A multilayer negative electrode, a secondary battery, and an electric device

Abstract

This application provides a multilayer negative electrode, a secondary battery, and an electrical device. This application achieves this through multilayer coating, ensuring that the gap between adjacent coatings satisfies 0.2 ≤ f. m =K m / K m‑1 -K m‑1 / K m‑2 / S m‑1 ≤1.2, K=C×H / B, S=(Dv90-Dv10) / Dv50, where C represents the content of conductive agent in a certain coating; B represents the content of silicon material in a certain coating; H is the thickness of a certain coating layer; and S represents the particle size parameter of silicon material in a certain coating. Satisfying the above relationships allows the negative electrode sheet to impart good dynamic performance to the battery even with a relatively large thickness. When the thickness of the negative electrode sheet is 200μm or more, it still imparts to the battery DCR≤0.42mΩ, 3C charging capacity retention ≥84.8%, and 80% capacity retention cycle count >1050 cycles at 25℃.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a multilayer negative electrode, a secondary battery, and an electrical device. Background Technology

[0002] With the widespread application of electrochemical energy storage in electric vehicles (EVs), the requirements and reliance on lithium-ion batteries (LIBs) have become increasingly stringent, especially for high-capacity batteries (e.g., 100kWh, with a range >700km). Silicon, due to its high theoretical specific capacity and low lithium insertion / extraction potential, is considered an ideal anode material for high-energy-density batteries. To further meet the demand for increased battery capacity, it is necessary to increase the silicon content in the anode or increase the thickness of the anode sheet. However, 1) increasing the silicon content leads to significant volume expansion, which in turn accelerates capacity decay; 2) increasing the thickness of the anode sheet reduces the kinetic performance of the lithium battery, affecting fast-charging applications.

[0003] Therefore, there is a need for a multilayer negative electrode for secondary batteries that combines high capacity and excellent kinetic performance. Summary of the Invention

[0004] The purpose of this application is to provide a multilayer negative electrode for secondary batteries that combines high capacity and excellent kinetic performance.

[0005] To achieve the above objectives, a first aspect of this application provides a multilayer negative electrode, comprising a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. The negative electrode active layer comprises different coatings stacked together. The coatings in the negative electrode active layer are sequentially designated as layer 1, layer 2, ... to layer m, starting from the side closest to the current collector, and the number of coating layers m ≥ 3. Each of the coatings independently comprises: a carbon material, a silicon material, a conductive agent, and a binder. The multilayer negative electrode satisfies the following relationship:

[0006] 0.2≤f m =|K m / K m-1 -K m-1 / K m-2 | / S m-1 ≤1.2

[0007] K = C × H / B

[0008] S=(Dv90-Dv10) / Dv50

[0009] K m ≠K m-1 ≠K m-2

[0010] In the formula, C represents the mass percentage content of the conductive agent based on the total weight of any of the coatings;

[0011] B represents the mass percentage of the silicon material based on the total weight of any of the coatings described;

[0012] Hμm represents the thickness of any of the coatings described;

[0013] Dv10μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 10%;

[0014] Dv50μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 50%;

[0015] Dv90μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 90%;

[0016] The subscript m indicates the m-th layer of coating; the subscript m-1 indicates the (m-1)-th layer of coating; the subscript m-2 indicates the (m-2)-th layer of coating.

[0017] As an embodiment of this application, the thickness H of any of the coatings satisfies: 50μm≤H≤150μm.

[0018] As an embodiment of this application, the multilayer negative electrode satisfies: 0.1% ≤ C ≤ 9%.

[0019] As an embodiment of this application, the multilayer negative electrode satisfies: 1% ≤ B ≤ 15%.

[0020] As an embodiment of this application, the mass percentage of the carbon material, based on the total weight of any of the coatings, is denoted as A, satisfying: 70% ≤ A ≤ 99%.

[0021] As an embodiment of this application, the mass percentage of the adhesive, based on the total weight of any of the coatings, is denoted as D, satisfying: 0.1% ≤ D ≤ 6%.

[0022] As an embodiment of this application, the particle size of the silicon material satisfies: 1μm≤Dv10≤6μm.

[0023] As an embodiment of this application, the particle size of the silicon material satisfies: 8μm≤Dv50≤10μm.

[0024] As an embodiment of this application, the particle size of the silicon material satisfies: 12μm≤Dv90≤16μm.

[0025] As an embodiment of this application, the particle size of the carbon material satisfies: 1μm≤Dv10'≤8μm, where Dv10' represents the particle size corresponding to when the cumulative volume of the carbon material reaches 10%, in μm.

[0026] As an embodiment of this application, the particle size of the carbon material satisfies: 9μm≤Dv50'≤14μm, D V 50' represents the particle size corresponding to when the cumulative volume of the carbon material reaches 50%, in μm.

[0027] As an embodiment of this application, the particle size of the carbon material satisfies: 16μm≤Dv90'≤24μm, D V 90' represents the particle size corresponding to when the cumulative volume of the carbon material reaches 90%, in μm.

[0028] A second aspect of this application provides a secondary battery comprising a positive electrode, an electrolyte, a separator, and the multilayer negative electrode described in the first aspect of this invention.

[0029] A third aspect of this application provides an electrical device comprising the secondary battery described in the second aspect of this application.

[0030] Compared with the prior art, the beneficial effects of this application are:

[0031] This application, through multi-layer coating and reasonable design of parameters such as the component dosage in each coating, enables adjacent coatings to satisfy the aforementioned specific relationships, thereby improving the conductive network structure of the entire negative electrode sheet. This allows the negative electrode sheet to still impart good dynamic performance to the battery even with a relatively large thickness.

[0032] The thickness of the negative electrode sheet in this application can reach 200μm or more, and up to 350μm, with DCR ≤ 0.42mΩ; 3C charging capacity retention rate ≥ 84.8%; and 80% capacity retention cycle number at 25℃ > 1050 cycles. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0035] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0036] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0037] A first aspect of this application provides a multilayer negative electrode, comprising a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. The negative electrode active layer comprises different coatings stacked together. The coatings in the negative electrode active layer are sequentially designated as layer 1, layer 2, ... to layer m, starting from the side closest to the current collector, and the number of coating layers m ≥ 3. Each of the coatings independently comprises: a carbon material, a silicon material, a conductive agent, and a binder. The multilayer negative electrode satisfies the following relationship:

[0038] 0.2≤f m =|K m / K m-1 -K m-1 / K m-2 | / S m-1 ≤1.2

[0039] K = C × H / B

[0040] S=(Dv90-Dv10) / Dv50

[0041] K m ≠K m-1 ≠K m-2

[0042] In the formula, C represents the mass percentage content of the conductive agent based on the total weight of any of the coatings;

[0043] B represents the mass percentage of the silicon material based on the total weight of any of the coatings described;

[0044] Hμm represents the thickness of any of the coatings described;

[0045] Dv10μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 10%;

[0046] Dv50μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 50%;

[0047] Dv90μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 90%;

[0048] The subscript m indicates the m-th layer of coating; the subscript m-1 indicates the (m-1)-th layer of coating; the subscript m-2 indicates the (m-2)-th layer of coating.

[0049] The negative electrode of a secondary battery is typically composed of a negative electrode active material (silicon or carbon), a conductive agent, and a binder. The conductive agent accelerates the conduction of ions and electrons; too low a content will affect the conductivity of the negative electrode, while too high a content will affect the capacity. The binder ensures good contact between the active materials and with the current collector, but too high a content will affect the kinetic performance of the negative electrode. A larger electrode thickness can increase the amount of active material per unit area, thereby increasing the energy density of the battery, but increasing the thickness will worsen the kinetic performance of the negative electrode and increase the risk of lithium plating.

[0050] In addition to the fact that the amount of each component in the negative electrode sheet has a certain impact on the battery performance, the interaction between the components also affects the distribution of each component in the active coating, thereby forming a coating with different microstructures. The microstructure of the coating affects the ionic conductivity and mechanical strength of the electrode sheet, and thus affects the rate performance and cycle stability of the battery.

[0051] Therefore, this application improves the conductive network structure of the entire negative electrode sheet by using multi-layer coating and rationally designing parameters such as component dosage and particle size structure in each coating to ensure that adjacent coatings meet the above-mentioned specific relationships. This allows the negative electrode sheet to still impart good dynamic performance to the battery, especially rate performance and cycle stability, even with a larger thickness.

[0052] In some embodiments of this application, the thickness H of any of the coatings satisfies: 50 μm ≤ H ≤ 150 μm. Specifically, the thickness can be any value or a range formed by any two of the following: 50 μm, 60 μm, 80 μm, 90 μm, 100 μm, and 150 μm. As the thickness increases, a higher energy density can be imparted to the secondary battery. Through the rational design of the negative electrode sheet in this application, within this thickness range, the battery can possess both high energy density and excellent charge-discharge kinetic performance.

[0053] In some embodiments of this application, the multilayer negative electrode satisfies: 0.1% ≤ C ≤ 9%. C represents the content of conductive agent in a certain coating. Within the above-mentioned suitable range, the conductive agent can impart excellent ion conductivity and capacity to the battery. The value of C can specifically be any value or a range formed by any two of the following: 0.1%, 0.6%, 0.8%, 3%, 6%, 9%.

[0054] In some embodiments of this application, the multilayer negative electrode satisfies: 1% ≤ B ≤ 15%. B represents the silicon content in a certain coating. Silicon material has a high theoretical specific capacity, reaching 400–4000 mAh / g, which can impart high energy density to the battery; it also has a low lithium insertion / extraction potential and helps to avoid lithium plating on the surface during charging, thereby improving battery safety. Therefore, silicon material is one of the promising negative electrode active materials in the art. When the silicon content in the coating is within the above range, the battery can possess both high specific capacity and good kinetic cycle performance. The value of B can be any value from 1%, 4%, 6%, 10%, 12%, and 15%, or a range formed by any two values.

[0055] In some embodiments of this application, the mass percentage of the carbon material, denoted as A, is based on the total weight of any of the coatings, satisfying: 70% ≤ A ≤ 99%. Carbon material is one of the common negative electrode active materials in the art, possessing excellent conductivity and capable of imparting excellent ion conduction and rate performance to the battery. Within the aforementioned suitable range, carbon material can endow the battery with excellent ion conduction performance and kinetic cycle stability. The value of A can be any value from 71.5%, 81%, 89.8%, 95.3%, 98.3%, or a range formed by any two values.

[0056] In addition, the particle size structure parameters of the negative electrode active material (including) will also affect its distribution in the coating. A suitable particle size distribution can ensure that lithium ions are inserted and extracted more quickly. Therefore, a reasonable adjustment of the particle size distribution of the active material helps to further improve the compaction density of the electrode and thus improve the volumetric energy density of the battery, while also improving the cycle and rate performance of the battery.

[0057] In some embodiments of this application, the particle size of the silicon material satisfies: 1μm≤Dv10≤6μm. The value of Dv10 can be any value among 1μm, 2μm, 3μm, 5μm, and 6μm, or a range formed by any two values.

[0058] In some embodiments of this application, the particle size of the silicon material satisfies: 8μm ≤ Dv50 ≤ 10μm. The value of Dv50 can be any value among 8μm, 9μm, and 10μm, or a range formed by any two values.

[0059] In some embodiments of this application, the particle size of the silicon material satisfies: 12μm≤Dv90≤16μm. The value of Dv90 can be any value among 12μm, 13μm, 14μm, 15μm, and 16μm, or a range formed by any two values.

[0060] In some embodiments of this application, the particle size of the carbon material satisfies: 1μm≤Dv10'≤8μm, where Dv10' represents the particle size corresponding to when the cumulative volume of the carbon material reaches 10%, in μm. The value of Dv10' can be any value among 1μm, 3μm, 5μm, and 8μm, or a range formed by any two values.

[0061] In some embodiments of this application, the particle size of the carbon material satisfies: 9μm≤Dv50'≤14μm, where Dv50' represents the particle size corresponding to when the cumulative volume of the carbon material reaches 50%, in μm. The value of Dv50' can be any value among 9μm, 11μm, 13μm, and 14μm, or a range formed by any two values.

[0062] In some embodiments of this application, the particle size of the carbon material satisfies: 16μm≤Dv90'≤24μm, where Dv90' represents the particle size corresponding to 90% of the total volume of the carbon material, in μm. The value of Dv90' can be any value among 16μm, 18μm, 20μm, 22μm, and 24μm, or a range formed by any two values.

[0063] In some embodiments of this application, the mass percentage of the adhesive, based on the total weight of any of the coatings, is denoted as D, satisfying: 0.1% ≤ D ≤ 6%. The value of D can specifically be any value from 0.1%, 0.5%, 1%, 2%, 3%, 6%, or a range formed by any two values.

[0064] This application does not limit the types of carbon and silicon materials. Commonly used carbon anode active materials, silicon anode active materials, and silicon-carbon composite anode active materials can all be used in this application to prepare multilayer anodes. For example, the carbon materials include, but are not limited to, at least one of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, and soft carbon. The silicon materials include, but are not limited to, at least one of silicon dioxide and silicon suboxide. The silicon-carbon composite anode active materials include, but are not limited to, at least one of carbon-coated silicon oxide, carbon-coated pre-lithiated silicon oxide, and carbon-coated pre-magnesiumized silicon oxide.

[0065] This application does not limit the types of conductive agents and binders. Common conductive agents and binders in the art can all be used in this application, and can be selected as needed. For example, the conductive agent includes, but is not limited to, at least one of conductive graphite, carbon black, carbon fiber, carbon nanotubes, and graphene. The binder includes, but is not limited to, at least one of polyvinyl alcohol, polyacrylic acid, polytetrafluoroethylene, sodium carboxymethyl cellulose, SBR rubber, fluorinated rubber, polyolefin, polyvinylidene fluoride, and polyurethane.

[0066] This application does not limit the type of negative electrode current collector; any negative electrode current collector commonly used in the art can be used to prepare the negative electrode sheet in this application. In some embodiments, the negative electrode current collector is preferably made of copper foil or carbon-coated copper foil, etc.

[0067] In this application, the fabrication process of the multilayer negative electrode includes the following steps:

[0068] (1) Dissolve the carbon material, silicon material, conductive agent and binder in a solvent and stir to form a uniform slurry, and prepare n portions of slurry using the same method. Depending on actual needs, the composition and structure of these n portions of slurry can be the same or different.

[0069] (2) The n portions of uniform slurry are simultaneously discharged through a die head with n discharge sections, and after drying in a drying oven and rolling in a roller press, the multilayer negative electrode is obtained.

[0070] In this application, the thickness of the active material layer is determined by the opening width of the die head and the rolling pressure.

[0071] In some embodiments, the solvent used to form the slurry in step (1) includes, but is not limited to, at least one of N-methylpyrrolidone and water. It should be noted that, in this application, the total weight of any of the above-mentioned "coatings" does not include the solvent used to form the slurry during the calculation process.

[0072] A second aspect of this application provides a secondary battery comprising a positive electrode, an electrolyte, a separator, and the multilayer negative electrode described in the first aspect of this invention.

[0073] The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, wherein the positive active layer includes a positive active material. This application does not limit the type of positive active material; commonly used positive active materials in the art can be used to prepare secondary batteries in this application. The positive active material includes, but is not limited to, at least one of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium nickel cobalt manganese oxide (NCM).

[0074] In this application, the type of positive electrode current collector is not limited. The positive electrode current collector can be made of metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, etc.; carbon materials such as carbon cloth and carbon paper; or composite materials formed by polymer and metal layer. In some embodiments, aluminum foil is preferably used as the positive electrode current collector.

[0075] In some embodiments, there is no limitation on the type of solvent used to form the positive electrode slurry, as long as it is a solvent capable of dissolving or dispersing the positive electrode active material, conductive agent, binder, and dispersant.

[0076] In the secondary battery described in this application, the type of separator is not particularly limited and can be selected according to actual needs. The separator can be a polypropylene membrane, a polyethylene membrane, a polyvinylidene fluoride membrane, a spandex membrane, an aramid membrane, or a multilayer composite membrane modified with a coating.

[0077] In some embodiments, the preparation of a secondary battery includes: stacking a positive electrode, a separator, and a negative electrode in sequence, with the separator acting as a separator between the positive and negative electrodes; then winding the cells into a square bare cell, inserting it into a battery casing, baking it at 65–95°C to remove water, injecting electrolyte, sealing it, and then performing processes such as settling, hot and cold pressing, formation, clamping, and capacity testing to obtain a secondary battery.

[0078] In some embodiments, the secondary battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging may also be a soft pack, such as a pouch, made of plastic, such as one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate. The shape of the secondary battery is not particularly limited; it may be cylindrical, square, or any other arbitrary shape.

[0079] A third aspect of this application provides an electrical device, which includes the secondary battery described in the second aspect of this application. The electrical device can be an application device such as a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool. Vehicles can be new energy vehicles, including pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles; spacecraft include airplanes, rockets, space shuttles, and spacecraft; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. This application does not impose special limitations on the above-mentioned device.

[0080] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[0081] Examples 1-9, Comparative Examples 1-3

[0082] A multilayer negative electrode is provided, and its preparation method includes the following steps:

[0083] (1) According to the formula in Table 1, carbon material (artificial graphite is selected in this embodiment), silicon material (SiO is selected in this embodiment), conductive agent acetylene black (Super P) and binder polyacrylic acid are dissolved in deionized water and stirred to form a uniform slurry. Three slurries are prepared using the same method.

[0084] (2) The three portions of slurry prepared in step (1) are fed into a die head with three openings through three feeding ports, and then simultaneously discharged onto a 4.5 μm copper foil. After drying in a drying oven and rolling in a roller press, a multilayer negative electrode with three active material layers coated on the current collector is obtained (compacted density of 1.6 g / cm³). 3 ), wherein the relevant parameters of each of the three negative electrodes are detailed in Table 1.

[0085] Table 1

[0086]

[0087]

[0088] Note: In Table 1, the particle size of silicon material is represented by Dv90, Dv50, and Dv10; the particle size of silicon material is represented by Dv90', Dv50', and Dv10'.

[0089] The negative electrode sheets prepared in the above embodiments and comparative examples were used to prepare secondary batteries, and then the kinetic performance of the secondary batteries was tested.

[0090] The preparation of secondary batteries includes the following steps:

[0091] Preparation of positive electrode sheet

[0092] The positive electrode active material (LiNi) 0.8 Co 0.1 Mn 0.1 A mixture of positive electrode active material (O2), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) at a mass ratio of 94:3:3 was thoroughly mixed and then uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black paste. This black paste was then coated onto both sides of an aluminum foil, baked, rolled, and cut into sheets to obtain a compacted density of 0.33 g / cm³. 3 The positive electrode sheet.

[0093] Electrolyte preparation

[0094] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) were mixed in a volume ratio of 3:6.5:0.5 to obtain a mixed organic solvent. LiPF6 was then dissolved in the mixed organic solvent and mixed evenly to obtain an electrolyte with a lithium ion concentration of 1 mol / L.

[0095] Assembly of secondary batteries

[0096] The prepared positive electrode, separator (polypropylene separator, Celgard 2300, purchased from Celgard in the United States), and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrodes. Then they are wound into a cell, shaped by hot pressing, and the tabs are welded to obtain a bare battery. The battery is then installed in a square aluminum shell and undergoes top and side sealing, electrolyte injection, formation, and sorting processes to obtain a lithium-ion secondary battery.

[0097] The specific performance tests for the secondary batteries are as follows:

[0098] (1) Room temperature internal resistance (DCR) test: At 25±2℃, the square aluminum shell lithium-ion secondary batteries obtained in the examples and comparative examples were charged to 4.25V at 1C, then discharged at 1C capacity for 30min, adjusted to 50% SOC, and then discharged at 3C constant current pulse discharge for 10s and charged for 10s. The DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current × 100%. The results are shown in Table 2.

[0099] (2) Room temperature rate charging test: At 25±2℃, the square aluminum-cased lithium-ion secondary batteries obtained in the examples and comparative examples were discharged to 2.5V at 1C and then charged to 4.25V at yC. The above discharge and charge process was repeated at y = 0.33, 0.5, 1, 2 and 3 respectively. The capacity obtained by charging at 0.33C was taken as the initial discharge capacity. The capacity retention rate at 1C, 2C, 3C and 4C was calculated by dividing the capacity obtained at yC by the initial discharge capacity by 100%. The results are shown in Table 2.

[0100] (3) Room temperature cycle performance test: At 25±2℃, the square aluminum-cased lithium-ion secondary batteries obtained in the examples and comparative examples were subjected to charge-discharge cycle tests in the range of 2.5~4.25V at a charge-discharge rate of 2.2C / 1C, and the number of cycles in which the battery capacity retention rate was 80% was recorded. 80% capacity retention rate = discharge capacity / first cycle discharge capacity × 100%, and the recorded data are shown in Table 2.

[0101] Table 2

[0102]

[0103]

[0104] The results above show that:

[0105] The lithium-ion batteries prepared according to the embodiments of this application exhibit superior overall performance, namely, with an electrode thickness ≥ 200 μm: DCR ≤ 0.42 mΩ; 3C charging capacity retention ≥ 84.8%; and 80% capacity retention cycle count at 25°C > 1050 cycles. Therefore, the multilayer electrodes prepared under the above conditions of this application can effectively reduce the DCR of lithium batteries, thereby improving the fast-charging performance of lithium batteries and increasing their service life to meet the increasing market demand for practical products.

[0106] As shown in Tables 1 and 2, a comparison between Example 1 and Comparative Example 1 reveals that when the total electrode thickness is consistent, the application of a multilayer electrode scheme can effectively reduce the DCR of the lithium battery, thereby improving the fast-charging performance and optimizing the cycle life. This is because the multilayer electrode scheme allows for a more rational allocation of the additive components in the electrode, further enhancing electrode conductivity.

[0107] In Tables 1 and 2, through comparisons of Examples 2 and 5 and Comparative Examples 2-4, it can be seen that when the content of each component, particle size distribution, and electrode thickness in the multilayer electrode form a functional relationship f... m Satisfy 0.2≤f m When the content is ≤1.2, the conductive agent and electrode structure corresponding to the change in silicon content can effectively improve the poor electronic conductivity of silicon materials. Combined with the advantage of the strong ionic conductivity of silicon materials, the DCR of lithium batteries is significantly reduced, and the fast charging performance and cycle life are also significantly improved.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A multilayer negative electrode, characterized in that, The multilayer negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active layer includes different coatings stacked together. In the negative electrode active layer, the coatings are sequentially labeled as layer 1, layer 2, ... to layer m, starting from the side closest to the current collector, and the number of coating layers m ≥ 3. Each of the coatings independently contains: carbon material, silicon material, conductive agent, and binder. The multilayer negative electrode satisfies the following relationship: 0.2≤f m =|K m / K m-1 -K m-1 / K m-2 | / S m-1 ≤1.2 K = C × H / B S=(Dv90-Dv10) / Dv50 K m ≠K m-1 ≠K m-2 In the formula, C represents the mass percentage content of the conductive agent based on the total weight of any of the coatings; B represents the mass percentage of the silicon material based on the total weight of any of the coatings described; Hμm represents the thickness of any of the coatings described; Dv10μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 10%; Dv50μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 50%; Dv90μm represents the particle size corresponding to when the cumulative volume of the silicon material reaches 90%; The subscript m indicates the m-th coating layer; the subscript m-1 indicates the (m-1)-th coating layer. The subscript m-2 indicates the (m-2)th coating layer.

2. The multilayer negative electrode according to claim 1, characterized in that, It satisfies: 50μm≤H≤150μm.

3. The multilayer negative electrode according to claim 1, characterized in that, The following condition must be met: 0.1% ≤ C ≤ 9%.

4. The multilayer negative electrode according to claim 1, characterized in that, The following condition must be met: 1% ≤ B ≤ 15%.

5. The multilayer negative electrode according to claim 1, characterized in that, Based on the total weight of the coating, the mass percentage of the carbon material is denoted as A, satisfying: 70% ≤ A ≤ 99%.

6. The multilayer negative electrode according to claim 1, characterized in that, Based on the total weight of the coating, the mass percentage of the adhesive is denoted as D, which satisfies the following condition: 0.1% ≤ D ≤ 6%.

7. The multilayer negative electrode according to claim 1, characterized in that, The particle size of the silicon material satisfies at least one of the following characteristics: (1) 1μm≤Dv10≤6μm; (2) 8μm≤Dv50≤10μm; (3) 12μm≤Dv90≤16μm.

8. The multilayer negative electrode according to claim 1, characterized in that, The particle size of the carbon material satisfies at least one of the following characteristics: (1) 1μm≤Dv10'≤8μm, where Dv10' represents the particle size corresponding to when the cumulative volume of the carbon material reaches 10%, in μm; (2) 9μm≤Dv50'≤14μm, where Dv50' represents the particle size corresponding to when the cumulative volume of the carbon material reaches 50%, in μm; (3) 16μm≤Dv90'≤24μm, where Dv90' represents the particle size corresponding to when the cumulative volume of the carbon material reaches 90%, in μm.

9. A secondary battery, characterized in that, It includes a positive electrode sheet, a separator, a multilayer negative electrode as described in any one of claims 1-8, and an electrolyte.

10. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in claim 9.

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