Negative electrode sheet, secondary battery and electrical device

Abstract

This application provides a negative electrode sheet, a secondary battery, and an electrical device, belonging to the technical field of batteries. The negative electrode active material layer of this application includes a first part and a second part along the thickness direction. The first part is the part close to the negative electrode current collector. When the battery is charged, the lithiation state of the second part is relatively high, the lithiation state of the first part is relatively low, and when the mass percentage of the silicon-based material in the first part of the first part is greater than the mass percentage of the silicon-based material in the second part of the second part, the problem of expansion of the silicon-based material in the negative electrode active material layer can be improved. By making C1 < C2, most of the lithium in the positive electrode is inserted into the second part to bear most of the capacity, and normal charge and discharge of the battery is possible even without inserting the silicon-based material in the first part until it reaches a saturated state. The silicon-based material in the first part does not need to operate at the maximum load, the overall expansion of the negative electrode sheet is significantly reduced, and the initial efficiency, cycle characteristics, and storage characteristics of the battery are improved.

Description

Technical Field

[0001] (Cross - reference to related applications) This application claims the priority of Chinese Patent Application No. 202310235493.6, titled "Negative Electrode Sheet, Secondary Battery, and Electric Device", filed on March 13, 2023, and all the contents of this application are incorporated herein by reference.

Background Art

[0002] Silicon - based materials are currently a type of anode material with a high capacity per gram, but neither their cycle characteristics nor their storage characteristics are ideal. This problem is mainly due to the fact that new SEI that consumes the active lithium of the cathode is constantly generated due to the expansion and pulverization of silicon particles in the silicon - based anode.

Summary of the Invention

[0003] In view of the above problems, this application provides a negative electrode sheet, a secondary battery, and an electric device that can improve the initial efficiency, cycle characteristics, and storage characteristics of silicon - based batteries.

[0004] In a first aspect, this application includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer includes a first part and a second part along the thickness direction. The first part is the part close to the negative electrode current collector, and the mass percentage of the silicon - based material in the first part is greater than that in the second part. Let the capacity per unit area of the first part be C1 and the capacity per unit area of the second part be C2, and C1 < C2. A negative electrode sheet is provided.

[0005] In the technical solution of the embodiment of the present application, the negative electrode active material layer of the embodiment of the present application includes a first portion and a second portion along the thickness direction. The first portion is the portion close to the negative electrode current collector. During the charge and discharge process, lithium is preferentially inserted into the second portion. That is, when the battery is charged, the lithiation state of the second portion is relatively high, and the lithiation state of the first portion is relatively low. Also, the second portion has a greater improvement in the electrochemical characteristics of the battery than the first portion. When the mass percentage of the silicon-based material in the first portion of the first portion is greater than the mass percentage of the silicon-based material in the second portion of the second portion, the problem of expansion of the silicon-based material in the negative electrode active material layer can be improved. Also, by making C1 < C2, most of the lithium in the positive electrode is inserted into the second portion to bear most of the capacity, and the capacity borne by the first portion is much smaller than the capacity borne by the second portion. Therefore, normal charge and discharge of the battery are possible without inserting the silicon-based material in the first portion until it reaches a saturated state. The performance of the battery approaches that of the second portion, and the silicon-based material in the first portion does not need to operate at maximum load. As a result, the overall expansion of the negative electrode sheet is significantly reduced, further improving the initial efficiency, cycle characteristics, and storage characteristics of the battery.

[0006] In some embodiments, 0.11C2 ≤ C1 ≤ 0.25C2. When 0.11C2 ≤ C1 ≤ 0.25C2, while maintaining the energy density of the battery, the initial efficiency, cycle characteristics, and storage characteristics of the battery are further improved.

[0007] In some embodiments, the first portion is a first anode active layer formed on the surface of the anode current collector, and the second portion is a second anode active layer formed on the surface of the first anode active layer, and the difference between the mass percentage of the silicon-based material of the first anode active layer in the first anode active layer and the mass percentage of the silicon-based material of the second anode active layer in the second anode active layer is 20% to 80%. The anode active material layer has a layered structure of the first anode active layer and the second anode active layer, and when the difference between the mass percentage of the silicon-based material of the first anode active layer in the first anode active layer and the mass percentage of the silicon-based material of the second anode active layer in the second anode active layer is 20% to 80%, the mass percentage of the silicon-based material of the first portion in the first portion is much greater than the mass percentage of the silicon-based material of the second portion in the second portion, thereby further alleviating the problem of expansion of the silicon-based material of the anode active material layer.

[0008] In some embodiments, the first portion includes 30 wt% to 70 wt% of a silicon-based material, the silicon-based material including a silicon-oxygen material and / or a silicon-carbon material. When the first portion includes 30 wt% to 70 wt% of a silicon-based material, the energy density of the entire negative electrode sheet is improved. Furthermore, even if the energy density is the same, the thickness of the first portion can be reduced, the diffusion paths of lithium ions can be reduced, and kinetic properties can be improved.

[0009] In some embodiments, the silicon-based material of the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 20 μm or less. If the particle size of the silicon-based material is too large, the lithium ion insertion ability is affected, the lithium insertion depth is increased, and the electrochemical properties of the battery are affected. If the particle size of the silicon-based material is too small, processing becomes difficult. Furthermore, since the mass percentage of the silicon-based material of the first portion is higher than the mass percentage of the silicon-based material of the second portion, when the silicon-based material of the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 20 μm or less, not only contributes to improving the electrochemical properties of the battery, but also achieves processability and reduces scratch damage to the substrate due to application.

[0010] In some embodiments, the first portion contains 10 wt% to 55 wt% graphite. The graphite in the first portion not only provides capacity, but also acts as a conductive agent to balance the conductivity of the positive electrode active material when the first portion contains 40 wt% to 80 wt% silicon-based material. When the first portion contains 10 wt% to 55 wt% graphite, both the conductive effect and the energy density of the negative electrode sheet can be achieved.

[0011] In some embodiments, the graphite in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 30 μm or less. Because the first portion has a low weight per unit area and a thin thickness, controlling the particle size of the graphite particles contributes to reducing the difficulty of application and substrate breakage due to damage caused by snagging of the copper foil, as well as improving the electronic conductivity of the first portion. When the graphite in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 30 μm or less, it not only does not interfere with the processing of the negative electrode sheet, but also provides the negative electrode sheet with good electrical conductivity.

[0012] In some embodiments, the first portion contains 3 wt% to 20 wt% of a binder, preferably with a glass transition temperature of 25°C or lower. The binder can limit the expansion of the silicon-based material. When the first portion contains 3 wt% to 20 wt% of a binder, the binder can control the volume effect of the silicon-based material to some extent. In addition, to ensure the processability of the negative electrode sheet and reduce the occurrence of cracks and film shedding in the negative electrode sheet, the coating process of the negative electrode active material is generally performed at room temperature and atmospheric pressure, and a binder with a glass transition temperature of 25°C or lower can meet the requirements for production at room temperature and atmospheric pressure.

[0013] In some embodiments, the first portion contains 0.15 wt% to 1.2 wt% carbon nanotubes, preferably single-walled carbon nanotubes. Carbon nanotubes have high tensile strength, high pressure resistance, and excellent electrical conductivity. When the first portion contains 0.15 wt% to 1.2 wt% carbon nanotubes, the electronic conductivity of the first portion can be significantly increased. Carbon nanotubes can be distributed on the surface of silicon-based material particles and reduce the swelling of the silicon-based material particles. However, carbon nanotubes have poor dispersibility and are prone to causing gelation of the slurry, so they cannot be added in large quantities. However, by controlling the carbon nanotube content to within 1.2 wt%, both improved electronic conductivity and improved processing performance can be achieved.

[0014] In some embodiments, the carbon nanotubes have an aspect ratio of greater than or equal to 1000. When the aspect ratio of the carbon nanotubes is greater than or equal to 1000, the ultra-large aspect ratio of the carbon nanotubes contributes to an improved electronic conductivity of the first portion.

[0015] In some embodiments, the first part further comprises 1 wt% to 5 wt% of a surfactant, preferably sodium carboxymethylcellulose, which contributes to uniform dispersion of the carbon nanotubes and stabilizes processing performance because the carbon nanotubes contained in the first part have poor dispersibility.

[0016] In some embodiments, the first portion contains 0.5 wt % to 5 wt % of a dotted conductive agent, preferably conductive carbon black, which can improve the conductivity and electrolyte retention capacity of the first portion.

[0017] In some embodiments, the first portion has a weight per unit area of ​​0.3 mg / cm 2 ~2.3mg / cm 2 The weight per unit area of ​​the first part is 0.3 mg / cm 2 ~2.3mg / cm 2In this case, the dynamic properties of the battery and industrial production can be compatible.

[0018] In some embodiments, the second portion comprises a graphite material and a silicon-based material in a mass ratio of (80-100):(0-20). The second portion provides a greater improvement to the electrochemical properties of the battery than the first portion, and the electrochemical properties of the battery are favorable when the mass ratio of the graphite material and the silicon-based material in the second portion is (80-100):(0-20).

[0019] In some embodiments, the Dv50 of the silicon-based material of the second portion is 1 μm to 8 μm, and the Dv50 of the graphite of the second portion is 1 μm to 20 μm. Since there are no technical problems in processing the second portion, there is no requirement for particle size. If the Dv50 of the silicon-based material of the second portion is 1 μm to 8 μm, and the Dv50 of the graphite of the second portion is 1 μm to 20 μm, production is possible.

[0020] In some embodiments, the negative electrode active material layer has a weight per unit area of ​​5.19 mg / cm 2 ~14.26mg / cm 2 and the compaction density is 1.4 g / cm 3 ~1.85g / cm 3 The weight per unit area of ​​the negative electrode active material layer is 5.19 mg / cm 2 ~14.26mg / cm 2 and the compaction density is 1.4 g / cm 3 ~1.85g / cm 3 If so, the battery has a high energy density.

[0021] In some embodiments, the thickness of the first portion is h1, the thickness of the second portion is h2, and h2 / h1 is greater than or equal to 2, preferably 45% or greater than h2 / h1 is greater than or equal to 2. Controlling the thickness of the first portion to less than half the thickness of the second portion contributes to reducing degradation of dynamic properties.

[0022] In some embodiments, h1 is 1.5 μm to 15.5 μm, and h2 is 34 μm to 66 μm. When h1 and h2 are within the above thickness ranges and satisfy h2÷h1≧2, this contributes to further reducing deterioration of dynamic properties.

[0023] In some embodiments, the second portion includes at least two sub-portions along the thickness direction, each sub-portion having a different mass percentage of silicon-based material. The second portion may further include multiple sub-portions, each sub-portion having a different mass percentage of silicon-based material to accommodate different structures and types of batteries.

[0024] In a second aspect, the present application provides a secondary battery including a positive electrode sheet and the negative electrode sheet of the above embodiment, wherein the positive electrode sheet includes a positive electrode active material layer, the capacity per unit area of ​​the positive electrode active material layer is C3, the capacity per unit area of ​​the negative electrode active material layer is C4, and 1.01C3≦C4≦1.2C3.

[0025] In the technical solutions of the embodiments of the present application, when 1.01C3≦C4≦1.2C3, the safety of the battery can be improved and lithium precipitation caused by excessive lithium insertion can be reduced.

[0026] In a third aspect, the present application provides an electric device including the secondary battery of the above embodiment.

[0027] The above description is merely a brief description of the technical solution of the present application. In order to make the technical solution of the present application more clearly understood and implemented according to the contents of the specification, and to make the above and other objectives, features and advantages of the present application more comprehensible, specific embodiments of the present application are given below.

[0028] Various other benefits and advantages will become apparent to those skilled in the art upon review of the detailed description of the preferred embodiments below. The drawings are only for purposes of illustrating the preferred embodiments and should not be construed as limiting the present application. Also, like reference numerals refer to like elements throughout the drawings. A description of the drawings follows. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a structural schematic diagram of a vehicle according to some embodiments of the present application; [Figure 2] 1 is an exploded structural schematic diagram of a battery according to some embodiments of the present application; [Figure 3] 1 is an exploded structural schematic diagram of a battery cell according to some embodiments of the present application; [Figure 4] FIG. 2 is a structural schematic diagram of a negative electrode sheet according to some examples of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0030] The following detailed description will be given of the embodiments of the technical solution of the present application with reference to the drawings. The following embodiments are merely examples, and should not be used to limit the scope of protection of the present application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used herein are for describing specific examples only and are not intended to limit this application. The terms "comprises" and "comprises" and any variations thereof in the specification, claims, and the above brief description of the drawings of this application are intended to cover a non-exclusive inclusion.

[0032] In the description of the examples of this application, technical terms such as "first," "second," etc. are merely used to distinguish different objects, and should not be understood as indicating or implying relative importance, or implying the number, specific order, or primary and secondary relationship of the technical features shown. In the description of the examples of this application, unless otherwise clearly and specifically limited, "plurality" means two or more.

[0033] When an "embodiment" is described herein, it means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an embodiment that is exclusively independent of or an alternative to other embodiments. It is explicitly or implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0034] In the description of the examples of this application, the term "and / or" is merely used to explain the relationship between related objects, and means that there may be three types of relationship; for example, A and / or B can mean that A exists alone, that A and B exist simultaneously, or that B exists alone. In addition, the symbol " / " in this specification generally means that the related objects before and after it are in an "or" relationship.

[0035] In describing the examples of this application, the term "plurality" refers to two or more (including two); similarly, "sets" refers to two or more (including two sets); and "plurality" refers to two or more (including two).

[0036] In describing the examples of the present application, orientations or positional relationships indicated by technical terms such as "center," "longitudinal direction," "lateral direction," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial direction," "radial direction," and "circumferential direction" are orientations or positional relationships shown based on the drawings, and are intended merely to make the examples of the present application easier to explain and simplify the description. They do not explicitly or implicitly indicate that the indicated devices or elements necessarily have a specific orientation, or are configured and operated in a specific orientation, and therefore should not be understood as limiting the examples of the present application.

[0037] In describing the embodiments of the present application, unless otherwise clearly defined or limited, technical terms such as "attach," "couple," "connect," and "fix" should be understood in a broad sense, and may refer to, for example, a fixed connection, a detachable connection, or an integral connection. They may also refer to a mechanical connection or an electrical connection. They may also refer to a direct connection, an indirect connection via an intermediate medium, an internal communication between two elements, or an interactive relationship between two elements. Those skilled in the art will be able to understand the specific meanings of the above terms in the embodiments of the present application according to specific circumstances.

[0038] Currently, in view of the development of the market situation, the applications of power batteries are expanding. Power batteries are not only applied to energy storage power supply systems such as hydroelectric power, thermal power, wind power and solar power plants, but also widely used in many fields such as electric transportation means such as electric bicycles, electric motorcycles and electric cars, military equipment and aerospace. With the expansion of the application fields of power batteries, the market demand is also increasing.

[0039] Silicon-based materials are currently one type of anode material with a high capacity per gram, and they also have advantages such as a low lithium insertion potential and abundant lithium supply sources, making them promising candidates for next-generation anode materials. However, silicon-based materials have less than ideal cycling and storage characteristics. This problem is primarily due to the expansion and pulverization of silicon particles in silicon-based anodes, which constantly generates new SEI, which consumes the active lithium in the cathode.

[0040] The applicant conducted research to alleviate the problem of new SEI constantly being generated due to the expansion and pulverization of silicon particles, which consumes the active lithium of the positive electrode. As a result, the applicant found that, during the charge and discharge process of a battery, lithium is preferentially inserted into a region of the negative electrode active material layer relatively close to the positive electrode active material layer in the thickness direction of the negative electrode active material layer. That is, during the charge and discharge process of a battery, the lithiation state of the negative electrode active material in the portion of the negative electrode active material layer close to the positive electrode active material layer is relatively high, while the lithiation state of the negative electrode active material in the portion away from the positive electrode active material layer (closer to the negative electrode current collector) is relatively low. In addition, the electrochemical characteristics of the battery approach the performance of the region close to the positive electrode active material layer. The more silicon-based material contained in the region of the negative electrode active material layer close to the positive electrode active material layer, the worse the initial efficiency, cycle characteristics, storage characteristics, etc. of the battery become.

[0041] Based on the above considerations, the present application examples design a negative electrode sheet to improve the initial efficiency, cycle characteristics, and storage characteristics of silicon-based batteries. The negative electrode active material layer includes a first portion and a second portion along the thickness direction. The first portion is the portion closest to the negative electrode current collector. During the charge / discharge process, lithium is preferentially inserted into the second portion. That is, when the battery is charged, the lithiation state of the second portion is relatively high and the lithiation state of the first portion is relatively low. The electrochemical characteristics of the battery are primarily determined by the second portion, and the second portion provides a greater improvement in the electrochemical characteristics than the first portion. If the mass percentage of the silicon-based material in the first portion is greater than the mass percentage of the silicon-based material in the second portion, the problem of expansion of the silicon-based material in the negative electrode active material layer can be improved. Capacity per unit area C = active layer weight per unit area (g / cm 2) It is the capacity (mAh / g) per gram of the active layer 1. Also, by setting C1 < C2, most of the lithium in the positive electrode is inserted into the second part and bears most of the capacity, and the capacity borne by the first part is much smaller than that borne by the second part. Therefore, even if the silicon-based material in the first part is not inserted until it reaches a saturated state, normal charge and discharge of the battery are possible, the performance of the battery approaches that of the second part, and the silicon-based material in the first part does not need to operate at maximum load. As a result, the overall expansion of the negative electrode sheet is significantly reduced, further improving the initial efficiency, cycle characteristics, and storage characteristics of the battery.

[0042] The battery mentioned in the embodiments of this application refers to a single physical module equipped with a plurality of battery cells to provide a higher voltage and capacity. Generally, the battery includes a battery box for enclosing a plurality of battery cells, and the battery box can prevent liquid or other foreign substances from affecting the charging or discharging of the battery cells.

[0043] Here, each battery cell is a secondary battery, which may be a lithium-ion battery or a lithium-sulfur battery, but is not limited thereto. The battery cell may be cylindrical, flat, cuboid, or other shapes. Generally, battery cells are classified into three types: cylindrical battery cells, prismatic battery cells, and pouch-type battery cells according to the packaging method.

[0044] A battery cell includes an electrode assembly and an electrolyte, and the electrode assembly consists of a positive electrode sheet, a negative electrode sheet, and a separator. The battery cell operates primarily through the movement of metal ions between the positive and negative electrode sheets. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode current collector, and the portion of the positive electrode current collector without the positive electrode active material layer protrudes from the positive electrode current collector coated with the positive electrode active material layer, forming a positive electrode tab. For example, in a lithium-ion battery, the positive electrode current collector may be made of aluminum, and the positive electrode active material may be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode current collector, and the portion of the negative electrode current collector without the negative electrode active material layer protrudes from the negative electrode current collector coated with the negative electrode active material layer, forming a negative electrode tab. The negative electrode current collector may be made of copper. To prevent melting when a large current flows, the positive electrode tabs are stacked together, and the negative electrode tabs are stacked together. The separator may be made of polypropylene (PP) or polyethylene (PE), etc. The electrode assembly may have a wound structure or a stacked structure, but the embodiments of the present application are not limited thereto.

[0045] The battery cell further includes a current collecting member that electrically connects the tab of the battery cell to the electrode terminal to transport electrical energy from the electrode assembly to the electrode terminal and also to the outside of the battery cell via the electrode terminal. Multiple battery cells are electrically connected to each other via the current collecting member, thereby realizing a series connection, parallel connection, or mixed connection of multiple battery cells.

[0046] The battery further includes a sampling terminal and a battery management system, the sampling terminal is connected to the current collecting member and acquires information of the battery cells, such as voltage or temperature, etc. The sampling terminal transmits the acquired information of the battery cells to the battery management system, and when the battery management system detects that the information of the battery cells deviates from a normal range, it limits the output power of the battery to achieve safety protection.

[0047] The electric devices using the batteries described in the embodiments of the present application may be in various forms. Examples include mobile phones, mobile devices, laptops, electric motorcycles, electric cars, boats, aircraft, electric toys, and power tools. For example, aircraft include airplanes, rockets, space shuttles, and spaceships. Electric toys include stationary and mobile electric toys, such as game consoles, electric toy cars, electric toy boats, and electric toy airplanes. Power tools include metal cutting tools, polishing tools, assembly tools, and railroad tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, electric impact drills, concrete vibrators, and electric planers.

[0048] The battery cells and batteries described in the examples of this application are not limited to application to the above-mentioned electrical devices, but can be applied to all electrical devices that use battery cells and batteries. However, for the sake of simplicity, the following examples will be described using an electric vehicle as an example.

[0049] Please refer to FIG. 1 , which is a structural schematic diagram of a vehicle provided in some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a natural gas vehicle, or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle, a range-extender vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 can be installed at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to supply power to the vehicle 1000, for example, the battery 100 can be used as an operating power source for the vehicle 1000. The vehicle 1000 may further include a controller 200 and a motor 300, where the controller 200 controls the battery 100 to supply power to the motor 300, for example, for operating power needs required for starting, navigation, and driving the vehicle 1000.

[0050] In some embodiments of the present application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but can also replace or partially replace fuel oil or natural gas as the driving power source for the vehicle 1000 to provide driving power for the vehicle 1000.

[0051] Please refer to FIG. 2, which is an exploded view of a battery provided in some embodiments of the present application. The battery 100 includes a box 10 and battery cells 20 housed in the box 10. The box 10 is for providing a storage space for the battery cells 20 and can have various structures. In some embodiments, the box 10 may include a first structure 11 and a second structure 12 that, when stacked together, define a storage space for the battery cells 20. The second structure 12 may be a hollow structure with an open end, the first structure 11 may be a plate-like structure, and the first structure 11 may be stacked on the open side of the second structure 12, thereby defining the storage space between the first structure 11 and the second structure 12. Alternatively, the first structure 11 and the second structure 12 may also be hollow structures with an open end, with the open side of the first structure 11 stacked on the open side of the second structure 12. Of course, the box 10 formed by the first structure 11 and the second structure 12 may have various shapes, such as a cylindrical shape, a rectangular parallelepiped shape, etc.

[0052] The battery 100 may include a plurality of battery cells 20, and the plurality of battery cells 20 may be connected in series, parallel, or a mixed connection. A mixed connection refers to both series and parallel connections among the plurality of battery cells 20. The plurality of battery cells 20 may be directly connected in series, parallel, or a mixed connection, and then the integrated plurality of battery cells 20 may be housed in the box 10. Of course, the battery 100 may also be formed by first connecting the plurality of battery cells 20 in series, parallel, or a mixed connection to form a battery module, and then further connecting the plurality of battery modules in series, parallel, or a mixed connection to form an integrated battery module and housed in the box 10. The battery 100 may further include other structures, for example, the battery 100 may further include a current collecting member for realizing electrical connection between the plurality of battery cells 20.

[0053] Here, each battery cell 20 is a secondary battery, and may be, but is not limited to, a lithium ion battery, a lithium sulfur battery, a sodium ion battery, or a magnesium ion battery. The battery cells 20 may be cylindrical, flat, rectangular, or have other shapes.

[0054] Please refer to Figure 3, which is an exploded structural schematic diagram of a first battery cell provided in some embodiments of the present application. A battery cell 20 refers to the smallest constituent unit of a battery. For example, as shown in Figure 3, the battery cell 20 includes an end cover 21, a case 22, an electrode assembly 23, and other functional components.

[0055] The end cover 21 is a component that fits over the opening of the case 22 and isolates the internal environment of the battery cell 20 from the external environment. The shape of the end cover 21 may be adapted to the shape of the case 22 so as to match the case 22, but is not limited thereto. Optionally, the end cover 21 may be made of a material (e.g., aluminum alloy) with a certain degree of hardness and strength so as to be resistant to deformation when pressed or hit. This provides the battery cell 20 with increased structural strength and improves safety performance to some extent. The end cover 21 may be provided with functional components such as electrode terminals. The electrode terminals are electrically connected to the electrode assembly 23 to output or input electrical energy to or from the battery cell 20. In some embodiments, the end cover 21 may further be provided with a pressure release mechanism for releasing internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The end cover 21 may be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, or plastic, but the embodiments of the present application are not particularly limited thereto. In some embodiments, an insulating member may be further provided inside the end cover 21 to isolate the electrical connection members in the case 22 from the end cover 21 and reduce the risk of short circuits. For example, the insulating member may be made of plastic, rubber, or the like.

[0056] The case 22, together with the end cover 21, is a component that forms the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The case 22 and the end cover 21 may be independent components, with an opening formed in the case 22. The internal environment of the battery cell 20 may be formed by overlapping the end cover 21 over the opening. Alternatively, the end cover 21 and the case 22 may be integrated, but this is not limited to this. Specifically, a common connection surface may be formed between the end cover 21 and the case 22 before other components are enclosed, and the end cover 21 may be overlapped on the case 22 when it is necessary to seal the interior of the case 22. The case 22 may have various shapes and sizes, such as a rectangular parallelepiped, cylindrical, or hexagonal prism. Specifically, the shape of the case 22 may be determined according to the specific shape and size of the electrode assembly 23. The case 22 may be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, or plastic, but the embodiments of the present application are not particularly limited thereto.

[0057] The electrode assembly 23 is a component that undergoes an electrochemical reaction in the battery cell 20. The case 22 may include one or more electrode assemblies 23. The electrode assembly 23 is typically formed by winding or stacking a positive electrode sheet and a negative electrode sheet, with a separator typically being provided between the positive electrode sheet and the negative electrode sheet. The portions of the positive electrode sheet and the negative electrode sheet that have active material form the main body of the electrode assembly, and the portions of the positive electrode sheet and the negative electrode sheet that do not have active material form tabs, respectively. The positive electrode tab and the negative electrode tab may be located at the same end of the main body, or at opposite ends of the main body. During the charge and discharge process of the battery, the positive electrode active material and the negative electrode active material react with the electrolyte, and the tabs are connected to the electrode terminals to form a current circuit.

[0058] In accordance with some embodiments of the present application, reference is made to FIG. 4, which is a structural schematic diagram of a negative electrode sheet according to some embodiments of the present application.

[0059] This application provides a negative electrode sheet 400, which includes a negative electrode current collector 410 and a negative electrode active material layer 420. The negative electrode active material layer 420 includes a first portion 421 and a second portion 422 along the thickness direction. The first portion 421 is a portion close to the negative electrode current collector 410. The mass percentage of the silicon-based material in the first portion 421 is greater than that in the second portion 422. Let the capacity per unit area of the first portion 421 be C1, and the capacity per unit area of the second portion 422 be C2, where C1 < C2.

[0060] The first portion 421 is a portion of the negative electrode active material layer 420 close to the negative electrode current collector 410.

[0061] The second portion 422 is a portion of the negative electrode active material layer 420 away from the negative electrode current collector 410, and is the portion obtained by removing the first portion 421 from the entire negative electrode active material layer 420.

[0062] As an example, the first portion 421 may be a first negative electrode active layer formed on the surface of the negative electrode current collector 410, and the second portion 422 may be a second negative electrode active layer formed on the surface of the first negative electrode active layer.

[0063] The mass percentage of the silicon-based material in the first portion 421 is the percentage that the mass of the silicon-based material occupies in the total mass of the first portion 421.

[0064] The mass percentage of the silicon-based material in the second portion 422 is the percentage that the mass of the silicon-based material occupies in the total mass of the second portion 422.

[0065] The capacity C1 per unit area of the first portion and the capacity C2 per unit area of the second portion are measured using a measurement method well-known in the art. As an example, it can be measured by the following method.

[0066] In S1, wash one side of the double-sided negative electrode sheet.

[0067] In S2, the single-sided negative electrode sheet is punched into a small disk with a radius of 7 mm using a die, and its area S is 0.49π, and the unit of area S is cm 2 is.

[0068] In S3, a single-sided negative electrode sheet with an area of ​​S is oven-dried and then transferred to a glove box to fabricate a lithium half-cell.

[0069] In S4, the capacity Q4 of the disk is measured using a measuring device from Wuhan Lan Electronics. The unit of capacity Q4 is mAh. The capacity C4 of the negative electrode active material layer per unit area is calculated as C4 = Q4 ÷ S. The unit of capacity C4 of the negative electrode active material layer per unit area is mAh / cm. 2 is.

[0070] In S5, the second portion is peeled off with tape from the single-sided negative electrode sheet processed in step S1.

[0071] In S6, the capacity Q1 of the first portion of the negative electrode sheet from which the second portion has been peeled off is measured in the same manner as in steps S2, S3, and S4. The unit of the capacity Q1 is mAh. The capacity C1 per unit area of ​​the first portion is calculated as C1 = Q1 ÷ S. The unit of the capacity C1 of the negative electrode active material layer per unit area is mAh / cm. 2 The capacity per unit area of ​​the second portion is C2 = C4 - C1. The capacity C2 of the negative electrode active material layer per unit area is expressed in mAh / cm. 2 is.

[0072] After designing the capacitance C1 per unit area of ​​the first part and the capacitance C2 per unit area of ​​the second part, two types of slurries are prepared so that the silicon content of the first slurry is greater than the silicon content of the second slurry, thereby making it possible to produce the first part and the second part with different silicon contents.

[0073] The negative electrode active material layer of the embodiment of the present application includes a first part and a second part along the thickness direction. The first part is the part close to the negative electrode current collector. During the charge-discharge process, lithium is preferentially inserted into the second part. That is, when the battery is charged, the lithiation state of the second part is relatively high, and the lithiation state of the first part is relatively low. Also, the second part has a greater improvement in the electrochemical characteristics of the battery than the first part. When the mass percentage of the silicon-based material in the first part in the first part is greater than the mass percentage of the silicon-based material in the second part in the second part, the problem of expansion of the silicon-based material in the negative electrode active material layer can be improved. Also, by making C1 < C2, most of the lithium in the positive electrode is inserted into the second part to bear most of the capacity, and the capacity borne by the first part is much smaller than the capacity borne by the second part. Therefore, normal charge and discharge of the battery are possible even without inserting the silicon-based material in the first part until it reaches a saturated state, and the performance of the battery approaches that of the second part. Also, the silicon-based material in the first part does not need to operate at the maximum load. As a result, the overall expansion of the negative electrode sheet is significantly reduced, further improving the initial efficiency, cycle characteristics, and storage characteristics of the battery.

[0074] According to some embodiments of the present application, optionally, 0.11C2 ≤ C1 ≤ 0.25C2.

[0075] When 0.11C2 ≤ C1 ≤ 0.25C2, while maintaining the energy density of the battery, the initial efficiency, cycle characteristics, and storage characteristics of the battery are further improved.

[0076] According to some embodiments of the present application, optionally, the first part is a first negative electrode active layer formed on the surface of the negative electrode current collector, and the second part is a second negative electrode active layer formed on the surface of the first negative electrode active layer. Also, the difference between the mass percentage of the silicon-based material in the first negative electrode active layer in the first negative electrode active layer and the mass percentage of the silicon-based material in the second negative electrode active layer in the second negative electrode active layer is 20% - 80%.

[0077] For example, the difference between the mass percentage of the silicon-based material of the first negative electrode active layer in the first negative electrode active layer and the mass percentage of the silicon-based material of the second negative electrode active layer in the second negative electrode active layer may be 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%.

[0078] The negative electrode active material layer has a layered structure of a first negative electrode active layer and a second negative electrode active layer, and when the difference between the mass percentage of the silicon-based material of the first negative electrode active layer in the first negative electrode active layer and the mass percentage of the silicon-based material of the second negative electrode active layer in the second negative electrode active layer is 20% to 80%, the mass percentage of the silicon-based material of the first portion in the first portion is much greater than the mass percentage of the silicon-based material of the second portion in the second portion, thereby further alleviating the problem of expansion of the silicon-based material of the negative electrode active material layer.

[0079] Optionally, the difference between the mass percentage of the silicon-based material of the first negative electrode active layer in the first negative electrode active layer and the mass percentage of the silicon-based material of the second negative electrode active layer in the second negative electrode active layer is 30% to 50%.

[0080] According to some embodiments of the present application, optionally, the first portion includes 30 wt% to 70 wt% of a silicon-based material, and the silicon-based material includes any one or more of elemental silicon, a silicon-oxygen material, and a silicon-carbon material.

[0081] By way of example, the first portion may include 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 70 wt% silicon-based material.

[0082] By way of example, the silicon-based material may be all elemental silicon, or all silicon-oxygen material, or all silicon-carbon material, or a mixture of elemental silicon and silicon-oxygen material, or a mixture of elemental silicon and silicon-carbon material, or a mixture of silicon-oxygen material and silicon-carbon material, or a mixture of elemental silicon, silicon-oxygen material and silicon-carbon material.

[0083] Optionally, the silicon-based material includes a silicon-oxygen material and / or a silicon-carbon material.

[0084] When the first portion contains 30 wt% to 70 wt% of silicon-based material, it contributes to improving the energy density of the entire negative electrode sheet, and even if the energy density is the same, it achieves a balance between reducing the thickness of the first portion, reducing the diffusion paths of lithium ions, and improving dynamic characteristics.

[0085] Optionally, the first portion comprises 50wt% to 60wt% silicon-based material.

[0086] According to some embodiments of the present application, optionally, the silicon-based material of the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 20 μm or less.

[0087] If the particle size of the silicon-based material is too large, it will affect the lithium ion's lithium insertion ability, increasing the lithium insertion depth and affecting the battery's electrochemical properties. If the particle size of the silicon-based material is too small, it will be difficult to process. Furthermore, since the mass percentage of the silicon-based material in the first portion is higher than that of the silicon-based material in the second portion, if the silicon-based material in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 20 μm or less, it will not only contribute to improving the battery's electrochemical properties, but also achieve processability and reduce scratch damage to the substrate caused by application.

[0088] According to some embodiments of the present application, optionally, the first portion includes 10 wt% to 55 wt% graphite.

[0089] By way of example, the first portion may include 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, or 55 wt% graphite.

[0090] The graphite in the first portion not only provides capacity, but also acts as a conductive agent to balance the conductivity of the positive electrode active material when the first portion contains a large amount of silicon-based material, if the first portion contains 40 wt% to 80 wt% of the silicon-based material.If the first portion contains 10 wt% to 55 wt% of the graphite, both the conductive effect and the energy density of the negative electrode sheet can be achieved.

[0091] According to some embodiments of the present application, optionally, the graphite of the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 30 μm or less.

[0092] Because the first portion has a low weight per unit area and a thin thickness, controlling the particle size of the graphite particles contributes to easier application and reduced substrate breakage due to copper foil snagging damage, as well as improving the electronic conductivity of the first portion. When the graphite in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 30 μm or less, it not only does not interfere with the processing of the negative electrode sheet, but also provides the negative electrode sheet with good electrical conductivity.

[0093] According to some embodiments of the present application, optionally, the first part includes 3 wt% to 20 wt% of a binder, and preferably, the binder has a glass transition temperature of 25°C or less.

[0094] By way of example, the first part may include 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt% of binder.

[0095] The binder can limit the expansion of the silicon-based material. When the first portion contains 3 wt% to 20 wt% of the binder, the binder can control the volume effect of the silicon-based material to a certain extent. In addition, to ensure the processability of the negative electrode sheet and reduce the occurrence of cracks and film shedding in the negative electrode sheet, the coating process of the negative electrode active material is generally carried out at room temperature and atmospheric pressure, and a binder with a glass transition temperature of 25°C or less can meet the production requirements at room temperature and atmospheric pressure.

[0096] Optionally, the binder is styrene butadiene rubber.

[0097] Styrene-butadiene rubber has a glass transition temperature below 0°C. Selecting styrene-butadiene rubber as the binder for the first part more effectively suppresses the expansion of silicon particles, ensuring better mechanical properties of the negative electrode sheet and ensuring the structural stability of the negative electrode sheet.

[0098] According to some embodiments of the present application, optionally, the first portion comprises 0.15 wt% to 1.2 wt% carbon nanotubes, preferably single-walled carbon nanotubes.

[0099] By way of example, the first portion may include 0.15 wt%, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, or 1.2 wt% carbon nanotubes.

[0100] Carbon nanotubes have high tensile strength, high pressure resistance, and excellent electrical conductivity. When the first portion contains 0.15 wt% to 1.2 wt% carbon nanotubes, the electronic conductivity of the first portion can be significantly increased. Carbon nanotubes can be distributed on the surface of silicon-based material particles, reducing the swelling of the silicon-based material particles. However, carbon nanotubes have poor dispersibility and are prone to causing gelation of the slurry, so they cannot be added in large quantities. Controlling their content to within 1.2 wt% can achieve both improved electronic conductivity and improved processing performance. Single-walled carbon nanotubes are linear materials.

[0101] According to some embodiments of the present application, the carbon nanotubes optionally have an aspect ratio of 1000 or greater.

[0102] By way of example, the aspect ratio of the carbon nanotubes may be 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500 or 10000.

[0103] When the aspect ratio of the carbon nanotube is 1000 or more, the ultra-large aspect ratio of the carbon nanotube contributes to improving the electronic conductivity of the first portion.

[0104] Optionally, the carbon nanotubes have an aspect ratio of 1,000 to 10,000.

[0105] According to some embodiments of the present application, optionally, the first part further comprises 1 wt% to 5 wt% of a surfactant, preferably sodium carboxymethylcellulose.

[0106] By way of example, the first part may further comprise 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt% of a surfactant.

[0107] Since the carbon nanotubes contained in the first portion have poor dispersibility, when the first portion further contains 1 wt % to 5 wt % of a surfactant, this contributes to uniform dispersion of the carbon nanotubes and stabilizes processing performance.

[0108] According to some embodiments of the present application, optionally, the first part contains 0.5 wt% to 5 wt% of a dot-like conductive agent, preferably conductive carbon black.

[0109] For example, the first portion may further include 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt% of a dotted conductive agent.

[0110] The dot-like conductive agent is a conductive material having an aspect ratio of less than 1.5.

[0111] The dotted conductive agent can improve the conductivity and electrolyte retention capacity of the first portion.

[0112] Optionally, the first portion includes 1 wt% to 2 wt% of the dotted conductive agent.

[0113] Optionally, the dot-like conductive agent includes any one or more of superconducting carbon, acetylene black, ketjen black, conductive carbon black, graphene, and carbon dots.

[0114] According to some embodiments of the present application, optionally, the first portion has a weight per unit area of ​​0.3 mg / cm 2 ~2.3mg / cm 2 is.

[0115] For example, the weight per unit area of ​​the first portion is 0.3 mg / cm 2 , 0.5 mg / cm 2 , 0.8 mg / cm 2 , 1 mg / cm 2 , 1.5 mg / cm 2 , 2 mg / cm 2 or 2.3 mg / cm 2 may be.

[0116] The weight per unit area of ​​the first part is 0.3 mg / cm 2 ~2.3mg / cm 2 In this case, the dynamic properties of the battery and industrial production can be compatible.

[0117] According to some embodiments of the present application, optionally, the second portion includes a graphite material and a silicon-based material in a mass ratio of (80-100):(0-20).

[0118] The second portion includes a graphite material and does not include a silicon-based material.

[0119] Alternatively, the second portion includes a graphite material and a silicon-based material.

[0120] By way of example, the mass ratio of graphite material to silicon-based material in the second portion may be 80:20, 85:15, 90:10, 95:5 or 100:0.

[0121] The second portion has a greater improvement in the electrochemical properties of the battery than the first portion, and therefore, when the mass ratio of the graphite material to the silicon-based material in the second portion is (80-100):(0-20), the electrochemical properties of the battery are favorable.

[0122] Optionally, the mass ratio of the graphite material to the silicon-based material in the second portion is 100:0, ie, the second portion does not contain any silicon-based material.

[0123] According to some embodiments of the present application, optionally, the silicon-based material of the second portion has a Dv50 of 1 μm to 8 μm, and the graphite of the second portion has a Dv50 of 1 μm to 20 μm.

[0124] The second part has low particle size requirements because there are no technical problems with processing it. Production is possible when the Dv50 of the silicon-based material of the second part is 1 μm to 8 μm and the Dv50 of the graphite of the second part is 1 μm to 20 μm.

[0125] According to some embodiments of the present application, the negative electrode active material layer may have a weight per unit area of ​​5.19 mg / cm. 2 ~14.26mg / cm 2 and the compaction density is 1.4 g / cm 3 ~1.85g / cm 3 is.

[0126] For example, the weight per unit area of ​​the negative electrode active material layer is 5.19 mg / cm 2 , 5.5 mg / cm 2 , 6 mg / cm 2 , 6.5 mg / cm 2 , 7 mg / cm 2 , 7.5 mg / cm 2 , 8 mg / cm 2 , 8.5 mg / cm 2 , 9 mg / cm 2 , 9.5 mg / cm 2 , 10 mg / cm 2 , 10.5 mg / cm 2 , 11 mg / cm 2 , 11.5 mg / cm 2 , 12 mg / cm2 , 12.5 mg / cm 2 , 13 mg / cm 2 , 13.5 mg / cm 2 , 14 mg / cm 2 or 14.26 mg / cm 2 may be.

[0127] For example, the compaction ratio of the negative electrode active material layer is 1.4 g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 or 1.85 g / cm 3 may be.

[0128] The weight per unit area of ​​the negative electrode active material layer is 5.19 mg / cm 2 ~14.26mg / cm 2 and the compaction density is 1.4 g / cm 3 ~1.85g / cm 3 If so, the battery has a high energy density.

[0129] According to some embodiments of the present application, optionally, the thickness of the first portion is h1, the thickness of the second portion is h2, and h2÷h1≧2, preferably 45≧h2÷h1≧2.

[0130] Controlling the thickness of the first portion to half or less of the thickness of the second portion contributes to reducing deterioration of dynamic characteristics.

[0131] According to some embodiments of the present application, optionally, h1 is between 1.5 μm and 15.5 μm, and h2 is between 34 μm and 66 μm.

[0132] By way of example, h1 may be 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm or 15.5 μm.

[0133] h2 may be 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, 50 μm, 51 μm, 52 μm, 53 μm, 54 μm, 55 μm, 56 μm, 57 μm, 58 μm, 59 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm or 66 μm.

[0134] When h1 and h2 are within the above thickness range and satisfy h2÷h1≧2, this contributes to further reducing the deterioration of dynamic properties.

[0135] According to some embodiments of the present application, optionally, the second portion includes at least two sub-portions along the thickness direction, each sub-portion having a different mass percentage of the silicon-based material.

[0136] The second portion may further include multiple sub-portions, each with a different mass percentage of silicon-based material to accommodate different structures and types of batteries.

[0137] Example 1 An embodiment of the present application provides a secondary battery and a method for fabricating the same, which includes the following steps:

[0138] S1. Preparation of negative electrode sheet Formation of the first part Silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose were thoroughly mixed in deionized water in a mass ratio of 50:37.2:10:1:0.3:1.5, to prepare a first negative electrode slurry. This was then uniformly applied to an 8 μm-thick copper current collector with a 2 μm-thick conductive carbon undercoat, and oven-dried to a mass per unit area of ​​0.81 mg / cm. 2 As a result, an intermediate product of a negative electrode sheet was obtained.

[0139] Here, the Dv50 of silicon monoxide was 5 μm, the Dv50 of artificial graphite was 4.7 μm, the Dv99 was 13 μm, and the aspect ratio of the single-walled carbon nanotube was 5,000.

[0140] Formation of the second part Artificial graphite, styrene butadiene rubber, sodium carboxymethyl cellulose, and conductive carbon black (Super-P, SP) were thoroughly mixed in deionized water in a mass ratio of 96.2:1.8:1.2:0.8 and stirred to prepare a second negative electrode slurry. This was then applied to the first part to form the second part, which was then oven-dried, cold-pressed, and slit to a compaction density of 1.65 g / cm. 3 , weight per unit area is 10.62 mg / cm 2 Thus, a negative electrode sheet having the formula:

[0141] Here, the Dv50 of the artificial graphite was 15.3 μm.

[0142] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0143] S2. Preparation of positive electrode sheet Lithium Nickel Manganese Cobalt Oxide LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811), conductive carbon black (Super P), and polyvinylidene fluoride were mixed in a weight ratio of 97.5:1.5:1 with an appropriate amount of N-methylpyrrolidone and thoroughly stirred to form a homogeneous positive electrode slurry. The positive electrode slurry was applied to the surface of the positive electrode current collector aluminum foil, oven-dried, cold-pressed, slit, and cut to a compaction density of 3.5 g / cm. 3 , weight per unit area is 18.04mg / cm 2 A positive electrode sheet having the following formula was obtained.

[0144] S3, Separator selection A polyethylene film with a thickness of 12 μm was used as the separator.

[0145] S4. Preparation of electrolyte solution Ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was then uniformly dissolved in the solution to obtain an electrolyte solution with a LiPF6 concentration of 1 mol / L.

[0146] S5. Preparation of secondary batteries A positive electrode sheet, a separator, and a negative electrode sheet were stacked in this order with the separator between the positive and negative electrode sheets to separate them, and lithium foil was placed on the surface of the non-reactive region, which was then rolled up to obtain an electrode assembly. The electrode assembly was placed in an outer case and dried, after which an electrolyte solution was injected, and the assembly was subjected to processes such as vacuum packaging, standing, chemical conversion, and molding to obtain a secondary battery.

[0147] Example 2 The examples of the present application provide a secondary battery and a method for manufacturing the same. In Example 2, the weight per unit area of ​​the intermediate product of the negative electrode sheet in Example 1 is 0.23 mg / cm. 2 The weight per unit area of ​​the negative electrode sheet was changed to 11.46 mg / cm 2 The procedure was the same as in Example 1, except for the change to

[0148] The silicon content of the negative electrode active material layer of the negative electrode sheet was 1.01 wt %.

[0149] Example 3 The examples of the present application provide a secondary battery and a method for manufacturing the same. In Example 3, the weight per unit area of ​​the intermediate product of the negative electrode sheet in Example 1 is 0.48 mg / cm. 2 The weight per unit area of ​​the negative electrode sheet was changed to 11.1 mg / cm 2 The procedure was the same as in Example 1, except for the change to

[0150] The silicon content of the negative electrode active material layer of the negative electrode sheet was 2.16 wt %.

[0151] Example 4 The examples of the present application provide a secondary battery and a method for manufacturing the same. In Example 4, the weight per unit area of ​​the intermediate product of the negative electrode sheet in Example 1 is 0.97 mg / cm. 2 The weight per unit area of ​​the negative electrode sheet was changed to 10.4 mg / cm 2 The procedure was the same as in Example 1, except for the change to

[0152] The silicon content of the negative electrode active material layer of the negative electrode sheet was 4.65 wt %.

[0153] Example 5 The examples of the present application provide a secondary battery and a method for manufacturing the same. In Example 5, the weight per unit area of ​​the intermediate product of the negative electrode sheet in Example 1 is 1.38 mg / cm. 2 The weight per unit area of ​​the negative electrode sheet was changed to 9.8 mg / cm 2 The procedure was the same as in Example 1, except for the change to

[0154] The silicon content of the negative electrode active material layer of the negative electrode sheet was 7.06 wt %.

[0155] Example 6 The examples of the present application provide a secondary battery and a method for manufacturing the same. In Example 6, the weight per unit area of ​​the intermediate product of the negative electrode sheet in Example 1 is 2.36 mg / cm. 2The weight per unit area of ​​the negative electrode sheet was changed to 8.4 mg / cm 2 The procedure was the same as in Example 1, except for the change to

[0156] The silicon content of the negative electrode active material layer of the negative electrode sheet was 14.03 wt %.

[0157] Example 7 The present invention provides a secondary battery and a method for manufacturing the same. Example 7 is the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 is changed to 20:67.2:10:1:0.3:1.5.

[0158] The silicon content of the negative electrode active material layer of the negative electrode sheet was 1.52 wt %.

[0159] Example 8 The present invention provides a secondary battery and a method for manufacturing the same. Example 8 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 30:55:12.2:1:0.3:1.5.

[0160] The silicon content of the negative electrode active material layer of the negative electrode sheet was 2.28 wt %.

[0161] Example 9 The present invention provides a secondary battery and a method for manufacturing the same. Example 9 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 40:47.2:10:1:0.3:1.5.

[0162] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.05 wt %.

[0163] Example 10 The present invention provides a secondary battery and a method for manufacturing the same. Example 10 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 60:27.2:10:1:0.3:1.5.

[0164] The silicon content of the negative electrode active material layer of the negative electrode sheet was 4.57 wt %.

[0165] Example 11 The present invention provides a secondary battery and a method for manufacturing the same. Example 11 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 70:17.2:10:1:0.3:1.5.

[0166] The silicon content of the negative electrode active material layer of the negative electrode sheet was 5.33 wt %.

[0167] Example 12 The present invention provides a secondary battery and a method for manufacturing the same. Example 12 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 80:7.2:10:1:0.3:1.5.

[0168] The silicon content of the negative electrode active material layer of the negative electrode sheet was 6.1 wt %.

[0169] Example 13 The present invention provides a secondary battery and a method for manufacturing the same. Example 13 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 50:44.2:3:1:0.3:1.5.

[0170] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0171] Example 14 The present invention provides a secondary battery and a method for manufacturing the same. Example 14 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 50:27.2:20:1:0.3:1.5.

[0172] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0173] Example 15 The present invention provides a secondary battery and a method for manufacturing the same. Example 15 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 50:37.7:10:0.5:0.3:1.5.

[0174] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0175] Example 16 The present invention provides a secondary battery and a method for manufacturing the same. Example 16 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 50:33.2:10:5:0.3:1.5.

[0176] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0177] Example 17 The present invention provides a secondary battery and a method for manufacturing the same. Example 17 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 50:37.95:10:1:0.05:1.

[0178] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0179] Example 18 The present invention provides a secondary battery and a method for manufacturing the same. Example 18 was the same as Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene-butadiene rubber, conductive carbon black (SP), single-walled carbon nanotubes, and sodium carboxymethyl cellulose in the first part in Example 1 was changed to 50:32.8:10:1:1.2:5.

[0180] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0181] Example 19 The examples of the present application provide a secondary battery and a method for manufacturing the same. Example 19 was the same as Example 1, except that the aspect ratio of the single-walled carbon nanotubes in Example 1 was changed to 1,000.

[0182] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0183] Example 20 The examples of the present application provide a secondary battery and a method for manufacturing the same. Example 20 was the same as Example 1, except that the aspect ratio of the single-walled carbon nanotubes in Example 1 was changed to 10,000.

[0184] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3.79 wt %.

[0185] Example 21 The present invention provides a secondary battery and a method for fabricating the same. In Example 21, the components of the second part in Example 1 were changed to artificial graphite, silicon monoxide, styrene-butadiene rubber, sodium carboxymethyl cellulose, and conductive carbon black (Super-P, SP), which were mixed in a blending ratio of 94.2:2:1.8:1.2:0.8, and the weight per unit area of ​​the negative electrode sheet was 10.06 mg / cm. 2 Other than that, the same procedure as in Example 1 was carried out.

[0186] The silicon content of the negative electrode active material layer of the negative electrode sheet was 4.84 wt %.

[0187] Example 22 The present invention provides a secondary battery and a method for fabricating the same. In Example 22, the components of the second part in Example 1 were changed to artificial graphite, silicon monoxide, styrene-butadiene rubber, sodium carboxymethyl cellulose, and conductive carbon black (Super-P, SP), which were mixed in a blending ratio of 91.2:5:1.8:1.2:0.8, and the weight per unit area of ​​the negative electrode sheet was 9.31 mg / cm. 2 Other than that, the same procedure as in Example 1 was carried out.

[0188] The silicon content of the negative electrode active material layer of the negative electrode sheet was 8.89 wt %.

[0189] Example 23 The present application provides a secondary battery and a method for fabricating the same. In Example 23, the components of the second part in Example 1 were replaced with artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-walled carbon nanotubes, which were mixed in a blending ratio of 86.2:10:1.8:1.2:0.6:0.2, and the weight per unit area of ​​the negative electrode sheet was 8.30 mg / cm. 2 Other than that, the same procedure as in Example 1 was carried out.

[0190] The silicon content of the negative electrode active material layer of the negative electrode sheet was 13.88 wt %.

[0191] Example 24 The examples of the present application provide a secondary battery and a method for fabricating the same. In Example 24, the components of the second part in Example 1 were changed to artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-walled carbon nanotubes, and mixed in a blending ratio of 81.2:15:1.8:1.2:0.5:0.3, and the weight per unit area of ​​the negative electrode sheet was 7.51 mg / cm. 2 Other than that, the same procedure as in Example 1 was carried out.

[0192] The silicon content of the negative electrode active material layer of the negative electrode sheet was 18.75 wt %.

[0193] Example 25 The present invention provides a secondary battery and a method for fabricating the same. In Example 25, the components of the second part in Example 1 were replaced with artificial graphite, silicon monoxide, styrene-butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-walled carbon nanotubes, which were mixed in a blending ratio of 76.2:20:1.8:1.2:0.5:0.3, and the weight per unit area of ​​the negative electrode sheet was 6.87 mg / cm. 2 Other than that, the same procedure as in Example 1 was carried out.

[0194] The silicon content of the negative electrode active material layer of the negative electrode sheet was 23.52 wt %.

[0195] Example 26 The present invention provides a secondary battery and a method for manufacturing the same. Example 26 was the same as Example 23, except that the silicon monoxide in the second portion of Example 23 was replaced with a silicon carbon material having a structure in which elemental silicon is deposited in pores in porous carbon.

[0196] The silicon content of the negative electrode active material layer of the negative electrode sheet was 13.88 wt %.

[0197] Comparative Example 1 The comparative examples of the present application provide a secondary battery and a method for manufacturing the same. In Comparative Example 1, the negative electrode sheet manufacturing method in Example 1 was changed to a negative electrode slurry prepared by thoroughly stirring and mixing artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-walled carbon nanotubes in a mass ratio of 93.2%, 3%, 1.8%, 1.2%, 0.7%, and 0.1% in deionized water. The negative electrode slurry was uniformly applied to a copper current collector with a thickness of 8 μm, and the resulting mixture was oven-dried, cold-pressed, and slit to a compaction density of 1.65 g / cm. 3 , weight per unit area is 10.77mg / cm 2 The procedure was the same as in Example 1, except that the method was changed to form a negative electrode sheet of

[0198] The silicon content of the negative electrode active material layer of the negative electrode sheet was 3 wt %.

[0199] Comparative Example 2 The comparative examples of the present application provide a secondary battery and a method for manufacturing the same. In comparative example 2, the method for manufacturing the negative electrode sheet in example 1 was changed to a negative electrode slurry prepared by thoroughly stirring and mixing artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-walled carbon nanotubes in a mass ratio of 90.2%, 6%, 1.8%, 1.2%, 0.7%, and 0.1% in deionized water. The negative electrode slurry was uniformly applied to an 8 μm-thick copper current collector, and the resulting mixture was oven-dried, cold-pressed, and slit to a compaction density of 1.65 g / cm. 3 , weight per unit area is 9.93 mg / cm 2 The procedure was the same as in Example 1, except that the method was changed to form a negative electrode sheet of

[0200] The silicon content of the negative electrode active material layer of the negative electrode sheet was 6 wt %.

[0201] Comparative Example 3 The comparative examples of the present application provide a secondary battery and a method for manufacturing the same. In comparative example 3, the method for manufacturing the negative electrode sheet in example 1 was changed to a negative electrode slurry prepared by thoroughly stirring and mixing artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-walled carbon nanotubes in a mass ratio of 83.2%, 13%, 1.8%, 1.2%, 0.5%, and 0.3% in deionized water. The negative electrode slurry was uniformly applied to a copper current collector with a thickness of 8 μm, and the copper current collector was oven-dried, cold-pressed, and slit to obtain a compaction density of 1.65 g / cm. 3 , weight per unit area is 8.402 mg / cm 2 The procedure was the same as in Example 1, except that the method was changed to form a negative electrode sheet of

[0202] The silicon content of the negative electrode active material layer of the negative electrode sheet was 13 wt %.

[0203] Comparative Example 4 The comparative examples of the present application provide a secondary battery and a method for manufacturing the same. In comparative example 4, the negative electrode sheet manufacturing method in example 1 was changed to a negative electrode slurry prepared by thoroughly stirring and mixing artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-walled carbon nanotubes in a mass ratio of 78.2%, 18%, 1.8%, 1.2%, 0.5%, and 0.3% in deionized water. The negative electrode slurry was uniformly applied to a copper current collector with a thickness of 8 μm, and the resulting mixture was oven-dried, cold-pressed, and slit to a compaction density of 1.65 g / cm. 3 , weight per unit area is 7.566mg / cm 2 The procedure was the same as in Example 1, except that the method was changed to form a negative electrode sheet of

[0204] The silicon content of the negative electrode active material layer of the negative electrode sheet was 18 wt %.

[0205] Comparative Example 5 The comparative examples of the present application provide a secondary battery and a method for manufacturing the same. In comparative example 5, the negative electrode sheet manufacturing method in example 1 was changed to a negative electrode slurry prepared by thoroughly stirring and mixing artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-walled carbon nanotubes in a mass ratio of 73.2%, 23%, 1.8%, 1.2%, 0.5%, and 0.3% in deionized water. The negative electrode slurry was uniformly applied to a copper current collector with a thickness of 8 μm, and the resulting mixture was oven-dried, cold-pressed, and slit to a compaction density of 1.65 g / cm. 3 , weight per unit area is 6.88mg / cm 2 The procedure was the same as in Example 1, except that the method was changed to form a negative electrode sheet of

[0206] The silicon content of the negative electrode active material layer of the negative electrode sheet was 23 wt %.

[0207] Comparative Example 6 The comparative examples of the present application provide a secondary battery and a method for manufacturing the same. Comparative Example 6 was the same as Comparative Example 3, except that a silicon carbon material having a structure in which elemental silicon is deposited in pores in porous carbon was used instead of silicon monoxide in Comparative Example 3.

[0208] The silicon content of the negative electrode active material layer of the negative electrode sheet was 13 wt %.

[0209] Comparative Example 7 The comparative example of the present application provides a secondary battery and a method for manufacturing the same. In Comparative Example 7, the weight per unit area of ​​the intermediate product of the negative electrode sheet in Example 1 was 2.53 mg / cm. 2 The weight per unit area of ​​the negative electrode sheet was changed to 8.154 mg / cm 2 The procedure was the same as in Example 1, except for the change to

[0210] The silicon content of the negative electrode active material layer of the negative electrode sheet was 15.49 wt %.

[0211] Comparative Example 8 The comparative examples of the present application provide a secondary battery and a method for manufacturing the same. Comparative Example 8 was the same as Example 25, except that the second part of Example 25 was designed as the first part, and the first part of Example 25 was designed as the second part.

[0212] The silicon content of the negative electrode active material layer of the negative electrode sheet was 23.52 wt %.

[0213] Table 1 shows the mass percentage of the silicon-based material in the first portion of the secondary batteries in Examples 1 to 26 and Comparative Examples 1 to 8, and the mass percentage of the silicon-based material in the second portion of the secondary batteries in Examples 1 to 26 and Comparative Examples 1 to 8, C1, C2, h1, h2, and h2 / h1.

[0214] [Table 1]

[0215] Here, the thickness h1 of the first portion and the thickness h2 of the second portion of the negative electrode sheet are measured by the following method.

[0216] A cross section of the negative electrode sheet is photographed using a scanning electron microscope (SEM) (for example, ZEISS Sigma 300), and the thickness h1 of the first portion and the thickness h2 of the second portion of the negative electrode sheet are measured and calculated.

[0217] The capacitance C1 per unit area of ​​the first portion and the capacitance C2 per unit area of ​​the second portion are measured by the following method.

[0218] In S1, one side of the double-sided negative electrode sheet is washed.

[0219] In S2, the single-sided negative electrode sheet is punched into a small disk with a radius of 7 mm using a die, and its area S = 0.49π, and the unit of area S is cm 2 is.

[0220] In S3, a single-sided negative electrode sheet with an area of ​​S is oven-dried and then transferred to a glove box to prepare a lithium half-cell.

[0221] In S4, the capacity Q4 of the disk is measured using a measuring device from Wuhan Lan Electronics. The unit of capacity Q4 is mAh. The capacity C4 of the negative electrode active material layer per unit area is calculated as C4 = Q4 ÷ S. The unit of capacity C4 of the negative electrode active material layer per unit area is mAh / cm. 2 is.

[0222] In S5, the second portion is peeled off from the single-sided negative electrode sheet processed in step S1 using tape.

[0223] In S6, the capacity Q1 of the first portion of the negative electrode sheet from which the second portion has been peeled off is measured in the same manner as in steps S2, S3, and S4. The unit of the capacity Q1 is mAh. The capacity C1 per unit area of ​​the first portion is calculated as C1 = Q1 ÷ S. The unit of the capacity C1 of the negative electrode active material layer per unit area is mAh / cm. 2 The capacity per unit area of ​​the second portion is C2 = C4 - C1. The capacity C2 of the negative electrode active material layer per unit area is expressed in mAh / cm. 2 is.

[0224] Table 2 shows the blending methods of the first and second parts of the secondary batteries of Examples 1 to 26 and Comparative Examples 1 to 8.

[0225] [Table 2]

[0226] The silicon-based material of the first portion in Examples 1 to 26 had a Dv50 of 6 μm and a Dv99 of 10.5 μm, the silicon-based material of the second portion in Examples 21 to 26 had a Dv50 of 6 μm, the graphite of the first portion in Examples 1 to 26 had a Dv50 of 5.1 μm and a Dv99 of 11.8 μm, and the graphite of the second portion in Examples 1 to 26 had a Dv50 of 14.8 μm. The silicon-based materials of Comparative Examples 1 to 8 had a Dv50 of 6 μm and a Dv99 of 10.5 μm, and the graphite had a Dv50 of 5.1 μm.

[0227] Test Example 1 For each of the secondary batteries produced in Examples 1 to 26 and Comparative Examples 1 to 8, the initial coulombic efficiency ICE, cycle capacity retention rate ρ1, 300 cycle expansion rate Δh300, and storage reversible capacity retention rate ρ2 were measured. The results are shown in Table 3.

[0228] Initial Coulombic Efficiency Test (Initial Efficiency) The battery was charged to 3.4 V at 0.02 C rate at 45°C, then charged to 3.75 V at 0.1 C rate, and the measured capacity was defined as C0. Next, the battery was charged to 4.25 V at 0.33 C rate at 25°C, and then charged at 0.05 C at a constant voltage of 4.25 V, and the measured capacity was defined as C1. Finally, the battery was discharged to 2.5 V at 0.33 C, and the measured capacity was defined as D0. The initial coulombic efficiency of the secondary battery, ICE, was defined as D0 / (C0+C1) × 100%.

[0229] Cycle Test The secondary battery was charged at a constant current of 1D0 in a constant temperature environment of 45°C until the voltage reached 4.25V, then charged at a constant voltage of 4.25V until the current reached 0.05D0 or less, and then allowed to stand for 5 minutes. Next, the battery was discharged at a constant current of 1C until the voltage reached 2.5V (the capacity at this point was designated C3), and then allowed to stand for 5 minutes. This method was repeated for 500 charge and discharge cycles (the discharge capacity at the 500th cycle was designated C500), and the cycle capacity retention rate of the secondary battery ρ1 = C500 ÷ C3 × 100% was calculated.

[0230] Negative electrode sheet expansion test The thickness of the negative electrode sheet of the secondary battery at the end of the cold pressing process was defined as h0. Using the cycle characteristic test method for secondary batteries at 45°C described above, the secondary battery was repeatedly charged and discharged 300 times, and was charged at a constant current of 1D0 until the voltage reached 4.25V. It was then charged at a constant voltage of 4.25V until the current reached 0.05C or less, and then allowed to stand for 5 minutes. At this point, the secondary battery was fully charged. After repeated charging and discharging in a drying chamber, the secondary battery was disassembled. The thickness of the negative electrode sheet after 300 cycles was defined as h300. The 300-cycle expansion rate of the secondary battery sheet at 45°C, Δh300 = (h300 - h0) / h0 * 100%, was calculated.

[0231] Storage Test The secondary battery was charged at a constant current of 0.33D0 in a 25°C environment until the voltage reached 4.25V. It was then charged at a constant voltage of 0.05D0 or less at 4.25V. It was then left to stand for 5 minutes and then discharged at a constant current of 0.33D0 until the voltage reached 2.5V (the capacity at this point was designated C4). The secondary battery was then charged at a constant current of 0.33D0 until the voltage reached 4.25V, and then discharged at a constant voltage of 0.05D0 or less at 4.25V. The fully charged secondary battery was then transferred to a 60°C environment and stored for 100 days. It was then transferred to a 25°C environment and discharged at a constant current of 0.33D0 until the voltage reached 2.5V. Finally, it was charged at a constant current of 0.33D0 until the voltage reached 4.25V. The battery was then charged at a constant voltage of 4.25 V until the current reached 0.05 D0 or less, then allowed to stand for 5 minutes, and then discharged at a constant current of 0.33 D0 until the voltage reached 2.5 V (the capacity at this step was defined as C100). The reversible storage capacity retention rate of the secondary battery ρ2 = C100 ÷ C4 × 100% was calculated.

[0232] [Table 3]

[0233] As can be seen from comparing Examples 2-3 and 7-8 with Comparative Example 1, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 1 was 3 wt%, while the silicon content of the negative electrode active material layer in the secondary batteries of Examples 2-3 and 7-8 was less than 3 wt%. The initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) of the secondary batteries of Examples 2-3 and 7-8 were all significantly higher than the initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) of the secondary battery of Comparative Example 1. The 300-cycle sheet expansion rate (Δh300) at 45°C of the secondary batteries of Examples 2-3 and 7-8 was significantly lower than the 300-cycle sheet expansion rate (Δh300) of the secondary battery of Comparative Example 1.

[0234] As can be seen by comparing Examples 1, 4, 9-11, and 13-21 with Comparative Example 1, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 1 was 3 wt %, while the silicon content of the negative electrode active material layer in the secondary batteries of Examples 1, 4, 9-11, and 13-21 was 3 wt % or more. The initial coulombic efficiencies (ICE) of the secondary batteries of Examples 1, 4, 9-11, and 13-20 were all higher than that of the secondary battery of Comparative Example 1. The secondary battery of Example 21 had a higher silicon content in the negative electrode active material layer than the secondary battery of Comparative Example 1, but its initial coulombic efficiencies (ICE) were slightly lower. The cycle capacity retention rates (ρ1) of the secondary batteries of Examples 1, 4, 9-10, and 13-20 were all higher than that of the secondary battery of Comparative Example 1. The secondary batteries of Examples 11 and 21 had a higher silicon content in the negative electrode active material layer than the secondary battery of Comparative Example 1, but their cycle capacity retention rates (ρ1) were slightly lower. The 300 cycle expansion coefficients Δh300 of the sheets at 45°C of the secondary batteries of Examples 1, 4, 9 to 11, and 13 to 21 were all lower than the 300 cycle expansion coefficient Δh300 of the sheets at 45°C of the secondary battery of Comparative Example 1. The reversible storage capacity retention rates ρ2 of the secondary batteries of Examples 1, 4, 9 to 10, and 13 to 20 were all higher than the reversible storage capacity retention rate ρ2 of the secondary battery of Comparative Example 1. The secondary batteries of Examples 11 and 21 had a higher silicon content in the negative electrode active material layer than the secondary battery of Comparative Example 1, but their reversible storage capacity retention rates ρ2 were slightly lower.

[0235] As can be seen by comparing Examples 5, 12, and 22 with Comparative Example 2, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 2 was 6 wt%, while the silicon content of the negative electrode active material layer in the secondary batteries of Examples 5, 12, and 22 was 6 wt% or more. The secondary batteries of Examples 5, 12, and 22 had a higher silicon content in the negative electrode active material layer than Comparative Example 2, but their initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) were all significantly higher. The 300-cycle expansion coefficient (Δh300) of the sheet at 45°C of the secondary batteries of Examples 5, 12, and 22 was significantly lower than the 300-cycle expansion coefficient (Δh300) of the sheet at 45°C of the secondary battery of Comparative Example 2.

[0236] As can be seen by comparing Examples 6, 23, and 26 with Comparative Example 3, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 3 was 13 wt%, while the silicon content of the negative electrode active material layer in the secondary batteries of Examples 6, 23, and 26 was 13 wt% or more. The secondary batteries of Examples 6, 23, and 26 had a higher silicon content in the negative electrode active material layer than Comparative Example 3, but their initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) were all significantly higher. The 300-cycle expansion coefficient (Δh300) of the sheet at 45°C of the secondary batteries of Examples 6, 23, and 26 was significantly lower than the 300-cycle expansion coefficient (Δh300) of the sheet at 45°C of the secondary battery of Comparative Example 3.

[0237] As can be seen by comparing Example 24 with Comparative Example 4, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 4 was 18 wt%, while the silicon content of the negative electrode active material layer in the secondary battery of Example 24 was 18 wt% or more. The secondary battery of Example 24 had a higher silicon content in the negative electrode active material layer than Comparative Example 4, but its initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) were all significantly higher. The 300-cycle expansion rate (Δh300) of the sheet of the secondary battery of Example 24 at 45°C was significantly lower than the 300-cycle expansion rate (Δh300) of the sheet of the secondary battery of Comparative Example 4 at 45°C.

[0238] As can be seen from comparing Example 25 and Comparative Example 5, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 5 was 23 wt%, while the silicon content of the negative electrode active material layer in the secondary battery of Example 25 was 23 wt% or more. The secondary battery of Example 25 had a higher silicon content in the negative electrode active material layer than Comparative Example 5, but its initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) were all significantly higher. The 300-cycle expansion rate (Δh300) of the sheet of the secondary battery of Example 25 at 45°C was significantly lower than the 300-cycle expansion rate (Δh300) of the sheet of the secondary battery of Comparative Example 5 at 45°C.

[0239] As can be seen from a comparison between Example 26, Comparative Example 3, and Comparative Example 6, Example 26 and Comparative Example 6 used a silicon carbon material instead of silicon monoxide. The secondary battery of Example 26 had a higher silicon content in the negative electrode active material layer than Comparative Examples 3 and 6, but its initial coulombic efficiency (ICE), cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 were all clearly higher. The initial coulombic efficiency (ICE), cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of Comparative Example 6 were clearly higher than the initial coulombic efficiency (ICE), cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of Comparative Example 3. The 300-cycle expansion rate Δh300 of the sheet of the secondary battery of Example 26 at 45°C was clearly lower than the 300-cycle expansion rate Δh300 of the sheet of the secondary batteries of Comparative Examples 3 and 6 at 45°C, and the 300-cycle expansion rate Δh300 of the sheet of the secondary battery of Comparative Example 6 at 45°C was clearly lower than the 300-cycle expansion rate Δh300 of the sheet of the secondary battery of Comparative Example 3 at 45°C.

[0240] As can be seen from a comparison between Example 1 and Comparative Example 7, in Comparative Example 7, the weight per unit area of ​​the intermediate product of the negative electrode sheet in Example 1 was 2.53 mg / cm 2 The weight per unit area of ​​the negative electrode sheet was changed to 8.154 mg / cm 2 The secondary battery of Comparative Example 7 was the same as in Example 1, except that the h2 / h1 of the secondary battery of Comparative Example 7 was only 0.9, i.e., h2 / h1<2. As a result, the silicon content of the negative electrode active material layer of the secondary battery of Comparative Example 7 was significantly increased, and the initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 thereof were all significantly lower than the initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of Example 1. The secondary battery of Comparative Example 7 had a sheet expansion rate Δh300 at 45°C for 300 cycles that was significantly higher than the sheet expansion rate Δh300 at 45°C of the secondary battery of Example 1.

[0241] As can be seen from comparing Example 25 and Comparative Example 8, in Comparative Example 8, the first portion of Example 25 was used as the second portion, and the second portion of Example 25 was used as the first portion. Assuming that the silicon content of the negative electrode active material layer was the same, the initial coulombic efficiency I C, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of Example 25 were all significantly higher than the initial coulombic efficiency I C, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of Comparative Example 8. The 300-cycle expansion rate Δh300 of the sheet at 45°C of the secondary battery of Example 25 was lower than the 300-cycle expansion rate Δh300 of the sheet at 45°C of the secondary battery of Comparative Example 8.

[0242] As can be seen from Examples 1, 8, and 11, when the silicon-based material content of the first portion was 30 wt% to 70 wt%, the initial coulombic efficiency (ICE) of the secondary battery was 92.3% to 93.5%, the cycle capacity retention rate (ρ1) was 92% to 94.6%, the 300-cycle expansion rate (Δh300) of the sheet at 45°C was 25.8% to 35.8%, and the reversible storage capacity retention rate (ρ2) was 95% to 96.9%. Comparing Example 7 with Examples 1, 8, and 11, the initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) of the secondary battery of Example 7 remained essentially unchanged and showed no significant increase, even when the silicon content of the negative electrode active material layer was reduced. Comparing Example 12 with Examples 1, 8, and 11, the 300-cycle expansion rate (Δh300) of the sheet at 45°C of the secondary battery of Example 12 was too high.

[0243] Finally, it should be noted that the above embodiments are merely for the purpose of illustrating the technical solutions of the present application, and are not intended to limit the same. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified or equivalently substituted for some or all of the technical features thereof, and that such modifications or substitutions do not deviate from the essence of the corresponding technical solutions and the scope of the technical solutions of the embodiments of the present application, and are all intended to be included in the scope of the claims and the description of the present application. In particular, as long as there is no structural contradiction, any technical features described in the embodiments may be arbitrarily combined. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions encompassed by the claims. [Explanation of symbols]

[0244] 1000 vehicles 100 batteries 200 Controller 300 motor 10 boxes 11 First structure 12 Second structure 20 battery cells 21 End cover 22 cases 23 Electrode assembly 400 negative electrode sheet 410 Negative electrode current collector 420 Negative electrode active material layer 421 Part 1 422 Part 2

Claims

1. a negative electrode current collector; and a negative electrode active material layer, the negative electrode active material layer including a first portion and a second portion along a thickness direction, the first portion being a portion close to the negative electrode current collector, the mass percentage of the silicon-based material in the first portion being greater than the mass percentage of the silicon-based material in the second portion being greater than the mass percentage of the silicon-based material in the second portion, and a capacity per unit area of ​​the first portion being C １ and the capacitance per unit area of ​​the second portion is C ２ Then, C １ <C ２ This is the negative electrode sheet.

2. 0.11C ２ ≦C １ ≦0.25C ２ The negative electrode sheet according to claim 1 ,

3. 3. The negative electrode sheet according to claim 1, wherein the first portion is a first negative electrode active layer formed on the surface of the negative electrode current collector, the second portion is a second negative electrode active layer formed on the surface of the first negative electrode active layer, and a difference between a mass percentage of the silicon-based material of the first negative electrode active layer in the first negative electrode active layer and a mass percentage of the silicon-based material of the second negative electrode active layer in the second negative electrode active layer is 20% to 80%.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein the first portion contains 30 wt% to 70 wt% of a silicon-based material, and the silicon-based material contains a silicon-oxygen material and / or a silicon-carbon material.

5. The negative electrode sheet according to claim 4, wherein the silicon-based material of the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 20 μm or less.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein the first portion contains 10 wt% to 55 wt% graphite.

7. 7. The negative electrode sheet according to claim 1, wherein the graphite in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99 of 30 μm or less.

8. 8. The negative electrode sheet according to claim 1, wherein the first portion contains 3 wt % to 20 wt % of a binder.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein the first portion contains 0.15 wt% to 1.2 wt% of carbon nanotubes.

10. The negative electrode sheet according to claim 9 , wherein the carbon nanotubes have an aspect ratio of 1000 or more.

11. 11. The negative electrode sheet according to claim 9, wherein the first portion further contains 1 wt % to 5 wt % of a surfactant.

12. The negative electrode sheet according to any one of claims 1 to 11, wherein the first portion contains 0.5 wt% to 5 wt% of a dot-like conductive agent.

13. The first portion has a weight per unit area of ​​0.3 mg / cm ２ ~2.3 mg / cm ２ The negative electrode sheet according to any one of claims 1 to 12, wherein

14. The negative electrode sheet according to any one of claims 1 to 13, wherein the second portion contains a graphite material and a silicon-based material in a mass ratio of (80 to 100): (0 to 20).

15. The negative electrode sheet according to claim 14, wherein the Dv50 of the silicon-based material of the second portion is 1 μm to 8 μm, and the Dv50 of the graphite of the second portion is 1 μm to 20 μm.

16. The negative electrode active material layer has a weight per unit area of ​​5.19 mg / cm ２ ~14.26mg / cm ２ and the compaction degree is 1.4 g / cm ３ ~1.85g / cm ３ The negative electrode sheet according to any one of claims 1 to 15,

17. The thickness of the first portion is h １ and the thickness of the second portion is h ２ Let, h ２ ÷h １ The negative electrode sheet according to any one of claims 1 to 16, wherein the R2 is ≧2.

18. The above h １ is 1.5 μm to 15.5 μm, and ２ The negative electrode sheet according to claim 17, wherein the thickness is 34 μm to 66 μm.

19. 19. The negative electrode sheet according to claim 1, wherein the second portion includes at least two sub-portions along the thickness direction, and the mass percentages of the silicon-based material in each of the sub-portions are different.

20. a positive electrode sheet and the negative electrode sheet according to any one of claims 1 to 19, wherein the positive electrode sheet includes a positive electrode active material layer, and the capacity per unit area of ​​the positive electrode active material layer is C ３ and the capacity per unit area of ​​the negative electrode active material layer is C ４ and 1.01C ３ ≦C ４ ≦1.2C ３ That is, a secondary battery.

21. An electrical device comprising the secondary battery of claim 20.

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