Battery cell, battery, and electric device

Abstract

The application discloses a battery monomer, a battery and a power utilization device. The battery monomer comprises a cylindrical shell, an electrode assembly, a first end cover assembly and a second end cover assembly. The cylindrical shell has a containing cavity and first and second openings communicating with the containing cavity. The electrode assembly is arranged in the containing cavity. The first end cover assembly covers the first opening. The second end cover assembly covers the second opening. The first end cover assembly comprises a first pressure relief mechanism. The second end cover assembly comprises a second pressure relief mechanism. The battery monomer further comprises an electrolyte. The electrolyte comprises a solvent. The solvent comprises dimethyl carbonate. The conductivity of the electrolyte at 25 DEG C is 8 mS / cm-16 mS / cm. The battery monomer satisfies (S1+S2) / C0 greater than or equal to 2.5 mm 2 / Ah. The battery monomer satisfies (S1+S2) / L greater than or equal to 0.6 mm. The application can make the battery have high energy density, good cycle performance and high reliability.

Description

[0001] This application is a divisional application based on the invention patent application with application number 202311763673.8, application date December 20, 2023, filed by CATL (Contemporary Amperex Technology Co., Limited), entitled "Battery Cell, Battery and Electrical Device". Technical Field

[0002] This application relates to a battery cell, a battery, and an electrical device. Background Technology

[0003] As batteries are used more widely, people's demands for them are also increasing, such as the requirement for higher energy density. Generally, as battery energy density increases, internal side reactions also increase. Currently, to prevent safety accidents such as fires and explosions, battery designs typically include a pressure relief mechanism. Under abusive conditions, internal side reactions increase, and the pressure relief mechanism releases these gases. However, in practical applications, problems often arise such as untimely or slow pressure relief, which can easily lead to fires and explosions under abusive conditions. Summary of the Invention

[0004] This application provides a battery cell, a battery, and an electrical device that enable the battery to have high energy density, good cycle performance, and high reliability.

[0005] In a first aspect, this application provides a battery cell, including a cylindrical housing, an electrode assembly, a first end cap assembly, and a second end cap assembly. The cylindrical housing has a receiving cavity and a first opening and a second opening communicating with the receiving cavity. The electrode assembly is placed within the receiving cavity. The first end cap assembly covers the first opening, and the second end cap assembly covers the second opening. The first end cap assembly includes a first pressure relief mechanism, and the second end cap assembly includes a second pressure relief mechanism. The battery cell also includes an electrolyte, which includes a solvent, specifically dimethyl carbonate. The electrolyte has a conductivity of 8 mS / cm to 16 mS / cm at 25°C. The first pressure relief mechanism has a first pressure relief section, the area of ​​which is denoted as S1 (in mm). 2 The second pressure relief mechanism has a second pressure relief section, the area of ​​which is denoted as S2, in mm. 2 The capacity of the battery cell is denoted as C0, in Ah, and the battery cell satisfies (S1+S2) / C0 greater than or equal to 2.5 mm². 2 / Ah; The axial dimension of the battery cell is denoted as L, in mm; The battery cell satisfies (S1+S2) / L greater than or equal to 0.6 mm.

[0006] By including dimethyl carbonate in the electrolyte solvent and adjusting the conductivity to the range of 8 mS / cm to 16 mS / cm, the electrolyte can be made to have low viscosity, facilitating its flow. This improves the electrolyte wettability of the electrode assembly and enhances the cycle performance of the battery cell. Integrating pressure relief mechanisms at both ends of the battery cell helps to quickly expel internal contaminants, achieving pressure relief in a short time. Simultaneously, the contaminants ejected from the two pressure relief mechanisms exert opposite impact forces on the cylindrical casing, thus reducing the risk of battery cell deformation and tearing to some extent. Adjusting (S1+S2) / C0 within the aforementioned range helps to achieve a dynamic balance between gas production and exhaust volume within the battery cell, effectively reducing or even preventing safety accidents such as battery fires and explosions.

[0007] Therefore, the battery cell provided in this application embodiment has good electrolyte wettability, which enables the battery cell to have good cycle performance. In addition, the battery cell provided in this application embodiment can also be rapidly depressurized under abuse conditions, which enables the battery cell to have high reliability.

[0008] In some embodiments, the battery cell satisfies (S1+S2) / C0 = 2.5mm. 2 / Ah ~5.5 mm 2 / Ah, optionally 4.0mm 2 / Ah-5.0mm 2 / Ah.

[0009] By adjusting (S1+S2) / C0 within the aforementioned range, it is helpful to achieve a dynamic balance between the gas production and exhaust volume of the battery cell, thereby effectively reducing or even preventing safety accidents such as battery fires and explosions. Simultaneously, it also ensures that the end cap assembly has good processing performance. A larger pressure relief area increases the processing difficulty of the end cap assembly, which is detrimental to reducing the cost of the battery cell and hindering its large-scale production.

[0010] In some embodiments, the battery cell satisfies (S1+S2) / L greater than or equal to 0.7 mm, optionally greater than or equal to 0.74 mm, and more preferably 0.74 mm-0.9 mm.

[0011] By adjusting the ratio (S1+S2) / L of the total area of ​​the pressure relief section of the two pressure relief mechanisms to the axial dimension of the battery cell within the above range, it helps to quickly discharge the emissions inside the battery cell and achieve the purpose of pressure relief in a short time. This can effectively reduce or even avoid safety accidents such as battery fires and explosions.

[0012] In some embodiments, the ratio of the area of ​​the first pressure relief portion to the area of ​​the second pressure relief portion is 0.8-1.2.

[0013] In some embodiments, the ratio of the area of ​​the first pressure relief portion to the area of ​​the first end cap assembly is greater than or equal to 0.02:1, and can be selected as (0.04-0.10):1.

[0014] This helps to quickly expel emissions from inside the battery cells, achieving pressure relief in a short time, thereby effectively reducing or even preventing safety accidents such as battery fires and explosions; at the same time, it also allows the first end cap assembly to have good processing performance.

[0015] In some embodiments, the ratio of the area of ​​the second pressure relief portion to the area of ​​the second end cap assembly is greater than or equal to 0.02:1, and can be selected as (0.04-0.10):1.

[0016] This helps to quickly expel emissions from inside the battery cells, achieving pressure relief in a short time, thereby effectively reducing or even preventing safety accidents such as battery fires and explosions; at the same time, it also allows the first end cap assembly to have good processing performance.

[0017] In some embodiments, the electrode assembly has a central hole extending along the axial direction of the battery cell, the diameter of which is greater than or equal to 5 mm, and optionally 6 mm to 8 mm.

[0018] By adjusting the diameter of the central hole within the aforementioned range, it is helpful to quickly discharge the emissions inside the battery cell, achieving the purpose of depressurization in a short time, thereby effectively reducing or even avoiding safety accidents such as battery fires and explosions.

[0019] In some embodiments, the diameter of the battery cell is greater than or equal to 40 mm, optionally 45 mm to 60 mm. This allows the battery to have a high capacity.

[0020] In some embodiments, the axial dimension L of the battery cell is greater than or equal to 130 mm, and can be selected as 150 mm to 320 mm. This allows the battery to have a high capacity.

[0021] In some embodiments, the capacity C0 of the battery cell is greater than or equal to 20Ah, and may be greater than or equal to 30Ah.

[0022] In some embodiments, the dimethyl carbonate in the solvent has a mass percentage of 50 wt% or greater, optionally 55 wt%-70 wt%. This improves the electrolyte wettability of the electrode assembly, resulting in good battery cycle performance.

[0023] In some embodiments, the solvent further includes one or both of ethylene carbonate and ethyl methyl carbonate. This allows the electrolyte to possess good fluidity, high ionic conductivity, and a wide electrochemical window, thereby enabling the battery to have better cycle performance.

[0024] Optionally, the ethylene carbonate content in the solvent is less than or equal to 25 wt%.

[0025] Optionally, the mass percentage of methyl ethyl carbonate in the solvent is less than or equal to 25 wt%.

[0026] In some embodiments, the electrolyte further includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, and lithium difluorophosphate.

[0027] In some embodiments, the electrolyte further includes additives, which include one or both of fluoroethylene carbonate and vinylene carbonate.

[0028] In some embodiments, the mass percentage of fluoroethylene carbonate is less than or equal to 5 wt% based on the total mass of the electrolyte, optionally 0.1 wt% to 3 wt%.

[0029] In some embodiments, the mass percentage of vinylene carbonate is less than or equal to 5 wt% based on the total mass of the electrolyte, and optionally 0.1 wt% to 3 wt%.

[0030] Additives can participate in the formation of a solid electrolyte interface film on the negative electrode surface, thereby helping to improve the cycle performance of the battery cell.

[0031] In some embodiments, the viscosity of the electrolyte at 25°C is less than or equal to 5 mPa·s; alternatively, the viscosity of the electrolyte at 25°C is less than or equal to 3 mPa·s.

[0032] In some embodiments, the electrolyte has a conductivity of 9 mS / cm-12 mS / cm at 25°C.

[0033] In some embodiments, the first pressure relief mechanism and the second pressure relief mechanism are symmetrically arranged. This ensures that the path of the emitted material is in a straight line, thereby facilitating the rapid discharge of materials from inside the battery cell and achieving pressure relief in a short time. This can effectively reduce or even prevent safety accidents such as battery fires and explosions.

[0034] In some embodiments, the electrolyte has a liquid retention coefficient of 2.5 g / Ah to 4.2 g / Ah, and optionally 2.8 g / Ah to 3.5 g / Ah.

[0035] In some embodiments, the first pressure relief mechanism and the second pressure relief mechanism may have shapes that are independently circular, elliptical, or racetrack-shaped.

[0036] In some embodiments, the first end cap assembly includes a first cover plate, and the first pressure relief mechanism is located on the first cover plate or is integrally formed with the first cover plate.

[0037] In some embodiments, the second end cap assembly includes a second cover plate, and the second pressure relief mechanism is located on the second cover plate or is integrally formed with the second cover plate.

[0038] In some embodiments, the first end cap assembly includes a first electrode terminal, the second end cap assembly includes a second electrode terminal, the first electrode terminal and the second electrode terminal have opposite polarities, and the distance between the geometric center point of the first pressure relief mechanism and the geometric center point of the first electrode terminal is 6mm-14mm; and / or, the distance between the geometric center point of the second pressure relief mechanism and the geometric center point of the second electrode terminal is 6mm-14mm.

[0039] In some embodiments, the electrode assembly includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes one or more of lithium phosphate and lithium transition metal oxide; optionally, the positive electrode active material includes lithium phosphate, and the mass percentage of the lithium phosphate in the positive electrode active material is greater than or equal to 60 wt%.

[0040] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material is 0.8 μm-10 μm.

[0041] In some embodiments, the coating weight of the positive electrode film is greater than or equal to 16 mg / cm³. 2 18mg / cm 2 -25mg / cm 2 .

[0042] In some embodiments, the compaction density of the positive electrode film is greater than or equal to 2.2 g / cm³. 3 2.25g / cm³ is an optional value. 3 -2.6g / cm 3 .

[0043] In some embodiments, the electrode assembly includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes one or more of carbon-based materials and silicon-based materials.

[0044] In some embodiments, the silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials.

[0045] In some embodiments, the silicon-based material accounts for more than or equal to 5 wt% of the mass of the negative electrode active material, and optionally 8 wt% to 20 wt%.

[0046] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material is 6μm~15μm, and optionally 8μm~13μm.

[0047] Secondly, this application provides a battery that includes the battery cell of the first aspect of this application.

[0048] Thirdly, this application provides an electrical device that includes the battery of the second aspect of this application, said battery being used to provide electrical energy.

[0049] The electrical device of this application includes the battery provided in this application, and therefore has at least the same advantages as the battery. Attached Figure Description

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

[0051] Figure 1 The diagram shows the structure of a vehicle provided in some embodiments of this application.

[0052] Figure 2 This is an exploded schematic diagram of a battery provided for some embodiments of this application.

[0053] Figure 3 for Figure 2 The diagram shows an exploded view of the battery module.

[0054] Figure 4 This is an exploded schematic diagram of a battery cell provided in some embodiments of this application.

[0055] Figure 5 This is a schematic diagram of the structure of a first end cap assembly provided in some embodiments of this application.

[0056] Figure 6 This is a schematic diagram of the structure of a second end cap assembly provided in some embodiments of this application.

[0057] Figure 7 This is a schematic diagram showing the connection between the first pressure relief mechanism and the first cover plate provided in some embodiments of this application.

[0058] Figure 8 This is a schematic diagram showing the connection between the second pressure relief mechanism and the second cover plate provided in some embodiments of this application.

[0059] The accompanying drawings are not necessarily drawn to scale.

[0060] The reference numerals in the attached drawings are explained as follows: 1. Vehicle; 2. Battery; 3. Controller; 4. Motor; 5. Housing; 5a. First housing section; 5b. Second housing section; 5c. Accommodation space; 6. Battery module; 7. Battery cell; 8. First end cap assembly; 81. First pressure relief mechanism; 811. First pressure relief section; 812. First connecting section; 82. First electrode terminal; 83. First cover plate; 84. Injection hole; 9. Second end cap assembly; 91. Second pressure relief mechanism; 911. Second pressure relief section; 912. Second connecting section; 92. Second electrode terminal; 93. Second cover plate; 10. Cylindrical shell. Detailed Implementation

[0061] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0062] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0064] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0065] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0066] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0067] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0068] In the description of the embodiments of this application, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0069] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0070] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0071] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs. A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or mixed through a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing can be part of the chassis structure of a vehicle. For example, a portion of the housing can be at least a part of the vehicle's floor, or a portion of the housing can be at least a part of the vehicle's crossbeams and longitudinal beams.

[0072] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0073] The technical solutions described in the embodiments of this application are applicable to batteries and electrical devices that use batteries.

[0074] Batteries can be used as a power source for electrical devices or as an energy storage unit for electrical devices. Electrical devices can be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0075] Electrical devices can choose the type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0076] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device.

[0077] Figure 1 The diagram shows the structure of a vehicle provided in some embodiments of this application.

[0078] like Figure 1 As shown, a battery 2 is installed inside the vehicle 1. The battery 2 can be located at the bottom, front, or rear of the vehicle 1. The battery 2 can be used to power the vehicle 1; for example, the battery 2 can serve as the operating power source for the vehicle 1.

[0079] Vehicle 1 may also include controller 3 and motor 4. Controller 3 is used to control battery 2 to supply power to motor 4, for example, for the power needs of vehicle 1 during start-up, navigation and driving.

[0080] In some embodiments, the battery 2 can not only serve as the operating power source for the vehicle 1, but also as the driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0081] Figure 2 This is a schematic diagram of a battery explosion provided for some embodiments of this application. For example... Figure 2 As shown, battery 2 includes a housing 5 and battery cells (not shown), with the battery cells housed within the housing 5.

[0082] The housing 5 is used to house individual battery cells, and the housing 5 can have various structures. In some embodiments, the housing 5 may include a first housing portion 5a and a second housing portion 5b, which overlap each other, and together define a housing space 5c for housing the individual battery cells. The second housing portion 5b may be a hollow structure with one end open, and the first housing portion 5a may be a plate-like structure, with the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c; alternatively, both the first housing portion 5a and the second housing portion 5b may be hollow structures with one side open, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as cylinders, cuboids, etc.

[0083] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0084] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0085] In battery 2, there can be one or more individual battery cells. If there are multiple individual battery cells, they can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple individual battery cells are connected in both series and parallel configurations. Multiple individual battery cells can be directly connected in series, in parallel, or in a mixed configuration and then housed in the housing 5. Alternatively, multiple individual battery cells can first be connected in series, in parallel, or in a mixed configuration to form a battery module 6, and then multiple battery modules 6 can be connected in series, in parallel, or in a mixed configuration to form a whole and housed in the housing 5.

[0086] Figure 3 for Figure 2 The diagram shows an exploded view of the battery module.

[0087] like Figure 3 As shown, in some embodiments, there are multiple battery cells 7, which are first connected in series, parallel, or mixed to form a battery module 6. The multiple battery modules 6 are then connected in series, parallel, or mixed to form a whole and housed in a casing.

[0088] Multiple battery cells 7 in battery module 6 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of multiple battery cells 7 in battery module 6.

[0089] The battery cells mentioned in the embodiments of this application may include lithium-ion battery cells.

[0090] Figure 4 This is an exploded schematic diagram of a battery cell provided in some embodiments of this application. Figure 5 This is a schematic diagram of the structure of a first end cap assembly provided in some embodiments of this application. Figure 6 This is a schematic diagram of the structure of a second end cap assembly provided in some embodiments of this application.

[0091] like Figures 4 to 6 As shown, the battery cell 7 includes a cylindrical housing 10, an electrode assembly (not shown), a first end cap assembly 8, and a second end cap assembly 9. The cylindrical housing 10 has a receiving cavity and a first opening and a second opening communicating with the receiving cavity. The electrode assembly is placed in the receiving cavity. The first end cap assembly 8 covers the first opening, and the second end cap assembly 9 covers the second opening. The first end cap assembly 8 includes a first pressure relief mechanism 81, and the second end cap assembly 9 includes a second pressure relief mechanism 91.

[0092] The battery cell 7 also includes an electrolyte, which includes a solvent, including dimethyl carbonate (DMC), and the mass percentage of dimethyl carbonate in the solvent is greater than or equal to 50 wt%.

[0093] The first pressure relief mechanism 81 has a first pressure relief section, the area of ​​which is denoted as S1, and the unit is mm. 2 The second pressure relief mechanism 91 has a second pressure relief section, the area of ​​which is denoted as S2, in mm. 2 The capacity of battery cell 7 is denoted as C0, in Ah, and battery cell 7 satisfies (S1+S2) / C0 greater than or equal to 2.5 mm². 2 / Ah.

[0094] With the widespread use of cylindrical battery cells, the demand for their capacity is increasing, leading to larger battery sizes. This can cause difficulties in electrolyte wetting, thus affecting the lifespan of the battery cells. This application addresses this issue by ensuring that the dimethyl carbonate content in the electrolyte solvent is greater than or equal to 50 wt%, resulting in a low-viscosity electrolyte that facilitates flow. This improves the electrolyte wetting properties of the electrode assembly and enhances the cycle performance of the battery cell. However, when the dimethyl carbonate content in the electrolyte solvent is greater than or equal to 50 wt%, the electrochemical window of the electrolyte is typically low. The electrolyte is more prone to decomposition and gas generation during battery cell use and under conditions of abuse, resulting in a higher amount of gas inside the battery cell. If the gas generated inside the battery cell cannot be expelled in time, it can compress the electrode assembly, affecting its electrolyte wetting properties, and in severe cases, causing fires, explosions, and other safety accidents.

[0095] A pressure relief mechanism is a component or part that is activated to release the internal pressure of a battery cell when it reaches a predetermined threshold. This threshold varies depending on the design requirements of the battery cell. Pressure relief mechanisms can take the form of explosion-proof valves, air valves, pressure relief valves, or safety valves, and can specifically employ pressure-sensitive elements or structures. That is, when the internal pressure of the battery cell reaches the predetermined threshold, the pressure relief mechanism actuates or a weak structure within the mechanism ruptures, thereby creating an opening or channel for the internal pressure to be released.

[0096] The term "actuation" as used in this application refers to the pressure relief mechanism being activated or undergoing a certain state, thereby releasing the internal pressure of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to, at least a portion of the mechanism rupturing, breaking, tearing, or opening. When the pressure relief mechanism is activated, the gas inside the battery cell is discharged outwards from the activated portion, thus allowing for pressure relief of the battery cell under controlled pressure conditions, thereby reducing the potential for more serious safety accidents such as fires and explosions.

[0097] The emissions from inside the battery cell mentioned in this application include, but are not limited to: electrolyte, dissolved or broken electrode sheets, fragments of the separator, and gases produced by the reaction.

[0098] The battery cell provided in this application embodiment has pressure relief mechanisms at both ends, which helps to quickly discharge the emissions inside the battery cell and achieve pressure relief in a short time. At the same time, the emissions ejected from the two pressure relief mechanisms exert opposite directions of impact force on the cylindrical shell, which can also reduce the risk of battery cell deformation and tearing to a certain extent.

[0099] As the capacity of a battery cell increases, the amount of gas produced by that cell typically increases as well, especially under abusive conditions, where the gas production further increases. By adjusting the area of ​​the pressure relief section per unit capacity, i.e., (S1+S2) / C0 within the aforementioned range, it is helpful to achieve a dynamic balance between the gas production and gas discharge of the battery cell, thereby effectively reducing or even preventing safety accidents such as battery fires and explosions.

[0100] Therefore, the battery cell provided in this application embodiment has good electrolyte wettability, which enables the battery cell to have good cycle performance. In addition, the battery cell provided in this application embodiment can also be rapidly depressurized under abuse conditions, which enables the battery cell to have high reliability.

[0101] The capacity C0 of a single battery cell can be obtained by testing as follows: At 25°C, let the battery cell stand for 5 minutes, then discharge it at a constant current of 0.33C to the lower cutoff voltage; after standing for 5 minutes, charge it at a constant current of 0.33C to the upper cutoff voltage, and then charge it at a constant voltage at the upper cutoff voltage until the current is 0.05C; after standing for 5 minutes, discharge it at a constant current of 0.33C to the lower cutoff voltage, and record the discharge capacity at this time, which is the capacity C0 of the battery cell.

[0102] The upper and lower cutoff voltages can be the charge / discharge voltages recommended in the product specifications of the individual battery cells.

[0103] For example, when the positive electrode active material includes lithium iron phosphate and the negative electrode active material includes graphite, the upper limit cutoff voltage of the battery cell can be 3.65V and the lower limit cutoff voltage can be 2.5V.

[0104] For example, positive electrode active materials include lithium transition metal oxides with a Ni molar percentage of less than 0.8, such as LiNi. 0.5 Co 0.2 Mn 0.3 When O2 is used and the negative electrode active material includes graphite, the upper limit cutoff voltage of the battery cell can be 4.35V and the lower limit cutoff voltage can be 2.8V.

[0105] For example, positive electrode active materials include lithium transition metal oxides with a Ni molar percentage of 0.8 or greater, such as LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.06 Mn 0.04 When O2 is used and the negative electrode active material includes graphite, the upper limit cutoff voltage of the battery cell can be 4.25V and the lower limit cutoff voltage can be 2.8V.

[0106] The molar percentage of Ni refers to the ratio of the molar amount of Ni to the total molar amount of transition metal elements in lithium transition metal oxides.

[0107] When the internal pressure of a single battery cell reaches a predetermined threshold, the pressure relief mechanism activates or a weak structure within the mechanism ruptures, thereby creating an opening or channel for internal pressure release. The area S1 of the first pressure relief section of the first pressure relief mechanism refers to the maximum area of ​​the opening or channel formed by the first pressure relief mechanism for internal pressure release. The area S2 of the second pressure relief section of the second pressure relief mechanism refers to the maximum area of ​​the opening or channel formed by the second pressure relief mechanism for internal pressure release.

[0108] The battery cell 7 satisfies (S1+S2) / C0 greater than or equal to 2.5mm. 2 / Ah, for example, can be 2.8mm 2 / Ah, 3.0mm 2 / Ah, 3.2mm 2 / Ah, 3.4mm 2 / Ah, 3.6mm 2 / Ah, 3.8mm 2 / Ah, 4.0mm 2 / Ah, 4.2mm 2 / Ah, 4.4mm 2 / Ah, 4.5mm 2 / Ah, 4.8mm 2 / Ah, 5.0mm 2 / Ah, 5.2mm 2 / Ah, 5.5mm 2 / Ah, or any range of the above values.

[0109] Optionally, (S1+S2) / C0 is 4.0 mm. 2 / Ah-5.5mm 2 / Ah, 4.0mm 2 / Ah-5.0mm 2 / Ah.

[0110] By adjusting the pressure relief area per unit capacity, i.e., (S1+S2) / C0 within the aforementioned range, it helps to achieve a dynamic balance between the gas production and gas discharge of the battery cell, thereby effectively reducing or even preventing safety accidents such as battery fires and explosions. Simultaneously, it also ensures the end cap assembly has good processing performance. A larger pressure relief area increases the processing difficulty of the end cap assembly, which is detrimental to reducing the cost of the battery cell and hinders its large-scale production.

[0111] Optionally, the mass percentage of dimethyl carbonate in the solvent can be 55wt%-70wt%. This can improve the electrolyte wettability of the electrode assembly, giving the battery good cycle performance.

[0112] In some embodiments, the solvent further includes one or both of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Optionally, the solvent may also include both ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0113] Dimethyl carbonate can give the electrolyte low viscosity, which facilitates electrolyte flow, but its ability to dissolve electrolyte salts is relatively weak. By mixing it with ethylene carbonate and / or methyl ethyl carbonate, the electrolyte can have good fluidity, high ionic conductivity, and a wide electrochemical window, thereby giving the battery better cycle performance.

[0114] Optionally, the mass percentage of ethylene carbonate in the solvent can be greater than 0 and less than or equal to 25 wt%.

[0115] Optionally, the mass percentage of methyl ethyl carbonate in the solvent can be greater than 0 and less than or equal to 25 wt%.

[0116] In some embodiments, the solvent includes dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC). The mass percentage of dimethyl carbonate in the solvent can be 55wt%-70wt%, the mass percentage of ethylene carbonate in the solvent is 5wt%-25wt%, and the mass percentage of ethyl methyl carbonate in the solvent is 5wt%-25wt%. This allows the electrolyte to have good fluidity, high ionic conductivity, and a wide electrochemical window, thereby enabling the battery to have better cycle performance.

[0117] In some embodiments, the electrolyte further includes an electrolyte salt. Optionally, the electrolyte salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0118] In some embodiments, the electrolyte may further include additives, which may include, but are not limited to, one or both of fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Optionally, the additives may include both fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

[0119] Optionally, based on the total mass of the electrolyte, the mass percentage of fluoroethylene carbonate (FEC) is less than or equal to 5 wt%, and can be 0.05 wt%-5 wt% or 0.1 wt%-3 wt%.

[0120] Optionally, based on the total mass of the electrolyte, the mass percentage of vinylene carbonate (VC) is less than or equal to 5 wt%, and can be 0.05 wt%-5 wt% or 0.1 wt%-3 wt%.

[0121] Additives can participate in the formation of a solid electrolyte interface film on the negative electrode surface, thereby helping to improve the cycle performance of the battery cell.

[0122] In some embodiments, the viscosity of the electrolyte at 25°C can be greater than 0 and less than or equal to 5 mPa·s, and optionally greater than 0 and less than or equal to 3 mPa·s. This helps to improve the electrolyte wettability of the electrode assembly, giving the battery good cycle performance.

[0123] The viscosity of the electrolyte can be tested using a viscometer. When the rotor rotates continuously at a constant speed in the sample, the shear force it experiences causes the spring to generate torque. The torque is proportional to the viscosity, thus yielding the viscosity value of the sample.

[0124] For example, the viscosity of the electrolyte can be tested as follows: Under ambient humidity <80%, take a 30mL sample and keep it at a constant temperature of 25℃ in a water bath for at least 30 minutes. Place a rotor (e.g., a No. 18 rotor) into the sample cup, add the sample to about 0.3cm from the rim, start the connected viscometer, select a speed of 70RPM and rotate for 5 minutes to obtain the viscosity value. Ten data points can be collected during the test, and the average value is taken. The testing instrument can be a Borelfeld DV-2TLV viscometer.

[0125] In some embodiments, the conductivity of the electrolyte at 25°C can be 8mS / cm-16mS / cm, and can be selected as 9mS / cm-12mS / cm.

[0126] The conductivity of the electrolyte can be obtained by testing with a conductivity meter. For example, a suitable amount of electrolyte can be taken, divided into three equal portions, and then the conductivity of each sample can be measured using a conductivity meter at 25°C. The average of the test results is then taken as the conductivity of the electrolyte. A DDS-307 conductivity meter can be used as the testing instrument.

[0127] In some embodiments, the electrolyte retention coefficient can be 2.5 g / Ah-4.2 g / Ah, and optionally 2.8 g / Ah-3.5 g / Ah.

[0128] The electrolyte retention coefficient refers to the ratio of the electrolyte retention capacity to the capacity C0 of a single battery cell.

[0129] The electrolyte retention capacity can be tested as follows: Weigh the battery cell and record the mass as m0; then disassemble the battery cell, centrifuge to separate the electrolyte, immerse all the disassembled solid components in acetonitrile solution, remove them after 2 hours, air dry at room temperature, then transfer them to a 60℃ oven to bake for at least 4 hours, and weigh them again, recording the mass as m1. The difference between the masses of m0 and m1 is taken as the electrolyte retention capacity.

[0130] The components and their contents in the electrolyte can be determined using methods conventional in the art. For example, ion chromatography (IC) can be used to determine the mass percentage of electrolyte salts in the electrolyte, and gas chromatography-mass spectrometry (GC-MS) can be used to determine the mass percentage of dimethyl carbonate (DMC) in the solvent.

[0131] Electrolyte can be obtained by sampling and analyzing during the preparation process, or by disassembling and centrifuging the prepared battery after it has been discharged.

[0132] like Figure 5 As shown, in some embodiments, the first end cap assembly 8 includes a first cover plate 83 that covers the first opening. The first cover plate 83 can have various structures, such as a plate-like structure.

[0133] The first pressure relief mechanism 81 may be located on the first cover plate 83. For example, the first pressure relief mechanism 81 and the first cover plate 83 may be two separate components, which may be connected by welding, riveting, bonding or other means. The first cover plate 83 has a first through hole, and the first pressure relief mechanism 81 may be located in the first through hole. Figure 7 This is a schematic diagram illustrating the connection between the first pressure relief mechanism and the first cover plate provided in some embodiments of this application. (See attached diagram.) Figure 7 As shown, the first pressure relief mechanism 81 can be located on the first cover plate 83. The first pressure relief mechanism 81 includes a first pressure relief part 811 and a first connecting part 812 disposed around the first pressure relief part 811. The first connecting part 812 can be disposed on the side wall of the first through hole by welding, riveting, bonding or other means.

[0134] Alternatively, the first pressure relief mechanism 81 may be integrally formed with the first cover plate 83. For example, the first pressure relief mechanism 81 may be a part of the first cover plate 83.

[0135] like Figure 6 As shown, in some embodiments, the second end cap assembly 9 includes a second cover plate 93 that covers the second opening. The second cover plate 93 can have various structures, such as a plate-like structure.

[0136] The second pressure relief mechanism 91 is located on the second cover plate 93. For example, the second pressure relief mechanism 91 and the second cover plate 93 can be two separate components, which are connected by welding, riveting, bonding or other means. The second cover plate 93 has a second through hole, and the second pressure relief mechanism 91 can be located in the second through hole. Figure 8 This is a schematic diagram illustrating the connection between the second pressure relief mechanism and the second cover plate provided in some embodiments of this application. For example... Figure 8 As shown, the second pressure relief mechanism 91 can be located on the second cover plate 93. The second pressure relief mechanism includes a second pressure relief part 911 and a second connecting part 912 disposed around the periphery of the second pressure relief part 911. The second connecting part 912 can be disposed on the side wall of the second through hole by welding, riveting, bonding or other means. Alternatively, the second pressure relief mechanism 91 can be integrally formed with the second cover plate 93. For example, the second pressure relief mechanism 91 can be a part of the second cover plate 93.

[0137] In some embodiments, the area of ​​the first pressure relief portion may be smaller than the area of ​​the first pressure relief mechanism, and the area of ​​the second pressure relief portion may be smaller than the area of ​​the second pressure relief mechanism. For example... Figure 7 and Figure 8 As shown, the area of ​​the first pressure relief part 811 is smaller than the area of ​​the first pressure relief mechanism 81, and the area of ​​the second pressure relief part 911 is smaller than the area of ​​the second pressure relief mechanism 91.

[0138] In some embodiments, the area of ​​the first pressure relief part may be equal to the area of ​​the first pressure relief mechanism, and the area of ​​the second pressure relief part may be equal to the area of ​​the second pressure relief mechanism.

[0139] In some embodiments, the axial dimension of the battery cell 7 is denoted as L, in mm; the battery cell 7 satisfies (S1+S2) / L greater than or equal to 0.6 mm, for example, it can be 0.6 mm, 0.63 mm, 0.66 mm, 0.69 mm, 0.7 mm, 0.74 mm, 0.77 mm, 0.8 mm, 0.82 mm, 0.84 mm, 0.86 mm, 0.88 mm, 0.9 mm, or any range of the above values.

[0140] Optionally, (S1+S2) / L can be 0.7mm-0.9mm.

[0141] Battery cell 7 is a cylindrical battery cell. The axial direction of battery cell 7 refers to the direction of the cylinder's rotational axis, that is, the direction common to the central axis. The radial direction of battery cell 7 is perpendicular to the axial direction, and the radial direction of battery cell 7 is the diameter direction of the cylinder's end face circle. The axial dimension of battery cell 7 is usually referred to as the length of battery cell 7.

[0142] The axial dimension L of the battery cell 7 refers to the distance between the outer surface of the first end cap assembly 8 and the outer surface of the second end cap assembly 9, which is the distance between the outer surface of the first cover plate 83 and the outer surface of the second cover plate 93. It should be understood that the axial dimension L of the battery cell 7 does not include the dimensions of the electrode terminals.

[0143] As the axial dimension of the battery cell increases, the venting path of the battery cell becomes longer. By adjusting the area of ​​the pressure relief section per unit length, i.e. (S1+S2) / L within the above range, it helps to quickly discharge the emissions inside the battery cell, achieving the purpose of pressure relief in a short time. This can effectively reduce or even avoid safety accidents such as battery fires and explosions.

[0144] In some embodiments, the ratio of the area of ​​the first pressure relief portion to the area of ​​the second pressure relief portion can be 0.8-1.2.

[0145] In some embodiments, the area of ​​the first pressure relief portion and the area of ​​the second pressure relief portion may be equal.

[0146] In some embodiments, the ratio of the area of ​​the first pressure relief portion to the area of ​​the first end cap assembly 8 can be greater than or equal to 0.02:1, and can be selected as (0.04-0.10):1, (0.06-0.08):1.

[0147] This helps to quickly expel emissions from inside the battery cells, achieving pressure relief in a short time, thereby effectively reducing or even preventing safety accidents such as battery fires and explosions; at the same time, it also allows the first end cap assembly to have good processing performance.

[0148] In some embodiments, the ratio of the area of ​​the second pressure relief portion to the area of ​​the second end cap assembly 9 may be greater than or equal to 0.02:1, and may be selected as (0.04-0.10):1, (0.06-0.08):1.

[0149] This helps to quickly expel emissions from inside the battery cells, achieving pressure relief in a short time, thereby effectively reducing or even preventing safety accidents such as battery fires and explosions; at the same time, it also allows the second end cap assembly to have good processing performance.

[0150] The electrode assembly includes a main body and tabs extending axially from the main body. The tabs are used to draw out the current generated in the main body. The main body is the core component of the battery cell, enabling its charging and discharging functions. The main body typically includes a positive electrode, a negative electrode, and a separator. In manufacturing the electrode assembly, the positive electrode, separator, and negative electrode are usually first connected to a winding needle. Then, the winding needle is rotated to wind the positive electrode, separator, and negative electrode onto the needle. After winding, the winding needle is pulled out to form a cylindrical electrode assembly. After the winding needle is pulled out, a central hole is usually formed at the center of the wound electrode assembly.

[0151] In some embodiments, the center of the electrode assembly has a central hole extending along the axial direction of the battery cell, and the diameter of the central hole is greater than or equal to 5 mm, optionally 6 mm-8 mm.

[0152] By adjusting the diameter of the central hole within the aforementioned range, it is helpful to quickly discharge the emissions inside the battery cell, achieving the purpose of depressurization in a short time, thereby effectively reducing or even avoiding safety accidents such as battery fires and explosions.

[0153] In some embodiments, the first pressure relief mechanism 81 and the second pressure relief mechanism 91 are symmetrically arranged. This ensures that the path of the emitted material is in a straight line, which helps to quickly discharge the material from inside the battery cell, achieving pressure relief in a short time, and thus effectively reducing or even preventing safety accidents such as battery fires and explosions.

[0154] In some embodiments, the first pressure relief mechanism 81 and the second pressure relief mechanism 91 may have shapes that are independently circular, elliptical, or racetrack-shaped.

[0155] In some embodiments, the first end cap assembly 8 includes a first electrode terminal 82, and the second end cap assembly 9 includes a second electrode terminal 92, wherein the polarities of the first electrode terminal 82 and the second electrode terminal 92 are opposite. The first electrode terminal 82 may be mounted on the first cover plate 83, and the second electrode terminal 92 may be mounted on the second cover plate 93.

[0156] The first electrode terminal 82 and the second electrode terminal 92 are used to be electrically connected to the electrode assembly to output the electrical energy generated by the electrode assembly.

[0157] In some embodiments, there may be two electrode tabs. The two electrode tabs are defined as a positive electrode tab and a negative electrode tab, respectively. The two electrode tabs are electrically connected to the first electrode terminal 82 and the second electrode terminal 92, respectively. The electrode tabs can be directly connected to the first electrode terminal 82 and the second electrode terminal 92 by means of welding or the like, or they can be indirectly connected to the first electrode terminal 82 and the second electrode terminal 92 by other components.

[0158] Optionally, the first electrode terminal 82 can be a positive terminal and the second electrode terminal can be a negative terminal.

[0159] Optionally, the positive electrode tab is electrically connected to the first electrode terminal 82, and the negative electrode tab is connected to the second electrode terminal 92.

[0160] In some embodiments, the distance between the geometric center point of the first pressure relief mechanism 81 and the geometric center point of the first electrode terminal 82 can be greater than or equal to 5 mm, and can be selected as 6 mm to 14 mm.

[0161] In some embodiments, the distance between the geometric center point of the second pressure relief mechanism 91 and the geometric center point of the second electrode terminal 92 can be greater than or equal to 5 mm, and can be selected as 6 mm to 14 mm.

[0162] In some embodiments, one of the first cover plate 83 and the second cover plate 93 is provided with an injection hole 84. For example... Figure 4 and Figure 5 As shown, the injection hole 84 is located on the first cover plate 83.

[0163] The electrolyte injection port is used to inject electrolyte into the battery cell.

[0164] In some embodiments, the diameter of the battery cell 7 can be greater than or equal to 40 mm, and is optionally 45 mm to 60 mm. This allows the battery to have a high capacity.

[0165] In some embodiments, the axial dimension of the battery cell 7 can be greater than or equal to 130 mm, and can be selected as 150 mm-320 mm, 200 mm-320 mm, 240 mm-320 mm, or 280 mm-320 mm. This allows the battery to have a high capacity.

[0166] In some embodiments, the capacity C0 of the battery cell 7 can be greater than or equal to 20Ah, and can be greater than or equal to 30Ah.

[0167] In some embodiments, the cylindrical housing 10 may be made of materials including but not limited to hard plastic, aluminum, or steel.

[0168] [Positive electrode plate] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer including a positive active material.

[0169] The positive electrode active material can extract and insert lithium ions.

[0170] In some embodiments, the positive electrode active material may include one or more of lithium phosphate and lithium transition metal oxide.

[0171] Lithium-containing phosphates may include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. The modified compounds for the above-mentioned cathode active materials may be for doping modification and / or surface coating modification of the cathode active materials.

[0172] Optionally, the positive electrode active material may include lithium phosphate. More preferably, the positive electrode active material may include one or more of lithium iron phosphate and its modified compounds. Optionally, the modified compounds of lithium iron phosphate may be obtained by one or more modification methods selected from elemental doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0173] In some embodiments, the positive electrode active material may include lithium phosphate, and the mass percentage of lithium phosphate in the positive electrode active material may be greater than or equal to 60 wt%, for example, it may be 60 wt%, 70 wt%, 80 wt%, 90 wt%, 100 wt%, or any range of the above values.

[0174] In some embodiments, the positive electrode active material may simultaneously include lithium phosphate and lithium transition metal oxide, wherein the mass percentage of lithium phosphate in the positive electrode active material may be 60wt%-99wt% and the mass percentage of lithium transition metal oxide in the positive electrode active material may be 1wt%-40wt%.

[0175] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material can be 0.8 μm-10 μm.

[0176] By adjusting the volume distribution particle size Dv50 of the positive electrode active material within the above range, battery side reactions can be reduced, the battery capacity decay rate can be decreased, and the battery can have a long cycle life.

[0177] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0178] In some embodiments, the positive electrode film layer may further include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0179] In some embodiments, the coating weight of the positive electrode film can be greater than or equal to 16 mg / cm³. 2 18mg / cm 2 -25mg / cm 2 This allows the battery to have a high energy density.

[0180] In some embodiments, the compaction density of the positive electrode film layer can be greater than or equal to 2.2 g / cm³. 3 For example, the compaction density of the positive electrode active layer is 2.25 g / cm³. 3 -2.6g / cm 3 This allows the battery to have a high energy density.

[0181] The compaction density of the positive electrode film refers to the ratio of the areal density of the positive electrode film to its thickness. The areal density of the positive electrode film refers to the ratio of the weight of the positive electrode film after coating, drying, and rolling to the coated area.

[0182] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0183] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and rolling. The positive electrode slurry is usually formed by dispersing positive electrode active materials, positive electrode binders, and positive electrode conductive agents in a solvent and stirring them evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0184] [Negative electrode plate] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0185] In some embodiments, the negative electrode active material may include one or more of carbon-based materials and silicon-based materials.

[0186] Alternatively, the carbon-based material may include, but is not limited to, one or more of artificial graphite and natural graphite.

[0187] Optionally, the silicon-based material may include, but is not limited to, one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials.

[0188] Optionally, the silicon-based material may further include one or more of alkali metals and alkaline earth metals. Optionally, the alkali metal includes Li. Optionally, the alkaline earth metal includes Mg. As an example, the silicon-based material may be a Li-intercalated silicon-based material.

[0189] In some embodiments, the mass percentage of silicon-based materials in the negative electrode active material can be greater than or equal to 5 wt%, and more preferably 8 wt%-20 wt%, thereby improving the energy density of the battery.

[0190] In some embodiments, the negative electrode active material may include carbon-based materials and silicon-based materials, wherein the mass percentage of silicon-based materials in the negative electrode active material may be 8wt%-20wt%, and the mass percentage of carbon-based materials in the negative electrode active material may be greater than or equal to 80wt%. This allows the battery to have both high energy density and long cycle life.

[0191] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material can be 6μm-15μm, and optionally 8μm-13μm.

[0192] By adjusting the volume distribution particle size Dv50 of the negative electrode active material within the above range, battery side reactions can be reduced, resulting in a longer cycle life for the battery.

[0193] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0194] In some embodiments, the negative electrode film layer may further include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0195] In some embodiments, the negative electrode film layer may also include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0196] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Examples of polymer substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0197] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer sandwiched between the negative electrode current collector and the negative electrode film layer and located on the surface of the negative electrode current collector, which may be composed of a conductive agent and a binder; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0198] The negative electrode sheet can be prepared as follows: The negative electrode active material, negative electrode binder, negative electrode conductive agent, and optional other additives are dispersed in a solvent and stirred evenly to form a negative electrode slurry; the negative electrode slurry is coated onto a negative electrode current collector, and after drying, rolling, and other processes, a negative electrode sheet is formed. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0199] The Dv50 of materials (e.g., positive electrode active materials, negative electrode active materials, etc.) has a well-known meaning in the art and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer (such as the Malvern Mastersizer 3000) in accordance with GB / T 19077-2016. The physical definition of Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for the material.

[0200] [Isolation membrane] The separator is located between the positive and negative electrodes and primarily serves to prevent internal short circuits. This application does not impose any particular restriction on the type of separator; any known porous membrane with good chemical and mechanical stability can be selected.

[0201] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and polyimide. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0202] The preparation methods for battery cells are well known.

[0203] In some embodiments, the preparation method includes the steps of: providing a cylindrical shell having a receiving cavity and a first opening and a second opening communicating with the receiving cavity; providing an electrode assembly and placing the electrode assembly inside the cylindrical shell; providing a first end cap assembly and a second end cap assembly, the first end cap assembly including a first pressure relief mechanism and the second end cap assembly including a second pressure relief mechanism, and covering the first opening with the first end cap assembly and the second end cap assembly covering the second opening with the second end cap assembly; injecting electrolyte into a battery cell, and then obtaining a battery cell through processes such as vacuum sealing, settling, and formation.

[0204] In some embodiments, a positive electrode, a separator, and a negative electrode can be connected to a winding needle, and then the winding needle is rotated to wind the positive electrode, the separator, and the negative electrode onto the winding needle. After winding is completed, the winding needle is pulled out to form a cylindrical electrode assembly.

[0205] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0206] Example 1 Lithium iron phosphate (LiFePO4), the positive electrode active material, polyvinylidene fluoride (PVDF), and the conductive agent Super P were mixed at a mass ratio of 97:2:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained. The coating weight of the positive electrode film was 19.5 mg / cm³. 2 The compacted density is 2.4 g / cm³. 3 .

[0207] Artificial graphite (negative electrode active material), Super P (conductive agent), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (thickener) were mixed thoroughly in an appropriate amount of deionized water at a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry was coated onto both surfaces of the copper foil (negative electrode current collector), and after drying and cold pressing, a negative electrode sheet was obtained. The coating weight of the negative electrode film was 9.4 mg / cm³. 2 The compacted density is 1.4 g / cm³. 3 .

[0208] The separator is made of porous PP membrane.

[0209] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a mass ratio of 60:20:20 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Fluorinated ethylene carbonate (FEC) and ethylene carbonate (VC) were then added, with the content of FEC and VC being 1 wt% of the total mass of the electrolyte.

[0210] The positive electrode, separator, and negative electrode are stacked in sequence and connected to a winding needle. The winding needle is then rotated to wind the positive electrode, separator, and negative electrode onto the needle. After winding, the winding needle is pulled out to form a cylindrical electrode assembly.

[0211] The electrode assembly is placed inside a cylindrical shell with openings at both ends. A first end cap assembly and a second end cap assembly are welded to the two ends of the cylindrical shell, respectively. The first end cap assembly includes a first pressure relief mechanism, and the second end cap assembly includes a second pressure relief mechanism. Then, electrolyte is injected, and the battery cell is obtained through processes such as vacuum sealing, settling, and formation.

[0212] The battery cell has a capacity C0 of 50.0 Ah, a diameter of 46 mm, an axial dimension L of 280 mm, a center hole diameter of 8 mm for the electrode assembly, and an area S1 of 112.5 mm² for the first pressure relief section of the first pressure relief mechanism. 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 112.5 mm². 2 .

[0213] Example 2 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0214] Dimethyl carbonate (DMC) and ethylene carbonate (EC) were mixed at a mass ratio of 80:20 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Fluoroethylene carbonate (FEC) and ethylene carbonate (VC) were then added, with the content of FEC being 1 wt% of the total mass of the electrolyte and the content of VC being 1 wt% of the total mass of the electrolyte.

[0215] Comparative Example 1 Lithium iron phosphate (LiFePO4), the positive electrode active material, polyvinylidene fluoride (PVDF), and the conductive agent Super P were mixed at a mass ratio of 97:2:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained. The coating weight of the positive electrode film was 19.5 mg / cm³. 2 The compacted density is 2.4 g / cm³. 3 .

[0216] Artificial graphite (negative electrode active material), Super P (conductive agent), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (thickener) were mixed thoroughly in an appropriate amount of deionized water at a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry was coated onto both surfaces of the copper foil (negative electrode current collector), and after drying and cold pressing, a negative electrode sheet was obtained. The coating weight of the negative electrode film was 9.4 mg / cm³. 2 The compacted density is 1.4 g / cm³. 3 .

[0217] The separator is made of porous PP membrane.

[0218] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a mass ratio of 30:50:20 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Fluoroethylene carbonate (FEC) and ethylene carbonate (VC) were then added, with the content of FEC and VC being 1 wt% of the total mass of the electrolyte.

[0219] Connect the positive electrode, separator, and negative electrode to a winding needle, then rotate the winding needle to wind the positive electrode, separator, and negative electrode onto the winding needle. After winding, pull out the winding needle to form a cylindrical electrode assembly.

[0220] The electrode assembly is placed inside a cylindrical shell with one end open. An end cap assembly is welded to the open end of the cylindrical shell. The end cap assembly includes a pressure relief mechanism. Then, electrolyte is injected, and the battery cell is obtained through processes such as vacuum sealing, settling, and formation.

[0221] The battery cell has a capacity C0 of 50.0 Ah, a diameter of 46 mm, an axial dimension L of 280 mm, a center hole diameter of 8 mm for the electrode assembly, and a pressure relief section area of ​​225.0 mm². 2 .

[0222] Comparative Example 2 Except for the following differences, the preparation of the battery cells is the same as that of Comparative Example 1.

[0223] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a mass ratio of 60:20:20 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Fluorinated ethylene carbonate (FEC) and ethylene carbonate (VC) were then added, with the content of FEC and VC being 1 wt% of the total mass of the electrolyte.

[0224] Comparative Example 3 Except for the following differences, the preparation of the battery cells is the same as that of Comparative Example 1.

[0225] The pressure relief section of the pressure relief mechanism has an area of ​​125.0 mm². 2 .

[0226] Comparative Example 4 Except for the following differences, the preparation of the battery cells is the same as that of Comparative Example 2.

[0227] The pressure relief section of the pressure relief mechanism has an area of ​​125.0 mm². 2 .

[0228] Battery cell performance testing (1) Capacity test of individual battery cells At 25℃, the battery cell is left to stand for 5 minutes, then discharged at a constant current of 0.33C to 2.5V; after standing for 5 minutes, it is charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage to a current of 0.05C; after standing for 5 minutes, it is discharged at a constant current of 0.33C to 2.5V. The discharge capacity at this time is recorded, which is the capacity C0 of the battery cell.

[0229] (2) Energy density test of individual battery cells At 25°C, the battery cell is charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the battery cell is discharged at a constant current of 0.33C to 2.5V to obtain the discharge energy Q.

[0230] The energy density of a single battery cell (Wh / L) = discharge energy Q / volume of the single battery cell V.

[0231] The volume V of a single battery cell can be calculated using the formula for the volume of a cylinder: V = (π × d × d) × L × 0.25. L is the axial dimension of the battery cell, and d is the diameter of the battery cell; both units are in mm.

[0232] (3) Cycle performance test of individual battery cells At 25°C, charge the battery cell at a constant current of 1C to the upper limit cutoff voltage of 3.65V, then charge at a constant voltage until the current is 0.05C. After resting for 5 minutes, discharge the battery cell at a constant current of 1C to 2.5V, and record the discharge capacity at this point, which is the discharge capacity of the first cycle. Perform cyclic charge-discharge tests on the battery cell using the above method until the capacity of the battery cell decays to 80% of the discharge capacity of the first cycle, and record the number of cycles for the battery cell.

[0233] (4) Overcharge performance test of individual battery cells At 25℃, the battery cells were charged at a constant current and constant voltage of 0.33C to the upper limit cutoff voltage of 3.65V. Then, they were charged at a constant voltage until the current reached 0.05C. Next, the battery cells were charged at a constant current of 1C for 1 hour, or until the battery cell voltage reached 1.5 times the upper limit cutoff voltage (3.65V). Charging was stopped when either condition was met, and the cells were left to stand for 1 hour to observe for failure. The criterion for a non-failure battery cell was that it did not catch fire or explode. Twenty battery cell samples were used, and the pass rate of the overcharge test was statistically analyzed.

[0234] Table 1

[0235] The test results of Examples 1 to 2 and Comparative Example 1 show that by making the mass percentage of dimethyl carbonate in the electrolyte solvent greater than or equal to 50 wt%, it is beneficial to the flow of the electrolyte and to improve the electrolyte wettability of the electrode assembly, thereby improving the cycle performance of the battery cell.

[0236] Comparative Examples 1 and 2 only have a pressure relief mechanism at one end of the battery cell, and the area of ​​the pressure relief part of the pressure relief mechanism is the same as the total area of ​​the pressure relief parts of the two pressure relief mechanisms in Example 1.

[0237] As can be seen from the test results of Example 1 and Comparative Example 2, when the capacity and electrolyte of the battery cell are the same, by setting a pressure relief mechanism at both ends of the battery cell, it is helpful to quickly discharge the emissions inside the battery cell and achieve the purpose of pressure relief in a short time. This allows the battery cell to have good cycle performance and a high overcharge test pass rate.

[0238] The test results of Comparative Examples 1 and 2 also show that reducing the mass percentage of dimethyl carbonate in the electrolyte solvent does not significantly improve the overcharge performance of the battery cell. This is because when the battery cell only has a pressure relief mechanism at one end, the path for the internal discharge of the battery cell is relatively long, which leads to problems such as untimely pressure relief and slow pressure relief speed. At the same time, the reduction in the mass percentage of dimethyl carbonate reduces the fluidity of the electrolyte and the electrolyte wettability of the electrode assembly, which in turn significantly reduces the cycle performance of the battery cell.

[0239] The test results from Comparative Examples 1 and 3, and Comparative Examples 2 and 4 also show that when a battery cell has a pressure relief mechanism at only one end, increasing the area of ​​the pressure relief section does not effectively improve the overcharge test ratio. This is because when a battery cell has a pressure relief mechanism at only one end, the path for the internal discharge material to escape is longer, resulting in untimely and slow pressure relief. Furthermore, due to the limited area of ​​the end cap assembly, a larger pressure relief section area increases the manufacturing difficulty of the end cap assembly, thereby increasing the cost of the battery cell and hindering mass production.

[0240] Example 3 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0241] The area S1 of the first pressure relief section of the first pressure relief mechanism is 125.0 mm². 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 125.0 mm². 2 .

[0242] Example 4 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0243] The area S1 of the first pressure relief section of the first pressure relief mechanism is 100.0 mm². 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 100.0 mm². 2 .

[0244] Example 5 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0245] The area S1 of the first pressure relief section of the first pressure relief mechanism is 62.5 mm². 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 62.5 mm². 2 .

[0246] Comparative Example 5 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0247] The area S1 of the first pressure relief section of the first pressure relief mechanism is 50.0 mm². 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 50.0 mm². 2 .

[0248] Table 2

[0249] As shown in Table 2, the ratio of the total area of ​​the pressure relief section of the two pressure relief mechanisms to the capacity of the battery cell (S1+S2) / C0 is greater than or equal to 2.5 mm. 2 / Ah can improve the reliability of individual battery cells.

[0250] The test results in Table 2 also show that the reliability of the battery cell can be further improved by adjusting the range of the ratio (S1+S2) / L between the total area of ​​the pressure relief section of the two pressure relief mechanisms and the axial dimension of the battery cell.

[0251] Example 6 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0252] The battery cell has a capacity C0 of 52.5 Ah and an axial dimension L of 320 mm. The area S1 of the first pressure relief section of the first pressure relief mechanism is 118.1 mm². 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 118.1 mm². 2 .

[0253] Example 7 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0254] The battery cell has a capacity C0 of 54.4 Ah and an axial dimension L of 400 mm. The area S1 of the first pressure relief section of the first pressure relief mechanism is 122.4 mm². 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 122.4 mm². 2 .

[0255] Table 3

[0256] Compared with Example 1, the diameter of the battery cell in Examples 6 and 7 remains unchanged, but the axial dimension is increased. At this time, the capacity of the battery cell will increase. By increasing the area of ​​the pressure relief part of the two pressure relief mechanisms in Examples 6 and 7 and keeping the ratio of the total area of ​​the pressure relief part of the two pressure relief mechanisms to the capacity of the battery cell (S1+S2) / C0 the same as in Example 1, the battery cell can have a higher overcharge test pass rate.

[0257] Furthermore, the test results of Examples 1, 6, and 7 also show that when the ratio of the total area of ​​the pressure relief part of the two pressure relief mechanisms to the capacity of the battery cell (S1+S2) / C0 is the same, increasing the ratio of the total area of ​​the pressure relief part of the two pressure relief mechanisms to the axial dimension of the battery cell (S1+S2) / L can give the battery cell a higher overcharge test pass rate.

[0258] Example 8 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0259] The capacity C0 of the single battery cell is 51.3 Ah, the diameter of the central hole of the electrode assembly is 5 mm, and the area S1 of the first pressure relief part of the first pressure relief mechanism is 115.4 mm². 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 115.4 mm². 2 .

[0260] Example 9 Except for the following differences, the preparation of the battery cells is the same as in Example 1.

[0261] The capacity C0 of the single battery cell is 52.6 Ah, the diameter of the central hole of the electrode assembly is 3 mm, and the area S1 of the first pressure relief part of the first pressure relief mechanism is 118.4 mm². 2 The area S2 of the second pressure relief section of the second pressure relief mechanism is 118.4 mm². 2 .

[0262] Table 4

[0263] The test results in Table 4 also show that when the ratio of the total area of ​​the pressure relief section of the two pressure relief mechanisms to the capacity of the battery cell (S1+S2) / C0 is the same, by further adjusting the diameter of the central hole, the battery cell can have a higher overcharge test pass rate while having a high energy density.

[0264] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, include: A cylindrical shell having a receiving cavity and a first opening and a second opening communicating with the receiving cavity; The electrode assembly is placed within the receiving cavity; A first end cap assembly covers the first opening; as well as The second end cap assembly covers the second opening. The first end cap assembly includes a first pressure relief mechanism, and the second end cap assembly includes a second pressure relief mechanism; The battery cell also includes an electrolyte, which includes a solvent, including dimethyl carbonate, and the electrolyte has a conductivity of 8 mS / cm to 16 mS / cm at 25°C. The first pressure relief mechanism has a first pressure relief section, the area of ​​which is denoted as S1, in mm. 2 ; The second pressure relief mechanism has a second pressure relief section, the area of ​​which is denoted as S2, in mm. 2 ; The capacity of the battery cell is denoted as C0, in Ah, and the battery cell satisfies (S1+S2) / C0 greater than or equal to 2.5 mm². 2 / Ah; The axial dimension of the battery cell is denoted as L, and the unit is mm; the battery cell satisfies (S1+S2) / L greater than or equal to 0.6 mm.

2. The battery cell according to claim 1, characterized in that, The battery cell satisfies (S1+S2) / C0 = 2.5mm. 2 / Ah ~5.5 mm 2 / Ah, optionally 4.0mm 2 / Ah-5.0mm 2 / Ah.

3. The battery cell according to any one of claims 1-2, characterized in that, The battery cell satisfies (S1+S2) / L greater than or equal to 0.7 mm, and optionally greater than or equal to 0.74 mm.

4. The battery cell according to claim 1, characterized in that, The battery cell meets the requirement that (S1+S2) / L is 0.74mm-0.9mm.

5. The battery cell according to claim 1, characterized in that, The ratio of the area of ​​the first pressure relief section to the area of ​​the second pressure relief section is 0.8-1.2; and / or, The ratio of the area of ​​the first pressure relief section to the area of ​​the first end cap assembly is greater than or equal to 0.02:1; and / or, The ratio of the area of ​​the second pressure relief section to the area of ​​the second end cap assembly is greater than or equal to 0.02:

1.

6. The battery cell according to claim 5, characterized in that, The ratio of the area of ​​the first pressure relief section to the area of ​​the first end cap assembly is (0.04-0.10):1; and / or, The ratio of the area of ​​the second pressure relief section to the area of ​​the second end cap assembly is (0.04-0.10):

1.

7. The battery cell according to claim 1, characterized in that, The electrode assembly has a central hole extending along the axial direction of the battery cell, and the diameter of the central hole is greater than or equal to 5 mm.

8. The battery cell according to claim 7, characterized in that, The diameter of the central hole is 6mm-8mm.

9. The battery cell according to claim 1, characterized in that, The diameter of the battery cell is greater than or equal to 40 mm; and / or, The axial dimension L of the battery cell is greater than or equal to 130 mm; and / or, The capacity C0 of the battery cell is greater than or equal to 20Ah.

10. The battery cell according to claim 9, characterized in that, The diameter of the battery cell is 45mm-60mm; and / or, The axial dimension L of the battery cell is 150mm-320mm; and / or, The capacity C0 of the battery cell is greater than or equal to 30Ah.

11. The battery cell according to any one of claims 1-10, characterized in that, The mass percentage of dimethyl carbonate in the solvent is greater than or equal to 50 wt%, and optionally 55 wt%-70 wt%.

12. The battery cell according to any one of claims 1-10, characterized in that, The solvent also includes one or both of ethylene carbonate and ethyl methyl carbonate.

13. The battery cell according to claim 12, characterized in that, The ethylene carbonate content in the solvent is less than or equal to 25 wt%; and / or, The mass percentage of methyl ethyl carbonate in the solvent is less than or equal to 25 wt%.

14. The battery cell according to any one of claims 1-10, characterized in that, The electrolyte also includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, and lithium difluorophosphate.

15. The battery cell according to any one of claims 1-10, characterized in that, The electrolyte also includes additives, which include one or both of fluoroethylene carbonate and vinylene carbonate.

16. The battery cell according to claim 15, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is less than or equal to 5 wt%, optionally ranging from 0.1 wt% to 3 wt%; and / or, Based on the total mass of the electrolyte, the mass percentage of vinylene carbonate is less than or equal to 5 wt%, and can be selected as 0.1 wt%-3 wt%.

17. The battery cell according to any one of claims 1-10, characterized in that, The viscosity of the electrolyte at 25°C is less than or equal to 5 mPa·s. Optionally, the viscosity of the electrolyte at 25°C is less than or equal to 3 mPa·s.

18. The battery cell according to any one of claims 1-10, characterized in that, The electrolyte has a conductivity of 9 mS / cm-12 mS / cm at 25°C.

19. The battery cell according to any one of claims 1-10, characterized in that, The electrolyte has a liquid retention coefficient of 2.5 g / Ah to 4.2 g / Ah.

20. The battery cell according to claim 19, characterized in that, The electrolyte has a liquid retention coefficient of 2.8 g / Ah to 3.5 g / Ah.

21. The battery cell according to any one of claims 1-10, characterized in that, The first pressure relief mechanism and the second pressure relief mechanism are arranged symmetrically.

22. The battery cell according to any one of claims 1-10, characterized in that, The first pressure relief mechanism and the second pressure relief mechanism each independently include a circular, elliptical, or racetrack-shaped form; and / or, The first end cap assembly includes a first cover plate, and the first pressure relief mechanism is located on the first cover plate or is integrally formed with the first cover plate; and / or, The second end cap assembly includes a second cover plate, and the second pressure relief mechanism is located on the second cover plate or is integrally formed with the second cover plate.

23. The battery cell according to any one of claims 1-10, characterized in that, The first end cap assembly includes a first electrode terminal, and the second end cap assembly includes a second electrode terminal, wherein the polarities of the first electrode terminal and the second electrode terminal are opposite. The distance between the geometric center point of the first pressure relief mechanism and the geometric center point of the first electrode terminal is 6mm-14mm; and / or, The distance between the geometric center point of the second pressure relief mechanism and the geometric center point of the second electrode terminal is 6mm-14mm.

24. The battery cell according to any one of claims 1-10, characterized in that, The electrode assembly includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes one or more of lithium phosphate and lithium transition metal oxide.

25. The battery cell according to claim 24, characterized in that, The positive electrode active material includes lithium phosphate, and the mass percentage of the lithium phosphate in the positive electrode active material is greater than or equal to 60 wt%.

26. The battery cell according to claim 24, characterized in that, The volume distribution particle size Dv50 of the positive electrode active material is 0.8μm-10μm.

27. The battery cell according to claim 24, characterized in that, The coating weight of the positive electrode film is greater than or equal to 16 mg / cm³. 2 18mg / cm 2 -25mg / cm 2 ; and / or, The compaction density of the positive electrode film is greater than or equal to 2.2 g / cm³. 3 2.25g / cm³ is an optional value. 3 -2.6g / cm 3 .

28. The battery cell according to any one of claims 1-10, characterized in that, The electrode assembly includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes one or more of carbon-based materials and silicon-based materials.

29. The battery cell according to claim 28, characterized in that, The silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials; and / or, The silicon-based material accounts for more than or equal to 5 wt% of the negative electrode active material, and can be selected as 8 wt% to 20 wt%.

30. The battery cell according to claim 28, characterized in that, The volume distribution particle size Dv50 of the negative electrode active material is 6μm~15μm, and can be selected as 8μm~13μm.

31. A battery, characterized in that, Includes the battery cell as described in any one of claims 1-30.

32. An electrical appliance, characterized in that, Includes the battery of claim 31, the battery being used to provide electrical energy.

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