Coated silicon negative electrode material, and preparation method and application thereof

Abstract

The application discloses a coated silicon negative electrode material and a preparation method and application thereof. The coated silicon negative electrode material comprises a silicon-containing active material and nanocellulose coated on the outer surface of the silicon-containing active material. The silicon negative electrode material can further comprise a conductive agent, and the conductive agent is also coated on the surface of the silicon-containing active material. The application introduces nanocellulose to coat the surface of the silicon-containing active material, preferably uses polyacrylate surface modified nanocellulose to coat the silicon-containing active material, so as to further improve the adhesion between the nanocellulose and the surface of the silicon-containing active material, thereby further improving the swelling aging problem of the silicon-containing active material in the cycle process and improving the comprehensive performance of the material in the battery.

Description

Technical Field

[0001] This invention relates to the field of negative electrode materials for secondary batteries, and more specifically, to a coated silicon negative electrode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, small size, and environmental friendliness, have been widely used in 3C, energy storage, and power industries. Improving the overall performance of lithium-ion batteries, including energy density and cycle life, is crucial for the industry. However, existing mature silicon anode materials still have some inherent problems and defects. Silicon anodes have a high lithium insertion / extraction capacity, but the volume change due to lithium insertion / extraction is significant. During repeated cycling, this leads to irreversible expansion of the material particles and pulverization of the material. Besides the inherent defects of silicon materials, there are also issues such as poor adhesion between active materials and between active materials and current collectors, irreversible expansion of materials due to cycle aging, side reactions with the electrolyte, and SEI film aging. These problems result in active powder fragmentation, affecting battery capacity and cycle stability, and even posing safety hazards.

[0003] Currently, the main methods for addressing the problems of silicon anodes are nano-sizing, alloying, surface coating, and silicon-carbon composites. Surface coating methods commonly employ amorphous carbon or graphene as coating materials. For example, patent CN106058257A uses graphene as a coating material, patent CN109950481A forms an amorphous carbon layer on the surface of the silicon-containing anode active material through high-temperature carbonization of polymers, and patent CN112635741A uses pitch as a coating material, which also ultimately requires high-temperature carbonization to form an amorphous carbon layer on the surface of the silicon-containing anode active material. These methods not only offer limited improvement to the relevant properties of silicon-carbon materials but also involve high-temperature carbonization, resulting in complex processes, high energy consumption, and high costs, which are unfavorable for industrial production.

[0004] Therefore, it is essential to provide a technology that is low-cost, simple to process, conducive to industrial production, and can improve the problems of expansion, pulverization, and breakage of silicon anode materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a coated silicon anode material, its preparation method, and its application. The present invention involves introducing nanocellulose to coat the surface of a silicon-containing active material. Preferably, nanocellulose modified with polyacrylate is used to coat the silicon-containing active material, thereby further improving the adhesion between the nanocellulose and the surface of the silicon-containing active material. This further mitigates the expansion and aging issues of the silicon-containing active material during cycling, enhancing the overall performance of the material in the battery.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a coated silicon anode material, comprising: a silicon-containing active material and nanocellulose uniformly coated on the outer surface of the silicon-containing active material.

[0008] In the aforementioned coated silicon anode material, as a preferred embodiment, the silicon anode material comprises, by mass percentage: 90%-99.9% silicon-containing active material and 0.1%-10% nanocellulose; more preferably, 90%-99.5% silicon-containing active material and 0.5%-10% nanocellulose.

[0009] In the aforementioned coated silicon anode material, as a preferred embodiment, the nanocellulose is nanocellulose that has undergone surface modification with polyacrylate. More preferably, the polyacrylate accounts for 0.1%-20% of the mass percentage of the unmodified nanocellulose.

[0010] In the above-mentioned coated silicon anode material, as a preferred embodiment, the silicon anode material further includes a conductive agent, wherein the conductive agent and nanocellulose are uniformly coated on the outer surface of the silicon-containing active material;

[0011] More preferably, the conductive agent replaces a portion of the silicon-containing active material, and the silicon anode material comprises, by mass percentage: 80%-99.4% silicon-containing active material; 0.5%-10% nanocellulose; and 0.1%-10% conductive agent.

[0012] In the above-mentioned coated silicon anode materials, as a preferred embodiment, the silicon-containing active material is a silicon-carbon composite material.

[0013] In the aforementioned coated silicon anode material, as a preferred embodiment, the nanocellulose comprises cellulose nanocrystals and / or cellulose nanofibers.

[0014] In the aforementioned coated silicon anode material, as a preferred embodiment, the conductive agent is one or more of conductive carbon black, carbon nanotubes, acetylene black, Ketjen black, and graphene.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned coated silicon anode material, comprising the following steps:

[0016] S1: The coating material and the silicon-containing active material are added to a solvent according to the above ratio and wet-mixed to obtain a uniformly mixed slurry. Then, the solvent in the slurry is removed to obtain a solvent-free mixture dry powder. The coating material is nanocellulose, or nanocellulose and a conductive agent.

[0017] S2: Grind the solvent-free mixture dry powder to obtain the coated silicon anode material.

[0018] In the above preparation method, as a preferred approach, the wet mixing includes one or more of the following: resonant acoustic mixing, high shear, and grinding.

[0019] And / or, the wet mixing is achieved by one or more of the following equipment: ball mill, electromagnetic ball mill, disc mill, pin mill, high-energy impact mill, fluid energy impact mill, jet mill, fluidized bed jet mill, hammer mill, and impact mill.

[0020] In the above preparation method, as a preferred method, the method for removing the solvent from the slurry includes one or more of vacuum drying, centrifugation, freeze drying, and spray drying.

[0021] In the above preparation method, as a preferred embodiment, the solvent is one or more of water, NMP, and ethanol.

[0022] In the above preparation method, as a preferred method, the grinding conditions are: grinding temperature 20-80℃, time 10min-300min.

[0023] And / or, the grinding process is performed by rod grinding, jet grinding, or hammer grinding.

[0024] In the above preparation method, as a preferred approach, the particle size range of the obtained silicon anode material is 0.5-20 μm.

[0025] Thirdly, the present invention provides the application of the above-described coated silicon anode material or the silicon anode material obtained by the above-described preparation method in lithium-ion batteries.

[0026] The silicon anode material that has undergone the above-mentioned coating treatment or the silicon anode material obtained by the above-mentioned preparation method can be used to make anode sheets.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention introduces nanocellulose to coat the surface of silicon-containing active materials, preferably using nanocellulose modified with polyacrylate to coat the silicon-containing active materials, in order to further improve the adhesion between the nanocellulose and the surface of the silicon-containing active materials, thereby further improving the expansion and aging problem of silicon-containing active materials during cycling and enhancing the overall performance of the materials in batteries.

[0029] The silicon anode material of this invention does not require high-temperature carbonization, and the process is simple, low-cost, and conducive to industrial production. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0032] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0033] In this invention, unless otherwise specified and / or stated, all numerical values ​​relating to component amounts are "parts by weight or mass percentage" throughout. Process parameters in the following examples that do not specify particular conditions are generally performed under conventional conditions.

[0034] This invention provides a coated silicon anode material, comprising: a silicon-containing active material and nanocellulose uniformly coated on the outer surface of the silicon-containing active material; by mass percentage, the silicon-containing active material comprises 90%-99.9% and the nanocellulose comprises 0.1%-10% of the silicon anode material. For example, the proportion of silicon-containing active material is 91%, 93%, 95%, 97%, or 98%, and the corresponding proportion of nanocellulose is 9%, 7%, 5%, 3%, or 2%.

[0035] Furthermore, the active material contains 90%-99.5% silicon; and the nanocellulose content is 0.5%-10%.

[0036] The nanocellulose comprises cellulose nanocrystals and / or cellulose nanofibers. The two types of nanocellulose can be mixed in any mass ratio or used alone, but considering the impact on the performance of the silicon anode material after coating, a mixture of the two types of nanocellulose is preferred. Cellulose nanocrystals exhibit better adhesion to silicon-containing active materials, while cellulose nanofibers offer better elasticity; mixing them allows for full utilization of their respective advantages. Specifically, the mass ratio of cellulose nanocrystals to cellulose nanofibers can be 0.1-10:1 (e.g., 0.2:1, 1.5:1, 2.5:1, 3:1, 4:1, 6:1, 8:1, or 9:1), more preferably 1:1. The nanocellulose used in this invention has a diameter range of 2nm-100nm and a length range of 200nm-100μm.

[0037] Specifically, cellulose nanocrystals include at least one of nanocrystalline cellulose, nanocrystalline cellulose, cellulose nanowhiskers, rod-shaped cellulose microcrystals, etc.

[0038] Cellulose nanofibers include at least one of nanofiberized cellulose, nanofiberized cellulose, microfiberized cellulose, and cellulose microfibers.

[0039] The silicon-containing active material can be any silicon-based anode active material, such as a silicon-based material or a silicon-carbon composite material. The silicon-based material can be nano-silicon, micron-silicon, porous silicon, amorphous silicon, or silicon suboxide, etc. However, considering the overall performance of silicon-based anode active materials, Si-C composite materials are preferred.

[0040] By introducing nanocellulose to coat the surface of silicon-containing active materials, problems such as irreversible expansion caused by cycle aging are mitigated, thereby improving the overall performance of silicon-carbon materials used in anodes. Specifically, because silicon anodes have a high lithium insertion / extraction capability, the volume change during lithium insertion / extraction is significant, leading to irreversible expansion and pulverization of the material particles during repeated cycling. Coating the surface of silicon particles with nanocellulose is equivalent to binding the silicon particles with nanowires that possess a certain degree of elasticity and strength. This suppresses and alleviates the pulverization caused by volume expansion during lithium insertion / extraction, thus improving the material's cycle performance.

[0041] To improve the adhesion between nanocellulose and silicon-containing active materials, preferably, the nanocellulose is surface-modified with polyacrylates to form polyacrylate-modified nanocellulose. The hydroxyl, carboxyl, and ester bonds in the polyacrylates interact with the hydroxyl and carboxyl groups on the surface of the nanocellulose. The monomers of the polyacrylates are selected from, but are not limited to, any one or a combination of at least two of the following: methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, isooctyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, hydroxypropyl methacrylate, or 2-hydroxyethyl methacrylate. Surface-modified nanocellulose can further improve the adhesion between the nanofibers and the surface of the silicon-containing active materials, resulting in higher adhesion for coating the silicon-containing active materials and achieving better performance enhancement.

[0042] Nanocellulose modified with polyacrylates is obtained by a mixed self-assembly method, which involves blending aqueous solutions or dispersions of both, and then allowing different components to self-assemble to achieve surface modification and coating of nanocellulose with polyacrylates.

[0043] The polyacrylate constitutes 0.1%-20% of the unmodified nanocellulose by mass. The amount of polyacrylate coating on the surface of the nanocellulose should not be too high, as excessive amounts are detrimental to ion conduction. Examples of possible polyacrylate percentages by mass in nanocellulose include 0.3%, 1%, 3%, 5%, 8%, 10%, 12%, or 14%.

[0044] More preferably, the mass concentration of the polyacrylate aqueous solution is 1%-40% (e.g., 2%, 5%, 9%, 15%, 20%, 25%, 30%, 35%, or 39%), and the mass content of nanocellulose in the nanocellulose aqueous dispersion is 0.1%-10% (e.g., 0.3%, 1%, 3%, 5%, 6%, 8%, or 9%).

[0045] The blending conditions are as follows: mechanical stirring or dispersion is used, and the stirring or dispersion time is preferably 5-60 minutes. To avoid the influence of foam on the dispersion effect during stirring, an appropriate amount of defoamer can be added to the system. The defoamer can be a conventional defoamer, such as organosiloxane or polyether defoamer.

[0046] To improve the conductivity of the silicon-containing active material, the silicon anode material further includes a conductive agent, which is uniformly coated with nanocellulose on the outer surface of the silicon-containing active material.

[0047] More preferably, the conductive agent replaces part of the silicon-containing active material. Specifically, by mass percentage, the silicon anode material comprises: 80%-99.4% silicon-containing active material; 0.5%-10% nanocellulose; and 0.1%-10% conductive agent (e.g., 0.5%, 1%, 3%, 5%, 7%, or 9%).

[0048] Introducing conductive agents along with nanocellulose coating increases the conductivity of the silicon surface. Furthermore, the conductive particles or wires, in conjunction with the nanocellulose, act as another anchoring point on the silicon surface, thus increasing the strength of the surface coating to some extent. When the surface of a silicon-containing active material is coated only with a conductive agent without nanocellulose coating, the conductive agent cannot act as an anchoring point on the silicon surface, resulting in low adhesion strength.

[0049] The conductive agent of the present invention includes one or more of conductive carbon black, carbon nanotubes, acetylene black, Ketjen black, graphene, etc.

[0050] The present invention also provides a method for preparing the above-mentioned coated silicon anode material, comprising the following steps:

[0051] S1: According to the above ratio, nanocellulose, conductive agent and silicon-containing active material are added to solvent and wet-mixed to obtain a uniformly mixed slurry. Then the solvent in the slurry is removed to obtain a solvent-free mixture dry powder.

[0052] Specifically, S1 can be: adding an appropriate amount of solvent (such as water, NMP, or ethanol) to the above-mentioned nanocellulose, conductive agent, and silicon-containing active material for wet mixing to form a uniform slurry of active material, nanocellulose, and conductive agent (the solid content of the slurry can be controlled at around 20-50%, such as 25%, 30%, 35%, 40%, or 45%), and then removing the solvent contained in the slurry by at least one of the methods such as vacuum drying, centrifugation, freeze drying, or spray drying to form a solvent-free mixed dry powder.

[0053] The wet mixing process described herein ensures uniform mixing of the nanocellulose component, conductive agent component, and silicon-containing active material component, guaranteeing the homogeneity of each component. The mixing process includes one or more of the following: resonant acoustic mixing, high-shear mixing, and grinding. The mixing operation may utilize one or more of the following: a disperser, ball mill, electromagnetic ball mill, disc mill, pin mill, high-energy impact mill, fluid energy impact mill, jet mill, fluidized bed jet mill, hammer mill, and impact mill.

[0054] S2: Grind the solvent-free mixture dry powder to obtain the coated silicon anode material.

[0055] This step involves further processing and post-treatment of the solvent-free mixture dry powder. Specifically, it can be achieved through rod milling, jet milling, or hammer milling to further pulverize the dry powder until the particle size is relatively uniform and free of large particles. The milling process breaks down and redisperses the dry powder. The preferred milling temperature is 20-80℃ (e.g., 25℃, 35℃, 45℃, 60℃, 70℃, or 75℃), and the time is 10min-5h (e.g., 20min, 50min, 1.5h, 2h, 3h, 4h, or 4.5h).

[0056] The silicon anode material obtained by grinding in step S2 has a particle size range of 1-20 μm (e.g., 2 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, or any range between two values). The particles have a narrow particle size distribution, uniform particle size, and no agglomeration.

[0057] This invention provides the application of the above-described coated silicon anode material or the silicon anode material obtained by the above preparation method in lithium-ion batteries.

[0058] The silicon anode material treated with the above coating or the silicon anode material obtained by the above preparation method can be used to fabricate anode sheets. The anode sheets can be prepared by dry method or wet method, and this invention does not limit the method.

[0059] The nanocellulose used in Examples 1-5 below has a diameter of 5nm-100nm and a length of 500nm-20μm. The nanocellulose is a mixture of cellulose nanocrystals and cellulose nanofibers with a mass ratio of 1:1.

[0060] Example 1

[0061] This embodiment provides a silicon anode material with surface-coated nanocellulose, the preparation method of which includes the following steps:

[0062] (1) Take 98 parts by weight of silicon anode active material (SiO, capacity 1350mAh / g) and 2 parts by weight of nanocellulose, add metered deionized water to prepare a dispersion slurry with a solid content of 40%, mix the materials, disperse at 800 rpm for 30 seconds using a disperser, and then disperse at 2000 rpm for 10 minutes to make the slurry uniformly dispersed. Remove the solvent and water from the dispersed slurry by vacuum drying at room temperature to obtain a solvent-free mixture.

[0063] (2) The obtained solvent-free mixture is ground into fine powder by mortar and pestle at a grinding temperature of 25°C for 25 min to obtain the silicon anode material with a uniform surface coating of nanocellulose and an average particle size of 5 μm.

[0064] Example 2

[0065] This embodiment provides a silicon anode material with surface-coated modified nanocellulose, the preparation method of which includes the following steps:

[0066] (1) Preparation of nanocellulose with polyacrylate surface modification:

[0067] An aqueous solution of ethyl polyacrylate (20% by mass) and an aqueous dispersion of nanocellulose (5% by mass) were mixed, wherein the mass ratio of ethyl polyacrylate to nanocellulose was 1:10. The mixing conditions were as follows: dispersion was carried out at 400 rpm for 30 seconds and then at 1000 rpm for 10 minutes.

[0068] (2) Take 98 parts by weight of silicon anode active material (SiO, capacity 1350mAh / g), and the mixture containing surface-modified nanocellulose from step (1) (the mixture contains 2 parts by weight of nanocellulose). Add a measured amount of deionized water to prepare a dispersion slurry with a solid content of 40%. Mix the slurry and disperse it at 800 rpm for 30 seconds using a disperser, then disperse it at 2000 rpm for 10 minutes to ensure uniform dispersion. Remove the solvent and water from the dispersed slurry by vacuum drying at room temperature to obtain a solvent-free mixture.

[0069] (3) The obtained solvent-free mixture is ground into fine powder by mortar and pestle at a grinding temperature of 25°C for 25 min to obtain the silicon anode material with a uniform surface coating of nanocellulose and an average particle size of 5.5 μm.

[0070] Example 3

[0071] This embodiment provides a silicon anode material with surface-coated modified nanocellulose and a conductive agent, the preparation method of which includes the following steps:

[0072] (1) Preparation of nanocellulose with polyacrylate surface modification:

[0073] An aqueous solution of polyethyl acrylate (20% by mass) and an aqueous dispersion of nanocellulose (5% by mass) were mixed, wherein the mass ratio of polyacrylate to nanocellulose was 1:5. The mixing conditions were as follows: dispersion was carried out at 400 rpm for 30 seconds and then at 1000 rpm for 10 minutes.

[0074] (2) Take 97 parts by weight of silicon anode active material (SiO, capacity 1350mAh / g), a mixture containing surface-modified nanocellulose (2 parts by weight of nanocellulose) from step (1), 1 part by weight of conductive carbon nanotubes, and add measured amounts of deionized water to prepare a dispersion slurry with a solid content of 40%. Mix the slurry and disperse it at 800 rpm for 30 seconds using a disperser, then disperse it at 2000 rpm for 10 minutes to ensure uniform dispersion. Remove the solvent and water from the dispersed slurry by vacuum drying at room temperature to obtain a solvent-free mixture.

[0075] (3) The obtained solvent-free mixture is ground into fine powder by mortar and pestle at a grinding temperature of 25°C for 25 min to obtain the silicon anode material with a uniform surface coating of nanocellulose and an average particle size of 5.5 μm.

[0076] Example 4

[0077] A silicon anode material with surface-coated modified nanocellulose and a conductive agent is prepared by the following steps:

[0078] (1) Preparation of nanocellulose with polyacrylate surface modification:

[0079] An aqueous solution of polyethyl acrylate (20% by mass) and an aqueous dispersion of nanocellulose (5% by mass) were mixed, wherein the mass ratio of polyacrylate to nanocellulose was 1:20. The mixing conditions were as follows: dispersion was carried out at 800 rpm for 30 seconds and then at 2000 rpm for 10 minutes.

[0080] (2) Take 95 parts by weight of silicon anode active material (SiO, capacity 1350mAh / g), a mixture containing surface-modified nanocellulose (2.5 parts by weight of nanocellulose) from step (1), and 2.5 parts by weight of conductive carbon nanotubes. Add a measured amount of deionized water to prepare a dispersion slurry with a solid content of 45%. Mix the slurry and disperse it at 800 rpm for 30 seconds using a disperser, then disperse it at 2000 rpm for 10 minutes to ensure uniform dispersion. Remove the solvent and water from the dispersed slurry by vacuum drying at room temperature to obtain a solvent-free mixture.

[0081] (3) The obtained solvent-free mixture is ground into fine powder by mortar and pestle at a grinding temperature of 35°C for 30 min to obtain the silicon anode material with a uniform surface coating of nanocellulose and an average particle size of 6.5 μm.

[0082] Example 5

[0083] The difference between this embodiment and embodiment 3 is that the amount of the three raw materials used in step (2) is different. Specifically, in this embodiment, the amount of silicon anode active material (SiO, capacity 1350mAh / g) is 82 parts by weight, the amount of surface-modified nanocellulose mixture in step (1) is 10 parts by weight of nanocellulose, and the amount of conductive carbon nanotubes is 8 parts by weight. Other processes are the same as in embodiment 3.

[0084] Comparative Example 1

[0085] The difference between this embodiment and embodiment 3 is that the substance used to modify nanocellulose in step (1) is sodium alginate, while the other processes are the same as in embodiment 3.

[0086] Comparative Example 2

[0087] This comparative example provides a negative electrode slurry:

[0088] Take 85 parts by weight of silicon anode active material (SiO, capacity 1350mAh / g), the mixture containing surface-modified nanocellulose prepared in step (1) of Example 3 (the mixture contains 2 parts by weight of nanocellulose), 5 parts by weight of conductive carbon black (Surper P), 10 parts by weight of binder PAA, add metered deionized water to prepare a dispersion slurry with a solid content of 40%, mix the materials, and use a disperser at 800 rpm for 30 seconds, 2000 rpm for 10 minutes to make the slurry dispersed evenly.

[0089] Comparative Example 3

[0090] The raw material silicon anode active material (SiO, capacity 1350mAh / g) used in this comparative example 1 was not coated in any way.

[0091] Performance testing

[0092] The modified silicon anode material prepared above is used to prepare a negative electrode sheet. Specifically, the silicon anode materials obtained in Examples 1-5 and Comparative Examples 1 and 3 are mixed with conductive carbon black (Surper P) and PAA binder at a mass ratio of 85:5:10 to obtain a slurry with a solid content of 40%. This slurry is then coated onto a 6-micrometer-thick copper foil with a coating thickness of 50 micrometers. After compaction, a negative electrode sheet is formed with a double-sided areal density of 160 g / m². 2 The slurry of Comparative Example 2 was directly coated onto copper foil according to the above standards to form a negative electrode sheet.

[0093] The prepared negative electrode sheet and lithium metal electrode sheet were assembled into a lithium-ion coin cell CR2016. LiPF6 was dissolved in an electrolyte with EC / DEC / EMC = 2:3:1 at a concentration of 1 mol / L. After the coin cell assembly was completed, the capacity first-efficiency and cycle tests were carried out according to the following steps: stand for 2 h; constant current discharge at 25 °C: 0.1C to 0.005V; 0.08C to 0.001V; 0.05C to 0.001V; 0.02C to 0.001V; stand for 10 min; constant current charging: 0.1C to 1.5V.

[0094] The test results are shown in Table 1.

[0095] Table 1

[0096] Example 1 91.6 77.1 Example 2 91.4 80.3 Example 3 90.2 81.7 Example 4 90.8 82.1 Example 5 91.3 82.9 Comparative Example 1 85.3 70.5 Comparative Example 2 83.2 43.6 Comparative Example 3 82.1 41.4

[0097] As shown in Table 1, the silicon anode material modified with nanocellulose has significant advantages over the unmodified silicon anode material in terms of initial efficiency and capacity retention after 50 cycles. The performance of the silicon anode material modified with nanocellulose by acrylates will be further improved.

[0098] A comparison of Comparative Example 1 and Example 3 shows that when the binder used for surface modification of nanocellulose is replaced with a binder other than acrylates, the effect of increasing the adhesion between nanocellulose and silicon-active materials becomes worse, and the 50-cycle capacity retention rate decreases slightly.

[0099] As shown in Comparative Example 2, when nanocellulose is directly added to the negative electrode slurry to prepare the negative electrode sheet, the nanocellulose cannot be uniformly coated on the outside of the silicon active material, resulting in an insignificant effect on inhibiting the expansion and aging of the silicon active material during cycling, and thus no significant improvement on the overall performance of the battery.

[0100] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A coated silicon anode material, characterized in that, include: Silicon-containing active material and nanocellulose uniformly coated on the outer surface of the silicon-containing active material; The nanocellulose is nanocellulose that has undergone surface modification with polyacrylates; The silicon anode material also includes a conductive agent, which is uniformly coated with nanocellulose on the outer surface of the silicon-containing active material. The conductive agent replaces part of the silicon-containing active material. By mass percentage, the silicon anode material comprises: 80%-99.4% silicon-containing active material; 0.5%-10% nanocellulose; and 0.1%-10% conductive agent.

2. The coated silicon anode material according to claim 1, characterized in that, The silicon-containing active material is a silicon-carbon composite material; And / or, the nanocellulose includes cellulose nanocrystals and / or cellulose nanofibers; And / or, the diameter of the nanocellulose ranges from 2 nm to 100 nm, and the length ranges from 200 nm to 100 μm; And / or, the polyacrylate accounts for 0.1%-20% of the mass of the unmodified nanocellulose; And / or, the conductive agent is one or more of conductive carbon black, carbon nanotubes, acetylene black, Ketjen black, and graphene.

3. The coated silicon anode material according to claim 2, characterized in that, The mass ratio of cellulose nanocrystals to cellulose nanofibers is 0.1-10:

1.

4. A method for preparing a coated silicon anode material as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: The coating material and the silicon-containing active material are added to a solvent and wet-mixed according to any one of the proportions of claims 1-3 to obtain a uniformly mixed slurry. Then, the solvent in the slurry is removed to obtain a solvent-free mixture dry powder. The coating material is nanocellulose and a conductive agent. S2: Grind the solvent-free mixture dry powder to obtain the coated silicon anode material.

5. The preparation method according to claim 4, characterized in that, The wet mixing process includes one or more combinations of resonant acoustic mixing, high shear, and grinding. And / or, the wet mixing is achieved by one or more of the following devices: electromagnetic ball mill, disc mill, pin mill, jet mill, fluidized bed jet mill, and hammer mill; And / or, the method for removing solvent from the slurry includes one or more of the following: vacuum drying, centrifugation, freeze drying, and spray drying; And / or, the solvent is one or more of water, NMP, and ethanol; And / or, in step S2, the grinding conditions are: grinding temperature 20-80℃, time 10min-300min; And / or, in step S2, the grinding process is completed by rod grinding, jet grinding, or hammer grinding.

6. The preparation method according to claim 4, characterized in that, The particle size range of the coated silicon anode material obtained is 0.5-20 μm.

7. The application of the coated silicon anode material as described in any one of claims 1-3 or the silicon anode material obtained by the preparation method as described in any one of claims 4-6 in lithium-ion batteries.