Silicon-based composite material, method for preparing the same, and battery

Abstract

The application provides a silicon-based composite material, a preparation method thereof and a battery, and the silicon-based composite material comprises a silicon-based matrix and an artificial SEI film coated on the surface of the silicon-based matrix, the artificial SEI film comprises a polymer material, monomers of the polymer material comprise a pyranose derivative, and the pyranose derivative comprises allyl, benzyloxy, hydroxyl, ether and phthalimide groups. The silicon-based composite material disclosed by the application can not only buffer the volume expansion of the silicon-based matrix, improve the structural stability, but also improve the rigidity of the silicon-based matrix, the interface stability and the lithium ion transmission path, so that the cycle performance, the rate performance and the fast charging performance of the battery are simultaneously improved through the synergistic effect of the multiple functional groups.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in consumer electronics and new energy vehicles. With the miniaturization of consumer electronics and the increasing demand for longer driving ranges in new energy vehicles, there is a need to develop lithium-ion batteries with high energy density, high power density, long cycle life, and high safety.

[0003] Traditional graphite anode materials are limited by their theoretical specific capacity, preventing the development of high-capacity lithium-ion batteries. Silicon-based materials, with their extremely high theoretical charge specific capacity, have become highly promising anode materials for lithium-ion batteries. However, silicon-based anode materials suffer from severe volume expansion (up to 300%) during charge and discharge, easily leading to electrode structure breakage and active material shedding, severely limiting their large-scale application. Furthermore, the poor interfacial stability and weak interfacial forces of the SEI film in silicon-based anode materials result in decreased battery cycle performance. In addition, the obstructed lithium-ion transport pathway leads to insufficient rate performance and fast-charging performance.

[0004] In existing technologies, the performance of silicon-based anode materials is improved by coating the surface of the silicon-based anode material with an artificial SEI film. However, conventional SEI films are mainly inorganic, which, while possessing good rigidity, have poor flexibility and insufficient stability during cycling. Existing technologies also use organic materials as coating materials, but organic materials have a single functional group, which can only alleviate volume expansion to a certain extent and cannot simultaneously meet the multiple requirements of structural stability, strong interfacial bonding, and optimized lithium-ion transport. Therefore, the improvement in fast charging performance and cycle stability is limited.

[0005] Based on the above research, there is a need to provide a silicon-based composite material whose SEI film can simultaneously improve structural stability, interfacial stability, and ion transport, thereby simultaneously improving the cycle performance, rate performance, and fast charging performance of the battery. Summary of the Invention

[0006] The purpose of this invention is to provide a silicon-based composite material, its preparation method, and a battery. The silicon-based composite material, by coating the surface of a silicon-based matrix with a specific polymer containing multiple functional groups, can not only buffer the volume expansion of the silicon-based matrix and improve its structural stability, but also improve the rigidity and interface stability of the silicon-based matrix and optimize the lithium-ion transport path. Thus, through the synergistic effect of multiple functional groups, the cycle performance, rate performance, and fast charging performance of the battery are improved simultaneously.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a silicon-based composite material, the silicon-based composite material comprising a silicon-based matrix and an artificial SEI film coated on the surface of the silicon-based matrix, the artificial SEI film comprising a polymer material, the monomers of the polymer material comprising pyranose derivatives, the pyranose derivatives comprising allyl, benzyloxy, hydroxyl, ether, and phthalimide groups.

[0009] This invention utilizes pyranose derivatives containing multiple functional groups as monomers for polymer materials. The pyranose ring serves as the connecting framework for other functional groups, its cyclic structure enhancing polymer stability and participating in SEI film formation, thus improving interfacial compatibility. Furthermore, the benzyloxy functional groups of the pyranose derivatives possess certain rigidity and strength, enhancing the structural strength of the silicon-based matrix, inhibiting silicon particle breakage, and improving the material's cycle stability. The hydroxyl functional groups can form a hydrogen bond network with the silicon-based matrix, increasing the interaction force between the artificial SEI film and the silicon-based matrix, thereby improving interfacial stability. The hydroxyl and ether functional groups can further optimize the lithium-ion transport pathway and reduce ion transfer... By reducing resistance to ion transport and improving the rate performance and fast charging capability of the material, the phthalimide functional group can regulate the electron cloud density of the polymer material through electronic effects, improve interfacial compatibility, promote the formation of a stable artificial SEI film, and reduce active lithium loss. The allyl group can polymerize to form a three-dimensional elastic network, which can adapt to the volume changes of the silicon matrix, buffer the stress caused by volume expansion, and maintain the structural integrity of the silicon matrix. Therefore, this invention achieves performance improvement of material structure stability, interface strength, and efficient ion transport through the synergistic effect of multiple functional groups, breaking through the limitations of single performance optimization, thereby simultaneously improving the cycle performance, rate performance, and fast charging performance of the battery.

[0010] Preferably, the pyranose derivative comprises 4-methoxyphenyl-3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimide-β-D-glucopyranoside (CAS: 1820583-64-9), with the following structural formula:

[0011] .

[0012] Preferably, the number-average molecular weight of the polymer material is 5 × 10⁻⁶. 4 g / mol ~5×10 5 g / mol, for example, could be 5 × 10 4 g / mol, 7×10 4 g / mol, 9×10 4 g / mol, 1×10 5 g / mol, 3×10 5 g / mol or 5×10 5The values ​​are in g / mol, but not limited to the listed values; other unlisted values ​​within the range also apply.

[0013] The number-average molecular weight of the polymer material described in this invention is preferably within a specific range. If the number-average molecular weight of the polymer material is too low, the mechanical properties of the artificial SEI film will be insufficient. However, if the number-average molecular weight of the polymer material is too high, it will lead to a high viscosity of the coating solution and poor coating uniformity, which will affect the performance of the silicon-based composite material.

[0014] Preferably, in the silicon-based composite material, the content of the artificial SEI film is 1wt% to 4wt%, for example, it can be 1wt%, 2wt%, 3wt% or 4wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the thickness of the artificial SEI film is 20nm~120nm, for example, it can be 20nm, 40nm, 60nm, 80nm, 100nm or 120nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] If the thickness of the artificial SEI film described in this invention is too thick, it will affect the ion transport performance, resulting in a deterioration in the rate performance and cycle performance of the battery. However, if the thickness of the artificial SEI film is too thin, the artificial SEI film is prone to cracking, affecting the performance of the silicon-based composite material.

[0017] Preferably, the silicon-based matrix comprises silicon-carbon material, specifically fumed silicon-carbon material.

[0018] Preferably, the particle size D50 of the silicon-carbon material is 4μm to 10μm, for example, it can be 4μm, 6μm, 8μm or 10μm, and the specific surface area is 1m². 2 / g~7m 2 / g, for example, could be 1m 2 / g、3m 2 / g、5m 2 / g or 7m 2 / g, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0019] If the particle size D50 of the silicon-carbon material described in this invention is too large, it will affect the ion transport performance of the material and reduce the rate performance of the battery. However, if the particle size D50 of the silicon-carbon material is too small, the silicon-based composite material will be difficult to disperse during the homogenization process.

[0020] Preferably, in the silicon-carbon material, the mass ratio of silicon to carbon 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.

[0021] In the silicon-carbon material described in this invention, the mass ratio of silicon to carbon is preferably within a specific range. If the silicon content is relatively too low, the specific capacity and first efficiency will be reduced. However, if the silicon content is relatively too high, the volume change of the silicon-based composite material during cycling will be increased.

[0022] Preferably, the silicon grain size in the silicon-carbon material is 0.5nm to 2nm, for example, it can be 0.5nm, 1nm, 1.5nm or 2nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] The silicon grain size in the silicon-carbon material described in this invention is preferably within a specific range. If the silicon grain size is too large, the material will expand significantly, leading to a decrease in cycle performance. If the silicon grain size is too small, the contact area between silicon and carbon will be too small, leading to a decrease in rate performance.

[0024] Preferably, the carbon in the silicon-carbon material is a hard carbon material.

[0025] Preferably, the hard carbon material includes micropores and mesopores.

[0026] Preferably, the pore size of the micropore is 0.8nm to 1.5nm, for example, it can be 0.8nm, 1nm, 1.3nm or 1.5nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the pore size of the mesopore is 5nm to 20nm, for example, it can be 5nm, 10nm, 15nm or 20nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] The hard carbon material described in this invention includes both micropores and mesopores of specific pore sizes. 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 hard carbon pore structure increases. If the mesopore size is too small, the material's buffer space is insufficient, and the silicon particles will compress the pore walls after expansion, leading to the cracking of the hard carbon skeleton. However, if the mesopore size is too large, the density of the hard carbon skeleton decreases, the electrode compaction density decreases, and the energy density loss of the battery increases.

[0029] Preferably, in the hard carbon material, the pore volume of micropores accounts for 20% to 40% of the total pore volume, 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.

[0030] Preferably, in the hard carbon material, the pore volume of mesopores accounts for 60% to 80% of the total pore volume, for example, it can be 60%, 65%, 70%, 75% or 80%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] In a second aspect, the present invention provides a method for preparing a silicon-based composite material as described in the first aspect, the method comprising the following steps:

[0032] The polymer material, the first organic solvent, and the silicon matrix are mixed and spray-dried to obtain the silicon-based composite material.

[0033] Preferably, the mixing temperature is 30℃~100℃, for example, 30℃, 60℃, 90℃ or 100℃, and the time is 5h~10h, for example, 5h, 6h, 7h, 8h, 9h or 10h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the inlet temperature of the spray dryer is 100℃~200℃, for example, 100℃, 120℃, 140℃, 160℃, 180℃ or 200℃, and the outlet temperature is 60℃~100℃, for example, 60℃, 70℃, 80℃, 90℃ or 100℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the mixing of the polymer material, the first organic solvent and the silicon matrix includes first dispersing the polymer material in the first organic solvent to prepare a mixed solution with a mass fraction of 5wt% to 30wt%, for example, 5wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%, and then adding the silicon matrix to the mixed solution for mixing.

[0036] Preferably, the method for preparing the polymer material includes the following steps:

[0037] A pyranose derivative, a second organic solvent, and an initiator are mixed and polymerized to obtain a polymer solution. The polymer solution is then added to the precipitating solvent, and 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.

[0038] Preferably, in the mixture obtained by mixing the pyranose derivative, solvent and initiator, the concentration of the pyranose derivative is 0.5 mol / L to 2 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.

[0039] Preferably, the amount of the initiator added is 0.2wt% to 0.9wt% of the mass of the pyranose derivative, for example, it can be 0.2wt%, 0.4wt%, 0.6wt% or 0.9wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the initiator includes any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide.

[0041] Preferably, the polymerization reaction temperature is 60℃~90℃, for example, 60℃, 70℃, 80℃ or 90℃, and the time is 5h~12h, for example, 5h, 7h, 9h or 12h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the settling time is 2h to 4h, for example, it can be 2h, 2.5h, 3h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] 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).

[0044] Preferably, the precipitation solvent includes any one or a combination of at least two of propanol, isopropanol, or acetone.

[0045] Thirdly, the present invention provides a battery comprising a silicon-based composite material as described in the first aspect.

[0046] Preferably, the electrolyte of the battery includes a first additive, a second additive, and a third additive, wherein the first additive includes LiFSI (lithium bis(fluorosulfonyl)imide), the second additive includes tris(4-nitrophenyl) phosphate, and the third additive includes LiBOB (lithium bis(oxalato)borate).

[0047] Preferably, the content of the first additive in the electrolyte of the battery is 2wt% to 4wt%, for example, it can be 2%, 2.5%, 3%, 3.5% or 4%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the content of the second additive 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.

[0049] Preferably, the content of the third 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.

[0050] The present invention adds LiFSI to the electrolyte, which can further reduce the interfacial impedance and has a synergistic effect with the silicon-based composite material described in the present invention. If tris(4-nitrophenyl) phosphate is added as other additives, and a low-impedance additive LiBOB is added, the rate performance of the battery can be further improved.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] This invention utilizes pyranose derivatives containing multiple functional groups as monomers for polymer materials. The pyranose ring serves as a connecting backbone for other functional groups, its cyclic structure enhancing polymer stability and participating in SEI film formation, thus improving interfacial compatibility. Furthermore, the benzyloxy functional groups of the pyranose derivatives possess certain rigidity and strength, enhancing the structural strength of the silicon-based matrix, inhibiting silicon particle breakage, and improving the material's cycle stability. The hydroxyl functional groups can form a hydrogen bond network with the silicon-based matrix, increasing the interaction force between the artificial SEI film and the silicon-based matrix, thereby improving interfacial stability. The hydroxyl and ether functional groups can further optimize the lithium-ion transport pathway and reduce ion transfer... By reducing resistance to ion transport and improving the rate performance and fast charging capability of the material, the phthalimide functional group can regulate the electron cloud density of the polymer material through electronic effects, improve interfacial compatibility, promote the formation of a stable artificial SEI film, and reduce active lithium loss. The allyl group can polymerize to form a three-dimensional elastic network, which can adapt to the volume changes of the silicon matrix, buffer the stress caused by volume expansion, and maintain the structural integrity of the silicon matrix. Therefore, this invention achieves performance improvement of material structure stability, interface strength, and efficient ion transport through the synergistic effect of multiple functional groups, breaking through the limitations of single performance optimization, thereby simultaneously improving the cycle performance, rate performance, and fast charging performance of the battery. Detailed Implementation

[0053] 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.

[0054] Example 1

[0055] This embodiment provides a silicon-based composite material, comprising a silicon-carbon material and an artificial SEI film coated on the surface of the silicon-carbon material. The artificial SEI film comprises a polymer material, wherein the monomer of the polymer material is 4-methoxyphenyl-3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimide-β-D-glucopyranoside, and the number-average molecular weight of the polymer material is 1×10⁻⁶. 5 g / mol;

[0056] In the silicon-based composite material, the content of the artificial SEI film is 2.5 wt%, and the thickness of the artificial SEI film is 70 nm;

[0057] The silicon-carbon material has a particle size D50 of 6 μm and a specific surface area of ​​4 m². 2 / g, and in the silicon-carbon material, the mass ratio of silicon to carbon is 0.8:1, and the silicon grain size in the silicon-carbon material is 1nm;

[0058] The carbon in the silicon-carbon material is a hard carbon material, which includes micropores with a pore size of 1 nm and mesopores with a pore size of 10 nm. The pore volume of the micropores accounts for 30% of the total pore volume of the hard carbon material, and the pore volume of the mesopores accounts for 70% of the total pore volume of the hard carbon material.

[0059] The preparation method of the silicon-based composite material includes the following steps:

[0060] (1) Using 4-methoxyphenyl-3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimide-β-D-glucopyranoside as a monomer, the monomer was added to N-methylpyrrolidone to obtain a solution with a monomer concentration of 1 mol / L. Then, 0.5 wt% of azobisisobutyronitrile was added to the solution, and the mixture was heated to 70 °C under argon protection and reacted for 8 h to obtain a polymer solution.

[0061] (2) Add the polymer solution from step (1) to propanol to obtain a polymer precipitate. After standing for 3 hours, wash the polymer precipitate 4 times and dry it to obtain the polymer material.

[0062] (3) Add the polymer material described in step (2) to N-methylpyrrolidone to obtain a polymer solution with a mass fraction of 10 wt%. Add silicon carbon material to the polymer solution according to the formula amount (the formula amount refers to the content of the artificial SEI film formed by the polymer in the silicon-based composite material is 2.5 wt%). Stir at 80°C for 7 h, and then spray dry the mixed liquid obtained by stirring to obtain the silicon-based composite material; wherein, the inlet temperature of the spray drying is 150°C and the outlet temperature is 80°C.

[0063] Example 2

[0064] This embodiment provides a silicon-based composite material, comprising a silicon-carbon material and an artificial SEI film coated on the surface of the silicon-carbon material. The artificial SEI film comprises a polymer material, wherein the monomer of the polymer material is 4-methoxyphenyl-3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimide-β-D-glucopyranoside, and the number-average molecular weight of the polymer material is 5 × 10⁻⁶. 4 g / mol;

[0065] In the silicon-based composite material, the content of the artificial SEI film is 4 wt%, and the thickness of the artificial SEI film is 120 nm.

[0066] The silicon-carbon material has a particle size D50 of 4 μm and a specific surface area of ​​7 m². 2 / g, and in the silicon-carbon material, the mass ratio of silicon to carbon is 1.2:1, and the silicon grain size in the silicon-carbon material is 2nm;

[0067] The carbon in the silicon-carbon material is a hard carbon material, which includes micropores with a pore size of 1.5 nm and mesopores with a pore size of 20 nm. The micropores account for 20% of the total pore volume of the hard carbon material, and the mesopores account for 80% of the total pore volume of the hard carbon material.

[0068] The preparation method of the silicon-based composite material includes the following steps:

[0069] (1) 4-methoxyphenyl-3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimide-β-D-glucopyranoside was used as a monomer. The monomer was added to N-methylpyrrolidone to obtain a solution with a monomer concentration of 2 mol / L. Then, 0.9 wt% of azobisisobutyronitrile was added to the solution. The mixture was heated to 60 °C under argon protection and reacted for 12 h to obtain a polymer solution.

[0070] (2) Add the polymer solution from step (1) to propanol to obtain a polymer precipitate. After standing for 4 hours, wash the polymer precipitate three times and dry it to obtain the polymer material.

[0071] (3) The polymer material described in step (2) is added to N-methylpyrrolidone to obtain a polymer solution with a mass fraction of 30 wt%. Silicon carbon material is added to the polymer solution according to the formula amount (the formula amount refers to the content of the artificial SEI film formed by the polymer in the silicon-based composite material is 4 wt%). The mixture is stirred at 100°C for 5 h. Then the mixed liquid obtained by stirring is spray-dried to obtain the silicon-based composite material. The inlet temperature of the spray drying is 200°C and the outlet temperature is 60°C.

[0072] Example 3

[0073] This embodiment provides a silicon-based composite material, comprising a silicon-carbon material and an artificial SEI film coated on the surface of the silicon-carbon material. The artificial SEI film comprises a polymer material, wherein the monomer of the polymer material is 4-methoxyphenyl-3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimide-β-D-glucopyranoside, and the number-average molecular weight of the polymer material is 5 × 10⁻⁶. 5 g / mol;

[0074] In the silicon-based composite material, the content of the artificial SEI film is 1 wt%, and the thickness of the artificial SEI film is 20 nm;

[0075] The silicon-carbon material has a particle size D50 of 10 μm and a specific surface area of ​​1 m². 2 / g, and in the silicon-carbon material, the mass ratio of silicon to carbon is 0.4:1, and the silicon grain size in the silicon-carbon material is 0.5nm;

[0076] The carbon in the silicon-carbon material is a hard carbon material, which includes micropores with a pore size of 0.8 nm and mesopores with a pore size of 5 nm. The pore volume of the micropores accounts for 40% of the total pore volume of the hard carbon material, and the pore volume of the mesopores accounts for 60% of the total pore volume of the hard carbon material.

[0077] The preparation method of the silicon-based composite material includes the following steps:

[0078] (1) Using 4-methoxyphenyl-3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimide-β-D-glucopyranoside as a monomer, the monomer was added to N,N-dimethylformamide to obtain a solution with a monomer concentration of 0.5 mol / L. Then, 0.2 wt% of azobisisoheptanenitrile was added to the solution, and the mixture was heated to 90 °C under argon protection and reacted for 5 h to obtain a polymer solution.

[0079] (2) The polymer solution described in step (1) is added to isopropanol to obtain a polymer precipitate. After standing for 2 hours, the polymer precipitate is washed 5 times and dried to obtain the polymer material.

[0080] (3) Add the polymer material described in step (2) to N,N-dimethylformamide to obtain a polymer solution with a mass fraction of 5wt%. Add the silicon carbon material to the polymer solution according to the formula amount (the formula amount refers to the content of the artificial SEI film formed by the polymer in the silicon-based composite material is 1wt%). Stir at 30°C for 10h, and then spray dry the mixed liquid obtained by stirring to obtain the silicon-based composite material; wherein, the inlet temperature of the spray drying is 100°C and the outlet temperature is 100°C.

[0081] Example 4

[0082] This embodiment provides a silicon-based composite material, wherein the number-average molecular weight of the silicon-based composite material, except for the polymer material, is 1×10⁻⁶. 4 Except for g / mol, everything else is the same as in Example 1;

[0083] The preparation method of the silicon-based composite material is the same as that in Example 1, except for the change in reaction time during polymer preparation.

[0084] Example 5

[0085] This embodiment provides a silicon-based composite material, wherein the number-average molecular weight of the silicon-based composite material, except for the polymer material, is 1×10⁻⁶. 6 Except for g / mol, everything else is the same as in Example 1;

[0086] The preparation method of the silicon-based composite material is the same as that in Example 1, except for the change in reaction time during polymer preparation.

[0087] Example 6

[0088] This embodiment provides a silicon-based composite material, which is the same as that in Embodiment 1 except that the thickness of the artificial SEI film is 10 nm (the proportion of the artificial SEI film varies adaptively);

[0089] 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.

[0090] Example 7

[0091] This embodiment provides a silicon-based composite material, which is the same as that in Example 1 except that the thickness of the artificial SEI film is 150 nm (the proportion of the artificial SEI film varies adaptively);

[0092] 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.

[0093] Example 8

[0094] This embodiment provides a silicon-based composite material, which is the same as that in Embodiment 1 except that the hard carbon material does not contain micropores and only contains mesopores.

[0095] 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.

[0096] Example 9

[0097] This embodiment provides a silicon-based composite material, which is the same as that in Embodiment 1 except that the hard carbon material does not contain mesopores but only micropores.

[0098] 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.

[0099] Comparative Example 1

[0100] This comparative example provides a silicon-based composite material, which is the same as that in Example 1 except that the monomer of the polymer material is allyl-α-D-glucopyranoside.

[0101] The preparation method of the silicon-based composite material is the same as that in Example 1, except for the change in monomer adaptability.

[0102] Comparative Example 2

[0103] This comparative example provides a silicon-based composite material, which is identical to Example 1 except that it does not contain an artificial SEI film.

[0104] 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:

[0105] (1) Testing instrument: gel permeation chromatograph, equipped with a differential refractive index detector (RI);

[0106] (2) Chromatographic column: A polystyrene gel column (suitable for organic phase testing) was selected, with a column temperature of 35℃;

[0107] (3) Mobile phase: N,N-dimethylformamide, flow rate: 1.0 mL / min;

[0108] (4) Standard sample: Using monodisperse polystyrene (PS) as the standard, a molecular weight calibration curve was plotted;

[0109] (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;

[0110] (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.

[0111] 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:

[0112] (1) Sample preparation: The silicon-based composite 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 copper grid of the carbon support film and air-dried for later use.

[0113] (2) Testing instrument: Field emission transmission electron microscope, accelerating voltage is 200kV;

[0114] (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.

[0115] (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.

[0116] 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:

[0117] (1) Testing instrument: Fully automatic specific surface area and pore size analyzer;

[0118] (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;

[0119] (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).

[0120] (4) Calculation of orifice capacity:

[0121] 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.

[0122] 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.

[0123] (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%;

[0124] 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.

[0125] 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:

[0126] (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.

[0127] (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.

[0128] (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 °.

[0129] (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.

[0130] 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:

[0131] (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.

[0132] (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.

[0133] (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.

[0134] (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.

[0135] The silicon-based composite materials obtained in the above examples and comparative examples were used to prepare lithium-ion batteries. The preparation process is as follows:

[0136] (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 to prepare a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil through a coating process, and then dried and cold-pressed to obtain the positive electrode sheet.

[0137] (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 drying and cold pressing processes are performed to obtain a negative electrode sheet.

[0138] (3) The above positive electrode, separator and negative electrode are stacked in sequence, so that the separator is between the positive electrode and the negative electrode to play a role in isolation. Then the bare cell is wound to obtain the bare cell. Then the bare cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing, formation and shaping, a lithium-ion battery is obtained. The electrolyte includes EC, DMC, DEC and FEC in a volume ratio of 20:40:30:10, 1 mol / L LiPF6, 3 wt% LiFSI, 1 wt% tris(4-nitrophenyl) phosphate and 0.3 wt% LiBOB. The separator includes a polyethylene film and a ceramic coating.

[0139] The obtained lithium-ion batteries were tested for electrochemical performance at room temperature (25℃) using the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd., with the charge and discharge voltage limited to 2.5V~4.2V. The test methods for initial coulombic efficiency (hereinafter referred to as first efficiency), cycle performance, rate performance, and fast charging performance are as follows:

[0140] (1) Initial Coulomb efficiency:

[0141] 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.

[0142] 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%.

[0143] (2) Capacity retention rate after 1200 cycles at room temperature (1C / 1C):

[0144] 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.

[0145] 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.

[0146] (3) Room temperature 6C rate performance - constant current charge ratio:

[0147] 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%.

[0148] (4) Capacity retention rate at room temperature 1C / 10C discharge:

[0149] 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%.

[0150] The test results are shown in Table 1 below:

[0151] Table 1

[0152]

[0153] As can be seen from Table 1 above:

[0154] As can be seen from Example 1 and Comparative Example 1, the monomer used in Comparative Example 1, allyl-α-D-glucopyranoside, does not contain the multiple functional groups found in the monomer of the present invention compared to the monomer of the present invention, resulting in a significant decrease in the battery's initial efficiency, cycle life, and rate performance. As can be seen from Example 1 and Comparative Example 2, the present invention, by coating a specific artificial SEI film, can effectively improve the stability of the silicon-based matrix, alleviate volume changes during charging and discharging, and also improve the rate performance of the material, thereby simultaneously improving the battery's cycle performance, rate performance, and fast charging performance. As can be seen from Example 1 and Examples 4-7, the number-average molecular weight of the polymer material and the thickness of the artificial SEI film described in the present invention both affect the effectiveness of the artificial SEI film, thus affecting the battery's performance. As can be seen from Example 1 and Examples 8-9, the hard carbon material in the silicon-based composite material described in the present invention includes both micropores and mesopores, which is beneficial for improving the overall stability of the material and buffering silicon expansion, thereby further improving the battery's comprehensive electrochemical performance.

[0155] 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 composite material, characterized in that, The silicon-based composite material includes a silicon-based matrix and an artificial SEI film coated on the surface of the silicon-based matrix. The artificial SEI film includes a polymer material, and the monomers of the polymer material include pyranose derivatives, which include allyl, benzyloxy, hydroxyl, ether, and phthalimide groups.

2. The silicon-based composite material according to claim 1, characterized in that, The pyranose derivatives include 4-methoxyphenyl-3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimide-β-D-glucopyranoside; Preferably, the number-average molecular weight of the polymer material is 5 × 10⁻⁶. 4 g / mol ~5×10 5 g / mol.

3. The silicon-based composite material according to claim 1 or 2, characterized in that, In the silicon-based composite material, the content of the artificial SEI film is 1wt%~4wt%; Preferably, the thickness of the artificial SEI film is 20nm~120nm.

4. The silicon-based composite material according to claim 1 or 2, characterized in that, The silicon-based matrix includes silicon-carbon materials; Preferably, the silicon-carbon material has a particle size D50 of 4 μm to 10 μm and a specific surface area of ​​1 m². 2 / g~7m 2 / g; Preferably, in the silicon-carbon material, the mass ratio of silicon to carbon is (0.4~1.2):1; Preferably, the silicon grain size in the silicon-carbon material is 0.5 nm to 2 nm.

5. The silicon-based composite material according to claim 4, characterized in that, The carbon in the silicon-carbon material is a hard carbon material; Preferably, the hard carbon material includes micropores and mesopores; Preferably, the pore size of the micropores is 0.8 nm to 1.5 nm; Preferably, the pore size of the mesopore is 5nm~20nm; Preferably, in the hard carbon material, the pore volume of micropores accounts for 20% to 40% of the total pore volume; Preferably, in the hard carbon material, the mesoporous pore volume accounts for 60% to 80% of the total pore volume.

6. A method for preparing a silicon-based composite material as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: The polymer material, the first organic solvent, and the silicon matrix are mixed and spray-dried to obtain the silicon-based composite 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 preparation method of the polymer material includes the following steps: A pyranose derivative, a second organic solvent, and an initiator are mixed and polymerized to obtain a polymer solution. The polymer solution is then added to the precipitating solvent, and the mixture is allowed to stand, washed, and dried to obtain the polymer material. Preferably, in the mixture obtained by mixing the pyranose derivative, solvent and initiator, the concentration of the pyranose derivative is 0.5 mol / L to 2 mol / L; Preferably, the amount of the initiator added is 0.2wt% to 0.9wt% of the mass of the pyranose derivative; Preferably, the initiator includes any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide; Preferably, the polymerization reaction is carried out at a temperature of 60°C to 90°C for a duration of 5 to 12 hours. Preferably, the settling time is 2h to 4h; 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 a silicon-based composite 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 a first additive, a second additive, and a third additive, wherein the first additive includes LiFSI, the second additive includes tris(4-nitrophenyl) phosphate, and the third additive includes LiBOB. Preferably, the content of the first additive in the electrolyte of the battery is 2wt%~4wt%; Preferably, the content of the second additive in the electrolyte of the battery is 0.5wt%~1.5wt%; Preferably, the content of the third additive in the electrolyte of the battery is 0.2wt% to 0.5wt%.

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