Silicon composite negative electrode material with multi-level coating structure, preparation method of silicon composite negative electrode material and secondary battery

Abstract

The invention provides a silicon composite negative electrode material with a multi-level coating structure, a preparation method of the silicon composite negative electrode material and a secondary battery. An inner core of the silicon composite negative electrode material with the multi-level coating structure comprises a silicon negative electrode material, a middle layer comprises an artificial SEI film layer, and an outermost layer comprises an oxide coating layer; wherein the material of the artificial SEI film layer comprises a phenylacetylene copolymer, and the structure of the phenylacetylene copolymer comprises a combination of a halogen group, an ether group and a group capable of forming a hydrogen bond. According to the invention, the silicon negative electrode material is modified by adopting a differentiated multi-stage surface coating structure, so that the heat resistance, the mechanical property and the interface dynamic property of the silicon negative electrode material are comprehensively improved, and the electrochemical property of a secondary battery under high magnification and high-temperature environment is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials, and in particular relates to a silicon composite negative electrode material with a multi-level coating structure, a preparation method thereof, and a secondary battery. Background Art

[0002] In recent years, improving the high-temperature performance and high-rate charge-discharge performance of secondary batteries has become a key development direction in modern battery technology. This not only improves the safety, cycle life, and energy density of secondary batteries, but also meets the needs of high-performance applications while reducing their environmental impact.

[0003] In the field of lithium-ion batteries, silicon negative electrode materials have attracted much attention due to their theoretical specific capacity far higher than that of traditional graphite negative electrode materials (4200mAh / g, compared to 372mAh / g of graphite). However, silicon materials have large volume changes (over 300%) and poor conductivity during charging and discharging, which leads to rapid attenuation of their lithium storage capacity and makes it difficult to meet the needs of high-performance applications. In addition, the stability of the solid electrolyte interface (SEI) film is crucial to the electrochemical performance of lithium-ion batteries. However, traditional SEI films have the disadvantage of unstable interface, and under high temperature conditions, the stability of the SEI film is significantly reduced. Moreover, as the temperature continues to rise, the side reactions at the electrolyte / electrode interface intensify and can easily cause thermal runaway of the battery.

[0004] While silicon anode materials have made progress in high-temperature and high-rate performance, their large volume expansion and unstable SEI membrane remain major limitations on their commercialization. For example, Chinese patent CN115810716A discloses a nanoscale functional artificial SEI membrane, primarily composed of inorganic substances. While it exhibits good rigidity, it suffers from poor flexibility, resulting in poor battery cycling stability.

[0005] Therefore, how to improve the overall thermal stability and rapid charge and discharge capabilities of silicon-based lithium-ion batteries is a technical problem that technicians in this field urgently need to solve. Summary of the Invention

[0006] To address the shortcomings of the prior art, the present invention aims to provide a silicon composite anode material with a multi-level coating structure, a preparation method thereof, and a secondary battery. The present invention utilizes a differentiated multi-level surface coating structure to modify the silicon anode material, thereby comprehensively improving its heat resistance, mechanical properties, and interfacial dynamics, thereby enhancing the electrochemical performance of the secondary battery at high rates and in high-temperature environments.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a silicon composite negative electrode material having a multi-level coating structure, wherein the core of the silicon composite negative electrode material having a multi-level coating structure includes a silicon negative electrode material, the middle layer includes an artificial SEI film layer, and the outermost layer includes an oxide coating layer;

[0009] The material of the artificial SEI film layer includes a phenylacetylene copolymer, and the structure of the phenylacetylene copolymer includes a combination of a halogen group, an ether group and a group capable of forming a hydrogen bond.

[0010] The silicon composite negative electrode material provided by the present invention has high rate performance and thermal stability, can improve the interface stability of lithium-ion batteries, enhance the ion transmission efficiency, and thus improve the overall cycle stability and service life of lithium-ion batteries.

[0011] On the one hand, the halogen groups contained in the phenylacetylene copolymer in the artificial SEI film can improve the thermal stability of the silicon anode material, effectively preventing electrochemical performance degradation or failure of lithium-ion batteries in high-temperature environments. At the same time, the ether groups in the phenylacetylene copolymer structure can improve the charge transfer process at the interface of the silicon anode material, further reducing the charge transfer resistance and ultimately improving the high-rate performance of the lithium-ion battery. Furthermore, the groups containing hydrogen bonding can form hydrogen bonds with the hydroxyl groups on the surface of the silicon anode material, thereby strengthening the bonding between the artificial SEI film and the anode material.

[0012] On the other hand, the oxide coating provided on the outermost layer of the present invention has suitable rigidity and strength, which can enhance the overall mechanical properties of the silicon negative electrode material. At the same time, the oxide coating also has excellent thermal stability. For example, during the operation of a lithium-ion battery, especially during charging and discharging at high rates or high temperatures, heat is generated inside the lithium ions, and the oxide coating can act as a thermal barrier, slowing the transfer of heat within the electrode and preventing deterioration of battery performance due to local overheating. In addition, the copolymer artificial SEI film layer and the oxide coating play a complementary role, giving the silicon negative electrode material good mechanical properties.

[0013] Preferably, the phenylethene copolymer includes a first structural unit and a second structural unit.

[0014] Preferably, the first structural unit includes a first halogen group and a substituted or unsubstituted ether group.

[0015] Preferably, the substituted group includes a second halo group.

[0016] Preferably, the first halogen group comprises a bromine atom.

[0017] Preferably, the second halogen group includes a fluorine atom. Fluorine atoms have a strong electronegativity and a large atomic radius, which can further stabilize the structure and thermal stability of the silicon anode material. In addition, fluorine atoms can form hydrogen bonds with hydroxyl groups on the surface of the silicon anode material, thereby strengthening the interaction between the artificial SEI film layer and the silicon anode material.

[0018] Preferably, the second structural unit includes a group capable of forming a hydrogen bond.

[0019] Preferably, the groups capable of forming hydrogen bonds include amine groups and / or hydroxyl groups, wherein the lone pair of electrons in the nitrogen atoms contained in the amine groups can participate in the charge transfer process, thereby improving the ionic conductivity of the silicon negative electrode material.

[0020] Preferably, the monomer forming the first structural unit includes a phenylacetylene compound containing a first halogen group and a substituted or unsubstituted ether group.

[0021] Preferably, the substituted group includes a second halo group.

[0022] Preferably, the first halogen group comprises a bromine atom.

[0023] Preferably, the second halogen group comprises a fluorine atom.

[0024] Preferably, the monomer forming the first structural unit includes 4-bromo-2-trifluoromethoxyphenylacetylene.

[0025] Preferably, the monomer forming the second structural unit includes a phenylacetylene compound containing a group capable of forming a hydrogen bond.

[0026] Preferably, the groups capable of forming hydrogen bonds include amine groups and / or hydroxyl groups.

[0027] Preferably, the monomer forming the second structural unit includes p-aminophenylacetylene.

[0028] Preferably, the glass transition temperature of the phenylethene copolymer is -20°C to 10°C, preferably -7°C to -3°C, for example, it can be -20°C, -18°C, -15°C, -12°C, -10°C, -8°C, -7°C, -6°C, -5°C, -3°C, -2°C, 0°C, 2°C, 5°C, 8°C or 10°C, and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0029] The present invention regulates the glass transition temperature of the phenylacetylene copolymer to achieve an artificial SEI layer with both good mechanical properties and thermal stability. If the glass transition temperature of the phenylacetylene copolymer is low, the mechanical properties of the artificial SEI layer formed are poor. If the glass transition temperature of the phenylacetylene copolymer is high, the phenylacetylene copolymer exhibits a glassy state at the battery operating temperature, and the resulting artificial SEI layer has poor flexibility.

[0030] Preferably, the decomposition temperature of the phenylacetylene copolymer is not lower than 200°C, preferably not lower than 220°C, for example, it can be 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C or 250°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0031] The present invention regulates the decomposition temperature of the phenylacetylene copolymer to ensure that the formed artificial SEI film has good structural and thermal stability. If the decomposition temperature of the phenylacetylene copolymer is too low, it will easily decompose during the charge and discharge of the lithium-ion battery, causing the formed artificial SEI film to fail.

[0032] Preferably, the number average molecular weight of the phenylacetylene copolymer is 15,000 Da to 80,000 Da, preferably 30,000 Da to 60,000 Da, for example, 15,000 Da, 18,000 Da, 20,000 Da, 22,000 Da, 25,000 Da, 28,000 Da, 30,000 Da, 32,000 Da, 35,000 Da, 38,000 Da, 40,000 Da, 42,000 Da, 45,000 Da, 48,000 Da, 50,000 Da, 55,000 Da, 60,000 Da, 65,000 Da, 70,000 Da, 75,000 Da or 80,000 Da, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0033] The present invention regulates the number-average molecular weight of the phenylacetylene copolymer to achieve excellent processing properties, mechanical strength, and ionic conductivity. Using a phenylacetylene copolymer with a lower number-average molecular weight results in poor film-forming properties and structural stability, making it ineffective in protecting silicon-based negative electrode materials. Using a phenylacetylene copolymer with a higher number-average molecular weight results in poor solubility and processing properties, hindering the coating process and potentially reducing ionic conductivity.

[0034] In the present invention, the tensile strength of the phenylacetylene copolymer is not less than 10 MPa. If the tensile strength of the phenylacetylene copolymer is low, the formed artificial SEI film layer is prone to rupture.

[0035] In the present invention, the elongation at break of the phenylacetylene copolymer is not less than 50%. If the elongation at break of the phenylacetylene copolymer is low, the artificial SEI film formed cannot better adapt to the volume change of the silicon-based negative electrode material.

[0036] In the present invention, the ionic conductivity of the phenylacetylene copolymer is 10 -4 S / cm~10 -3 S / cm, preferably 5×10 -4 S / cm. If the ionic conductivity of the phenylacetylene copolymer is low, it will affect the high-rate performance of the lithium-ion battery. If the ionic conductivity of the phenylacetylene copolymer is high, the stability of the formed artificial SEI film layer will be significantly reduced.

[0037] Preferably, based on the total mass of the silicon negative electrode material coated with the artificial SEI film layer as 100%, the mass percentage of the material of the artificial SEI film layer is 1% to 6%, for example, it can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8% or 6%, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the thickness of the artificial SEI film layer is 30 nm to 90 nm, for example, it can be 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm or 90 nm, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0039] The present invention regulates the thickness of the artificial SEI film layer to ensure both good structural stability and high ionic conductivity, thereby comprehensively improving the cycle performance and rate performance of the assembled lithium-ion battery. If the artificial SEI film layer is too thin, it is prone to cracking, resulting in loss of active lithium; if the artificial SEI film layer is too thick, it will have poor ion transport performance, and the cycle performance and rate performance of the assembled lithium-ion battery will be reduced.

[0040] Preferably, the material of the oxide coating layer includes non-metallic oxide.

[0041] Preferably, the non-metal oxide comprises silicon dioxide.

[0042] Preferably, the average particle size of the non-metallic oxide is 10 nm to 90 nm, preferably 20 nm to 45 nm, etc., for example, it can be 10 nm, 20 nm, 22 nm, 25 nm, 28 nm, 30 nm, 32 nm, 35 nm, 38 nm, 40 nm, 42 nm, 45 nm, 50 nm, 60 nm, 70 nm, 80 nm or 90 nm, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, based on the total mass of the silicon negative electrode material coated with the artificial SEI film layer as 100%, the mass percentage of the material of the oxide coating layer is 1% to 6%, for example, it can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8% or 6%, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] The present invention further improves the structural strength and thermal stability of the silicon composite negative electrode material by regulating the mass percentage of the material of the oxide coating layer.

[0045] In the present invention, the silicon negative electrode material exemplarily includes silicon-carbon material.

[0046] Furthermore, the average particle size of the silicon-carbon material is 4μm to 8μm, for example, it can be 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, 5.2μm, 5.5μm, 5.8μm, 6μm, 6.2μm, 6.5μm, 6.8μm, 7μm, 7.2μm, 7.5μm, 7.8μm or 8μm, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] The present invention regulates the average particle size of the silicon-carbon material to facilitate subsequent processing, thereby better balancing the cycle performance and rate performance of lithium-ion batteries. Using a silicon-carbon material with a smaller average particle size may cause the particles to agglomerate, while using a silicon-carbon material with a larger average particle size may result in poor lithium-ion transport performance, thereby degrading the rate performance of the lithium-ion battery.

[0048] Preferably, the specific surface area of ​​the silicon-carbon material is 1m 2 / g~8m 2 / g, for example, 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2m2 / g, 2.2m 2 / g, 2.5m 2 / g, 2.8m 2 / g、3m 2 / g, 3.2m 2 / g, 3.5m 2 / g, 3.8m 2 / g、4m 2 / g, 4.2m 2 / g, 4.5m 2 / g, 4.8m 2 / g、5m 2 / g, 5.2m 2 / g, 5.5m 2 / g, 5.8m 2 / g、6m 2 / g, 6.2m 2 / g, 6.5m 2 / g, 6.8m 2 / g、7m 2 / g, 7.2m 2 / g, 7.5m 2 / g, 7.8m 2 / g or 8m 2 / g, etc., are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] Preferably, the mass percentage of silicon material in the silicon-carbon material is 35% to 56%, for example, it can be 35%, 38%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55% or 56%, etc., and is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0050] The present invention achieves both high gram capacity and good cycling performance by regulating the mass percentage of silicon in the silicon-carbon material. Using a silicon-carbon material with a lower silicon content results in a lower gram capacity, thus reducing the energy density of the lithium-ion battery. Using a silicon-carbon material with a higher silicon content results in a collapse of the negative electrode structure due to the volume expansion of the silicon, thus reducing the service life and stability of the material.

[0051] In a second aspect, the present invention provides a method for preparing the silicon composite negative electrode material having a multi-level coating structure according to the first aspect, the method comprising the following steps:

[0052] S1. Mixing a silicon anode material with a phenylacetylene copolymer solution having a structure including a halogen group, an ether group, and a group capable of forming a hydrogen bond, and spray drying the mixture to obtain a silicon anode material coated with an artificial SEI film;

[0053] S2. Performing an oxide coating treatment on the silicon negative electrode material coated with the artificial SEI film layer to obtain the silicon composite negative electrode material having a multi-level coating structure.

[0054] Preferably, the mass concentration of the phenylacetylene copolymer solution in step S1 is 5% to 17%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16% or 17%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0055] Preferably, the method for preparing the phenylacetylene copolymer in the phenylacetylene copolymer solution in step S1 comprises the following steps:

[0056] The monomer forming the first structural unit, the monomer forming the second structural unit, an initiator and an organic solvent are reacted to obtain the phenylacetylene copolymer.

[0057] Preferably, the molar ratio of the monomer forming the first structural unit to the monomer forming the second structural unit is 1:(1-5), preferably 1:(2.8-3.2), for example, it can be 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.8 or 1:5, etc., not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

[0058] The present invention regulates the molar ratio of the monomer forming the first structural unit to the monomer forming the second structural unit, so that the formed negative electrode artificial SEI film layer not only has good structural stability and thermal stability, but also can improve its own ionic conductivity, thereby improving the rate performance of the secondary battery. If a lower molar content of the monomer forming the second structural unit is used, the binding ability between the artificial SEI film layer and the negative electrode material will be weakened, and the structural stability of the artificial SEI film layer cannot be further improved. In addition, the electron-withdrawing effect caused by the excess halogen atoms will weaken the electron delocalization ability of the phenylacetylene conjugated molecular chain. If a higher molar content of the monomer forming the second structural unit is used, the functional groups in the copolymer structure will not be able to form a good synergistic effect, wherein the lower ether bond content leads to a decrease in the rate performance of the secondary battery, and the lower halogen content is not conducive to improving the thermal safety performance of the secondary battery.

[0059] Preferably, the reaction is carried out under an inert atmosphere, which exemplarily includes argon and / or nitrogen.

[0060] Preferably, the reaction temperature is 60°C to 100°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0061] Preferably, the reaction time is 5 h to 10 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0062] In the present invention, the initiator exemplarily includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or dibenzoyl peroxide (BPO). Furthermore, based on the total mass of the comonomers as 100%, the mass percentage of the initiator is 0.3% to 1%, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0063] In the present invention, the organic solvent illustratively includes at least one of benzene, tetrahydrofuran (THF), N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF).

[0064] In the present invention, after the reaction, the following steps are further included: adding the reaction solution after the reaction into a precipitation solvent to obtain a phenylacetylene copolymer precipitate, and then washing and drying the phenylacetylene copolymer precipitate to obtain the phenylacetylene copolymer.

[0065] In the present invention, the precipitation solvent illustratively includes at least one of propanol, isopropanol or acetone.

[0066] Preferably, the mixing temperature in step S1 is 60°C to 100°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0067] Preferably, the mixing time in step S1 is 5 h to 10 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0068] Preferably, the inlet temperature of the spray drying in step S1 is 120°C to 200°C, for example, 120°C, 150°C, 180°C or 200°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0069] Preferably, the outlet temperature of the spray drying in step S1 is 60°C to 98°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 98°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0070] Preferably, the oxide coating process in step S2 includes grinding the silicon negative electrode material coated with the artificial SEI film layer and the non-metallic oxide to obtain the silicon composite negative electrode material with a multi-level coating structure.

[0071] Preferably, the grinding method includes ball milling.

[0072] Preferably, the ball-to-material ratio of the ball mill is (5-9):1, for example, it can be 5:1, 6:1, 7:1, 8:1 or 9:1, etc., and is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0073] Preferably, the ball milling speed is 200 rpm to 600 rpm, for example, 200 rpm, 300 rpm, 400 rpm, 500 rpm or 600 rpm, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0074] Preferably, the ball milling time is 10 h to 20 h, for example, 10 h, 12 h, 15 h, 18 h or 20 h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0075] In a third aspect, the present invention provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises the silicon composite negative electrode material with a multi-level coating structure according to the first aspect.

[0076] In the present invention, the electrolyte further includes an additive, and the additive includes diethyl thioester (DTD).

[0077] In the present invention, vinyl sulfate can produce a synergistic effect with the phenylacetylene copolymer artificial SEI film material, thereby further reducing the interface impedance.

[0078] Furthermore, the mass percentage of the additive in the electrolyte is 1% to 3%, for example, it can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8% or 3%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0079] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0080] Compared with the prior art, the present invention has the following beneficial effects:

[0081] The present invention provides a silicon composite negative electrode material with a multi-level coating structure, which has high rate performance and thermal stability, can improve the interface stability of lithium-ion batteries, enhance the ion transmission efficiency, and thus improve the overall cycle stability and service life of lithium-ion batteries.

[0082] On the one hand, the halogen groups contained in the phenylacetylene copolymer in the artificial SEI film can improve the thermal stability of silicon-based anode materials, effectively preventing electrochemical performance degradation or failure of lithium-ion batteries in high-temperature environments. At the same time, the ether groups in the phenylacetylene copolymer structure can improve the charge transfer process at the interface of silicon-based anode materials, further reducing charge transfer resistance and ultimately improving the high-rate performance of lithium-ion batteries. Furthermore, groups capable of forming hydrogen bonds can form hydrogen bonds with hydroxyl groups on the surface of silicon-based anode materials, thereby strengthening the bonding between the artificial SEI film and the anode material.

[0083] On the other hand, the oxide coating provided on the outermost layer of the present invention has suitable rigidity and strength, which can enhance the overall mechanical properties of the silicon-based negative electrode material. At the same time, the oxide coating also has excellent thermal stability. For example, during the operation of a lithium-ion battery, especially during charging and discharging at high rates or high temperatures, heat is generated inside the lithium ions, and the oxide coating can act as a thermal barrier, slowing down the transfer of heat inside the electrode and preventing the deterioration of battery performance caused by local overheating. In addition, the copolymer artificial SEI film layer and the oxide coating play a complementary role, giving the silicon-based negative electrode material good mechanical properties. DETAILED DESCRIPTION

[0084] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0085] Example 1

[0086] This embodiment provides a silicon composite negative electrode material with a multi-level coating structure, wherein the core of the silicon composite negative electrode material with a multi-level coating structure includes a silicon-carbon negative electrode material, the middle layer includes an artificial SEI film layer, and the outermost layer includes a nano-silicon dioxide coating layer.

[0087] The artificial SEI layer comprises a copolymer of 4-bromo-2-trifluoromethoxyphenylacetylene and p-aminophenylacetylene. The copolymer has a glass transition temperature of -5°C, a decomposition temperature of 220°C, and a number-average molecular weight of 47,500 Da. Based on the total mass of the silicon-carbon anode material coated with the artificial SEI layer as 100%, the weight percentage of the material in the artificial SEI layer is 3.5%, and the thickness of the artificial SEI layer is 60 nm.

[0088] The average particle size of the nano-silicon dioxide is 33 nm. Based on the total mass of the silicon-carbon negative electrode material coated with the artificial SEI film layer being 100%, the mass percentage of the material of the nano-silicon dioxide coating layer is 3.5%.

[0089] This embodiment also provides a method for preparing the silicon composite negative electrode material having a multi-level coating structure, the preparation method comprising the following steps:

[0090] S1. p-Aminophenylacetylene and 4-bromo-2-trifluoromethoxyphenylacetylene in a molar ratio of 3:1 were added to a tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 80° C. under an argon atmosphere for a copolymerization reaction for 7 h to obtain a reaction solution;

[0091] The reaction solution is added to a propanol solvent to precipitate a copolymer, and the copolymer precipitate is washed and dried to obtain a copolymer;

[0092] The copolymer was dissolved in tetrahydrofuran solvent to obtain a copolymer solution with a mass concentration of 11%; the silicon carbon material (with an average particle size of 6 μm and a specific surface area of ​​4.5 m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 46%) was added to the copolymer solution and stirred at 80°C for 7 hours to obtain a mixed solution, which was spray-dried at an inlet temperature of 160°C and an outlet temperature of 80°C to obtain a silicon-carbon anode material coated with an artificial SEI film layer;

[0093] S2. The silicon-carbon negative electrode material coated with the artificial SEI film layer and nano-silica were ball-milled with an ethanol solvent at a speed of 400 rpm for 15 hours, wherein the ball-to-material ratio was 7:1, to obtain the silicon composite negative electrode material having a multi-level coating structure.

[0094] Example 2

[0095] This embodiment provides a silicon composite negative electrode material with a multi-level coating structure, wherein the core of the silicon composite negative electrode material with a multi-level coating structure includes a silicon-carbon negative electrode material, the middle layer includes an artificial SEI film layer, and the outermost layer includes a nano-silicon dioxide coating layer.

[0096] The artificial SEI layer comprises a copolymer of 4-bromo-2-trifluoromethoxyphenylacetylene and p-aminophenylacetylene. The copolymer has a glass transition temperature of -7°C, a decomposition temperature of 225°C, and a number-average molecular weight of 60,000 Da. Based on the total mass of the silicon-carbon anode material coated with the artificial SEI layer as 100%, the weight percentage of the artificial SEI layer is 5%, and the thickness of the artificial SEI layer is 80 nm.

[0097] The average particle size of the nano-silicon dioxide is 20 nm. Based on the total mass of the silicon-carbon negative electrode material coated with the artificial SEI film layer being 100%, the mass percentage of the material of the nano-silicon dioxide coating layer is 2%.

[0098] This embodiment also provides a method for preparing the silicon composite negative electrode material having a multi-level coating structure, the preparation method comprising the following steps:

[0099] S1. p-Aminophenylacetylene and 4-bromo-2-trifluoromethoxyphenylacetylene in a molar ratio of 2.8:1 were added to a tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 90° C. under an argon atmosphere for a copolymerization reaction for 6 h to obtain a reaction solution;

[0100] The reaction solution is added to a propanol solvent to precipitate a copolymer, and the copolymer precipitate is washed and dried to obtain a copolymer;

[0101] The copolymer was dissolved in tetrahydrofuran solvent to obtain a copolymer solution with a mass concentration of 15%; the silicon carbon material (average particle size of 6 μm, specific surface area of ​​4.5 m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 54%) was added to the copolymer solution and stirred at 80°C for 7 hours to obtain a mixed solution, which was spray-dried at an inlet temperature of 160°C and an outlet temperature of 80°C to obtain a silicon-carbon anode material coated with an artificial SEI film layer;

[0102] S2. The silicon-carbon negative electrode material coated with the artificial SEI film layer and nano-silica were ball-milled with an ethanol solvent at a speed of 400 rpm for 15 hours, wherein the ball-to-material ratio was 7:1, to obtain the silicon composite negative electrode material having a multi-level coating structure.

[0103] Example 3

[0104] This embodiment provides a silicon composite negative electrode material with a multi-level coating structure, wherein the core of the silicon composite negative electrode material with a multi-level coating structure includes a silicon-carbon negative electrode material, the middle layer includes an artificial SEI film layer, and the outermost layer includes a nano-silicon dioxide coating layer.

[0105] The artificial SEI layer comprises a copolymer of 4-bromo-2-trifluoromethoxyphenylacetylene and p-aminophenylacetylene. The copolymer has a glass transition temperature of -3°C, a decomposition temperature of 230°C, and a number-average molecular weight of 30,000 Da. Based on the total mass of the silicon-carbon anode material coated with the artificial SEI layer as 100%, the weight percentage of the material in the artificial SEI layer is 1.5%, and the thickness of the artificial SEI layer is 39 nm.

[0106] The average particle size of the nano-silicon dioxide is 45 nm. Based on the total mass of the silicon-carbon negative electrode material coated with the artificial SEI film layer being 100%, the mass percentage of the material of the nano-silicon dioxide coating layer is 5%.

[0107] This embodiment also provides a method for preparing the silicon composite negative electrode material having a multi-level coating structure, the preparation method comprising the following steps:

[0108] S1. p-Aminophenylacetylene and 4-bromo-2-trifluoromethoxyphenylacetylene in a molar ratio of 3.2:1 were added to tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 70° C. under an argon atmosphere for a copolymerization reaction for 8 h to obtain a reaction solution;

[0109] The reaction solution is added to a propanol solvent to precipitate a copolymer, and the copolymer precipitate is washed and dried to obtain a copolymer;

[0110] The copolymer was dissolved in tetrahydrofuran solvent to obtain a copolymer solution with a mass concentration of 6%; the silicon carbon material (with an average particle size of 6 μm and a specific surface area of ​​4.5 m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 39%) was added to the above copolymer solution and stirred at 80°C for 7 hours to obtain a mixed solution, which was spray-dried at an inlet temperature of 160°C and an outlet temperature of 80°C to obtain a silicon-carbon anode material coated with an artificial SEI film layer;

[0111] S2. The silicon-carbon negative electrode material coated with the artificial SEI film layer and nano-silica were ball-milled with an ethanol solvent at a speed of 400 rpm for 15 hours, wherein the ball-to-material ratio was 7:1, to obtain the silicon composite negative electrode material having a multi-level coating structure.

[0112] Example 4

[0113] This embodiment provides a silicon composite negative electrode material with a multi-level coating structure, wherein the core of the silicon composite negative electrode material with a multi-level coating structure includes a silicon-carbon negative electrode material, the middle layer includes an artificial SEI film layer, and the outermost layer includes a nano-silicon dioxide coating layer.

[0114] The artificial SEI layer comprises a copolymer of 4-bromo-2-trifluoromethoxyphenylacetylene and p-aminophenylacetylene. The copolymer has a glass transition temperature of -20°C, a decomposition temperature of 200°C, and a number-average molecular weight of 15,000 Da. Based on the total mass of the silicon-carbon anode material coated with the artificial SEI layer as 100%, the weight percentage of the material in the artificial SEI layer is 1%, and the thickness of the artificial SEI layer is 30 nm.

[0115] The average particle size of the nano-silicon dioxide is 10 nm. Based on the total mass of the silicon-carbon negative electrode material coated with the artificial SEI film layer being 100%, the mass percentage of the material of the nano-silicon dioxide coating layer is 1%.

[0116] This embodiment also provides a method for preparing the silicon composite negative electrode material having a multi-level coating structure, the preparation method comprising the following steps:

[0117] S1. p-Aminophenylacetylene and 4-bromo-2-trifluoromethoxyphenylacetylene in a molar ratio of 1:1 were added to a tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 60° C. under an argon atmosphere for a copolymerization reaction for 10 hours to obtain a reaction solution;

[0118] The reaction solution is added to a propanol solvent to precipitate a copolymer, and the copolymer precipitate is washed and dried to obtain a copolymer;

[0119] The copolymer was dissolved in tetrahydrofuran solvent to obtain a copolymer solution with a mass concentration of 5%; the silicon carbon material (with an average particle size of 4 μm and a specific surface area of ​​8 m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 35%) are added to the above copolymer solution and stirred at 80°C for 7 hours to obtain a mixed solution, which is then spray-dried at an inlet temperature of 160°C and an outlet temperature of 80°C to obtain a silicon-carbon anode material coated with an artificial SEI film layer;

[0120] S2. The silicon-carbon negative electrode material coated with the artificial SEI film layer and nano-silica were ball-milled with an ethanol solvent at a speed of 400 rpm for 15 hours, wherein the ball-to-material ratio was 7:1, to obtain the silicon composite negative electrode material having a multi-level coating structure.

[0121] Example 5

[0122] This embodiment provides a silicon composite negative electrode material with a multi-level coating structure, wherein the core of the silicon composite negative electrode material with a multi-level coating structure includes a silicon-carbon negative electrode material, the middle layer includes an artificial SEI film layer, and the outermost layer includes a nano-silicon dioxide coating layer.

[0123] The artificial SEI layer comprises a copolymer of 4-bromo-2-trifluoromethoxyphenylacetylene and p-aminophenylacetylene. The copolymer has a glass transition temperature of 10°C, a decomposition temperature of 235°C, and a number-average molecular weight of 80,000 Da. Based on the total mass of the silicon-carbon anode material coated with the artificial SEI layer as 100%, the weight percentage of the artificial SEI layer is 6%, and the thickness of the artificial SEI layer is 90 nm.

[0124] The average particle size of the nano-silicon dioxide is 90 nm. Based on the total mass of the silicon-carbon negative electrode material coated with the artificial SEI film layer being 100%, the mass percentage of the material of the nano-silicon dioxide coating layer is 6%.

[0125] This embodiment also provides a method for preparing the silicon composite negative electrode material having a multi-level coating structure, the preparation method comprising the following steps:

[0126] S1. p-Aminophenylacetylene and 4-bromo-2-trifluoromethoxyphenylacetylene in a molar ratio of 5:1 were added to tetrahydrofuran solvent, and then azobisisobutyronitrile was added as an initiator. The mixture was heated to 100° C. under an argon atmosphere for a copolymerization reaction for 5 hours to obtain a reaction solution;

[0127] The reaction solution is added to a propanol solvent to precipitate a copolymer, and the copolymer precipitate is washed and dried to obtain a copolymer;

[0128] The copolymer was dissolved in tetrahydrofuran solvent to obtain a copolymer solution with a mass concentration of 17%; the silicon carbon material (with an average particle size of 8 μm and a specific surface area of ​​1 m 2 / g, and the mass percentage of silicon material in the silicon-carbon material is 56%) was added to the above copolymer solution and stirred at 80°C for 7 hours to obtain a mixed solution, which was spray-dried at an inlet temperature of 160°C and an outlet temperature of 80°C to obtain a silicon-carbon anode material coated with an artificial SEI film layer;

[0129] S2. The silicon-carbon negative electrode material coated with the artificial SEI film layer and nano-silica were ball-milled with an ethanol solvent at a speed of 400 rpm for 15 hours, wherein the ball-to-material ratio was 7:1, to obtain the silicon composite negative electrode material having a multi-level coating structure.

[0130] Example 6

[0131] The difference between this embodiment and embodiment 1 is that the molar ratio of p-aminophenylacetylene to 4-bromo-2-trifluoromethoxyphenylacetylene in step S1 is 0.5:1, and the other steps are the same as those in embodiment 1.

[0132] Example 7

[0133] The difference between this embodiment and embodiment 1 is that the molar ratio of p-aminophenylacetylene to 4-bromo-2-trifluoromethoxyphenylacetylene in step S1 is 10:1, and the other steps are the same as those in embodiment 1.

[0134] Example 8

[0135] The difference between this embodiment and embodiment 1 is that the glass transition temperature of the copolymer in step S1 is -30°C, and the other aspects are the same as those in embodiment 1.

[0136] Example 9

[0137] The difference between this embodiment and embodiment 1 is that the glass transition temperature of the copolymer in step S1 is 15° C., and the other aspects are the same as those in embodiment 1.

[0138] Example 10

[0139] The difference between this embodiment and embodiment 1 is that the decomposition temperature of the copolymer in step S1 is 150° C., and the rest is the same as embodiment 1.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 1 is that no coating treatment is performed on the silicon-carbon material, only one silicon-carbon material is provided, and the average particle size, specific surface area and mass percentage of the silicon material provided are the same as those in Example 1.

[0142] Comparative Example 2

[0143] The difference between this comparative example and Example 1 is that the p-aminophenylacetylene in step S1 is replaced by 4-bromo-2-trifluoromethoxyphenylacetylene in an equimolar content, and the rest is the same as Example 1.

[0144] Comparative Example 3

[0145] The difference between this comparative example and Example 1 is that the 4-bromo-2-trifluoromethoxyphenylacetylene in step S1 is replaced by p-aminophenylacetylene in an equimolar amount, and the rest is the same as Example 1.

[0146] Comparative Example 4

[0147] The difference between this comparative example and Example 1 is that the artificial SEI film coating treatment in step S1 is not performed, that is, only the nano-silicon dioxide coating treatment in step S2 is performed on the silicon-carbon material, and the rest is the same as Example 1.

[0148] Comparative Example 5

[0149] The difference between this comparative example and Example 1 is that the nano-silicon dioxide coating treatment in step S2 is not performed, that is, only the artificial SEI film coating treatment in step S1 is performed on the silicon-carbon material, and the rest is the same as Example 1.

[0150] Application Examples 1-10 and Comparative Application Examples 1-5

[0151] The silicon-carbon negative electrode materials provided in Examples 1 to 10 and Comparative Examples 1 to 5 were used to prepare negative electrode sheets, and then assembled to obtain lithium-ion batteries. The specific preparation method is as follows:

[0152] Preparation of negative electrode sheet:

[0153] The silicon-carbon negative electrode material, conductive carbon black Super-P, single-walled carbon nanotubes (SWCNTs) and polyacrylic acid binder (PAA) provided in the above embodiments and comparative examples were mixed and stirred uniformly with water in a mass ratio of 80:9:1:10 to obtain a negative electrode slurry, and the solid content was controlled to be 30%. The negative electrode slurry was then coated on a copper foil current collector through a coating process, and then vacuum dried and cold pressed to obtain a negative electrode sheet.

[0154] Preparation of positive electrode:

[0155] The ternary cathode material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 The active material O2, polyvinylidene fluoride binder (PVDF) and conductive carbon black Super-P are mixed and stirred evenly with N-methylpyrrolidone solvent in a mass ratio of 96:2:2 to obtain a positive electrode slurry, and then the positive electrode slurry is coated on an aluminum foil through a coating process, and then dried and cold pressed to obtain a positive electrode sheet.

[0156] Electrolyte:

[0157] Ethylene carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate are mixed in a volume ratio of 20:40:30:10 to obtain an organic solvent. Thoroughly dried lithium salt LiPF6 is then dissolved in the organic solvent to prepare an electrolyte having a LiPF6 concentration of 1 mol / L. The electrolyte also includes a vinyl sulfate additive, with the weight percentage of vinyl sulfate being 2% based on the total weight of the electrolyte being 100%.

[0158] Preparation of lithium-ion batteries:

[0159] The positive electrode sheet, separator (including a polyethylene-based film and a ceramic coating provided on one side of the polyethylene-based film) and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming and shaping processes, a lithium-ion battery is obtained.

[0160] Comparative Application Example 6

[0161] The difference between this comparative application example and application example 1 is that no vinyl sulfate additive is added to the electrolyte, and the content of the organic solvent is adaptively adjusted so that the total content of the electrolyte is 100%. The rest is the same as application example 1.

[0162] Test conditions

[0163] The lithium-ion batteries provided in Application Examples 1 to 10 and Comparative Application Examples 1 to 6 were subjected to performance tests. The rate performance of the batteries was tested under lithium-ion battery test conditions. The tests were conducted on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. at room temperature (25°C). The charge and discharge voltages were limited to 2.5V to 4.2V. The test conditions are as follows:

[0164] (1) First Coulombic efficiency

[0165] At 25°C, the lithium-ion battery was charged to 4.2V at a constant current and constant voltage rate of 0.33C and allowed to stand for 10 minutes. Then, the lithium-ion battery was discharged to 2.5V at a constant current rate of 0.33C and allowed to stand for 10 minutes. The first coulombic efficiency of the lithium-ion battery was calculated.

[0166] First coulombic efficiency (%)=(first discharge total capacity of the lithium-ion battery at a rate of 0.33C / first charge total capacity of the lithium-ion battery at a rate of 0.33C)×100%.

[0167] (2) Capacity retention after 1000 cycles at 1C / 2C at room temperature

[0168] At 25°C, the lithium-ion battery is charged to 4.2V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C, and allowed to stand for 10 minutes. Then, the lithium-ion battery is discharged to 2.5V at a constant current rate of 2C and allowed to stand for 10 minutes. This is considered one charge and discharge cycle. The lithium-ion battery is charged and discharged 1200 times according to the above method. The capacity retention rate of the lithium-ion battery after 1000 charge and discharge cycles at 1C / 2C is calculated.

[0169] Capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0170] (3) Room temperature 6C rate performance - constant current charging ratio

[0171] At 25°C, the lithium-ion battery was discharged at a constant current rate of 1C to 2.5V and allowed to stand for 10 minutes. The lithium-ion battery was then charged at a constant current and constant voltage rate of 6C to 4.2V with a cut-off current of 0.05C and allowed to stand 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 charging ratio of the 6C rate charging was calculated according to the following formula: 6C rate charging constant current charging ratio = (constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2) × 100%.

[0172] (4) 1C / 8C discharge capacity retention rate at room temperature

[0173] At 25°C, the divided lithium-ion battery is charged to 4.2V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C; it is left to stand for 10 minutes; then the lithium-ion battery is discharged to 2.5V at a constant current rate of 1C, and its discharge capacity Q is recorded. 1C As the initial discharge capacity; then at 25 ° C, the lithium ion battery is charged to 4.2V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C; let it stand for 10 minutes; then the fully charged lithium ion battery is discharged to 2.5V at a constant current rate of 8C, and its discharge capacity Q is recorded. 8C ; Calculate the discharge capacity retention rate (%) of lithium-ion batteries at 1C / 8C rate = (discharge capacity Q at 8C rate) 8C / Discharge capacity Q at 1C rate 1C )×100%.

[0174] (5) Initial expansion rate of negative electrode

[0175] ① Before assembling the lithium-ion battery, use a micrometer to measure the initial thickness of the negative electrode sheet and record it as h1. The thickness of the negative electrode current collector is recorded as h0.

[0176] ② Fully charged: At 25°C, after assembling the battery cells, charge the lithium-ion battery at a constant current and constant voltage rate of 0.33C to 4.2V, with a cut-off current of 0.05C, and let it stand for 120 minutes;

[0177] ③ Disassemble the fully charged lithium-ion battery to obtain the negative electrode sheet, clean the negative electrode sheet with dimethyl carbonate, and measure the thickness of the cleaned negative electrode sheet, which is recorded as h2;

[0178] ④The initial expansion rate of the negative electrode is: (h2-h1) / (h1-h0)×100%.

[0179] (6) Battery cell thermal runaway ARC test

[0180] Start the ARC adiabatic thermal runaway test (the test sample is heated from room temperature to 45±2°C in the chamber, and after 90 minutes, the temperature rise rate of the lithium-ion battery is detected). If the temperature rise exceeds 0.2°C within 10 minutes (i.e., the self-heating temperature rise rate, referred to as SHR, SHR>0.02°C / min), it is considered that a self-exothermic reaction has occurred inside the lithium-ion battery, and the adiabatic environment is maintained until the lithium-ion battery thermal runaway occurs; if the temperature rise does not exceed 0.2°C within 10 minutes (i.e., SHR≤0.02°C / min), continue to the next step temperature rise test; each temperature step is 5°C, and the steps are repeated at each temperature step. The ARC test temperature range is 45°C-300°C, the starting temperature of self-heating is T1 (temperature rise rate SHR>0.02°C / min), and the starting temperature of thermal runaway is T2 (temperature rise rate SHR>1°C / min).

[0181] The test results are shown in Table 1:

[0182] Table 1

[0183]

[0184]

[0185] As can be seen from Table 1, compared with Comparative Application Example 1, Application Examples 1 to Application Examples 5 of the present invention further improve the safety, high rate performance and high temperature performance of lithium-ion batteries by regulating the structure and composition of the silicon composite negative electrode material, especially adopting a multi-level coating structure.

[0186] Comparison of Application Examples 1, 6, and 7 reveals that the molar ratio of p-aminophenylacetylene to 4-bromo-2-trifluoromethoxyphenylacetylene significantly impacts the structural stability, thermal stability, and ion transport properties of the artificial SEI film. By optimizing the molar ratio of p-aminophenylacetylene to 4-bromo-2-trifluoromethoxyphenylacetylene, the present invention achieves an artificial SEI film with suitable mechanical strength and ion conductivity, thereby comprehensively improving the electrochemical performance of lithium-ion batteries at high rates and high temperatures.

[0187] Comparison of Application Examples 1, 8, and 9 demonstrates that the glass transition temperature of the copolymer significantly influences the mechanical properties and thermal stability of the resulting artificial SEI layer. By optimizing the glass transition temperature of the copolymer within an appropriate range, the present invention effectively suppresses the volume expansion of the silicon-carbon anode material and improves the safety of lithium-ion batteries.

[0188] Comparing Application Example 1 with Application Example 10, it can be seen that the present invention optimizes the decomposition temperature of the copolymer so that the formed artificial SEI film has good structural stability and thermal stability, thereby improving the high-temperature performance of the lithium-ion battery.

[0189] Comparing Application Examples 1, 2 and 3, it can be seen that if only a composite negative electrode material formed by a homopolymer obtained from a certain monomer is used, it is impossible to take into account both the high rate performance and high temperature performance of the lithium-ion battery.

[0190] Comparing Application Examples 1, 4 and 5, it can be seen that if only one type of coating layer is used, the full technical effects of the technical solution of the present invention cannot be achieved.

[0191] By comparing Application Example 1 with Comparative Application Example 6, it can be seen that the specific type of artificial SEI film layer provided by the present invention has a synergistic effect with the vinyl sulfate additive in the electrolyte, thereby further reducing the interfacial impedance between the electrode and the electrolyte and optimizing the overall performance of the lithium-ion battery.

[0192] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A silicon composite negative electrode material with a multi-level coating structure, characterized in that: The core of the silicon composite negative electrode material with a multi-level coating structure includes a silicon negative electrode material, the middle layer includes an artificial SEI film layer, and the outermost layer includes an oxide coating layer; The material of the artificial SEI film layer includes a phenylacetylene copolymer, and the structure of the phenylacetylene copolymer includes a combination of a halogen group, an ether group and a group capable of forming a hydrogen bond.

2. The silicon composite negative electrode material with a multi-level coating structure according to claim 1, characterized in that: The phenylacetylene copolymer includes a first structural unit and a second structural unit; Preferably, the first structural unit comprises a first halogen group and a substituted or unsubstituted ether group; Preferably, the substituted group includes a second halogen group; Preferably, the first halogen group comprises a bromine atom; Preferably, the second halogen group comprises a fluorine atom; Preferably, the second structural unit comprises a group capable of forming a hydrogen bond; Preferably, the groups capable of forming hydrogen bonds include amine groups and / or hydroxyl groups.

3. The silicon composite negative electrode material with a multi-level coating structure according to claim 2, characterized in that: The monomer forming the first structural unit includes a phenylacetylene compound containing a first halogen group and a substituted or unsubstituted ether group; Preferably, the substituted group includes a second halogen group; Preferably, the first halogen group comprises a bromine atom; Preferably, the second halogen group comprises a fluorine atom; Preferably, the monomer forming the first structural unit includes 4-bromo-2-trifluoromethoxyphenylacetylene; Preferably, the monomer forming the second structural unit includes a phenylacetylene compound containing a group capable of forming a hydrogen bond; Preferably, the groups capable of forming hydrogen bonds include amine groups and / or hydroxyl groups; Preferably, the monomer forming the second structural unit includes p-aminophenylacetylene.

4. The silicon composite negative electrode material with a multi-level coating structure according to any one of claims 1 to 3, characterized in that: The glass transition temperature of the phenylacetylene copolymer is -20°C to 10°C, preferably -7°C to -3°C; Preferably, the decomposition temperature of the phenylacetylene copolymer is not lower than 200°C, preferably not lower than 220°C; Preferably, the number average molecular weight of the phenylethene copolymer is 15,000 Da to 80,000 Da, preferably 30,000 Da to 60,000 Da.

5. The silicon composite negative electrode material with a multi-level coating structure according to any one of claims 1 to 4, characterized in that: Taking the total mass of the silicon negative electrode material coated by the artificial SEI film layer as 100%, the mass percentage of the material of the artificial SEI film layer is 1% to 6%; Preferably, the thickness of the artificial SEI film layer is 30 nm to 90 nm.

6. The silicon composite negative electrode material with a multi-level coating structure according to any one of claims 1 to 5, characterized in that: The material of the oxide coating layer includes non-metallic oxide; Preferably, the non-metallic oxide comprises silicon dioxide; Preferably, the average particle size of the non-metallic oxide is 10 nm to 90 nm, preferably 20 nm to 45 nm; Preferably, based on the total mass of the silicon negative electrode material coated with the artificial SEI film layer being 100%, the mass percentage of the material of the oxide coating layer is 1% to 6%.

7. A method for preparing a silicon composite negative electrode material having a multi-level coating structure according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1. Mixing a silicon anode material with a phenylacetylene copolymer solution having a structure including a halogen group, an ether group, and a group capable of forming a hydrogen bond, and spray drying the mixture to obtain a silicon anode material coated with an artificial SEI film; S2. Performing an oxide coating treatment on the silicon negative electrode material coated with the artificial SEI film layer to obtain the silicon composite negative electrode material having a multi-level coating structure.

8. The method according to claim 7, characterized in that The mass concentration of the phenylacetylene copolymer solution in step S1 is 5% to 17%; Preferably, the method for preparing the phenylacetylene copolymer in the phenylacetylene copolymer solution in step S1 comprises the following steps: reacting the monomer forming the first structural unit, the monomer forming the second structural unit, an initiator, and an organic solvent to obtain the phenylacetylene copolymer; Preferably, the molar ratio of the monomer forming the first structural unit to the monomer forming the second structural unit is 1:(1-5), preferably 1:(2.8-3.2); Preferably, the reaction is carried out under an inert atmosphere; Preferably, the reaction temperature is 60°C to 100°C; Preferably, the reaction time is 5h to 10h; Preferably, the mixing temperature in step S1 is 60°C to 100°C; Preferably, the mixing time in step S1 is 5 h to 10 h; Preferably, the inlet temperature of the spray drying in step S1 is 120°C to 200°C; Preferably, the outlet temperature of the spray drying in step S1 is 60°C to 98°C.

9. The method according to claim 7 or 8, characterized in that The oxide coating process in step S2 includes grinding the silicon negative electrode material coated with the artificial SEI film layer and the non-metallic oxide to obtain the silicon composite negative electrode material with a multi-level coating structure; Preferably, the grinding method includes ball milling; Preferably, the ball-to-material ratio of the ball mill is (5-9):1; Preferably, the ball milling speed is 200 rpm to 600 rpm; Preferably, the ball milling time is 10 h to 20 h.

10. A secondary battery, characterized in that: The secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. The negative electrode sheet includes a negative electrode active material. The negative electrode active material includes the silicon composite negative electrode material with a multi-level coating structure according to any one of claims 1 to 6.

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