Silicon-based negative electrode material, preparation method thereof and electrochemical device

Abstract

The application provides a silicon-based negative electrode material, a preparation method thereof and an electrochemical device. The silicon-based negative electrode material comprises a silicon-based base material and an SEI film coated on the surface of the silicon-based base material, and the SEI film comprises an allyl polymer material, the repeating unit in the allyl polymer material comprises a main chain and a side chain, the main chain and the side chain are connected through an ester group, and the side chain comprises a sugar ring structure. The silicon-based negative electrode material provided by the application is coated and modified by using the allyl polymer material with a special group structure as the SEI film on the silicon-based base material, the volume expansion of the silicon-based material in the charging and discharging process is relieved, the interface stability and interface bonding force of the SEI film and the silicon-based base material are improved, and the lithium ion transmission efficiency is improved, so that the electrochemical performance of the lithium ion battery is improved.

Description

Technical Field

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

[0002] With the increasing demand for high-energy-density lithium-ion batteries from electric vehicles, large-scale energy storage systems, and portable electronic devices, the development of next-generation high-capacity anode materials has become crucial for industrial development. Silicon (Si) is considered one of the most promising next-generation anode materials due to its extremely high theoretical specific capacity (approximately 4200 mAh / g, far exceeding the 372 mAh / g of traditional graphite), suitable lithium intercalation potential, and abundant reserves.

[0003] However, silicon-based materials still face several severe fundamental challenges in their path to large-scale commercial application, significantly limiting their electrochemical performance and cycle life. First, silicon materials undergo enormous volume changes (>300%) during charge and discharge, leading to structural mechanical failure. Second, the instability of the solid electrolyte interphase (SEI) film and weak interfacial forces result in continuous degradation of cycle performance. Third, the sluggish lithium-ion transport kinetics lead to poor fast-charging and rate performance.

[0004] Therefore, how to solve the above problems is an urgent issue that needs to be explored. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a silicon-based anode material, its preparation method, and an electrochemical device. The silicon-based anode material provided by the present invention uses an allyl polymer material with a special functional group structure as an SEI film to coat and modify the silicon-based substrate material. This alleviates the volume expansion of the silicon-based material during charging and discharging, improves the interfacial stability and interfacial adhesion between the SEI film and the silicon-based substrate material, and enhances lithium-ion transport efficiency, thereby improving the electrochemical performance of the lithium-ion battery.

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

[0007] In a first aspect, the present invention provides a silicon-based anode material, the silicon-based anode material comprising a silicon-based substrate material and an SEI film coated on the surface of the silicon-based substrate material, the SEI film comprising an allyl polymer material, wherein the repeating unit in the allyl polymer material comprises a main chain and a side chain, the main chain and the side chain being connected by an ester group, and the side chain comprising a sugar ring structure.

[0008] Preferably, the sugar ring structure includes a glucose ring structure, wherein the glucose ring structure includes 3 to 4 hydroxyl groups.

[0009] Preferably, the glucose ring structure includes a D-glucose ring structure.

[0010] Preferably, the monomer of the allyl polymer material includes allyl D-glucuronide.

[0011] Preferably, the number-average molecular weight of the allyl polymer material is 6 × 10⁻⁶. 5 g / mol ~ 8 × 10 6 g / mol.

[0012] Preferably, the silicon-based matrix material includes a fumed silicon-carbon material, which comprises a porous hard carbon substrate and silicon material located in the pores of the porous hard carbon substrate.

[0013] Preferably, the porous hard carbon substrate has a pore structure comprising micropores and mesopores.

[0014] Preferably, the pore size of the micropores is 0.8 nm to 1.5 nm, and the pore size of the mesopores is 5 nm to 20 nm.

[0015] Preferably, the pore volume of the micropores accounts for 20% to 40% of the total pore volume of the porous hard carbon substrate.

[0016] Preferably, the pore volume of the mesopores accounts for 60% to 80% of the total pore volume of the porous hard carbon substrate.

[0017] Preferably, the median particle size D of the fumed silicon-carbon material is... V50 The size ranges from 3μm to 9μm.

[0018] Preferably, the specific surface area of ​​the fumed silicon-carbon material is 1 m². 2 / g~7m 2 / g.

[0019] Preferably, the mass ratio of porous hard carbon substrate to silicon material in the fumed silicon-carbon material is 1:(0.4~1.2).

[0020] Preferably, the grain size of the silicon material is 0.5 nm to 2 nm.

[0021] Preferably, the mass of the SEI film is 2% to 5% of the mass of the silicon-based substrate material.

[0022] Preferably, the thickness of the SEI film is 35nm~150nm.

[0023] In a second aspect, the present invention provides a method for preparing a silicon-based anode material as described in the first aspect, the method comprising the following steps:

[0024] A mixture of allyl polymer material and silicon matrix material is coated to obtain the silicon-based anode material.

[0025] The repeating unit in the allyl polymer material includes a main chain and a side chain, which are connected by ester groups, and the side chain includes a sugar ring structure.

[0026] Preferably, the preparation method of the allyl polymer material includes:

[0027] The monomer, initiator and first solvent are mixed and polymerized. The solution after polymerization is precipitated to obtain the allyl polymer material.

[0028] Preferably, the amount of the initiator added is 0.2% to 0.9% of the mass of the monomer.

[0029] Preferably, the concentration of the monomer in the first solvent is 0.3 mol / L to 1.5 mol / L.

[0030] Preferably, the polymerization reaction temperature is 60℃~95℃, and the polymerization reaction time is 4h~10h.

[0031] Preferably, the precipitation treatment includes adding a precipitating agent to the solution after the polymerization reaction to induce precipitation.

[0032] Preferably, the precipitation time is 2h to 4h.

[0033] Preferably, after the precipitation reaction, the product is washed and dried in sequence.

[0034] Preferably, the method for mixing the allyl polymer material and the silicon-based matrix material includes liquid-phase mixing, which includes: preparing an allyl polymer material solution and then adding the silicon-based matrix material for mixing.

[0035] Preferably, the mass fraction of the allyl polymer material solution is 5% to 30%.

[0036] Preferably, the coating treatment method includes a stirring treatment, wherein the stirring treatment temperature is 30℃~100℃ and the stirring treatment time is 5h~10h.

[0037] Preferably, after the coating treatment, a spray drying process is performed.

[0038] Thirdly, the present invention also provides an electrochemical device, the electrochemical device comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode active layer located on at least one side surface of the negative current collector, the negative electrode active layer comprising a silicon-based negative electrode material as described in the first aspect or a silicon-based negative electrode material prepared by the preparation method described in the second aspect.

[0039] Preferably, the electrochemical device further includes a positive electrode, a separator, and an electrolyte.

[0040] Preferably, the electrolyte comprises an organic solvent and a basic lithium salt, and the electrolyte further comprises lithium salt additives and solvent additives.

[0041] Preferably, the lithium salt additive includes LiFSI and / or LiBOB.

[0042] Preferably, the amount of LiFSI added is 2% to 4% based on the total mass of the organic solvent and the basic lithium salt as 100%.

[0043] Preferably, the amount of LiBOB added is 0.2% to 0.5% based on the total mass of the organic solvent and the basic lithium salt as 100%.

[0044] Preferably, the solvent additive comprises tris(4-nitrophenyl) phosphate, and the amount of tris(4-nitrophenyl) phosphate added is 0.5% to 1.5% based on the total mass of the organic solvent and the base lithium salt as 100%.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The SEI film provided by this invention, which involves coating an allyl polymer material onto a silicon-based substrate, achieves a comprehensive improvement in the performance of the silicon-based anode by leveraging the unique functional group structure and synergistic effects of the polymer. Specific advantages include: the hydroxyl groups in the sugar rings can form a dense hydrogen bond network with the silicon substrate surface, significantly improving the interfacial forces between the SEI film and the silicon substrate, enhancing interfacial stability, and preventing coating delamination. Simultaneously, the sugar ring structure also imparts higher chemical stability to the polymer material, further enhancing the durability of the SEI film; the sugar ring structural groups and ester matrix in the allyl polymer material exhibit good affinity and... The solvation regulation capability can reduce the desolvation energy barrier of lithium ions at the interface and provide a low-resistance polar path for their transport in the SEI film. It can stably bind with lithium ions to form a stable interface binding layer, while reducing lithium ion migration resistance, improving lithium ion transport efficiency, and optimizing fast charging performance. The SEI film formed by the allyl polymer material as a flexible gel layer also has excellent elastic deformation capability, which can adapt to the volume change of the silicon-based matrix material, buffer the stress caused by volume expansion, effectively suppress the breakage of silicon material in the silicon-based group material, and maintain the integrity of the negative electrode structure. Thus, it improves the battery's first efficiency, cycle and rate performance. Detailed Implementation

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

[0048] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0049] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0050] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0051] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0052] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0053] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0054] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0055] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0056] In this invention, "optional" means that something is optional, that is, it refers to either "with" or "without". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0057] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0058] In one embodiment, a first aspect of the present invention provides a silicon-based anode material, the silicon-based anode material comprising a silicon-based substrate material and an SEI film coated on the surface of the silicon-based substrate material, the SEI film comprising an allyl polymer material, wherein the repeating unit in the allyl polymer material comprises a main chain and a side chain, the main chain and the side chain being connected by an ester group, and the side chain comprising a sugar ring structure.

[0059] The SEI film provided by this invention, which involves coating an allyl polymer material onto a silicon-based substrate, achieves a comprehensive improvement in the performance of the silicon-based anode by leveraging the unique functional group structure and synergistic effects of the polymer. Specific advantages include: the hydroxyl groups in the sugar rings can form a dense hydrogen bond network with the silicon substrate surface, significantly improving the interfacial forces between the SEI film and the silicon substrate, enhancing interfacial stability, and preventing coating delamination. Simultaneously, the sugar ring structure also imparts higher chemical stability to the polymer material, further enhancing the durability of the SEI film; the sugar ring structural groups and ester matrix in the allyl polymer material exhibit good affinity and... The solvation regulation capability can reduce the desolvation energy barrier of lithium ions at the interface and provide a low-resistance polar path for their transport in the SEI film. It can stably bind with lithium ions to form a stable interface binding layer, while reducing lithium ion migration resistance, improving lithium ion transport efficiency, and optimizing fast charging performance. The SEI film formed by the allyl polymer material as a flexible gel layer also has excellent elastic deformation capability, which can adapt to the volume change of the silicon-based matrix material, buffer the stress caused by volume expansion, effectively suppress the breakage of silicon material in the silicon-based group material, and maintain the integrity of the negative electrode structure. Thus, it improves the battery's first efficiency, cycle and rate performance.

[0060] In some embodiments, the sugar ring structure includes a glucose ring structure comprising 3 to 4 hydroxyl groups, for example, 3 or 4.

[0061] This invention uses a glucose ring structure and controls it to contain 3 to 4 hydroxyl groups, which can form a denser hydrogen bond network with the silicon-based matrix material, enhance interfacial bonding, reduce SEI film shedding, and improve cycle stability.

[0062] In some embodiments, the glucose ring structure includes a D-glucose ring structure.

[0063] In some embodiments, the monomers of the allyl polymer material include allyl D-glucuronide.

[0064] In some embodiments, the structural formula selected in this invention is as follows: Using allyl D-glucuronide as a monomer material ensures that the number of hydroxyl and carbonyl groups in each repeating unit of the polymer material is appropriate, which can better form a hydrogen bond network with silicon-based anode materials, enhance interfacial bonding, and also better improve the lithium-ion transport efficiency.

[0065] In some embodiments, the number-average molecular weight of the allyl polymer material is 6 × 10⁻⁶. 5 g / mol ~ 8 × 10 6 g / mol, for example 6 × 10 5 g / mol, 7×10 5 g / mol, 8×10 5 g / mol, 9×10 5 g / mol, 1×10 6 g / mol, 2×10 5 g / mol, 3×10 6 g / mol, 4×10 6 g / mol, 5×10 6 g / mol, 6×10 6 g / mol, 7×10 6 g / mol, 8×10 6 g / mol, etc.

[0066] This invention selects a number-average molecular weight of 6×10⁻⁶. 5 ~8×10 6 Allyl polymer materials can yield polymer chains with higher flexibility and elasticity, which can further alleviate the problem of charge-discharge volume expansion of silicon-based matrix materials.

[0067] In some embodiments, the silicon-based matrix material includes a fumed silicon-carbon material, which comprises a porous hard carbon substrate and silicon material located in the pores of the porous hard carbon substrate.

[0068] In this invention, fumed silicon-carbon material generally refers to silicon-carbon composite material prepared by chemical vapor deposition (CVD); and this invention does not limit the specific source of fumed silicon-carbon material, which can be purchased directly according to needs or prepared by oneself. Without violating the overall inventive concept of this invention, any conventional preparation method known within a reasonable scope is applicable to this invention.

[0069] This invention selects fumed silicon-carbon materials, especially hard carbon-based fumed silicon-carbon materials, as the silicon-based matrix material. The porous hard carbon substrate acts as a first-level buffer against the volume expansion of the silicon material and also has excellent conductivity. Furthermore, it provides a large number of uniform anchoring points for the formation of a high-strength hydrogen bond network and covalent bonding, thereby improving the interfacial bonding effect with allyl polymer materials and reducing side reactions caused by surface defects.

[0070] In some embodiments, the pore structure of the porous hard carbon substrate includes micropores and mesopores.

[0071] In this invention, a porous hard carbon substrate with a multi-level pore structure is selected. On the one hand, this ensures the mechanical strength of the substrate and avoids structural collapse. On the other hand, it is more conducive to the recombination of silicon materials in the pores and improves the effect of buffering the volume expansion of silicon materials.

[0072] In some embodiments, the pore size of the micropore is 0.8nm to 1.5nm, such as 0.8nm, 0.9nm, 1nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm or 1.5nm.

[0073] This invention uses a microporous structure with a pore size of 0.8nm to 1.5nm, which not only ensures that there is enough pore structure to accommodate silicon material, but also improves the mechanical structure of the pore structure and the porous hard carbon substrate.

[0074] In some embodiments, the pore size of the mesopore is 5nm to 20nm, such as 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm or 20nm.

[0075] This invention uses a mesoporous structure with a pore size of 5nm to 20nm, which provides sufficient space for the recombination of silicon materials in the porous structure and for buffering after expansion. This avoids the silicon materials from squeezing the pore walls after expansion, which would cause the hard carbon skeleton to break. In addition, it can also better improve the density of the porous hard carbon substrate and avoid the loss of energy density.

[0076] In some embodiments, the pore volume of the micropores accounts for 20% to 40% of the total pore volume of the porous hard carbon substrate, for example, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, or 40%.

[0077] In some embodiments, the pore volume of the mesopores accounts for 60% to 80% of the total pore volume of the porous hard carbon substrate's pore structure, for example, 60%, 63%, 65%, 68%, 70%, 73%, 75%, 78%, or 80%.

[0078] In some embodiments, the median particle size D of the fumed silicon-carbon material V50 The value ranges from 3μm to 9μm, for example, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, or 9μm.

[0079] In an embodiment of the present invention, the median particle size D of the fumed silicon-carbon material is controlled. V50 With a thickness of 3μm to 9μm, it better improves lithium-ion transport performance and also enhances the homogenization stability of the corresponding anode material during the anode sheet preparation process.

[0080] Preferably, the specific surface area of ​​the fumed silicon-carbon material is 1 m². 2 / g~7m 2 / g, for example, 1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g, 5.5m 2 / g、6m 2 / g, 6.5m 2 / g or 7m 2 / g etc.

[0081] In some embodiments, the mass ratio of porous hard carbon substrate to silicon material in the fumed silicon-carbon material is 1:(0.4~1.2), for example 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1 or 1:1.2, etc.

[0082] It is understandable that the silicon content in the fumed silicon-carbon material is closely related to the final performance. Further limiting the mass ratio of porous hard carbon substrate to silicon material in the fumed silicon-carbon material to 1:(0.4~1.2) ensures that the specific capacity, first efficiency and cycle performance are taken into account, and achieves the simultaneous improvement of multiple performances.

[0083] In some embodiments, the grain size of the silicon material is 0.5nm to 2nm, such as 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.5nm, 1.6nm, 1.7nm, 1.8nm, 1.9nm, or 2nm.

[0084] In some embodiments, the mass of the SEI film is 2% to 5% of the mass of the silicon-based substrate material, such as 2%, 2.3%, 2.5%, 2.8%, 3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, or 5%.

[0085] In some embodiments, the thickness of the SEI film is 35nm to 150nm, such as 35nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm or 150nm.

[0086] In the embodiments of the present invention, the mass of the SEI film is controlled to be 2% to 5% of the mass of the silicon substrate material and / or the thickness of the SEI film is 35nm to 150nm. This further improves the continuity, uniformity and density of the SEI film coating the silicon substrate material, better alleviates the volume expansion of the silicon substrate material, and ensures the effective performance of energy density and lithium-ion transport efficiency.

[0087] It is understood that, in the embodiments of the present invention, the test methods for the relevant parameter characteristics of the fumed silicon-carbon material are all conventional test methods, wherein the pore size, pore volume, and specific surface area can be determined by gas adsorption method. V50 The grain size of the corresponding silicon material was determined using a laser particle size analyzer via laser diffraction.

[0088] In one embodiment, a second aspect of the present invention provides a method for preparing a silicon-based anode material as described in the first aspect, the method comprising the following steps:

[0089] A mixture of allyl polymer material and silicon matrix material is coated to obtain the silicon-based anode material.

[0090] The repeating unit in the allyl polymer material includes a main chain and a side chain, which are connected by ester groups, and the side chain includes a sugar ring structure.

[0091] The preparation method provided by this invention yields silicon-based anode materials with excellent structural stability through a simple coating process.

[0092] In some embodiments, the preparation method of the allyl polymer material includes:

[0093] The monomer, initiator and first solvent are mixed and polymerized. The solution after polymerization is precipitated to obtain the allyl polymer material.

[0094] In some embodiments, the amount of the initiator added is 0.2% to 0.9% of the mass of the monomer, for example, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%.

[0095] In some embodiments, the concentration of the monomer in the first solvent is 0.3 mol / L to 1.5 mol / L, for example, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, or 1.5 mol / L.

[0096] In some embodiments, the polymerization reaction temperature is 60°C to 95°C, for example, 60°C, 70°C, 80°C, 90°C or 95°C, and the polymerization reaction time is 4h to 10h, for example, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0097] In some embodiments, the precipitation treatment includes adding a precipitating agent to the solution after the polymerization reaction to induce precipitation.

[0098] In some embodiments, the precipitating agent includes, but is not limited to, any one or a combination of at least two of propanol, isopropanol, or acetone.

[0099] In some embodiments, the precipitation time is 2h to 4h, for example 2h, 3h or 4h.

[0100] In some embodiments, after the precipitation reaction, the product is washed and dried sequentially.

[0101] It is understood that the monomer material in this invention yields the desired allyl polymer material through a direct free radical polymerization of carbon-carbon double chains, and the corresponding reaction can be directly and unambiguously derived. This invention obtains an allyl polymer material with the target number-average molecular weight by controlling the corresponding polymerization and precipitation conditions. In addition, the types of substances of the first solvent and initiator in this invention are conventional technical solutions, which can achieve the purpose of polymerization. For example, the first solvent includes, but is not limited to, at least one of benzene, toluene, N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF), and the initiator includes, but is not limited to, any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile or benzoyl peroxide (BPO).

[0102] In some embodiments, the method for mixing the allyl polymer material and the silicon-based matrix material includes liquid-phase mixing, which includes: preparing an allyl polymer material solution and then adding the silicon-based matrix material for mixing.

[0103] Furthermore, the second solvent in the allyl polymer material includes, but is not limited to, at least one of benzene, toluene, N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF).

[0104] In some embodiments, the number-average molecular weight of the allyl polymer material is 6 × 10⁻⁶. 5 g / mol ~ 8 × 10 6 g / mol, for example 6 × 10 5 g / mol, 7×10 5 g / mol, 8×10 5 g / mol, 9×10 5 g / mol, 1×10 6 g / mol, 2×10 5 g / mol, 3×10 6 g / mol, 4×10 6 g / mol, 5×10 6 g / mol, 6×10 6 g / mol, 7×10 6 g / mol, 8×10 6 g / mol, etc.

[0105] In the preparation stage, this invention adjusts the number-average molecular weight of the allyl polymer material to 6 × 10⁻⁶. 5 g / mol ~ 8 × 10 6 The g / mol ratio improves the coating effect and ensures that the corresponding allyl polymer material solution has a suitable viscosity, thus better improving the coating uniformity.

[0106] In some embodiments, the mass fraction of the allyl polymer material solution is 5% to 30%, for example, 5%, 10%, 15%, 20%, 25%, or 30%.

[0107] In some embodiments, the coating treatment method includes a stirring process, more specifically:

[0108] The temperature of the stirring treatment is 30℃~100℃, for example, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃, etc., and the stirring treatment time is 5h~10h, for example, 5h, 6h, 7h, 8h, 9h or 10h, etc.

[0109] In some embodiments, the coating process is followed by spray drying.

[0110] In the embodiments of the present invention, the coating treatment, especially the liquid phase mixing and stirring coating treatment, is followed by spray drying, which is more conducive to improving the coating uniformity of allyl polymer materials, obtaining a continuous and dense SEI film coating layer, and can also quickly remove solvent, avoiding structural damage caused by long-term drying.

[0111] It is understood that the purpose of spray drying in this invention is to remove the solvent (i.e., the second solvent) during the coating process. No further limitations are made on the specific preparation details of spray drying. Within a reasonable range, it is guaranteed that the solvent can be removed without causing particle breakage. This invention applies to all such cases.

[0112] Example, but not limitation, of the preparation details of spray drying, including:

[0113] The inlet temperature of the spray dryer can be 100℃~220℃, such as 100℃, 130℃, 150℃, 180℃, 190℃, 200℃, 210℃ or 220℃, etc., and the outlet temperature of the spray dryer can be 60℃~120℃, such as 60℃, 70℃, 80℃, 90℃, 100℃, 110℃ or 120℃, etc.

[0114] In one embodiment, particularly in an application embodiment, the third aspect of the present invention also provides an electrochemical device, the electrochemical device comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode active layer located on at least one side surface of the negative current collector, the negative electrode active layer comprising a silicon-based negative electrode material as described in the first aspect or a silicon-based negative electrode material prepared by the preparation method described in the second aspect.

[0115] In the electrochemical device of the present invention, especially in the lithium-ion-based electrochemical device, the silicon-based negative electrode material provided by the present invention is used as the active material at the negative electrode in the corresponding negative electrode sheet, thereby improving the first-efficiency, cycle and rate performance of the corresponding electrochemical device.

[0116] In some embodiments, the electrochemical device further includes a positive electrode, a diaphragm, and an electrolyte.

[0117] This invention does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this invention. In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer is disposed on one or both surfaces of the positive current collector. The aforementioned "surface" can be a portion of the surface of the positive current collector or the entire surface of the positive current collector. This invention does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this invention. For example, the positive current collector can contain aluminum foil or aluminum alloy foil, etc. The positive active material layer of this invention contains a positive active material. This invention does not impose any particular limitation on the type of positive active material, as long as it achieves the purpose of this invention. For example, the positive active material can contain at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate, etc. In this invention, the positive active material can also contain non-metallic elements, which can include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. These elements can further improve the stability of the positive active material. In this invention, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the objective of this invention can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm. The thickness of the single-layer positive electrode active material layer is 30 μm to 120 μm. Optionally, the positive electrode active material layer may further include at least one of a conductive agent or a binder. This invention does not particularly limit the types of conductive agents and binders in the positive electrode active material layer, as long as the objective of this invention can be achieved. This invention does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer; those skilled in the art can choose according to actual needs, as long as the objective of this invention can be achieved.

[0118] The separator of this invention is disposed between the positive electrode and the negative electrode to separate them. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this invention. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The separator type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane. This invention does not impose any particular limitation on the thickness of the separator, as long as it achieves the purpose of this invention.

[0119] In some embodiments, the electrolyte comprises an organic solvent and a base lithium salt, and the electrolyte further comprises lithium salt additives and solvent additives.

[0120] In some embodiments, the lithium salt additive includes LiFSI and / or LiBOB.

[0121] In some embodiments, the LiFSI in the electrolyte accounts for 2% to 4% of the total mass of the organic solvent and the base lithium salt, for example, 2%, 2.5%, 3%, 3.5% or 4%.

[0122] In some embodiments, the LiBOB in the electrolyte is 0.2% to 0.5% by mass, for example, 0.2%, 0.3%, 0.4% or 0.5%, based on the total mass of the organic solvent and the base lithium salt as 100%.

[0123] In some embodiments, the solvent additive includes tris(4-nitrophenyl) phosphate, and the tris(4-nitrophenyl) phosphate accounts for 0.5% to 1.5% of the total mass of the organic solvent and the base lithium salt in the electrolyte, for example, 0.5%, 0.8%, 1%, 1.3% or 1.5%.

[0124] In the electrolyte of this invention, in addition to the basic electrolyte (i.e., a combined electrolyte system of organic solvent and basic lithium salt), additional additives can be added, such as lithium salt additives of LiFSI and / or LiBOB. The allyl polymer material in the corresponding silicon-based anode material can also synergistically cooperate with the lithium salt therein to promote the dissociation of lithium salt and improve the ionic conductivity of the electrolyte. Furthermore, the addition of solvent additives such as tris(4-nitrophenyl)phosphate can spontaneously form a new dense SEI film on the basis of the original SEI film, further improving the cycle stability.

[0125] The basic electrolytes mentioned are all conventional technical selections. Those skilled in the art can choose appropriate non-aqueous solvents and lithium salts according to actual needs.

[0126] For example, but not limitingly, the lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, or lithium difluoroborate. This invention does not limit the content of the lithium salt in the electrolyte, as long as the purpose of this invention is achieved. This invention does not particularly limit the use of non-aqueous solvents, as long as the purpose of this invention is achieved. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, or vinylethylene carbonate. Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0127] In some embodiments, the negative electrode active layer further includes a conductive agent and a binder.

[0128] Furthermore, whether it is the conductive agent and binder of the positive electrode or the conductive agent and binder of the negative electrode, the conductive agent includes, but is not limited to, conductive carbon black and carbon nanotubes; the binder includes at least one of polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, nitrile rubber, styrene-ethylene-butene-styrene copolymer, styrene-butadiene-styrene copolymer, lithium polyacrylate, sodium polyacrylate, sodium alginate or lithium alginate; the conductive agent includes at least one of acetylene black, Ketjen black, Super-P, carbon nanotubes, carbon fibers or graphene.

[0129] In some embodiments, the electrochemical device is a lithium-ion battery, which, in addition to the aforementioned positive electrode, separator, electrolyte, and negative electrode, also includes a housing. The housing houses the positive electrode, negative electrode, separator, electrolyte, and other components known in batteries, and this invention does not limit the scope of these other components. This invention does not impose any particular limitation on the housing; it can be any housing known in the art, as long as it achieves the purpose of this invention.

[0130] The preparation process of the lithium-ion battery in this invention is well known to those skilled in the art. This invention is not particularly limited, but can include, but is not limited to, the following steps: stacking the separator, positive electrode, separator and negative electrode in sequence, and winding, folding or other operations as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it; and obtaining a battery through formation, degassing, shaping and other processes; or stacking the separator, positive electrode, separator and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it; and obtaining a lithium-ion battery through formation, degassing, shaping and other processes.

[0131] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0132] Example 1

[0133] This embodiment provides a silicon-based anode material. The silicon-based material includes a silicon-based matrix material and an SEI film coated on the surface of the silicon-based matrix material, i.e., a fumed silicon-carbon material. The SEI film is an allyl polymer material. The repeating unit in the allyl polymer material includes a main chain and a side chain. The main chain and the side chain are connected by ester groups. The monomer of the allyl polymer material is allyl D-glucuronide, which is a free radical polymer, and the side chain is a glucose ring.

[0134] The median particle size D of the fumed silicon carbide material V50 Its thickness is 5 μm, and its specific surface area is 4.5 m². 2 / g; The fumed silicon-carbon material comprises a porous hard carbon substrate and silicon material located in the pores of the porous hard carbon substrate. The porous hard carbon substrate has micropores (pore size of 0.8nm~1.2nm) and mesopores (5nm~10nm), and the pore volume of the micropores accounts for 30% of the total pore volume of the total pore structure, and the pore volume of the mesopores accounts for 70% of the total pore volume of the total pore structure. The mass ratio of the porous hard carbon substrate to the silicon material is 1:0.8, and the grain size of the silicon material is 0.5nm~1nm.

[0135] The number-average molecular weight of the allyl polymer material is 1×10⁻⁶. 6 g / mol.

[0136] The mass of the SEI film is 3.5% of the mass of the silicon substrate material, and the thickness of the SEI film is 95 nm.

[0137] The method for preparing the silicon-based anode material includes:

[0138] (a) Preparation of allyl polymer materials:

[0139] Allyl D-glucuronide (CAS No.: 188717-04-6) monomer and DMF were mixed to obtain a monomer solution with a concentration of 1 mol / L. Then, an initiator was added at a concentration of 0.5% of the monomer mass. The polymerization reaction was carried out at 80℃ for 6 hours to obtain a polymer solution. Isopropanol was added as a precipitant to the polymer solution to induce precipitation. The precipitation reaction was carried out for 4 hours. The polymer was washed three times with deionized water and dried to obtain a product with a number average molecular weight of 1 × 10⁻⁶. 6 g / mol of allyl polymer materials;

[0140] (b) Dissolve the allyl polymer material in toluene solvent to form an allyl polymer material solution with a mass fraction of 15%, then add fumed silicon carbon material, ensuring that the amount of allyl polymer material added is 3.5% of the mass of fumed silicon carbon material. After mixing, stir at 50°C for 8 hours, and spray dry the stirred solution with an inlet temperature of 180°C and an outlet temperature of 90°C to obtain the silicon-based anode material.

[0141] Example 2

[0142] This embodiment provides a silicon-based anode material. The silicon-based material includes a silicon-based matrix material and an SEI film coating the surface of the silicon-based matrix material, i.e., a fumed silicon-carbon material. The SEI film includes an allyl polymer material. The repeating unit in the allyl polymer material includes a main chain and a side chain. The main chain and the side chain are connected by ester groups. The monomer of the allyl polymer material is allyl D-glucuronide, which is a free radical polymer, and the side chain is a glucose ring.

[0143] The median particle size D of the fumed silicon carbide material V50 It has a thickness of 3μm and a specific surface area of ​​7m². 2 / g; The fumed silicon-carbon material comprises a porous hard carbon substrate and silicon material located in the pores of the porous hard carbon substrate. The porous hard carbon substrate has micropores (pore size of 1nm~1.5nm) and mesopores (10nm~20nm), and the pore volume of the micropores is 20% of the total pore volume of the total pore structure, and the pore volume of the mesopores is 80% of the total pore volume of the total pore structure. The mass ratio of the porous hard carbon substrate to the silicon material is 1:0.4, and the grain size of the silicon material is 1nm~2nm.

[0144] The allyl polymer material has a number-average molecular weight of 6 × 10⁻⁶. 5 g / mol.

[0145] The mass of the SEI film is 2% of the mass of the silicon substrate material, and the thickness of the SEI film is 35 nm.

[0146] The method for preparing the silicon-based anode material includes:

[0147] (a) Preparation of allyl polymer materials:

[0148] Allyl D-glucuronide monomer and DMF were mixed to obtain a monomer solution with a concentration of 0.3 mol / L. Then, an initiator was added at a concentration of 0.2% of the monomer mass. The polymerization reaction was carried out at 95°C for 4 hours to obtain a polymer solution. Isopropanol was added as a precipitant to the polymer solution to induce precipitation. The precipitation reaction was carried out for 2 hours. The polymer was washed four times with deionized water and dried to obtain a product with a number average molecular weight of 6 × 10⁻⁶. 5 g / mol of allyl polymer materials;

[0149] (b) Dissolve the allyl polymer material in toluene solvent to form an allyl polymer material solution with a mass fraction of 30%, then add fumed silicon carbon material, ensuring that the amount of allyl polymer material added is 2% of the mass of fumed silicon carbon material. After mixing, stir at 100°C for 5 hours, and spray dry the stirred solution with an inlet temperature of 200°C and an outlet temperature of 100°C to obtain the silicon-based anode material.

[0150] Example 3

[0151] This embodiment provides a silicon-based anode material. The silicon-based material includes a silicon-based matrix material and an SEI film coating the surface of the silicon-based matrix material, i.e., a fumed silicon-carbon material. The SEI film includes an allyl polymer material. The repeating unit in the allyl polymer material includes a main chain and a side chain. The main chain and the side chain are connected by ester groups. The monomer of the allyl polymer material is allyl D-glucuronide, which is a free radical polymer, and the side chain is a glucose ring.

[0152] The median particle size D of the fumed silicon carbide material V50 Its thickness is 9 μm, and its specific surface area is 1.5 m². 2 / g; The fumed silicon-carbon material comprises a porous hard carbon substrate and silicon material located in the pores of the porous hard carbon substrate. The porous hard carbon substrate has micropores (pore size of 1nm~1.3nm) and mesopores (8nm~12nm), and the pore volume of the micropores accounts for 40% of the total pore volume of the total pore structure, and the pore volume of the mesopores accounts for 60% of the total pore volume of the total pore structure. The mass ratio of the porous hard carbon substrate to the silicon material is 1:1.2, and the grain size of the silicon material is 0.8nm~1.3nm.

[0153] The allyl polymer material has a number-average molecular weight of 8 × 10⁻⁶. 6 g / mol.

[0154] The mass of the SEI film is 5% of the mass of the silicon substrate material, and the thickness of the SEI film is 150 nm.

[0155] The method for preparing the silicon-based anode material includes:

[0156] (a) Preparation of allyl polymer materials:

[0157] Allyl D-glucuronide monomer and DMF were mixed to obtain a monomer solution with a concentration of 1.5 mol / L. Then, an initiator was added at a concentration of 0.9% of the monomer mass. The polymerization reaction was carried out at 60 °C for 10 h to obtain a polymer solution. Isopropanol was added as a precipitant to the polymer solution to induce precipitation. The precipitation reaction was carried out for 3 h. The polymer was washed three times with deionized water and dried to obtain a product with a number average molecular weight of 8 × 10⁻⁶. 6 g / mol of allyl polymer materials;

[0158] (b) Dissolve the allyl polymer material in toluene solvent to form an allyl polymer material solution with a mass fraction of 5%, then add fumed silicon carbon material, ensuring that the amount of allyl polymer material added is 5% of the mass of fumed silicon carbon material. After mixing, stir at 30°C for 5 hours, and spray dry the stirred solution with an inlet temperature of 220°C and an outlet temperature of 80°C to obtain the silicon-based anode material.

[0159] Example 4

[0160] The difference between this embodiment and Embodiment 1 is that the silicon-based matrix material in this embodiment is pure nano-silicon material with a median particle size D. V50 It is 200nm.

[0161] All other conditions remain the same as in Example 1.

[0162] Example 5

[0163] The difference between this embodiment and Embodiment 1 is that the porous hard carbon substrate of the fumed silicon-carbon material in this embodiment contains only mesoporous structures.

[0164] All other conditions remain the same as in Example 1.

[0165] Example 6

[0166] The difference between this embodiment and Embodiment 1 is that the porous hard carbon substrate of the fumed silicon-carbon material in this embodiment contains only microporous structures.

[0167] All other conditions remain the same as in Example 1.

[0168] Example 7

[0169] The difference between this embodiment and Embodiment 1 is that the number-average molecular weight of the allyl polymer material in this embodiment is 5 × 10⁻⁶. 5 g / mol.

[0170] In the corresponding preparation method, the mass of the initiator is increased until a number-average molecular weight of 6 × 10⁻⁶ is obtained. 5 g / mol.

[0171] All other conditions remain the same as in Example 1.

[0172] Example 8

[0173] The difference between this embodiment and Embodiment 1 is that the number-average molecular weight of the allyl polymer material in this embodiment is 9 × 10⁻⁶. 6 g / mol.

[0174] In the corresponding preparation method, the mass of the initiator added is reduced until a number-average molecular weight of 9 × 10⁻⁶ is obtained. 6 g / mol.

[0175] All other conditions remain the same as in Example 1.

[0176] Example 9

[0177] The difference between this embodiment and Embodiment 1 is that the thickness of the SEI film in this embodiment is 25nm, and the amount of raw materials added to the corresponding SEI film can be adjusted.

[0178] All other conditions remain the same as in Example 1.

[0179] Example 10

[0180] The difference between this embodiment and Embodiment 1 is that the thickness of the SEI film in this embodiment is 160nm, and the amount of raw materials added to the corresponding SEI film can be adjusted.

[0181] All other conditions remain the same as in Example 1.

[0182] Comparative Example 1

[0183] The difference between this comparative example and Example 1 is that the silicon-based anode material in this comparative example is a gas-phase silicon-carbon material.

[0184] Comparative Example 2

[0185] The difference between this comparative example and Example 1 is that the monomer of the allyl polymer material in this comparative example is propylene, that is, the polymer material is polypropylene (CAS:9003-07-0).

[0186] In the preparation method, the preparation of polymer materials is not carried out, and step (b) is carried out directly.

[0187] Comparative Example 3

[0188] The difference between this comparative example and Example 1 is that the monomer of the allyl polymer material in this comparative example is allyl-alpha-D-glucopyranoside (CAS: 7464-56-4). The repeating unit in the allyl polymer material includes a main chain and a side chain, which are connected by ether bonds and are free radical polymerized. The side chain is a sugar ring.

[0189] All other conditions remain the same as in Example 1.

[0190] Comparative Example 4

[0191] The difference between this comparative example and Example 4 is that the silicon-based anode material in this comparative example is the same as the pure silicon material in Example 4.

[0192] The silicon-based anode materials provided in the above embodiments and comparative examples are used in lithium-ion batteries, as detailed below.

[0193] Application Example 1

[0194] This application example provides a lithium-ion battery, which includes a positive electrode, a separator, a negative electrode, and an electrolyte.

[0195] Positive electrode: using ternary material NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 The positive electrode active material (O2), binder PVDF (polyvinylidene fluoride), and conductive agent SP (super-P conductive carbon black) are mixed and stirred evenly at a mass ratio of 96:2:2 to obtain a positive electrode slurry. The positive electrode slurry is then coated onto aluminum foil through a coating process, and after drying and cold pressing, a positive electrode sheet is obtained.

[0196] Negative electrode sheet: The silicon-based negative electrode material, conductive agent SP (Super-P conductive carbon black), SWCNT (single-walled carbon nanotubes), and binder PAA (polyacrylic acid) from Example 1 are mixed and stirred evenly in a mass ratio of 85:4:1:10 to obtain a negative electrode slurry. The solid content is controlled at 30%. Then, the negative electrode slurry is coated onto a copper foil current collector through a coating process. After vacuum drying and cold pressing, a negative electrode sheet is obtained.

[0197] Electrolyte: The organic solvent is selected from ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC): fluoroethylene carbonate (FEC) with a corresponding volume ratio of 20:40:30:10, and the lithium salt is LiPF6 with a lithium salt concentration of 1 mol / L.

[0198] Diaphragm: Polyethylene ceramic diaphragm is selected.

[0199] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0200] Application Example 2-10 and Comparative Example 1-4

[0201] The difference between Application Examples 2-10 and Comparative Examples 1-4 and Application Example 1 is that the silicon-based anode materials provided in Examples 2-10 and Comparative Examples 1-4 are used as anode active materials to prepare anode sheets, respectively.

[0202] All other application conditions remain the same as in Application Example 1.

[0203] Performance testing

[0204] The batteries provided in the above application examples and comparative application examples were tested on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd. under normal temperature (25℃) conditions, with the charge and discharge voltage limited to 2.5V~4.2V. The specific test conditions were as follows:

[0205] 1) First Coulomb efficiency

[0206] At 25°C, the lithium-ion battery was charged at a constant current and constant voltage of 0.33C to 4.2V, allowed to stand for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V, allowed to stand for 10 minutes. The initial coulombic efficiency of the lithium-ion battery was calculated.

[0207] Initial coulombic efficiency (%) = Total capacity of lithium-ion battery during initial discharge at 0.33C / Total capacity of lithium-ion battery during initial charge at 0.33C × 100%.

[0208] 2) Capacity retention after 1200 cycles at room temperature (1°C) / 1°C

[0209] At 25°C, the lithium-ion battery was charged at a constant current and constant voltage of 1C to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the lithium-ion battery was discharged at a constant current of 1C to 2.5V and then rested for 10 minutes. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 1200 charge-discharge cycles using the above method. The capacity retention rate of the lithium-ion battery after 900 charge-discharge cycles at 1C / 1C was calculated.

[0210] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0211] 3) Room temperature 6C rate performance - constant current charge ratio

[0212] At 25℃, the lithium-ion battery was discharged at a 1C rate to 2.5V under constant current, allowed to stand for 10 minutes, and then charged at a 6C rate to 4.2V under constant current and constant voltage, with a cutoff current of 0.05C. After a 10-minute stand, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 were recorded. The constant current charge ratio at the 6C rate was calculated using the following formula: 6C rate charging constant current charge ratio = Constant current charging capacity Q1 / Total constant current and constant voltage charging capacity Q2 × 100%.

[0213] 4) Capacity retention rate at room temperature (1C / 10C discharge)

[0214] The lithium-ion battery, after capacity gradation, was charged at 25℃ using a 1C rate with constant current and constant voltage to 4.2V, with a cutoff current of 0.05C; it was then allowed to stand for 10 minutes; next, the lithium-ion battery was discharged at a 1C rate with constant current to 2.5V, and its discharge capacity Q1C was recorded as the initial discharge capacity; then, the lithium-ion battery was charged at 25℃ using a 1C rate with constant current and constant voltage to 4.2V, with a cutoff current of 0.05C; it was allowed to stand for 10 minutes; then, the fully charged battery was discharged at a 10C rate with constant current to 2.5V, and its discharge capacity Q10C was recorded; the discharge capacity retention rate (%) of the lithium-ion battery at 1C / 10C rate was calculated as: discharge capacity Q10C at 10C rate / discharge capacity Q1C at 1C rate × 100%.

[0215] The test results of the above performance tests are shown in Table 1.

[0216] Table 1

[0217]

[0218] From Table 1, we can conclude that:

[0219] The silicon-based anode material provided by this invention uses allyl polymer materials with special groups as the SEI film of the silicon-based matrix material, which effectively improves the first efficiency, cycle and rate performance of the battery.

[0220] Data analysis of Examples 1 and 4 shows that the silicon-based matrix material in this invention can be either pure silicon or silicon-carbon silicon-based composite material, with fumed silicon-carbon material being preferred as the silicon-based matrix material. The porous hard carbon substrate in the substrate acts as a first-level buffer against the volume expansion of the silicon material and also has excellent conductivity. Furthermore, it provides a large number of uniform anchoring points for the formation of a high-strength hydrogen bond network and covalent bonding, improving the interfacial bonding effect with the allyl polymer material, reducing side reactions caused by surface defects, and further improving the battery's initial efficiency, cycle life, and rate performance.

[0221] Analysis of the data from Examples 1, 5, and 6 shows that the porous hard carbon substrate in the fumed silicon-carbon material has a multi-level pore structure, especially with both microporous and mesoporous structures, which better enhances the buffering effect of silicon material volume expansion, thereby significantly improving the battery's initial efficiency, cycle life, and rate performance.

[0222] Data analysis of Examples 1, 7, and 8 showed that the number-average molecular weight of the allyl polymer material was controlled to be 6 × 10⁻⁶. 5 ~8×10 6 It can achieve uniform and effective coating of silicon-based substrate materials, and ensure the high elasticity of SEI film, which greatly improves the first efficiency, cycle and rate performance of battery.

[0223] Data analysis of Examples 1, 9, and 10 shows that in the silicon-based anode material of the present invention, the thickness of the SEI film coating layer directly affects the coating effect and the performance of the SEI film. By controlling the mass of the SEI film to 2% to 5% of the mass of the silicon-based substrate material and / or the thickness of the SEI film to 35 nm to 150 nm, the continuity, uniformity, and density of the SEI film coating on the silicon-based substrate material are further improved, which better alleviates the volume expansion of the silicon-based substrate material and ensures the effective performance of energy density and lithium-ion transport efficiency, thereby further improving the battery's first-efficiency, cycle, and rate performance.

[0224] Analysis of the data from Example 1, Comparative Examples 1, 2, and 3, as well as Example 4 and Comparative Example 4, reveals that the present invention selects allyl polymer materials with special functional groups as the SEI film of the silicon-based substrate material. These materials also have sugar ring groups with side chains, which, in conjunction with the ester matrix, connect the main chain and side chains. This approach can simultaneously solve the problems of volume expansion of the silicon-based substrate material during charging and discharging, poor interfacial bonding between the film layer and the substrate material, and slow lithium-ion transport in the silicon-based anode material.

[0225] Application Example 11

[0226] The difference between this application example and application example 1 is that the electrolyte in this application example also includes a lithium salt additive of LiFSI, and the mass of the additive is 3% of the mass of the electrolyte provided in application example 1, i.e., the basic electrolyte.

[0227] All other application conditions remain the same as in Application Example 1.

[0228] Application Example 12

[0229] The difference between this application example and application example 1 is that the electrolyte in this application example also includes a lithium salt additive of LiBOB, and the mass of the additive is 3% of the mass of the electrolyte provided in application example 1, i.e., the basic electrolyte.

[0230] All other application conditions remain the same as in Application Example 1.

[0231] Application Example 13

[0232] The difference between this application example and application example 1 is that the electrolyte in this application example also includes a solvent additive of tris(4-nitrophenyl)phosphate, and the additive is 1% of the mass of the electrolyte provided in application example 1, i.e., the basic electrolyte.

[0233] All other application conditions remain the same as in Application Example 1.

[0234] Application Examples 11, 12, and 13 were tested under the same conditions as Application Example 1, and the test results are shown in Table 2.

[0235] Table 2

[0236]

[0237] Analysis of Table 2 yields the following results:

[0238] When the silicon-based anode material provided by this invention is used in lithium-ion batteries, it is used in conjunction with electrolytes containing different additives. In particular, the electrolyte additives used in Application Examples 11-13 are selected, which also achieves a synergistic effect between the silicon-based anode material and the electrolyte, significantly improving the battery's initial efficiency, cycle life, and rate performance.

[0239] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A silicon-based anode material, characterized in that, The silicon-based anode material includes a silicon-based substrate material and an SEI film coated on the surface of the silicon-based substrate material. The SEI film includes an allyl polymer material, and the repeating unit in the allyl polymer material includes a main chain and a side chain. The main chain and the side chain are connected by ester groups, and the side chain includes a sugar ring structure.

2. The silicon-based anode material according to claim 1, characterized in that, The sugar ring structure includes a glucose ring structure, wherein the glucose ring structure includes 3 to 4 hydroxyl groups; Preferably, the glucose ring structure includes a D-glucose ring structure; Preferably, the monomer of the allyl polymer material includes allyl D-glucuronide; Preferably, the number average molecular weight of the allyl-based polymeric material is 6 x 10 5 g / mol ~ 8 x 10 6 g / mol.

3. The silicon-based anode material according to claim 1, characterized in that, The silicon-based matrix material includes fumed silicon-carbon material, which includes a porous hard carbon substrate and silicon material located in the pores of the porous hard carbon substrate.

4. The silicon-based anode material according to claim 3, characterized in that, The porous hard carbon substrate has a pore structure including micropores and mesopores; Preferably, the pore size of the micropores is 0.8 nm to 1.5 nm, and the pore size of the mesopores is 5 nm to 20 nm; Preferably, the pore volume of the micropores accounts for 20% to 40% of the total pore volume of the porous hard carbon substrate. Preferably, the pore volume of the mesopores accounts for 60% to 80% of the total pore volume of the porous hard carbon substrate's pore structure; Preferably, the median particle size D of the fumed silicon-carbon material is... V50 The thickness ranges from 3μm to 9μm. Preferably, the specific surface area of ​​the fumed silicon-carbon material is 1 m². 2 / g~7m 2 / g; Preferably, the mass ratio of porous hard carbon substrate to silicon material in the fumed silicon-carbon material is 1:(0.4~1.2). Preferably, the grain size of the silicon material is 0.5 nm to 2 nm.

5. The silicon-based anode material according to claim 1, characterized in that, The mass of the SEI film is 2% to 5% of the mass of the silicon-based substrate material; Preferably, the thickness of the SEI film is 35nm~150nm.

6. A method for preparing a silicon-based anode material as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: A mixture of allyl polymer material and silicon matrix material is coated to obtain the silicon-based anode material. The repeating unit in the allyl polymer material includes a main chain and a side chain, which are connected by ester groups, and the side chain includes a sugar ring structure.

7. The preparation method according to claim 6, characterized in that, The preparation method of the allyl polymer material includes: The monomer, initiator and first solvent are mixed and polymerized. The solution after polymerization is precipitated to obtain the allyl polymer material. Preferably, the amount of the initiator added is 0.2% to 0.9% of the mass of the monomer; Preferably, the concentration of the monomer in the first solvent is 0.3 mol / L to 1.5 mol / L; Preferably, the polymerization reaction temperature is 60℃~95℃, and the polymerization reaction time is 4h~10h; Preferably, the precipitation treatment includes: adding a precipitating agent to the solution after the polymerization reaction to induce precipitation; Preferably, the precipitation time is 2h to 4h; Preferably, after the precipitation reaction, the product is washed and dried in sequence.

8. The preparation method according to claim 6 or 7, characterized in that, The method for mixing the allyl polymer material and the silicon-based matrix material includes liquid-phase mixing, which includes: preparing an allyl polymer material solution and then adding the silicon-based matrix material for mixing; Preferably, the mass fraction of the allyl polymer material solution is 5% to 30%; Preferably, the coating treatment method includes a stirring treatment, wherein the stirring treatment temperature is 30℃~100℃ and the stirring treatment time is 5h~10h; Preferably, after the coating treatment, a spray drying process is performed.

9. An electrochemical device, characterized in that, The electrochemical device includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer located on at least one side of the surface of the negative current collector, the negative active layer including the silicon-based negative electrode material as described in any one of claims 1-5 or the silicon-based negative electrode material prepared by the preparation method as described in any one of claims 6-8.

10. The electrochemical device according to claim 9, characterized in that, The electrochemical device also includes a positive electrode, a diaphragm, and an electrolyte; Preferably, the electrolyte comprises an organic solvent and a basic lithium salt, and the electrolyte further comprises lithium salt additives and solvent additives; Preferably, the lithium salt additive includes LiFSI and / or LiBOB; Preferably, the amount of LiFSI added is 2% to 4% based on the total mass of the organic solvent and the basic lithium salt as 100%; Preferably, the amount of LiBOB added is 0.2% to 0.5% based on the total mass of the organic solvent and the basic lithium salt as 100%. Preferably, the solvent additive comprises tris(4-nitrophenyl) phosphate, and the amount of tris(4-nitrophenyl) phosphate added is 0.5% to 1.5% based on the total mass of the organic solvent and the base lithium salt as 100%.

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