Silicon-containing negative electrode sheet, method for manufacturing the same, and lithium ion battery

Abstract

This invention provides a silicon-containing anode sheet, its preparation method, and a lithium-ion battery, relating to the field of battery material technology. The silicon-containing anode sheet includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector. The negative electrode material layer comprises a first silicon-containing layer, a second silicon-containing layer, and a third graphite layer sequentially stacked on the surface of the negative electrode current collector along a direction away from the current collector. The first silicon-containing layer contains capacity-type graphite and a novel porous silicon-carbon material; the second silicon-containing layer contains rate-type graphite and a pre-lithiated silicon-oxygen material; and the third graphite layer contains rate-type graphite. Through the synergistic effect of the three-layer structure (first silicon-containing layer, second silicon-containing layer, and third graphite layer), a gradient channel for lithium-ion transport is established vertically, effectively preventing the shedding of active material due to large particle expansion. This effectively improves rate performance and fast-charge cycle performance while maintaining energy density. This invention also provides a method for preparing the aforementioned silicon-containing anode sheet.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a silicon-containing negative electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] Silicon-based anodes possess advantages such as high energy density and wide availability of raw materials, making them a promising next-generation lithium-ion battery anode material. Currently, there are two main approaches to silicon-based anodes: the silicon-oxygen route (primarily silicon suboxide) and the silicon-carbon route (primarily nano-silicon-carbon). Among these, novel porous silicon-carbon anodes (i.e., nano-silicon vapor-deposited in porous carbon materials) exhibit significant advantages in specific capacity, full-charge expansion rate, and cycle performance. Pre-lithiated silicon-oxygen anodes offer some advantages in rate performance. A major challenge lies in balancing energy density with the fast-charging and cycle performance of silicon anodes. Therefore, a more rational design of the electrode ends is necessary.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] In view of the shortcomings and defects of the existing technology, the present invention aims to provide a silicon-containing anode sheet, its preparation method and a lithium-ion battery.

[0005] To achieve the above objectives, the following technical solution is adopted:

[0006] The primary objective of this invention is to provide a silicon-containing negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector;

[0007] The negative electrode material layer includes a first silicon-containing layer disposed on the surface of the negative electrode current collector, a second silicon-containing layer disposed on the surface of the first silicon-containing layer, and a third graphite layer disposed on the surface of the second silicon-containing layer.

[0008] The first silicon-containing layer comprises capacity-type graphite and novel porous silicon-carbon material, the second silicon-containing layer comprises rate-type graphite and pre-lithiated silicon-oxygen material, and the third graphite layer comprises rate-type graphite.

[0009] Furthermore, based on the above technical solution of the present invention, in the first silicon-containing layer, the capacity of the capacity-type graphite is 355-360 mAh / g, and the compaction is 1.6-1.7 g / cm³. 3 ;

[0010] And / or, the novel porous silicon-carbon material has a capacity of 1600-1750 mAh / g at 5mV-0.8V.

[0011] Furthermore, based on the above technical solution of the present invention, the rate-multiplier graphite capacity in the second silicon-containing layer and the third graphite layer is 345-355 mAh / g, and the compaction is 1.5-1.65 g / cm³. 3 Preferably, the rate factor of the rate-multiplied graphite in the second silicon-containing layer is 1-1.5C lower than that of the rate factor of the rate-multiplied graphite in the third graphite layer.

[0012] And / or, the pre-lithiated silicon oxide material in the second silicon-containing layer has a capacity of 1200-1350 mAh / g at 5mV-0.8V.

[0013] Furthermore, based on the above-mentioned technical solution of the present invention, the raw materials used to form the first silicon-containing layer include capacity-type graphite, novel porous silicon-carbon material, conductive agent and binder. With the total mass of the raw materials used to form the first silicon-containing layer being 100%, the mass fraction ratio of capacity-type graphite, novel porous silicon-carbon material, conductive agent and binder is (83.5%-88.4%):(7.6%-11.5%):(0.5%-1%):(3.5%-4%).

[0014] And / or, the raw materials used to form the second silicon-containing layer include rate-multiplied graphite, pre-lithiated silicon oxide material, conductive agent and binder, with the total mass of the raw materials used to form the second silicon-containing layer being 100%, the mass fraction ratio of the rate-multiplied graphite, pre-lithiated silicon oxide material, conductive agent and binder is (78.2%-88.5%):(7.5%-16.3%):(1%-1.5%):(3%-4%);

[0015] And / or, the raw materials used to form the third graphite layer include rate-multiplied graphite, conductive agent and binder, and the mass ratio of the rate-multiplied graphite, conductive agent and binder is (95.5%-96.5%):(1%-1.5%):(2.5%-3%), with the total mass of the raw materials used to form the third graphite layer being 100%.

[0016] Furthermore, based on the above technical solution of the present invention, the conductive agent in the first silicon-containing layer, the second silicon-containing layer and the third graphite layer includes conductive carbon black and / or carbon nanotubes.

[0017] And / or, the binder in the first silicon-containing layer, the second silicon-containing layer and the third graphite layer includes at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylic acid or lithium polyacrylate;

[0018] And / or, the mass fraction of the binder in the second silicon-containing layer is less than or equal to the mass fraction of the binder in the first silicon-containing layer.

[0019] Furthermore, based on the above technical solution of the present invention, the conductive agent in the first silicon-containing layer and the second silicon-containing layer includes conductive carbon black and single-walled carbon nanotubes.

[0020] And / or, the binders in the first and second silicon-containing layers include styrene-butadiene rubber and lithium polyacrylate.

[0021] Furthermore, based on the above technical solution of the present invention, the composite capacity of the second silicon-containing negative electrode is less than or equal to the composite capacity of the first silicon-containing negative electrode.

[0022] And / or, the areal density of the first silicon-containing layer accounts for 30%-60% of the areal density of the negative electrode material, the areal density of the second silicon-containing layer accounts for 30%-50% of the areal density of the negative electrode material, and the areal density of the third graphite layer accounts for 10%-20% of the areal density of the negative electrode material.

[0023] The second objective of this invention is to provide a method for preparing the aforementioned silicon-containing anode sheet, comprising the following steps:

[0024] (a) A material for forming a first silicon-containing layer and a material for forming a second silicon-containing layer are coated on at least one side of the current collector by a double-layer coating technique, and then dried to form a first silicon-containing layer and a second silicon-containing layer, and then the first silicon-containing layer and the second silicon-containing layer are rolled.

[0025] (b) Coating the surface of the second silicon-containing layer with raw materials for forming the third graphite layer, then drying to form the third graphite layer, and then rolling the entire electrode sheet to obtain a silicon-containing negative electrode sheet.

[0026] Furthermore, based on the above technical solution of the present invention, in step (a), the rolling process includes a first rolling process and a second rolling process, wherein the compaction of the first rolling process is 1.3-1.4 g / cm³. 3 The second roller compaction yielded a density of 1.6-1.65 g / cm³. 3 ;

[0027] And / or, in step (b), the roller compaction is 1.55-1.6 g / cm³. 3 .

[0028] The third objective of this invention is to provide a lithium-ion battery comprising a silicon-containing anode sheet provided in the first objective of this invention and a silicon-containing anode sheet prepared by the preparation method provided in the second objective of this invention.

[0029] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0030] (1) The present invention provides a silicon-containing negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector. The negative electrode material layer comprises a first silicon-containing layer, a second silicon-containing layer and a third graphite layer sequentially stacked on the surface of the negative electrode current collector in a direction away from the current collector. The first silicon-containing layer comprises capacity-type graphite and a novel porous silicon-carbon material, the second silicon-containing layer comprises rate-type graphite and a pre-lithiated silicon-oxygen material, and the third graphite layer comprises rate-type graphite. Through the synergistic effect of the three-layer structure of the first silicon-containing layer, the second silicon-containing layer and the third graphite layer, a gradient channel (fast-buffered-slow) for lithium-ion transport is established in the longitudinal direction, and the phenomenon of active material shedding due to large particle expansion can be effectively avoided, thereby effectively improving rate performance and fast-charging cycle performance while ensuring energy density.

[0031] (2) The present invention provides a method for preparing the above-mentioned silicon-containing anode sheet. It is simple to operate and saves time and baking costs compared with the conventional three-layer structure anode material layer, where each layer is coated with a single layer. Moreover, the entire coating process can be realized on the basis of existing equipment without increasing equipment costs.

[0032] (3) The present invention provides a lithium-ion battery comprising the aforementioned silicon-containing anode sheet. Given the advantages of the silicon-containing anode sheet, the lithium-ion battery made from it possesses good energy density, as well as good rate performance and fast-charge cycle performance. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the silicon-containing negative electrode sheet of the present invention;

[0034] In the figure, 1-current collector; 2-first silicon-containing layer; 3-second silicon-containing layer; 4-third graphite layer. Detailed Implementation

[0035] 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. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0036] 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.

[0037] According to a first aspect of the present invention, a silicon-containing negative electrode is provided, the structural schematic diagram of which is shown below. Figure 1 As shown, the silicon-containing negative electrode sheet specifically includes a negative electrode current collector 1 and a negative electrode material layer disposed on the surface of the current collector;

[0038] The negative electrode material layer includes a first silicon-containing layer 2 disposed on the surface of the negative electrode current collector, a second silicon-containing layer 3 disposed on the surface of the first silicon-containing layer, and a third graphite layer 4 disposed on the surface of the second silicon-containing layer;

[0039] The first silicon-containing layer 2 contains capacity-type graphite and novel porous silicon-carbon material, the second silicon-containing layer 3 contains rate-type graphite and pre-lithiated silicon-oxygen material, and the third graphite layer 4 contains rate-type graphite.

[0040] Based on the inherent properties of the materials, this invention provides a more rational design for the electrode end: The graphite layer (i.e., the third graphite layer) is placed as the outermost layer, utilizing the rapid lithium-ion diffusion characteristic of rate-adjustable graphite to effectively improve the overall rate performance of the electrode and prevent lithium plating on the negative electrode surface; the silicon-oxygen layer (i.e., the second silicon-containing layer) is placed as the intermediate layer, mainly taking advantage of the better rate performance of silicon-oxygen negative electrodes compared to silicon-carbon negative electrodes, providing a buffer layer for the slowed lithium-ion diffusion rate. Considering the significant expansion of silicon-oxygen negative electrodes, placing it in the intermediate layer provides effective buffer space for particle expansion in the longitudinal thickness direction, reducing the expansion of the electrode itself; the silicon-carbon layer (i.e., the first silicon-containing layer) is placed as the inner layer, mainly considering the high capacity and small expansion of silicon-carbon, ensuring the cell's energy density while preventing active material shedding due to significant particle expansion, thus guaranteeing cycle life. Through the synergistic effect of the three-layer structure consisting of the first silicon-containing layer, the second silicon-containing layer, and the third graphite layer, a gradient channel (fast-buffered-slow) for lithium-ion transport is established in the vertical direction. This effectively avoids the shedding of active material due to large particle expansion, thereby improving rate performance and fast charging cycle performance while ensuring energy density.

[0041] Compared to traditional methods that improve the anode material itself (such as coating, doping, or modification), this invention designs the electrode end based on the material properties. The raw materials used are simple and readily available, requiring no additional processing, resulting in a significant cost advantage and greater feasibility for industrialization.

[0042] As an optional embodiment of the technical solution of the present invention, the capacity of the high-capacity graphite in the first silicon-containing layer is 355-360 mAh / g (e.g., 355 mAh / g, 356 mAh / g, 358 mAh / g, or 360 mAh / g, etc.), and the compaction is 1.6-1.7 g / cm³. 3 (For example, 1.6g / cm) 3 1.62g / cm 3 1.64 g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.68g / cm 3 1.7g / cm 3 wait);

[0043] And / or, the source of the novel porous silicon-carbon material (i.e., nano-silicon vapor-deposited in porous carbon material) in the first silicon-containing layer is not limited; it can be prepared by existing technology or purchased commercially. Its capacity is further limited; the capacity of the novel porous silicon-carbon material at 5mV-0.8V is 1600-1750 mAh / g (e.g., 1600 mAh / g, 1620 mAh / g, 1650 mAh / g, 1660 mAh / g, 1680 mAh / g, 1700 mAh / g, 1720 mAh / g, 1740 mAh / g, or 1750 mAh / g, etc.). The preparation method of the novel porous silicon-carbon material is not specifically limited, as long as the capacity meets the requirements.

[0044] By further limiting the capacity of the capacity-type graphite and the novel porous silicon-carbon material in the first silicon-containing layer, the energy density of the battery cell is guaranteed.

[0045] As an optional embodiment of the technical solution of the present invention, the rate-multiplier graphite capacity in the second silicon-containing layer and the third graphite layer is 345-355 mAh / g (e.g., 345 mAh / g, 346 mAh / g, 348 mAh / g, 350 mAh / g, 352 mAh / g, 354 mAh / g, or 355 mAh / g, etc.), and the compaction is 1.5-1.65 g / cm³. 3 (For example, 1.5g / cm) 3 1.52g / cm 3 1.54g / cm 3 1.56g / cm 3 1.58g / cm 3 1.6g / cm 3 1.62g / cm 3 1.64 g / cm 3 Or 1.65g / cm 3 wait);

[0046] Preferably, the rate of the rate-modified graphite in the second silicon-containing layer is 1-1.5C lower than that in the third graphite layer; thus, while ensuring the construction of a gradient channel for lithium-ion transport (fast-buffered), it also helps to reduce material costs (the higher the rate of the rate-modified graphite, the more expensive it is).

[0047] As an optional embodiment of the technical solution of the present invention, the pre-lithiated silicon oxide material in the second silicon-containing layer has a capacity of 1200-1350 mAh / g at 5mV-0.8V (e.g., 1200 mAh / g, 1220 mAh / g, 1250 mAh / g, 1260 mAh / g, 1280 mAh / g, 1300 mAh / g, 1320 mAh / g, 1340 mAh / g, or 1350 mAh / g, etc.). The preparation method of the pre-lithiated silicon oxide material is not specifically limited, as long as the capacity meets the requirements.

[0048] As an optional embodiment of the technical solution of the present invention, the raw materials used to form the first silicon-containing layer include capacity-type graphite, novel porous silicon-carbon material, conductive agent, and binder. Based on the total mass of the above raw materials as 100%, the mass fraction of capacity-type graphite is 83.5%-88.4% (e.g., 83.5%, 84%, 85%, 86%, 87%, or 88%), the mass fraction of novel porous silicon-carbon material is 7.6%-11.5% (e.g., 7.6%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, or 11.5%), the mass fraction of conductive agent is 0.5%-1% (e.g., 0.6%, 0.7%, 0.8%, or 1.0%), and the mass fraction of binder is 3.5%-4% (e.g., 3.6%, 3.7%, 3.8%, or 4.0%). That is, the mass fraction ratio of volumetric graphite, novel porous silicon carbide material, conductive agent and binder is (83.5%-88.4%): (7.6%-11.5%): (0.5%-1%): (3.5%-4%).

[0049] As an optional embodiment of the technical solution of the present invention, the raw materials used to form the second silicon-containing layer include rate-multiplier graphite, pre-lithiated silicon oxide material, conductive agent, and binder. Based on the total mass of the above raw materials as 100%, the mass fraction of rate-multiplier graphite is 78.2%-88.5% (e.g., 78.2%, 80%, 82%, 84%, 85%, 86%, 87%, or 88%), and the mass fraction of pre-lithiated silicon oxide material is 7.5%-16.3% (e.g., 7.5%, 8%, 9%, 10%, 12%, or 14%). The mass fraction of the conductive agent is 1%-1.5% (e.g., 1%, 1.2%, 1.4%, or 1.5%), and the mass fraction of the binder is 3%-4% (e.g., 3.0%, 3.2%, 3.5%, 3.6%, 3.7%, 3.8%, or 4.0%). That is, the mass fraction ratio of the rate-multiplied graphite, pre-lithiated silicon oxide material, conductive agent, and binder is (78.2%-88.5%): (7.5%-16.3%): (1%-1.5%): (3%-4%).

[0050] As an optional embodiment of the technical solution of the present invention, the raw materials used to form the third graphite layer include rate-multiplying graphite, a conductive agent, and a binder. With the total mass of the above raw materials as 100%, the mass fraction of the rate-multiplying graphite is 95.5%-96.5% (e.g., 95.5%, 95.8%, 96.0%, 96.2%, 96.4%, or 96.5%), the mass fraction of the conductive agent is 1%-1.5% (e.g., 1%, 1.2%, 1.4%, or 1.5%), and the mass fraction of the binder is 2.5%-3% (e.g., 2.6%, 2.7%, 2.8%, or 3.0%). That is, the mass fraction ratio of the rate-multiplying graphite, the conductive agent, and the binder is (95.5%-96.5%):(1%-1.5%):(2.5%-3%).

[0051] As an optional embodiment of the technical solution of the present invention, the conductive agent in the first silicon-containing layer, the second silicon-containing layer, and the third graphite layer includes conductive carbon black and / or carbon nanotubes; wherein, the carbon nanotubes include single-walled and / or multi-walled carbon nanotubes. Preferably, the conductive agent in the first silicon-containing layer and the second silicon-containing layer includes conductive carbon black and single-walled carbon nanotubes; more preferably, the mass ratio of the conductive agent in the second silicon-containing layer is greater than or equal to the mass ratio of the conductive agent in the first silicon-containing layer.

[0052] As an optional embodiment of the technical solution of the present invention, the binder in the first silicon-containing layer, the second silicon-containing layer and the third graphite layer includes at least one of styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), polyacrylic acid (PAA) or lithium polyacrylate (PAA-Li).

[0053] Preferably, the binders in the first and second silicon-containing layers include styrene-butadiene rubber and lithium polyacrylate; more preferably, the mass fraction ratio of the binder in the second silicon-containing layer is less than or equal to the mass fraction ratio of the binder in the first silicon-containing layer.

[0054] By further defining the specific types and relative mass ratios of binders in the first and second silicon-containing layers, the expansion of the first and second silicon-containing layers can be effectively suppressed, and the conductivity of the second silicon-containing layer can be ensured (styrene-butadiene rubber and lithium polyacrylate have a good suppressive effect on the expansion of the electrode, but the more binder there is, the worse the conductivity).

[0055] As an optional embodiment of the technical solution of the present invention, the composite capacity of the second silicon-containing negative electrode is less than or equal to the composite capacity of the first silicon-containing negative electrode.

[0056] The formula for calculating the specific capacity of the first silicon-containing negative electrode is: Specific capacity = (graphite capacity × graphite mass ratio + silicon-carbon capacity × silicon-carbon mass ratio) / (graphite mass ratio + silicon-carbon mass ratio).

[0057] The formula for calculating the specific capacity of the second silicon-containing negative electrode is: Specific capacity = (graphite capacity × graphite mass ratio + silicon-oxygen capacity × silicon-oxygen mass ratio) / (graphite mass ratio + silicon-oxygen mass ratio).

[0058] As an optional embodiment of the technical solution of the present invention, the areal density of the first silicon-containing layer accounts for 30%-60% (e.g., 30%, 35%, 40%, 45%, 50%, 55%, or 60%) of the areal density of the entire electrode (excluding the current collector) negative electrode material layer (i.e., the first silicon-containing layer + the second silicon-containing layer + the third graphite layer), the areal density of the second silicon-containing layer accounts for 30%-50% (e.g., 30%, 35%, 40%, 45%, or 50%) of the areal density of the negative electrode material layer, and the areal density of the third graphite layer accounts for 10%-20% (e.g., 10%, 12%, 15%, 18%, or 20%) of the areal density of the negative electrode material layer.

[0059] According to a second aspect of the present invention, a method for preparing the above-mentioned silicon-containing negative electrode is also provided, comprising the following steps:

[0060] (a) A material for forming a first silicon-containing layer and a material for forming a second silicon-containing layer are coated on at least one side of the current collector by a double-layer coating technique, and then dried to form a first silicon-containing layer and a second silicon-containing layer, and then the first silicon-containing layer and the second silicon-containing layer are rolled.

[0061] (b) Coating the surface of the second silicon-containing layer with raw materials for forming the third graphite layer, then drying to form the third graphite layer, and then rolling the entire electrode sheet to obtain a silicon-containing negative electrode sheet.

[0062] This preparation method can be achieved using existing equipment (currently, dual-head coating machines are more common, while triple-head coating machines require custom-made equipment) without increasing equipment costs. Furthermore, the properties (viscosity and solid content) of the first silicon-containing layer and the second silicon-containing layer slurry are similar, making dual-layer coating easier to operate (avoiding interface problems such as pinholes) and cost-saving (saving time and baking costs compared to single-layer coating).

[0063] As an optional embodiment of the technical solution of the present invention, in step (a), the rolling pressing includes a first rolling pressing and a second rolling pressing, wherein the compaction of the first rolling pressing is 1.3-1.4 g / cm³. 3 (e.g., 1.32g / cm) 3 1.35g / cm 3 1.38g / cm 3 Or 1.4g / cm 3 (etc.), the second roller compaction is 1.6-1.65 g / cm³. 3 (e.g., 1.60g / cm) 3 1.62g / cm 3 Or 1.65g / cm 3 (etc.). The secondary rolling process can effectively improve the full-charge expansion and rate performance of silicon anodes.

[0064] As an optional embodiment of the technical solution of the present invention, in step (b), the roller compaction is 1.55-1.6 g / cm³. 3 (e.g., 1.55g / cm) 3 1.58g / cm 3 Or 1.60g / cm 3 wait).

[0065] According to a third aspect of the present invention, a lithium-ion battery is also provided, comprising the above-described silicon-containing negative electrode sheet and the silicon-containing negative electrode sheet prepared by the above-described preparation method.

[0066] Given the advantages of the silicon-containing anode sheet provided by the present invention, the lithium-ion battery made from it has good energy density, as well as good rate performance and fast charging cycle performance.

[0067] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0068] Example 1

[0069] This embodiment provides a silicon-containing negative electrode sheet, including a negative electrode current collector (carbon-coated copper foil) and a negative electrode material layer disposed on the surface of the current collector;

[0070] The negative electrode material layer includes a first silicon-containing layer (first coating) disposed on the surface of the negative electrode current collector, a second silicon-containing layer (second coating) disposed on the surface of the first silicon-containing layer, and a third graphite layer (third coating) disposed on the surface of the second silicon-containing layer;

[0071] The first silicon-containing layer comprises high-capacity graphite (capacity of 355 mAh / g, compaction of 1.6 g / cm³). 3 The first silicon-containing layer negative electrode has a specific capacity of 500 mAh / g and a novel porous silicon-carbon material (commercially available, with a capacity of 1620 mAh / g at 5mV-0.8V); the first silicon-containing layer negative electrode has a specific capacity of 500 mAh / g; in the first silicon-containing layer, the mass fractions of capacity-type graphite, novel porous silicon-carbon material, conductive agent and binder are 83.6%, 11.4%, 1% and 4%, respectively.

[0072] The second silicon-containing layer comprises rate-modified graphite 1 (rate 2.5C, capacity 350mAh / g, compaction 1.6g / cm³). 3 The second silicon-containing layer anode composite has a specific capacity of 460 mAh / g and pre-lithiated silicon oxide material (commercially available, with a capacity of 1250 mAh / g at 5mV-0.8V); the third silicon-containing layer anode composite has a specific capacity of 460 mAh / g. In the second silicon-containing layer, the mass fractions of rate-multiplying graphite 1, pre-lithiated silicon oxide material, conductive agent, and binder are 83.3%, 11.7%, 1.5%, and 3.5%, respectively.

[0073] The third graphite layer contains rate-modified graphite 2 (4C rate, capacity 350mAh / g, compaction 1.55g / cm³). 3 In the third graphite layer, the mass fractions of rate-multiplier graphite 2, conductive agent, and binder are 95.9%, 1.3%, and 2.8%, respectively.

[0074] The method for preparing the silicon-containing negative electrode in this embodiment includes the following steps:

[0075] (1) Capacitive graphite, novel porous silicon carbide material, conductive carbon black, single-walled carbon nanotubes, SBR, and PAA-Li are mixed with deionized water in a mass ratio of 83.6%:11.4%:0.9%:0.1%:1%:3% for the first silicon-containing layer to form slurry 1.

[0076] The high-ratio graphite 1, pre-lithiated silicon oxide material, conductive carbon black, single-walled carbon nanotubes, SBR, and PAA-Li were mixed with deionized water in a mass ratio of 83.3%:11.7%:1.4%:0.1%:1%:2.5% to form slurry 2.

[0077] Slurry 1 and slurry 2 were coated onto the current collector using a double-layer coating technique. The areal density of the first silicon-containing layer was controlled to be 40% of the areal density of the entire electrode (excluding the current collector), and the areal density of the second silicon-containing layer was also controlled to be 40% of the areal density of the entire electrode (excluding the current collector). After drying, a second rolling process was performed, with the first rolling compaction reaching 1.3 g / cm³. 3 The second roller compaction yielded a density of 1.6 g / cm³. 3 .

[0078] (2) Mix the rate-multiplier graphite 2, conductive carbon black, CMC-Na, and SBR with deionized water in a mass ratio of 95.9%:1.3%:1.3%:1.5% for the third graphite layer to form a slurry 3. Coat the slurry 3 onto the surface of the second silicon-containing layer, controlling the areal density of the third graphite layer to be 20% of the areal density of the entire electrode (excluding the current collector). After drying, roll-press the slurry, controlling the compaction to be 1.55 g / cm³. 3 This yields a silicon-containing negative electrode.

[0079] Example 2

[0080] This embodiment provides a silicon-containing negative electrode and its preparation method. This embodiment is basically the same as that of embodiment 1, except that the areal densities of the first silicon-containing layer, the second silicon-containing layer and the third graphite layer in steps (1) and (2) account for 50%, 30% and 20% of the entire electrode (excluding the current collector) respectively.

[0081] Example 3

[0082] This embodiment provides a silicon-containing negative electrode and its preparation method. This embodiment is basically the same as that of embodiment 1, except that the areal densities of the first silicon-containing layer, the second silicon-containing layer and the third graphite layer in steps (1) and (2) account for 60%, 20% and 20% of the areal density of the entire electrode (excluding the current collector), respectively.

[0083] Comparative Example 1

[0084] This comparative example provides a silicon-containing negative electrode sheet. Compared with Example 1, except that the second silicon-containing layer is not disposed between the first silicon-containing layer and the third graphite layer, and the areal density of the first silicon-containing layer is 80% of the areal density of the entire electrode sheet (excluding the current collector), and the areal density of the third graphite layer is 20% of the areal density of the entire electrode sheet (excluding the current collector), the remaining structural composition is the same as that of Example 1.

[0085] The comparative method for preparing a silicon-containing anode sheet includes the following steps:

[0086] (1) Capacitive graphite, novel porous silicon carbide material, conductive carbon black, single-walled carbon nanotubes, SBR, and PAA-Li are mixed with deionized water in a mass ratio of 83.6%:11.4%:0.9%:0.1%:1%:3% for the first silicon-containing layer to form slurry 1.

[0087] Slurry 1 is coated onto the current collector, and its areal density is controlled to be 80% of the entire electrode (excluding the current collector). After drying, it is subjected to a second rolling process. The compaction of the first rolling is 1.3 g / cm³. 3 The second roller compaction yielded a density of 1.6 g / cm³. 3 The first silicon-containing layer is obtained;

[0088] (2) Mix the ratio-type graphite 2, conductive carbon black, CMC-Na, and SBR with deionized water in a mass ratio of 95.9%:1.3%:1.3%:1.5% of the third graphite layer composition to form slurry 3.

[0089] Slurry 3 is coated onto the surface of the first silicon-containing layer. The areal density of the third graphite layer is controlled to be 20% of the areal density of the entire electrode (excluding the current collector). After drying, it is rolled and compacted to a density of 1.55 g / cm³. 3 This yields a silicon-containing negative electrode.

[0090] Comparative Example 2

[0091] This comparative example provides a silicon-containing negative electrode sheet, including a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector;

[0092] The negative electrode material layer includes a first silicon-containing layer disposed on the surface of the negative electrode current collector and a third graphite layer disposed on the surface of the first silicon-containing layer;

[0093] The first silicon-containing layer comprises high-capacity graphite (capacity of 355 mAh / g, compaction of 1.6 g / cm³). 3 The first silicon-containing layer negative electrode composite has a specific capacity of 460 mAh / g, consisting of pre-lithiated silicon oxide material (capacity of 1250 mAh / g for 5mV-0.8V) and pre-lithiated silicon oxide material (capacity of 1250 mAh / g for 5mV-0.8V). In the first silicon-containing layer, the mass fractions of capacity-type graphite, pre-lithiated silicon oxide material, conductive agent and binder are 83.8%, 11.2%, 1.5% and 3.5%, respectively.

[0094] The third graphite layer contains rate-modified graphite 2 (rate 4C, 350mAh / g, compacted to 1.55g / cm³). 3 In the third graphite layer, the mass fractions of rate-multiplier graphite 2, conductive agent, and binder are 95.9%, 1.3%, and 2.8%, respectively.

[0095] The comparative method for preparing a silicon-containing anode sheet includes the following steps:

[0096] (1) Capacitive graphite, pre-lithiated silicon oxide material, conductive carbon black, single-walled carbon nanotubes, SBR, and PAA-Li were mixed with deionized water at a mass ratio of 83.8%: 11.2%: 1.4%: 0.1%: 1%: 2.5% for the first silicon-containing layer to form a slurry. The slurry was then coated onto the current collector, and its areal density was controlled to be 80% of the entire electrode (excluding the current collector). After drying, a second rolling process was performed, with the first rolling compaction reaching 1.3 g / cm³. 3 The second roller compaction yielded a density of 1.6 g / cm³. 3 The first silicon-containing layer was obtained;

[0097] (2) Mix the rate-multiplier graphite 2, conductive carbon black, CMC-Na, and SBR with deionized water at a mass ratio of 95.9% : 1.3% : 1.3% : 1.5% for the third graphite layer to form a slurry. Coat the slurry onto the surface of the first silicon-containing layer. Control the areal density of the third graphite layer to be 20% of the entire electrode (excluding the current collector). After drying, roll-press the slurry to a compaction density of 1.55 g / cm³. 3 This yields a silicon-containing negative electrode.

[0098] Comparative Example 3

[0099] This comparative example provides a silicon-containing negative electrode sheet, including a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector;

[0100] The negative electrode material layer includes a first silicon-containing layer disposed on the surface of the negative electrode current collector and a third graphite layer disposed on the surface of the first silicon-containing layer;

[0101] The first silicon-containing layer comprises high-capacity graphite (capacity of 355 mAh / g, compaction of 1.6 g / cm³). 3 The first silicon-containing layer negative electrode composite has a specific capacity of 500 mAh / g and a pre-lithiated silicon oxide material (capacity of 1250 mAh / g for 5mV-0.8V). In the first silicon-containing layer, the mass fractions of capacity-type graphite, pre-lithiated silicon oxide material, conductive agent and binder are 79.6%, 15.4%, 1% and 4%, respectively.

[0102] The third graphite layer contains rate-modified graphite 2 (rate 4C, 350mAh / g, compacted to 1.55g / cm³). 3 In the third graphite layer, the mass fractions of rate-multiplier graphite 2, conductive agent, and binder are 95.9%, 1.3%, and 2.8%, respectively.

[0103] The comparative method for preparing a silicon-containing anode sheet includes the following steps:

[0104] (1) Capacitive graphite, pre-lithiated silicon oxide material, conductive carbon black, single-walled carbon nanotubes, SBR, and PAA-Li were mixed with deionized water at a mass ratio of 79.6%:15.4%:0.9%:0.1%:1%:3% (this mass ratio is calculated based on the same compound capacity; the graphite to silicon oxide ratio differs from Comparative Example 1 due to the smaller capacity of silicon oxide, while the proportions of the other components are the same) to form a slurry. The slurry was then coated onto the current collector, and its areal density was controlled to be 80% of the entire electrode sheet (excluding the current collector). After drying, a second rolling press was performed, with the first rolling compaction reaching 1.3 g / cm³. 3 The second roller compaction yielded a density of 1.6 g / cm³. 3 The first silicon-containing layer is obtained;

[0105] (2) Mix the rate-multiplier graphite 2, conductive carbon black, CMC-Na, and SBR with deionized water in a mass ratio of 95.9%:1.3%:1.3%:1.5% for the third graphite layer to form a slurry. Coat the slurry onto the surface of the first silicon-containing layer. Control the areal density of the third graphite layer to be 20% of the entire electrode (excluding the current collector). After drying, roll-press the slurry to a compaction density of 1.55 g / cm³. 3 This yields a silicon-containing negative electrode.

[0106] Comparative Example 4

[0107] This comparative example provides a silicon-containing negative electrode sheet, including a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector;

[0108] The negative electrode material layer includes rate-controlled graphite 2 (4C rate, 350mAh / g, compacted at 1.55g / cm³). 3 The composite material has a specific capacity of 460 mAh / g and a novel porous silicon-carbon material (capacity of 1620 mAh / g for 5mV-0.8V). In the negative electrode material layer, the mass fractions of rate-type graphite 2, novel porous silicon-carbon material, conductive agent and binder are 86.7%, 8.3%, 1.5% and 3.5%, respectively.

[0109] The comparative method for preparing a silicon-containing anode sheet includes the following steps:

[0110] A slurry was prepared by mixing rate-adjustable graphite 2, novel porous silicon-carbon material, conductive carbon black, single-walled carbon nanotubes, SBR, and PAA-Li with deionized water in a mass ratio of 86.7%:8.3%:1.4%:0.1%:1%:2.5%. This slurry was then coated onto a current collector and dried before undergoing a second rolling process. The first rolling compaction resulted in a density of 1.3 g / cm³. 3 The second roller compaction yielded a density of 1.55 g / cm³. 3 This yields a silicon-containing negative electrode.

[0111] Comparative Example 5

[0112] This comparative example provides a silicon-containing negative electrode sheet, including a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector;

[0113] The negative electrode material layer includes rate-controlled graphite 2 (4C rate, 350mAh / g, compacted at 1.55g / cm³). 3 The composite material consists of a pre-lithiated silicon oxide material (capacity of 1250 mAh / g at 5mV-0.8V) and a specific capacity of 460 mAh / g. In the negative electrode material layer, the mass fractions of rate-type graphite 2, pre-lithiated silicon oxide material, conductive agent and binder are 83.3%, 11.7%, 1.5% and 3.5%, respectively.

[0114] The comparative method for preparing a silicon-containing anode sheet includes the following steps:

[0115] A slurry was prepared by mixing high-ratio graphite 2, pre-lithiated silicon oxide material, conductive carbon black, single-walled carbon nanotubes, SBR, and PAA-Li with deionized water in a mass ratio of 83.3%:11.7%:1.4%:0.1%:1%:2.5%. The slurry was then coated onto a current collector and dried before undergoing a second rolling process. The first rolling compaction resulted in a density of 1.3 g / cm³. 3 The second roller compaction yielded a density of 1.55 g / cm³. 3 This yields a silicon-containing negative electrode.

[0116] Comparative Example 6

[0117] This comparative example provides a silicon-containing negative electrode sheet, including a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector;

[0118] The negative electrode material layer includes rate-controlled graphite 2 (4C rate, 350mAh / g, compacted at 1.55g / cm³). 3 In the negative electrode material layer, the mass fractions of rate-multiplying graphite 2, conductive agent, and binder are 95.9%, 1.3%, and 2.8%, respectively.

[0119] The comparative method for preparing a silicon-containing anode sheet includes the following steps:

[0120] A slurry was prepared by mixing ratio-type graphite 2, conductive carbon black, CMC-Na, and SBR with deionized water at a mass ratio of 95.9%:1.3%:1.3%:1.5%. The slurry was then coated onto a current collector, dried, and rolled to a compaction density of 1.55 g / cm³. 3 This yields the negative electrode.

[0121] Comparative Example 7

[0122] This comparative example provides a silicon-containing negative electrode sheet, including a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector;

[0123] The negative electrode material layer includes a first silicon-containing layer disposed on the surface of the negative electrode current collector, a second silicon-containing layer disposed on the surface of the first silicon-containing layer, and a third graphite layer disposed on the surface of the second silicon-containing layer.

[0124] The first silicon-containing layer comprises high-capacity graphite (capacity of 355 mAh / g, compaction of 1.6 g / cm³). 3 The first silicon-containing layer contains a composite of a pre-lithiated silicon oxide material (capacity of 1250 mAh / g at 5mV-0.8V) and a pre-lithiated silicon oxide material (capacity of 1250 mAh / g at 5mV-0.8V), with a specific capacity of 460 mAh / g. The mass fractions of the capacity-type graphite, pre-lithiated silicon oxide material, conductive agent and binder in the first silicon-containing layer are 84.3%, 11.2%, 1% and 3.5%, respectively.

[0125] The second silicon-containing layer comprises rate-modified graphite 1 (rate 2.5C, 350mAh / g, compacted at 1.6g / cm³). 3 The composite material contains a novel porous silicon-carbon material (capacity of 1620 mAh / g at 5mV-0.8V) with a specific capacity of 500 mAh / g. In the second silicon-containing layer, the mass fractions of rate-multiplier graphite 1, novel porous silicon-carbon, conductive agent and binder are 83.2%, 11.3%, 1.5% and 4%, respectively.

[0126] The third graphite layer contains rate-modified graphite 2 (rate 4C, 350mAh / g, compacted to 1.55g / cm³). 3 In the third graphite layer, the mass fractions of rate-multiplier graphite 2, conductive agent, and binder are 95.9%, 1.3%, and 2.8%, respectively.

[0127] The comparative method for preparing a silicon-containing anode sheet includes the following steps:

[0128] (1) Capacitive graphite, pre-lithiated silicon oxide material, conductive carbon black, single-walled carbon nanotubes, SBR, and PAA-Li are mixed with deionized water in a mass ratio of 84.3%:11.2%:0.9%:0.1%:1%:2.5% of the first silicon-containing layer to form slurry 1.

[0129] Slurry 2 is formed by mixing deionized water with a ratio of 1: 83.2%: 11.3%: 1.4%: 0.1%: 1%: 3% of the second silicon-containing layer.

[0130] Slurry 1 and slurry 2 were coated onto the current collector using a double-layer coating technique. The areal density of the first silicon-containing layer was controlled to be 40% of the entire electrode (excluding the current collector), and the areal density of the second silicon-containing layer was also controlled to be 40% of the entire electrode (excluding the current collector). After drying, a second rolling process was performed, with the compaction point of the first rolling being 1.3 g / cm³. 3The second roller compaction yielded a density of 1.6 g / cm³. 3 .

[0131] (2) Mix the rate-multiplier graphite 2, carbon black, CMC-Na, and SBR with deionized water at a mass ratio of 95.9%:1.3%:1.3%:1.5% for the third graphite layer to form a slurry 3. Coat the slurry 3 onto the surface of the second silicon-containing layer, controlling the areal density of the third graphite layer to be 20% of the entire electrode (excluding the current collector). After drying, roll-press the slurry, controlling the compaction to be 1.55 g / cm³. 3 This yields a silicon-containing negative electrode.

[0132] The electrode compositions of Examples 1-3 and Comparative Examples 1-7 are briefly summarized as shown in Table 1.

[0133] Table 1

[0134]

[0135]

[0136] In order to compare the technical effects of the various embodiments and comparative examples, the following experimental examples are provided.

[0137] The specific manufacturing method of the lithium-ion batteries assembled from the silicon-containing negative electrode sheets obtained in Examples 1-3 and Comparative Examples 1-7 is as follows:

[0138] Positive electrode sheet: NCM-9 series as the positive electrode active material, conductive carbon black as the conductive agent, and PVDF as the binder are mixed with NMP at a mass ratio of 96.7%:2%:1.3% to obtain a positive electrode slurry. The positive electrode slurry is coated onto the surface of the positive electrode current collector aluminum foil, and then dried, rolled, and slit to obtain the positive electrode sheet. The positive electrode compaction is 3.45 g / cm³. 3 The surface density of the positive electrode is 300-400 g / m³. 2 (The areal density is designed based on an N / P ratio of 1.12. The N / P ratio is the ratio of the negative electrode capacity to the positive electrode capacity for the same area. Since the negative electrode areal density is the same in this invention, the positive electrode areal density needs to be calculated using the N / P ratio.)

[0139] Negative electrode sheet: The negative electrode sheet obtained in the examples and comparative examples is cut to obtain the cut negative electrode sheet.

[0140] The above-mentioned positive electrode, negative electrode and separator (purchased) are stacked to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried and then injected with electrolyte (1M LiPF6, DMC:EMC:FEC:EC=40:40:15:5), and after vacuum sealing, standing, formation, aging and capacity testing, a lithium-ion battery is obtained.

[0141] The lithium-ion batteries prepared in each embodiment and comparative example were then subjected to electrical performance tests, and the test results are shown in Table 2.

[0142] The negative electrode surface density was determined by weighing 10 cm⁻¹ using an analytical balance. 2 The wafer mass was obtained, and the negative electrode surface density (g / m³) was calculated. 2 = 10cm of the negative electrode sheet (including foil) 2 Disc mass value (mg / 10cm) 2 )- 10cm of foil 2 Disc mass value (mg / 10cm) 2 );

[0143] Energy density (Wh / kg) = Discharge energy obtained from battery capacity testing (Wh) / Battery weight (kg);

[0144] Method for detecting the full-charge expansion rate of negative electrode sheet: Use a micrometer to measure the thickness of the negative electrode sheet after rolling and in the fully charged state, and calculate the full-charge expansion rate using the formula: Full-charge expansion rate = (Thickness of negative electrode sheet in the fully charged state - Thickness of negative electrode sheet after rolling) / (Thickness of negative electrode sheet after rolling - Thickness of foil material).

[0145] 4C rate charging capacity retention rate test method: At 25℃, use the Xinwei charge and discharge test cabinet to charge the battery at a constant current rate of 0.33C to 4.2V, and record the battery charging capacity as C0. Then, discharge the battery at a constant current rate of 0.33C to 2.5V, and then charge the battery at a constant current rate of 4C to 4.2V, and record the 4C charging capacity as C1. 4C rate charging capacity retention rate = C1 / C0;

[0146] 2.5C / 1C Fast Charging Cycle Test Method: At 25℃, use the Xinwei charge / discharge test cabinet to perform charge / discharge cycles on the battery according to the following steps: 1) Charge at a constant current of 2.5C step to 4.2V, then charge at a constant voltage of 0.05C; 2) Let stand for 5 minutes; 3) Discharge at a constant current of 1C rate to 2.8V; 4) Let stand for 5 minutes; Perform cycle tests according to steps 1)-4). When the capacity retention rate reaches 80% or below in the nth cycle, n is counted as the number of 2.5C / 1C fast charging cycles. Capacity retention rate = discharge capacity in the nth cycle / discharge capacity in the 1st cycle.

[0147] Table 2

[0148]

[0149]

[0150] Comparing the data from Examples 1-3 and Comparative Examples 1-7, it can be demonstrated that: when the silicon-containing layer is on the outermost layer (closest to the separator), the rate performance of silicon-carbon / silicon-oxygen is worse than that of graphite, resulting in a lower 4C rate charging capacity retention rate and a shorter 2.5C / 1C cycle life (Comparative Examples 4 and 5); when the graphite layer is on the outermost layer, the 4C rate charging capacity retention rate of the cell is better, with the negative electrode being a pure graphite layer (Comparative Example 6), which has the best rate performance and the longest fast charging cycle life, but the lowest energy density; when only one silicon-containing layer is set inside the graphite layer (Comparative Examples 1, 2, and 3), due to the respective characteristics of silicon-carbon and silicon-oxygen... The battery cannot simultaneously achieve high energy density and long fast-charging cycle life (the inner layer only has one layer of graphite / novel porous silicon-carbon anode, and the new porous silicon-carbon anode has poor rate performance, resulting in little improvement in fast-charging performance; the inner layer only has one layer of graphite / silicon-oxygen anode, and the silicon-oxygen anode expands greatly when fully charged, making it prone to active material peeling, leading to a drop in cycle life); when the silicon-oxygen layer is the innermost layer (closest to the current collector side) and the silicon-carbon layer is the middle layer (Comparative Example 7), the silicon-oxygen anode expands greatly when fully charged, making it prone to active material peeling, resulting in cycle deterioration, and the silicon-carbon layer has poor rate performance, so as an intermediate layer, it cannot help lithium ions migrate quickly to the inner layer.

[0151] It is evident that a more rational design of the electrode end is needed based on the inherent characteristics of the material itself. This invention sets the graphite layer as the outermost layer, utilizing the rapid lithium-ion diffusion characteristic of rate-adjustable graphite to effectively improve the overall rate performance of the electrode and prevent lithium plating on the negative electrode surface. The silicon-oxygen layer is set as the middle layer, primarily utilizing the better rate performance of silicon-oxygen negative electrodes compared to silicon-carbon negative electrodes, providing a buffer layer for the slowed lithium-ion diffusion rate. Considering the significant expansion of silicon-oxygen negative electrodes, placing it in the middle layer provides effective buffer space for particle expansion in the longitudinal thickness direction, reducing the expansion of the electrode itself. The silicon-carbon layer is set as the inner layer, mainly considering the high capacity and small expansion of silicon-carbon, ensuring the cell's energy density while preventing active material shedding due to significant particle expansion, thus guaranteeing cycle life. The synergistic effect of the three layers establishes a gradient channel (fast-buffered-slow) for lithium-ion transport in the longitudinal direction, enabling the cell to balance energy density and fast-charging performance (Examples 1, 2, and 3).

[0152] Furthermore, a comparison of Examples 1, 2, and 3 shows that the areal density ratio of the three-layer structure also has a certain impact on performance. When the areal density ratio of the first silicon-containing layer, the second silicon-containing layer, and the third graphite layer is 50%:30%:20%, the cell exhibits the best overall performance.

[0153] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A silicon-containing negative electrode sheet, characterized by, It includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the current collector; The negative electrode material layer includes a first silicon-containing layer disposed on the surface of the negative electrode current collector, a second silicon-containing layer disposed on the surface of the first silicon-containing layer, and a third graphite layer disposed on the surface of the second silicon-containing layer. The first silicon-containing layer comprises capacity-enhancing graphite and porous silicon-carbon material; the second silicon-containing layer comprises rate-enhancing graphite and pre-lithiated silicon oxide material; and the third graphite layer comprises rate-enhancing graphite. The capacity of the capacity-enhancing graphite in the first silicon-containing layer is 355-360 mAh / g, and the compaction density is 1.6-1.7 g / cm³. 3 The porous silicon-carbon material has a capacity of 1600-1750 mAh / g at 5mV-0.8V; the rate-multiplier graphite in the second silicon-containing layer and the third graphite layer has a capacity of 345-355 mAh / g and a compaction density of 1.5-1.65 g / cm³. 3 The rate factor of the rate-multiplier graphite in the second silicon-containing layer is 1-1.5C lower than that of the rate-multiplier graphite in the third graphite layer; the pre-lithiated silicon oxide material in the second silicon-containing layer has a capacity of 1200-1350mAh / g at 5mV-0.8V. The areal density of the first silicon-containing layer accounts for 50-55% of the areal density of the negative electrode material, the areal density of the second silicon-containing layer accounts for 30-35% of the areal density of the negative electrode material, and the areal density of the third graphite layer accounts for 10-20% of the areal density of the negative electrode material. The raw materials used to form the first silicon-containing layer include capacity-type graphite, porous silicon-carbon material, conductive agent, and binder. With the total mass of all raw materials used to form the first silicon-containing layer being 100%, the mass fraction ratio of the capacity-type graphite, porous silicon-carbon material, conductive agent, and binder is (83.5%-88.4%): (7.6%-11.5%): (0.5%-1%): (3.5%-4%). The raw materials used to form the second silicon-containing layer include rate-multiplied graphite, pre-lithiated silicon oxide material, conductive agent, and binder. With the total mass of all raw materials used to form the second silicon-containing layer being 100%, the mass fraction ratio of the rate-multiplied graphite, pre-lithiated silicon oxide material, conductive agent, and binder is (83.3%-88.5%): (7.5%-11.7%): (1%-1.5%): (3%-4%). The raw materials used to form the third graphite layer include rate-multiplied graphite, a conductive agent, and a binder. With the total mass of all raw materials used to form the third graphite layer being 100%, the mass ratio of the rate-multiplied graphite, the conductive agent, and the binder is (95.5%-96.5%):(1%-1.5%):(2.5%-3%). The binders in the first and second silicon-containing layers include styrene-butadiene rubber and lithium polyacrylate, and the mass fraction ratio of the binders in the second silicon-containing layer is less than or equal to the mass fraction ratio of the binders in the first silicon-containing layer.

2. The silicon-containing negative electrode sheet according to claim 1, characterized by The conductive agents in the first silicon-containing layer, the second silicon-containing layer, and the third graphite layer include conductive carbon black and / or carbon nanotubes; And / or, the binder in the third graphite layer includes at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylic acid, or lithium polyacrylate.

3. The silicon-containing negative electrode sheet according to claim 2, characterized by The conductive agents in the first silicon-containing layer and the second silicon-containing layer include conductive carbon black and single-walled carbon nanotubes.

4. The silicon-containing negative electrode sheet according to claim 1, characterized by The specific capacity of the second silicon-containing negative electrode composite is less than or equal to that of the first silicon-containing negative electrode composite.

5. The method of producing a silicon-containing negative electrode sheet according to any one of claims 1 to 4, characterized by, Includes the following steps: (a) A raw material for forming a first silicon-containing layer and a raw material for forming a second silicon-containing layer are coated on at least one side of the current collector using a double-coating technique, and then dried to form a first silicon-containing layer and a second silicon-containing layer, respectively, and then the first silicon-containing layer and the second silicon-containing layer are rolled. (b) Coating the surface of the second silicon-containing layer with raw materials for forming the third graphite layer, then drying to form the third graphite layer, and then rolling the entire electrode sheet to obtain a silicon-containing negative electrode sheet.

6. The method of producing a silicon-containing negative electrode sheet according to claim 5, characterized by, In step (a), the rolling comprises a first rolling and a second rolling, the first rolling is compacted to 1.3-1.4 g / cm 3 , and the second rolling is compacted to 1.6-1.65 g / cm 3 . And / or, in the step (b), the roller compaction is 1.55-1.6 g / cm 3 .

7. A lithium-ion battery, characterized by It includes the silicon-containing anode sheet according to any one of claims 1-4 and the silicon-containing anode sheet prepared by the preparation method according to claim 5 or 6.

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