Secondary battery and electrical device

Abstract

Disclosed in the present application are a secondary battery and an electrical device. The secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and negative electrode active layers arranged on two opposite sides of the negative electrode current collector; the areal density of the negative electrode current collector is 0.02 g / 1540.25 mm2-0.06 g / 1540.25 mm2, and the tensile strength of the negative electrode current collector is greater than or equal to 350 MPa; each negative electrode active layer comprises a silicon-containing material, and the mass proportion of silicon in the negative electrode active layer is 15%-90%. The combination of the high-specific-capacity negative electrode active material and the light-weight and high-strength negative electrode current collector is beneficial to improving the energy density of the secondary battery and simultaneously improving the cycle performance of the secondary battery.

Description

Secondary batteries and electrical equipment

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application 202510126565.2, filed on January 27, 2025, entitled “Secondary Battery and Electrical Equipment”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of new energy technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0004] Lithium-ion batteries are widely used in wireless communication, transportation, aerospace, and other fields. As the demands for battery life from electrical devices continue to increase, the need for high energy density lithium-ion batteries is growing. Therefore, a high-energy-density lithium-ion battery design is required, while simultaneously considering the battery's cycle performance. This presents challenges to the selection of materials and structural design for various components of the lithium-ion battery, including electrode materials, current collectors, and electrolytes. The above statements are for providing background information related to this application only and do not necessarily constitute prior art. Summary of the Invention

[0005] The main technical problem solved by this application is to provide a secondary battery and electrical device that uses a high-specific-capacity negative electrode active material in combination with a lightweight and high-strength negative electrode current collector, thereby improving the energy density of the secondary battery and improving its cycle performance.

[0006] To solve the above-mentioned technical problems, one technical solution adopted in this application is: providing a secondary battery, comprising: a positive electrode sheet, the positive electrode sheet including a positive current collector and positive active layers disposed on opposite sides of the positive current collector; a negative electrode sheet, the negative electrode sheet including a negative current collector and negative active layers disposed on opposite sides of the negative current collector; the areal density of the negative current collector is 0.02 g / 1540.25 mm². 2 ~0.06g / 1540.25mm 2 The tensile strength of the negative electrode current collector is greater than or equal to 350 MPa; the negative electrode active layer includes silicon-containing materials, and the mass percentage of silicon in the negative electrode active layer is 15% to 90%.

[0007] The negative electrode active layer includes a silicon-containing material, with silicon accounting for 15% to 90% of its mass. Since silicon's theoretical specific capacity is much higher than that of traditional graphite anode materials, the negative electrode active material in this application has a higher specific capacity compared to graphite anode materials. However, due to the significant volume change of silicon during charging and discharging, which affects battery stability, the mass percentage of silicon in the negative electrode active layer in this application is within the aforementioned range. This allows for improved specific capacity while maintaining a certain level of structural stability. Simultaneously, it is paired with an areal density of 0.02 g / 1540.25 mm². 2 ~0.06g / 1540.25mm 2 The negative electrode current collector can reduce its weight, thereby reducing the weight ratio of inactive materials in the negative electrode sheet. Furthermore, the tensile strength of the negative electrode current collector is greater than or equal to 350 MPa, which helps to alleviate the stress caused by the volume expansion and contraction of the active material during battery charging and discharging, thereby improving the cycle stability of the battery. Therefore, the combination of high specific capacity negative electrode active material and lightweight, high-strength negative electrode current collector is beneficial to improving the energy density of secondary batteries and improving their cycle performance.

[0008] In one embodiment, the negative electrode current collector includes a first base layer, the material of which includes any one of carbon materials and titanium; or the negative electrode current collector includes a second base layer and a conductive coating, the conductive coating being disposed on opposite sides of the second base layer, the material of which includes any one of titanium and polyimide. With the above configuration, a negative electrode current collector with low areal density, high tensile strength, and good conductivity can be provided.

[0009] In one embodiment, the conductive coating contains at least one of copper, nickel, silver, and gold. Copper, nickel, silver, and gold have good electrical conductivity; therefore, the conductive coating helps to improve the conductivity of the negative electrode current collector and improve the power performance of the battery.

[0010] In one embodiment, the second base layer contains titanium, and the thickness of the conductive coating is 0.3 μm to 1.5 μm; or the second base layer contains polyimide, and the thickness of the conductive coating is 0.5 μm to 1.5 μm. The conductive coating helps improve the conductivity of the negative electrode current collector, compensates for the poor conductivity of polymer materials, and improves the power performance of the battery.

[0011] In one embodiment, the carbon material includes at least one of carbon fiber and graphene. Carbon fiber, graphene, and composites of carbon fiber and graphene can meet the requirements of lightweight, high strength, and appropriate elongation for current collectors.

[0012] In one embodiment, the second base layer contains polyimide and satisfies at least one of the following conditions: (1) the polyimide is at least partially biphenyl polyimide, and the molar percentage of biphenyl polyimide in the polyimide is greater than or equal to 70%; (2) the tensile strength of the polyimide is greater than or equal to 400 MPa; (3) the thickness of the polyimide is 4 μm to 7 μm. When the molar percentage of biphenyl polyimide is greater than or equal to 70%, the tensile strength of the polyimide is relatively large, which can meet the high strength requirements of the current collector; when the tensile strength of the polyimide is greater than or equal to 400 MPa, as the second base layer of the negative electrode current collector, it can meet the high strength requirements of the current collector, thereby suppressing the volume expansion of the silicon-containing negative electrode system; when the thickness of the polyimide is 4 μm to 7 μm, the negative electrode current collector has high strength and reliability, and at the same time, the thickness of the negative electrode current collector can be reduced, thereby improving the specific capacity of the negative electrode.

[0013] In one embodiment, the thickness of the negative electrode current collector is 4 μm to 8.5 μm. A thickness within this range helps reduce the proportion of the negative electrode current collector in the negative electrode sheet, allowing the negative electrode sheet to accommodate more active material, thereby increasing the specific capacity of the negative electrode and the energy density of the battery. Simultaneously, the negative electrode current collector has high strength, which helps improve the reliability of both the negative electrode current collector and the negative electrode sheet.

[0014] In one embodiment, the elongation of the negative electrode current collector is 2% to 16%. An appropriate elongation is beneficial to improving the flexibility of the negative electrode current collector, allowing it to adapt to volume expansion and contraction during battery charging and discharging, improving the stability of the negative electrode current collector, and increasing the bonding tightness between the negative electrode current collector and the negative electrode active layer, thereby improving the cycle stability and safety of the battery.

[0015] In one embodiment, the tensile strength of the negative electrode current collector is greater than or equal to 500 MPa. Further increasing the tensile strength of the negative electrode current collector can further suppress electrode stretching caused by the volume expansion of the negative electrode active layer, thereby further improving the safety performance of the battery.

[0016] In one embodiment, the difference between the elongation of the negative electrode current collector and the elongation of the negative electrode sheet is less than or equal to 2%. A small difference in elongation between the negative electrode current collector and the negative electrode sheet indicates that the current collector has strong resistance to elongation, which can reduce the wrinkling and cracking of the electrode sheet caused by the expansion of the active material.

[0017] In one embodiment, the silicon-containing material includes at least one of elemental silicon, silicon-based alloys, silicon-carbon composite materials, and silicon-oxygen materials. This configuration broadens the selection range of negative electrode active materials to meet diverse application requirements.

[0018] In one embodiment, the silicon-containing material includes a silicon-carbon composite material, wherein the silicon-carbon composite material accounts for 20% to 95% of the mass of the negative electrode active layer. The mass percentage of the silicon-carbon composite material in the negative electrode active layer is within the above range, resulting in a negative electrode active layer with both high specific capacity and high conductivity.

[0019] In one embodiment, the silicon-carbon composite material comprises porous carbon and silicon material dispersed in the pores of the porous carbon. The porous carbon, acting as a framework, provides buffer space, which can accommodate the volume changes of silicon during charging and discharging, thus improving the stability of the silicon-containing material; the silicon material enables the negative electrode active material to have a high specific capacity, which is beneficial to improving the energy density of the secondary battery.

[0020] In one embodiment, the silicon-carbon composite material includes a carbon-containing coating layer located on the surface of porous carbon and / or silicon materials. The carbon-containing coating layer can act as a physical barrier, reducing direct contact between the silicon materials and the electrolyte, thereby reducing side reactions and contributing to improved battery cycle life.

[0021] In one embodiment, the porous carbon is hard carbon. Hard carbon can provide support for silicon-containing materials, which is beneficial to improving the cycle stability of silicon-carbon composites.

[0022] In one embodiment, the negative electrode active layer further includes graphite with an aspect ratio greater than or equal to 1.3, and the graphite accounts for 5% to 70% of the mass of the negative electrode active layer. The long aspect ratio of graphite provides lubrication and is beneficial for improving the battery's dynamic performance. When the mass percentage of graphite in the negative electrode active layer is within the above range, its conductivity and stability are well utilized, thereby further optimizing the overall performance of the negative electrode.

[0023] In one embodiment, the negative electrode active layer further includes graphene, with the graphene accounting for 0.5% to 10% of the total mass of the negative electrode active layer. Adding an appropriate amount of graphene to the negative electrode active layer can further improve the electron and ion transport capabilities of the negative electrode sheet and improve the power performance of the battery.

[0024] In one embodiment, the negative electrode active layer further includes carbon nanotubes, with the carbon nanotubes accounting for 0.05% to 5% of the mass of the negative electrode active layer. Adding an appropriate amount of carbon nanotubes to the negative electrode active layer can further improve the electron and ion transport capabilities of the negative electrode sheet and improve the power performance of the battery.

[0025] In one embodiment, the carbon nanotubes include single-walled carbon nanotubes. Single-walled carbon nanotubes have better conductivity than multi-walled carbon nanotubes, which is beneficial for improving the conductivity of the negative electrode.

[0026] In one embodiment, the areal density of the negative electrode active layer is 0.04 g / 1540.25 mm. 2~0.14g / 1540.25mm 2 Having the areal density of the negative electrode active layer within the above-mentioned range is beneficial for improving the energy density of the battery, while also resulting in better rate performance.

[0027] In one embodiment, the compaction density of the negative electrode active layer is 0.9 g / cm³. 3 ~1.5g / cm 3 A compaction density of the negative electrode active layer within the above-mentioned range is beneficial for improving the energy density of the battery, while reducing internal resistance, reducing polarization loss, and extending the cycle life of the battery.

[0028] In one embodiment, the areal density of the positive electrode current collector is 0.02 g / 1540.25 mm². 2 ~0.07 / 1540.25mm 2 When the areal density of the positive electrode current collector is within the above range, the weight of the positive electrode current collector can be reduced, thereby reducing the weight ratio of inactive materials in the positive electrode sheet, increasing the specific capacity of the positive electrode sheet, and thus improving the energy density of the secondary battery.

[0029] In one embodiment, the positive electrode current collector includes an aluminum foil or a composite current collector; the composite current collector includes a polymer substrate and metal layers disposed on opposite sides of the polymer substrate. The aluminum foil positive electrode current collector and the composite current collector have relatively low mass and good conductivity, which helps to reduce the weight ratio of the positive electrode current collector in the positive electrode sheet, increase the specific capacity of the positive electrode sheet and the energy density of the battery, and simultaneously improve the power performance of the battery.

[0030] In one embodiment, the polymer base layer comprises at least one of polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyimide, polytetrafluoroethylene, polyurethane, and epoxy resin; the metal layer comprises at least one of aluminum layer and aluminum alloy layer. With the above configuration, the composite current collector is lightweight and highly conductive.

[0031] In one embodiment, the thickness of the positive electrode current collector is 8 μm to 15 μm. A thickness within this range helps reduce the weight of the positive electrode current collector and its proportion of thickness in the negative electrode, thereby allowing the positive electrode to accommodate more active material and improving the specific capacity of the positive electrode and the energy density of the battery.

[0032] In one embodiment, the thickness of the positive electrode current collector is 8 μm to 13 μm. A thickness within this range is advantageous for further reducing the weight of the positive electrode current collector and its proportion of thickness in the negative electrode, thereby further improving the energy density of the battery.

[0033] In one embodiment, the positive electrode active layer includes lithium-containing nickel-cobalt-manganese oxide, wherein the proportion of nickel in the sum of the molar amounts of nickel, cobalt, and manganese is greater than or equal to 80%; and / or the mass proportion of the lithium-containing nickel-cobalt-manganese oxide in the positive electrode active layer is greater than or equal to 95%. When the nickel content is greater than or equal to 80%, the capacity of the positive electrode active material is larger, which is beneficial for improving the energy density of the battery; the lithium-containing nickel-cobalt-manganese oxide, as the main contributor to the capacity of the positive electrode sheet, having a mass proportion greater than or equal to 95%, is beneficial for further improving the capacity of the positive electrode sheet and the energy density of the battery.

[0034] In one embodiment, the positive electrode active layer includes a lithium-containing nickel-cobalt-manganese oxide, wherein the proportion of nickel in the sum of the molar amounts of nickel, cobalt, and manganese is greater than or equal to 90%; and / or the mass proportion of the lithium-containing nickel-cobalt-manganese oxide in the positive electrode active layer is greater than or equal to 97%. This configuration helps to further improve the energy density of the battery.

[0035] In one embodiment, the areal density of the positive electrode active layer is 0.35 g / 1540.25 mm². 2 ~0.6g / 1540.25mm 2 The above settings help to increase the positive electrode capacity and extend the battery's cycle life.

[0036] In one embodiment, the compaction density of the positive electrode active layer is 3.3 g / cm³. 3 ~3.65g / cm 3 The above settings help improve the battery's rate performance and capacity retention.

[0037] In one embodiment, the secondary battery has a gravimetric energy density greater than or equal to 400 Wh / kg. In this case, the secondary battery can provide a strong endurance for the electrical equipment.

[0038] In one embodiment, the secondary battery has a gravimetric energy density greater than or equal to 420 Wh / kg. In this case, the secondary battery can provide the electrical equipment with a longer operating range.

[0039] In one embodiment, the secondary battery further includes an electrolyte comprising a solvent, additives, and a lithium salt; the solvent includes ethylene carbonate, and further includes at least one of diethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate; the additives include vinylene carbonate and fluoroethylene carbonate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide. The electrolyte stably conducts lithium ions, the solvent dissolves the lithium salt and provides a carrier for the lithium ions, and ethylene carbonate helps extend the battery's lifespan; the lithium salt provides lithium ions and transports them between the positive and negative electrodes; when the battery negative electrode includes silicon-containing materials, the additives vinylene carbonate and fluoroethylene carbonate can promote the formation of a solid electrolyte interface film on the surface of the negative electrode material, thereby protecting the negative electrode material and extending the lifespan of the battery's negative electrode active material.

[0040] In one embodiment, the mass percentage of ethylene carbonate in the solvent is greater than or equal to 28%. This is beneficial for increasing battery life.

[0041] In one embodiment, the mass percentage of fluoroethylene carbonate in the electrolyte is greater than or equal to 5%; the mass percentage of vinylene carbonate in the electrolyte is greater than or equal to 0.5%. This is beneficial for extending the lifespan of the battery's negative electrode active material.

[0042] In one embodiment, lithium hexafluorophosphate accounts for 5% to 15% of the mass of the electrolyte; and / or, lithium bis(trifluoromethanesulfonyl)imide accounts for less than or equal to 5% of the mass of the electrolyte; and / or, lithium bis(fluorosulfonyl)imide accounts for less than or equal to 5% of the mass of the electrolyte. The aforementioned lithium salts can form an fluorine-rich inorganic SEI film, improving battery life and kinetic performance.

[0043] In one embodiment, the secondary battery further includes a casing, within which positive and negative electrode plates are housed. The casing has a melting point greater than or equal to 1000°C. Since silicon-containing negative electrode systems release significant heat upon failure, a casing melting point greater than or equal to 1000°C reduces the risk of the casing melting through, thus improving battery safety.

[0044] In one embodiment, the shell material includes steel or titanium. Both steel and titanium have melting points exceeding 1000°C, which meets the shell requirements.

[0045] In one embodiment, the melting point of the casing is greater than or equal to 2000°C. This can further improve the safety performance of the battery.

[0046] In one embodiment, the secondary battery further includes an end cap that covers the opening of the casing; the end cap is provided with an explosion-proof valve, the area of ​​which is 20% to 70% of the area of ​​the end cap. The explosion-proof valve, with an area of ​​20% to 70% of the area of ​​the end cap, can quickly release gases generated due to thermal runaway, thereby improving the safety performance of the battery.

[0047] In one embodiment, the area of ​​the explosion-proof valve is 30% to 50% of the area of ​​the end cap. This allows for the rapid release of gases generated by thermal runaway, improving battery safety performance and also enhancing the structural strength of the battery end cap.

[0048] To address the aforementioned technical problems, another technical solution adopted in this application is to provide an electrical device that includes a secondary battery according to any of the above embodiments. The electrical device possesses at least the same advantages as a battery, namely, improved battery life.

[0049] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 is a schematic diagram of the structure of the negative electrode sheet according to an embodiment of this application;

[0052] Figure 2 is a schematic diagram of the structure of the negative electrode sheet according to an embodiment of this application;

[0053] Figure 3 shows the tensile stress-strain curves of the negative electrode current collectors in Embodiments 2, 4 and Comparative Example 1 of this application;

[0054] Figure 4 shows the tensile stress-strain curves of the negative electrode sheets of Embodiments 2, 4 and Comparative Example 1 of this application;

[0055] Figure 5 is an exploded structural diagram of a battery according to one or more embodiments of this application;

[0056] Figure 6 is an exploded structural diagram of a battery cell according to one or more embodiments of this application;

[0057] Figure 7 is a structural schematic diagram of a vehicle according to one or more embodiments of this application.

[0058] In the attached image:

[0059] 1000, Vehicle; 300, Motor; 200, Controller; 100, Battery; 10, Housing; 11, First Part; 12, Second Part; 20, Battery Cell; 21, End Cap; 21a, Electrode Terminal; 21b, Explosion-proof Valve; 22, Housing; 23, Electrode Assembly; 30, Negative Electrode Sheet; 31, Negative Electrode Current Collector; 31a, First Substrate; 31b, Second Substrate; 31c, Conductive Plating; 32, Negative Electrode Active Layer. Embodiments of the present invention

[0060] To make the objectives, technical solutions, and effects of this application clearer and more explicit, the embodiments of the technical solutions of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of this application, and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0062] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces), unless otherwise explicitly specified.

[0063] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0064] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0065] Quantities, ratios, and other numerical values ​​are presented in range format in this document. It should be understood that this range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0066] Unless otherwise specified, all steps of this application may be performed sequentially, randomly, or in parallel, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially, or steps (a) and (b) may be performed simultaneously in parallel. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0067] As the demands for extended battery life from electrical devices continue to rise, the need for high energy density lithium-ion batteries is growing. This necessitates a high-energy-density battery design, involving material selection and structural design. Among the anode active materials for lithium-ion batteries, silicon anode materials possess extremely high theoretical specific capacity (approximately 10 times that of graphite, reaching 4200 mAh / g), and are considered the preferred anode material for next-generation high-energy-density batteries. However, silicon anode materials exhibit high system expansion characteristics, requiring matching with a negative electrode current collector possessing high tensile strength. Furthermore, the current collector needs to be lightweight to meet the requirements of high-energy-density battery designs.

[0068] Based on this, this application provides a secondary battery, comprising: a positive electrode sheet, the positive electrode sheet including a positive current collector and positive active layers disposed on opposite sides of the positive current collector; and a negative electrode sheet, the negative electrode sheet including a negative current collector and negative active layers disposed on opposite sides of the negative current collector; the areal density of the negative current collector is 0.02 g / 1540.25 mm². 2 ~0.06g / 1540.25mm 2 The tensile strength of the negative electrode current collector is greater than or equal to 350 MPa; the negative electrode active material includes silicon-containing materials, and the mass ratio of silicon element in the negative electrode active layer is 15% to 90%.

[0069] In this battery, the current collector in the electrode serves to carry the active material and collect and output the current generated by the active material. The active layer in the electrode provides the active material and is responsible for transferring charge to or receiving charge from the electrolyte; it is the main site of electrochemical reactions in the battery.

[0070] The negative electrode active layer includes a silicon-containing material, which is used as the negative electrode active material. The mass percentage of silicon in the negative electrode active layer is 15% to 90%. Since the theoretical specific capacity of silicon is much higher than that of traditional graphite negative electrode materials, the negative electrode active material of this application has a higher specific capacity compared to graphite negative electrode materials. However, because silicon undergoes significant volume changes during charge and discharge, affecting battery stability, the mass percentage of silicon in the negative electrode active layer of this application is within the aforementioned range. This allows for improved specific capacity while maintaining a certain level of structural stability. Simultaneously, it is paired with an areal density of 0.02 g / 1540.25 mm². 2 ~0.06g / 1540.25mm 2 The negative electrode current collector can reduce its weight, thereby reducing the weight ratio of inactive materials in the negative electrode sheet. Furthermore, the tensile strength of the negative electrode current collector is greater than or equal to 350 MPa, which helps to alleviate the stress caused by the volume expansion and contraction of the active material during battery charging and discharging, thereby improving the cycle stability of the battery. Therefore, the combination of high specific capacity negative electrode active material and lightweight, high-strength negative electrode current collector is beneficial to improving the energy density of secondary batteries and improving their cycle performance.

[0071] The mass percentage of silicon in the negative electrode active layer refers to the mass percentage of silicon in the negative electrode active material and other negative electrode active layer materials (including but not limited to binders, conductive agents, dispersants, etc.). Besides silicon-containing materials, negative electrode active materials also include other types of negative electrode active materials, including but not limited to graphite, hard carbon, and graphene. The mass percentage of silicon can be 15%, 18%, 20%, 25%, 30%, 33%, 40%, 45%, 48%, 50%, 65%, 70%, 83%, 85%, 90%, or any range of two of the above values, such as 15%~18%, 20%~30%, 33%~40%, 45%~50%, 65%~85%, 70%~90%, etc.

[0072] The areal density of the negative electrode current collector refers to the mass of the negative electrode current collector over a given area. A lower areal density means a lighter negative electrode current collector, which is more beneficial for improving the energy density of the battery. The areal density of the negative electrode current collector can be 0.02 g / 1540.25 mm². 2 0.025g / 1540.25mm 2 0.03g / 1540.25mm 2 0.037g / 1540.25mm 2 0.04g / 1540.25mm 2 0.05g / 1540.25mm 20.06g / 1540.25mm 2 etc., or a range consisting of any two of the above values, for example, 0.02~0.025g / 1540.25mm. 2 0.03~0.037g / 1540.25mm 2 0.04~0.06g / 1540.25mm 2 wait.

[0073] The tensile strength of the negative electrode current collector refers to its ability to withstand the maximum stress without breaking under tensile force. It reflects the strength of the current collector. A higher strength current collector can suppress electrode stretching caused by the volume expansion of the negative electrode active layer, thus improving battery safety. The tensile strength of the negative electrode current collector can be 350MPa, 400MPa, 420MPa, 500MPa, 600MPa, 700MPa, 800MPa, 1000MPa, or any range of two of these values, such as 350MPa~400MPa, 420MPa~500MPa, 600MPa~800MPa, 800MPa~1000MPa, etc.

[0074] In one embodiment, please refer to FIG1, which is a schematic diagram of the structure of the negative electrode sheet according to an embodiment of the present application. The negative electrode current collector 31 includes a first base layer 31a, and the material of the first base layer 31a includes any one of carbon material and titanium.

[0075] In Figure 1, the negative electrode current collector 31 includes a first base layer 31a, which is a single-layer structure with a simple structure, which is beneficial to improving production efficiency. The first base layer 31a is made of either carbon or titanium. These materials have the characteristics of high strength and low density. The tensile strength of titanium foil reaches 800 MPa, and the tensile strength of carbon fiber reaches over 1000 MPa. Applying these materials to the negative electrode current collector 31 can reduce the areal density of the current collector and increase its tensile strength. At the same time, these materials have good conductivity, which can meet the power performance requirements of the battery.

[0076] In one embodiment, the carbon material includes at least one of carbon fiber and graphene.

[0077] The carbon material used as the first base layer for the current collector can be carbon fiber, graphene, or a composite material of carbon fiber and graphene. Carbon fiber current collectors have low mass and high strength, and also have a three-dimensional porous structure, which can effectively alleviate the volume expansion of the negative electrode during battery cycling; graphene current collectors have good mechanical flexibility and are very thin and light; composite materials of carbon fiber and graphene combine the advantages of both, and carbon fiber, graphene, and carbon fiber and graphene composite materials can meet the requirements of lightweight, high strength, and appropriate elongation of current collectors.

[0078] In one embodiment, please refer to FIG2, which is a schematic diagram of the structure of the negative electrode sheet according to an embodiment of the present application. The negative current collector 31 includes a second type of base layer 31b and a conductive plating layer 31c. The conductive plating layer 31c is disposed on opposite sides of the second type of base layer 31b. The material of the second type of base layer 31b includes any one of titanium and polyimide.

[0079] In Figure 2, the negative electrode current collector 31 includes a second base layer 31b and a conductive plating layer 31c, with the conductive plating layer 31c disposed on opposite sides of the second base layer 31b. The negative electrode current collector 31 has a multi-layer structure. The second base layer 31b serves as the main structure of the current collector, providing mechanical support, strength, and flexibility. The material of the second base layer 31b includes either titanium or polyimide. Similarly, polyimide also has the characteristics of high strength and low density, which can reduce the areal density of the current collector and increase its tensile strength. The conductive plating layer 31c is used to improve the conductivity of the current collector to meet the power performance requirements of the battery.

[0080] In one embodiment, the conductive coating contains at least one of copper (Cu), nickel (Ni), silver (Ag), and gold (Au). Copper, nickel, silver, and gold have good electrical conductivity; therefore, the conductive coating helps to improve the conductivity of the negative electrode current collector and improve the power performance of the battery.

[0081] In one embodiment, the second base layer contains titanium, and the thickness of the conductive coating is 0.3 μm to 1.5 μm.

[0082] Copper, nickel, silver, and gold possess excellent electrical conductivity, superior to that of titanium. Therefore, applying conductive plating to both sides of the titanium foil can further improve the conductivity of the negative electrode current collector, thereby enhancing the battery's power performance. The aforementioned thickness refers to the thickness of a single-sided conductive plating layer. When the thickness of the conductive plating layer is between 0.3 μm and 1.5 μm, the surface smoothness of the conductive plating layer is good, effectively improving the conductivity of the negative electrode current collector, while also enhancing welding reliability and processing performance. The thickness of the conductive plating layer can be 0.3 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.5 μm, or any range of two of the above values, such as 0.3 μm to 0.5 μm, 0.6 μm to 1 μm, or 0.8 μm to 1.5 μm.

[0083] In one embodiment, the second base layer contains polyimide, and the thickness of the conductive coating is 0.5 μm to 1.5 μm.

[0084] Polyimide (PI) refers to a high molecular weight polymer containing an imide structure in its main chain. It possesses excellent mechanical properties, heat resistance, and processability, with a low coefficient of thermal expansion and a lower density than metallic materials, exhibiting lightweight and high strength. The conductive coating, including a metallic material with good conductivity, helps improve the conductivity of the negative electrode current collector, compensating for the poor conductivity of polymeric materials and improving the battery's power performance. The thickness mentioned above refers to the thickness of a single-sided conductive coating. A conductive coating thickness of 0.5μm to 1.5μm provides good flatness and effectively improves the conductivity of the negative electrode current collector. The thickness of the conductive coating can be 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.5μm, or any range of two of the above values, such as 0.5μm~0.6μm, 0.7μm~0.8μm, 0.9μm~1.5μm, etc.

[0085] In one embodiment, the second base layer contains polyimide and satisfies at least one of the following conditions: (1) the polyimide is at least partially biphenyl polyimide, and the molar percentage of biphenyl polyimide in the polyimide is greater than or equal to 70%; (2) the tensile strength of the polyimide is greater than or equal to 400 MPa; (3) the thickness of the polyimide is 4 μm to 7 μm.

[0086] Polyimides are mainly classified into biphenyl-type polyimides and pyromellitic-type polyimides. The general structural formula of biphenyl-type polyimides is: Its main chain is relatively rigid and there are large interactions between molecules. Therefore, when the molar ratio of biphenyl polyimide is greater than or equal to 70%, the tensile strength of polyimide is relatively large, which can meet the high strength requirements of current collectors.

[0087] Among them, the tensile strength of polyimide is greater than or equal to 400MPa. As the second base layer of the negative electrode current collector, it can meet the high strength requirements of the current collector, thereby suppressing the volume expansion of the silicon-containing negative electrode system.

[0088] When the polyimide thickness is 4μm to 7μm, it serves as the main structure of the negative electrode current collector, giving the current collector high strength and reliability. Simultaneously, it allows for a reduction in the current collector's thickness, thereby increasing the specific capacity of the negative electrode. The polyimide thickness can be 4μm, 4.5μm, 5μm, 5.6μm, 6μm, 6.8μm, 7μm, or any range of two of these values, such as 4μm to 4.5μm, 5μm to 5.6μm, or 6μm to 7μm.

[0089] In one embodiment, the thickness of the negative electrode current collector is 4 μm to 8.5 μm. A thickness within this range is beneficial for reducing the weight of the negative electrode current collector and its proportion of thickness within the negative electrode sheet, thereby allowing the negative electrode sheet to accommodate more active material, increasing the specific capacity of the negative electrode and the energy density of the battery. Simultaneously, the negative electrode current collector has high strength, which is beneficial for improving the reliability of both the negative electrode current collector and the negative electrode sheet, as well as the safety and cycle performance of the battery. The thickness of the negative electrode current collector can be 4 μm, 4.5 μm, 5 μm, 5.6 μm, 6 μm, 6.8 μm, 7 μm, 8 μm, 8.5 μm, etc., or a range consisting of any two of the above values, such as 4 μm to 4.5 μm, 5 μm to 5.6 μm, 6 μm to 7 μm, 8 μm to 8.5 μm, etc.

[0090] In one embodiment, the elongation of the negative electrode current collector is 2% to 16%. Elongation at break, also known as elongation at break, refers to the rate of change in length of the negative electrode current collector when stretched from its initial state to the point of fracture under external force. Elongation at break = (L...) f -L0) / L f ×100%, where L0 refers to the initial sample length, L f It is the sample length at the time of fracture.

[0091] An appropriate elongation rate is beneficial for improving the flexibility of the negative electrode current collector, allowing it to adapt to volume expansion and contraction during battery charging and discharging, thus enhancing its stability and the bonding tightness between the current collector and the negative electrode active layer, thereby improving the battery's cycle stability and safety. The elongation rate of the negative electrode current collector can be 2%, 2.5%, 3%, 5%, 8%, 10%, 12%, 13.5%, 15%, 16%, or any range of two of the above values, such as 2%~3%, 5%~8%, 10%~12%, 13.5%~16%, etc.

[0092] In one embodiment, the tensile strength of the negative electrode current collector is greater than or equal to 500 MPa. Further increasing the tensile strength of the negative electrode current collector can further suppress electrode elongation caused by the volume expansion of the negative electrode active layer, thereby further improving the safety performance of the battery. The tensile strength of the negative electrode current collector can be 500 MPa, 600 MPa, 700 MPa, 800 MPa, 1000 MPa, or any range of two of the above values, such as 500 MPa~600 MPa, 600 MPa~800 MPa, 800 MPa~1000 MPa, etc.

[0093] In one embodiment, the difference between the elongation of the negative electrode current collector and the elongation of the negative electrode sheet is less than or equal to 2%. The difference between the elongation of the negative electrode current collector and the elongation of the negative electrode sheet refers to the value obtained by subtracting the elongation of the negative electrode sheet from the elongation of the negative electrode current collector. The surface of the negative electrode current collector is coated with a negative electrode active layer, and the negative electrode sheet is obtained after pressing and other steps. A small difference in elongation between the negative electrode current collector and the negative electrode sheet indicates that the current collector has strong resistance to stretching, which can reduce the wrinkling and cracking of the electrode sheet caused by the active material. The difference between the elongation of the negative electrode current collector and the elongation of the negative electrode sheet can be -2.2%, -0.50%, 0, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc., or a range of any two of the above values, such as -2.2%~0, 0~1.2%, 1.4%~1.6%, 1.8%~2%, etc.

[0094] Please refer to Figure 3, which shows the tensile stress-strain curves of the negative electrode current collectors of Embodiments 2, 4, and Comparative Example 1 of this application. Figure 4 shows the tensile stress-strain curves of the negative electrode sheets of Embodiments 2, 4, and Comparative Example 1 of this application. The three curves in the figures correspond to copper foil current collectors (Cu), titanium foil current collectors (Ti), and Cu / PI / Cu current collectors (PI is the second type of base layer, and Cu is the conductive coating). As can be seen from the figures, the difference between the elongation of the negative electrode current collector provided in this application and the elongation of the negative electrode sheet based on the negative electrode current collector is less than or equal to 2%, while the difference between the elongation of the copper foil current collector and the negative electrode sheet based on the copper foil current collector is greater than 5%. Therefore, the negative electrode current collector provided in this application can reduce the risk of electrode sheet cracking due to excessive elongation.

[0095] In one embodiment, the silicon-containing material includes at least one of elemental silicon, silicon-based alloys, silicon-carbon composite materials, and silicon-oxygen materials. This configuration broadens the selection range of negative electrode active materials to meet diverse application requirements.

[0096] In one embodiment, the silicon-containing material includes a silicon-carbon composite material, wherein the silicon-carbon composite material accounts for 20% to 95% of the mass of the negative electrode active layer. The silicon-carbon composite material includes nano-silicon-carbon negative electrode materials, hard carbon-based silicon-carbon negative electrode materials, etc. The mass percentage of silicon-carbon material in the negative electrode active layer within the above-mentioned range results in the negative electrode active layer having both high specific capacity and high conductivity. The mass percentage of silicon-carbon material in the negative electrode active layer can be 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, etc., or a range consisting of any two of the above values, such as 20%~25%, 30%~50%, 60%~70%, 80%~95%, etc.

[0097] In one embodiment, the silicon-carbon composite material comprises porous carbon and silicon material dispersed in the pores of the porous carbon. The porous carbon, acting as a framework, provides buffer space, which can accommodate the volume changes of silicon during charging and discharging, thus improving the stability of the silicon-containing material; the silicon material enables the negative electrode active material to have a high specific capacity, which is beneficial to improving the energy density of the secondary battery.

[0098] In one embodiment, the silicon-carbon composite material includes a carbon-containing coating layer located on the surface of porous carbon and / or silicon materials. The carbon-containing coating layer can act as a physical barrier, reducing direct contact between the silicon materials and the electrolyte, thereby reducing side reactions and contributing to improved battery cycle life.

[0099] In one embodiment, the porous carbon is hard carbon. Hard carbon is amorphous carbon, meaning it is difficult to graphitize and has high mechanical hardness. Hard carbon can provide support for silicon-containing materials, which is beneficial for improving the cycle stability of silicon-carbon composites.

[0100] In addition to silicon-containing materials, the negative electrode active layer also includes other types of negative electrode active materials. When used together with silicon-containing materials, it can combine the advantages of multiple negative electrode active materials and improve the overall performance of the negative electrode sheet.

[0101] In one embodiment, the negative electrode active layer further includes graphite, the aspect ratio of which is greater than or equal to 1.3, and the mass percentage of graphite in the negative electrode active layer is 5% to 70%.

[0102] Graphite has a layered structure, formed by stacking graphite sheets. The aspect ratio of graphite refers to the ratio of its longest diameter to its shortest diameter. A relatively long aspect ratio of graphite serves two purposes: first, it provides lubrication, protecting the hard silicon-carbon composite material and reducing the risk of crushing due to particle interaction during cold pressing; second, it increases the specific surface area of ​​graphite, increasing lithium intercalation sites and improving battery kinetic performance. As the negative electrode active material in the negative electrode active layer, graphite possesses excellent conductivity, structural stability, and cycle stability. It can compensate for the shortcomings of silicon-containing materials in terms of conductivity and stability, optimizing the overall performance of the negative electrode. When the mass proportion of graphite in the negative electrode active layer is within the aforementioned range, its conductivity and stability are well utilized, further optimizing the overall performance of the negative electrode. The mass percentage of graphite in the negative electrode active layer can be 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, etc., or any range of two of the above values, such as 5%~10%, 15%~20%, 30%~40%, 50%~70%, etc.

[0103] In one embodiment, the negative electrode active layer further includes graphene, with the graphene accounting for 0.5% to 10% of the total mass of the negative electrode active layer. Graphene is a planar two-dimensional nanomaterial composed of carbon atoms, possessing an extremely large specific surface area and a large interlayer spacing, which is beneficial for the rapid insertion and extraction of lithium ions. It also exhibits good conductivity, providing excellent electron transport channels and stability. Adding an appropriate amount of graphene to the negative electrode active layer can further improve the electron and ion transport capabilities of the negative electrode sheet, thereby improving the power performance of the battery. The mass percentage of graphene in the negative electrode active layer can be 0.5%, 1%, 2%, 2.6%, 4%, 5%, 6%, 8%, 10%, etc., or any range of two of the above values, such as 0.5% to 1%, 2% to 2.6%, 4% to 6%, 8% to 10%, etc.

[0104] In one embodiment, the negative electrode active layer further includes carbon nanotubes, with the carbon nanotubes accounting for 0.05% to 5% of the total mass of the negative electrode active layer. Carbon nanotubes are tubular structures composed of single or multiple layers of coaxial carbon sheets, with radial dimensions on the nanometer scale and axial dimensions on the micrometer scale. Single-layer carbon nanotubes are single-walled, while multi-layer carbon nanotubes are multi-walled. Carbon nanotube negative electrode active materials exhibit high conductivity and stability, and possess good electron conduction and ion transport capabilities. Adding an appropriate amount of carbon nanotubes to the negative electrode active layer can further improve the electron and ion transport capabilities of the negative electrode sheet, thereby improving the power performance of the battery. The mass percentage of carbon nanotubes in the negative electrode active layer can be 0.05%, 0.1%, 0.2%, 0.25%, 0.4%, 0.5%, 1%, 2%, 2.6%, 4%, 5%, etc., or any range of two of the above values, such as 0.05% to 0.25%, 0.4% to 0.5%, 1% to 2.6%, 4% to 5%, etc.

[0105] In one embodiment, the carbon nanotubes include single-walled carbon nanotubes. Single-walled carbon nanotubes have better conductivity than multi-walled carbon nanotubes, which is beneficial for improving the conductivity of the negative electrode. In another embodiment, single-walled carbon nanotubes are coated on the surface of a silicon-containing material, which can limit the volume expansion of the silicon-containing material and improve its stability.

[0106] Based on the parameter design of the above-mentioned negative electrode active material, the performance parameter design of the negative electrode active layer can be obtained.

[0107] In one embodiment, the areal density of the negative electrode active layer is 0.04 g / 1540.25 mm. 2 ~0.14g / 1540.25mm 2 The areal density of the active layer refers to the mass per unit area of ​​the active layer coated on one side of the current collector. An areal density of the negative electrode active layer within the aforementioned range is beneficial for improving the battery's energy density and also results in better rate performance. The areal density of the negative electrode active layer can be 0.04 g / 1540.25 mm². 2 0.06g / 1540.25mm 2 0.08g / 1540.25mm 2 0.1g / 1540.25mm 2 0.12g / 1540.25mm 2 0.14g / 1540.25mm 2 etc., or a range consisting of any two of the above values, for example, 0.04~0.06g / 1540.25mm. 2 0.08~0.1g / 1540.25mm 2 0.12~0.14g / 1540.25mm 2 wait.

[0108] In one embodiment, the compaction density of the negative electrode active layer is 0.9 g / cm³. 3 ~1.5g / cm 3 The compaction density of the active layer refers to the mass of the active layer coated on one side of the current collector per unit volume. A compaction density of the negative electrode active layer within the aforementioned range is beneficial for improving the battery's energy density, while simultaneously reducing internal resistance, polarization loss, and extending the battery's cycle life. The compaction density of the negative electrode active layer can be 0.9 g / cm³. 3 1.0g / cm 3 1.2g / cm 3 1.4g / cm 3 1.5g / cm 3 Etc., or a range consisting of any two of the above values, for example, 0.9 g / cm³. 3 ~1.0g / cm 3 1.2g / cm 3 ~1.4g / cm 3 1.2g / cm 3 ~1.5g / cm 3 wait.

[0109] High-energy-density battery design requires not only increasing the specific capacity of the negative electrode but also the specific capacity of the positive electrode, as well as matching a suitable electrolyte system and separator material.

[0110] In one embodiment, the areal density of the positive electrode current collector is 0.02 g / 1540.25 mm². 2 ~0.07g / 1540.25mm 2 .

[0111] The areal density of the positive electrode current collector refers to the mass of the current collector over a given area. A lower areal density means a lighter current collector, which is more conducive to improving the energy density of the battery. Within the aforementioned range, a lighter current collector reduces the weight of the current collector, thereby decreasing the weight percentage of inactive materials in the positive electrode, increasing the specific capacity of the positive electrode, and ultimately improving the energy density of the secondary battery. An areal density of 0.02 g / 1540.25 mm² can be considered suitable. 2 0.025g / 1540.25mm 2 0.03g / 1540.25mm 2 0.037g / 1540.25mm 2 0.04g / 1540.25mm 2 0.05g / 1540.25mm 2 0.07g / 1540.25mm 2Or, a range consisting of any two of the above values, for example, 0.02~0.025g / 1540.25mm. 2 0.03~0.037g / 1540.25mm 2 0.04~0.07g / 1540.25mm 2 wait.

[0112] In one embodiment, the positive electrode current collector includes an aluminum foil or a composite current collector; the composite current collector includes a polymer base layer and metal layers disposed on opposite sides of the polymer base layer. The aluminum foil positive electrode current collector and the composite current collector have relatively low mass and good conductivity, which helps to reduce the weight ratio of the positive electrode current collector in the positive electrode sheet, thereby increasing the weight ratio of the positive electrode active layer, thus increasing the specific capacity of the positive electrode sheet, improving the energy density of the battery, and simultaneously improving the power performance of the battery.

[0113] In one embodiment, the polymer base layer comprises at least one of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polymethyl methacrylate (PMMA), polyimide (PI), polytetrafluoroethylene (PTFE), polyurethane (PU), and epoxy resin (EP); the metal layer comprises at least one of aluminum layer and aluminum alloy layer. With the above configuration, the composite current collector is lightweight and highly conductive.

[0114] In one embodiment, the thickness of the positive electrode current collector is 8 μm to 15 μm. A thickness within this range helps reduce the weight of the positive electrode current collector and its proportion of thickness in the negative electrode, thereby allowing the positive electrode to accommodate more active material and improving the specific capacity of the positive electrode and the energy density of the battery. The thickness of the positive electrode current collector can be 8 μm, 8.5 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, etc., or a range consisting of any two of the above values, such as 8 μm to 8.5 μm, 9 μm to 10 μm, 12 μm to 15 μm, etc.

[0115] In one embodiment, the thickness of the positive electrode current collector is 8 μm to 13 μm. A thickness within this range is beneficial for further reducing the weight of the positive electrode current collector and its proportion of thickness in the negative electrode, thereby further improving the energy density of the battery. The thickness of the positive electrode current collector can be 8 μm, 8.5 μm, 9 μm, 10 μm, 12 μm, 13 μm, etc., or a range consisting of any two of the above values, such as 8 μm to 8.5 μm, 9 μm to 10 μm, 12 μm to 13 μm, etc.

[0116] In one embodiment, the positive electrode active layer includes lithium-containing nickel-cobalt-manganese oxide, wherein the proportion of nickel in the sum of the molar amounts of nickel, cobalt and manganese is greater than or equal to 80%; and / or the mass proportion of lithium-containing nickel-cobalt-manganese oxide in the positive electrode active layer is greater than or equal to 95%.

[0117] Lithium-containing nickel-cobalt-manganese oxide is a layered battery cathode active material that combines the advantages of nickel (Ni), cobalt (Co), and manganese (Mn). It significantly improves the specific capacity and stability of the electrode material while reducing manufacturing costs. The main role of nickel is to enhance the capacity of the cathode material, thereby increasing the battery's energy density. Therefore, when the nickel content is greater than or equal to 80%, the cathode active material has a larger capacity, which is beneficial for improving the battery's energy density.

[0118] Furthermore, lithium-containing nickel-cobalt-manganese oxides, as the main contributor to the capacity of the positive electrode, account for more than or equal to 95% of the mass, which is beneficial to further improve the capacity of the positive electrode and the energy density of the battery.

[0119] In one embodiment, the positive electrode active layer includes a lithium-containing nickel-cobalt-manganese oxide, wherein the proportion of nickel in the sum of the molar amounts of nickel, cobalt, and manganese is greater than or equal to 90%; and / or the mass proportion of the lithium-containing nickel-cobalt-manganese oxide in the positive electrode active layer is greater than or equal to 97%. This configuration helps to further improve the energy density of the battery.

[0120] In one embodiment, the areal density of the positive electrode active layer is 0.35 g / 1540.25 mm². 2 ~0.6g / 1540.25mm 2 The above settings help to improve the positive electrode capacity and extend the battery's cycle life. The areal density of the positive electrode active layer can be 0.35g / 1540.25mm². 2 0.4g / 1540.25mm 2 0.45g / 1540.25mm 2 0.5g / 1540.25mm 2 0.55g / 1540.25mm 2 0.6g / 1540.25mm 2 etc., or a range consisting of any two of the above values, for example, 0.35~0.4g / 1540.25mm. 2 0.45~0.5g / 1540.25mm 2 0.55~0.6g / 1540.25mm 2 wait.

[0121] In one embodiment, the compaction density of the positive electrode active layer is 3.3 g / cm³.3 ~3.65g / cm 3 The above settings help improve the battery's rate performance and capacity retention. The compaction density of the positive electrode active layer can be 3.3 g / cm³. 3 3.35g / cm 3 3.4g / cm 3 3.45g / cm 3 3.5g / cm 3 3.55g / cm 3 3.6g / cm 3 3.65g / cm 3 etc., or a range consisting of any two of the above values, for example, 3.3 g / cm³. 3 ~3.35g / cm 3 3.4g / cm 3 ~3.45g / cm 3 3.5g / cm 3 ~3.65g / cm 3 wait.

[0122] By selecting appropriate active materials and designing suitable current collectors for the positive and negative electrode systems of the secondary battery, the specific capacity of the active materials is increased, while the weight percentage of the inactive current collectors decreases, resulting in a higher gravimetric energy density for the secondary battery. In one embodiment, the gravimetric energy density of the secondary battery is greater than or equal to 400 Wh / kg.

[0123] The mass energy density of a secondary battery refers to the electrical energy released per unit mass of the battery. Battery mass energy density = battery capacity × discharge plateau / weight. The higher the battery's mass energy density, the more electrical energy is stored per unit weight. In this embodiment, a secondary battery mass energy density greater than or equal to 400Wh / kg refers to a single cell mass energy density greater than or equal to 400Wh / kg. At this level, the secondary battery can provide strong endurance for electrical devices.

[0124] In one embodiment, the secondary battery has a gravimetric energy density greater than or equal to 420 Wh / kg. In this case, the secondary battery can provide the electrical equipment with a longer operating range.

[0125] In one embodiment, the secondary battery further includes an electrolyte comprising a solvent, an additive, and a lithium salt; the solvent includes ethylene carbonate (EC), and also includes at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC); the additive includes vinylene carbonate (VC) and fluoroethylene carbonate (FEC); the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0126] The primary function of the electrolyte is to stably conduct lithium ions. The solvent, the main component of the electrolyte, dissolves the lithium salt and provides a carrier for the lithium ions; ethylene carbonate (EC) helps extend battery life. The lithium salt, the solute in the electrolyte, provides lithium ions and transports them between the positive and negative electrodes. Additives are used to improve the electrolyte's performance in certain aspects. In cases where the battery negative electrode contains silicon-containing materials, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) can promote the formation of a solid electrolyte interphase (SEI) film on the surface of the negative electrode material, thereby protecting the negative electrode material and extending the lifespan of the battery's negative electrode active material.

[0127] In one embodiment, the mass percentage of ethylene carbonate in the solvent is greater than or equal to 28%. This is beneficial for increasing battery life.

[0128] In one embodiment, the mass percentage of fluoroethylene carbonate in the electrolyte is greater than or equal to 5%; the mass percentage of vinylene carbonate in the electrolyte is greater than or equal to 0.5%. This is beneficial for extending the lifespan of the battery's negative electrode active material.

[0129] In one embodiment, lithium hexafluorophosphate accounts for 5% to 15% of the mass of the electrolyte; and / or, lithium bis(trifluoromethanesulfonyl)imide accounts for less than or equal to 5% of the mass of the electrolyte; and / or, lithium bis(fluorosulfonyl)imide accounts for less than or equal to 5% of the mass of the electrolyte. The aforementioned lithium salts can form an fluorine-rich inorganic SEI film, improving battery life and kinetic performance.

[0130] In one embodiment, the secondary battery further includes a separator, which includes a polymer base layer made of polyethylene or polypropylene; the separator also includes an adhesive layer and an anti-oxidation layer, the adhesive layer being made of polyvinylidene fluoride or polymethyl methacrylate, and the anti-oxidation layer being made of alumina or boehmite.

[0131] The separator, located between the positive and negative electrodes, primarily functions to separate the active materials of the electrodes, reducing the risk of short circuits caused by contact. The polymer base layer forms the basic structure of the separator, providing its overall strength and stability. Polyethylene (PE) and polypropylene (PP) are stable materials with good mechanical strength and electrolyte resistance. The adhesive layer tightly bonds the polymer base layer and the anti-oxidation layer together, reducing layer-to-layer separation and improving the separator's stability. The anti-oxidation layer enhances the separator's heat resistance and puncture resistance, improving battery safety. Furthermore, alumina and boehmite have good affinity for the electrolyte, enhancing its absorption rate and contributing to a more uniform distribution of lithium ions.

[0132] In one embodiment, the secondary battery further includes a casing, within which positive and negative electrode plates are housed. The casing has a melting point greater than or equal to 1000°C. Since silicon-containing negative electrode systems release significant heat upon failure, a casing melting point greater than or equal to 1000°C reduces the risk of the casing melting through, thus improving battery safety.

[0133] In one embodiment, the shell material includes steel or titanium. Both steel and titanium have melting points exceeding 1000°C, which meets the shell requirements.

[0134] In one embodiment, the melting point of the casing is greater than or equal to 2000°C. This can further improve the safety performance of the battery.

[0135] In one embodiment, the secondary battery further includes an end cap that covers the opening of the housing; the end cap is provided with an explosion-proof valve, the area of ​​which is 20% to 70% of the area of ​​the end cap.

[0136] The end cap and housing cooperate to form the internal environment of the battery cell, which can accommodate electrode components, electrolyte, and other parts. The explosion-proof valve is a pressure relief mechanism used to actuate and release the internal pressure of the battery in the event of thermal runaway. Specifically, when thermal runaway occurs inside the battery, the explosion-proof valve actuates and opens to release gases and other substances generated during thermal runaway. When the area of ​​the explosion-proof valve is 20% to 70% of the area of ​​the end cap, it can quickly release gases and other substances generated during thermal runaway, improving battery safety. The area of ​​the explosion-proof valve can be 20%, 25%, 30%, 34%, 40%, 50%, 60%, 70%, or any range of two of these values, such as 20%~25%, 30%~40%, 50%~70%, etc.

[0137] In one embodiment, the area of ​​the explosion-proof valve is 30% to 50% of the area of ​​the end cap. This allows for the rapid release of gases generated by thermal runaway, improving battery safety and enhancing the structural strength of the battery end cap. The area of ​​the explosion-proof valve can be 30%, 34%, 40%, 45%, 50% of the end cap area, or a range of any two of these values, such as 30% to 34%, 40% to 45%, or 40% to 50%.

[0138] In one embodiment, the secondary battery provided in this application can be used as a battery cell. Please refer to Figure 5, which is an exploded structural diagram of a battery according to one or more embodiments of this application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a accommodating space for the battery cell 20, and the housing 10 can adopt various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, and together define a accommodating space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, with the first portion 11 covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 together define the accommodating space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the box 10 formed by the first part 11 and the second part 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0139] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0140] Each battery cell 20 includes at least the secondary battery provided in this application, and may also include other secondary or primary batteries; including but not limited to lithium-sulfur batteries, sodium-ion batteries, or magnesium-ion batteries. The battery cell 20 may be cylindrical, flat, cuboid, or other shapes.

[0141] Please refer to Figure 6, which is an exploded structural diagram of a battery cell according to one or more embodiments of this application. A battery cell 20 refers to the smallest unit that makes up a battery. As shown in Figure 6, the battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0142] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, giving battery cell 20 higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with electrode assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold, the pressure relief mechanism including explosion-proof valve 21b. The material of end cap 21 can also be various, including but not limited to copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0143] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 closes the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The housing 22 can be made of various materials, including but not limited to copper, iron, aluminum, stainless steel, aluminum alloy, and plastic.

[0144] Electrode assembly 23 is the component in the battery cell 100 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the electrode assembly, while the portions of the positive and negative electrode sheets without active material each constitute a tab. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals to form a current loop.

[0145] In some embodiments, the positive electrode includes a current collector and positive active layers disposed on opposite sides of the positive current collector.

[0146] The positive electrode material layer includes a positive electrode active material. In some embodiments, the positive electrode active material includes a nickel-cobalt-manganese ternary material, wherein the proportion of nickel in the sum of the molar amounts of nickel, cobalt, and manganese is greater than or equal to 80%; and / or the mass percentage of the positive electrode active material in the positive electrode active layer is greater than or equal to 95%. In some embodiments, the positive electrode active material includes a nickel-cobalt-manganese ternary material, wherein the proportion of nickel in the sum of the molar amounts of nickel, cobalt, and manganese is greater than or equal to 90%; and / or the mass percentage of the positive electrode active material in the positive electrode active layer is greater than or equal to 97%.

[0147] In some embodiments, the positive electrode active material may further include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0148] In one embodiment, the active layer of the positive electrode material further includes a conductive agent and a binder; the conductive agent includes one or more of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes, graphene, Ketjen black, and acetylene black; the binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, acrylate, and polyurethane.

[0149] The conductive agent imparts conductivity to the electrode. The positive electrode conductive material can include any conductive material as long as it does not cause a chemical change. Non-limiting examples of positive electrode conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof. Optionally, the conductive agent includes one or more of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes, graphene, Ketjen black, and acetylene black.

[0150] The adhesive improves the adhesion stability of the active layer and reduces the probability of powder shedding. The adhesive can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB). Optionally, the adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, acrylate, and polyurethane.

[0151] In some embodiments, the separator includes a polymer base layer made of polyethylene or polypropylene; the separator also includes an adhesive layer and an anti-oxidation layer, the adhesive layer being made of polyvinylidene fluoride or polymethyl methacrylate, and the anti-oxidation layer being made of alumina or boehmite.

[0152] In one embodiment, the electrolyte includes a solvent, an additive, and a lithium salt; the solvent includes ethylene carbonate, and further includes at least one of diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the additive includes vinylene carbonate and fluoroethylene carbonate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0153] In one embodiment, the proportion of ethylene carbonate in the solvent is greater than or equal to 28%.

[0154] In one embodiment, the mass percentage of fluoroethylene carbonate in the electrolyte is greater than or equal to 5%; the mass percentage of vinylene carbonate in the electrolyte is greater than or equal to 0.5%.

[0155] In one embodiment, the mass percentage of lithium hexafluorophosphate in the electrolyte is 5% to 15%; and / or, the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is less than or equal to 5%; and / or, the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte is less than or equal to 5%.

[0156] In other embodiments, the electrolyte may further comprise one or a mixture of several of amine solvents, sulfone solvents, and nitrile solvents. Amine solvents include at least one of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide. Sulfone solvents include at least one of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, and dipropyl sulfone. Nitrile solvents include at least one of acetonitrile, succinic anionibacterium, adiponitrile, and glutaronitrile.

[0157] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active layer disposed on opposite sides of the negative current collector, the negative active layer comprising a negative active material.

[0158] In some embodiments, the areal density of the negative electrode current collector is 0.02 g / 1540.25 mm². 2 ~0.06g / 1540.25mm 2 The tensile strength of the negative electrode current collector is greater than or equal to 350 MPa.

[0159] In some embodiments, the negative electrode active material includes a silicon-containing material, wherein the mass percentage of silicon in the negative electrode active layer is 15% to 90%.

[0160] In some embodiments, the negative electrode active material also includes carbon-based negative electrode materials, tin-based negative electrode materials, lithium titanate negative electrode materials, and lithium metal negative electrode materials; specifically including but not limited to graphite materials, graphene materials, carbon nanotube materials, and tin-based materials; more specifically including natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 One or more of Li-Al alloys.

[0161] In some embodiments, the negative electrode active layer may further include a binder, a conductive agent, and other optional additives. As examples, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers. As examples, the binder may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB). As examples, other optional additives may be thickeners and dispersants (e.g., sodium carboxymethyl cellulose CMC-Na) and PTC thermistor materials.

[0162] In some embodiments, this application also provides an electrical device, such as an electrochemical device. The application of this electrochemical device is not particularly limited and can be used in any electronic device known in the prior art. The battery disclosed in the embodiments of this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. That is, an electrical device is provided. In some embodiments, the electrical device of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, ships, spacecraft, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0163] Electrical equipment can be equipped with individual battery cells, battery modules, or battery packs depending on its usage requirements.

[0164] Please refer to Figure 7, which is a structural schematic diagram of a vehicle according to one or more embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power requirements of the vehicle 1000 during startup, navigation, and driving.

[0165] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0166] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0167] (I) Preparation of secondary batteries

[0168] Example 1:

[0169] 1. Preparation of the positive electrode sheet: The positive electrode active material NCM811 (a ternary material containing lithium nickel cobalt manganese oxide, with a molar ratio of Ni, Co, and Mn of 8:1:1), conductive agent carbon black, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) were mixed uniformly in an N-methylpyrrolidone (NMP) solution at a mass ratio of 97:1.5:0.5:1 to prepare a positive electrode slurry with a solid content of 70%. This slurry was then coated onto a sheet with a thickness of 13 μm and an areal density of 0.054 g / 1540.25 mm using an extrusion coating machine. 2 The aluminum foil surface is dried to obtain a positive electrode film. The coated electrode is then cold-pressed using a cold press to prepare the final positive electrode. The positive electrode film is coated on both sides of the aluminum foil, with a thickness of 76.4 μm on each side. The areal density of the single-sided film layer is 400 mg / 1540.25 mm². 2 The compaction density of the single-sided film layer of the positive electrode sheet is 3.4 g / cm³. 3;

[0170] 2. Preparation of the negative electrode sheet: A silicon-carbon-graphite hybrid material (negative electrode active material), carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) are thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 92:0.5:6.4:1.1 to form a uniform negative electrode slurry with a solid content of 45%. The silicon-carbon-graphite hybrid material is prepared by uniformly mixing silicon-carbon composite material and graphite material (graphite with an aspect ratio of 1.9) at a mass ratio of 8:2. The negative electrode slurry is coated onto the prepared negative electrode current collector, and after drying and other processes, the negative electrode sheet is obtained. The negative electrode film layer is coated on both sides of the aluminum foil, with a thickness of 37.5 μm on each side. The areal density of the single-sided film layer of the negative electrode sheet is 63.5 mg / 1540.25 mm². 2 The compaction density of the single-sided film layer of the negative electrode sheet is 1.1 g / cm³. 3 .

[0171] The preparation of the negative electrode current collector includes:

[0172] Ti plates were repeatedly cold-pressed using a multi-roll cold press to obtain Ti foil with a thickness of 4.6 μm. A mixed acid solution was prepared by mixing 98% concentrated sulfuric acid (mass fraction), 65% concentrated nitric acid (mass fraction), and water in a molar ratio of 1:1:18 (the concentration of sulfuric acid is based on the molar number of sulfuric acid, and the concentration of nitric acid is based on the molar number of nitric acid). The Ti foil was activated with the above mixed acid solution for 10 min, and then Cu layers were electroplated on both sides of the Ti foil. The electroplating solution formula was 200 g / L copper sulfate, 50 g / L sulfuric acid, 0.8 g / L polyethylene glycol (PEG), and 5 mg / L sodium polydisulfide dipropane sulfonate, with a current density of 10 A / dm³. 2 The electroplating temperature was 25℃, and the electroplating tape speed was 6m / min. Finally, a Cu layer with a thickness of 0.5μm was prepared on both sides of the Ti foil, thus obtaining the Cu / Ti / Cu negative electrode current collector.

[0173] 3. Separating membrane: The polymer base layer is made of polyethylene with a thickness of 7μm; the adhesive layer is made of polyvinylidene fluoride with a thickness of 1.5μm; and the anti-oxidation layer is made of boehmite with a thickness of 3μm.

[0174] 4. Electrolyte: Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. The fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. Lithium bis(fluorosulfonyl)imide (LiFSI) is added, accounting for 3.50% of the total mass of the electrolyte. Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are added as additives, accounting for 12% and 1.5% of the total mass of the electrolyte, respectively.

[0175] 5. Battery assembly: The positive electrode, separator, and negative electrode are stacked in sequence to obtain an electrode assembly; the electrode assembly is placed in a packaging shell made of stainless steel with a melting point of 1400℃, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion secondary battery is obtained.

[0176] Example 2:

[0177] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. The negative electrode active material was a mixture of silicon-oxygen material and graphite material, with a mass ratio of silicon-oxygen material to graphite material of 8:2. The negative electrode current collector was a Ti foil with a thickness of 5.6 μm obtained by repeatedly cold pressing Ti plates using a multi-roll cold press.

[0178] Example 3:

[0179] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1, except that the thickness of the positive electrode current collector aluminum foil was 15 μm.

[0180] Example 4:

[0181] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. The mass ratio of the positive electrode active material NCM811, conductive agent carbon black, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) was 97.6:1:0.5:0.9. The negative electrode current collector was prepared by first sputtering a 50nm nickel-chromium alloy onto the PI surface using magnetron sputtering, and then electroplating a Cu layer in a plating solution containing 200g / L copper sulfate, 50g / L sulfuric acid, 0.8g / L polyethylene glycol (PEG), and 5mg / L sodium dithiopropane sulfonate at a current density of 5A / dm³. 2 The electroplating temperature is 25℃ (room temperature), and the tape speed is 3m / min; the PI thickness is 4.5μm, and the single-sided copper layer thickness is 1μm.

[0182] The molar percentage of biphenyl PI in PI is 100%, and the strength of PI is 508 MPa.

[0183] Example 5:

[0184] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. The positive electrode active material was NCM911 (a ternary material containing lithium nickel cobalt manganese oxide, with a molar ratio of Ni, Co, and Mn of 90:0.5:0.5). The positive electrode current collector was a composite current collector with polyethylene terephthalate (PET) as the polymer base layer, a thickness of 10 μm, and an aluminum layer as the metal layer. The aluminum layer on one side was 1 μm thick. The positive electrode current collector was prepared by vapor deposition of an Al layer on the PET surface.

[0185] The preparation method of the negative electrode current collector is the same as in Example 4.

[0186] Examples 6-7:

[0187] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. In Example 5, the mass ratio of silicon-carbon composite material to graphite material was 9:1, and in Example 6, the mass ratio of silicon-carbon composite material to graphite material was 3:7.

[0188] Examples 8-9:

[0189] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. The preparation methods for graphene / Cu composite material and CNT / Cu composite material were as follows: graphene or CNT film was deposited by CVD vapor deposition, and then Cu layer was electroplated on the substrate surface obtained by the above vapor deposition method.

[0190] Example 10:

[0191] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. The mass ratio of the positive electrode active material NCM811, the conductive agent carbon black, the carbon nanotubes, and the binder polyvinylidene fluoride (PVDF) was 95:3:0.5:1.5, and the thickness of the positive electrode film on one side was 106.7 μm. In the preparation of the negative electrode current collector, the belt speed was adjusted to 4 m / min. Finally, a Cu layer with a thickness of 1.5 μm was prepared on both sides of the Ti foil, and the thickness of the negative electrode film on one side was 47.6 μm.

[0192] Example 11:

[0193] Some parameters in the battery fabrication process were adjusted, as detailed in Tables 1 and 2. The fabrication steps were the same as in Example 1, except that the thickness of the single-sided positive electrode film was 68.9 μm. The preparation method of the negative electrode current collector was the same as in Example 4, but the current density was adjusted to 5 A / dm³. 2Finally, Cu layers with a thickness of 0.5 μm were prepared on both sides of the PI, and the thickness of the negative electrode film on one side was 40.1 μm.

[0194] Example 12:

[0195] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. However, the amount of silicon deposited in the silicon-carbon composite material was increased for the negative electrode active material, and the FEC accounted for 20% of the total mass of the electrolyte.

[0196] Example 13:

[0197] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. However, the amount of silicon deposited in the silicon-carbon composite material was increased for the negative electrode active material, and the FEC accounted for 20% of the total mass of the electrolyte.

[0198] Examples 14-16:

[0199] Some parameters in the battery preparation were adjusted, as detailed in Tables 1 and 2. The preparation steps were the same as in Example 1. The negative electrode active materials were elemental silicon and graphite, and FEC accounted for 20% of the total mass of the electrolyte.

[0200] Comparative Example 1:

[0201] The difference from Example 1 is that a copper foil with a thickness of 6 μm is used as the negative electrode current collector, while the other steps are the same as in Example 1.

[0202] Comparative Example 2:

[0203] The difference from Example 1 is that a composite current collector (Cu / PP / Cu) with copper plating on both sides of polypropylene (PP) is used as the negative electrode current collector. The PP thickness is 4.5 μm and the Cu layer thickness is 1 μm. The preparation method is as follows: First, a 50 nm nickel-chromium alloy is sputtered onto the PP surface using magnetron sputtering. Then, a Cu layer is electroplated in a plating solution containing 200 g / L copper sulfate, 50 g / L sulfuric acid, 0.8 g / L polyethylene glycol (PEG), and 5 mg / L sodium dipropane sulfonate, at a current density of 5 A / dm³. 2 The electroplating temperature is 25℃ (room temperature), and the conveyor belt speed is 3m / min.

[0204] The other steps are the same as in Example 1.

[0205] Comparative Example 3:

[0206] The difference from Example 1 is that the mass ratio of silicon-carbon composite material to graphite material is changed, thereby changing the mass percentage of silicon in the negative electrode active layer. Specifically, the mass ratio of silicon-carbon composite material to graphite material in Comparative Example 3 is 2:8, and the other steps are the same as in Example 1.

[0207] (II) Material parameters and performance testing

[0208] 1. Areal density

[0209] The electrode sheet is punched to obtain a circular sample, and the cross-sectional area A of the sample thickness is measured. The mass m1 of the sample is obtained, and the thickness d1 of the sample is measured. The number of faces of the electrode sheet is confirmed, whether it is 1 or 2. The sample is cleaned to remove the active material, resulting in the anode substrate and the cathode substrate. The anode sample is cleaned with water, and the cathode sample is cleaned with NMP (N-methylpyrrolidone) solution.

[0210] The mass m2 of the substrate is obtained, and the thickness d2 of the substrate is measured; the areal density of the active layer of the electrode is (m1-m2) / (number of surfaces × A); the areal density of the current collector is m2 / A.

[0211] 2. Tensile strength and elongation

[0212] Lay the negative electrode current collector flat on a horizontal table and cut it into sections, each about 16cm long. Turn on the tensile testing machine, pass the negative electrode current collector through the upper and lower clamps, step on the air valve to clamp the upper clamp first, maintaining a weak connection, and then clamp the lower clamp. Perform the test by pulling both clamps outward at a speed of 50mm / min until the negative electrode current collector breaks in the middle. The test is complete. The stress at which the negative electrode current collector breaks is the tensile strength, and the elongation at break is the elongation rate.

[0213] 3. Compacted density

[0214] In this application, the compaction density of the active layer of the electrode sheet can be tested using the following method: Disassemble the battery, take the electrode sheet, punch it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1; measure the thickness of the active layer and record it as T; then wipe off the weighed active layer, weigh the remaining electrode sheet, and record it as M0. The compaction density of the active layer PD = (M1 - M0) / (S1 × T). It can be understood that when the electrode sheet is a positive electrode sheet, the compaction density of the positive electrode active layer can be tested. When the electrode sheet is a negative electrode sheet, the compaction density of the negative electrode active layer can be tested.

[0215] 4. Current collector thickness

[0216] Take any uncoated tab location and use a micrometer to directly read the thickness of the current collector. Take the average value of multiple measurements.

[0217] 5. Conductive coating thickness

[0218] The cross-section of the current collector was observed using a scanning electron microscope (SEM), model Sigma300, to determine the thickness of the conductive coating.

[0219] 6. Graphite's aspect ratio

[0220] After the fully disassembled electrode is subjected to plasma quenching, cross-sectional scanning electron microscopy (SEM, model Sigma300) is performed. Ten graphite particles are randomly selected, and energy dispersive spectroscopy (EDS) is used to determine the purity of C element. The longest and shortest radii passing through the center point are measured, and the ratio is calculated and averaged.

[0221] (III) Performance Testing of Secondary Batteries

[0222] 1. Energy density test: At 25℃, the corresponding battery is first weighed and its mass m is recorded. It is then charged to 4.25V at a constant current of 1 / 3C, and then charged to a current of 0.05C at a constant voltage of 4.25V. After resting for 5 minutes, it is discharged to 2.5V at 1 / 3C. The cycle is repeated for 3 cls. The energy of the third cycle is recorded as W. Energy density = W / m.

[0223] 2. Cycle Life Test: At 25℃, the prepared battery was left to stand for 30 minutes, then discharged to 2.8V with a constant current of 1 / 3C. Afterwards, charge-discharge cycles were performed as follows: After standing for 5 minutes, the battery was charged to 4.15V with a constant current of 1 / 2C, then charged at a constant voltage until the current dropped to 0.05C, and the charging capacity at this point was recorded as C0; after standing for 5 minutes, the battery was discharged to 2.8V with a constant current of 1 / 2C, and the discharge capacity at this point was recorded as C0'. This cycle was repeated 500 times, and the discharge capacity of the 500th cycle, C500, was recorded. The capacity retention rate of the battery after 500 cycles was calculated using the following formula:

[0224] Capacity retention rate (%) after 500 cycles: C500 / C0'×100%.

[0225] Table 1. Parameters of the positive electrode sheets in each embodiment and comparative example.

[0226]

[0227] Note: "Mass percentage" refers to the mass percentage of the positive electrode active material in the positive electrode active layer.

[0228] Table 2. Parameters of the negative electrode sheets in each embodiment and comparative example.

[0229]

[0230] Note: (1) "Silicon-carbon (silicon-oxygen) / graphite" is a mixture of silicon-carbon composite material (or silicon-oxygen material) and graphite material; "mass ratio" is the mass ratio of silicon-carbon composite material (or silicon-oxygen material) to graphite material; "mass percentage" is the mass percentage of negative electrode active material in negative electrode active layer; "Si mass percentage" is the mass percentage of silicon element in negative electrode active layer; (2) Cu / Ti / Cu is a negative electrode current collector with copper plating on both sides of titanium foil; Cu / PI / Cu is a negative electrode current collector with copper plating on both sides of PI; Cu / PP / Cu is a negative electrode current collector with copper plating on both sides of PP; graphene / Cu is a current collector prepared by a composite material of graphene and Cu; CNT / Cu is a current collector prepared by a composite material of carbon nanotube and Cu; (3) "difference in elongation" is the difference between the elongation of negative electrode current collector and the elongation of negative electrode sheet.

[0231] Table 3 Battery performance parameters for each embodiment and comparative example

[0232]

[0233] (iv) Analysis of lithium-ion battery performance test results

[0234] The battery performance test results from the examples and comparative examples show that the lithium-ion secondary batteries prepared by the high-energy-density battery design schemes provided in Examples 1 to 16 of this application have high energy density and high capacity retention after 500 cycles, indicating that the battery's cycle performance is improved. Specifically, Examples 12 and 13 increased the mass proportion of silicon in the negative electrode active layer by increasing the proportion of silicon-carbon composite material and the amount of silicon deposited in the silicon-carbon composite material; Examples 14 to 16 further increased the mass proportion of silicon in the negative electrode active layer by using elemental silicon. With the increase in the mass proportion of silicon and the adjustment of the electrolyte composition, the energy density of the secondary battery is improved, and the cycle performance remains at a high level.

[0235] Furthermore, compared to Example 1, Comparative Example 1 has a higher areal density of the negative electrode current collector, resulting in a lower energy density of the battery; Comparative Example 2 has a lower tensile strength of the negative electrode current collector, resulting in poorer cycle stability of the battery; and Comparative Example 3 has too low a mass percentage of silicon in the negative electrode active layer, thus failing to balance energy density and cycle stability, resulting in a lower energy density. Example 1, however, improves the energy density and cycle performance of the secondary battery by using a high-specific-capacity negative electrode active material combined with a lightweight and high-strength negative electrode current collector.

[0236] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

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