Silicon-based negative electrode material, preparation method thereof and battery

Abstract

The invention provides a silicon-based negative electrode material, a preparation method thereof and a battery, the silicon-based negative electrode material comprises an inner core and an artificial SEI film coating the surface of the inner core, the inner core comprises a silicon-containing material, and the artificial SEI film comprises a polymer material; monomers of the polymer material contain a triazine ring, at least two trihalomethyl groups and at least one furan ring. The artificial SEI film of the silicon-based negative electrode material is a specific polymer containing multiple functional groups, the high-temperature stability, the conductivity, the fast charging capacity, the structural stability and the like of a silicon-containing material can be improved at the same time, the performance defects of the silicon-containing material are comprehensively overcome, and particularly the high-temperature application requirement of a battery is further met.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a silicon-based anode material, its preparation method, and a battery. Background Technology

[0002] Currently, graphite is the primary material used in lithium-ion battery anodes. However, the theoretical specific capacity of commercially available graphite anode materials is relatively low. To further improve battery energy density, finding anode materials with higher specific capacity has become a research focus. Silicon-based anode materials are mainly composed of silicon and graphite. They have high theoretical specific capacity, good safety, abundant reserves, and low cost. They can provide channels for lithium-ion insertion and extraction from various directions and have excellent fast-charging performance, making them the most promising next-generation lithium-ion battery anode material.

[0003] However, silicon-based anode materials also have significant drawbacks. Significant volume changes occur during charge and discharge, leading to particle pulverization and repeated SEI film rupture and regeneration. This continuously consumes active lithium and electrolyte, drastically reducing the battery's cycle life. Current technologies improve the performance of silicon-based anode materials by coating them with artificial SEI films. However, existing artificial SEI films suffer from poor coating uniformity, easy oxidation of the silicon surface at high temperatures, insufficient conductivity, and an imbalance between mechanical support and ion conduction, making them unsuitable for applications in high-temperature environments.

[0004] Based on the above research, there is a need to provide a silicon-based anode material that can comprehensively improve the performance defects of silicon materials and meet the application requirements in high-temperature environments. Summary of the Invention

[0005] The purpose of this invention is to provide a silicon-based anode material, its preparation method, and a battery. The artificial SEI film of the silicon-based anode material is a specific polymer containing multiple functional groups, which not only improves the high-temperature stability, conductivity, fast charging capability, and structural stability of silicon-containing materials, but also comprehensively improves the performance defects of silicon-containing materials, and in particular meets the high-temperature application requirements of batteries.

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

[0007] In a first aspect, the present invention provides a silicon-based anode material, the silicon-based anode material comprising a core and an artificial SEI film coated on the surface of the core, the core comprising a silicon-containing material and the artificial SEI film comprising a polymer material;

[0008] The structural formula of the monomer of the polymer material is shown in Formula I):

[0009] ;

[0010] Formula I);

[0011] Among them, at least two of R1, R2 and R3 contain trihalomethyl groups and at least one contains a furan ring.

[0012] This invention employs a triazine polymer containing multiple functional groups as an artificial SEI film. The furan ring in the polymer material is located on the side chain of the molecular chain and forms a conjugated structure with the triazine ring, significantly improving the conductivity of the artificial SEI film, overcoming the inherent low conductivity defect of silicon-based materials, optimizing the lithium-ion transport path, and improving fast-charging performance. Simultaneously, the rigid structure of the furan ring enhances the mechanical strength of the artificial SEI film, inhibiting the breakage of silicon-containing materials. Furthermore, the good compatibility of the furan ring with the electrolyte further improves the interfacial stability of the battery at high temperatures, overcoming the limitations of insufficient high-temperature performance of existing triazine materials and improving the interfacial stability of silicon-containing materials at high temperatures. The triazine ring in the polymer material, as the core framework of the molecular chain, provides good rigidity and chemical stability, and the conjugated system with the furan ring further optimizes the electron transport path and reduces charge transfer resistance. The material also contains trihalomethyl groups, with two trihalomethyl groups in each repeating unit. These trihalomethyl groups can release halogens at high temperatures to form a passivation layer, inhibiting oxidation on the surface of silicon-containing materials. Simultaneously, they can adjust the density of the artificial SEI film, forming a network structure with a specific porosity, balancing ion conduction efficiency and mechanical support capability. This ensures rapid lithium-ion migration while buffering the volume expansion stress of silicon particles. Furthermore, the vinyl groups in the monomers of the polymer material described in this invention form a rigid framework after polymerization and cross-linking. Combined with the rigid structure of the furan ring and the stable properties of the triazine ring, this significantly enhances the structural strength of the silicon-containing material, suppressing the breakage and shedding of silicon particles during charging and discharging. Therefore, the synergistic effect of the furan ring, triazine ring, and trihalomethyl groups in this invention comprehensively improves the performance defects of silicon-based anodes, while also enhancing the battery's cycle performance, fast charging performance, rate performance, and high-temperature performance.

[0013] Preferably, both R1 and R2 contain trihalomethyl groups.

[0014] Preferably, R3 contains a furan ring.

[0015] In the monomers of the polymer material described in this invention, one side of the furan ring also contains an alkyl chain, such as methyl, which can enhance the flexibility of the polymer molecular chain, improve the adhesion of the artificial SEI film to the surface of the silicon-containing material, and enhance the interfacial bonding force.

[0016] Preferably, the trihalomethyl group includes a trichloromethyl group.

[0017] Preferably, the monomers of the polymer material include (CAS: 156360-76-8) and / or (CAS: 154880-05-4).

[0018] Preferably, the number-average molecular weight of the polymer material is 8 × 10⁻⁶. 4 g / mol ~ 9 × 10 7 g / mol, for example, could be 8 × 10⁻⁶ g / mol. 4 g / mol, 8×10 5 g / mol, 8×10 6 g / mol or 9×10 7 The values ​​are in g / mol, but not limited to the listed values; other unlisted values ​​within the range also apply.

[0019] The number-average molecular weight of the polymer material of the present invention is preferably within the above-mentioned range, which enables the artificial SEI membrane to have both good mechanical strength and ion transport efficiency, thereby improving the cycle performance and rate performance of the battery. If the number-average molecular weight of the polymer material is too low, the mechanical properties of the artificial SEI membrane will be insufficient. However, if the number-average molecular weight of the polymer material is too high, the viscosity of the polymer solution will be too high, affecting the uniformity of the coating of the artificial SEI membrane.

[0020] Preferably, in the silicon-based anode material, the mass percentage of the artificial SEI film is 0.3wt% to 4wt%, for example, it can be 0.3wt%, 1.3wt%, 2.3wt%, 3.3wt% or 4wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the thickness of the artificial SEI film is 30nm~120nm, for example, it can be 30nm, 60nm, 90nm or 120nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] The thickness of the artificial SEI membrane described in this invention affects the ion transport performance and structural stability of the material. If the thickness of the artificial SEI membrane is too large, the ion transport performance of the material will be reduced, resulting in poor rate performance and cycle performance of the battery. However, if the thickness is too thin, the artificial SEI membrane is prone to breakage.

[0023] Preferably, the porosity of the artificial SEI membrane is 15% to 30%, for example, it can be 15%, 20%, 25% or 30%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] The porosity of the artificial SEI membrane described in this invention is within a preferred range, enabling the artificial SEI membrane to balance ion transport performance and mechanical strength. If the porosity of the artificial SEI membrane is too low, the lithium-ion transport channels of the material are insufficient, resulting in a decrease in the fast-charging performance of the battery. However, if the porosity of the artificial SEI membrane is too high, the mechanical strength of the artificial SEI membrane is insufficient, and it cannot effectively suppress the expansion of silicon particles, resulting in a deterioration in the cycle stability of the battery.

[0025] Preferably, the particle size D50 of the silicon-containing material is 3μm to 7μm, for example, it can be 3μm, 4μm, 5μm, 6μm or 7μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] If the particle size D50 of the silicon-containing material described in this invention is too large, the ion transport performance of the material will deteriorate, resulting in a decrease in the rate performance of the battery. However, if the particle size D50 of the silicon-containing material is too small, the silicon-based anode material will be difficult to disperse during the homogenization process.

[0027] Preferably, the specific surface area of ​​the silicon-containing material is 1 m². 2 / g~4m 2 / g, for example, could be 1m 2 / g、2m 2 / g、3m 2 / g or 4m 2 / g, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0028] Preferably, the silicon-containing material includes silicon-carbon material (vapor-phase silicon-carbon material).

[0029] Preferably, the silicon-carbon material comprises silicon grains and a hard carbon substrate.

[0030] Preferably, the mass ratio of the silicon grains to the hard carbon substrate is (0.4~1.2):1, for example, it can be 0.4:1, 0.6:1, 0.8:1, 1:1 or 1.2:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] In the silicon-carbon material described in this invention, if the silicon content is too low, the specific capacity and initial efficiency will decrease; if the silicon content is too high, the expansion rate of the silicon-carbon material will be large.

[0032] Preferably, the hard carbon substrate includes micropores and mesopores.

[0033] Preferably, the pore size of the micropores is 0.8nm to 1.5nm, for example, it can be 0.8nm, 1nm, 1.2nm or 1.5nm, and the pore volume accounts for 20% to 40% of the total pore volume of the hard carbon substrate, for example, it can be 20%, 25%, 30%, 35% or 40%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] The micropore size in the hard carbon substrate described in this invention is within a specific range. If the micropore size is too small, it cannot effectively accommodate the small volume deformation of silicon particles. However, if the micropore size is too large, the risk of collapse of the pore structure of the hard carbon substrate increases.

[0035] Preferably, the pore size of the mesopore is 5nm to 20nm, for example, it can be 5nm, 10nm, 15nm or 20nm, and the pore volume accounts for 60% to 80% of the total pore volume of the hard carbon substrate, for example, it can be 60%, 65%, 70%, 75% or 80%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] The hard carbon substrate of the present invention has a mesopore diameter within a specific range. If the mesopore diameter is too small, there is insufficient space to buffer the expansion of silicon particles. After the silicon particles expand, they squeeze the pore walls, which will cause the hard carbon skeleton to break. However, if the mesopore diameter is too large, the skeleton density of the hard carbon substrate will decrease, thereby reducing the compaction density of the electrode and the energy density of the battery.

[0037] Therefore, the hierarchical porous structure of the hard carbon substrate of the present invention provides a buffer space for the volume expansion of silicon particles, forming a dual protection with the artificial SEI film, effectively suppressing the collapse of the material structure.

[0038] Preferably, the size of the silicon grain is 0.8nm to 2nm, for example, it can be 0.8nm, 1nm, 1.5nm or 2nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] When the silicon grain size is too large, the expansion rate of the silicon-carbon material is large, resulting in poor battery cycle performance. If the silicon grain size is too small, the contact area between the silicon grain and hard carbon is small, resulting in a decrease in the rate performance of the battery.

[0040] Secondly, the present invention provides a method for preparing a silicon-based anode material as described in the first aspect, the method comprising the following steps:

[0041] A silicon-containing material, a polymer material, and a first organic solvent are mixed to obtain a mixed slurry, which is then spray-dried to obtain the silicon-based anode material.

[0042] Preferably, the mixing temperature is 30℃~100℃, for example, 30℃, 50℃, 70℃ or 100℃, and the time is 5h~10h, for example, 5h, 7h, 9h or 10h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the mixing of the silicon-containing material, the polymer material, and the first organic solvent includes first dispersing the polymer material in the first organic solvent to prepare a mixed solution with a mass fraction of 10wt% to 29wt%, for example, 10wt%, 12wt%, 20wt%, 25wt%, or 29wt%, and then adding the silicon-containing material to the mixed solution for mixing.

[0044] Preferably, the inlet temperature of the spray dryer is 100℃~200℃, for example, 100℃, 130℃, 150℃, 170℃ or 200℃, and the outlet temperature is 60℃~100℃, for example, 60℃, 80℃, 90℃ or 100℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the method for preparing the polymer material includes:

[0046] The monomers of the polymer material, the second organic solvent and the initiator are mixed and polymerized to obtain a polymer solution. The polymer solution is added to the precipitated solvent, and then the mixture is allowed to stand, washed (3 to 5 times, for example, 3, 4 or 5 times) and dried to obtain the polymer material.

[0047] Preferably, the polymerization reaction temperature is 60℃~110℃, for example, 60℃, 80℃, 100℃ or 110℃, and the time is 4h~9h, for example, 4h, 6h, 8h or 9h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the settling time is 2h to 4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, in the mixture obtained by mixing the monomer of the polymer material, the second organic solvent and the initiator, the concentration of the monomer of the polymer material is 0.5 mol / L to 2.0 mol / L, for example, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, the amount of the initiator added is 0.1wt% to 0.8wt% of the monomer mass of the polymer material, for example, it can be 0.1wt%, 0.3wt%, 0.5wt% or 0.8wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] Preferably, the initiator includes any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide.

[0052] Preferably, the first organic solvent and the second organic solvent each independently comprise any one or a combination of at least two of benzene, toluene, NMP (N-methylpyrrolidone) or DMF (N,N-dimethylformamide).

[0053] Preferably, the precipitation solvent includes any one or a combination of at least two of propanol, isopropanol, or acetone.

[0054] Thirdly, the present invention provides a battery comprising the silicon-based anode material as described in the first aspect.

[0055] Preferably, the electrolyte of the battery includes lithium salt additives, phosphate ester additives, and low impedance additives.

[0056] The electrolyte of the battery described in this invention preferably further includes lithium salt additives, phosphate ester additives, and low impedance additives.

[0057] Preferably, the lithium salt additive includes LiFSI (lithium bisfluorosulfonylimide).

[0058] Preferably, the phosphate ester additive includes tris(4-nitrophenyl) phosphate.

[0059] Preferably, the low-resistance additive includes LiBOB (lithium bis(oxalatoborate)).

[0060] Preferably, the content of lithium salt additive in the electrolyte of the battery is 2wt% to 4wt%, for example, it can be 2wt%, 2.5wt%, 3wt%, 3.5wt% or 4wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] Preferably, the content of phosphate ester additives in the electrolyte of the battery is 0.5wt% to 1.5wt%, for example, it can be 0.5wt%, 0.7wt%, 0.9wt%, 1.1wt%, 1.3wt% or 1.5wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] Preferably, the content of low-resistance additive in the electrolyte of the battery is 0.2wt% to 0.5wt%, for example, it can be 0.2wt%, 0.3wt%, 0.4wt% or 0.5wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] The electrolyte of this invention contains LiFSI, which can form a coordination effect with the triazine ring, further reducing the interfacial impedance. Combined with tris(4-nitrophenyl) phosphate, it can form a stable complex with the furan ring, improving the stability of the SEI film at high temperatures and reducing the loss of active lithium. In addition, the low-impedance additive LiBOB can further improve the rate performance of the battery.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] (1) Significantly improved structural stability: The rigid skeleton formed by the cross-linking of the vinyl monomers in the polymer material described in this invention, in conjunction with the rigid structure of furan ring and triazine ring, effectively suppresses the volume expansion and breakage of silicon particles. Combined with the porous structure of hard carbon substrate, it significantly improves the structural stability of silicon-based anode material.

[0066] (2) Excellent high-temperature performance: Trihalomethyl groups can release halogens at high temperatures to form a passivation layer, inhibiting silicon surface oxidation. At the same time, furan rings improve electrolyte compatibility and can further enhance the high-temperature performance of the battery.

[0067] (3) Outstanding conductivity and fast charging capability: The conjugated structure of furan ring and triazine ring optimizes the electron and ion transport path, which can significantly improve the fast charging performance of the material;

[0068] (4) Good performance balance: Trihalomethyl groups can adjust the density of artificial SEI membranes to form a network structure with specific porosity, so that artificial SEI membranes can balance ion conduction efficiency and mechanical support, thus breaking through the performance contradiction of traditional materials.

[0069] (5) Significantly improved overall performance: Compared with triazine rings and their derivatives that do not contain functional groups, the polymer material described in this invention has made significant breakthroughs in high temperature stability, conductivity, fast charging capability and structural integrity, meeting the high temperature application requirements of high energy density batteries. Detailed Implementation

[0070] 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.

[0071] Example 1

[0072] This embodiment provides a silicon-based anode material, comprising a core and an artificial SEI film coated on the surface of the core. The core comprises a silicon-carbon material, and the artificial SEI film comprises a polymer material, wherein the monomer of the polymer material is... The number-average molecular weight of the polymer material is 8 × 10⁻⁶. 5 g / mol;

[0073] In the silicon-based anode material, the artificial SEI film accounts for 2 wt% of the mass, the thickness of the artificial SEI film is 80 nm, and the porosity is 22%.

[0074] The silicon-carbon material has a particle size D50 of 4 μm and a specific surface area of ​​2 m². 2 / g; The silicon-carbon material comprises silicon grains and a hard carbon substrate in a mass ratio of 0.8:1. The size of the silicon grains is 1.2 nm. The hard carbon substrate comprises micropores and mesopores. The pore size of the micropores is 1.2 nm, and the pore volume accounts for 30% of the total pore volume of the hard carbon substrate. The pore size of the mesopores is 15 nm, and the pore volume accounts for 70% of the total pore volume of the hard carbon substrate.

[0075] The method for preparing the silicon-based anode material includes the following steps:

[0076] (1) The monomer of the polymer material is mixed with N-methylpyrrolidone to obtain a monomer solution with a concentration of 1 mol / L. Azobisisobutyronitrile (0.5 wt% of the monomer mass of the polymer material) is added to the monomer solution. The mixture is heated to 80 °C under argon protection and polymerized for 6.5 h to obtain the polymer solution.

[0077] (2) The polymer solution described in step (1) is added to acetone to precipitate the polymer. After standing for 3 hours, the polymer precipitate is washed 4 times and dried to obtain the polymer material.

[0078] (3) Add the polymer material described in step (2) to N-methylpyrrolidone to form a solution with a mass fraction of 20 wt%. Then add the formulated amount of silicon carbon material to the solution (the formulated amount refers to the content of the artificial SEI film formed by the polymer in the silicon-based anode material is 2 wt%). Stir at 300 r / min for 7 h at 70 °C to obtain a mixed slurry. Spray dry the mixed slurry at an inlet temperature of 150 °C and an outlet temperature of 80 °C to obtain the silicon-based anode material.

[0079] Example 2

[0080] This embodiment provides a silicon-based anode material, comprising a core and an artificial SEI film coated on the surface of the core. The core comprises a silicon-carbon material, and the artificial SEI film comprises a polymer material, wherein the monomer of the polymer material is... The number-average molecular weight of the polymer material is 8 × 10⁻⁶. 4 g / mol;

[0081] In the silicon-based anode material, the artificial SEI film accounts for 4 wt% by mass, the artificial SEI film has a thickness of 120 nm, and a porosity of 30%.

[0082] The silicon-carbon material has a particle size D50 of 3 μm and a specific surface area of ​​4 m². 2 / g; The silicon-carbon material comprises silicon grains and a hard carbon substrate in a mass ratio of 1.2:1. The size of the silicon grains is 2nm. The hard carbon substrate comprises micropores and mesopores. The pore size of the micropores is 0.8nm, and the pore volume accounts for 40% of the total pore volume of the hard carbon substrate. The pore size of the mesopores is 5nm, and the pore volume accounts for 60% of the total pore volume of the hard carbon substrate.

[0083] The method for preparing the silicon-based anode material includes the following steps:

[0084] (1) The monomer of the polymer material is mixed with N-methylpyrrolidone to obtain a monomer solution with a concentration of 2.0 mol / L. Azobisisobutyronitrile (0.8 wt% of the monomer mass of the polymer material) is added to the monomer solution. The mixture is heated to 110 °C under argon protection and polymerized for 9 h to obtain a polymer solution.

[0085] (2) The polymer solution described in step (1) is added to acetone to precipitate the polymer. After standing for 2 hours, the polymer precipitate is washed 3 times and dried to obtain the polymer material.

[0086] (3) Add the polymer material described in step (2) to N-methylpyrrolidone to form a solution with a mass fraction of 10 wt%. Then add the formulated amount of silicon carbon material to the solution (the formulated amount refers to the content of the artificial SEI film formed by the polymer in the silicon-based anode material is 4 wt%). Stir at 300 r / min for 5 h at 100 °C to obtain a mixed slurry. Spray dry the mixed slurry at an inlet temperature of 100 °C and an outlet temperature of 60 °C to obtain the silicon-based anode material.

[0087] Example 3

[0088] This embodiment provides a silicon-based anode material, comprising a core and an artificial SEI film coated on the surface of the core. The core comprises a silicon-carbon material, and the artificial SEI film comprises a polymer material, wherein the monomer of the polymer material is... The number-average molecular weight of the polymer material is 9 × 10⁻⁶. 7 g / mol;

[0089] In the silicon-based anode material, the artificial SEI film accounts for 0.3 wt% by mass, the artificial SEI film has a thickness of 30 nm, and a porosity of 15%.

[0090] The silicon-carbon material has a particle size D50 of 7 μm and a specific surface area of ​​1 m². 2 / g; The silicon-carbon material comprises silicon grains and a hard carbon substrate in a mass ratio of 0.4:1. The size of the silicon grains is 0.8 nm. The hard carbon substrate comprises micropores and mesopores. The pore size of the micropores is 1.5 nm, and the pore volume accounts for 20% of the total pore volume of the hard carbon substrate. The pore size of the mesopores is 20 nm, and the pore volume accounts for 80% of the total pore volume of the hard carbon substrate.

[0091] The method for preparing the silicon-based anode material includes the following steps:

[0092] (1) The monomer of the polymer material is mixed with N-methylpyrrolidone to obtain a monomer solution with a concentration of 0.5 mol / L. Azobisisobutyronitrile (0.1 wt% of the monomer mass of the polymer material) is added to the monomer solution. The mixture is heated to 60°C under argon protection and polymerized for 4 h to obtain a polymer solution.

[0093] (2) The polymer solution described in step (1) is added to propanol to precipitate the polymer. After standing for 4 hours, the polymer precipitate is washed 5 times and dried to obtain the polymer material.

[0094] (3) The polymer material described in step (2) is added to N-methylpyrrolidone to form a solution with a mass fraction of 29 wt%. Then, the formulated amount of silicon carbon material is added to the solution (the formulated amount refers to the content of the artificial SEI film formed by the polymer in the silicon-based anode material is 0.3 wt%). After stirring at 300 r / min for 10 h at 30 °C, a mixed slurry is obtained. The mixed slurry is spray-dried at an inlet temperature of 200 °C and an outlet temperature of 100 °C to obtain the silicon-based anode material.

[0095] Example 4

[0096] This embodiment provides a silicon-based anode material, wherein the number-average molecular weight of the polymer material, excluding the polymer material, is 1×10⁻⁶. 4Except for g / mol, everything else is the same as in Example 1;

[0097] The preparation method of the silicon-based anode material is the same as that in Example 1, except for the time-adaptive change in the polymerization reaction.

[0098] Example 5

[0099] This embodiment provides a silicon-based anode material, wherein the number-average molecular weight of the polymer material, excluding the polymer material, is 5 × 10⁻⁶. 8 Except for g / mol, everything else is the same as in Example 1;

[0100] The preparation method of the silicon-based anode material is the same as that in Example 1, except for the time-adaptive change in the polymerization reaction.

[0101] Example 6

[0102] This embodiment provides a silicon-based anode material, which is the same as in Embodiment 1 except that the thickness of the artificial SEI film is 15nm (the proportion of the artificial SEI film varies adaptively).

[0103] The preparation method of the silicon-based composite material is the same as that in Example 1, except that the formulation amount is adapted to change.

[0104] Example 7

[0105] This embodiment provides a silicon-based anode material, which is the same as in Embodiment 1 except that the thickness of the artificial SEI film is 150 nm (the proportion of the artificial SEI film varies adaptively).

[0106] The preparation method of the silicon-based composite material is the same as that in Example 1, except that the formulation amount is adapted to change.

[0107] Example 8

[0108] This embodiment provides a silicon-based anode material, which is the same as in Embodiment 1 except that the porosity of the artificial SEI film is 10%.

[0109] The preparation method of the silicon-based composite material is the same as that in Example 1, except that step (3) involves forming a solution with a mass fraction of 35 wt% and step (3) involves rotating at a speed of 200 r / min.

[0110] Example 9

[0111] This embodiment provides a silicon-based anode material, which is the same as in Embodiment 1 except that the porosity of the artificial SEI film is 35%.

[0112] The preparation method of the silicon-based composite material is the same as that in Example 1, except that step (3) involves forming a solution with a mass fraction of 15 wt% and step (3) involves rotating at a speed of 400 r / min.

[0113] Example 10

[0114] This embodiment provides a silicon-based anode material, which is the same as in Embodiment 1 except that the hard carbon substrate is replaced by artificial graphite material.

[0115] The preparation method of the silicon-based composite material is the same as that in Example 1, except for the change in the raw materials.

[0116] Example 11

[0117] This embodiment provides a silicon-based anode material, which is the same as that in Embodiment 1 except that the hard carbon substrate contains only micropores and no mesopores.

[0118] The preparation method of the silicon-based composite material is the same as that in Example 1, except for the change in the raw materials.

[0119] Example 12

[0120] This embodiment provides a silicon-based anode material, which is the same as that in Embodiment 1 except that the hard carbon substrate contains only mesopores and no micropores.

[0121] The preparation method of the silicon-based composite material is the same as that in Example 1, except for the change in the raw materials.

[0122] Comparative Example 1

[0123] This comparative example provides a silicon-based anode material, which is identical to that in Example 1 except that it does not contain an artificial SEI film.

[0124] Comparative Example 2

[0125] This comparative example provides a silicon-based anode material, wherein the silicon-based anode material contains, in addition to the monomers of the polymer material, a Except for (CAS: 3194-70-5), all other aspects are the same as in Example 1;

[0126] The preparation method of the silicon-based composite material is the same as that in Example 1, except for the change in monomer type.

[0127] In the above examples and comparative examples, gel permeation chromatography was used to test the number-average molecular weight of the polymers. The specific test conditions and steps are as follows:

[0128] (1) Testing instrument: gel permeation chromatograph, equipped with a differential refractive index detector (RI);

[0129] (2) Chromatographic column: A polystyrene gel column (suitable for organic phase testing) was selected, with a column temperature of 35℃;

[0130] (3) Mobile phase: N,N-dimethylformamide, flow rate: 1.0 mL / min;

[0131] (4) Standard sample: Using monodisperse polystyrene (PS) as the standard, a molecular weight calibration curve was plotted;

[0132] (5) Sample preparation: Dissolve the polymer sample in the corresponding mobile phase to prepare a clear solution with a concentration of 2 mg / mL, and filter it through a 0.22 μm organic filter membrane;

[0133] (6) Testing and calculation: Inject 100 μL of the filtered sample solution, record the chromatogram, and calculate the number-average molecular weight of the polymer based on the calibration curve.

[0134] In the above embodiments and comparative examples, the thickness of the artificial SEI film was tested using a combination of transmission electron microscopy and scanning transmission electron microscopy. The specific steps are as follows:

[0135] (1) Sample preparation: The silicon-based anode material was fully dispersed in anhydrous ethanol and ultrasonically dispersed for 13 min to form a uniform suspension. Two drops of the suspension were dropped onto the carbon support film copper grid and air-dried for later use.

[0136] (2) Testing instrument: Field emission transmission electron microscope, accelerating voltage is 200kV;

[0137] (3) Testing and measurement: Place the prepared sample on the electron microscope stage, find the clear interface between the silicon core and the artificial SEI film on the surface in TEM / STEM mode, select at least 10 different particles, select 3 to 5 different test points for each particle, and measure the thickness of the artificial SEI film.

[0138] (4) Calculation of results: The arithmetic mean of the thickness values ​​of all test points is taken as the final thickness of the artificial SEI membrane.

[0139] In the above examples and comparative examples, nitrogen adsorption-desorption (BET) combined with density functional theory (DFT) and the Barrett-Joyner-Hallenda method (BJH) were used to analyze and test the micropore volume ratio and mesopore volume ratio in hard carbon materials. The specific test conditions and steps are as follows:

[0140] (1) Testing instrument: Fully automatic specific surface area and pore size analyzer;

[0141] (2) Sample pretreatment: Take 0.15g of dry hard carbon material sample, place it in a sample tube, and degas it under vacuum at 150℃ for 7h to remove the moisture and impurities adsorbed on the sample surface;

[0142] (3) Nitrogen adsorption test: Place the degassed sample tube in the instrument and perform nitrogen adsorption-desorption isotherm test at 77K (liquid nitrogen temperature). Record the amount of nitrogen adsorbed under different relative pressures (P / P0).

[0143] (4) Calculation of orifice capacity:

[0144] Micropores (pore size 0.8nm~1.5nm): The total pore volume of micropores in hard carbon materials was calculated by analyzing the nitrogen adsorption isotherm using the DFT method.

[0145] Mesopores (pore size 5nm~20nm): The total pore volume of the mesopores in the hard carbon material was calculated by analyzing the nitrogen desorption isotherm using the BJH method.

[0146] (5) Calculation of pore volume ratio: Micropore volume ratio (%) = [micropore volume / (micropore volume + mesopore volume)] × 100%; Mesopore volume ratio (%) = [mesopore volume / (micropore volume + mesopore volume)] × 100%;

[0147] Note: Each sample was tested in parallel 3 times during the test, and the average value was taken as the final pore volume and percentage result.

[0148] In the above embodiments and comparative examples, X-ray diffraction (XRD) combined with the Scherrer formula calculation method was used to test the silicon grain size. The testing instrument was a fully automated X-ray powder diffractometer. The specific testing steps and calculation methods are as follows:

[0149] (1) Sample pretreatment: Take the gas phase silicon carbide powder sample, grind it thoroughly in an agate mortar, pass it through a 200-mesh standard sieve, take the sieve-filled powder evenly into the XRD test sample cell, press it flat with a glass slide, and ensure that the sample surface is flush with the reference surface of the sample cell and there is no preferred orientation.

[0150] (2) Test conditions: Cu Kα target was used as the X-ray source, the X-ray wavelength λ=0.15406nm, the tube voltage was set to 40kV, and the tube current was set to 40mA; the test scanning range 2θ was 10°~80°, the step scanning mode was adopted, the step size was 0.02°, the dwell time of each step was 2s, and the test was conducted at room temperature throughout the process.

[0151] (3) Data processing and calculation: Select the characteristic diffraction peaks (2θ≈28.4°) corresponding to the silicon (111) crystal plane. Subtract the background and fit the diffraction peak shape using the instrument's built-in software to obtain the full width at half maximum (FWHM, in radians). Use the Scherrer formula to calculate the average size of the silicon grains. The Scherrer formula is as follows: D=βcosθKλ, where D is the average size of the silicon grains in nm; K is the Scherrer constant, with a value of 0.89; λ is the X-ray wavelength, with a value of 0.15406 nm; β is the full width at half maximum (FWHM) of the diffraction peaks of the silicon (111) crystal plane, which needs to be subtracted for instrument broadening effect, in rad; θ is the Bragg diffraction angle corresponding to the diffraction peaks of the silicon (111) crystal plane, in °.

[0152] (4) Result values: Each sample was tested in parallel 3 times, and the arithmetic mean of the 3 calculation results was taken as the final size of silicon grains in the gas phase silicon-carbon material.

[0153] In the above embodiments and comparative examples, the particle size D50 of silicon-carbon materials was tested using laser diffraction (wet mode). The testing principle is based on the scattering effect of laser light by particles. Particles of different sizes produce scattered light at different angles. The particle size distribution is calculated by fitting the spatial distribution of the scattered light. The testing instrument is a fully automated laser particle size analyzer. The specific testing steps are as follows:

[0154] (1) Sample pretreatment: Take 0.2g of silicon carbide powder sample, add it to 10mL of anhydrous ethanol, shake well and place it in an ultrasonic disperser. Disperse it under ultrasonic power at 100W for 5min to prepare a uniform sample suspension. During the ultrasonic process, control the system temperature to not exceed 30℃ to avoid particle agglomeration or breakage.

[0155] (2) Test conditions: Wet test mode is adopted, anhydrous ethanol is used as the dispersion medium, and the test circulation pump speed is set to 1800 r / min; before the test, background calibration is completed to eliminate the interference between the dispersion medium and the ambient light; the prepared sample suspension is slowly dripped into the sample cell of the instrument, and the sample shading degree is controlled within the range of 8%~12%. The test is started after the shading degree value is stable.

[0156] (3) Data definition and processing: The particle size D50 is the median particle size of the volume reference, that is, the particle diameter corresponding to the cumulative volume distribution percentage of silicon-carbon material particles reaching 50%; during the test, the instrument automatically collects the scattered light signal, and obtains the particle size distribution curve of the particles by fitting the Mie scattering theory, and directly reads the D50 value; in the Mie scattering model, the refractive index of silicon is 3.88, the absorption coefficient is 0.01, and the refractive index of anhydrous ethanol is 1.36.

[0157] (4) Result values: Each sample was tested in parallel 3 times, and each test was repeated 3 times. The arithmetic mean of the results of the 3 parallel tests was taken as the final D50 size of the silicon carbide powder particles.

[0158] The silicon-based anode materials obtained in the above embodiments and comparative examples were used to prepare lithium-ion batteries. The preparation process is as follows:

[0159] (1) The ternary material NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2), polyvinylidene fluoride and conductive carbon black are mixed in a mass ratio of 96:2:2, and then a positive electrode slurry is prepared. The positive electrode slurry is coated onto aluminum foil through a coating process, and after drying and cold pressing, a positive electrode sheet is obtained.

[0160] (2) The silicon-based composite material, conductive carbon black, single-walled carbon nanotubes and polyacrylic acid obtained in the above examples and comparative examples are mixed in a mass ratio of 85:4:1:10, and then a negative electrode slurry with a solid content of 30% is prepared. The negative electrode slurry is coated onto copper foil through a coating process, and then vacuum dried and cold pressed to obtain a negative electrode sheet.

[0161] (3) EC, DMC, DEC and FEC with a volume ratio of 20:40:30:10 were used as electrolyte solvents, and LiPF6, LiFSI, tris(4-nitrophenyl) phosphate and LiBOB were used as electrolyte additives. The concentration of LiPF6 in the electrolyte was 1 mol / L, the content of LiFSI was 3 wt%, the content of tris(4-nitrophenyl) phosphate was 1 wt%, and the content of LiBOB was 0.3 wt%.

[0162] Polyethylene + ceramic material is used as the separator membrane;

[0163] (4) Stack the above positive electrode, separator and negative electrode in sequence, so that the separator is between the positive electrode and the negative electrode to play the role of isolation. Then, wind them to obtain the bare cell. Then place the bare cell in the outer packaging shell, dry it and inject electrolyte. After vacuum sealing, standing, formation and shaping, etc., the lithium-ion battery is obtained.

[0164] The prepared lithium-ion batteries were subjected to performance testing, specifically on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd., under normal temperature (25℃) conditions. The charge and discharge voltages were limited to 2.5V~4.2V. The test conditions for initial coulombic efficiency (first efficiency), cycle performance, rate performance, fast charging performance, and high-temperature performance are as follows:

[0165] (1) Initial Coulomb efficiency:

[0166] At 25°C, the lithium-ion battery was charged at a constant current and constant voltage of 0.33C to 4.2 V, allowed to stand for 10 min, and then discharged at a constant current of 0.33C to 2.5 V, allowed to stand for 10 min. The initial coulombic efficiency of the lithium-ion battery was calculated.

[0167] Initial coulombic efficiency (%) = Total capacity of lithium-ion battery during initial discharge at 0.33C / Total capacity of lithium-ion battery during initial charge at 0.33C × 100%.

[0168] (2) Capacity retention rate after 1200 cycles at room temperature (1C / 1C):

[0169] At 25°C, the lithium-ion battery was charged at a constant current and constant voltage of 1C to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the lithium-ion battery was discharged at a constant current of 1C to 2.5V and then rested for 10 minutes. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 1200 charge-discharge cycles using the above method. The capacity retention rate of the lithium-ion battery after 1200 charge-discharge cycles at 1C / 1C was calculated.

[0170] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0171] (3) Room temperature 6C rate performance - constant current charge ratio:

[0172] At 25℃, the lithium-ion battery was discharged at a constant current rate of 1C to 2.5V, left to stand for 10 minutes, and then charged at a constant current and constant voltage rate of 6C to 4.2V with a cutoff current of 0.05C. After standing for 10 minutes, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 of the lithium-ion battery were recorded. The constant current charge ratio of the 6C rate charging was calculated according to the following formula: 6C rate charging constant current charge ratio = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 × 100%.

[0173] (4) Capacity retention rate at room temperature 1C / 10C discharge:

[0174] At 25℃, the capacity-graded lithium-ion battery was charged at a 1C rate using constant current and constant voltage to 4.2 V, with a cutoff current of 0.05C; it was then allowed to stand for 10 minutes; next, the lithium-ion battery was discharged at a 1C rate using constant current to 2.5 V, and its discharge capacity Q1C was recorded as the initial discharge capacity; then, at 25℃, the lithium-ion battery was charged at a 1C rate using constant current and constant voltage to 4.2 V, with a cutoff current of 0.05C; it was allowed to stand for 10 minutes; then, the fully charged battery was discharged at a 10C rate using constant current to 2.5 V, and its discharge capacity Q10C was recorded; the discharge capacity retention rate (%) of the lithium-ion battery at 1C / 10C rate was calculated as: discharge capacity Q10C at 10C rate / discharge capacity Q1C at 1C rate × 100%.

[0175] (5) High temperature performance: Under constant temperature environment of 45℃, the lithium-ion battery is charged to 4.2V with constant current and constant voltage at 1C rate (cutoff current 0.05C), left to stand for 10min, and then discharged to 2.5V with constant current at 1C rate, left to stand for 10min. This is one cycle. After 1000 cycles, the capacity retention rate is calculated.

[0176] The test results are shown in Table 1 below:

[0177] Table 1

[0178]

[0179] As can be seen from Table 1 above:

[0180] As shown in Example 1 and Comparative Example 1, the present invention, by coating a specific artificial SEI film onto the surface of silicon-containing materials, can comprehensively improve the performance defects of silicon materials, while adapting the battery to the application requirements of high-temperature environments, significantly improving the battery's cycle performance, rate performance, fast charging performance, and high-temperature performance. As shown in Example 1 and Comparative Example 2, the polymer material of the present invention, compared to conventional triazine polymers, contains furan rings and trihalomethyl groups that not only synergistically enhance material stability, interfacial strength, and ion transport performance with the triazine rings, but also improve the high-temperature performance of silicon-based materials. As shown in Example 1 and Examples 4-5, the present invention preferably uses polymer materials with a number-average molecular weight within a specific range, enabling the artificial SEI film to possess both good mechanical strength and ion transport efficiency, thereby simultaneously improving the battery's performance. The battery's cycle performance, rate performance, and fast charging performance are all improved. As shown in Examples 1 and 6-7, the thickness of the artificial SEI film in this invention is preferably within a specific range, which can optimize the ion transport performance and structural stability of the material, thereby improving the battery's rate performance and cycle performance. As shown in Examples 1 and 8-9, the porosity of the artificial SEI film in this invention is within a preferred range, which enables the artificial SEI film to balance ion transport performance and mechanical strength, thereby improving the overall performance of the battery. As shown in Examples 1 and 10-12, the carbon in the silicon-carbon material in this invention is preferably a hard carbon substrate, and preferably the hard carbon substrate contains both micropores and mesopores, so that the hierarchical porous structure of the hard carbon substrate can further provide buffer space for the volume expansion of silicon particles, and work synergistically with the artificial SEI film to further improve the overall electrochemical performance of the battery.

[0181] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A silicon-based anode material, characterized in that, The silicon-based anode material includes a core and an artificial SEI film coated on the surface of the core. The core includes a silicon-containing material, and the artificial SEI film includes a polymer material. The structural formula of the monomer of the polymer material is shown in Formula I): ； Formula I); Among them, at least two of R1, R2 and R3 contain trihalomethyl groups and at least one contains a furan ring.

2. The silicon-based anode material according to claim 1, characterized in that, Both R1 and R2 contain trihalomethyl groups; Preferably, R3 contains a furan ring; Preferably, the trihalomethyl group comprises a trichloromethyl group; Preferably, the monomers of the polymer material include and / or .

3. The silicon-based anode material according to claim 1 or 2, characterized in that, The number-average molecular weight of the polymer material is 8 × 10⁻⁶. 4 g / mol ~ 9 × 10 7 g / mol; Preferably, in the silicon-based anode material, the artificial SEI film accounts for 0.3wt% to 4wt% by mass. Preferably, the thickness of the artificial SEI film is 30nm~120nm; Preferably, the porosity of the artificial SEI membrane is 15% to 30%.

4. The silicon-based anode material according to claim 1 or 2, characterized in that, The particle size D50 of the silicon-containing material is 3μm~7μm; Preferably, the specific surface area of ​​the silicon-containing material is 1 m². 2 / g~4m 2 / g; Preferably, the silicon-containing material includes silicon-carbon material; Preferably, the silicon-carbon material comprises silicon grains and a hard carbon substrate.

5. The silicon-based anode material according to claim 4, characterized in that, The mass ratio of silicon grains to hard carbon substrate is (0.4~1.2):1; Preferably, the hard carbon substrate includes micropores and mesopores; Preferably, the pore size of the micropores is 0.8 nm to 1.5 nm, and the pore volume accounts for 20% to 40% of the total pore volume of the hard carbon substrate; Preferably, the pore size of the mesopores is 5 nm to 20 nm, and the pore volume accounts for 60% to 80% of the total pore volume of the hard carbon substrate; Preferably, the size of the silicon grains is 0.8 nm to 2 nm.

6. A method for preparing a silicon-based anode material as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: A silicon-containing material, a polymer material, and a first organic solvent are mixed to obtain a mixed slurry, which is then spray-dried to obtain the silicon-based anode material.

7. The preparation method according to claim 6, characterized in that, The mixing temperature is 30℃~100℃, and the time is 5h~10h; Preferably, the inlet temperature of the spray dryer is 100℃~200℃, and the outlet temperature is 60℃~100℃.

8. The preparation method according to claim 6 or 7, characterized in that, The method for preparing the polymer material includes: The monomers of the polymer material, a second organic solvent, and an initiator are mixed and polymerized to obtain a polymer solution. The polymer solution is then added to the precipitated solvent, and the mixture is allowed to stand, washed, and dried to obtain the polymer material. Preferably, the polymerization reaction is carried out at a temperature of 60°C to 110°C for a duration of 4 to 9 hours. Preferably, the settling time is 2h to 4h; Preferably, in the mixture obtained by mixing the monomer of the polymer material, the second organic solvent and the initiator, the concentration of the monomer of the polymer material is 0.5 mol / L to 2.0 mol / L; Preferably, the amount of the initiator added is 0.1 wt% to 0.8 wt% of the monomer mass of the polymer material; Preferably, the initiator includes any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide; Preferably, the first organic solvent and the second organic solvent each independently comprise any one or a combination of at least two of benzene, toluene, NMP, or DMF; Preferably, the precipitation solvent includes any one or a combination of at least two of propanol, isopropanol, or acetone.

9. A battery, characterized in that, The battery comprises the silicon-based anode material as described in any one of claims 1-5.

10. The battery according to claim 9, characterized in that, The electrolyte of the battery includes lithium salt additives, phosphate ester additives, and low impedance additives. Preferably, the lithium salt additive includes LiFSI; Preferably, the phosphate ester additive includes tris(4-nitrophenyl) phosphate; Preferably, the low-resistivity additive includes LiBOB; Preferably, the electrolyte of the battery contains 2wt% to 4wt% lithium salt additive. Preferably, the electrolyte of the battery contains 0.5 wt% to 1.5 wt% phosphate ester additives. Preferably, the electrolyte of the battery contains 0.2wt% to 0.5wt% of low-resistance additives.

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