Silicon-carbon composite material, negative electrode sheet, negative electrode sheet preparation method, and battery

Abstract

The application provides a silicon-carbon composite material, a negative electrode sheet, a negative electrode sheet preparation method and a battery, comprising a core and a shell, the shell coats the core, the core comprises a modified silicon-carbon material, the shell comprises a composite coating layer, the composite coating layer comprises a barrier outer layer and an in-situ passivation inner layer, the in-situ passivation inner layer coats the surface of the core, and the barrier outer layer coats the surface of the in-situ passivation inner layer. The silicon-carbon composite material provided by the application is characterized in that the in-situ passivation inner layer reacts with the surface active sites of the modified silicon-carbon material to form a dense passivation layer with high ion conductivity, blocks the active sites on the surface of silicon particles that are prone to react with water, inhibits gas production, the barrier outer layer forms a physical barrier, further blocks the contact path of water and the silicon-carbon core, effectively prevents water from penetrating into the core, the barrier outer layer and the in-situ passivation inner layer cooperate with each other to eliminate the hydrolysis gas production reaction and block the penetration of external water, inhibit the gas production of the silicon-carbon negative electrode material, and optimize and improve the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a silicon-carbon composite material, a negative electrode, a method for preparing the negative electrode, and a battery. Background Technology

[0002] In existing technologies, to address the performance degradation of silicon-carbon anode materials in lithium-ion batteries due to the easy reaction of nano-silicon with water to produce hydrogen gas, single physical barrier methods such as carbon coating, oxide coating, or polymer coating are mainly employed. While these technologies can isolate moisture from the silicon surface to some extent, they still have significant shortcomings: carbon coating is complex and costly, oxide coating may lead to a decrease in ion conductivity, and polymer coating is prone to cracking and failure during long-term cycling due to material volume expansion. Furthermore, existing solutions often rely on organic solvent systems, which are environmentally unfriendly, and their overall protective effect is limited. It is difficult to simultaneously achieve high stability, low cost, and the requirements of industrial production, thus hindering the large-scale application of silicon-carbon anode materials. Summary of the Invention

[0003] To address the problem that the application of nano-silicon in the negative electrode of batteries easily leads to hydrolysis and gas generation, resulting in a decrease in battery performance, this paper provides a silicon-carbon composite material, a negative electrode sheet, a method for preparing the negative electrode sheet, and a battery.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: On one hand, the present invention provides a silicon-carbon composite material, including a core and a shell, wherein the shell covers the core, the core includes a modified silicon-carbon material, the shell includes a composite coating layer, the composite coating layer includes a barrier outer layer and an in-situ passivation inner layer, the in-situ passivation inner layer covers the surface of the core, and the barrier outer layer covers the surface of the in-situ passivation inner layer.

[0005] Optionally, the raw material of the outer barrier layer includes a modified polyethylene oxide-polysiloxane block copolymer, and the raw material of the in-situ passivation inner layer includes an amino-containing organoboron compound. The mass ratio of the raw material of the outer barrier layer to the raw material of the inner passivation layer in the composite coating layer is 2~5:1.

[0006] Optionally, the molecular weight of the modified polyethylene oxide-polysiloxane block copolymer is 5000~20000; In the modified polyethylene oxide-polysiloxane block copolymer, the percentage of the polysiloxane block is 30-50%.

[0007] Optionally, the amino-containing organoboron compound includes one or more of 4-aminomethylphenylboronic acid salt and 3-aminophenylboronic acid.

[0008] Optionally, the modified silicon-carbon material is a silicon-carbon material modified by the first modifier; The silicon-carbon material includes porous carbon material and nano-silicon located in the pores of the porous carbon material. The nano-silicon has a particle size of 50~200nm, and the mass ratio of nano-silicon to porous carbon material in the silicon-carbon material is 1:(3~5).

[0009] Optionally, the first modifier comprises an aminosilane coupling agent, wherein the aminosilane coupling agent comprises one or more of KH560 and KH792.

[0010] Optionally, the thickness of the composite coating layer is 20-50 nm, the thickness of the outer barrier layer is 15-35 nm, and the thickness of the in-situ passivation inner layer is 5-15 nm.

[0011] On the other hand, the present invention provides a negative electrode sheet, including a current collector and a negative electrode material layer, wherein the negative electrode material layer includes the aforementioned silicon-carbon composite material.

[0012] Optionally, the negative electrode material layer further includes an additive, which includes a compound of fluoroalkyl polyether phosphate and a second modifier, wherein the mass ratio of the fluoroalkyl polyether phosphate to the second modifier is 1:(1~3). The second modified product includes an aminosilane coupling agent.

[0013] Optionally, the method for preparing the negative electrode sheet includes the following operations: Silicon-carbon material is placed in a first solvent and dispersed. After dispersion, a first modifier is added. After reaction at high temperature, the mixture is dried to obtain modified silicon-carbon material. The raw materials for the outer barrier layer and the raw materials for the in-situ passivation inner layer are mixed with a second solvent, dissolved, and then modified silicon-carbon material is added. Under a protective atmosphere, the mixture is treated at high temperature, and after the reaction, it is dried to form a composite coating layer on the surface of the core, thus obtaining a silicon-carbon composite material. The third solvent and dispersant were mixed and then added to the silicon-carbon composite material to obtain a pre-dispersion. Additives are added to the pre-dispersion liquid, then binder and conductive agent are added, and after mixing, a negative electrode slurry is obtained. The negative electrode slurry is coated onto the current collector, and after drying, a negative electrode sheet is obtained.

[0014] Optionally, the negative electrode slurry comprises the following components by mass: 40-60 parts of silicon-carbon material, 3-10 parts of raw material for the outer barrier layer, 0.5-3.5 parts of raw material for the in-situ passivation inner layer, 0.5-3 parts of additives, 3-8 parts of binder, 1-5 parts of dispersant, 2-6 parts of conductive agent, and 20-40 parts of third solvent.

[0015] Optionally, both the first solvent and the second solvent are organic solvents, wherein the organic solvent is anhydrous ethanol, and the third solvent is deionized water.

[0016] Optionally, in the preparation of modified silicon-carbon materials, the high temperature is 60~80℃ and the reaction time is 2~4h; In the preparation of silicon-carbon composite materials, the high temperature is 50~70℃ and the reaction time is 3~6h.

[0017] On the other hand, the present invention provides a battery comprising the aforementioned negative electrode sheet, or a negative electrode sheet prepared by the method for preparing the aforementioned negative electrode sheet.

[0018] The beneficial effects of this application are as follows: The silicon-carbon composite material provided in this application includes a core and a shell. The shell covers the core, and the core comprises a modified silicon-carbon material. The shell includes a composite coating layer, which comprises a barrier outer layer and an in-situ passivation inner layer. The in-situ passivation inner layer coats the surface of the core, and the barrier outer layer coats the surface of the in-situ passivation inner layer. The in-situ passivation inner layer, coated on the surface of the core, can react in-situ with the active sites on the surface of the modified silicon-carbon material to form a dense passivation layer with high ion conductivity, which can directly block the surface of silicon particles that are easily reactive with water. The active sites suppress gas production at the source. The barrier outer layer, which coats the outside of the in-situ passivation inner layer, can form a physical barrier, further blocking the contact path between moisture and the silicon-carbon core, effectively preventing moisture from penetrating into the core. At the same time, the double-layer structure of this composite coating can effectively buffer the volume expansion stress of silicon-carbon materials during charging and discharging. The barrier outer layer and the in-situ passivation inner layer work together to eliminate the source of hydrolysis gas production reaction and physically block the penetration of external moisture, thereby suppressing gas production of silicon-carbon anode materials and optimizing and improving the electrochemical performance of the battery. Detailed Implementation

[0019] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] The present invention provides a silicon-carbon composite material, comprising a core and a shell, wherein the shell covers the core, the core comprises a modified silicon-carbon material, and the shell comprises a composite coating layer comprising a barrier outer layer and an in-situ passivation inner layer, wherein the in-situ passivation inner layer covers the surface of the core, and the barrier outer layer covers the surface of the in-situ passivation inner layer.

[0021] Specifically, the silicon-carbon composite material provided in this application includes a core and a shell, wherein the shell covers the core, the core comprises a modified silicon-carbon material, and the shell comprises a composite coating layer comprising a barrier outer layer and an in-situ passivation inner layer. The in-situ passivation inner layer covers the surface of the core, and the barrier outer layer covers the surface of the in-situ passivation inner layer. The in-situ passivation inner layer covering the surface of the core can react in-situ with the active sites on the surface of the modified silicon-carbon material to form a dense passivation layer with high ion conductivity, which can directly block the surface of silicon particles from easily reacting with water. The corresponding active sites inhibit gas production at the source. The barrier outer layer, which coats the outer side of the in-situ passivation inner layer, can form a physical barrier, further blocking the contact path between moisture and the silicon-carbon core, effectively preventing moisture from penetrating into the core. At the same time, the double-layer structure of this composite coating can effectively buffer the volume expansion stress of silicon-carbon materials during charging and discharging. The barrier outer layer and the in-situ passivation inner layer work together to eliminate the source of hydrolysis gas production reaction and physically block the penetration of external moisture, thereby suppressing gas production in silicon-carbon anode materials and optimizing and improving the electrochemical performance of the battery.

[0022] In some embodiments, the material of the outer barrier layer includes a modified polyethylene oxide-polysiloxane block copolymer, and the material of the in-situ passivation inner layer includes an amino-containing organoboron compound. The mass ratio of the raw material of the outer barrier layer to the raw material of the inner passivation layer in the composite coating layer is 2~5:1.

[0023] Specifically, the amino-containing organoboron compound can form a dense, highly ion-conducting passivation inner layer by undergoing covalent and coordination reactions (forming Si-N bonds) with the amino groups on the surface of modified silicon carbon; the hydrophobic segments of the block copolymer can enhance the hydrophobic properties of the outer barrier layer, while the lithiophilic segments of polyethylene oxide ensure rapid lithium-ion conduction. In this process, setting the mass ratio of the raw material of the outer barrier layer to the raw material of the in-situ passivation inner layer in the composite coating layer to 2~5:1 can ensure a balance between sufficient physical barrier thickness of the outer layer and dense passivation effect of the inner layer, avoiding the inner layer being too thick and affecting ion conduction or the outer layer being too thin and causing water penetration.

[0024] Furthermore, in the modified polyethylene oxide-polysiloxane block copolymer, the modified polyethylene oxide refers to the introduction of at least one functional group among epoxy, hydroxyl, or carboxyl groups on the end or side groups of the polyethylene oxide chain segment to improve the interfacial bonding strength with silicon carbon materials and the coating layer.

[0025] In some embodiments, the molecular weight of the modified polyethylene oxide-polysiloxane block copolymer is 5000~20000; In the modified polyethylene oxide-polysiloxane block copolymer, the percentage of the polysiloxane block is 30-50%.

[0026] Specifically, a molecular weight of 5,000 to 20,000 can ensure that the block copolymer has good film-forming properties, avoiding discontinuous film formation due to too low a molecular weight and difficulty in dissolution or uneven coating due to too high a molecular weight. An excessively high proportion of polysiloxane can affect lithium-ion conductivity, while an excessively low proportion weakens the hydrophobic barrier effect of the outer layer. A polysiloxane block content of 30-50% can achieve a balance between hydrophobic and lithiophilic properties. This parameter range ensures that the outer layer has both excellent water barrier properties and lithium-ion conductivity.

[0027] In some embodiments, the amino-containing organoboron compound includes one or more of 4-aminomethylphenylboronic acid salt and 3-aminophenylboronic acid.

[0028] Specifically, the selected aminophenylboronic acid compounds have high amino activity, which can quickly react in situ with the hydroxyl groups on the modified silicon carbon surface to form stable Si-N bonds. At the same time, the boric acid groups can further strengthen the binding force between the inner layer and the core through coordination, forming a denser passivation layer. The hydrochloride form can improve its solubility in organic solvents, ensuring uniform reaction and avoiding defects in the inner layer coating caused by uneven dissolution of raw materials, thereby ensuring the sealing effect of the inner layer on the active sites.

[0029] In some embodiments, the modified silicon-carbon material is a silicon-carbon material modified by a first modifier; The silicon-carbon material includes porous carbon material and nano-silicon located in the pores of the porous carbon material. The nano-silicon has a particle size of 50~200nm, and the mass ratio of nano-silicon to porous carbon material in the silicon-carbon material is 1:(3~5).

[0030] Specifically, porous carbon, as a carrier, can buffer the volume expansion of nano-silicon. The nano-silicon particle size of 50~200nm can balance the lithium storage capacity and volume effect of silicon (too small a particle size is prone to agglomeration, while too large a particle size results in large volume expansion stress). The mass ratio of nano-silicon to porous carbon material of 1:(3~5) can ensure that nano-silicon is uniformly dispersed in the pores of porous carbon, avoiding the risk of agglomeration and hydrolysis gas generation caused by direct contact of silicon particles. At the same time, porous carbon can improve the conductivity of the material, make up for the defect of poor conductivity of silicon itself, and achieve a balance between high capacity and high stability.

[0031] Furthermore, the particle size of the nano-silicon includes, but is not limited to, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm or 200nm; The mass ratio of the nano-silicon to the porous carbon material includes, but is not limited to, 1:3, 1:4, or 1:5.

[0032] In some embodiments, the first modifier comprises an aminosilane coupling agent, wherein the aminosilane coupling agent comprises one or more of KH560 and KH792.

[0033] Specifically, the above-mentioned coupling agent can directionally introduce active functional groups such as hydroxyl and epoxy groups on the surface of silicon-carbon materials through hydrolysis reaction, providing stable and uniform reaction anchors for the subsequent in-situ passivation inner layer formation, ensuring that the amino-containing organoboron compound can undergo directional covalent and coordination reactions with the silicon-carbon core. Meanwhile, KH560 and KH792 possess high reactivity, enabling uniform activation of the silicon-carbon material surface. This effectively avoids localized coating defects caused by uneven activation, preventing localized gas generation from the root cause. Furthermore, they strengthen the interfacial bonding between the silicon-carbon core and the composite coating layer, enhancing the density and structural stability of the double-layer coating structure. In addition, the functional groups introduced by these coupling agents do not impair the lithium storage performance and ion conductivity of the silicon-carbon material itself. They also provide reaction conditions for the subsequent ring-opening grafting reaction between the outer barrier layer and the in-situ passivated inner layer, which is beneficial for forming a continuous silicon-carbon core composite coating layer structure.

[0034] The silicon-carbon material is activated by the first modifier, introducing epoxy groups. In a nitrogen atmosphere, the amino organoboron reacts with the hydroxyl groups on the activated silicon surface to form an in-situ passivation inner layer (Si-N bond + coordination bond); the hydrophobic block copolymer reacts with the inner layer amino group to form an outer layer.

[0035] In some embodiments, the thickness of the composite coating layer is 20-50 nm, the thickness of the outer barrier layer is 15-35 nm, and the thickness of the in-situ passivation inner layer is 5-15 nm.

[0036] Specifically, the in-situ passivation inner layer, with a thickness of 5-15 nm, can form a dense passivation layer while avoiding excessive thickness that could affect lithium-ion conduction; the barrier outer layer, with a thickness of 15-35 nm, can provide sufficient physical barrier properties while also considering film formation and flexibility; the composite coating layer, with a thickness of 20-50 nm, can ensure that the entire composite coating layer has good flexibility, can buffer the volume expansion during silicon-carbon charging and discharging, avoid cracking of the coating layer, and at the same time, will not increase the internal resistance of the electrode due to excessive thickness, thus achieving a balance between protective performance and electrochemical performance.

[0037] Furthermore, the thickness of the in-situ passivation inner layer includes, but is not limited to, 5nm, 8nm, 10nm, 12nm or 15nm; the thickness of the barrier outer layer includes, but is not limited to, 15nm, 20nm, 25nm, 30nm or 35nm. The thickness of the composite coating layer includes, but is not limited to, 20nm, 25nm, 30nm, 33nm, 40nm, 45nm, or 50nm.

[0038] Another embodiment of the present invention provides a negative electrode sheet, including a current collector and a negative electrode material layer, wherein the negative electrode material layer includes the aforementioned silicon-carbon composite material.

[0039] Specifically, the negative electrode includes the silicon-carbon composite material provided in this application. The silicon-carbon composite material includes a core and a shell, with the shell covering the core. The core includes a modified silicon-carbon material, and the shell includes a composite coating layer. The composite coating layer includes a barrier outer layer and an in-situ passivation inner layer. The in-situ passivation inner layer coats the surface of the core, and the barrier outer layer coats the surface of the in-situ passivation inner layer. The in-situ passivation inner layer, coated on the surface of the core, can react in-situ with the active sites on the surface of the modified silicon-carbon material to form a dense passivation layer with high ion conductivity, which can directly block silicon. The active sites on the particle surface that readily react with water inhibit gas production at the source. The outer barrier layer, which coats the outside of the in-situ passivation inner layer, forms a physical barrier, further blocking the contact path between moisture and the silicon-carbon core, effectively preventing moisture from penetrating into the core. At the same time, the double-layer structure of this composite coating layer can effectively buffer the volume expansion stress of the silicon-carbon material during charging and discharging. The outer barrier layer and the in-situ passivation inner layer work together in the composite coating layer to eliminate the source of hydrolysis gas production reaction and physically block the penetration of external moisture, thereby suppressing gas production in the silicon-carbon anode material and optimizing and improving the electrochemical performance of the battery.

[0040] In some embodiments, the negative electrode material layer further includes an additive, which includes a compound of fluoroalkyl polyether phosphate and a second modifier, wherein the mass ratio of the fluoroalkyl polyether phosphate to the second modifier is 1:(1~3). The second modified product includes an aminosilane coupling agent.

[0041] Specifically, the fluoroalkyl polyether phosphate has excellent surface activity and hydrophobicity, which can further improve the hydrophobic performance of the negative electrode material layer and enhance the moisture barrier effect; the silane coupling agent can improve the interfacial bonding force between the silicon-carbon composite material and the binder and current collector, and improve the structural stability of the negative electrode sheet. The compounding of fluoroalkyl polyether phosphate with the second modifier in a mass ratio of 1:(1~3) can achieve a balance between surface activity and interfacial bonding force, avoid excessive additives affecting electrode conductivity or insufficient additives leading to inadequate interfacial bonding, and improve the processing performance and cycle stability of the negative electrode sheet.

[0042] Furthermore, the mass ratio of the fluoroalkyl polyether phosphate to the second modified material includes, but is not limited to, 1:1, 1:2, or 1:3.

[0043] It should be noted that both the second modifier and the first modifier can be selected from aminosilane coupling agents. Although silane coupling agents are used twice in this application, in the silicon carbon modification stage and the negative electrode slurry preparation stage, there is no mutual interference. On the contrary, they have a synergistic effect. The core reason is that the functional group action mechanism, reaction stage and target of the two are completely different. Specifically, in the silicon carbon modification stage, the aminosilane coupling agent introduces epoxy groups on the silicon carbon surface through hydrolysis reaction, strengthens the interfacial bonding force between the silicon carbon core and the subsequent composite coating layer, and provides a reaction anchor point for the formation of the in-situ passivation inner layer. In the negative electrode slurry preparation stage, the coupling agent is compounded with fluoroalkyl polyether phosphate as an auxiliary component. Its amino functional groups can undergo ring-opening reaction with the epoxy groups remaining on the surface of the composite coating layer. At the same time, it can also improve the interfacial compatibility between silicon-carbon composite materials and binders and current collectors, and achieve a tight connection between the coating layer and electrode components. The two step-by-step reactions have no competition or interference relationship, and the ring-opening reaction of epoxy-amino further constructs a continuous interface structure of "silicon-carbon core-composite coating layer-electrode matrix", which significantly improves the hydrolysis resistance and cycle stability of the material.

[0044] In some embodiments, the method for preparing the negative electrode sheet includes the following operations: Silicon-carbon material is placed in a first solvent and dispersed. After dispersion, a first modifier is added. After reaction at high temperature, the mixture is dried to obtain modified silicon-carbon material. The raw materials for the outer barrier layer and the raw materials for the in-situ passivation inner layer are mixed with 80 parts of the second solvent (anhydrous ethanol) at a mass ratio of 3:1. After stirring and dissolving, 40-60 parts of modified silicon-carbon material are added. The mixture is stirred and reacted at 60°C for 4 hours in a nitrogen atmosphere, centrifuged, and vacuum dried at 80°C for 3 hours to form a composite coating layer on the core surface, thus obtaining a silicon-carbon composite material. 30 parts of the third solvent (deionized water) and 3 parts of the dispersant (sodium naphthalene sulfonate formaldehyde condensate) were added to a stirred tank and mixed. The mixture was stirred at a low speed of 300 rpm for 10 min and then added to the silicon-carbon composite material. The mixture was dispersed at a high speed of 2500 rpm for 1.5 h to obtain a pre-dispersion. One part of the additive (fluoroalkyl polyether phosphate and KH560 in a mass ratio of 1:2) was added to the pre-dispersion liquid, and the mixture was ultrasonically treated at 400W and 30kHz for 30 minutes. Then, five parts of the binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:3) and the conductive agent were added. The mixture was stirred at low speed of 400rpm for 3 hours under a nitrogen atmosphere. The viscosity was adjusted to 10000mPa.s to obtain the negative electrode slurry. The negative electrode slurry was coated onto the current collector and dried to obtain the negative electrode sheet.

[0045] The method for preparing the negative electrode sheet includes the following specific operations: 50 parts of silicon-carbon material were ultrasonically dispersed in 100 parts of the first solvent (ethanol) for 40 min. After dispersion, 1 part of the first modifier (KH560) was added, and the mixture was stirred at 70 °C for 3 h. After filtration, the mixture was vacuum dried at 100 °C for 2 h to obtain the modified silicon-carbon material. The raw materials for the outer barrier layer and the raw materials for the in-situ passivation inner layer are mixed with a second solvent, dissolved, and then modified silicon-carbon material is added. Under a protective atmosphere, the mixture is treated at high temperature, and after the reaction, it is dried to form a composite coating layer on the surface of the core, thus obtaining a silicon-carbon composite material. The third solvent and dispersant were mixed and then added to the silicon-carbon composite material to obtain a pre-dispersion. Additives are added to the pre-dispersion liquid, then binder and conductive agent are added, and after mixing, a negative electrode slurry is obtained. The negative electrode slurry is coated onto the current collector, and after drying, a negative electrode sheet is obtained.

[0046] Furthermore, the silicon-carbon material is activated by the first modifier to introduce epoxy groups, thereby obtaining a modified silicon-carbon material; In a protective atmosphere, the amino groups in the amino-containing organoboron compound of the in-situ passivation inner layer react with the hydroxyl groups on the activated silicon surface of the modified silicon carbon material to form an in-situ passivation inner layer (Si-N bond + coordination bond). The raw material of the barrier outer layer, modified polyethylene oxide-polysiloxane block copolymer, reacts with the amino group in the in-situ passivation inner layer to form a barrier outer layer. The polysiloxane is hydrophobic and the polyethylene oxide is lithiophilic. After centrifugation and drying, a barrier outer layer and an in-situ passivation inner layer with a layered structure are formed on the surface of the modified silicon carbon material. In the above operations, the modified silicon-carbon preparation stage introduces active sites through high-temperature reaction; the composite coating stage avoids silicon surface oxidation during the reaction process through a protective atmosphere (nitrogen), and forms a layered coating structure rather than a mixed layer through the directional reaction of raw materials (the inner layer is first formed in situ, and the outer layer is grafted through a ring-opening reaction); the subsequent pre-dispersion, slurry preparation and coating can achieve uniform distribution of silicon-carbon composite material on the current collector, ensure the performance consistency of the negative electrode, and solve the problems of complex process and poor environmental performance of existing methods.

[0047] In some embodiments, the negative electrode slurry comprises the following components by mass: 40-60 parts of silicon-carbon material, 3-10 parts of raw material for the outer barrier layer, 0.5-3.5 parts of raw material for the in-situ passivation inner layer, 0.5-3 parts of additives, 3-8 parts of binder, 1-5 parts of dispersant, 2-6 parts of conductive agent, and 20-40 parts of third solvent.

[0048] Specifically, 40-60 parts of silicon-carbon material can ensure the high capacity of the negative electrode sheet, 0.5-3 parts of additives can enhance hydrophobicity and interfacial bonding, 3-8 parts of binder can ensure the structural stability of the negative electrode material layer, 1-5 parts of dispersant can ensure the uniform dispersion of silicon-carbon material, and 20-40 parts of third solvent (deionized water) can realize an environmentally friendly slurry system (replacing existing organic solvents). Optimization of the dosage of each component can achieve good rheological properties and coating properties of the negative electrode slurry, avoid slurry agglomeration and uneven coating, and at the same time reduce production costs and environmental pressure.

[0049] In some embodiments, the first solvent and the second solvent are both organic solvents, the organic solvent is anhydrous ethanol, and the third solvent is deionized water.

[0050] Specifically, anhydrous ethanol, as the solvent for the first two steps of the reaction, ensures good solubility of the raw materials (block copolymers, organoboron compounds, and silane coupling agents) and avoids water interference with the active sites on the modified silicon carbon surface and the in-situ reaction of the inner layer. Deionized water, as the third solvent, replaces the existing organic solvent system, significantly reducing environmental pressure and production costs. At the same time, through the synergistic effect of dispersants and additives, it can achieve uniform dispersion of silicon carbon composite materials in the aqueous system, solving the problem of easy agglomeration of silicon carbon materials in the aqueous system.

[0051] In some embodiments, during the preparation of modified silicon carbon materials, the high temperature is 60~80℃ and the reaction time is 2~4h; In the preparation of silicon-carbon composite materials, the high temperature is 50~70℃ and the reaction time is 3~6h.

[0052] Specifically, in the preparation of modified silicon-carbon materials, a high temperature of 60-80℃ and a reaction time of 2-4h can ensure that the silane coupling agent is fully hydrolyzed and reacts with the silicon-carbon surface to form uniform active sites. In the preparation of silicon-carbon composite materials, a high temperature of 50~70℃ and a reaction time of 3~6h are used to ensure that the organoboron compound reacts fully with the hydroxyl groups on the silicon-carbon surface to form the inner layer, while the block copolymer reacts fully with the inner layer amino group to form the outer layer. This avoids the decomposition of raw materials due to excessively high temperature or the incomplete reaction due to excessively low temperature, thus ensuring the compactness and uniformity of the double-layer coating structure.

[0053] Another embodiment of the present invention provides a battery including the aforementioned negative electrode sheet, or a negative electrode sheet prepared by the method for preparing the aforementioned negative electrode sheet.

[0054] The present invention will be further illustrated by the following examples.

[0055] Table 1 Example 1 This embodiment is used to illustrate the negative electrode sheet, negative electrode sheet preparation method, and battery disclosed in this invention: Preparation of negative electrode sheet 50 parts of silicon-carbon material were placed in the first solvent and dispersed. After dispersion, 1 part of the first modifier (KH560) was added. After reaction at high temperature, the mixture was dried to obtain the modified silicon-carbon material. Among them, the particle size of nano-silicon in silicon-carbon material is 100nm, and the mass ratio of nano-silicon to porous carbon material is 1:3; The raw material of the barrier outer layer, modified polyethylene oxide-polysiloxane block copolymer, and the raw material of the in-situ passivation inner layer were mixed with 80 parts of the second solvent (anhydrous ethanol) at a mass ratio of 3:1. After stirring and dissolving, 40 parts of modified silicon carbon material were added. The mixture was stirred and reacted at 60°C for 4 hours in a nitrogen atmosphere, centrifuged, and vacuum dried at 80°C for 3 hours to form a composite coating layer on the surface of the core, thus obtaining a silicon carbon composite material. 30 parts of the third solvent (deionized water) and 3 parts of the dispersant (sodium naphthalene sulfonate formaldehyde condensate) were added to a stirred tank and mixed. The mixture was stirred at a low speed of 300 rpm for 10 min and then added to the silicon-carbon composite material. The mixture was dispersed at a high speed of 2500 rpm for 1.5 h to obtain a pre-dispersion. One part of the additive (fluoroalkyl polyether phosphate and KH560 in a mass ratio of 1:2) was added to the pre-dispersion liquid, and the mixture was ultrasonically treated at 400W and 30kHz for 30 minutes. Then, five parts of the binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:3) and two parts of the conductive agent were added. The mixture was stirred at low speed of 400rpm for 3 hours under a nitrogen atmosphere to adjust the viscosity to 10000mPa.s, thus obtaining the negative electrode slurry. The negative electrode slurry was coated onto the current collector and dried to obtain the negative electrode sheet.

[0056] The positive electrode can be any type of positive electrode conventionally used in the field, and this application does not impose any special restrictions on the positive electrode.

[0057] A battery is obtained by assembling the negative electrode, positive electrode, separator, and casing, and then injecting electrolyte.

[0058] Examples 2-7 Examples 2-7 illustrate the negative electrode sheet, negative electrode sheet preparation method, and battery disclosed in this invention, with the following differences: The raw materials of the in-situ passivation inner layer, the mass ratio of the raw materials of the barrier outer layer to the raw materials of the in-situ passivation inner layer, the amount of silicon-carbon material, the amount of the first modifier, the nano-silicon particle size in the silicon-carbon material, the mass ratio of nano-silicon to porous carbon material, as well as the thickness of the barrier outer layer, the thickness of the in-situ passivation inner layer, and the thickness of the composite coating layer in Examples 2-7 are all recorded in Table 1.

[0059] Comparative Example 1 This comparative example is used to illustrate the negative electrode sheet, negative electrode sheet preparation method and battery disclosed in this invention, including most of the operations in Example 1, with the following differences: The raw materials for the outer barrier layer and the raw materials for the in-situ passivation inner layer were mixed with 80 parts of the second solvent (anhydrous ethanol) at a mass ratio of 3:1. After stirring and dissolving, 40 parts of modified silicon-carbon material were added. The mixture was stirred and reacted at 60°C for 4 hours in a nitrogen atmosphere, centrifuged, and vacuum dried at 80°C for 3 hours to form a composite coating layer on the surface of the core, thus obtaining a silicon-carbon composite material. That is, the silicon-carbon material in the silicon-carbon material has not undergone the first modifier modification treatment.

[0060] Comparative Example 2 This comparative example is used to illustrate the negative electrode sheet, negative electrode sheet preparation method and battery disclosed in this invention, including most of the operations in Example 1, with the following differences: Preparation of negative electrode sheet 50 parts of silicon-carbon material were placed in the first solvent and dispersed. After dispersion, 1 part of the first modifier was added. After reaction at high temperature, the mixture was dried to obtain the modified silicon-carbon material. Among them, the particle size of nano-silicon in silicon-carbon material is 100nm, and the mass ratio of nano-silicon to porous carbon material is 1:3; Mix (3 parts) of the raw material for the outer barrier layer with 80 parts of the second solvent (anhydrous ethanol), stir and dissolve, then add (40 parts) of the modified silicon-carbon material, stir and react at 60°C for 4 hours in a nitrogen atmosphere, centrifuge, and vacuum dry at 80°C for 3 hours to form a coating layer on the core surface, thus obtaining a silicon-carbon composite material. That is, there is no in-situ passivation inner layer in the silicon-carbon composite material.

[0061] Comparative Example 3 This comparative example is used to illustrate the negative electrode sheet, negative electrode sheet preparation method and battery disclosed in this invention, including most of the operations in Example 1, with the following differences: Preparation of negative electrode sheet 50 parts of silicon-carbon material were placed in the first solvent and dispersed. After dispersion, 1 part of the first modifier was added. After reaction at high temperature, the mixture was dried to obtain the modified silicon-carbon material. Among them, the particle size of nano-silicon in silicon-carbon material is 100nm, and the mass ratio of nano-silicon to porous carbon material is 1:3; Mix (1 part) of the raw material for the in-situ passivation inner layer with 80 parts of the second solvent (anhydrous ethanol), stir and dissolve, then add (40 parts) of the modified silicon-carbon material, stir and react at 60°C for 4 hours in a nitrogen atmosphere, centrifuge and separate, vacuum dry at 80°C for 3 hours to form a coating layer on the surface of the core, and obtain the silicon-carbon composite material. That is, there is no barrier outer layer in the silicon-carbon composite material.

[0062] Performance testing The following performance tests were performed on Examples 1-7 and Comparative Examples 1-3 prepared above: Gas production detection method: Check the airtightness of the sealed reaction device and the drainage and gas collection device to ensure there are no leaks; Weigh 50g of silicon carbide material and place it in a reaction flask. Add 500ml of deionized water and quickly seal the device. Stir the reaction at room temperature and normal pressure until no more gas is produced, and record the change in the volume of water in the gas collection device. The volume change value is the gas production rate. The average value of three parallel tests is used to calculate the gas production rate per unit mass of silicon-carbon.

[0063] Cyclic life test In a constant temperature chamber at (25±2)℃, the lithium-ion battery was charged to 4.3V at a constant current and constant voltage of 0.2C, then charged to 0.05C at a constant voltage. After resting for 5 minutes, it was discharged to 3.0V at 0.2C. The capacity obtained in this step was taken as the initial capacity. Cyclic tests were performed using 1C charge / 1C discharge. The number of cycles when the cycle capacity retention reached 70% was recorded as the cycle life.

[0064] The test results are entered into Table 2.

[0065] Table 2 As can be seen from the test results in Table 2, the test performance of Examples 1-7 is significantly better than that of Comparative Examples 1-3; specifically, the gas production of Examples 1-7 is only 0.1-0.6 ml / g, which is at an extremely low level, while the gas production of Comparative Examples 1-3 is as high as 5-10 ml / g. In the battery cycle life test, the battery cycle life of Examples 1 to 7 can reach 890-1000 cycles, while that of Comparative Examples 1 to 3 is only 300-310 cycles. The comparison shows that Examples 1-7 are better than Comparative Examples 1-3 in terms of eliminating hydrolysis gas production and battery cycle performance.

[0066] Furthermore, in Example 3, the mass ratio of the outer barrier material to the in-situ passivation inner material was 5:1, and its tested gas production was the lowest (0.1 ml / g), but its cycle life was as high as 1000 cycles. In Example 2, the mass ratio of the outer barrier material to the in-situ passivation inner material was 2:1, the gas production was 0.6 ml / g, and the cycle life was 895 cycles. Through Examples 2 and 3, it is shown that appropriately increasing the proportion of the outer barrier layer within the scope of this application can significantly enhance the physical barrier effect and prevent moisture from penetrating into the core.

[0067] The in-situ passivation inner layer thickness of Example 4 was 15 nm, the gas production rate was 0.2 ml / g, and the cycle life was 950 cycles. The inner layer thickness of Example 5 was 8 nm, the gas production rate was 0.5 ml / g, and the cycle life was 890 cycles. The results of Examples 4 and 5 show that thickening the in-situ passivation inner layer can enhance the active site blocking effect, reduce the gas production rate, and extend the cycle life.

[0068] Examples 6 and 7 used 3-aminophenylboronic acid as the inner layer raw material, with a gas production of 0.3 ml / g and a cycle life of 920 cycles, which is close to the performance of Example 1 (4-aminomethylphenylboronic acid salt), indicating that both organoboron compounds can achieve good passivation effects.

[0069] Compared to the embodiments of this application, Comparative Example 3 has no barrier outer layer, only retains the in-situ passivated inner layer, lacks a physical barrier, and moisture can easily penetrate the inner layer to contact the silicon-carbon core. The gas production is as high as 10 ml / g, and the cycle life is only 300 times, which is the worst performance. This further highlights the key role of the barrier outer layer in blocking moisture penetration. Comparative Example 2 had no in-situ passivated inner layer, only the barrier outer layer was retained, which could not block the active sites on the silicon-carbon surface. The gas production was 6 ml / g and the cycle life was 310 cycles, indicating that the in-situ passivated inner layer is the core structure for inhibiting gas production. The silicon-carbon material in Comparative Example 1 was not modified with an aminosilane coupling agent. Although it had a double-layer coating structure, it lacked a coating layer, resulting in a weak bond between the double-layer coating structure and the core. The gas production was 5 ml / g, and the cycle life was 310 cycles.

[0070] Comparing the test results of the above embodiments and comparative examples, it can be seen that the silicon-carbon composite material provided by the present invention has an in-situ passivation inner layer that reacts in-situ with the active sites on the surface of the modified silicon-carbon material to form a dense passivation layer with high ion conductivity. This blocks the active sites on the surface of silicon particles that are prone to react with water, inhibiting gas production. The outer layer forms a physical barrier, further blocking the contact path between water and the silicon-carbon core, effectively preventing water from penetrating into the core. The outer layer and the in-situ passivation inner layer work together to eliminate hydrolysis gas production reaction and block external water penetration, thereby suppressing gas production in the silicon-carbon anode material and optimizing and improving the electrochemical performance of the battery.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, It includes a core and a shell, the shell covering the core, the core comprising a modified silicon-carbon material, the shell comprising a composite coating layer comprising a barrier outer layer and an in-situ passivation inner layer, the in-situ passivation inner layer covering the surface of the core, and the barrier outer layer covering the surface of the in-situ passivation inner layer.

2. The silicon-carbon composite material according to claim 1, characterized in that, The outer barrier layer is made of a modified polyethylene oxide-polysiloxane block copolymer, and the inner passivation layer is made of an amino-containing organoboron compound. The mass ratio of the raw material of the outer barrier layer to the raw material of the inner passivation layer in the composite coating layer is (2~5):

1.

3. The silicon-carbon composite material according to claim 2, characterized in that, The molecular weight of the modified polyethylene oxide-polysiloxane block copolymer is 5000~20000; In the modified polyethylene oxide-polysiloxane block copolymer, the percentage of the polysiloxane block is 30-50%.

4. The silicon-carbon composite material according to claim 2, characterized in that, The amino-containing organoboron compounds include one or more of 4-aminomethylphenylboronic acid salt and 3-aminophenylboronic acid.

5. The silicon-carbon composite material according to claim 1, characterized in that, The modified silicon-carbon material is a silicon-carbon material modified by the first modifier; The silicon-carbon material includes porous carbon material and nano-silicon located in the pores of the porous carbon material. The nano-silicon has a particle size of 50~200nm, and the mass ratio of nano-silicon to porous carbon material in the silicon-carbon material is 1:(3~5).

6. The silicon-carbon composite material according to claim 5, characterized in that, The first modified material includes an aminosilane coupling agent, wherein the aminosilane coupling agent includes one or more of KH560 and KH792.

7. The silicon-carbon composite material according to claim 1, characterized in that, The thickness of the composite coating layer is 20~50nm, the thickness of the outer barrier layer is 15~35nm, and the thickness of the in-situ passivation inner layer is 5~15nm.

8. A negative electrode sheet, characterized in that, It includes a current collector and a negative electrode material layer, wherein the negative electrode material layer includes a silicon-carbon composite material as described in any one of claims 1 to 7.

9. The negative electrode sheet according to claim 8, characterized in that, The negative electrode material layer also includes an additive, which includes a compound of fluoroalkyl polyether phosphate and a second modifier, wherein the mass ratio of the fluoroalkyl polyether phosphate to the second modifier is 1:(1~3). The second modified product includes an aminosilane coupling agent.

10. The method for preparing the negative electrode sheet according to claim 8, characterized in that, Includes the following operations: Silicon-carbon material is placed in a first solvent and dispersed. After dispersion, a first modifier is added. After reaction at high temperature, the mixture is dried to obtain modified silicon-carbon material. The raw materials for the outer barrier layer and the raw materials for the in-situ passivation inner layer are mixed with a second solvent, dissolved, and then modified silicon-carbon material is added. Under a protective atmosphere, the mixture is treated at high temperature, and after the reaction, it is dried to form a composite coating layer on the surface of the core, thus obtaining a silicon-carbon composite material. The third solvent and dispersant were mixed and then added to the silicon-carbon composite material to obtain a pre-dispersion. Additives are added to the pre-dispersion liquid, then binder and conductive agent are added, and after mixing, a negative electrode slurry is obtained. The negative electrode slurry is coated onto the current collector, and after drying, a negative electrode sheet is obtained.

11. The method for preparing the negative electrode sheet according to claim 10, characterized in that, The negative electrode slurry comprises the following components by mass: 40-60 parts of silicon-carbon material, 3-10 parts of raw material for the outer barrier layer, 0.5-3.5 parts of raw material for the in-situ passivation inner layer, 0.5-3 parts of additives, 3-8 parts of binder, 1-5 parts of dispersant, 2-6 parts of conductive agent, and 20-40 parts of third solvent.

12. The method for preparing the negative electrode sheet according to claim 10, characterized in that, Both the first solvent and the second solvent are organic solvents, the organic solvent is anhydrous ethanol, and the third solvent is deionized water.

13. The method for preparing the negative electrode sheet according to claim 10, characterized in that, In the preparation of modified silicon-carbon materials, the high temperature is 60~80℃ and the reaction time is 2~4h; In the high-temperature reaction operation for preparing silicon-carbon composite materials, the high temperature is 50~70℃ and the reaction time is 3~6h.

14. A battery, characterized in that, The negative electrode sheet includes the negative electrode sheet according to any one of claims 8 to 9, or the negative electrode sheet prepared by the method according to any one of claims 10 to 13.

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