160-220°C, including but not limited to 160°C, 170°C, 180°C, 190°C, 200°C or 210°C, preferably 180°C.

[0082] In some embodiments, the hydrothermal reaction time is 8-18 hours, including but not limited to 9 hours, 11 hours, 13 hours, 15 hours or 17 hours, preferably 12 hours.

[0083] In the embodiments of this application, the hydrothermal reaction can be carried out in reaction vessels, including but not limited to conventional hydrothermal reactors.

[0084] In some embodiments, the filtration method includes, but is not limited to, at least one of centrifugal separation, vacuum filtration, etc., with centrifugal separation being preferred.

[0085] In some embodiments, the carbonization temperature is 300-1100°C, including but not limited to 400°C, 600°C, 800°C, 1000°C, 700°C or 1100°C, preferably 600°C.

[0086] In some embodiments, the carbonization time is 0.5-2 hours, including but not limited to 0.5 hours, 1 hour, 1.5 hours or 2 hours, preferably 1 hour.

[0087] In some embodiments, the heating rate of the carbonization is 1-10°C / min, including but not limited to 2°C / min, 5°C / min, 7°C / min or 10°C / min, preferably 5°C / min.

[0088] In some embodiments, the cooling method after carbonization is natural cooling.

[0089] In some embodiments, the carbonization atmosphere is an inert gas atmosphere or a mixed gas atmosphere, wherein the mixed gas is a mixture of inert gas and hydrogen.

[0090] For example, inert gases include, but are not limited to, at least one of nitrogen, argon, helium, etc.

[0091] For example, the volume ratio of inert gas to hydrogen in the mixed gas is (90-97):(3-10), including but not limited to 90:10, 92:8, 95:5 or 97:3, etc.

[0092] In some embodiments, the gas flow rate is 100-800 sccm, including but not limited to 200 sccm, 400 sccm, 500 sccm or 700 sccm, preferably 500 sccm.

[0093] For example, the carbonization is carried out in a quartz tube furnace, but is not limited to a quartz tube furnace; it can also be any other reactor in the art capable of carrying out the carbonization reaction.

[0094] In some embodiments, the drying methods described above include, but are not limited to, baking, spray drying, vacuum drying, etc., such as drying to constant weight in a constant temperature oven at 120°C.

[0095] In some embodiments, the preparation method of the hollow cage-like silicon-carbon composite anode material further includes the steps of washing and drying after carbonization.

[0096] In the embodiments of this application, the purpose of washing is to remove ash and residual chelating agents such as phosphoric acid.

[0097] For example, the washing method described above involves rinsing with deionized water to remove ash and residual chelating agents such as phosphoric acid.

[0098] For example, the drying methods after carbonization include, but are not limited to, baking, spray drying, vacuum drying, etc., such as drying in a constant temperature oven at 80°C to constant weight.

[0099] In some embodiments, in order to further improve the theoretical specific capacity of the hollow cage-like silicon-carbon composite anode material, the preparation method of the hollow cage-like silicon-carbon composite anode material further includes the step of loading other types of anode materials inside the hollow cage-like structure of the hollow cage-like silicon-carbon composite anode material after carbonization.

[0100] For example, the other types of anode materials include, but are not limited to, at least one of silicon nanowires (SiNWs), silicon nanoparticles (SiNPs), silicon microparticles (SiMPs), silicon suboxide, elemental tin, tin oxide, etc.

[0101] In some embodiments, the method of loading silicon and / or tin materials after carbonization includes, but is not limited to, at least one of in-situ growth, physical mixing (i.e., physical loading).

[0102] For example, the mass of the other type of negative electrode material is 20-80% of the total mass of the hollow cage-like silicon-carbon composite negative electrode material loaded with the other type of negative electrode material (the sum of the mass of the other type of negative electrode material and the mass of the hollow cage-like silicon-carbon composite negative electrode material before loading the other type of negative electrode material), including but not limited to 30%, 40%, 50%, 60% or 70%.

[0103] In some embodiments, the hydrothermal reaction in step S101 can be replaced by a wet ball milling process, such as... Figure 2 As shown.

[0104] In some embodiments, the process conditions for wet ball milling are as follows: rotation speed of 350-450 rpm, ball-to-material ratio of (6-8):2, grinding balls of zirconium oxide, grinding ball diameter of 0.3-0.5 mm, and grinding time of 20-40 min.

[0105] For example, in a wet ball milling process, the rotation speed includes, but is not limited to, 370 rpm, 390 rpm, 410 rpm or 430 rpm, the ball-to-material ratio includes, but is not limited to, 6.5:2, 7:2 or 7.5:2, the grinding ball diameter includes, but is not limited to, 0.3 mm or 0.5 mm, and the grinding time includes, but is not limited to, 25 min, 30 min or 35 min.

[0106] As an alternative example, the process conditions for wet ball milling are: a rotation speed of 400 rpm, a ball-to-material ratio of 7:2, zirconium oxide grinding balls with a diameter of 0.5 mm, and a grinding time of 30 min.

[0107] In the embodiments of this application, the solvent used in the wet ball milling process is not limited. For example, in the wet ball milling process, the solvent includes at least one of organic solvents such as water and alcohol.

[0108] The method for preparing the hollow cage-like silicon-carbon composite anode material in this application embodiment can bring at least the following technical effects:

[0109] Using one-dimensional linear silicon materials (e.g., silicon nanowires) as a framework, a 3D network structure is formed through cross-linking with organic carbon sources. This network structure is then further processed through chelation and carbonization to create a hollow cage-like structure (i.e., a cage-like structure with a hollow interior). This cage-like structure exhibits significantly superior performance. Specifically:

[0110] 1. By using one-dimensional linear silicon materials (e.g., silicon nanowires) as a framework and constructing a hollow cage-like structure through complexing agents and self-assembly processes, the microcrystalline carbon and one-dimensional linear silicon materials (e.g., silicon nanowires) contained in the structure have higher capacity compared to porous carbon framework structures, which can improve the capacity of anode materials.

[0111] 2. Its 3D mesh structure constructs a microcrystalline carbon conductive network that can more effectively conduct lithium ions, improving the first-efficiency and cycle performance of the anode material.

[0112] 3. The hollow cage-like structure formed by stacking spherical carbon has a lower specific surface area than porous carbon, which can better improve the first efficiency and cycle performance of the anode material.

[0113] 4. The formed negative electrode material has a 3D network structure and good toughness. After loading other types of negative electrode materials, especially silicon-based negative electrode materials, inside the cage structure, it can provide a certain buffer and restraint capacity for their expansion, alleviate the macroscopic volume expansion of the electrode caused by silicon expansion, maintain its structural stability, and improve cycle performance.

[0114] The following non-limiting embodiments further illustrate certain features of the present technology.

[0115] I. Examples and Comparative Examples

[0116] Example 1

[0117] The preparation method of the hollow cage-like silicon-carbon composite anode material in this embodiment includes the following steps:

[0118] (1) Grind and mix 1 part by weight of lignin and 0.3 parts by weight of silicon nanowire powder evenly in a mortar, add 100 parts by weight of deionized water, and then add 1 part by weight of hexamethylenediamine and mix well to obtain a mixture.

[0119] (2) The mixture obtained in step (1) is added to a hydrothermal reactor and hydrothermally reacted at 180°C for 12 hours. The supernatant is then removed by centrifugation, leaving the solid, which has a 3D network structure (e.g., Figure 3 (As shown).

[0120] (3) Add 1 part by weight of 46wt% phosphoric acid to fully wet the solid obtained in step (2), and dry it in a constant temperature oven at 120℃ to constant weight to obtain a solid containing chelating agent.

[0121] (4) The solid containing chelating agent obtained in step (3) is placed in a quartz tube furnace and heated to 600°C at 5°C / min in a nitrogen atmosphere of 500 sccm for 1 hour. Then it is cooled naturally to obtain the carbonized product.

[0122] (5) The carbonized product obtained in step (4) is rinsed with deionized water to remove ash and residual phosphoric acid, and dried in a constant temperature oven at 80°C to constant weight to obtain the hollow cage-like silicon-carbon composite anode material of this embodiment.

[0123] Example 2 (Compared to Example 1, the ratio of carbon source: silicon source: crosslinking agent: chelating agent: water = 1:0.1:0.5:0.1:100)

[0124] This embodiment is basically the same as embodiment 1, except that:

[0125] Step (1) is as follows: Grind and mix 1 part by weight of lignin and 0.1 part by weight of silicon nanowire powder evenly in a mortar, add 100 parts by weight of deionized water, and then add 0.5 parts by weight of hexamethylenediamine and mix evenly to obtain a mixture.

[0126] Step (3) involves adding 0.1 parts by weight of 47 wt% phosphoric acid to fully wet the solid obtained in step (2) and drying it in a constant temperature oven at 120°C to a constant weight to obtain a solid containing a chelating agent.

[0127] Example 3 (Compared to Example 1, carbon source: silicon source: crosslinking agent: chelating agent: water = 1:1:2:3:150)

[0128] This embodiment is basically the same as embodiment 1, except that:

[0129] Step (1) is as follows: Grind and mix 1 part by mass of lignin and 1 part by mass of silicon nanowire powder evenly in a mortar, add 150 parts by mass of deionized water, and then add 2 parts by mass of hexamethylenediamine and mix evenly to obtain a mixture.

[0130] Step (3) involves adding 3 parts by weight of 45wt% phosphoric acid to fully wet the solid obtained in step (2) and drying it in a constant temperature oven at 120℃ to a constant weight to obtain a solid containing a chelating agent.

[0131] Example 4 (Compared to Example 1, the ratio of carbon source: silicon source: crosslinking agent: chelating agent: water is 1:0.55:1.25:2:125)

[0132] This embodiment is basically the same as embodiment 1, except that:

[0133] Step (1) is as follows: Grind and mix 1 part by weight of lignin and 0.55 parts by weight of silicon nanowire powder evenly in a mortar and pestle, add 125 parts by weight of deionized water, and then add 1.25 parts by weight of hexamethylenediamine and mix evenly to obtain a mixture.

[0134] Step (3) involves adding 2 parts by weight of 46wt% phosphoric acid to fully wet the solid obtained in step (2) and drying it in a constant temperature oven at 120℃ to a constant weight to obtain a solid containing a chelating agent.

[0135] Example 5 (Compared to Example 1, a wet ball milling process was used instead of a hydrothermal synthesis process to crosslink organic compounds)

[0136] This embodiment is basically the same as embodiment 1, except that:

[0137] Step (2) involves wet grinding the mixture obtained in step (1), followed by centrifugation to remove the clear liquid and retaining the solid, which has a 3D network structure.

[0138] The wet grinding process conditions are as follows: rotation speed of 400 rpm, ball-to-material ratio of 7:2, grinding balls of zirconium oxide with a diameter of 0.5 mm, grinding time of 30 min, and solvent of deionized water.

[0139] Example 6 (Compared to Example 2, a wet ball milling process was used instead of a hydrothermal synthesis process to crosslink organic compounds)

[0140] This embodiment is basically the same as embodiment 2, except that:

[0141] Step (2) involves wet grinding the mixture obtained in step (1), followed by centrifugation to remove the clear liquid and retaining the solid, which has a 3D network structure.

[0142] The wet grinding process conditions are as follows: rotation speed of 400 rpm, ball-to-material ratio of 7:2, grinding balls of zirconium oxide with a diameter of 0.5 mm, grinding time of 30 min, and solvent of deionized water.

[0143] Example 7 (Compared to Example 1, carbon nanotubes are used instead of silicon nanowires)

[0144] This embodiment is basically the same as embodiment 1, except that:

[0145] Replace the silicon nanowires in step (1) with carbon nanotubes.

[0146] Example 8 (Compared to Example 2, carbon nanotubes are used instead of silicon nanowires)

[0147] This embodiment is basically the same as embodiment 2, except that:

[0148] Replace the silicon nanowires in step (1) with carbon nanotubes.

[0149] Comparative Example 1 (using phenolic resin instead of carbon source compared to Example 1)

[0150] This comparative example is basically the same as Example 1, except that:

[0151] Replace the lignin in step (1) with phenolic resin.

[0152] Comparative Example 2 (compared to Example 2, using phenolic resin instead of carbon source)

[0153] This comparative example is basically the same as Example 2, except that:

[0154] Replace the lignin in step (1) with phenolic resin.

[0155] Comparative Example 3 (compared to Example 1, the step of adding phosphoric acid in the process is omitted)

[0156] This comparative example is basically the same as Example 1, except that:

[0157] Step (3) is excluded.

[0158] Comparative Example 4 (compared to Example 2, the step of adding phosphoric acid in the process is omitted)

[0159] This comparative example is basically the same as Example 2, except that:

[0160] Step (3) is excluded.

[0161] II. Material Characterization and Performance Testing

[0162] 1. Material Characterization

[0163] (1) Composition / Structural Characterization

[0164] The hollow cage-like silicon-carbon composite anode material and silicon-carbon composite material prepared in Example 1 and Comparative Example 3 were tested using scanning electron microscopy (SEM).

[0165] Figure 3 This is a scanning electron microscope (SEM) image of the hollow cage-like silicon-carbon composite anode material prepared in Example 1. From... Figure 3 As can be seen, the hollow cage-like silicon-carbon composite anode material prepared in Example 1 has a hollow cage-like structure, with a size of about several hundred micrometers, and is composed of carbon spheres about 10 micrometers in size. The size of the carbon spheres is similar to the length of the silicon nanowires, and the silicon nanowires are completely encapsulated in the carbon framework.

[0166] Figure 4 This is a scanning electron microscope (SEM) image of the silicon-carbon composite material prepared in Comparative Example 3. From... Figure 4 It can be seen that, under the same conditions, without the addition of the chelating agent phosphoric acid, the silicon-carbon composite material prepared in Comparative Example 3 does not have a hollow cage structure. Figure 4 No hollow cage-like structure was observed. The silicon nanowires, with lengths of 5-9 micrometers, were scattered across the carbon particles. This indicates that the chelating agent phosphate plays a crucial role in the material's self-assembly process.

[0167] 2. Electrochemical performance testing

[0168] Hollow cage-like silicon-carbon composite anode materials / silicon-carbon composite materials obtained in various embodiments or comparative examples were ultrasonically mixed with nano-silicon powder (50-100nm) in anhydrous ethanol solution for 15 min, followed by filtration and drying to obtain hollow cage-like silicon-carbon composite anode materials / silicon-carbon composite materials loaded with nano-silicon powder. This material was mixed with binder polyvinylidene fluoride (PVDF) and conductive agent Super-P in a mass ratio of 8:1:1, ground, coated, and slurried, and then used to prepare coin half-cells with lithium sheets. The capacity, first-efficiency, and cycle performance of the material were tested.

[0169] The electrochemical performance test results are shown in Table 1.

[0170] Table 1 Electrochemical performance test results

[0171] Examples / Comparative Examples Capacity, mA·h / g Capacity retention rate after 300 cycles, % First-time effect, % Example 1 1323.2 91.5 89.5 Example 2 875.4 94.6 91.4 Example 3 2254.6 85.6 87.6 Example 4 1158.7 92.4 90.1 Example 5 1225.9 81.2 83.4 Example 6 815.5 83.4 82.9 Example 7 235.9 93.5 82.5 Example 8 258.4 92.8 81.4 Comparative Example 1 1286.7 72.3 85.6 Comparative Example 2 825.3 73.1 82.7 Comparative Example 3 1314.5 68.6 84.3 Comparative Example 4 867.1 70.4 83.5

[0172] As can be seen from Table 1, Examples 1-4 have relatively excellent capacity, first-efficiency, and cycling performance. However, Examples 5-6, due to the use of wet ball milling instead of hydrothermal synthesis, resulted in irregular polyhedral structures formed by grinding and extrusion of the crosslinked products during the grinding process, rather than the spherical structures formed by hydrothermal synthesis. This led to a certain decrease in first-efficiency. Examples 7-8, using carbon nanotubes instead of silicon nanowires, were able to form the same structure, but due to the much lower capacity of carbon compared to silicon, the capacity decreased to some extent. However, the increased conductivity improved the first-efficiency and cycling performance to some extent. Comparative Examples 1-2 used phenolic resin instead of carbon source, resulting in flattened spherical carbonized products with incomplete coating. Due to the low carbon yield, a 3D network could not be constructed during chelation and carbonization, and a cage-like network could not be built. The cycling performance of the products declined sharply. Comparative Examples 3-4 lacked the self-assembly of phosphate chelating agents, and similarly, a cage-like network could not be constructed.

[0173] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0174] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0175] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A hollow cage-like silicon-carbon composite negative electrode material, characterized by, The hollow cage-like silicon-carbon composite anode material has an internally hollow cage-like structure; the cage-like structure is formed by the self-assembly connection of a 3D network structure, and the 3D network structure includes a skeleton and multiple carbon spheres. The skeleton includes silicon material, and the silicon material includes one-dimensional linear silicon material. The multiple carbon spheres are attached to the silicon material.

2. The hollow cage-like silicon-carbon composite negative electrode material according to claim 1, characterized in that The plurality of carbon spheres are connected in series or coated on the silicon material.

3. The hollow cage-like silicon-carbon composite negative electrode material according to claim 1, characterized in that The one-dimensional linear silicon material includes at least one of silicon nanowires and silicon nanotubes.

4. The hollow cage-like silicon-carbon composite negative electrode material according to claim 1, characterized in that, The cage-like structure is loaded with other types of negative electrode materials; the other types of negative electrode materials include at least one of silicon nanowires, silicon nanoparticles, silicon micron particles, silicon suboxide, elemental tin, and tin oxide.

5. A method for preparing a hollow cage-like silicon-carbon composite negative electrode material, characterized by, include: A carbon source and a silicon material are mixed to obtain a silicon material with a carbon source adsorbed on its surface; the silicon material includes a one-dimensional linear silicon material. The silicon material with carbon source adsorbed on its surface and the crosslinking agent are subjected to hydrothermal reaction or wet ball milling in a reaction solvent, followed by filtration to obtain a 3D network structure. The 3D network structure is fully wetted with a chelating agent, then dried and carbonized to obtain the hollow cage-like silicon-carbon composite anode material.

6. The production method according to claim 5, wherein The carbon source includes biomass carbon; and / or, The one-dimensional linear silicon material includes at least one of silicon nanowires and silicon nanotubes; and / or, The crosslinking agent includes at least one of hexamethylenediamine, glutaraldehyde, and polyvinyl alcohol; and / or, The chelating agent includes at least one of phosphoric acid, ethylenediaminetetraacetic acid, and aminotrimethylenephosphonic acid; and / or, The reaction solvent includes water.

7. The preparation method according to claim 6, characterized in that, The carbon source is lignin; and / or, The silicon material is silicon nanowires; and / or, The crosslinking agent is hexamethylenediamine; and / or, The chelating agent is phosphoric acid.

8. The preparation method according to claim 5, characterized in that, The mass ratio of the carbon source, the silicon material, the crosslinking agent, the chelating agent, and the reaction solvent is 1:(0.1-1):(0.5-2.0):(0.1-3):(100-150).

9. The preparation method according to claim 5, characterized in that, The hydrothermal reaction temperature is 160-220℃; and / or, The hydrothermal reaction time is 8-18 hours; and / or, The carbonization temperature is 300-1100℃; and / or, The carbonization time is 0.5-2 hours; and / or, The carbonization heating rate is 1-10 °C / min; and / or, The cooling method following carbonization is natural cooling; and / or, The carbonization atmosphere is an inert gas atmosphere or a mixed gas atmosphere, wherein the mixed gas is a mixture of inert gas and hydrogen, and the volume ratio of inert gas to hydrogen in the mixed gas is (90-97):(3-10).

10. The method of claim 5, wherein, The method of mixing the carbon source and silicon material includes at least one of grinding, ultrasonic dispersion, mechanical stirring, and magnetic stirring; and / or, The filtration method includes at least one of centrifugal separation and vacuum filtration; and / or, The method for preparing the hollow cage-like silicon-carbon composite anode material further includes a step of loading other types of anode materials inside the hollow cage-like structure of the hollow cage-like silicon-carbon composite anode material after carbonization. The other types of anode materials include at least one of silicon nanowires, silicon nanoparticles, silicon micron particles, silicon suboxide, elemental tin, and tin oxide.

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