Electrode assembly, secondary battery and electric device

Abstract

The present application provides an electrode assembly, a secondary battery, and an electric device, which belong to the battery technical field. The negative electrode active material layer includes first and second portions along the thickness direction, with the first portion being closer to the negative electrode current collector. During charge and discharge, the second portion preferentially intercalates lithium. During battery charging, the lithiation state of the second portion increases, while the lithiation state of the first portion decreases. The improvement in the electrochemical performance of the battery due to the second portion is greater than the improvement in the electrochemical performance of the battery due to the first portion. When 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 expansion problem of the silicon-based material in the negative electrode active material layer is alleviated. By setting 30%≦C2 / C1≦95%, the second portion can contribute 30% to 95% of the capacity from the positive electrode, further improving the initial efficiency, cycle life, and storage performance of the battery.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to Chinese Patent Application No. 202310235462.0, filed on March 13, 2023, for invention entitled "Electrode Assembly, Secondary Battery and Electrical Device," the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of battery technology, and more particularly to electrode assemblies, secondary batteries and electrical devices. [Background technology]

[0003] Silicon-based materials are currently used as negative electrode materials with relatively high gram capacities, but their cycle and storage performance are not ideal. The main cause of this problem is the constant generation of new SEI due to the expansion and pulverization of silicon particles in silicon-based negative electrodes, which consumes the active lithium in the positive electrode. Summary of the Invention

[0004] In view of the above problems, the present application provides an electrode assembly, a secondary battery and an electric device that can improve the initial efficiency, cycle and storage performance of silicon-based batteries.

[0005] In a first aspect, the present application provides an electrode assembly including a positive electrode piece and a negative electrode piece, wherein the negative electrode piece includes a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes a first portion and a second portion along a thickness direction, the first portion is a portion close to the negative electrode current collector, 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 positive electrode piece includes a positive electrode active material layer, the positive electrode active material layer has a unit area capacity C1, and the second portion has a unit area capacity C2, and 30%≦C2 / C1≦95%.

[0006] In the technical solution of the present embodiment, the negative electrode active material layer of the present embodiment includes a first portion and a second portion along the thickness direction, the first portion being the portion closest to the negative electrode current collector, and the second portion preferentially intercalates lithium during charging and discharging. That is, when the battery is charged, the second portion has a relatively high lithiation state, while the first portion has a relatively low lithiation state. The improvement in the electrochemical performance of the second portion relative to the battery is greater than the improvement in the electrochemical performance of 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 expansion problem of the silicon-based material in the negative electrode active material layer can be alleviated. At the same time, by setting 30%≦C2 / C1≦95%, the second portion can contribute 30% to 95% of the capacity from the positive electrode, further improving the initial efficiency, cycle life, and storage performance of the battery.

[0007] In some embodiments, 70%≦C2 / C1≦90%. When 70%≦C2 / C1≦90%, the second portion can contribute 70% to 90% of the capacity from the positive electrode, further improving the initial efficiency, cycle and storage performance of the battery, and allowing the battery to have a high energy density.

[0008] In some embodiments, the first portion is a first negative electrode active layer formed on a 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 the difference between the mass percentage of the silicon-based material in the first portion and the mass percentage of the silicon-based material in the second portion is 30% to 80%. When the negative electrode active material layer has a layered structure of a first negative electrode active material layer and a second negative electrode active material layer, and the difference between the mass percentage of the silicon-based material in the first negative electrode active material layer and the mass percentage of the silicon-based material in the second negative electrode active material layer is 30% to 80%, the mass percentage of the silicon-based material in the first portion is much greater than the mass percentage of the silicon-based material in the second portion, thereby further improving the expansion problem of the silicon-based material in the negative electrode active material layer.

[0009] In some embodiments, the capacity per unit area of ​​the first portion is C3, and 20%≦(C1−C2) / C3≦90%. When 20%≦(C1−C2) / C3≦90%, the second portion only needs to insert lithium to 20%-90%, which reduces the relative expansion of the silicon-based material with a small amount of lithium insertion, reduces the number of damaged areas of the silicon-based material, and improves the initial efficiency, cycle and storage performance of the battery.

[0010] In some embodiments, the capacity per unit area of ​​the first portion is C3, and 50%≦(C1−C2) / C3≦75%. When 50%≦(C1−C2) / C3≦75%, the second portion only needs to insert lithium to 50%-75%, which reduces the relative expansion of the silicon-based material with a small amount of lithium insertion, reduces the number of damaged areas of the silicon-based material, improves the initial efficiency, cycle and storage performance of the battery, and further increases the energy density of the battery.

[0011] In some embodiments, the first portion comprises 40 wt% to 80 wt% of a silicon-based material, the silicon-based material comprising silicon oxygen and / or silicon carbon. When the first portion comprises 40 wt% to 80 wt% of a silicon-based material, it is useful for improving the energy density of the entire negative electrode piece, and at the same time, it is possible to reduce the thickness of the first portion while maintaining a constant energy density, thereby reducing the diffusion path of lithium ions and improving kinetic performance.

[0012] In some embodiments, the silicon-based material in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99≦20 μm. If the particle size of the silicon-based material is too large, it will affect the lithium insertion ability of lithium ions, increasing the lithium insertion depth and affecting the electrochemical performance of the battery. However, 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 the mass percentage of the silicon-based material in the second portion, if the silicon-based material has a Dv50 of 1 μm to 8 μm and a Dv99≦20 μm, it will not only improve the electrochemical performance of the battery, but also improve processability and reduce scratches caused by application.

[0013] In some embodiments, the first portion contains 10% to 55% by weight of graphite. The graphite in the first portion not only provides capacity, but also, when the first portion contains 40% to 80% by weight of silicon-based material, the graphite can also function as a conductive agent to adjust the conductivity of the positive electrode active material when the silicon-based material in the first portion is relatively large. When the first portion contains 10% to 55% by weight of graphite, it can provide both conductive effects and improve the energy density of the negative electrode pieces.

[0014] In some embodiments, the graphite in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99≦30 μm. Because the first portion has a low weight per unit area and a relatively thin thickness, controlling the particle size of the graphite particles helps to ease the difficulty of coating, reduces the coating cracking caused by scratches on the copper foil, and is advantageous for improving the electronic conductivity of the first portion. When the graphite has a Dv50 of 1 μm to 8 μm and a Dv99≦30 μm, it not only does not affect the processing of the negative electrode pieces, but also ensures that the negative electrode pieces have relatively good electrical conductivity.

[0015] In some embodiments, the first portion comprises 3 wt% to 20 wt% of an adhesive, preferably with a glass transition temperature of ≦25°C. The adhesive can further suppress the expansion of the silicon-based material. When the first portion comprises 3 wt% to 20 wt% of an adhesive, the adhesive can control the volume effect of the silicon-based material to various degrees. In addition, to improve the processability of the negative electrode pieces and reduce the occurrence of cracking and peeling of the negative electrode pieces, the coating process of the negative electrode active material is usually carried out at room temperature and normal pressure, and an adhesive with a glass transition temperature ≦25°C can meet the production needs of room temperature and normal pressure.

[0016] In some embodiments, the first portion contains 0.5% to 5% by weight of a dot-shaped 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 contains 0.05 wt % to 1.2 wt % carbon nanotubes, preferably single-arm carbon nanotubes. Carbon nanotubes have high tensile strength, high pressure resistance, and excellent electrical conductivity. When the first portion contains 0.05 wt % to 1.2 wt % carbon nanotubes, the electronic conductivity of the first portion can be significantly improved. The carbon nanotubes can reduce particle swelling of the silicon-based material by distributing on the surface of the silicon-based material particles. However, the dispersibility of carbon nanotubes is relatively low, and they are prone to gelling in 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.

[0018] In some embodiments, the aspect ratio of the carbon nanotube is > 1000. When the aspect ratio of the carbon nanotube is > 1000, the extremely large aspect ratio of the carbon nanotube serves to further enhance the electronic conductivity of the first portion.

[0019] In some embodiments, the first part further comprises 1 wt% to 5 wt% of a surfactant, preferably sodium carboxymethylcellulose. Because the first part contains carbon nanotubes, but the carbon nanotubes have relatively low dispersibility, further comprising 1 wt% to 5 wt% of a surfactant in the first part is beneficial for uniform dispersion of the carbon nanotubes, thereby stabilizing processing performance.

[0020] In some embodiments, the weight per unit area of ​​the first portion is 0.5 mg / cm 2 ~3.6mg / cm 2 The unit area weight of the first part is 0.5 mg / cm 2 ~3.6mg / cm 2 In this case, it is possible to achieve both the dynamic performance of the battery and the feasibility of industrial production.

[0021] In some embodiments, the second portion comprises a graphite material and a silicon-based material in a mass ratio of (80-100):(0-20). When the mass ratio of the graphite material to the silicon-based material in the second portion is (80-100):(0-20), the electrochemical performance of the battery is better because the improvement in the electrochemical performance of the second portion to the battery is greater than the improvement in the electrochemical performance of the first portion to the battery.

[0022] In some embodiments, the Dv50 of the silicon-based material in the second portion is 1 μm to 8 μm, and the Dv50 of the graphite in the second portion is 1 μm to 20 μm. Because there are no technical problems in processing the second portion, the requirements for particle size are relatively low, and production can be met when the Dv50 of the silicon-based material in the second portion is 1 μm to 8 μm, and the Dv50 of the graphite in the second portion is 1 μm to 20 μm.

[0023] 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 compression density is 1.4 g / cm 3 ~1.85g / cm 3 The unit area weight of the negative electrode active material layer is 5.19 mg / cm 2 ~14.26mg / cm 2 and the compression density is 1.4 g / cm 3 ~1.85g / cm 3 If , the battery has a relatively high energy density.

[0024] In some embodiments, the thickness of the first portion is h1 and the thickness of the second portion is h2, where h2 / h1≧0.9, and preferably 20≧h2 / h1≧2. Controlling the ratio of second portion thickness / first portion thickness≧0.9 is advantageous in mitigating deterioration of dynamic performance.

[0025] In some embodiments, h1 is 3 μm to 21.5 μm, and h2 is 19 μm to 62.5 μm. When h1 and h2 are within the above thickness ranges and satisfy h2 / h1≧0.9, it is advantageous to further reduce deterioration of dynamic performance.

[0026] In some embodiments, the positive electrode piece includes a positive electrode active material layer, and the negative electrode active material layer has a unit area capacity of C4, where 1.01C1≦C4≦1.2C1. When 1.01C1≦C4≦1.2C1, the safety of the battery can be improved and the phenomenon of lithium precipitation due to excessive lithium insertion can be reduced.

[0027] In some embodiments, the second portion includes at least two sub-portions along the thickness direction, each having a different mass percentage of the silicon-based material. The second portion may further include multiple sub-portions, each having a different mass percentage of the silicon-based material, to accommodate different structures and types of batteries.

[0028] In a second aspect, the present application provides a secondary battery comprising the electrode assembly of the above embodiment.

[0029] In a third aspect, the present application provides an electric device comprising the secondary battery of the above embodiment.

[0030] The above description is merely a summary of the technical solution of the present application. In order to more clearly understand the technical means of the present application and to implement the present application in accordance with the contents of the specification, and to more clearly and easily understand the above and other objects, features and advantages of the present application, specific embodiments of the present application are specifically listed below. [Brief explanation of the drawings]

[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments. The drawings are for the purpose of illustrating the preferred embodiments only and are not to be construed as limiting the present application. In the drawings, like elements are designated by like reference numerals throughout. [Figure 1] 1 is a structural schematic diagram of a vehicle according to some embodiments of the present application. [Figure 2] 1 is a schematic exploded view of a battery according to some embodiments of the present application; [Figure 3] 1 is a schematic exploded view of a battery cell according to some embodiments of the present application; [Figure 4] 1 is a structural schematic diagram of a negative electrode piece according to some embodiments of the present application;

[0032] The reference numerals shown in the drawings relating to specific embodiments are as follows: 1000: vehicle, 100: battery, 200: controller, 300: motor, 10: case, 11: first structure, 12: second structure, 20: battery cell, 21: end cap, 22: casing, 23: electrode assembly, 400: negative electrode piece, 410: negative electrode current collector, 420: negative electrode active material layer, 421: first part, 422: second part DETAILED DESCRIPTION OF THE INVENTION

[0033] The following detailed description will be given of the embodiments of the technical solution of the present application in conjunction with the accompanying drawings. The following embodiments are merely for the purpose of more clearly illustrating the technical solution of the present application, and are therefore merely examples, and do not limit the scope of the claims of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. The terms used herein are for describing specific embodiments only and are not intended to limit the present application. The terms "comprises" and "includes" and any variations thereof in the specification, claims, and description of the drawings of this application are intended to cover a non-exclusive inclusion.

[0035] In the description of the embodiments of the present application, technical terms such as "first", "second", etc. are merely used to distinguish different objects, but should not be understood as indicating or implying relative importance, or the quantity, specific order, and priority relationship of the indicated technical features. In the description of the embodiments of the present application, "plurality" means two or more, unless otherwise clearly and specifically limited.

[0036] The term "embodiment" as used herein means that the specific feature, structure, or characteristic described in connection with the embodiment is 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 independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art will understand, both explicitly and implicitly, that the embodiments described herein can be combined with other embodiments.

[0037] In the description of the embodiments of the present application, the term "and / or" is simply a relation that describes related objects and indicates that three types of relations can exist. For example, A and / or B can represent three cases: the presence of only A, the simultaneous presence of A and B, and the presence of only B. In addition, the symbol " / " in this specification generally indicates that the related objects before and after it are in an "or" relationship.

[0038] In describing the embodiments of the present application, the term "plurality" refers to two or more (including two); similarly, "multiple sets" refers to two or more sets (including two sets); and "multiple sheets" refers to two or more (including two sheets).

[0039] In the description of the embodiments of the present application, orientations or positional relationships indicated by "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," "circumferential direction," etc. are orientations or positional relationships shown based on the drawings, and are intended merely to simplify the description and explanation of the embodiments of the present application. They do not indicate or imply that the devices or elements shown necessarily have a specific orientation, are configured, or must operate in a specific orientation, and therefore should not be understood as limiting the embodiments of the present application.

[0040] In describing the embodiments of the present application, unless otherwise clearly specified or limited, technical terms such as "attached," "coupled," "connected," and "fixed" should be understood in a broad sense, and may refer to, for example, a fixed connection, a detachable connection, or integration, a mechanical connection, an electrical connection, a direct connection, an indirect connection via an intermediate medium, 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.

[0041] Judging from the current market development, the application of power batteries will become more and more widespread. Power batteries are not only applied to energy storage power systems such as hydroelectric power generation, thermal power generation, wind power generation and solar power generation, but also widely used in electric transportation such as electric bicycles, electric motorcycles and electric cars, as well as in multiple fields such as military equipment and aerospace. As the application fields of power batteries continue to expand, their market demand will also continue to increase.

[0042] Silicon-based materials are currently anode materials with relatively high gram capacities, and they also have the advantages of low lithium insertion potential and wide supply sources, making them expected to become next-generation anode materials. However, the cycle performance and storage performance of silicon-based materials are not ideal, and the main cause of this problem is that new SEI is constantly generated due to the expansion and pulverization of silicon particles in silicon-based anodes, consuming active lithium from the cathode.

[0043] To alleviate the problem of new SEI constantly being generated due to the expansion and pulverization of silicon particles, consuming the active lithium of the positive electrode, the applicant has found through research that, during the charge and discharge process of a battery, lithium insertion occurs preferentially in the portion closer to the positive electrode active material layer along 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 closer to the positive electrode active material layer becomes increasingly higher, while the lithiation state of the negative electrode active material in the portion farther from the positive electrode active material layer (closer to the negative electrode current collector) becomes increasingly lower. At the same time, the electrochemical performance of the battery tends to approach the performance of the portion closer to the positive electrode active material layer. If a portion of the negative electrode active material layer close to the positive electrode active material layer contains more silicon-based material, the initial efficiency, cycle and storage performance of the battery will be relatively low.

[0044] Considering the above, in order to improve the initial efficiency, cycle life, and storage performance of silicon-based batteries, the present embodiment designs an electrode assembly in which the negative electrode active material layer includes a first portion and a second portion along the thickness direction, the first portion being the portion closest to the negative electrode current collector, and the second portion preferentially intercalates lithium during charging and discharging, i.e., 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, and the electrochemical performance of the battery is dominated by the second portion, and the improvement in the electrochemical performance of the battery by the second portion is greater than that of the first portion, and when 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 expansion problem of the silicon-based material in the negative electrode active material layer can be improved. Unit area capacity C = unit area weight (g / cm), while limiting 30%≦C2 / C1≦95%. 2 ) × gram capacity of the active layer (mAh / g), the second part can bear 30% to 95% of the capacity from the positive electrode, further improving the initial efficiency, cycling and storage performance of the battery.

[0045] The battery referred to in the embodiments of this application refers to a single physical module that includes multiple battery cells to provide higher voltage and capacity. The battery generally includes a battery case for enclosing the multiple battery cells, and the battery case can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells.

[0046] Each battery cell is a secondary battery, which may be, but is not limited to, a lithium-ion battery or a lithium-sulfur battery. The battery cells may be cylindrical, flat, rectangular, or have other shapes. Battery cells are generally divided into three types based on the encapsulation method: cylindrical battery cells, prismatic battery cells, and soft-pack battery cells.

[0047] A battery cell includes an electrode assembly and an electrolyte, and the electrode assembly is composed of a positive electrode piece, a negative electrode piece, and a separator. The battery cell functions primarily by relying on the movement of metal ions between the positive and negative electrode pieces. The positive electrode piece 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 positive electrode current collector without the positive electrode active material layer protrudes from the positive electrode current collector with the positive electrode active material layer coated thereon. The positive electrode current collector without the positive electrode active material layer is called 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, etc. The negative electrode piece 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 negative electrode current collector without the negative electrode active material layer protrudes from the negative electrode current collector with the negative electrode active material layer coated thereon. The negative electrode current collector without the negative electrode active material layer is called a negative electrode tab. The material of the negative electrode current collector may be copper. To ensure large current flow without fusing, multiple positive electrode tabs are stacked, and multiple negative electrode tabs are stacked. The material of the separator may be polypropylene (PP) or polyethylene (PE), etc. Furthermore, the electrode assembly may have a coil structure or a stacked structure, and the embodiment of the present application is not limited thereto.

[0048] The battery cell further includes a current collecting component, which is used to electrically connect the tab of the battery cell to the electrode terminal, thereby transporting electrical energy from the electrode assembly to the electrode terminal and then to the outside of the battery cell via the electrode terminal. Multiple battery cells are electrically connected via bus members to realize a series connection, parallel connection, or series-parallel connection of multiple battery cells.

[0049] The battery further includes a sampling terminal and a battery management system, and the sampling terminal is connected to the bus member to collect information of the battery cells, such as voltage or temperature, etc. The sampling terminal transmits the collected information of the battery cells to the battery management system, and when the battery management system detects that the information of the battery cells exceeds a normal range, it limits the output power of the battery to achieve safety protection.

[0050] The electric devices suitable for using the batteries described in the embodiments of the present application may be in various forms, such as mobile phones, portable devices, laptops, electric scooters, electric vehicles, boats, spacecraft, electric toys, and power tools, where, for example, spacecraft include airplanes, rockets, space shuttles, and spaceships, etc., electric toys include stationary or mobile electric toys such as game consoles, electric car toys, electric boat toys, and electric plane toys, and power tools include metal cutting power tools, grinding power tools, assembly power tools, and railroad power tools, such as power drills, power grinders, power wrenches, power screwdrivers, power hammers, impact drills, concrete vibrators, and power planers.

[0051] The battery cells and batteries described in the embodiments of the present application are not limited to application in the above-mentioned electrical devices, but may also be applied to all electrical devices that use battery cells and batteries. However, for the sake of simplicity, the following embodiments will be described using an electric vehicle as an example.

[0052] Referring to FIG. 1, FIG. 1 is a structural schematic diagram of a vehicle provided by some embodiments of the present application. The vehicle 1000 may be a fuel-powered vehicle, a gas-powered vehicle, or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle, a range-extended vehicle, etc. A battery 100 is installed inside the vehicle 1000, and the battery 100 can be installed at the bottom, head, or tail of the vehicle 1000. The battery 100 is used to supply power to the vehicle 1000. For example, the battery 100 can function as an operating power source for the vehicle 1000. The vehicle 1000 may further include a controller 200 and a motor 300. The controller 200 controls the battery 100 to supply power to the motor 300, for example, to meet the operating power needs of the vehicle 1000 during starting, navigation, and driving.

[0053] In some embodiments of the present application, the battery 100 is not only used as the operating power source for the vehicle 1000, but can also provide driving power to the vehicle 1000, completely or partially replacing fuel or natural gas as the driving power source for the vehicle 1000.

[0054] Please refer to FIG. 2, which is an exploded view provided according to some embodiments of the present application. The battery 100 includes a case 10 and battery cells 20, which are housed within the case 10. Here, the case 10 is used to provide a housing space for the battery cells 20, and the case 10 can adopt various structures. In some embodiments, the case 10 may include a first structure 11 and a second structure 12, which are covered by each other, and which together define a housing space for housing the battery cells 20. The second structure 12 may be a hollow structure with one end open, the first structure 11 may be a plate-like structure, and the first structure 11 is covered by the open side of the second structure 12 so that the first structure 11 and the second structure 12 together define an accommodating space, and the first structure 11 and the second structure 12 may both be hollow structures with one end open, and the open side of the first structure 11 is covered by the open side of the second structure 12. Naturally, the shape of the case 10 formed by the first structure 11 and the second structure 12 may be various shapes such as a cylinder or a rectangular parallelepiped.

[0055] The battery 100 may include multiple battery cells 20, and the multiple battery cells 20 may be connected in series, parallel, or series-parallel. A series-parallel connection refers to multiple battery cells 20 being connected in both series and parallel. The multiple battery cells 20 are connected in direct series, parallel, or series-parallel, and the entire battery cell set is housed in the case 10. Of course, the battery 100 may also be formed by first connecting multiple battery cells 20 in series, parallel, or series-parallel to form a battery module, and then connecting the multiple battery modules in series, parallel, or series-parallel to form the entire battery module housed in the case 10. The battery 100 may also include other structures, for example, the battery 100 may further include a bus member for electrically connecting the multiple battery cells 20.

[0056] Each battery cell 20 is a secondary battery, which may be, but is not limited to, a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, and may have a cylindrical, flat, rectangular, or other shape.

[0057] 3, which is a schematic exploded view of a first battery cell 20 according to some embodiments of the present application. A battery cell 20 refers to the smallest unit constituting a battery. As shown in FIG. 3, the battery cell 20 includes an end cap 21, a casing 22, an electrode assembly 23, and other functional components.

[0058] The end cap 21 refers to a member that covers the opening of the casing 22 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the end cap 21 may be adapted to the shape of the casing 22 so as to fit snugly within the casing 22. Optionally, the end cap 21 may be made of a material with a certain hardness and strength (e.g., aluminum alloy). This makes the end cap 21 less likely to deform when subjected to pressure or impact, allowing the battery cell 20 to have higher structural strength and improved safety performance. Functional members such as electrode terminals may be installed on the end cap 21. The electrode terminals may be used to electrically connect with the electrode assembly 23 for inputting or outputting electrical energy to or from the battery cell 20. In some embodiments, the end cap 21 may further be installed 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 cap 21 may be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, or plastic, and is not particularly limited in the embodiments of the present application. In some embodiments, an insulating member may be further installed inside the end cap 21, and the insulating member may be used to isolate the electrical connections in the casing 22 from the end cap 21 so as to reduce the risk of short circuits. Illustratively, the insulating member may be plastic, rubber, or the like.

[0059] The casing 22 is an assembly that mates with the end cap 21 to form an internal environment of the battery cell 20, which can be used to accommodate the electrode assembly 23, electrolyte, and other components. The casing 22 and the end cap 21 may be separate components, or an opening may be formed in the casing 22, with the end cap 21 covering the opening to form the internal environment of the battery cell 20. The end cap 21 and the casing 22 may be integrated, but are not limited to these. Specifically, the end cap 21 and the casing 22 may first form a common connection surface before other components are inserted into the casing. If the interior of the casing 22 needs to be sealed, the end cap 21 covers the casing 22. The casing 22 may have various shapes and dimensions, such as a rectangular parallelepiped, cylindrical, or hexagonal prism. The shape of the casing 22 may be determined based on the specific shape and dimensions of the electrode assembly 23. The casing 22 may be made of various materials such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and is not particularly limited in the embodiment of the present application.

[0060] The electrode assembly 23 is a component that initiates an electrochemical reaction in the battery cell 20. The casing 22 may house one or more electrode assemblies 23. The electrode assembly 23 is typically formed by winding or stacking positive and negative electrode pieces, with a separator typically disposed between the positive and negative electrode pieces. The portions of the positive and negative electrode pieces containing active material constitute the main body of the electrode assembly, while the portions of the positive and negative electrode pieces not containing active material constitute tabs, respectively. The positive and negative electrode tabs may be located together at one end of the main body, or at both ends of the main body. During the charge and discharge process of the battery, the positive and negative electrode active materials react with the electrolyte, and the tabs are connected to electrode terminals to form a current loop.

[0061] According to some embodiments of the present application, please refer to FIG. 4, which is a structural schematic diagram of a negative electrode piece according to some embodiments of the present application.

[0062] The present application provides an electrode assembly including a positive electrode piece and a negative electrode piece 400, the negative electrode piece 400 including a negative electrode active material layer 420 and a negative electrode current collector 410, the negative electrode active material layer 420 including a first portion 421 and a second portion 422 along the thickness direction, the first portion 421 being a portion close to the negative electrode current collector 410, the mass percentage of the silicon-based material in the first portion 421 being greater than the mass percentage of the silicon-based material in the second portion 422, the positive electrode piece having a unit area capacity C1, the second portion 422 having a unit area capacity C2, and 30%≦C2 / C1≦95%.

[0063] The first portion 421 is a portion of the negative electrode active material layer 420 that is close to the negative electrode current collector 410 .

[0064] The second portion 422 is a portion of the negative electrode active material layer 420 that is separated from the negative electrode current collector 410, and is the remaining portion of the entire negative electrode active material layer 420 after the first portion 421 has been removed.

[0065] The mass percentage of the silicon-based material in the first portion 421 is the mass percentage that the mass of the silicon-based material accounts for in the total mass of the first portion 421 .

[0066] The mass percentage of the silicon-based material in the second portion 422 is the mass percentage that the mass of the silicon-based material accounts for in the total mass of the second portion 422.

[0067] The capacitance C1 per unit area of ​​the positive electrode active material layer is measured using a test method known in the art. For example, it can be measured by the following method.

[0068] S1: Clean one side of the double-sided positive electrode piece.

[0069] S2, using a die, the single-sided positive electrode piece is punched into a small circular sheet with a radius of 7 mm, and its area is S = 0.49π, and the unit of area S is cm 2 is.

[0070] S3, a single-sided cathode piece having an area of ​​S, is dried and then transferred to a glove box to prepare a mating lithium half-cell.

[0071] S4. The capacity Q1 of the circular sheet is measured using a Wuhan blue-electricity testing instrument. The unit of capacity Q1 is mAh. The capacity C1 of the positive electrode active material layer per unit area is calculated as C1 = Q1 ÷ S, and the unit of capacity C1 of the positive electrode active material layer per unit area is mAh / cm. 2 is.

[0072] The capacitance C2 of the second portion is measured using a test method known in the art. For example, it can be measured by the following method.

[0073] S1: Clean one side of the double-sided negative electrode piece.

[0074] S2, using a die, the single-sided negative electrode piece is punched into a small circular sheet with a radius of 7 mm, and its area is S = 0.49π, and the unit of area S is cm 2 is.

[0075] S3, a single-sided negative electrode piece having an area of ​​S, is dried and then transferred to a glove box to prepare a mating lithium half-cell.

[0076] S4, the capacity Q4 of the circular sheet is measured using a Wuhan blue-electricity testing instrument, and 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, and the unit of capacity C4 of the negative electrode active material layer per unit area is mAh / cm 2 is.

[0077] S5, peel off the second portion of the single-sided negative electrode piece treated in step S1 with tape.

[0078] In step S6, the capacity Q3 of the first portion is measured on the peeled negative electrode piece of the second portion in the same manner as in steps S2, S3, and S4. The unit of the capacity Q3 is mAh. The unit area capacity C3 of the first portion is calculated as C3 = Q3 ÷ S, and the unit area capacity C3 of the negative electrode active material layer is mAh / cm. 2and the unit area capacity of the second portion C2 = C4 - C3, and the unit of the capacity C2 of the negative electrode active material layer per unit area is mAh / cm 2 is.

[0079] By way of example, the value of C2 / C1 may be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%.

[0080] The negative electrode active material layer of the present invention includes a first portion and a second portion along the thickness direction, the first portion being closest to the negative electrode current collector, and the second portion preferentially intercalating lithium during charging and discharging. That is, during charging, the second portion achieves a relatively high lithiation state, while the first portion achieves a relatively low lithiation state. The second portion's electrochemical performance improvement relative to the battery is greater than that of the first portion. When 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 expansion problem of the silicon-based material in the negative electrode active material layer can be alleviated. At the same time, by setting the C2 / C1 ratio to 30% or less and 95% or less, the second portion can contribute 30% to 95% of the capacity from the positive electrode, further improving the initial efficiency, cycling, and storage performance of the battery.

[0081] According to some embodiments of the present application, optionally, 70%≦C2 / C1≦90%.

[0082] When 70%≦C2 / C1≦90%, the second portion can bear 70% to 90% of the capacity from the positive electrode, further improving the initial efficiency, cycle and storage performance of the battery, and making the battery have a high energy density.

[0083] According to some embodiments of the present application, optionally, the capacitance per unit area of ​​the first portion is C3, and 20%≦(C1−C2) / C3≦90%.

[0084] The capacitance C3 per unit area of ​​the first portion is measured based on the test method for the capacitance C2 per unit area of ​​the second portion.

[0085] As examples, the value of (C1-C2) / C3 may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0086] When 20%≦(C1-C2) / C3≦90%, the second part only needs to insert lithium to 20%~90%, which reduces the relative expansion of the silicon-based material with a small amount of lithium insertion, reduces the damaged areas of the silicon-based material, and improves the initial efficiency, cycle and storage performance of the battery.

[0087] According to some embodiments of the present application, optionally, the first portion is a first negative electrode active layer formed on the surface of the negative electrode current collector, and the second portion is a second negative electrode active layer formed on the surface of the first negative electrode current collector, and the difference between the mass percentage of the silicon-based material in the first negative electrode active layer and the mass percentage of the silicon-based material in the second negative electrode active layer is 30% to 80%.

[0088] For example, the difference between the mass percentage of the silicon-based material in the first negative electrode active layer and the mass percentage of the silicon-based material in the second negative electrode active layer may be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%.

[0089] When the negative electrode active material layer has a layered structure of a first negative electrode active material layer and a second negative electrode active material layer, and the difference between the mass percentage of the silicon-based material in the first negative electrode active material layer and the mass percentage of the silicon-based material in the second negative electrode active material layer is 30% to 80%, the mass percentage of the silicon-based material in the first portion is much greater than the mass percentage of the silicon-based material in the second portion, thereby further improving the expansion problem of the silicon-based material in the negative electrode active material layer.

[0090] Optionally, the difference between the mass percentage of the silicon-based material in the first negative electrode active layer and the mass percentage of the silicon-based material in the second negative electrode active layer is 30% to 50%.

[0091] According to some embodiments of the present application, optionally, the capacitance per unit area of ​​the first portion is C3, and 50%≦(C1−C2) / C3≦75%.

[0092] When 50%≦(C1-C2) / C3≦75%, the second part only needs to insert lithium to 50%-75%, which reduces the relative expansion of the silicon-based material with a small amount of inserted lithium, reduces the damaged areas of the silicon-based material, improves the initial efficiency, cycle and storage performance of the battery, and further improves the energy density of the battery.

[0093] According to some embodiments of the present application, optionally, the first portion includes 40% to 80% by weight of a silicon-based material, and the silicon-based material includes any one or more of elemental silicon, silicon oxygen, and silicon carbon.

[0094] By way of example, the first portion may include 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80% by weight of silicon-based material.

[0095] By way of example, the silicon-based material may be all elemental silicon, or all silicon oxygen, or all silicon carbon, or a mixture of elemental silicon and silicon oxygen, or a mixture of elemental silicon and silicon carbon, or a mixture of elemental silicon, silicon oxygen, and silicon carbon.

[0096] Optionally, the silicon-based material comprises silicon oxygen and / or silicon carbon.

[0097] When the first portion contains 40 wt % to 80 wt % of silicon-based material, it helps to improve the energy density of the entire negative electrode piece, and at the same time, under the condition that the energy density is constant, it reduces the thickness of the first portion, reduces the diffusion path of lithium ions, and also improves the kinetic performance.

[0098] Optionally, the first portion comprises 50% to 60% by weight of the silicon-based material.

[0099] According to some embodiments of the present application, optionally, the silicon-based material in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99≦20 μm.

[0100] If the particle size of the silicon-based material is too large, it will affect the lithium ion intercalation ability, increasing the depth of lithium intercalation and affecting the electrochemical performance of the battery, while if the particle size of the silicon-based material is too small, it will be difficult to process.In addition, 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 has a Dv50 of 1 μm to 8 μm and a Dv99 of 20 μm or less, it will not only help improve the electrochemical performance of the battery, but also improve processability and reduce scratches caused by application.

[0101] According to some embodiments of the present application, optionally, the first portion includes 10% to 55% by weight of graphite.

[0102] By way of example, the first portion may include 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or 55% graphite by weight.

[0103] The graphite in the first portion not only provides capacity, but also acts as a conductive agent to adjust the conductivity of the positive electrode active material when the first portion contains 40% to 80% by weight of silicon-based material. When the first portion contains a relatively large amount of silicon-based material, the graphite can adjust the conductivity of the positive electrode active material as a conductive agent. When the first portion contains 10% to 55% by weight of graphite, both the conductive effect and the energy density of the negative electrode piece can be achieved.

[0104] Optionally, the first portion comprises 30% to 40% by weight graphite.

[0105] According to some embodiments of the present application, optionally, the graphite in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99≦30 μm.

[0106] Because the first portion has a low weight per unit area and a relatively thin thickness, controlling the particle size of the graphite particles helps to ease the difficulty of coating, reduces the coating cracking caused by scratches on the copper foil, and is also advantageous for improving the electronic conductivity of the first portion. When the Dv50 of the graphite is 1 μm to 8 μm and Dv99≦30 μm, it not only does not affect the processing of the negative electrode pieces, but also allows the negative electrode pieces to have relatively good electrical conductivity.

[0107] According to some embodiments of the present application, optionally, the first part contains 3% to 20% by weight of an adhesive, and preferably, the adhesive has a glass transition temperature of ≦25°C.

[0108] By way of example, the first portion may include 3%, 5%, 8%, 10%, 12%, 15%, 18% or 20% adhesive by weight.

[0109] The adhesive can further suppress the expansion of the silicon-based material. When the first portion contains 3 wt% to 20 wt% of the adhesive, the adhesive can control the volume effect of the silicon-based material to various degrees. In addition, to improve the processing performance of the negative electrode pieces and reduce the occurrence of cracking and peeling of the negative electrode pieces, the coating process of the negative electrode active material is usually carried out at room temperature and normal pressure, and an adhesive with a glass transition temperature of ≦25°C can meet the production needs at room temperature and normal pressure.

[0110] Optionally, the first portion comprises 12% to 15% by weight of adhesive.

[0111] Optionally, the adhesive is a styrene butadiene rubber.

[0112] The glass transition temperature of styrene butadiene rubber is lower than 0°C. By selecting styrene butadiene rubber as the adhesive for the first part, the expansion of the silicon particles can be more effectively inhibited, while at the same time ensuring that the negative electrode pieces have better mechanical properties and the structural stability of the negative electrode pieces.

[0113] According to some embodiments of the present application, optionally, the first portion contains 0.5% to 5% by weight of a dot-shaped conductive agent, preferably conductive carbon black.

[0114] The dot-shaped conductive material is a conductive material with an aspect ratio of less than 1.5.

[0115] For example, the first portion may further include 0.5 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, or 5 wt % of dot-shaped conductive agent.

[0116] The dot-shaped conductive agent can improve the conductivity and electrolyte retention capacity of the first portion.

[0117] Optionally, the first portion contains 1% to 2% by weight of the dot-shaped conductive agent.

[0118] Optionally, the dot-shaped conductive agent includes any one or more of superconducting carbon, acetylene black, ketjen black, conductive carbon black, graphene, and carbon dots.

[0119] According to some embodiments of the present application, optionally, the first portion comprises 0.05 wt % to 1.2 wt % of carbon nanotubes, preferably single-arm carbon nanotubes.

[0120] By way of example, the first portion may include 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1% or 1.2% by weight of carbon nanotubes.

[0121] Carbon nanotubes have high tensile strength, high pressure resistance, and excellent electrical conductivity. When the first portion contains 0.05% to 1.2% by weight of carbon nanotubes, the electronic conductivity of the first portion can be significantly improved. The carbon nanotubes can reduce particle swelling of the silicon-based material by distributing on the surface of the silicon-based material particles. However, the dispersibility of carbon nanotubes is relatively low, and they are prone to gelation in the slurry, so they cannot be added in large quantities. Controlling the carbon nanotube content to within 1.2% by weight can achieve both improved electronic conductivity and improved processing performance. Single-arm carbon nanotubes are linear materials.

[0122] Optionally, the first portion comprises 0.1% to 0.4% by weight of carbon nanotubes.

[0123] According to some embodiments of the present application, optionally, the aspect ratio of the carbon nanotubes is ≧1000.

[0124] 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.

[0125] When the aspect ratio of the carbon nanotube is ≧1000, the extremely large aspect ratio of the carbon nanotube serves to further improve the electronic conductivity of the first portion.

[0126] Optionally, the aspect ratio of the carbon nanotubes is 1,000-10,000.

[0127] According to some embodiments of the present application, optionally, the first part further comprises 1% to 5% by weight of a surfactant, preferably sodium carboxymethylcellulose.

[0128] By way of example, the first part may further comprise 1%, 2%, 3%, 4% or 5% by weight of a surfactant.

[0129] The first part contains carbon nanotubes, but the dispersibility of the carbon nanotubes is relatively low. Therefore, if the first part further contains 1% by weight to 5% by weight of a surfactant, it is advantageous for uniform dispersion of the carbon nanotubes, thereby stabilizing processing performance.

[0130] Optionally, the first portion further comprises 1.5% to 3% by weight of a surfactant.

[0131] According to some embodiments of the present application, optionally, the weight per unit area of ​​the first portion is 0.5 mg / cm 2 ~3.6mg / cm 2 is.

[0132] For example, the weight per unit area of ​​the first portion is 0.5 mg / cm 2 , 0.8 mg / cm 2 , 1 mg / cm 2 , 1.5 mg / cm 2 , 2 mg / cm 2 , 2.5 mg / cm 2 , 3 mg / cm 2 , 3.5 mg / cm 2 or 3.6 mg / cm 2 may be.

[0133] The weight per unit area of ​​the first portion is 0.5 mg / cm 2 ~3.6mg / cm 2 In this case, it is possible to achieve both the dynamic performance of the battery and the feasibility of industrial production.

[0134] 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).

[0135] The second portion includes a graphite material and does not include a silicon-based material.

[0136] Alternatively, the second portion includes a graphite material and a silicon-based material.

[0137] As examples, 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.

[0138] Since the improvement in the electrochemical performance of the second part for the battery is greater than the improvement in the electrochemical performance of the first part for the battery, when the mass ratio of the graphite material to the silicon-based material in the second part is (80-100):(0-20), the electrochemical performance of the battery is better.

[0139] 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.

[0140] According to some embodiments of the present application, optionally, the silicon-based material in the second portion has a Dv50 of 1 μm to 8 μm, and the graphite in the second portion has a Dv50 of 1 μm to 20 μm.

[0141] Since there are no technical problems in processing the second part, the requirements for particle size are relatively low, and the production requirements can be met when the Dv50 of the silicon-based material in the second part is 1 μm to 8 μm and the Dv50 of the graphite in the second part is 1 μm to 20 μm.

[0142] According to some embodiments of the present application, the negative electrode active material layer may have a unit area weight of 5.19 mg / cm 2 ~14.26mg / cm 2 and the compression density is 1.4 g / cm 3 ~1.85g / cm 3 is.

[0143] For example, the unit area weight 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 / cm 2 , 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.

[0144] For example, the compression density 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.

[0145] The unit area weight of the negative electrode active material layer is 5.19 mg / cm 2 ~14.26mg / cm 2 and the compression density is 1.4 g / cm 3 ~1.85g / cm 3 If , the battery has a relatively high energy density.

[0146] According to some embodiments of the present application, optionally, the thickness of the first portion is h1 and the thickness of the second portion is h2, where h2÷h1≧0.9, and preferably 20≧h2÷h1≧2.

[0147] Controlling the ratio of the thickness of the second portion to the thickness of the first portion to be ≧0.9 is advantageous in reducing deterioration of dynamic performance.

[0148] According to some embodiments of the present application, optionally, h1 is between 3 μm and 21.5 μm, and h2 is between 19 μm and 62.5 μm.

[0149] By way of example, h1 may be 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, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm or 21.5 μm.

[0150] h2 may be 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 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 or 61.5 μm.

[0151] When h1 and h2 are within the above thickness ranges and satisfy h2 / h1≧0.9, this is advantageous in that deterioration of dynamic performance can be further reduced.

[0152] According to some embodiments of the present application, optionally, the positive electrode piece includes a positive electrode active material layer, and the negative electrode active material layer has a unit area capacity C4, where 1.01C1≦C4≦1.2C1.

[0153] When 1.01C1≦C4≦1.2C1, the safety of the battery can be improved and the phenomenon of lithium precipitation due to excessive lithium insertion can be reduced.

[0154] 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.

[0155] 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.

[0156] The secondary battery of the present invention will be described in more detail below with reference to examples. Example 1 An embodiment of the present application provides a secondary battery and a method for manufacturing the same, which includes the following steps. S1, negative electrode piece production

[0157] Forming the first part: Silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose were mixed in deionized water in a mass ratio of 50:32.2:15:1:0.3:1.5 with sufficient stirring to prepare a first negative electrode slurry, which was then uniformly applied to a copper current collector having a thickness of 8 μm and a conductive carbon undercoat of 2 μm, and dried to a unit area weight of 0.990 mg / cm. 2 Thus, semi-finished negative electrode pieces are obtained.

[0158] Among them, the Dv50 of silicon monoxide is 5 μm, the Dv50 of artificial graphite is 4.7 μm, the Dv99 is 13 μm, and the aspect ratio of single-arm carbon nanotubes is 5000.

[0159] Forming the second part: Artificial graphite, styrene butadiene rubber, sodium carboxymethyl cellulose, and conductive carbon black (Super-P, SP) were mixed in deionized water in a mass ratio of 96.2:1.8:1.2:0.8 with sufficient stirring to prepare a second negative electrode slurry, which was then applied to the first part to form a second part, followed by drying, cold pressing, and cutting to obtain a pressed electrode with a density of 1.65 g / cm. 3 , unit area weight is 10.418mg / cm 2 A negative electrode piece is obtained.

[0160] Among them, the Dv50 of artificial graphite is 15.3 μm.

[0161] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.75 wt %. S2, manufacturing of positive electrode pieces Lithium Nickel Cobalt Manganese 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 by thorough stirring to form a uniform positive electrode slurry. The positive electrode slurry was then applied to the surface of the positive electrode current collector aluminum foil, dried, cold pressed, stripped, and cut to a density of 3.5 g / cm. 3 The unit area weight is 18.04 mg / cm 2 A positive electrode piece is obtained. S3, Separator selection A 12 μm thick polyethylene film is used as the separator.

[0162] S4, Electrolyte production Ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the solution to obtain an electrolyte solution with a LiPF6 concentration of 1 mol / L. S5, secondary battery manufacturing The positive electrode pieces, separator, and negative electrode pieces are stacked in this order, with the separator positioned between the positive electrode pieces and the negative electrode pieces to act as an insulator, and lithium foil is placed on the surface of the non-reactive area, which is then wound up to obtain an electrode assembly. The electrode assembly is placed in an outer casing, dried, and then an electrolyte is injected. After vacuum sealing, standing, chemical formation, shaping, and other processes, a secondary battery is obtained.

[0163] Example 2 Example 2, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 3.532 mg / cm 2 The unit area weight of the negative electrode piece was changed to 6.882 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0164] The silicon content of the negative electrode active material layer of the negative electrode piece was 25.66 wt %.

[0165] Example 3 Example 3, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 2.603 mg / cm 2 The unit area weight of the negative electrode piece was changed to 8.174 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0166] The silicon content of the negative electrode active material layer of the negative electrode piece is 15.92 wt %.

[0167] Example 4 Example 4, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 1.669 mg / cm 2 The unit area weight of the negative electrode piece was changed to 9.472 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0168] The silicon content of the negative electrode active material layer of the negative electrode piece is 8.81 wt %.

[0169] Example 5 Example 5, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 0.5 mg / cm 2 The unit area weight of the negative electrode piece was changed to 11.1 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0170] The silicon content of the negative electrode active material layer of the negative electrode piece was 2.25 wt %.

[0171] Example 6 Example 6, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 1.168 mg / cm 2 The unit area weight of the negative electrode piece was changed to 11.769 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0172] The silicon content of the negative electrode active material layer of the negative electrode piece is 4.96 wt %.

[0173] Example 7 Example 7, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 0.73 mg / cm 2 and the unit area weight of the negative electrode piece was changed to 10.779 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0174] The silicon content of the negative electrode active material layer of the negative electrode piece is 3.39 wt %.

[0175] Example 8 Example 8, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 0.93 mg / cm 2 and the unit area weight of the negative electrode piece was changed to 10.945 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0176] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.25 wt %.

[0177] Example 9 Example 9, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 0.7 mg / cm 2 and the unit area weight of the negative electrode piece was changed to 10.565 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0178] The silicon content of the negative electrode active material layer of the negative electrode piece was 3.31 wt %.

[0179] Example 10 Example 10, which is an example of the present application, is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 0.7 mg / cm 2 The unit area weight of the negative electrode piece was changed to 10.821 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0180] The silicon content of the negative electrode active material layer of the negative electrode piece is 3.23 wt %.

[0181] Example 11 Example 11, which is an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first part is changed to 30:63.7:3.5:1:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 1.26 mg / cm 2 and the unit area weight of the negative electrode piece was changed to 10.692 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0182] The silicon content of the negative electrode active material layer of the negative electrode piece was 3.54 wt %.

[0183] Example 12 Example 12, which is an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first part is changed to 40:55:2.2:1:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 1.08 mg / cm. 2 and the unit area weight of the negative electrode piece was changed to 10.496 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0184] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.12 wt %.

[0185] Example 13 Example 13, which is an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first part is changed to 60:22.2:15:1:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 0.88 mg / cm. 2 and the unit area weight of the negative electrode piece was changed to 10.294 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0186] The silicon content of the negative electrode active material layer of the negative electrode piece was 5.13 wt %.

[0187] Example 14 Example 14, which is an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first part is changed to 70:12.2:15:1:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 0.78 mg / cm 2 The unit area weight of the negative electrode piece was changed to 10.219 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0188] The silicon content of the negative electrode active material layer of the negative electrode piece was 5.34 wt %.

[0189] Example 15 Example 15, an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first part is changed to 80:10:7.2:1:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 0.69 mg / cm. 2 and the unit area weight of the negative electrode piece was changed to 10.130 mg / cm 2The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0190] The silicon content of the negative electrode active material layer of the negative electrode piece was 5.45 wt %.

[0191] Example 16 Example 16, which is an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first part is changed to 90:5:2.2:1:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 0.63 mg / cm. 2 and the unit area weight of the negative electrode piece was changed to 10.045 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0192] The silicon content of the negative electrode active material layer of the negative electrode piece was 5.64 wt %.

[0193] Example 17 Example 17, which is an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first part is changed to 50:44.2:3:1:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 0.95 mg / cm 2 and the unit area weight of the negative electrode piece was changed to 10.358 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0194] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.59 wt %.

[0195] Example 18 Example 18, an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first portion is changed to 50:27.2:20:1:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 1.02 mg / cm 2 and the unit area weight of the negative electrode piece was changed to 10.427 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0196] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.89 wt %.

[0197] Example 19 Example 19, which is an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first portion was changed to 50:32.7:15:0.5:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece was 0.99 mg / cm. 2 and the unit area weight of the negative electrode piece was changed to 10.413 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0198] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.75 wt %.

[0199] Example 20 Example 20, an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first portion is changed to 50:28.2:15:5:0.3:1.5, and the unit area weight of the semi-finished negative electrode piece is 1.00 mg / cm. 2 and the unit area weight of the negative electrode piece was changed to 10.444 mg / cm 2The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0200] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.79 wt %.

[0201] Example 21 Example 21, an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first part is changed to 50:32.95:15:1:0.05:1, and the unit area weight of the semi-finished negative electrode piece is 0.99 mg / cm. 2 and the unit area weight of the negative electrode piece was changed to 10.410 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0202] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.75 wt %.

[0203] Example 22 Example 22, which is an example of the present application, is based on Example 1, except that the compounding ratio of silicon monoxide, artificial graphite, styrene butadiene rubber, conductive carbon black (SP), single-arm carbon nanotubes, and sodium carboxymethyl cellulose in the first portion was changed to 50:27.8:15:1:1.2:5, and the unit area weight of the semi-finished negative electrode piece was 1.01 mg / cm. 2 and the unit area weight of the negative electrode piece was changed to 10.434 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0204] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.84 wt %.

[0205] Example 23 Example 23, which is an example of the present application, provides a secondary battery and a manufacturing method thereof based on Example 1, except that the aspect ratio of the arm carbon nanotube is changed to 1000, and the other aspects are not changed.

[0206] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.75 wt %.

[0207] Example 24 Example 24, which is an example of the present application, provides a secondary battery and a manufacturing method thereof based on Example 1, except that the aspect ratio of the arm carbon nanotube is changed to 10000, and other aspects are not changed.

[0208] The silicon content of the negative electrode active material layer of the negative electrode piece was 4.75 wt %.

[0209] Example 25 Example 25, an example of the present application, is based on Example 1, except that the components of the second part are changed to artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, and conductive carbon black (Super-P, SP), which are mixed in a blending ratio of 94.2:2:1.8:1.2:0.8, and the unit area weight of the negative electrode piece is 9.889 mg / cm. 2 The present invention provides a secondary battery and a method for manufacturing the same, in which the above-mentioned components are the same as those in the first embodiment.

[0210] The silicon content of the negative electrode active material layer of the negative electrode piece was 6.72 wt %.

[0211] Example 26 Example 26, which is an example of the present application, is based on Example 1, but the components of the second part 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 unit area weight of the negative electrode piece was 9.17 mg / cm. 2 The present invention provides a secondary battery and a method for manufacturing the same, in which the above-mentioned components are the same as those in the first embodiment.

[0212] The silicon content of the negative electrode active material layer of the negative electrode piece was 9.77 wt %.

[0213] Example 27 Example 27, an example of the present application, is based on Example 1, but the components of the second part 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 86.2:10:1.8:1.2:0.6:0.2, and the unit area weight of the negative electrode piece was 8.199 mg / cm. 2 The present invention provides a secondary battery and a method for manufacturing the same, which are otherwise unchanged.

[0214] The silicon content of the negative electrode active material layer of the negative electrode piece is 14.75 wt %.

[0215] Example 28 Example 28, an example of the present application, is based on Example 1, but the components of the second part 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 81.2:15:1.8:1.2:0.5:0.3, and the unit area weight of the negative electrode piece was 7.433 mg / cm. 2 The present invention provides a secondary battery and a method for manufacturing the same, which are otherwise unchanged.

[0216] The silicon content of the negative electrode active material layer of the negative electrode piece was 19.58 wt %.

[0217] Example 29 Example 29, an example of the present application, is based on Example 1, but the components of the second part 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 76.2:20:1.8:1.2:0.4:0.4, and the unit area weight of the negative electrode piece was 6.814 mg / cm. 2 The present invention provides a secondary battery and a method for manufacturing the same, which are otherwise unchanged.

[0218] The silicon content of the negative electrode active material layer of the negative electrode piece is 24.28 wt %.

[0219] Example 30 Example 30, an example of the present application, is based on Example 27, and provides a secondary battery and a manufacturing method thereof, in which the silicon monoxide in the second portion is replaced with a silicon carbon material, and the silicon carbon material has a structure in which elemental silicon is deposited in the pores of porous carbon, and the rest is unchanged.

[0220] The silicon content of the negative electrode active material layer of the negative electrode piece is 14.75 wt %.

[0221] Comparative Example 1 The comparative example 1 of the present application is based on the example 1, and the manufacturing method of the negative electrode piece is changed as follows: artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-arm carbon nanotubes are mixed in deionized water with sufficient stirring in a mass ratio of 93.2%:3%:1.8%:1.2%:0.7%:0.1% to prepare a negative electrode slurry, which is then uniformly coated on an 8 μm-thick copper current collector, dried, cold pressed, and cut to a compact density of 1.65 g / cm. 3 , unit area weight is 10.79 mg / cm 2 The present invention provides a secondary battery and a method for manufacturing the same, in which the negative electrode pieces are obtained.

[0222] The silicon content of the negative electrode active material layer of the negative electrode piece is 3 wt %.

[0223] Comparative Example 2 The comparative example 2 of the present application is based on the example 1, and the manufacturing method of the negative electrode piece is changed as follows: artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-arm carbon nanotubes are mixed in deionized water in a mass ratio of 91.2%:5%:1.8%:1.2%:0.7%:0.1% with sufficient stirring to prepare a negative electrode slurry, which is then uniformly coated on an 8 μm-thick copper current collector, dried, cold pressed, and cut to a compact density of 1.65 g / cm. 3 , unit area weight is 10.211 mg / cm 2The present invention provides a secondary battery and a method for manufacturing the same, in which the negative electrode pieces are obtained.

[0224] The silicon content of the negative electrode active material layer of the negative electrode piece is 5 wt %.

[0225] Comparative Example 3 The comparative example 3 of the present application is based on the example 1, and the manufacturing method of the negative electrode piece is changed as follows: artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-arm carbon nanotubes are mixed in deionized water with sufficient stirring in a mass ratio of 87.2%:9%:1.8%:1.2%:0.5%:0.3% to prepare a negative electrode slurry, which is then uniformly coated on an 8 μm-thick copper current collector, dried, cold pressed, and cut to a compact density of 1.65 g / cm. 3 , unit area weight is 9.22 mg / cm 2 The present invention provides a secondary battery and a method for manufacturing the same, in which the negative electrode pieces are obtained.

[0226] The silicon content of the negative electrode active material layer of the negative electrode piece is 9 wt %.

[0227] Comparative Example 4 The comparative example 4 of the present application is based on the example 1, and the manufacturing method of the negative electrode piece is changed as follows: artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-arm carbon nanotubes are mixed in deionized water with sufficient stirring in a mass ratio of 82.2%:14%:1.8%:1.2%:0.5%:0.3% to prepare a negative electrode slurry, which is then uniformly coated on an 8 μm-thick copper current collector, dried, cold pressed, and cut to a compact density of 1.65 g / cm. 3 , unit area weight is 8.221 mg / cm 2 The present invention provides a secondary battery and a method for manufacturing the same, in which the negative electrode pieces are obtained.

[0228] The silicon content of the negative electrode active material layer of the negative electrode piece is 14 wt %.

[0229] Comparative Example 5 The comparative example 5 of the present application is based on the example 1, and the manufacturing method of the negative electrode piece is changed as follows: artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-arm carbon nanotubes are mixed in deionized water in a mass ratio of 77.2%:19%:1.8%:1.2%:0.5%:0.3% with sufficient stirring to prepare a negative electrode slurry, which is then uniformly coated on an 8 μm-thick copper current collector, dried, cold pressed, and cut to a compact density of 1.65 g / cm. 3 , unit area weight is 7.418mg / cm 2 The present invention provides a secondary battery and a method for manufacturing the same, in which the negative electrode pieces are obtained.

[0230] The silicon content of the negative electrode active material layer of the negative electrode piece is 19 wt %.

[0231] Comparative Example 6 Comparative Example 6 of the present application is based on Example 1, with the manufacturing method of the negative electrode piece changed as follows: Artificial graphite, silicon monoxide, styrene butadiene rubber, sodium carboxymethyl cellulose, conductive carbon black (Super-P, SP), and single-arm carbon nanotubes were mixed in deionized water with sufficient stirring in a mass ratio of 72.2%:24%:1.8%:1.2%:0.5%:0.3% to prepare a negative electrode slurry, which was uniformly coated on an 8 μm-thick copper current collector, dried, cold pressed, and cut to a compact density of 1.65 g / cm. 3 , unit area weight is 6.758mg / cm 2 The negative electrode piece of the present invention is obtained by the secondary battery and the manufacturing method thereof.

[0232] The silicon content of the negative electrode active material layer of the negative electrode piece is 24 wt %.

[0233] Comparative Example 7 The present application provides a comparative example 7 based on comparative example 4, in which silicon monoxide is replaced with a silicon carbon material, and the silicon carbon material has a structure in which elemental silicon is deposited in the pores of porous carbon, with other changes remaining unchanged, and provides a secondary battery and a manufacturing method thereof.

[0234] The silicon content of the negative electrode active material layer of the negative electrode piece is 14 wt %.

[0235] Comparative Example 8 Comparative Example 8 of the present application is based on Example 1, and the unit area weight of the semi-finished negative electrode piece is 3.75 mg / cm 2 The unit area weight of the negative electrode piece was changed to 6.581 mg / cm 2 The present invention provides a secondary battery and a manufacturing method thereof, in which the above-mentioned components are changed and the other components are not changed.

[0236] The silicon content of the negative electrode active material layer of the negative electrode piece was 28.5 wt %.

[0237] Comparative Example 9 The comparative example of the present application provides a secondary battery and a manufacturing method thereof, in which Comparative Example 9 is designed so that the first part of Example 29 is the second part, and the second part of Example 29 is the first part, and the rest is unchanged.

[0238] The silicon content of the negative electrode active material layer of the negative electrode piece is 24.28 wt %.

[0239] The mass percentage of the silicon-based material in the first portion of the secondary batteries of Examples 1 to 30 and Comparative Examples 1 to 9, the mass percentage of the silicon-based material in the second portion of the secondary batteries, C2 / C1, (C1-C2) / C3×100%, h1, h2, and h2 / h1 are as shown in Table 1.

[0240] [Table 1]

[0241] The thickness h1 of the first portion of the negative electrode piece and the thickness h2 of the second portion of the negative electrode piece are measured by the following method. A cross-sectional photograph of the negative electrode piece is taken using a scanning electron microscope (SEM) (for example, Sigma300 manufactured by ZEISS), and the thickness h1 of the first portion of the negative electrode piece and the thickness h2 of the second portion are measured and calculated.

[0242] The unit area capacity C1 of the positive electrode active material layer is measured by the following method: S1: Clean one side of the double-sided positive electrode piece. S2, using a die, the single-sided positive electrode piece is punched into a small circular sheet with a radius of 7 mm, and its area is S = 0.49π, and the unit of area S is cm 2 is. S3, a single-sided cathode piece having an area of ​​S, is dried and then transferred to a glove box to prepare a mating lithium half-cell. S4. The capacity Q1 of the circular sheet is measured using a Wuhan blue-electricity testing instrument. The unit of capacity Q1 is mAh. The capacity C1 of the positive electrode active material layer per unit area is calculated as C1 = Q1 ÷ S, and the unit of capacity C1 of the positive electrode active material layer per unit area is mAh / cm. 2 is.

[0243] The capacitance C2 per unit area of ​​the second portion and the capacitance C3 per unit area of ​​the first portion are measured by the following method. S1: Clean one side of the double-sided negative electrode piece. S2, using a die, the single-sided negative electrode piece is punched into a small circular sheet with a radius of 7 mm, and its area is S = 0.49π, and the unit of area S is cm 2 is. S3, a single-sided negative electrode piece having an area of ​​S, is dried and then transferred to a glove box to prepare a mating lithium half-cell. S4, the capacity Q4 of the circular sheet was measured using a test instrument manufactured by Wuhan Lan Electronics Co., Ltd. The unit of capacity Q4 is mAh, and the capacity C4 of the negative electrode active material layer per unit area is calculated as C4 = Q4 ÷ S, and the unit of capacity C4 of the negative electrode active material layer per unit area is mAh / cm 2 is. S5, peel off the second portion of the single-sided negative electrode piece treated in step S1 with tape. In step S6, the capacity Q3 of the first portion is measured on the peeled negative electrode piece of the second portion in the same manner as in steps S2, S3, and S4. The unit of the capacity Q3 is mAh. The unit area capacity C3 of the first portion is calculated as C3 = Q3 ÷ S, and the unit area capacity C3 of the negative electrode active material layer is mAh / cm. 2 and the unit area capacity of the second portion C2 = C4 - C3, and the unit of the capacity C2 of the negative electrode active material layer per unit area is mAh / cm 2 is.

[0244] Table 2 shows the compositions of the first and second parts of the secondary batteries of Examples 1 to 30 and Comparative Examples 1 to 9.

[0245] [Table 2]

[0246] The silicon-based material in the first portion of Examples 1 to 30 had a Dv50 of 6 μm and a Dv99 of 10.5 μm, the silicon-based material in the second portion of Examples 25 to 30 had a Dv50 of 6 μm, the graphite in the first portion of Examples 1 to 30 had a Dv50 of 5.1 μm and a Dv99 of 11.8 μm, the graphite in the second portion of Examples 1 to 30 had a Dv50 of 14.8 μm, and the silicon-based material in Comparative Examples 1 to 9 had a Dv50 of 6 μm, a Dv99 of 10.5 μm, and a Dv50 of 5.1 μm.

[0247] Test Example 1 The secondary batteries of Examples 1 to 30 and Comparative Examples 1 to 9 were each measured for initial coulombic efficiency ICE, capacity retention rate ρ1, 300 cycle expansion rate Δh300, and reversible storage capacity retention rate ρ2. The results are shown in Table 3.

[0248] First Coulombic Efficiency Measurement (First Efficiency): The battery was charged at 45°C at a rate of 0.02C to 3.4V, then charged at a rate of 0.1C to 3.75V and the measured capacity was recorded as C0. It was then charged at 25°C at a rate of 0.33C to 4.25V, and then charged at a constant voltage of 4.25V to 0.05C and the measured capacity was recorded as C1. Finally, it was discharged at 0.33C to 2.5V and the measured capacity was recorded as D0. The initial coulombic efficiency of the secondary battery ICE = D0 / (C0 + C1) × 100%.

[0249] Cycle test: The secondary battery is charged at a constant current of 1D0 in a constant temperature environment of 45°C until the voltage reaches 4.25V, then further charged at a constant voltage of 4.25V until the current falls to 0.05D0 or less, then left to stand for 5 minutes, then discharged at a constant current of 1C until the voltage reaches 2.5V (the capacity at this step is designated as C3), then left to stand for 5 minutes, and the secondary battery is charged and discharged 500 times according to the above method (the discharge capacity at the 500th cycle is designated as C500), and the cycle capacity retention rate of the secondary battery is calculated as ρ1 = C500 ÷ C3 × 100%.

[0250] Negative electrode piece expansion test: The thickness of the negative electrode piece of the secondary battery after the cold pressing process is completed is denoted as h0. According to the above-mentioned secondary battery cycle performance test method at 45°C, the secondary battery is cycled 300 times, and is charged at a constant current at a rate of 1D0 until the voltage reaches 4.25V, and then is charged at a constant voltage of 4.25V until the current falls below 0.05C, and then is left to stand for 5 minutes, at which point the secondary battery is fully charged. The secondary battery is then disassembled in a drying room after cycling, and the thickness of the negative electrode piece after 300 cycles is denoted as h100. The expansion rate of the secondary battery's electrode piece at 45°C after 300 cycles is Δh300=(h300-h0) / h0×100%.

[0251] Storage test: The secondary battery is charged at a constant current of 0.33D0 in a 25°C environment until the voltage reaches 4.25V, then further charged at a constant voltage of 4.25V until the current reaches 0.05D0 or less, then left to stand for 5 minutes, and then discharged at a constant current of 0.33D0 until the voltage reaches 2.5V (the capacity of this step is designated as C4). The secondary battery was then charged at a constant current of 0.33D0 until the voltage reached 4.25V, then at a constant voltage of 0.05D0 or less at 4.25V. At this point, the secondary battery was fully charged. It was then transferred to a 60°C environment and stored for 100 days. The secondary battery 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, and then 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 step is referred to as C100). The reversible storage capacity retention rate of the secondary battery was calculated as follows: ρ2 = C100 ÷ C4 × 100%

[0252] [Table 3]

[0253] As can be seen from a comparison between Example 5 and 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 battery of Example 5 was <3 wt %. The initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of the secondary battery of Example 5 were all 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 expansion rate Δh300 of the electrode pieces of the secondary battery of Example 5 at 45°C was significantly lower than the 300 cycle expansion rate Δh300 of the electrode pieces of the secondary battery of Comparative Example 1 at 45°C.

[0254] As can be seen from a comparison between Examples 1, 6 to 12, and 17 to 24 and Comparative Example 1, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 1 was 3 wt %, and the silicon content of the negative electrode active material layer in the secondary batteries of Examples 1, 6 to 12, and 17 to 24 was ≧3 wt %. The secondary batteries of Examples 1, 6 to 12, and 17 to 24 have a higher silicon content in the negative electrode active material layer, and therefore their initial coulombic efficiency (ICE) is higher than that of the secondary battery of Comparative Example 1. The cycle capacity retention rates ρ1 of the secondary batteries of Examples 1, 6 to 12, and 17 to 24 are all higher than that of the secondary battery of Comparative Example 1. The 300 cycle expansion rates Δh300 at 45°C of the electrode pieces of the secondary batteries of Examples 1, 6 to 11, 18 to 20, and 22 to 24 are all lower than that of the electrode piece of the secondary battery of Comparative Example 1. The secondary battery of Example 21 has a higher silicon content in the negative electrode active material layer, and therefore its 300 cycle expansion rate Δh300 at 45°C is lower than that of the electrode piece of the secondary battery of Comparative Example 1. 00, and the secondary batteries of Examples 12 and 17, given that the silicon content in the negative electrode active material layer is higher, have a 300 cycle expansion rate Δh300 of the electrode pieces at 45°C that is slightly higher than the 300 cycle expansion rate Δh300 of the electrode pieces of the secondary battery of Comparative Example 1. The reversible storage capacity retention rates ρ2 of the secondary batteries of Examples 1, 7 to 12, 18 to 20, and 23 to 24 are all higher than the reversible storage capacity retention rate ρ2 of the secondary battery of Comparative Example 1. The secondary batteries of Examples 21 and 22, given that the silicon content in the negative electrode active material layer is higher, have a reversible storage capacity retention rate ρ2 equal to that of the secondary battery of Comparative Example 1. The secondary batteries of Examples 6 and 17, given that the silicon content in the negative electrode active material layer is higher, have a reversible storage capacity retention rate ρ2 slightly lower than that of the secondary battery of Comparative Example 1.

[0255] As can be seen from a comparison between Examples 4, 13 to 16, and 25 and Comparative Example 2, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 2 was 5 wt %, and the silicon content of the negative electrode active material layer in the secondary batteries of Examples 4, 13 to 16, and 25 was 5 wt % or more. The initial coulombic efficiencies ICE of the secondary batteries of Examples 13 to 16, and 25 were all higher than that of the secondary battery of Comparative Example 2. The secondary battery of Example 4 had a higher silicon content in the negative electrode active material layer, and its initial coulombic efficiencies ICE were slightly lower than that of the secondary battery of Comparative Example 2. The cycle capacity retention rates ρ1 of the secondary batteries of Examples 13 to 16, and 25 were all higher than that of the secondary battery of Comparative Example 2. Under conditions of higher carbon content, the cycle capacity retention rate ρ1 was slightly lower than that of the secondary battery of Comparative Example 2, the 300 cycle expansion rates Δh300 at 45°C of the pole pieces of the secondary batteries of Examples 4, 13 to 16, and 25 were all lower than that of the pole pieces of the secondary battery of Comparative Example 2, and the reversible storage capacity retention rates ρ2 of the secondary batteries of Examples 4, 13 to 16, and 25 were all higher than that of the secondary battery of Comparative Example 2.

[0256] As can be seen from a comparison between Example 26 and Comparative Example 3, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 3 was 9 wt %, and the silicon content of the negative electrode active material layer in the secondary battery of Example 26 was 9 wt % or greater. Given the higher silicon content of the negative electrode active material layer, the initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) of the secondary battery of Example 26 were all significantly higher than those of Comparative Example 3. Furthermore, the expansion coefficient (Δh300) of the electrode pieces of the secondary battery of Example 26 at 45°C for 300 cycles was significantly lower than that of the electrode pieces of the secondary battery of Comparative Example 3.

[0257] As can be seen from a comparison between Examples 3 and 27 and Comparative Example 4, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 4 was 14 wt %, while the silicon content of the negative electrode active material layer in the secondary batteries of Examples 3, 27, and 30 was ≥ 14 wt %. Given the higher silicon content of the negative electrode active material layer, the secondary batteries of Examples 3, 27, and 30 all had significantly higher initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 than those of Comparative Example 4. Furthermore, the 300 cycle expansion coefficients Δh300 at 45°C of the electrode pieces of the secondary batteries of Examples 3, 27, and 30 were significantly lower than the 300 cycle expansion coefficients Δh300 at 45°C of the electrode pieces of the secondary battery of Comparative Example 4.

[0258] As can be seen from a comparison between Example 28 and Comparative Example 5, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 5 was 19 wt %, and the silicon content of the negative electrode active material layer in the secondary battery of Example 28 was 19 wt % or greater. Given the higher silicon content of the negative electrode active material layer, the initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) of the secondary battery of Example 28 were all significantly higher than those of Comparative Example 5. Furthermore, the expansion coefficient (Δh300) of the electrode pieces of the secondary battery of Example 28 at 45°C for 300 cycles was significantly lower than that of the electrode pieces of the secondary battery of Comparative Example 5.

[0259] As can be seen from a comparison between Examples 2 and 29 and Comparative Example 6, the silicon content of the negative electrode active material layer in the secondary battery of Comparative Example 6 was 24 wt %, while the silicon content of the negative electrode active material layer in the secondary battery of Example 29 was ≥ 24 wt %. Given the higher silicon content of the negative electrode active material layer, the secondary batteries of Examples 2 and 29 all had significantly higher initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 than those of Comparative Example 6. Furthermore, the 300 cycle expansion coefficients Δh300 at 45°C of the electrode pieces of the secondary batteries of Examples 2 and 29 were significantly lower than those of the electrode pieces of the secondary battery of Comparative Example 6.

[0260] As can be seen from the comparison between Example 30, Comparative Example 4, and Comparative Example 7, Example 30 and Comparative Example 7 use a silicon carbon material instead of silicon monoxide. Given that the secondary battery of Example 30 has a higher silicon content in the negative electrode active material layer, its initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 are all significantly higher than those of Comparative Examples 4 and 7. Furthermore, the initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of Comparative Example 7 are significantly higher than those of Comparative Example 4. The expansion rate Δh300 at 45°C of the pole pieces of the secondary battery of Example 30 after 300 cycles is significantly lower than the expansion rate Δh300 at 45°C of the pole pieces of the secondary batteries of Comparative Examples 4 and 7, and the expansion rate Δh300 at 45°C of the pole pieces of the secondary battery of Comparative Example 7 after 300 cycles is significantly lower than the expansion rate Δh300 at 45°C of the pole pieces of the secondary battery of Comparative Example 4.

[0261] As can be seen from the comparison between Example 1 and Comparative Example 8, Comparative Example 8 is based on Example 1 and has a negative electrode piece semi-finished product with a unit area weight of 3.75 mg / cm 2 The unit area weight of the negative electrode piece was changed to 6.581 mg / cm 2With the other changes unchanged, the secondary battery of Comparative Example 8 has an h2 / h1 of only 0.7 and h2 / h1<0.9. Therefore, the silicon content in the negative electrode active material layer of the secondary battery of Comparative Example 8 is significantly increased, and its initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 are all significantly lower than those of Example 1. The expansion coefficient Δh300 of the electrode pieces of the secondary battery of Comparative Example 8 at 45°C for 300 cycles is significantly higher than that of the electrode pieces of the secondary battery of Example 1 at 45°C for 300 cycles.

[0262] As can be seen from the comparison between Example 29 and Comparative Example 9, in Comparative Example 9, the first portion of Example 29 is designed as the second portion, and the second portion of Example 29 is designed as the first portion. Assuming that the total silicon content of the negative electrode active material layer remains unchanged, the initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of Example 29 are all significantly higher than the initial coulombic efficiency ICE, cycle capacity retention rate ρ1, and reversible storage capacity retention rate ρ2 of Comparative Example 9. The expansion coefficient Δh300 after 300 cycles at 45°C of the electrode pieces of the secondary battery of Example 29 is lower than the expansion coefficient Δh300 after 300 cycles at 45°C of the electrode pieces of the secondary battery of Comparative Example 9.

[0263] As can be seen from Examples 1 and 12 to 15, when the content of the silicon-based material in the first portion is 40% by weight to 80% by weight, the secondary battery has an initial coulombic efficiency (ICE) of 92.7% to 92.9%, a cycle capacity retention rate (ρ1) of 92.6% to 93.4%, a 300-cycle expansion rate (Δh300) of the electrode piece at 45°C of 34% to 40%, and a reversible storage capacity retention rate (ρ2) of 94.7% to 95.6%. A comparison of Example 11 with Examples 1 and 12 to 15 shows that, under conditions where the silicon content of the negative electrode active material layer is lower, the initial coulombic efficiency (ICE), cycle capacity retention rate (ρ1), and reversible storage capacity retention rate (ρ2) of the secondary battery of Example 11 remain essentially unchanged and do not significantly improve. A comparison of Example 16 with Examples 1 and 12 to 15 shows that the 300-cycle expansion rate (Δh300) of the electrode piece at 45°C of the secondary battery of Example 16 is too high.

[0264] Finally, it should be noted that the above embodiments are used only to explain 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 still understand that the technical solutions described in the above embodiments can be modified or some or all of the technical features can be equivalently replaced, and such modifications or replacements do not deviate from the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and should all be included in the scope of the claims and description of the present application. In particular, as long as there is no structural contradiction, the technical features mentioned in the embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions included in the scope of the claims.

Claims

1. An electrode assembly including a positive electrode piece and a negative electrode piece, The negative electrode piece includes a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes a first portion and a second portion along a thickness direction, the first portion is a portion close to the negative electrode current collector, and a mass percentage of the silicon-based material in the first portion is greater than a mass percentage of the silicon-based material in the second portion; The positive electrode piece includes a positive electrode active material layer, and the positive electrode active material layer has a unit area capacity of C １ and The capacitance per unit area of ​​the second portion is C ２ and 30%≦C ２ / C １ ≦95%; the second portion includes a graphite material and a silicon-based material in a mass ratio of (80-100):(0-20); The negative electrode active material layer has a weight per unit area of ​​5.19 mg / cm 2 to 14.26 mg / cm 2 and a compressed density of 1.4 g / cm 3 to 1.85 g / cm 3 .

2. 70%≦C ２ / C １ 10. The electrode assembly of claim 1, wherein the porosity is ≦90%.

3. the first portion is a first negative electrode active layer formed on a surface of the negative electrode current collector, the second portion is a second negative electrode active layer formed on a surface of the first negative electrode active layer, 2. The electrode assembly according to claim 1, wherein a difference between a mass percentage of the silicon-based material in the first negative electrode active layer and a mass percentage of the silicon-based material in the second negative electrode active layer is 30% to 80%.

4. The capacitance per unit area of ​​the first portion is C ３ and 20%≦(C １ -C ２ ) / C ３ 4. The electrode assembly according to claim 1, wherein the resistance is ≦90%.

5. The capacitance per unit area of ​​the first portion is C ３ and 50%≦(C １ -C ２ ) / C ３ 4. The electrode assembly according to claim 1, wherein the resistance is ≦75%.

6. 4. The electrode assembly of claim 1, wherein the first portion comprises 40% to 80% by weight of a silicon-based material, and the silicon-based material comprises a silicon-oxygen material and / or a silicon-carbon material.

7. 7. The electrode assembly of claim 6, wherein the silicon-based material in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99≦20 μm.

8. 4. The electrode assembly according to claim 1, wherein the first portion comprises 10% to 55% by weight of graphite.

9. 9. The electrode assembly according to claim 8, wherein the graphite in the first portion has a Dv50 of 1 μm to 8 μm and a Dv99≦30 μm.

10. The electrode assembly according to claim 1 , wherein the first portion contains 3% to 20% by weight of an adhesive.

11. 4. The electrode assembly according to claim 1, wherein the first portion contains 0.5% to 5% by weight of the dot-shaped conductive agent.

12. 4. The electrode assembly according to claim 1, wherein the first portion comprises 0.05% to 1.2% by weight of carbon nanotubes.

13. 13. The electrode assembly of claim 12, wherein the carbon nanotubes have an aspect ratio of ≥ 1000.

14. The electrode assembly of claim 12, wherein the first portion further comprises 1% to 5% by weight of a surfactant.

15. The weight per unit area of ​​the first portion is 0.5 mg / cm ２ ~3.6 mg / cm ２ 4. The electrode assembly according to claim 1, wherein:

16. 4. The electrode assembly according to claim 1, wherein the silicon-based material in the second portion has a Dv50 of 1 μm to 8 μm, and the graphite in the second portion has a Dv50 of 1 μm to 20 μm.

17. The thickness of the first portion is h １ and the thickness of the second portion is h ２ and h ２ ÷h １ 4. The electrode assembly according to claim 1, wherein the ρ is ≧0.

9.

18. The above h １ is 3 μm to 21.5 μm, and ２ 18. The electrode assembly of claim 17, wherein is 19 μm to 62.5 μm.

19. The unit area capacity of the negative electrode active material layer is C ４ and 1.01C １ ≦C ４ ≦1.2C １ 4. The electrode assembly according to claim 1, wherein:

20. the second portion includes at least two sub-portions along a thickness direction; 4. The electrode assembly of claim 1, wherein the mass percentage of the silicon-based material in each of the at least two sub-portions is different.

21. A secondary battery comprising the electrode assembly according to any one of claims 1 to 3.

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

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