Silicon-carbon negative electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery, and the silicon-carbon negative electrode material comprises a composite core composed of a silicon-based material and a porous MOFs material, and a carbon layer coated on the surface of the composite core; at least a part of the silicon-based material is embedded into the pore channel of the porous MOFs material; and the average pore diameter of the porous MOFs material is 400-1000 nm. At least a part of the silicon-based material is embedded into the pore channel of the porous MOFs material, so that the capacity advantage of the silicon material is fully exerted, the existence of the large pore diameter further improves the capacity of the silicon-carbon negative electrode material, and the volume expansion of the silicon is inhibited; and the carbon layer wraps the exposed silicon-based material which is not embedded into the pore channel, so that the structural stability and the conductivity of the material are improved. Therefore, the silicon-carbon negative electrode material constructed by the application has excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a silicon-carbon anode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are mainly composed of three parts: the positive electrode, the negative electrode, and the separator. Changes in the performance of any of these parts will indirectly affect the overall battery. Currently, the mainstream negative electrode material for lithium-ion batteries is graphite. However, graphite has a relatively low theoretical specific capacity of 372 mAh / g, and current graphite materials have basically reached their capacity limits.

[0003] Currently, the main research direction for lithium-ion battery anodes is to improve lithium-ion battery performance by changing the substrate material or adding other high-capacity materials to carbon-based materials. While confining silicon-carbon materials within a core using a hard asphalt structure solves the silicon volume expansion problem to some extent, the relative non-expansion of silicon does not provide more effective capacity for the anode. Furthermore, while the hard carbon structure can buffer silicon volume expansion to some extent, adding too much silicon, due to the low hardness of the asphalt material, cannot completely suppress silicon expansion. This may lead to structural collapse and other material damage caused by silicon volume expansion, resulting in rapid decay of reversible capacity and reduced cycle performance.

[0004] Therefore, how to efficiently suppress the volume expansion of silicon and improve the capacity of silicon-carbon anode materials is an urgent technical problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a silicon-carbon anode material, its preparation method, and a lithium-ion battery. This invention constructs a novel silicon-carbon anode material by embedding at least a portion of a silicon-based material into the pores of a pore-forming MOF (Metal-Oxide-Factory) material with an average pore size of 400-1000 nm. This not only fully utilizes the capacity advantage of silicon but also further enhances the capacity of the silicon-carbon anode material and suppresses silicon volume expansion through the presence of a large pore size. Furthermore, the exposed silicon-based material not embedded in the pores is encapsulated by a carbon layer, preventing direct contact with the electrolyte and improving the material's structural stability and conductivity. Therefore, the silicon-carbon anode material constructed in this invention exhibits excellent capacity performance and coulombic efficiency, as well as low EIS (electrochemical impedance spectroscopy), and excellent CV (cycle) and rate performance.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a silicon-carbon anode material, the silicon-carbon anode material comprising a composite core composed of a silicon-based material and a pore-forming MOF material, and a carbon layer covering the surface of the composite core;

[0008] At least a portion of the silicon-based material is embedded in the pores of the pore-forming MOFs material;

[0009] The average pore size of the MOFs material after pore formation is 400-1000 nm.

[0010] This invention constructs a novel silicon-carbon anode material by embedding at least a portion of a silicon-based material into the pores of a pore-formed MOF (Metal-Oxide-Factory) material with an average pore size of 400-1000 nm. This not only fully utilizes the capacity advantage of silicon but also further enhances the capacity of the silicon-carbon anode material and suppresses silicon volume expansion through the presence of a large pore size. Furthermore, the exposed silicon-based material not embedded in the pores is encapsulated by a carbon layer, preventing direct contact with the electrolyte and improving the material's structural stability and conductivity. Therefore, the silicon-carbon anode material constructed in this invention exhibits excellent capacity performance and coulombic efficiency, as well as low EIS (Electro-Induced Sequence) and excellent CV (Continuous Voltage) and rate performance.

[0011] As a preferred technical solution of the present invention, the MOFs material after pore formation includes HKUST-1.

[0012] Preferably, the average pore size of the MOFs material after pore formation is 500-800 nm.

[0013] Preferably, the porosity of the MOFs material after pore formation is 10-60%, more preferably 20-40%.

[0014] Preferably, the silicon-based material includes any one or a combination of at least two of nano-silicon, micro-silicon, or silicon oxide.

[0015] Preferably, the particle size D50 of the silicon-based material is 20-200 nm, and more preferably 20-60 nm.

[0016] Preferably, the mass ratio of the silicon-based material to the pore-forming MOFs material is 1:(2-5).

[0017] As a preferred embodiment of the present invention, the thickness of the carbon layer is 100-1000 nm, preferably 200-500 nm.

[0018] In a second aspect, the present invention provides a method for preparing a silicon-carbon anode material as described in the first aspect, the method comprising the following steps:

[0019] (1) Mix the pore-forming MOFs material with the silicon-based material and heat to obtain a composite material;

[0020] (2) The composite material and carbon source are mixed and carbonized to obtain the silicon-carbon anode material.

[0021] Preferably, the heating temperature in step (1) is 80-100℃.

[0022] Preferably, the heating time in step (1) is 4-6 hours.

[0023] As a preferred technical solution of the present invention, the MOFs material after pore formation in step (1) is prepared by the following method, which includes the following steps: mixing organic ligands, metal salts and pore-forming agents to obtain the MOFs material after pore formation.

[0024] In a preferred embodiment of the present invention, the pore-forming agent is a soluble inorganic salt.

[0025] Preferably, the soluble inorganic salt includes any one or a combination of at least two of sodium, potassium, magnesium, or aluminum salts. Preferably, the mass ratio of the organic ligand, pore-forming agent, and metal salt is (0.5-1):(1-5):(0.5-1).

[0026] Preferably, the blending method includes ball milling.

[0027] Preferably, the ball milling time is 1-6 hours.

[0028] Preferably, the ball mill rotates at a speed of 100-400 rpm.

[0029] Preferably, the ball-to-material ratio in the ball mill is (1-10):1.

[0030] As a preferred technical solution of the present invention, the carbon source in step (2) includes any one or a combination of at least two of organic carbon sources, graphite materials or porous carbon materials.

[0031] Preferably, the mass ratio of the composite material to the carbon source in step (2) is 1:(0.5-1.5).

[0032] Preferably, the carbonization temperature in step (2) is 80-100℃.

[0033] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0034] (Ⅰ) Tristyric acid, pore-forming agent and soluble copper salt were ball-milled and mixed according to the mass ratio of (0.5-1):(1-5):(0.5-1), and the mixture was washed and dried to obtain the pore-forming MOF material.

[0035] The ball milling time is 1-6 hours, the ball milling speed is 100-400 rpm, and the ball-to-material ratio is (1-10):1.

[0036] (II) The pore-forming MOFs material and silicon-based material are mixed in a solvent at a mass ratio of (2-5):1, heated, filtered and dried to obtain a composite material.

[0037] The heating temperature is 80-100℃, and the heating time is 4-6 hours.

[0038] (III) The composite material and carbon source are mixed at a mass ratio of 1:(0.5-1.5) and carbonized at 80-100℃ for 4-6 hours to obtain the silicon-carbon anode material.

[0039] In this invention, the carbonization process can be carried out by rotary evaporation or oil bath.

[0040] Thirdly, the present invention provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the silicon-carbon negative electrode material as described in the first aspect.

[0041] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The present invention constructs a novel silicon-carbon anode material by embedding at least a portion of the silicon-based material into the channels of the MOFs material after pore formation with an average pore size of 400-1000nm. This not only fully utilizes the capacity advantage of silicon material, but also further improves the capacity of silicon-carbon anode material by the presence of large pore size and suppresses the volume expansion of silicon. Furthermore, the exposed silicon-based material not embedded in the channels is wrapped by carbon layer coating to prevent it from directly contacting the electrolyte, thereby improving the structural stability and conductivity of the material.

[0044] (2) The silicon-carbon anode material constructed in this invention not only has excellent capacity performance, cycle performance and coulombic efficiency, but also has low electrochemical impedance and excellent rate performance. Attached Figure Description

[0045] Figure 1 This is a SEM image of HKUST-1 after pore formation prepared in Example 1 of the present invention.

[0046] Figure 2 This is a SEM image of the silicon-carbon anode material prepared in Example 1 of the present invention. Detailed Implementation

[0047] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0048] In the prior art, Zhang et al. used graphite and nano-silicon to fully ball-mill and mix them, and then used pitch to calcine the ball-milled composite material at 850°C for 2 hours in a nitrogen atmosphere. The pitch was carbonized at high temperature to coat the carbon-silicon composite material, thus preparing a core-shell structure to suppress the volume expansion of silicon, thereby giving the material high specific capacity and stable cycle performance. The specific steps include: (1) grinding graphite and nano-silicon in a planetary ball mill for 2 hours; (2) mixing the ground carbon-silicon composite material with pitch and calcining it in a tube furnace at 850°C with nitrogen for 2 hours. At this temperature, the pitch is fully carbonized, coating the silicon-carbon material prepared in the first step, forming a core-shell structure, and successfully preparing the anode material.

[0049] Although Zhang et al. successfully carbonized pitch and coated it onto the surface of silicon-carbon materials, this method is energy-intensive and expensive to produce. In addition, while confining the silicon-carbon materials in the core through the hard pitch structure solves the problem of silicon volume expansion to some extent, the relative non-expansion of silicon cannot provide more effective capacity for the anode. Furthermore, although the hard carbon structure can buffer the problem of silicon volume expansion to some extent, if too much silicon is added, the low hardness of the pitch material cannot completely suppress the expansion of silicon, which may lead to structural collapse and other material damage caused by silicon volume expansion. This will cause a rapid decay of reversible capacity and reduce the cycling performance of the material.

[0050] Therefore, based on the above problems, developing a new type of silicon-carbon anode material to efficiently suppress the volume expansion of silicon and improve the capacity of silicon-carbon anode materials is an urgent technical problem to be solved.

[0051] In one specific embodiment of the present invention, a silicon-carbon anode material is provided, the silicon-carbon anode material comprising a composite core composed of a silicon-based material and a pore-formed MOF material, and a carbon layer covering the surface of the composite core;

[0052] At least a portion of the silicon-based material is embedded in the pores of the pore-forming MOFs material;

[0053] The average pore size of the MOFs material after pore formation is 400-1000nm, for example, it can be 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm or 1000nm, etc.

[0054] This invention constructs a novel silicon-carbon anode material by embedding at least a portion of a silicon-based material into the pores of a pore-formed MOF (Metal-Oxide-Factory) material with an average pore size of 400-1000 nm. This not only fully utilizes the capacity advantage of silicon but also further enhances the capacity of the silicon-carbon anode material and suppresses silicon volume expansion through the presence of a large pore size. Furthermore, the exposed silicon-based material not embedded in the pores is encapsulated by a carbon layer, preventing direct contact with the electrolyte and improving the material's structural stability and conductivity. The silicon-carbon anode material constructed in this invention exhibits excellent capacity performance, cycle performance, and coulombic efficiency, as well as low EIS (Electro-Induced Sequence) and excellent rate performance.

[0055] In this invention, the pore size of the MOFs material after pore formation is in the range of 400-1000 nm, which allows for the embedding of more silicon, thereby increasing the material's capacity. If the pore size is too small, the amount of embedded silicon will be insufficient, affecting the improvement of the material's capacity; if the pore size is too large, the material structure will be unstable and prone to collapse.

[0056] Furthermore, the MOFs material after pore formation includes macroporous MOFs material, preferably HKUST-1.

[0057] In this invention, HKUST-1 is prepared in a simple and efficient manner. It can be prepared by a simple ball milling method and a water washing process in two steps, which has certain industrialization prospects.

[0058] Furthermore, the average pore size of the MOFs material after pore formation is 500-800 nm.

[0059] Furthermore, the porosity of the MOFs material after pore formation is 10-60%, for example, it can be 10%, 20%, 30%, 40%, 50% or 60%, etc., preferably 20-40%.

[0060] In this invention, if the porosity of the MOFs material after pore formation is too small, too little nano-silicon will be embedded, resulting in the inability to fully utilize the structural advantages of the MOFs material and the high capacity advantage of the nano-silicon; if the porosity of the MOFs material after pore formation is too large, too much silicon-based material will be embedded, and the mechanical properties provided by the MOFs will be insufficient to support the stress caused by the volume expansion of silicon, thereby causing the MOFs structure to be destroyed and the material performance to be unstable.

[0061] Furthermore, the silicon-based material includes any one or a combination of at least two of nano-silicon, micro-silicon, or silicon oxide.

[0062] It should be noted that silicon oxide refers to SiO. x, where 0 < x ≤ 2, for example, it can be 0.5, 1, 1.5, 2, etc.

[0063] Furthermore, the particle size D50 of the silicon-based material is 20 - 200 nm, for example, it can be 20 nm, 50 nm, 100 nm, 15 nm, or 200 nm, etc., and preferably 20 - 60 nm.

[0064] In the present invention, if the particle size D50 of the silicon-based material is too large, it cannot be well embedded into the pores of the post-pored MOFs material; if the particle size D50 of the silicon-based material is too small, the cost is too high.

[0065] Furthermore, the mass ratio of the silicon-based material to the post-pored MOFs material is 1:(2 - 5), for example, it can be 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5, etc.

[0066] In the present invention, the mass ratio of the silicon-based material to the post-pored MOFs material affects the amount of the silicon-based material embedded in the post-pored MOFs material. If the mass ratio of the silicon-based material to the post-pored MOFs material is too small, that is, the amount of the post-pored MOFs material used is too large, the silicon-based material cannot completely occupy the pores of the post-pored MOFs material, resulting in the material's capacity not being maximized; if the mass ratio of the silicon-based material to the post-pored MOFs material is too large, that is, the amount of the post-pored MOFs material used is too small, too much silicon-based material will be embedded, forming more exposed structures, causing the material's performance to be unstable.

[0067] Furthermore, the thickness of the carbon layer is 100 - 1000 nm, for example, it can be 100 nm, 300 nm, 500 nm, 700 nm, 900 nm, or 1000 nm, etc., and preferably 200 - 500 nm.

[0068] In the present invention, by controlling the thickness of the carbon layer, it is not only beneficial to enhance the conductivity but also can ensure the stability of the silicon-based material, thereby further facilitating the carbon layer to inhibit the volume expansion of silicon during charge and discharge.

[0069] In another specific embodiment of the present invention, a preparation method of the silicon-carbon negative electrode material as described above is provided, and the preparation method includes the following steps:

[0070] (1) Mix the post-pored MOFs material and the silicon-based material, and heat to obtain a composite material;

[0071] (2) Mix the composite material and a carbon source, and perform carbonization treatment to obtain the silicon-carbon negative electrode material.

[0072] The method provided by this invention has low energy consumption, is easy to prepare, is highly efficient and pollution-free, is environmentally friendly, and can be industrialized.

[0073] Furthermore, the heating temperature in step (1) is 80-100℃, for example, it can be 80℃, 90℃ or 100℃.

[0074] Furthermore, the heating time in step (1) is 4-6 hours, for example, it can be 4 hours, 5 hours or 6 hours.

[0075] Further, the pore-forming MOFs material described in step (1) is prepared by the following method, which includes the following steps: mixing organic ligands, metal salts and pore-forming agents to obtain the pore-forming MOFs material.

[0076] Furthermore, the pore-forming agent is a soluble inorganic salt.

[0077] Furthermore, the soluble inorganic salt includes any one or a combination of at least two of sodium, potassium, magnesium, or aluminum salts. For example, it could be sodium chloride, potassium chloride, magnesium chloride, or aluminum chloride.

[0078] Furthermore, the organic ligand includes pyromellitic acid.

[0079] Furthermore, the metal salt includes a copper salt, which includes any one or a combination of at least two of copper acetate, copper nitrate, copper sulfate, copper phosphate, and copper halide.

[0080] Further, the mass ratio of the organic ligand, pore-forming agent, and metal salt is (0.5-1):(1-5):(0.5-1), wherein the organic ligand selection range "0.5-1" can be, for example, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, etc., the pore-forming agent selection range "1-5" can be, for example, 1, 2, 3, 4, or 5, etc., and the metal salt selection range "0.5-1" can be, for example, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, etc.

[0081] Furthermore, the blending method includes ball milling.

[0082] Furthermore, the ball milling time is 1-6 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, etc.

[0083] Furthermore, the rotational speed of the ball mill is 100-400 rpm, for example, it can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm or 400 rpm, etc.

[0084] Furthermore, the ball-to-material ratio of the ball mill is (1-10):1, for example, it can be 1:1, 3:1, 5:1, 7:1 or 10:1, etc.

[0085] Furthermore, after the blending is completed, the resulting material undergoes post-processing, which includes washing and drying.

[0086] The present invention does not limit the detergent used in the washing process; for example, it may be ethanol or water.

[0087] The present invention does not limit the drying method; for example, it may be vacuum drying.

[0088] Furthermore, the carbon source in step (2) includes any one or a combination of at least two of organic carbon sources, graphite materials, or porous carbon materials. For example, it could be citric acid, tannic acid, sucrose, or glucose.

[0089] Further, the mass ratio of the composite material and the carbon source in step (2) is 1:(0.5-1.5), for example, it can be 1:0.5, 1:0.7, 1:0.9, 1:1.1, 1:1.3 or 1:1.5, etc.

[0090] Further, the carbonization temperature in step (2) is 80-100℃, for example, it can be 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃ or 100℃, etc.

[0091] Furthermore, the carbonization process in step (2) takes 4-6 hours, for example, 4 hours, 5 hours or 6 hours.

[0092] Furthermore, the preparation method includes the following steps:

[0093] (Ⅰ) Tristyric acid, pore-forming agent and soluble copper salt were ball-milled and mixed according to the mass ratio of (0.5-1):(1-5):(0.5-1), and the mixture was washed and dried to obtain the pore-forming MOF material.

[0094] The ball milling time is 1-6 hours, the ball milling speed is 100-400 rpm, and the ball-to-material ratio is (1-10):1.

[0095] (II) The pore-forming MOFs material and silicon-based material are mixed in a solvent at a mass ratio of (2-5):1, heated, filtered and dried to obtain a composite material.

[0096] The heating temperature is 80-100℃, and the heating time is 4-6 hours.

[0097] (III) The composite material and carbon source are mixed at a mass ratio of 1:(0.5-1.5) and carbonized at 80-100℃ for 4-6 hours to obtain the silicon-carbon anode material.

[0098] In this invention, the carbonization process can be carried out by rotary evaporation or oil bath.

[0099] In another specific embodiment of the present invention, a lithium-ion battery is provided, wherein the negative electrode of the lithium-ion battery includes the silicon-carbon negative electrode material as described above.

[0100] Example 1

[0101] This embodiment provides a silicon-carbon anode material, which includes a composite core composed of nano-silicon and pore-formed HKUST-1, and a carbon layer covering the surface of the composite core. At least a portion of the nano-silicon is embedded in the pores of the pore-formed HKUST-1, and the average pore size of the pore-formed MOFs material is 700 nm.

[0102] The porosity of the HKUST-1 after pore formation is 23.62%, the particle size D50 of the nano-silicon is 100nm, the mass ratio of the nano-silicon to the HKUST-1 after pore formation is 1:2, and the thickness of the carbon layer is 500nm.

[0103] This embodiment also provides a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0104] (1) 1g of pyromellitic acid, 1g of sodium chloride and 1g of copper acetate were put into a ball mill in a mass ratio of 1:1:1 and mixed by ball milling. Then the mixture was washed, filtered and dried to remove the pore-forming agent and obtain the pore-forming HKUST-1.

[0105] The ball-to-material ratio in the ball mill was 10:1, the milling time was 1.5 hours, and the milling speed was 250 rpm.

[0106] (2) Mix 2g of the pore-forming HKUST-1 and 1g of nano-silicon in water at a mass ratio of 2:1, heat at 90°C for 5h, filter and dry to obtain the composite material;

[0107] (3) Mix 1g of the composite material and 1g of citric acid at a mass ratio of 1:1 and perform carbonization treatment at 90°C for 5h to obtain the silicon-carbon anode material.

[0108] Figure 1 and Figure 2SEM images of HKUST-1 prepared in this embodiment and HKUST-1 after carbon coating are shown respectively. As can be seen from the figures, the outer layer is a carbon layer and the inner layer is a structure in which nano-silicon is embedded in the pores of HKUST-1.

[0109] Example 2

[0110] This embodiment provides a silicon-carbon anode material, which includes a composite core composed of nano-silicon and pore-formed HKUST-1, and a carbon layer covering the surface of the composite core. At least a portion of the nano-silicon is embedded in the pores of the pore-formed HKUST-1, and the average pore size of the pore-formed HKUST-1 is 400 nm.

[0111] The porosity of the HKUST-1 after pore formation is 32.58%, the particle size D50 of the nano-silicon is 20nm, the mass ratio of the nano-silicon to the HKUST-1 after pore formation is 1:5, and the thickness of the carbon layer is 100nm.

[0112] This embodiment also provides a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0113] (1) 0.5g of pyromellitic acid, 5g of potassium chloride and 0.5g of copper nitrate were put into a ball mill in a mass ratio of 0.5:5:0.5, and then the mixture was ball-milled and mixed. After washing, filtration and drying, the pore-forming agent was removed to obtain the pore-forming HKUST-1.

[0114] The ball-to-material ratio of the ball mill is 10:1, the milling time is 1 hour, and the milling speed is 400 rpm.

[0115] (2) 2g of the pore-forming HKUST-1 and 0.4g of nano-silicon were stirred and mixed in water at a mass ratio of 5:1, heated at 90°C for 4 hours, filtered and dried to obtain the composite material;

[0116] (3) Mix 1g of the composite material and 0.5g of citric acid at a mass ratio of 1:0.5 and perform carbonization treatment at 80°C for 5h to obtain the silicon-carbon anode material.

[0117] Example 3

[0118] This embodiment provides a silicon-carbon anode material, which includes a composite core composed of nano-silicon and pore-formed HKUST-1, and a carbon layer covering the surface of the composite core. At least a portion of the nano-silicon is embedded in the pores of the pore-formed HKUST-1, and the average pore size of the pore-formed HKUST-1 is 1000 nm.

[0119] The porosity of the HKUST-1 after pore formation is 28.37%, the particle size D50 of the nano-silicon is 200nm, the mass ratio of the nano-silicon to the HKUST-1 after pore formation is 1:3.5, and the thickness of the carbon layer is 1000nm.

[0120] This embodiment also provides a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0121] (1) 0.7g of pyromellitic acid, 3g of magnesium chloride and 0.7g of copper acetate were put into a ball mill in a mass ratio of 0.7:3:0.7, and then the mixture was ball-milled and mixed. After washing, filtration and drying, the pore-forming agent was removed to obtain the pore-forming HKUST-1.

[0122] The ball-to-material ratio in the ball mill was 10:1, the milling time was 2 hours, and the milling speed was 100 rpm.

[0123] (2) 1.4g of the pore-forming HKUST-1 and 0.4g of nano-silicon were stirred and mixed in water at a mass ratio of 3.5:1, heated at 100°C for 4 hours, filtered and dried to obtain the composite material;

[0124] (3) Mix 1g of the composite material and 1.5g of citric acid at a mass ratio of 1:1.5 and perform carbonization treatment at 100°C for 4h to obtain the silicon-carbon anode material.

[0125] Example 4

[0126] The difference between this embodiment and embodiment 1 is that the amount of sodium chloride used in step (1) is adjusted so that the porosity of the HKUST-1 after pore formation is 5%.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Example 5

[0129] The difference between this embodiment and embodiment 1 is that the amount of sodium chloride used in step (1) is adjusted so that the porosity of the HKUST-1 after pore formation is 65%.

[0130] The remaining preparation methods and parameters are consistent with those in Example 1.

[0131] Example 6

[0132] The difference between this embodiment and Embodiment 1 is that the particle size D50 of the silicon-based material is 10 nm.

[0133] The remaining preparation methods and parameters are consistent with those in Example 1.

[0134] Example 7

[0135] The difference between this embodiment and Embodiment 1 is that the particle size D50 of the silicon-based material is 210 nm.

[0136] The remaining preparation methods and parameters are consistent with those in Example 1.

[0137] Example 8

[0138] The difference between this embodiment and embodiment 1 is that the amount of citric acid used in step (3) is adjusted so that the thickness of the carbon layer is 80 nm.

[0139] The remaining preparation methods and parameters are consistent with those in Example 1.

[0140] Example 9

[0141] The difference between this embodiment and embodiment 1 is that the amount of citric acid used in step (3) is adjusted so that the thickness of the carbon layer is 1100 nm.

[0142] The remaining preparation methods and parameters are consistent with those in Example 1.

[0143] Example 10

[0144] The difference between this embodiment and Embodiment 1 is that the mass ratio of the nano-silicon to the HKUST-1 after pore formation is 1:1.

[0145] The remaining preparation methods and parameters are consistent with those in Example 1.

[0146] Example 11

[0147] The difference between this embodiment and Embodiment 1 is that the mass ratio of the nano-silicon to the HKUST-1 after pore formation is 1:6.

[0148] The remaining preparation methods and parameters are consistent with those in Example 1.

[0149] Example 12

[0150] The difference between this comparative example and Example 1 is that the pore-forming HKUST-1 is replaced with the pore-forming ZIF-67, that is, step (1) is replaced with the following steps: cobalt acetate, 2-methylimidazole and 40 mL of ethanol are mixed in a mass ratio of 1:1, centrifuged and dried to obtain ZIF-67, and then ZIF-67 and tannic acid are mixed to obtain the pore-forming ZIF-67.

[0151] The remaining preparation methods and parameters are consistent with those in Example 1.

[0152] Comparative Example 1

[0153] The difference between this comparative example and Example 1 is that sodium chloride is not added in step (1), that is, HKUST-1 is not used to create pores, but the obtained HKUST-1 is directly mixed with nano-silicon.

[0154] The remaining preparation methods and parameters are consistent with those in Example 1.

[0155] Comparative Example 2

[0156] The difference between this comparative example and Example 1 is that the amount of sodium chloride used in step (1) is adjusted so that the average pore size of the HKUST-1 after pore formation is 300 nm.

[0157] The remaining preparation methods and parameters are consistent with those in Example 1.

[0158] Comparative Example 3

[0159] The difference between this comparative example and Example 1 is that the amount of sodium chloride used in step (1) is adjusted so that the average pore size of the HKUST-1 after pore formation is 1100 nm.

[0160] The remaining preparation methods and parameters are consistent with those in Example 1.

[0161] Comparative Example 4

[0162] The difference between this comparative example and Example 1 is that steps (1)-(3) are omitted, i.e., the silicon-carbon anode material is replaced with nano-silicon as the anode material.

[0163] Comparative Example 5

[0164] The difference between this comparative example and Example 1 is that steps (1)-(3) are omitted, i.e., the silicon-carbon anode material is replaced with graphite anode material.

[0165] Performance testing

[0166] The negative electrode materials prepared in Examples 1-12 and Comparative Examples 1-5 were mixed with conductive carbon black and polyacrylic acid in a mass ratio of 90:5:5 in deionized water. The mixture was then mechanically stirred on a magnetic stirrer for 12 hours. After stirring, the resulting slurry was slowly and evenly coated onto copper foil to obtain a negative electrode sheet. The negative electrode sheet was placed in a vacuum drying oven and dried at 80°C for 12 hours. The next day, the sheet was removed and cut into 12mm round pieces using a Shenzhen Kejing cutting machine for later use.

[0167] The prepared negative electrode sheet was transferred to a glove box to assemble a full cell. Using a 2032 battery case, a polypropylene separator, and commercial LB315 electrolyte, a half cell was assembled with the prepared negative electrode sheet as the negative electrode and a lithium sheet as the counter electrode. The assembled battery needed to stand for 12 hours before the following electrochemical tests were performed.

[0168] Various technical tests were conducted using the Newway button cell tester, including charge / discharge cycle and rate performance tests.

[0169] The test conditions were: constant temperature and humidity at 25℃, voltage range of 0.01-1.5V; the rate performance test consisted of 5 cycles at each current density, i.e., at 0.1Ag. -1 2Ag -1 0.1Ag -1 The test was conducted at a specific current density. The results are shown in Table 1.

[0170] Table 1

[0171]

[0172] It should be noted that "plummeting" refers to a sudden drop in battery capacity, reaching a stage where it is basically impossible to charge or discharge.

[0173] analyze:

[0174] As shown in the table above, this invention embeds at least a portion of the silicon-based material into the pores of the pore-formed MOFs material with a pore size of 400-1000 nm. This not only fully utilizes the capacity advantage of silicon but also effectively suppresses the volume expansion of silicon due to the large pore size. Furthermore, the exposed silicon-based material not embedded in the pores is encapsulated by a carbon layer, preventing direct contact with the electrolyte and improving the structural stability and conductivity of the material. The resulting silicon-carbon anode material not only exhibits excellent capacity performance, cycle performance, and coulombic efficiency but also low electrochemical impedance, as well as excellent kinetic and rate performance.

[0175] A comparison of the data results from Examples 1 and 4-5 shows that if the porosity of HKUST-1 after pore formation is too small, too little nano-silicon will be embedded, resulting in the inability to fully utilize the structural advantages of the HKUST-1 material after pore formation and the high capacity advantage of nano-silicon. If the porosity of HKUST-1 after pore formation is too large, too much silicon-based material will be embedded, and the mechanical properties provided by MOFs will be insufficient to support the stress caused by the volume expansion of silicon, thereby causing the MOF structure to be destroyed and the material performance to be unstable.

[0176] A comparison of the data results from Examples 1 and 6-7 shows that if the particle size D50 of the silicon-based material is too large, it cannot be well embedded into the channels of HKUST-1 after pore formation, resulting in a decrease in material performance; if the particle size D50 of the silicon-based material is too small, although the performance is better, the cost is too high.

[0177] A comparison of the data results from Examples 1 and 8-9 shows that by controlling the thickness of the carbon layer, it is not only beneficial to enhance conductivity, but also to ensure the stability of silicon-based materials, thereby further helping the carbon layer to suppress the volume expansion of silicon during charging and discharging.

[0178] A comparison of the data results from Examples 1 and 10-11 shows that the mass ratio of nano-silicon to the pore-forming HKUST-1 affects the amount of nano-silicon embedded in the pore-forming HKUST-1. If the mass ratio of nano-silicon to the pore-forming HKUST-1 is too small, that is, if the amount of pore-forming HKUST-1 is too large, the nano-silicon cannot completely occupy the pores of the pore-forming HKUST-1, resulting in the material's capacity not being effectively improved. If the mass ratio of nano-silicon to the pore-forming HKUST-1 is too large, that is, if the amount of pore-forming HKUST-1 is too small, too much nano-silicon will be embedded, forming more exposed structures and causing the material's performance to be unstable.

[0179] A comparison of the data results from Example 1 and Example 12 shows that if the HKUST-1 after pore formation is replaced with the ZIF-67 after pore formation, the capacity retention rate and rate performance will decrease to varying degrees.

[0180] Comparing the data results of Example 1 and Comparative Example 1, it can be seen that if HKUST-1 is not pore-formed, the nano-silicon cannot be embedded in the pores, resulting in the nano-silicon being exposed on the outside and potentially coming into direct contact with the electrolyte. Although the carbon layer provides some protection, after a certain number of cycles, the carbon layer is destroyed, and the exposed nano-silicon cannot be effectively protected, leading to the failure of the material's electrochemical performance.

[0181] A comparison of the data results from Example 1 and Comparative Examples 2-3 shows that the pore size of the HKUST-1 after pore formation is in the range of 400-1000 nm, which allows for the embedding of more silicon, thus increasing the material's capacity. If the pore size is too small, the amount of embedded silicon will be insufficient, affecting the improvement of the material's capacity; if the pore size is too large, the material structure will be unstable and prone to collapse, affecting the improvement of the material's performance.

[0182] A comparison of the data results from Example 1 and Comparative Examples 4-5 shows that if only nano-silicon or graphite is used as the negative electrode material, nano-silicon, although having a high capacity, is prone to premature failure of its electrochemical performance after a certain number of cycles; graphite, although having excellent capacity retention, has a low initial capacity and low specific capacity, making it difficult to meet the current market demand for cell energy density.

[0183] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material comprises a composite core consisting of silicon-based material and MOFs material after pore formation, and a carbon layer covering the surface of the composite core. At least a portion of the silicon-based material is embedded in the pores of the MOFs material after pore formation, and the exposed silicon-based material not embedded in the pores is encapsulated by a carbon layer. The average pore size of the MOFs material after pore formation is 400-800 nm; The mass ratio of the silicon-based material to the pore-forming MOFs material is 1:(2-5); The thickness of the carbon layer is 100-1000 nm.

2. The silicon-carbon anode material according to claim 1, characterized in that, The MOFs material after pore formation includes HKUST-1; And / or, the average pore size of the MOFs material after pore formation is 500-800 nm; And / or, the porosity of the MOFs material after pore formation is 10-60%; And / or, the silicon-based material includes any one or a combination of at least two of nano-silicon, micro-silicon, or silicon oxide; And / or, the particle size D50 of the silicon-based material is 20-200 nm.

3. The silicon-carbon anode material according to claim 2, characterized in that, The porosity of the MOFs material after pore formation is 20-40%; And / or, the particle size D50 of the silicon-based material is 20-60 nm.

4. The silicon-carbon anode material according to claim 1, characterized in that, The thickness of the carbon layer is 200-500 nm.

5. A method for preparing the silicon-carbon anode material as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: (1) Mix the pore-forming MOFs material with the silicon-based material and heat to obtain a composite material; (2) The composite material and carbon source are mixed and carbonized to obtain the silicon-carbon anode material.

6. The preparation method according to claim 5, characterized in that, The heating temperature in step (1) is 80-100℃; And / or, the heating time is 4-6 hours.

7. The preparation method according to claim 5, characterized in that, The MOFs material after pore formation in step (1) is prepared by the following method, which includes the following steps: Organic ligands, metal salts and pore-forming agents are blended, and the pore-forming agent is removed to obtain pore-forming MOF materials.

8. The preparation method according to claim 7, characterized in that, The pore-forming agent is a soluble inorganic salt; The soluble inorganic salt includes any one or a combination of at least two of sodium, potassium, magnesium, or aluminum salts; And / or, the mass ratio of the organic ligand, pore-forming agent and metal salt is (0.5-1):(1-5):(0.5-1); And / or, the blending method includes ball milling; The ball milling time is 1-6 hours; The ball mill rotates at a speed of 100-400 rpm; The ball-to-material ratio of the ball mill is (1-10):

1.

9. The preparation method according to claim 5, characterized in that, The carbon source in step (2) includes any one or a combination of at least two of organic carbon sources, graphite materials, or porous carbon materials; And / or, the mass ratio of the composite material to the carbon source in step (2) is 1:(0.5-1.5); And / or, the carbonization temperature in step (2) is 80-100℃.

10. The preparation method according to claim 5, characterized in that, The preparation method includes the following steps: (I) The organic ligand, pore-forming agent and metal salt in the MOF material are ball-milled and mixed according to the mass ratio of (0.5-1):(1-5):(0.5-1), and the mixture is washed and dried to obtain the pore-forming MOF material. The ball milling time is 1-6 hours, the ball milling speed is 100-400 rpm, and the ball-to-material ratio is (1-10):

1. (II) The pore-forming MOFs material and silicon-based material are mixed in a solvent at a mass ratio of (2-5):1, heated, filtered and dried to obtain a composite material; The heating temperature is 80-100℃, and the heating time is 4-6 hours. (III) The composite material and carbon source are mixed at a mass ratio of 1:(0.5-1.5) and carbonized at 80-100℃ for 4-6 hours to obtain the silicon-carbon anode material.

11. A lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery includes the silicon-carbon negative electrode material as described in any one of claims 1-4.

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