Cylindrical battery cell, battery device, electric device

Abstract

This disclosure provides a cylindrical battery cell, a battery device, and a power consumption device. The cylindrical battery cell includes a negative electrode and a positive electrode. The negative electrode includes a negative current collector and a negative electrode film. The negative electrode film includes a negative active material, which includes a silicon-based material and a graphite material. The silicon-based material includes silicon (Si) element, and the mass percentage of Si element based on the mass of the negative electrode film is more than 0.5%. The positive electrode includes a positive current collector and a positive electrode film. The positive electrode film includes a positive active material, which includes a lithium transition metal oxide (LiMO) with a single-crystal morphology. The positive electrode film also includes carbon nanotubes. The average particle size of the silicon-based material is 1 μm to 12 μm, and the compaction density of the negative electrode film is 1 g / cm³. 3 Up to 1.65 g / cm 3 Cylindrical battery cells combine high energy density, good cycle performance, good storage performance, and good kinetic performance.

Description

[0001] This application claims priority to PCT International Application PCT / CN2026 / 092390, filed on April 22, 2026, entitled “Cylindrical Battery Cell, Battery Device, Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

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

[0003] Battery cells, especially cylindrical battery cells, are widely used in electronic devices such as laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools. With the development of cylindrical battery cells, the performance requirements for them are also gradually increasing. How to enable cylindrical battery cells to possess both high energy density and good cycle performance, storage performance, and kinetic performance is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This disclosure provides a cylindrical battery cell, a battery device, and an electrical device. The cylindrical battery cell has high energy density, good cycle performance, good storage performance, and good kinetic performance.

[0005] In a first aspect, this disclosure provides a cylindrical battery cell, including a casing and an electrode assembly. The casing includes a metal body, and the outer diameter of the casing is 30 mm to 80 mm. The axial dimension of the casing along the cylindrical battery cell is 1.3 to 2.6 times the outer diameter of the casing. The electrode assembly is housed within the casing. The electrode assembly includes a negative electrode and a positive electrode. The negative electrode includes a negative current collector and a negative electrode film. At least one side of the negative current collector is provided with a negative electrode film, which includes a negative electrode active material, including a silicon-based material and graphite. The materials include silicon-based materials, with Si comprising at least 0.5% of the negative electrode film by mass. The positive electrode comprises a positive current collector and a positive electrode film, with the positive electrode film disposed on at least one side of the current collector. The positive electrode film comprises a positive active material, including lithium transition metal oxide, which includes single-crystal lithium transition metal oxide. The positive electrode film also includes carbon nanotubes. The average particle size of the silicon-based materials is 1 μm to 12 μm, and the compaction density of the negative electrode film is 1 g / cm³. 3 Up to 1.65 g / cm 3 .

[0006] The negative electrode sheet disclosed herein comprises silicon-based materials and graphite materials. The silicon-based material includes silicon (Si), and the mass percentage of Si, based on the mass of the negative electrode film, is 0.5% or more. That is, the negative electrode sheet of this disclosure is a silicon-containing negative electrode sheet. Compared with silicon-free negative electrode sheets, the silicon-containing negative electrode sheet of this disclosure can enable the battery cell to have a higher energy density. This disclosure also uses silicon-based materials with an average particle size of 1 μm to 12 μm. Using micron-sized silicon-based materials can reduce interfacial side reactions and improve the storage performance of the battery cell. However, silicon-based materials have a low intrinsic ion diffusion coefficient and poor ion transport performance, resulting in poor kinetic performance of the battery cell.

[0007] Electrochemical reactions and heat generation occur during the charging and discharging of a single battery cell. Since the battery cell disclosed herein is a cylindrical cell with a wound electrode assembly, its heat dissipation path is long, heat distribution is uneven, and heat is not easily dissipated, resulting in a high temperature rise during charging and discharging. Increased temperature can improve ion diffusion rate, thereby compensating for the poor kinetic performance of silicon-based materials and balancing the energy density and kinetic performance of the battery cell. However, due to the limited internal space of the cylindrical battery cell and the constraint of the metal casing, the internal stress is high, which affects electrolyte wetting and reflux, thus impacting the performance of the cylindrical battery cell.

[0008] To address the issue of poor electrolyte wetting and reflux in cylindrical battery cells, this disclosure also adjusts the compaction density of the negative electrode film. The compaction density of the negative electrode film in this disclosure is 1.65 g / cm³. 3 This allows for more expansion space for silicon-based material particles, reducing mutual compression between negative electrode active material particles and decreasing volume expansion at the negative electrode layer level. It also reduces internal stress within the cylindrical battery cell, improving electrolyte wetting and reflux in the electrode assembly. A low compaction density and high thickness of the negative electrode film reduce the number of electrode turns in a cylindrical battery cell of the same volume, further reducing internal stress, minimizing damage to the electrode structure, and improving electrolyte wetting and reflux in the electrode assembly. This ultimately improves the cycle performance of the cylindrical battery cell. Simultaneously, the compaction density of the negative electrode film must meet the requirement of 1 g / cm³. 3 In summary, this enables the negative electrode film to have a continuous electron conduction network, while also ensuring high bonding strength between the negative electrode film and the negative electrode current collector, reducing problems such as powder shedding and film detachment in the later stages of cycling, and also helping to increase the energy density of cylindrical battery cells.

[0009] The positive electrode active material includes lithium transition metal oxides, including single-crystal lithium transition metal oxides, which can improve the cycle performance and storage performance of cylindrical battery cells.

[0010] To reduce the compressive damage to the positive electrode caused by the volume expansion of the negative electrode, this disclosure also incorporates carbon nanotubes into the positive electrode film. Carbon nanotubes are long-range ordered conductive materials with good toughness; their inclusion in the positive electrode film can alleviate the compressive damage caused by the volume expansion of the negative electrode. As a one-dimensional material with excellent conductivity, carbon nanotubes can connect multiple positive electrode active material particles, constructing a three-dimensional continuous electron-ion transport network within the positive electrode film. This allows for the equalization of ion concentration within the positive electrode film through potential difference, homogenizing the ion insertion / extraction capability within the positive electrode film, reducing the concentration difference along the thickness direction of the positive electrode film, and thus reducing over-lithiation on the surface of the positive electrode film. Over-lithiation on the surface of the positive electrode film easily leads to lattice collapse of the positive electrode active material, intensified dissolution of transition metals, and increased interfacial side reactions, deteriorating the cycle performance and storage performance of the cylindrical battery cell.

[0011] Therefore, by adjusting the negative and positive electrodes of the cylindrical battery cell, this disclosure enables the cylindrical battery cell to possess both high energy density and good cycle performance, storage performance, and kinetic performance.

[0012] In some embodiments, based on the mass of the positive electrode film, the mass percentage of carbon nanotubes in the positive electrode film is 0.05% to 0.5%. This can better mitigate the squeezing damage to the positive electrode film caused by the volume expansion of the negative electrode sheet, better balance the ion concentration of the positive electrode film, homogenize the ion insertion / extraction capability inside the positive electrode film, and reduce the concentration difference in the thickness direction of the positive electrode film, thereby further improving the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0013] In some embodiments, the length of carbon nanotubes in the positive electrode film is 5 μm to 10 μm. This can better mitigate the squeezing damage to the positive electrode film caused by the volume expansion of the negative electrode sheet, better balance the ion concentration of the positive electrode film, homogenize the ion insertion / extraction capability inside the positive electrode film, and reduce the concentration difference in the thickness direction of the positive electrode film, thereby further improving the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0014] In some embodiments, at least a portion of the carbon nanotubes are located on the surface of the positive electrode active material in the positive electrode film layer. This can further improve the cycle performance and kinetic performance of the cylindrical battery cell.

[0015] In some embodiments, the average particle size of the positive electrode active material is 1.5 μm to 7.5 μm. When the average particle size of the positive electrode active material is within the above range, the solid-phase diffusion path of ions in the bulk of the positive electrode active material particles can be shortened, the ion solid-phase diffusion coefficient can be increased, and the concentration polarization between the inside and the surface of the particles can be reduced, thereby improving the capacity performance of the cylindrical battery cell; at the same time, the surface activity of the particles will not be too high, thereby reducing interfacial side reactions and improving the cycle performance, storage performance and kinetic performance of the cylindrical battery cell.

[0016] In some embodiments, the positive electrode active material includes lithium transition metal oxide, which includes single-crystal lithium transition metal oxide, and the proportion of single-crystal lithium transition metal oxide is 80%-100% based on the total number of lithium transition metal oxides. This can improve the cycle performance and storage performance of cylindrical battery cells.

[0017] In some embodiments, the compaction density of the positive electrode film is 3.1 g / cm³. 3 Up to 3.6 g / cm 3 3.3g / cm³ is an option. 3 Up to 3.5g / cm 3 This effectively balances the energy density, cycle performance, and kinetic performance of cylindrical battery cells.

[0018] In some embodiments, the one-sided density of the positive electrode film is 155 mg / 1540.25 mm². 2 Up to 320mg / 1540.25mm 2 The option is 220mg / 1540.25mm. 2 Up to 280mg / 1540.25mm 2 When the unilateral density of the positive electrode film is within the above range, the capacity of the positive electrode film will not be too low, the internal stress of the cylindrical battery cell will not be too high, and the ion transport path of the positive electrode film will not be too long. This enables the cylindrical battery cell to achieve high energy density, good cycle performance, and kinetic performance.

[0019] In some embodiments, the positive electrode active material includes a lithium transition metal oxide, which includes a non-lithium metal element, including Ni. Based on the mass of the positive electrode film, the mass percentage of Ni is 44% to 55.5%, optionally 48% to 55%. This allows the cylindrical battery cell to have high energy density while mitigating the damage to the negative electrode SEI film caused by Ni leaching, resulting in good cycle performance and storage performance for the cylindrical battery cell.

[0020] In some embodiments, the positive electrode active material includes a lithium transition metal oxide, which includes a non-lithium metal element, including Ni. Based on the total molar amount of the non-lithium metal element, the molar percentage of Ni is 75% to 95%, optionally 80% to 93%. This allows the cylindrical battery cell to have high energy density while mitigating the damage to the SEI film of the negative electrode caused by Ni dissolution, resulting in good cycle performance and storage performance for the cylindrical battery cell.

[0021] In some embodiments, the mass percentage of Si element is 0.5% to 20% based on the mass of the negative electrode film. Within this range, the mass percentage of Si element can both increase the energy density of the cylindrical battery cell and prevent excessive volume expansion of the negative electrode sheet. This reduces the adverse effects of negative electrode sheet volume expansion on the electrolyte wettability and interfacial film stability of the electrode assembly, thereby improving the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0022] In some embodiments, based on the mass of the negative electrode film, the mass percentage of Si element is 0.5% to 5%, and the compaction density of the negative electrode film is 1.3 g / cm³. 3 Up to 1.65 g / cm 3 .

[0023] In some embodiments, based on the mass of the negative electrode film, the mass percentage of Si element is greater than 5% and less than or equal to 10%, and the compaction density of the negative electrode film is 1.2 g / cm³. 3 Up to 1.55 g / cm 3 .

[0024] In some embodiments, based on the mass of the negative electrode film, the mass percentage of Si element is greater than 10% and less than or equal to 20%, and the compaction density of the negative electrode film is 1 g / cm³. 3 Up to 1.45 g / cm 3 .

[0025] This effectively balances the energy density, cycle performance, storage performance, and kinetic performance of cylindrical battery cells.

[0026] In some embodiments, the one-sided density of the negative electrode film is 85 mg / 1540.25 mm². 2 Up to 180mg / 1540.25mm 2 When the unilateral density of the negative electrode film is within the above range, the internal stress of the cylindrical battery cell will not be too high, which can reduce the crushing damage to the electrode structure, improve the electrolyte wetting and reflux of the electrode assembly, and the ion transport path of the negative electrode film will not be too long. Thus, the cylindrical battery cell can achieve high energy density, good cycle performance and kinetic performance.

[0027] In some embodiments, silicon-based materials include one or more of elemental silicon, silicon-carbon materials, and silicon-oxygen materials.

[0028] In some embodiments, the silicon-based material includes one or more of silicon-carbon materials and silicon-oxygen materials. Silicon-carbon materials and silicon-oxygen materials have lower volume expansion, which can improve the stability of the SEI film, reduce the consumption of active lithium, and further reduce the volume expansion of the negative electrode sheet, thereby reducing the adverse effects of the negative electrode sheet volume expansion on the electrolyte wettability of the electrode assembly and improving the cycle performance and storage performance of the cylindrical battery cell.

[0029] In some embodiments, the graphite material includes one or more of natural graphite and artificial graphite.

[0030] In some embodiments, the graphite material includes natural graphite and synthetic graphite. This helps to further improve the cycle performance and storage performance of cylindrical battery cells.

[0031] Optionally, based on the mass of the negative electrode film, the mass percentage of natural graphite is less than that of artificial graphite. This helps to further improve the cycle performance and storage performance of the cylindrical battery cell.

[0032] In some embodiments, the average particle size of the graphite material is 10 μm to 18 μm.

[0033] In some embodiments, the negative electrode film layer includes a first film layer and a second film layer stacked along the thickness direction, the first film layer being located between the negative electrode current collector and the second film layer, the negative electrode active material in the second film layer including silicon-based material and graphite material, and the negative electrode active material in the first film layer including graphite material.

[0034] In some embodiments, the first film layer does not contain Si.

[0035] In some embodiments, the negative electrode active material in the first film layer further includes a silicon-based material, which includes Si element, and the mass percentage of Si element in the first film layer based on the mass of the first film layer is less than the mass percentage of Si element in the second film layer based on the mass of the second film layer.

[0036] Compared to graphite materials, silicon-based materials have poorer ion transport capabilities. Therefore, by making the second film layer, which is far from the negative electrode current collector, contain more Si elements, the ion transport distance can be shortened, thereby improving the kinetic performance of the cylindrical battery cell.

[0037] The first film layer near the negative electrode current collector contains no Si element or contains less Si element than the second film layer far from the negative electrode current collector. As a result, the volume expansion of the first film layer is small, and the first film layer can have a good electronic conduction network. This can reduce the problem of electronic conduction interruption caused by the large volume expansion of the first film layer under high current fast charge and discharge conditions, and improve the fast charge cycle performance of the cylindrical battery cell.

[0038] In some embodiments, based on the mass of the first film layer, the negative electrode active material in the first film layer further includes a silicon-based material, which includes Si element, and the mass percentage of Si element in the first film layer is greater than 0 and less than or equal to 1%.

[0039] In some embodiments, based on the mass of the first film layer, the negative electrode active material in the first film layer further includes a silicon-based material, which includes Si element, and the mass percentage of the silicon-based material in the first film layer is greater than 0 and less than or equal to 2%.

[0040] In some embodiments, based on the mass of the second film layer, the mass percentage of Si element in the second film layer is 10% to 40%. This prevents excessive volume expansion of the second film layer of the negative electrode, thereby reducing the adverse effects of negative electrode volume expansion on the electrolyte wettability and interfacial film stability of the electrode assembly, and improving the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0041] In some embodiments, based on the mass of the second film layer, the mass percentage of silicon-based material in the second film layer is 20% to 80%. This prevents excessive volume expansion of the second film layer of the negative electrode, thereby reducing the adverse effects of negative electrode volume expansion on the electrolyte wettability and interfacial film stability of the electrode assembly, and improving the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0042] In some embodiments, the compaction density of the second film layer is lower than that of the first film layer. The lower compaction density of the second film layer results in higher porosity, which provides expansion space for the silicon-based material, thereby reducing the volume expansion of the negative electrode layer. The higher compaction density of the first film layer can improve the energy density of the cylindrical battery cell and simultaneously create an electronic conductivity gradient distribution along the thickness direction of the negative electrode film layer, which is beneficial for improving the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0043] In some embodiments, the porosity of the second film layer is greater than that of the first film layer. The higher porosity of the second film layer provides expansion space for the silicon-based material, thereby reducing the volume expansion of the negative electrode layer. The lower porosity of the first film layer can improve the energy density of the cylindrical battery cell and simultaneously create an electronic conductivity gradient distribution along the thickness direction of the negative electrode film layer, which is beneficial to improving the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0044] In some embodiments, the cylindrical battery cell further includes an electrolyte, the mass ratio of which to the capacity of the cylindrical battery cell is between 1.2 g / Ah and 2.1 g / Ah. This balances the cycle performance and storage performance of the cylindrical battery cell.

[0045] In some embodiments, the electrolyte includes a chain ester solvent, wherein the chain ester solvent accounts for 25.5% to 76.5% of the mass of the electrolyte. This can improve the cycle performance and kinetic performance of the cylindrical battery cell.

[0046] In some embodiments, the chain ester solvent includes chain carbonates, which constitute 4% to 70% of the electrolyte by mass. This can further improve the cycle performance and kinetic performance of the cylindrical battery cell.

[0047] In some embodiments, the chain ester solvent includes chain carbonates, which include compounds of Formula I. Formula I, In formula I, R 11 and R 12 Each independently includes C1 to C3 alkyl or C1 to C3 haloalkyl.

[0048] In some embodiments, the chain ester solvent further includes chain carboxylic esters, which constitute 4% to 70% of the electrolyte by mass. This can further improve the cycle performance and kinetic performance of the cylindrical battery cell.

[0049] In some embodiments, the chain ester solvent further includes chain carboxylic esters, which include compounds represented by Formula II. Formula II, In Equation II, R 21 Includes hydrogen atoms, halogen atoms, C1 to C3 alkyl groups, or C1 to C3 haloalkyl groups; R 22 Includes C1 to C3 alkyl or C1 to C3 haloalkyl.

[0050] In some embodiments, the electrolyte comprises an electrolyte salt, which includes one or more of lithium hexafluorophosphate and lithium sulfonylimide.

[0051] In some embodiments, the electrolyte comprises an electrolyte salt with a molar concentration of 0.5 mol / L to 2 mol / L. This is beneficial for further improving the stability of the electrolyte salt and for increasing the conductivity and ion migration rate of the electrolyte, thereby improving the cycle performance and kinetic performance of the cylindrical battery cell.

[0052] In some embodiments, lithium sulfonamide salts comprise anion represented by formula A. Formula A, In formula A, R1 and R2 each independently include a halogen atom or a C1 to C6 haloalkyl group.

[0053] In some embodiments, the housing includes a housing and an end cap, the housing including a sidewall and an end wall connected to the sidewall, the housing having an opening, the end cap being connected to the sidewall and covering the opening, and the end cap and the end wall being opposite each other along the axial direction of the cylindrical battery cell.

[0054] In some embodiments, the base material of the sidewall is steel, and the thickness of the sidewall is 0.2 mm to 0.6 mm.

[0055] In some embodiments, the dimension of the housing along the axial direction of the cylindrical battery cell is 1.3 to 2.6 times the outer diameter of the housing.

[0056] In some embodiments, the housing has an axial dimension of 50 mm to 150 mm along the cylindrical battery cell.

[0057] In some embodiments, the outer diameter of the housing is 40 mm to 60 mm.

[0058] In a second aspect, this disclosure provides a battery device comprising a plurality of cylindrical battery cells according to the first aspect of this disclosure.

[0059] Thirdly, this disclosure provides an electrical device that includes a cylindrical battery cell according to the first aspect of this disclosure or a battery device according to the second aspect of this disclosure. Attached Figure Description

[0060] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments of this disclosure will be briefly described below. Obviously, the drawings described below are merely some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0061] Figure 1 This is a schematic diagram of the structure of a vehicle provided for some embodiments of this disclosure.

[0062] Figure 2 This is a schematic diagram of the structure of a battery device provided in some embodiments of this disclosure.

[0063] Figure 3 for Figure 2 The diagram shows the structure of the battery module.

[0064] Figure 4 This is a schematic diagram of the structure of a cylindrical battery cell provided in some embodiments of this disclosure.

[0065] Figure 5 for Figure 4 The diagram shows an exploded view of a cylindrical battery cell.

[0066] The accompanying drawings are not drawn to scale.

[0067] The reference numerals in the attached drawings are explained as follows: 1. Vehicle; 2. Battery unit; 3. Controller; 4. Motor; 5. Housing; 5a. First housing; 5b. Second housing; 6. Battery module; 7. Cylindrical battery cell; 10. Electrode assembly; 20. Outer casing; 21. Housing; 211. End wall; 212. Side wall; 22. End cap; 1111. Positive electrode tab; 1211. Negative electrode tab; 30. Electrode terminal; 40. First current collector; 50. Second current collector; Z, Axial axis. Detailed Implementation

[0068] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the cylindrical battery cell, battery assembly, and power-consuming device of this disclosure. 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 disclosure and are not intended to limit the subject matter of the claims.

[0069] In this disclosure, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this disclosure. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0070] In the description of this disclosure, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0071] In the description of this disclosure, unless otherwise specified, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact 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.

[0072] In the embodiments of this disclosure, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of this disclosure shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this disclosure.

[0073] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the 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 expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​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 disclosure, 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.

[0074] Unless otherwise specified, all steps in this disclosure 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 mention that the method may also include step (c) indicates 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.

[0075] Unless otherwise specified, in this disclosure, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0076] In this disclosure, the terms "multiple" or "a variety" refer to two or more kinds.

[0077] Unless otherwise stated, the test temperature for all parameters mentioned in this disclosure is 25°C.

[0078] Cylindrical battery cells can be rechargeable, meaning they can be reused after being discharged by recharging to reactivate the active materials. A battery assembly is a single physical module comprising one or more cylindrical battery cells to provide higher voltage and capacity.

[0079] A cylindrical battery cell includes a casing and an electrode assembly, with the electrode assembly housed within the casing. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the positive and negative electrodes. During the charging and discharging process of the cylindrical battery cell, lithium ions repeatedly insert and extract between the positive and negative electrodes.

[0080] Currently, to obtain high-energy-density cylindrical battery cells, the negative electrode film typically contains silicon-based materials. Compared to graphite materials, silicon-based materials have a higher theoretical specific capacity and can provide higher energy density. However, during charging, silicon-based materials typically undergo significant volume expansion, leading to poor stability of the SEI film and easy consumption of active lithium. Simultaneously, the negative electrode also experiences substantial volume expansion. This large volume expansion results in tighter contact between the negative electrode, separator, and positive electrode, and stress is easily transmitted rapidly along the tightly contacted interlayer interface. This leads to the continuous accumulation of internal residual stress, which in turn affects electrolyte wetting and reflux, damages the interface film between the positive and negative electrodes, increases interfacial side reactions and interfacial impedance, and deteriorates the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0081] Therefore, existing cylindrical battery cells cannot simultaneously achieve high energy density, good cycle performance, storage performance, and kinetic performance.

[0082] In view of this, the present disclosure provides a technical solution that, by adjusting the composition of the negative electrode and the positive electrode, enables a cylindrical battery cell to have high energy density while also having good cycle performance, storage performance and kinetic performance.

[0083] The cylindrical battery cells described in this disclosure are applicable to battery devices and electrical devices that use cylindrical battery cells or battery devices.

[0084] The electrical devices disclosed in this embodiment can be devices that use cylindrical battery cells or battery devices as power sources, or various energy storage systems that use cylindrical battery cells or battery devices as energy storage elements. Electrical devices can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0085] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device.

[0086] Figure 1 This is a schematic diagram of the structure of a vehicle provided for some embodiments of this disclosure.

[0087] like Figure 1 As shown, a battery device 2 is installed inside the vehicle 1. The battery device 2 can be located at the bottom, front, or rear of the vehicle 1. The battery device 2 can be used to power the vehicle 1; for example, the battery device 2 can serve as the operating power source for the vehicle 1.

[0088] The vehicle 1 may also include a controller 3 and a motor 4. The controller 3 is used to control the battery device 2 to supply power to the motor 4, for example, for the power needs of the vehicle 1 during starting, navigation and driving.

[0089] In some embodiments of this disclosure, the battery device 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.

[0090] Figure 2 This is a schematic diagram of the structure of a battery device provided in some embodiments of this disclosure.

[0091] In some embodiments, the battery device 2 may include one or more battery cell assemblies for providing voltage and capacity.

[0092] A battery cell assembly may include multiple cylindrical battery cells ( Figure 2 (Not shown) Multiple cylindrical battery cells are connected in series, parallel, or mixed series via a busbar. Mixed series refers to multiple cylindrical battery cells being connected in both series and parallel.

[0093] In some embodiments, the battery cell assembly is typically formed by arranging multiple cylindrical battery cells; as an example, the battery cell assembly can be a battery module 6, which is formed by arranging and fixing multiple cylindrical battery cells to form an independent module.

[0094] In some embodiments, the battery device 2 may be a battery pack, which includes a housing 5 and one or more battery cell assemblies housed within the housing 5. As an example, the battery cell assembly may be a battery module 6, which can be housed within the housing 5 by securing the battery module 6 to the housing. Alternatively, the battery cell assembly may be housed within the housing 5 by directly securing multiple cylindrical battery cells to the housing.

[0095] In some embodiments, the housing 5 is used to house cylindrical battery cells, and the housing 5 can have various structures.

[0096] In some embodiments, the housing 5 may include a first housing 5a and a second housing 5b. The first housing 5a and the second housing 5b are fastened together to form a closed space inside the housing 5 to house the battery cell assembly. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first housing may be a top cover or a bottom plate.

[0097] In some embodiments, the housing 5 may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are respectively connected to the frame, forming an enclosed space inside the housing to accommodate individual battery cells. As an example, the frame may include multiple side beams.

[0098] In some embodiments, the housing 5 may be part of the vehicle's chassis structure. For example, a portion of the housing 5 may be at least a portion of the vehicle's floor, or a portion of the housing 5 may be at least a portion of the vehicle's crossbeams and longitudinal beams.

[0099] In some embodiments, the battery device 2 may be an energy storage device.

[0100] Energy storage devices can be used in energy storage power stations, wind power generation systems, solar power generation systems, mobile power systems, or temporary power supply systems. Energy storage devices can store electrical energy as needed and output it when appropriate. For example, energy storage devices can store electrical energy during off-peak hours and provide power to relevant users or electrical devices during peak hours.

[0101] In some embodiments, the energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0102] Figure 3 for Figure 2 The diagram shows the structure of the battery module.

[0103] In some embodiments, such as Figure 3 As shown, there are multiple cylindrical battery cells 7. These multiple cylindrical battery cells 7 are first connected in series, parallel, or in a mixed manner to form a battery module 6. The multiple battery modules 6 are then connected in series, parallel, or in a mixed manner to form a whole, which is housed in the casing 5.

[0104] Multiple cylindrical battery cells 7 in battery module 6 can be electrically connected through busbars to achieve parallel, series, or mixed connection of multiple cylindrical battery cells 7 in battery module 6. There can be one or more busbars, each used to electrically connect at least two cylindrical battery cells 7.

[0105] Figure 4 This is a schematic diagram of the structure of a cylindrical battery cell provided in some embodiments of this disclosure; Figure 5 for Figure 4 The diagram shows an exploded view of a cylindrical battery cell.

[0106] like Figure 4 and Figure 5 As shown, the cylindrical battery cell 7 includes a housing 20 and an electrode assembly 10, with the electrode assembly 10 housed within the housing 20.

[0107] The outer casing 20 is a hollow structure, and its interior forms a space for accommodating the electrode assembly 10 and the electrolyte. The outer casing 20 of the cylindrical battery cell 7 is a cylindrical outer casing.

[0108] As an example, the housing 20 includes a housing 21 and an end cap 22, the housing 21 having an opening and the end cap 22 for closing the opening.

[0109] The housing 21 is a component used to fit the end cap 22 to form the internal cavity of the cylindrical battery cell 7. The formed internal cavity can be used to accommodate the electrode assembly 10, electrolyte, and other components.

[0110] The housing 21 and the end cap 22 can be separate components. For example, an opening can be provided on the housing 21, and the end cap 22 can be used to close the opening to form an internal cavity for the cylindrical battery cell 7.

[0111] The shape of the end cap 22 can be adapted to the shape of the housing 21 to fit the housing 21. The material of the end cap 22 can be the same as or different from the material of the housing 21.

[0112] The end cap 22 is connected to the housing 21 by welding, bonding, snap-fitting or other means.

[0113] The housing 21 may be open at one end or open at both ends. In some examples, the housing 21 may be a structure with an opening on one side, and one end cap 22 is provided to cover the housing 21. In other examples, the housing 21 may also be a structure with openings on both sides, and two end caps 22 are provided, with the two end caps 22 respectively covering the two openings of the housing 21.

[0114] Electrode assembly 10 is the component in the cylindrical battery cell 7 where the electrochemical reaction occurs.

[0115] The electrode assembly 10 includes a positive electrode and a negative electrode. During the charging and discharging process of the cylindrical battery cell, lithium ions are inserted and extracted back and forth between the positive and negative electrode.

[0116] The positive electrode includes a positive current collector and a positive electrode film layer. The positive electrode film layer is provided on at least one side of the positive current collector, and the positive electrode film layer includes a positive electrode active material. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0117] In some embodiments, the positive electrode film layer further includes a positive electrode conductive agent. As an example, the positive electrode conductive agent includes, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

[0118] In some embodiments, the positive electrode film layer further includes a positive electrode binder. As examples, the positive electrode binder includes, 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.

[0119] 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 includes a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. Examples of metal materials include, but are not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Examples of polymeric material substrates include, but are not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0120] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing positive electrode active materials, positive electrode conductive agents, positive electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0121] The negative electrode sheet includes a negative current collector and a negative electrode film layer. The negative electrode film layer is disposed on at least one side of the negative current collector, and the negative electrode film layer includes a negative electrode active material. As an example, the negative current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0122] In some embodiments, the negative electrode film layer further includes a negative electrode conductive agent. As an example, the negative electrode conductive agent includes, 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.

[0123] In some embodiments, the negative electrode film layer includes a negative electrode binder. As an example, the negative electrode binder includes, 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).

[0124] In some embodiments, the negative electrode film layer further includes other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0125] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. 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 copper, copper 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, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0126] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, negative electrode conductive agent, negative electrode binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0127] like Figure 5 As shown, in some embodiments, the positive current collector includes a positive electrode tab 1111, and the negative current collector includes a negative electrode tab 1211. As an example, the positive electrode tab 1111 is not covered by a positive electrode film layer, and the negative electrode tab 1211 is not covered by a negative electrode film layer.

[0128] Along the axial direction Z of the cylindrical battery cell 7, the positive electrode tab 1111 and the negative electrode tab 1211 can be disposed at the same end of the electrode assembly 10, or they can be disposed at opposite ends of the electrode assembly 10.

[0129] In some embodiments, the positive electrode tab 1111 is disposed at one end of the electrode assembly 10 facing the end wall 211, and the negative electrode tab 1211 is disposed at one end of the electrode assembly 10 facing the end cap 22.

[0130] In some embodiments, the positive electrode tab 1111 is wound into multiple turns. Optionally, the positive electrode tab 1111 is formed into a cylindrical structure by a flattening or smoothing process.

[0131] In some embodiments, the negative electrode tab 1211 is wound into multiple turns. Optionally, the negative electrode tab 1211 is formed into a cylindrical structure by a flattening or smoothing process.

[0132] like Figure 5 As shown, in some embodiments, the cylindrical battery cell 7 further includes an electrode terminal 30 disposed on the end wall 211, one of the positive electrode tab 1111 and the negative electrode tab 1211 being electrically connected to the electrode terminal 30, and the other being electrically connected to the end wall 211.

[0133] The end wall 211 and the electrode terminal 30 can serve as two electrodes of the cylindrical battery cell 7 and are located on the same side of the cylindrical battery cell 7. When multiple cylindrical battery cells 7 are assembled into a group, it is convenient to connect the busbar to the end wall 211 or the busbar to the electrode terminal 30, simplifying the structure of the battery device.

[0134] like Figure 5 As shown, in some embodiments, the cylindrical battery cell 7 further includes a first current collector 40 and a second current collector 50, which are located on opposite sides of the electrode assembly 10 along the axial direction Z. The first current collector 40 is connected to one of the positive electrode tab 1111 and the negative electrode tab 1211, and the second current collector 50 is connected to the other of the positive electrode tab 1111 and the negative electrode tab 1211.

[0135] The first current collector 40 is connected to the electrode terminal 30, and the second current collector 50 is connected to at least one of the end cap 22 and the side wall 212.

[0136] In some embodiments, the first current collector 40 is connected to the electrode terminal 30 and the positive electrode tab 1111.

[0137] In some embodiments, the second current collector 50 connects the end cap 22 and the negative electrode tab 1211, such that the negative electrode tab 1211 is electrically connected to the end wall 211 through the second current collector 50, the end cap 22, and the side wall 212. In other embodiments, the second current collector 50 is connected to the side wall 212, and the negative electrode tab 1211 is electrically connected to the end wall 211 through the second current collector 50 and the side wall 212; optionally, the end wall 211 is insulated from the side wall 212.

[0138] In some embodiments, the electrode assembly 10 further includes a separator disposed between the positive and negative electrode plates. The separator serves to prevent short circuits between the positive and negative electrodes while allowing lithium ions to pass through. The separator can be a single component located between the positive and negative electrode plates, or it can be attached to the surface of either the positive or negative electrode plate.

[0139] In some embodiments, the separator is a separator membrane. This disclosure does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0140] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0141] Optionally, an inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating may also be applied to the surface of the separator.

[0142] In some embodiments, the cylindrical battery cell 7 further includes an electrolyte contained within the housing 20.

[0143] During the charging and discharging process of the cylindrical battery cell 7, lithium ions are inserted and extracted back and forth between the positive and negative electrode plates, and the electrolyte plays the role of conducting lithium ions between the positive and negative electrode plates.

[0144] In some embodiments, the electrode assembly 10 is a wound structure. Exemplarily, the positive electrode, the separator, and the negative electrode are wound into a cylindrical wound structure along the winding direction.

[0145] In some embodiments, the cylindrical battery cell 7 includes a housing 20 and an electrode assembly 10. The housing 20 includes a metal body and has an outer diameter of 30 mm to 80 mm. The electrode assembly 10 is housed within the housing 20.

[0146] The electrode assembly 10 includes a negative electrode and a positive electrode. The negative electrode includes a negative current collector and a negative electrode film. At least one side of the negative current collector has a negative electrode film. The negative electrode film includes a negative electrode active material, which may be a silicon-based material or a graphite material. The silicon-based material includes silicon (Si), and the mass percentage of Si is at least 0.5% based on the mass of the negative electrode film. The positive electrode includes a positive current collector and a positive electrode film. At least one side of the positive current collector has a positive electrode film. The positive electrode film includes a positive electrode active material. The positive electrode film also includes carbon nanotubes. The average particle size of the silicon-based material is 1 μm to 12 μm, and the compaction density of the negative electrode film is 1 g / cm³. 3 Up to 1.65 g / cm 3 .

[0147] Silicon-based materials are anode active materials that provide at least Si. Silicon-based materials can also provide other elements, such as C and O. Graphite materials are anode active materials that provide at least C.

[0148] The negative electrode sheet disclosed herein comprises silicon-based materials and graphite materials. The silicon-based material includes silicon (Si), and the mass percentage of Si, based on the mass of the negative electrode film, is 0.5% or more. That is, the negative electrode sheet of this disclosure is a silicon-containing negative electrode sheet. Compared with silicon-free negative electrode sheets, the silicon-containing negative electrode sheet of this disclosure can enable the battery cell to have a higher energy density. This disclosure also uses silicon-based materials with an average particle size of 1 μm to 12 μm. Using micron-sized silicon-based materials can reduce interfacial side reactions and improve the storage performance of the battery cell. However, silicon-based materials have a low intrinsic ion diffusion coefficient and poor ion transport performance, resulting in poor kinetic performance of the battery cell.

[0149] Electrochemical reactions and heat generation occur during the charging and discharging of a single battery cell. Since the battery cell disclosed herein is a cylindrical cell with a wound electrode assembly, its heat dissipation path is long, heat distribution is uneven, and heat is not easily dissipated, resulting in a high temperature rise during charging and discharging. Increased temperature can improve ion diffusion rate, thereby compensating for the poor kinetic performance of silicon-based materials and balancing the energy density and kinetic performance of the battery cell. However, due to the limited internal space of the cylindrical battery cell and the constraint of the metal casing, the internal stress is high, which affects electrolyte wetting and reflux, thus impacting the performance of the cylindrical battery cell.

[0150] To address the issue of poor electrolyte wetting and reflux in cylindrical battery cells, this disclosure also adjusts the compaction density of the negative electrode film. A high compaction density of the negative electrode film results in less expansion space for silicon-based material particles, thus exacerbating the mutual compression of negative electrode active material particles, increasing the volume expansion of the negative electrode sheet, leading to poor interfacial film stability, and tighter contact between the negative electrode sheet, separator, and positive electrode sheet. Stress is easily transmitted rapidly along the tightly contacted interlayer interface, preventing effective stress release through the pores of the negative electrode film, leading to the continuous accumulation of internal residual stress. This also affects electrolyte wetting and reflux, consequently impacting the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell. Conversely, a low compaction density of the negative electrode film makes it difficult for the cylindrical battery cell to achieve high energy density, and the electron conduction of the negative electrode film becomes discontinuous. Furthermore, the bonding strength between the negative electrode film and the negative current collector decreases, making problems such as powder shedding and film detachment more likely in later stages of cycling. The compaction density of the negative electrode film in this disclosure is 1.65 g / cm³. 3This allows for more expansion space for silicon-based material particles, reducing mutual compression between negative electrode active material particles and decreasing volume expansion at the negative electrode layer level. It also reduces internal stress within the cylindrical battery cell, improving electrolyte wetting and reflux in the electrode assembly. A low compaction density and high thickness of the negative electrode film reduce the number of electrode turns in a cylindrical battery cell of the same volume, further reducing internal stress, minimizing damage to the electrode structure, and improving electrolyte wetting and reflux in the electrode assembly. This ultimately improves the cycle performance of the cylindrical battery cell. Simultaneously, the compaction density of the negative electrode film must meet the requirement of 1 g / cm³. 3 In summary, this enables the negative electrode film to have a continuous electron conduction network, while also ensuring high bonding strength between the negative electrode film and the negative electrode current collector, reducing problems such as powder shedding and film detachment in the later stages of cycling, and also helping to increase the energy density of cylindrical battery cells.

[0151] The negative electrode sheet disclosed herein is a silicon-containing negative electrode sheet. Compared with silicon-free negative electrode sheets, silicon-containing negative electrode sheets usually have a larger volume expansion. After the negative electrode sheet expands in volume, it is easy to squeeze the positive electrode sheet. Under the squeezing action, the positive electrode film layer is prone to problems such as cracking of positive electrode active material particles and powder shedding.

[0152] To mitigate the compressive damage to the positive electrode film caused by the volume expansion of the negative electrode sheet, this disclosure also incorporates carbon nanotubes into the positive electrode film. Carbon nanotubes are long-range ordered conductive materials with good toughness; their inclusion in the positive electrode film can alleviate the compressive damage caused by the volume expansion of the negative electrode sheet. As a one-dimensional material with excellent conductivity, carbon nanotubes can connect multiple positive electrode active material particles, constructing a three-dimensional continuous electron-ion transport network within the positive electrode film. This allows for the equalization of ion concentration within the positive electrode film through potential difference, homogenizing the ion insertion / extraction capability within the positive electrode film, reducing the concentration difference along the thickness direction of the positive electrode film, and thus reducing over-lithiation on the surface of the positive electrode film. Over-lithiation on the surface of the positive electrode film easily leads to lattice collapse of the positive electrode active material, intensified dissolution of transition metals, and increased interfacial side reactions, deteriorating the cycle performance and storage performance of the cylindrical battery cell.

[0153] Therefore, by adjusting the negative and positive electrodes of the cylindrical battery cell, this disclosure enables the cylindrical battery cell to possess both high energy density and good cycle performance, storage performance, and kinetic performance.

[0154] In some embodiments, based on the mass of the positive electrode film, the mass percentage of carbon nanotubes in the positive electrode film is 0.05% to 0.5%, for example, it can be 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or any range of the above values.

[0155] The amount of carbon nanotubes used is small, which cannot effectively alleviate the compression damage to the positive electrode film caused by the volume expansion of the negative electrode sheet, nor can it effectively balance the ion concentration of the positive electrode film, homogenize the ion insertion / extraction ability inside the positive electrode film, or reduce the concentration difference in the thickness direction of the positive electrode film.

[0156] As the amount of carbon nanotubes used increases, their dispersibility in the cathode slurry decreases, the risk of carbon nanotube aggregation increases, and thus the ion concentration of the cathode film cannot be effectively balanced, the ion intercalation / deintercalation ability inside the cathode film cannot be homogenized, and the concentration difference in the thickness direction of the cathode film cannot be reduced.

[0157] When the mass ratio of carbon nanotubes in the positive electrode film is within the above range, it can better alleviate the squeezing damage to the positive electrode film caused by the volume expansion of the negative electrode sheet, better balance the ion concentration of the positive electrode film, homogenize the ion insertion / extraction ability inside the positive electrode film, and reduce the concentration difference in the thickness direction of the positive electrode film, thereby further improving the cycle performance, storage performance and kinetic performance of the cylindrical battery cell.

[0158] In some embodiments, the length of the carbon nanotubes in the positive electrode film layer is 5 μm to 10 μm, for example, it can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or any range of the above values.

[0159] The short length of carbon nanotubes results in poor long-range performance, which is not conducive to building a better three-dimensional continuous electron-ion transport network inside the cathode film; the long length of carbon nanotubes increases the risk of aggregation.

[0160] The length of carbon nanotubes within the above range is beneficial for constructing a better three-dimensional continuous electron-ion transport network inside the positive electrode film. This can better alleviate the squeezing damage to the positive electrode film caused by the volume expansion of the negative electrode sheet, better balance the ion concentration of the positive electrode film, homogenize the ion insertion / extraction capacity inside the positive electrode film, and reduce the concentration difference in the thickness direction of the positive electrode film. This can further improve the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0161] In some embodiments, at least a portion of the carbon nanotubes are located on the surface of the positive electrode active material in the positive electrode film layer.

[0162] By placing at least some carbon nanotubes on the surface of the positive electrode active material, the crystal structure of the positive electrode active material can be stabilized, the particle strength of the positive electrode active material can be improved, and the volume change of the positive electrode active material during charge and discharge can be reduced. This helps to form a stable interfacial film on the surface of the positive electrode active material, reduce interfacial side reactions, and reduce the dissolution of transition metals, thereby helping to improve the cycle performance and storage performance of the battery cell. At the same time, placing at least some carbon nanotubes on the surface of the positive electrode active material also facilitates the construction of a better three-dimensional continuous electron-ion transport network inside the positive electrode film layer. This can better alleviate the compression damage to the positive electrode film layer caused by the volume expansion of the negative electrode sheet, better balance the ion concentration of the positive electrode film layer, homogenize the ion insertion / extraction capacity inside the positive electrode film layer, and reduce the concentration difference in the thickness direction of the positive electrode film layer, thereby further improving the cycle performance and kinetic performance of the cylindrical battery cell.

[0163] In some embodiments, the average particle size of the positive electrode active material is from 1.5 μm to 7.5 μm, for example, it can be 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm, 6.2 μm, 6.5 μm, 6.8 μm, 7 μm, 7.2 μm, 7.5 μm, or any range of the above values.

[0164] The average particle size of the positive electrode active material refers to the average particle size of all positive electrode active material particles in the entire positive electrode film layer.

[0165] When the average particle size of the positive electrode active material is within the above range, the solid-phase diffusion path of ions in the particle body of the positive electrode active material can be shortened, the solid-phase diffusion coefficient of ions can be increased, and the concentration polarization between the inside and the surface of the particles can be reduced, thereby improving the capacity performance of the cylindrical battery cell. At the same time, the surface activity of the particles will not be too high, which can also reduce interfacial side reactions and improve the cycle performance, storage performance and kinetic performance of the cylindrical battery cell.

[0166] Optionally, the average particle size of the positive electrode active material is 3 μm to 5 μm.

[0167] The average particle size of the positive electrode active material can be measured using ion polishing cross-sectional morphology analysis (CP) combined with scanning electron microscopy (SEM). SEM images of the positive electrode film are obtained using CP and SEM. Multiple test areas (e.g., 5) are randomly selected, and at a certain magnification (e.g., 500x or higher), the number and size of positive electrode active material particles in each test area are counted. The arithmetic mean of the particle sizes of all positive electrode active material particles in each test area is taken as the average particle size of the positive electrode active material. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be used for the above test, and the average value of each test sample is taken as the final test result. It should be noted that when the particles are irregularly shaped, the distance between the two farthest points on the particle is taken as the particle size.

[0168] In some embodiments, the positive electrode active material includes lithium transition metal oxide, which includes single-crystal lithium transition metal oxide, and the proportion of single-crystal lithium transition metal oxide is 80%-100% based on the total number of lithium transition metal oxides, for example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any range of the above values.

[0169] Compared to polycrystalline lithium transition metal oxides, single-crystal lithium transition metal oxides have higher Young's modulus, greater compressive strength, and no or only a small number of grain boundaries. This reduces particle cracking, thereby reducing the amount of fresh interface exposed due to particle cracking and minimizing interfacial side reactions. Furthermore, single-crystal lithium transition metal oxide particles are mostly in point contact, allowing for deformation and slippage under compression. This buffers the volume expansion of the negative electrode, reducing its impact on the positive electrode film and ultimately improving the cycle performance and storage performance of cylindrical battery cells.

[0170] Optionally, based on the total number of lithium transition metal oxides, the proportion of single-crystal lithium transition metal oxides is 85%-100%, 90%-100%, or 95%-100%.

[0171] In some embodiments, the percentage of lithium transition metal oxides with single-crystal morphology is 100% based on the total number of lithium transition metal oxides.

[0172] The terms "single-crystal lithium transition metal oxides" and "polycrystalline lithium transition metal oxides" have meanings well-known in the art. "Single-crystal lithium transition metal oxides" also include quasi-single-crystal (or near-single-crystal) lithium transition metal oxides. Quasi-single-crystal (or near-single-crystal) lithium transition metal oxides are well-known in the art and typically refer to lithium transition metal oxides composed of a small number, for example, less than 10 primary particles, with a small number of grain boundaries within the particles. Polycrystalline lithium transition metal oxides refer to lithium transition metal oxides composed of a large number, for example, 10 or more secondary particles, with a large number of grain boundaries within the particles. "Single-crystal lithium transition metal oxides" and "polycrystalline lithium transition metal oxides" can be distinguished using scanning electron microscopy.

[0173] Based on the total number of lithium transition metal oxides (LiMOs), the proportion of single-crystal LiMOs can be determined using ion-polished cross-sectional morphology analysis (CP) combined with scanning electron microscopy (SEM). SEM images of the cathode film are obtained using CP combined with SEM. Multiple test areas (e.g., 5 areas) are randomly selected, and at a certain magnification (e.g., 500x or higher), the number of all single-crystal LiMO particles and the number of all polycrystalline LiMO particles in each test area are counted. The proportion of single-crystal LiMOs is calculated as: (Number of all single-crystal LiMO particles) / (Number of all single-crystal LiMO particles + Number of all polycrystalline LiMO particles). To ensure the accuracy of the test results, multiple test samples (e.g., 10 samples) can be used, and the average value of each sample is taken as the final test result.

[0174] In some embodiments, the compaction density of the positive electrode film is 3.1 g / cm³. 3 Up to 3.6 g / cm 3 For example, it can be 3.1 g / cm³. 3 3.12 g / cm 3 3.14 g / cm 3 3.16 g / cm 3 3.18 g / cm 3 3.2g / cm 3 3.22g / cm 3 3.24 g / cm 3 3.26 g / cm 3 3.28g / cm 3 3.3g / cm 3 3.32g / cm 3 3.34 g / cm3 3.36 g / cm 3 3.38g / cm 3 3.4g / cm 3 3.42 g / cm 3 3.44 g / cm 3 3.46 g / cm 3 3.48 g / cm 3 3.5g / cm 3 3.52g / cm 3 3.54g / cm 3 3.56g / cm 3 3.58g / cm 3 3.6g / cm 3 or a range consisting of any of the above values.

[0175] The high compaction density of the positive electrode film results in greater resistance to liquid phase transport of ions within the pores of the positive electrode film. Simultaneously, the increased number of winding turns of the electrode sheets in the cylindrical battery cell can exacerbate internal stress within the cylindrical battery cell, intensifying the compression damage to the electrode sheet structure. It can also affect electrolyte wetting and reflux, impacting the cycle performance and kinetic performance of the cylindrical battery cell.

[0176] The low compaction density of the positive electrode film makes it difficult for cylindrical battery cells to achieve high energy density. Furthermore, the electron conduction of the positive electrode film becomes discontinuous. At the same time, the bonding strength between the positive electrode film and the positive electrode current collector decreases, making it prone to problems such as powder shedding and demolding in the later stages of cycling.

[0177] When the compaction density of the positive electrode film is within the above range, it can effectively balance the energy density, cycle performance, and kinetic performance of the cylindrical battery cell.

[0178] Optionally, the compaction density of the positive electrode film is 3.2 g / cm³. 3 Up to 3.6 g / cm 3 3.2g / cm 3 Up to 3.54 g / cm 3 3.3g / cm 3 Up to 3.54 g / cm 3 3.3g / cm 3 Up to 3.52 g / cm 3 3.3g / cm 3 Up to 3.5g / cm 3 .

[0179] In some embodiments, the one-sided density of the positive electrode film is 155 mg / 1540.25 mm². 2 Up to 320mg / 1540.25mm 2For example, it can be 155mg / 1540.25mm², 165mg / 1540.25mm², 175mg / 1540.25mm², 185mg / 1540.25mm², 195mg / 1540.25mm², 200mg / 1540.25mm², 205mg / 1540.25mm², 210mg / 1540.25mm², 215mg / 1540.25mm², 220mg / 1540.25mm², 225mg / 1540.25mm², 230mg / 1540.25mm², 235mg / 1540.25mm², 240mg / 1540.25mm², 245 ... mg / 1540.25mm², 250mg / 1540.25mm², 255mg / 1540.25mm², 260mg / 1540.25mm², 265mg / 1540.25mm², 270mg / 1540.25mm², 275mg / 1540.25mm², 280mg / 1540.25mm², 285mg / 1540.25mm², 290mg / 1540.25mm², 295mg / 1540.25mm², 300mg / 1540.25mm², 310mg / 1540.25mm², 320mg / 1540.25mm², or any range of the above values.

[0180] The positive electrode film has a low density on one side, a small thickness, and a small surface capacity, resulting in a low energy density in cylindrical battery cells. Furthermore, the increased number of turns of the electrode sheets in cylindrical battery cells of the same volume can easily exacerbate the internal stress of the cylindrical battery cells, intensify the compression damage to the electrode sheet structure, and affect the electrolyte wetting and reflux, thus impacting the cycle performance and kinetic performance of the cylindrical battery cells.

[0181] The high density on one side of the positive electrode film results in a long ion transport path within the film, which increases the internal resistance of the cylindrical battery cell and also affects its cycle performance and kinetic performance.

[0182] When the unilateral density of the positive electrode film is within the above range, the capacity of the positive electrode film will not be too low, the internal stress of the cylindrical battery cell will not be too high, and the ion transport path of the positive electrode film will not be too long. This enables the cylindrical battery cell to achieve high energy density, good cycle performance, and kinetic performance.

[0183] Optionally, the single-sided density of the positive electrode film is 185 mg / 1540.25 mm. 2 Up to 320mg / 1540.25mm 2 200mg / 1540.25mm 2Up to 320mg / 1540.25mm 2 200mg / 1540.25mm 2 Up to 300mg / 1540.25mm 2 210mg / 1540.25mm 2 Up to 290mg / 1540.25mm 2 220mg / 1540.25mm 2 Up to 280mg / 1540.25mm 2 .

[0184] The compaction density of the positive electrode film = density of one side of the positive electrode film / thickness of one side of the positive electrode film.

[0185] The unilateral density of the positive electrode film can be tested as follows: After fully discharging the cylindrical battery cell (0% SOC), disassemble the positive electrode sheet, take the positive electrode sheet with single-sided coating (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1; then wipe off the positive electrode film layer of the positive electrode sheet after weighing, weigh the positive current collector, and record it as M0; the unilateral density of the positive electrode film = (M1-M0) / S1.

[0186] In this disclosure, a cylindrical battery cell being in a fully discharged state means that, at 25°C, the cylindrical battery cell is discharged at a constant current rate of 0.33C to the lower cutoff voltage. At this point, the cylindrical battery cell is considered to be in a fully discharged state, i.e., 0% SOC. The lower cutoff voltage is known in the art and can be the voltage recommended in the product specification sheet. For example, the positive electrode active material includes lithium transition metal oxides, such as LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.92 Co 0.02 Mn 0.06 O2, LiNi 0.93 Co 0.06 Mn 0.01 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.88 Co 0.09 Al 0.03 O2, LiNi 0.88 Co 0.06 Mn0.03 Al 0.03 One or more of O2, the negative electrode active material includes silicon-based materials and graphite materials, and the lower cutoff voltage can be 2.5V.

[0187] In some embodiments, the positive electrode active material includes a lithium transition metal oxide, which includes non-lithium metal elements, including Ni. Non-lithium metal elements refer to all metal elements other than lithium.

[0188] In some embodiments, based on the mass of the positive electrode film, the mass percentage of Ni element is 44% to 55.5%, for example, it can be 44%, 44.5%, 45%, 45.5%, 46%, 46.5%, 47%, 47.5%, 48%, 48.5%, 49%, 49.5%, 50%, 50%, 50.5%, 51%, 51.5%, 52%, 52.5%, 53%, 53.5%, 54%, 54.5%, 55%, 55.5%, 56%, 50%, 50.5%, 51%, 51.5%, 52%, 52.5%, 53%, 53.5%, 54%, 54.5%, 55%, 55.5%, or any range of the above values.

[0189] Ni (provided by lithium transition metal oxide) has a high mass proportion in the positive electrode film, which can enable cylindrical battery cells to have higher energy density. However, Ni is more likely to dissolve during cycling, and Ni deposition on the negative electrode can damage the SEI film of the negative electrode, affecting the cycle performance and storage performance of the cylindrical battery cells.

[0190] This disclosure enables cylindrical battery cells to have high energy density and mitigates the damage to the SEI film of the negative electrode caused by Ni dissolution by keeping the mass ratio of Ni within the above-mentioned range, thereby giving the cylindrical battery cells good cycle performance and storage performance.

[0191] Optionally, based on the mass of the positive electrode film, the mass percentage of Ni element is 48% to 55%.

[0192] In some embodiments, the lithium transition metal oxide may be one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt aluminum oxide, and modified materials thereof. The modified material may be doped and / or surface coated.

[0193] In some embodiments, the lithium transition metal oxide is a layered positive electrode active material.

[0194] In some embodiments, the lithium transition metal oxide includes a non-lithium metal element, including Ni, and the molar percentage of Ni is 75% to 95% based on the total molar amount of the non-lithium metal element, for example, it can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or any range of the above values.

[0195] Ni has a high molar percentage among non-lithium metals, which can give cylindrical battery cells higher energy density. However, the structural stability of lithium transition metal oxides deteriorates, and Ni is more likely to dissolve during cycling. Ni deposition on the negative electrode can damage the SEI film of the negative electrode, affecting the cycle performance and storage performance of the cylindrical battery cell.

[0196] This disclosure enables cylindrical battery cells to have high energy density and mitigates the damage to the SEI film of the negative electrode caused by Ni dissolution by keeping the molar ratio of Ni within the above-mentioned range, thereby giving the cylindrical battery cells good cycle performance and storage performance.

[0197] Optionally, the molar percentage of Ni is 80% to 93% based on the total molar amount of non-lithium metal elements.

[0198] The content of non-lithium metal elements (including Ni) can be tested using ICP-OES. During testing, the positive electrode is removed from the cylindrical battery cell, cleaned with dimethyl carbonate and dried. Approximately 0.4 g (accurate to 0.0001 g) of the dried positive electrode film powder is placed in a 25 ml beaker, and 2 ml to 5 ml of nitric acid is added. The mixture is left overnight, then placed on a hot plate and heated at approximately 100°C until the powder is digested. 0.5 ml of perchloric acid is then added, and the mixture is heated at approximately 140°C until all white fumes are emitted. The residue should be white; otherwise, nitric acid and perchloric acid should be added again for repeated digestion. Finally, the mixture is dissolved and extracted with 7% (volume fraction) hydrochloric acid. The volume is adjusted to an appropriate level based on the content of the element to be tested, and then tested using ICP-OES.

[0199] Based on the mass of the positive electrode film, the mass percentage of Ni = the mass of Ni tested / the mass of the positive electrode film powder. Based on the total molar amount of non-lithium metal elements, the molar percentage of Ni = the molar amount of Ni tested / the total molar amount of all non-lithium metal elements tested.

[0200] In some embodiments, lithium transition metal oxides include those with the general formula Li a Ni b Co c M d O e Af At least one of the compounds and their modified compounds, 0.8≤a≤1.2, 0.75≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more elements selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes one or more elements selected from N, F, S, and Cl.

[0201] Optionally, 0.75 ≤ b ≤ 0.95. More alternatively, 0.80 ≤ b ≤ 0.95. Further alternatively, 0.80 ≤ b ≤ 0.93.

[0202] In some embodiments, examples of lithium transition metal oxides include, but are not limited to, one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof.

[0203] Lithium nickel cobalt aluminum oxide contains aluminum, which makes the structure more stable, less prone to oxygen release, reduces side reactions, and is beneficial to improving cycle performance and storage performance.

[0204] As an example, lithium transition metal oxides include, but are not limited to, LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.92 Co 0.02 Mn 0.06 O2, LiNi 0.93 Co 0.06 Mn 0.01 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.88 Co 0.09 Al 0.03 O2, LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 One or more of O2.

[0205] The modified compounds for the above-mentioned positive electrode active materials can be used to dope and / or surface-coat modify the positive electrode active materials, such as carbon coating modification, fast ion conductor coating modification, etc.

[0206] During the charging and discharging process, cylindrical battery cells undergo the insertion / extraction and consumption of active ions such as Li. The molar content of Li varies depending on the discharge state of the cylindrical battery cell. In the examples of positive electrode active materials in this disclosure, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li may change when the positive electrode active material is applied to the battery system. Similarly, in the examples of positive electrode active materials in this disclosure, the molar content of oxygen is only a theoretical value. Lattice oxygen release can cause changes in the molar content of oxygen, resulting in fluctuations in the actual molar content of oxygen.

[0207] Negative electrode active materials include silicon-based materials and graphite materials.

[0208] In some embodiments, silicon-based materials include one or more of elemental silicon, silicon-carbon materials, and silicon-oxygen materials.

[0209] Optionally, silicon-based materials include one or more of silicon-carbon materials and silicon-oxygen materials.

[0210] Compared with elemental silicon, silicon-carbon and silicon-oxygen materials have lower volume expansion, which can improve the stability of the SEI film, reduce the consumption of active lithium, and further reduce the volume expansion of the negative electrode sheet. This reduces the adverse effects of the negative electrode sheet volume expansion on the electrolyte wettability of the electrode assembly, and improves the cycle performance and storage performance of cylindrical battery cells.

[0211] Silicon-based materials may or may not have pre-embedded alkali metals and / or alkaline earth metals. Optionally, the alkali metal is Li and the alkaline earth metal is Mg.

[0212] In some embodiments, the silicon-carbon material comprises a porous carbon substrate and silicon located in the pores of the porous carbon substrate. This reduces the volume expansion of the silicon-carbon material, thereby contributing to improved cycle performance of cylindrical battery cells.

[0213] In some embodiments, the silicon-based material includes silicon-oxygen materials. Silicon-oxygen materials have low surface activity and fewer interfacial side reactions, which helps to improve the cycle performance and storage performance of cylindrical battery cells.

[0214] In some embodiments, the graphite material includes one or more of natural graphite and artificial graphite.

[0215] Alternatively, graphite materials may include both natural and artificial graphite.

[0216] Natural graphite possesses slip properties; when silicon-based materials undergo volume expansion, natural graphite can provide expansion space for the silicon-based materials through slippage, thereby reducing the volume expansion of the negative electrode to some extent. However, natural graphite has numerous surface defects and internal pores, resulting in high surface activity and numerous interfacial side reactions. To reduce interfacial side reactions, this disclosure also introduces artificial graphite. Compared with natural graphite, artificial graphite has fewer surface defects and internal pores, which is conducive to the formation of a more stable SEI film, thereby helping to further improve the cycle performance and storage performance of cylindrical battery cells.

[0217] Optionally, based on the mass of the negative electrode film, the mass percentage of natural graphite is less than that of artificial graphite.

[0218] This will help to further improve the cycle performance and storage performance of cylindrical battery cells.

[0219] The average particle size of the silicon-based material is from 1 μm to 12 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 11 μm, 12 μm, or any combination of the above values.

[0220] The average particle size of silicon-based materials refers to the average particle size of all silicon-based material particles in the entire negative electrode film layer.

[0221] In some embodiments, the average particle size of the graphite material is from 10 μm to 18 μm, for example, it can be 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, or any range of the above values.

[0222] The average particle size of graphite materials refers to the average particle size of all graphite material particles in the entire negative electrode film layer. Graphite materials include artificial graphite and natural graphite.

[0223] The average particle size of silicon-based materials and graphite materials can be tested as follows: Using a scanning electron microscope combined with energy dispersive spectroscopy (EDS), obtain a SEM-EDS image of the cross-section of the negative electrode sheet. Randomly select a test sample (e.g., 50mm x 100mm). Within the test sample, randomly select multiple test regions (e.g., 5 regions). At a certain magnification (e.g., 500x or higher), count the quantity and particle size of silicon-based and graphite materials in each test region. Take the arithmetic mean of the particle sizes of all silicon-based materials in each test region as the average particle size of the silicon-based material, and take the arithmetic mean of the particle sizes of all graphite materials in each test region as the average particle size of the graphite material. To ensure the accuracy of the test results, multiple test samples (e.g., 10 samples) can be used for the above test, and the average value of each test sample can be taken as the final test result. It should be noted that when the particles are irregularly shaped, the distance between the two farthest points on the particle is taken as the particle size.

[0224] The mass percentage of Si can be measured using an inductively coupled plasma (ICP) spectrometer. The testing standard can be found in JY / T 015-1996.

[0225] The compaction density of the negative electrode film = density of one side of the negative electrode film / thickness of one side of the negative electrode film.

[0226] The one-sided density of the negative electrode film can be tested as follows: After fully discharging the cylindrical battery cell (0% SOC), disassemble the negative electrode sheet, take the negative electrode sheet with single-sided coating (if it is a double-sided coated negative electrode sheet, wipe off the negative electrode film on one side first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1; then wipe off the negative electrode film of the weighed negative electrode sheet, weigh the negative current collector, and record it as M0; the one-sided density of the negative electrode film = (M1-M0) / S1.

[0227] The compaction density of the negative electrode film is 1 g / cm³. 3 Up to 1.65 g / cm 3For example, it can be 1g / cm³, 1.02g / cm³, 1.04g / cm³, 1.06g / cm³, 1.08g / cm³, 1.1g / cm³, 1.12g / cm³, 1.14g / cm³, 1.16g / cm³, 1.18g / cm³, 1.2g / cm³, 1.22g / cm³, 1.24g / cm³, 1.26g / cm³, 1.28g / cm³, 1.3g / cm³, 1. 32g / cm³, 1.34g / cm³, 1.36g / cm³, 1.38g / cm³, 1.4g / cm³, 1.42g / cm³, 1.44g / cm³, 1.46g / cm³, 1.48 g / cm³, 1.5g / cm³, 1.52g / cm³, 1.54g / cm³, 1.56g / cm³, 1.58g / cm³, 1.6g / cm³, 1.62g / cm³, 1.65g / cm 3 Or a range consisting of any of the above values.

[0228] In some embodiments, based on the mass of the negative electrode film, the mass percentage of Si element is 0.5% to 20%, for example, it can be 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any range of the above values.

[0229] When the mass percentage of Si is within the above range, it can improve the energy density of the cylindrical battery cell and prevent the volume expansion of the negative electrode sheet from being too large. This can reduce the adverse effects of the volume expansion of the negative electrode sheet on the electrolyte wettability and interfacial film stability of the electrode assembly, and improve the cycle performance, storage performance and kinetic performance of the cylindrical battery cell.

[0230] In some embodiments, based on the mass of the negative electrode film, the mass percentage of Si element is 0.5% to 5%, and the compaction density of the negative electrode film is 1.3 g / cm³. 3 Up to 1.65 g / cm 3 .

[0231] For example, the mass percentage of Si can be 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range of the above values.

[0232] For example, the compaction density of the negative electrode film can be 1.3 g / cm³, 1.32 g / cm³, 1.34 g / cm³, 1.36 g / cm³, 1.38 g / cm³, 1.4 g / cm³, 1.42 g / cm³, 1.44 g / cm³, 1.46 g / cm³, 1.48 g / cm³, 1.5 g / cm³, 1.52 g / cm³, 1.54 g / cm³, 1.56 g / cm³, 1.58 g / cm³, 1.6 g / cm³, 1.62 g / cm³, or 1.65 g / cm³. 3 Or a range consisting of any of the above values.

[0233] In some embodiments, based on the mass of the negative electrode film, the mass percentage of Si element is greater than 5% and less than or equal to 10%, and the compaction density of the negative electrode film is 1.2 g / cm³. 3 Up to 1.55 g / cm 3 .

[0234] For example, the mass percentage of Si can be 5.1%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any of the above values.

[0235] For example, the compaction density of the negative electrode film can be 1.2 g / cm³, 1.22 g / cm³, 1.24 g / cm³, 1.26 g / cm³, 1.28 g / cm³, 1.3 g / cm³, 1.32 g / cm³, 1.34 g / cm³, 1.36 g / cm³, 1.38 g / cm³, 1.4 g / cm³, 1.42 g / cm³, 1.44 g / cm³, 1.46 g / cm³, 1.48 g / cm³, 1.5 g / cm³, 1.52 g / cm³, 1.55 g / cm³, or any range of the above values.

[0236] In some embodiments, based on the mass of the negative electrode film, the mass percentage of Si element is greater than 10% and less than or equal to 20%, and the compaction density of the negative electrode film is 1 g / cm³. 3 Up to 1.45 g / cm 3 .

[0237] For example, the mass percentage of Si can be 10.1%, 10.5%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any range of the above values.

[0238] For example, the compaction density of the negative electrode film can be 1 g / cm³, 1.02 g / cm³, 1.04 g / cm³, 1.06 g / cm³, 1.08 g / cm³, 1.1 g / cm³, 1.12 g / cm³, 1.14 g / cm³, 1.16 g / cm³, 1.18 g / cm³, 1.2 g / cm³, 1.22 g / cm³, 1.24 g / cm³, 1.26 g / cm³, 1.28 g / cm³, 1.3 g / cm³, 1.32 g / cm³, 1.34 g / cm³, 1.36 g / cm³, 1.38 g / cm³, 1.4 g / cm³, 1.42 g / cm³, 1.45 g / cm³, or any range of the above values.

[0239] When the mass percentage of Si is relatively small, the volume expansion of the negative electrode sheet is small, and the adverse effects of the volume expansion of the negative electrode sheet on the electrolyte wettability and interfacial film stability of the electrode assembly are small. By making the negative electrode film layer have a large compaction density, the energy density, cycle performance, storage performance and kinetic performance of the cylindrical battery cell can be effectively balanced.

[0240] When the mass proportion of silicon is relatively large, the energy density of cylindrical battery cells is higher, but the volume expansion of the negative electrode is usually also large. By making the negative electrode film layer have a smaller compaction density, a buffer space can be provided for the volume expansion of silicon-based materials. This can reduce the volume expansion of the negative electrode layer, improve the stability of the interface film, reduce the internal stress of the cylindrical battery cell, and improve the problem of difficult wetting and reflow of the cylindrical battery cell. Thus, the energy density, cycle performance, storage performance and kinetic performance of the cylindrical battery cell can be effectively balanced.

[0241] In some embodiments, the one-sided density of the negative electrode film is 85 mg / 1540.25 mm². 2 Up to 180mg / 1540.25mm 2 For example, the dosage can be 85mg / 1540.25mm², 90mg / 1540.25mm², 100mg / 1540.25mm², 110mg / 1540.25mm², 120mg / 1540.25mm², 125mg / 1540.25mm², 130mg / 1540.25mm², 135mg / 1540.25mm², or 140mg / 1540.25mm². mm², 145mg / 1540.25mm², 150mg / 1540.25mm², 155mg / 1540.25mm², 160mg / 1540.25mm², 165mg / 1540.25mm², 170mg / 1540.25mm², 175mg / 1540.25mm², 180mg / 1540.25mm², or any range of the above values.

[0242] The negative electrode film has a low density on one side and a small thickness. This increases the number of turns of the electrode sheet in a cylindrical battery cell of the same volume. This can easily aggravate the internal stress of the cylindrical battery cell, exacerbate the crushing damage to the electrode sheet structure, and also affect the electrolyte wetting and reflux, thus affecting the cycle performance and kinetic performance of the cylindrical battery cell.

[0243] The high density on one side of the negative electrode film results in a long ion transport path within the negative electrode film, which increases the internal resistance of the cylindrical battery cell and also affects its cycle performance and kinetic performance.

[0244] When the unilateral density of the negative electrode film is within the above range, the internal stress of the cylindrical battery cell will not be too high, which can reduce the crushing damage to the electrode sheet structure, improve the electrolyte wetting and reflux of the electrode assembly, and the ion transport path of the negative electrode film will not be too long. Thus, the cylindrical battery cell can achieve high energy density, good cycle performance and kinetic performance.

[0245] Optionally, the single-sided density of the negative electrode film is 90 mg / 1540.25 mm. 2 Up to 180mg / 1540.25mm 2 90mg / 1540.25mm 2 Up to 170mg / 1540.25mm 2 90mg / 1540.25mm 2 Up to 160mg / 1540.25mm 2 90mg / 1540.25mm 2 Up to 155mg / 1540.25mm 2 90mg / 1540.25mm 2 Up to 150mg / 1540.25mm 2 100mg / 1540.25mm 2 Up to 145mg / 1540.25mm 2 .

[0246] In some embodiments, the negative electrode film layer is at least two layers. In some embodiments, the negative electrode film layer may include two layers, three layers, four layers, or even more layers.

[0247] The following explanation will take the example of a two-layer negative electrode film.

[0248] In some embodiments, the negative electrode film layer includes a first film layer and a second film layer stacked along the thickness direction. The first film layer is located between the negative electrode current collector and the second film layer. The negative electrode active material in the second film layer includes silicon-based materials and graphite materials. The negative electrode active material in the first film layer includes graphite materials and the first film layer does not contain Si elements.

[0249] The interface between the first and second membrane layers can be regular or irregular.

[0250] The second film layer can be understood as the layer in the negative electrode film layer that is farthest from the negative electrode current collector. Compared to the first film layer, the second film layer is closer to the separator. During charging, ions pass through the second film layer and the first film layer in sequence.

[0251] In some embodiments, the first film layer does not contain Si.

[0252] In some embodiments, the negative electrode active material in the first film layer further includes a silicon-based material, which includes Si element, and the mass percentage of Si element in the first film layer based on the mass of the first film layer is less than the mass percentage of Si element in the second film layer based on the mass of the second film layer.

[0253] Compared to graphite materials, silicon-based materials have poorer ion transport capabilities. Therefore, by making the second film layer, which is far from the negative electrode current collector, contain more Si elements, the ion transport distance can be shortened, thereby improving the kinetic performance of the cylindrical battery cell.

[0254] The first film layer near the negative electrode current collector contains no Si element or contains less Si element than the second film layer far from the negative electrode current collector. As a result, the volume expansion of the first film layer is small, and the first film layer can have a good electronic conduction network. This can reduce the problem of electronic conduction interruption caused by the large volume expansion of the first film layer under high current fast charge and discharge conditions, and improve the fast charge cycle performance of the cylindrical battery cell.

[0255] In some embodiments, the negative electrode active material in the first film layer further includes a silicon-based material, which includes Si element, and based on the mass of the first film layer, the mass percentage of Si element in the first film layer is greater than 0 and less than or equal to 1%.

[0256] When the mass percentage of Si in the first film layer is within the above range, the volume expansion of the first film layer is small, and the first film layer can have a good electronic conduction network. This can reduce the problem of interruption of electronic conduction caused by the large volume expansion of the first film layer under high current fast charge and discharge conditions, and improve the fast charge cycle performance of the cylindrical battery cell.

[0257] In some embodiments, the negative electrode active material in the first film layer further includes a silicon-based material, which includes Si element, and based on the mass of the first film layer, the mass percentage of the silicon-based material in the first film layer is greater than 0 and less than or equal to 2%.

[0258] The mass ratio of silicon-based material in the first film layer is within the above range. The volume expansion of the first film layer is small, and the first film layer can have a good electronic conduction network. This can reduce the problem of interruption of electronic conduction caused by the large volume expansion of the first film layer under high current fast charging and discharging conditions, and improve the fast charging cycle performance of the cylindrical battery cell.

[0259] In some embodiments, based on the mass of the second film layer, the mass percentage of Si element in the second film layer is 10% to 40%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, or any range of the above values.

[0260] When the mass percentage of Si in the second film layer is within the above range, the volume expansion of the second film layer of the negative electrode sheet will not be too large. This can reduce the adverse effects of the volume expansion of the negative electrode sheet on the electrolyte wettability and interfacial film stability of the electrode assembly, and improve the cycle performance, storage performance and kinetic performance of the cylindrical battery cell.

[0261] In some embodiments, based on the mass of the second film layer, the mass percentage of silicon-based material in the second film layer is 20% to 80%, for example, it can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, or any range of the above values.

[0262] If the mass ratio of silicon-based material in the second film layer is within the above range, the volume expansion of the second film layer of the negative electrode sheet will not be too large. This can reduce the adverse effects of the volume expansion of the negative electrode sheet on the electrolyte wettability and interfacial film stability of the electrode assembly, and improve the cycle performance, storage performance and kinetic performance of the cylindrical battery cell.

[0263] In some embodiments, the graphite material in the second film layer includes one or more of natural graphite and artificial graphite.

[0264] Optionally, in the second film layer, the graphite material includes natural graphite and artificial graphite.

[0265] Natural graphite possesses slip properties; when silicon-based materials undergo volume expansion, natural graphite can provide expansion space for the silicon-based materials through slippage, thereby reducing the volume expansion of the second film layer to some extent. However, natural graphite has numerous surface defects and internal pores, resulting in high surface activity and numerous interfacial side reactions. To reduce interfacial side reactions, this disclosure also introduces artificial graphite into the second film layer. Compared with natural graphite, artificial graphite has fewer surface defects and internal pores, which is conducive to the formation of a more stable SEI film, thereby helping to further improve the cycle performance and storage performance of cylindrical battery cells.

[0266] In some embodiments, the graphite material in the first film layer includes one or more of natural graphite and artificial graphite.

[0267] Optionally, in the first film layer, the graphite material includes artificial graphite.

[0268] Artificial graphite has fewer surface defects and internal pores, which is conducive to the formation of a more stable SEI film, thereby helping to further improve the cycle performance and storage performance of cylindrical battery cells.

[0269] In some embodiments, the compaction density of the second membrane layer is less than that of the first membrane layer.

[0270] The second film layer is positioned away from the negative electrode current collector, while the first film layer is positioned close to it. The second film layer has a low compaction density and high porosity, which can provide expansion space for the silicon-based material, thereby reducing the volume expansion of the negative electrode layer. The first film layer has a high compaction density, which can improve the energy density of the cylindrical battery cell. At the same time, it can create an electronic conductivity gradient distribution in the thickness direction of the negative electrode film layer, which is beneficial to improving the cycle performance, storage performance and dynamic performance of the cylindrical battery cell.

[0271] In some embodiments, the porosity of the second membrane layer is greater than that of the first membrane layer.

[0272] The second film layer is positioned away from the negative electrode current collector, while the first film layer is positioned close to the negative electrode current collector. The second film layer has a large porosity, which can provide expansion space for the silicon-based material, thereby reducing the volume expansion of the negative electrode layer. The first film layer has a small porosity, which can improve the energy density of the cylindrical battery cell. At the same time, it can create an electronic conductivity gradient distribution in the thickness direction of the negative electrode film layer, which is beneficial to improving the cycle performance, storage performance and dynamic performance of the cylindrical battery cell.

[0273] The first and second films can be distinguished as follows: After the cylindrical battery cell is fully discharged (0% SOC), the negative electrode sheet is disassembled, cleaned with dimethyl carbonate and dried, and then cut into 5cm*5cm samples. The samples are placed in a CT device for multi-angle scanning. After the scanning is completed, a three-dimensional image is generated using a reconstruction algorithm. Since the Si content in the first and second films is different, the first and second films can be distinguished.

[0274] In some embodiments, the cylindrical battery cell includes an electrolyte contained within a housing 20, and the electrolyte includes an electrolyte salt and an organic solvent.

[0275] In some embodiments, the ratio of the mass of the electrolyte to the capacity of the cylindrical battery cell is from 1.2 g / Ah to 2.1 g / Ah, for example, it can be 1.20 g / Ah, 1.25 g / Ah, 1.30 g / Ah, 1.35 g / Ah, 1.40 g / Ah, 1.45 g / Ah, 1.50 g / Ah, 1.55 g / Ah, 1.60 g / Ah, 1.65 g / Ah, 1.70 g / Ah, 1.75 g / Ah, 1.80 g / Ah, 1.85 g / Ah, 1.90 g / Ah, 1.95 g / Ah, 2.00 g / Ah, 2.05 g / Ah, 2.10 g / Ah, or any range of the above values.

[0276] A small ratio of electrolyte mass to the capacity of a cylindrical battery cell may not meet the requirements for electrode film formation and wetting, easily accelerating capacity decay; a large ratio of electrolyte mass to the capacity of a cylindrical battery cell will result in an increase in free electrolyte and interfacial side reactions, affecting the storage performance of the cylindrical battery cell.

[0277] When the ratio of electrolyte mass to the capacity of a cylindrical battery cell is within the above range, the cycle performance and storage performance of the cylindrical battery cell can be balanced.

[0278] Optionally, the ratio of the mass of the electrolyte to the capacity of the cylindrical battery cell is from 1.35 g / Ah to 1.95 g / Ah.

[0279] The mass of the electrolyte can be tested as follows: Weigh the cylindrical battery cell and record the mass as m0; then disassemble the cylindrical battery cell, centrifuge to separate the electrolyte, immerse all the disassembled solid components in acetonitrile solution, remove them after soaking for 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 mass of m0 and m1 is taken as the mass of the electrolyte.

[0280] The capacity of a cylindrical battery cell can be obtained by testing as follows: At 25°C, discharge the cylindrical battery cell at a constant current of 0.33C to the lower cutoff voltage, let it stand for 10 minutes, charge it at a constant current of 0.33C to the upper cutoff voltage, then charge it at a constant voltage at the upper cutoff voltage until the current is 0.05C, let it stand for 10 minutes, discharge it at a constant current of 0.33C to the lower cutoff voltage, let it stand for 10 minutes, and record the discharge capacity at this time, which is the capacity of the cylindrical battery cell.

[0281] The upper and lower cutoff voltages can be the charge and discharge voltages recommended in the product specifications of the cylindrical battery cells.

[0282] In some embodiments, the electrolyte includes a chain ester solvent, the chain ester solvent comprising 25.5% to 76.5% by mass in the electrolyte, for example, 25.5%, 26%, 27%, 28%, 29%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 76.5%, or any range of the above values.

[0283] Chain-like ester solvents have low viscosity and good fluidity. By making the electrolyte contain a high content of chain-like ester solvents, the electrolyte wettability of high-energy-density cylindrical battery cells can be improved, allowing the electrolyte to fully contact the electrode active materials, reducing interfacial impedance, and improving the cycle performance and kinetic performance of cylindrical battery cells.

[0284] Optionally, the chain ester solvent accounts for 42.5% to 70% of the mass of the electrolyte.

[0285] In some embodiments, the chain ester solvent includes chain carbonates. Chain carbonates can improve the conductivity of the electrolyte and increase the ion migration rate of the electrolyte, thereby further improving the cycle performance and kinetic performance of the cylindrical battery cell.

[0286] The chain carbonate has a mass percentage of 4% to 70% in the electrolyte, for example, 4%, 4.5%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range of the above values.

[0287] When the mass percentage of chain carbonates is within the above range, the conductivity and ion migration rate of the electrolyte can be improved, thereby further improving the cycle performance and kinetic performance of cylindrical battery cells.

[0288] Optionally, the chain carbonate accounts for 4% to 42.5% of the mass of the electrolyte.

[0289] In some embodiments, the chain carbonate includes compounds represented by Formula I. Formula I, In formula I, R 11 and R 12 Each independently includes C1 to C3 alkyl or C1 to C3 haloalkyl.

[0290] The chain carbonates mentioned above are compounds that can further improve the cycle performance and kinetic performance of cylindrical battery cells.

[0291] Optionally, R 11 and R 12 Each independently includes C1 to C3 alkyl or C1 to C3 fluoroalkyl.

[0292] Optionally, the chain carbonate includes one or more compounds from Formula I-1 to Formula I-6.

[0293] Optionally, the chain carbonate includes compounds shown in Formula I-1. Formula I-1.

[0294] For example, the chain carbonate includes the compound shown in Formula I-1, wherein the compound shown in Formula I-1 accounts for 4% to 42.5% by mass in the electrolyte, optionally from 8.5% to 35%.

[0295] In some embodiments, the chain ester solvent also includes chain carboxylic acid esters.

[0296] The combined use of chain carboxylic esters and chain carbonates can improve the conductivity and ion migration rate of the electrolyte, thereby further improving the cycle performance and kinetic performance of cylindrical battery cells. Of course, chain carboxylic esters can also be used alone as solvents.

[0297] The mass percentage of the chain carboxylic acid ester in the electrolyte is 4% to 70%, for example, it can be 4%, 4.5%, 5%, 8%, 8.5%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range of the above values.

[0298] When the mass percentage of chain carboxylic esters in the electrolyte is within the above range, the conductivity and ion migration rate of the electrolyte can be improved, thereby further improving the cycle performance and kinetic performance of cylindrical battery cells.

[0299] Optionally, the chain carboxylic acid ester accounts for 8.5% to 60% of the mass of the electrolyte.

[0300] In some embodiments, the chain carboxylic acid ester includes compounds represented by Formula II. Formula II, In Equation II, R 21 Includes hydrogen atoms, halogen atoms, C1 to C3 alkyl groups, or C1 to C3 haloalkyl groups; R 22 Includes C1 to C3 alkyl or C1 to C3 haloalkyl.

[0301] Optionally, R 21 It includes hydrogen atoms, fluorine atoms, C1 to C3 alkyl groups, or C1 to C3 fluoroalkyl groups.

[0302] Optionally, R 22 Includes C1 to C3 alkyl or C1 to C3 fluoroalkyl.

[0303] Optionally, the chain carboxylic acid ester includes one or more compounds of formula II-1 to formula II-6.

[0304] Optionally, the chain carboxylic acid ester includes one or both of the compounds shown in Formula II-2 and Formula II-3.

[0305] For example, chain carboxylic esters include compounds of formula II-2, wherein the mass percentage of compounds of formula II-2 in the electrolyte is 20% to 55%.

[0306] For example, chain carboxylic esters include compounds of formula II-3, wherein the mass percentage of compounds of formula II-3 in the electrolyte is 20% to 55%.

[0307] For example, chain carboxylic esters include compounds shown in Formula II-2 and Formula II-3, wherein the total mass percentage of compounds shown in Formula II-2 and Formula II-3 in the electrolyte is 20% to 55%.

[0308] For example, the chain ester solvent of the electrolyte may include the compound shown in Formula I-1 and the compound shown in Formula II-2, wherein the chain ester solvent accounts for 25.5% to 76.5% of the mass of the electrolyte, optionally 42.5% to 70%; for example, the compound shown in Formula I-1 accounts for 8.5% to 35% of the mass of the electrolyte, and the compound shown in Formula II-2 accounts for 20% to 55% of the mass.

[0309] For example, the chain ester solvent of the electrolyte may include the compound shown in Formula I-1 and the compound shown in Formula II-3, wherein the chain ester solvent accounts for 25.5% to 76.5% of the mass of the electrolyte, optionally 42.5% to 70%; for example, the compound shown in Formula I-1 accounts for 8.5% to 35% of the mass of the electrolyte, and the compound shown in Formula II-3 accounts for 20% to 55% of the mass of the electrolyte.

[0310] For example, the chain ester solvent of the electrolyte may include the compound shown in Formula I-1, the compound shown in Formula II-2, and the compound shown in Formula II-3, wherein the chain ester solvent accounts for 25.5% to 76.5% of the mass of the electrolyte, optionally 42.5% to 70%; for example, the compound shown in Formula I-1 accounts for 8.5% to 35% of the mass of the electrolyte, the compound shown in Formula II-2 accounts for 8.5% to 35% of the mass of the electrolyte, and the compound shown in Formula II-3 accounts for 8.5% to 35% of the mass of the electrolyte.

[0311] In some embodiments, the electrolyte salt includes lithium hexafluorophosphate and / or lithium sulfonamide salt.

[0312] Alternatively, the electrolyte salt includes lithium hexafluorophosphate and lithium sulfonamide salt.

[0313] The combined use of lithium hexafluorophosphate and lithium sulfonylimide salts results in relatively high thermal stability of the electrolyte system, which can improve the stability of the electrolyte and enhance the cycle performance, storage performance and kinetic performance of cylindrical battery cells.

[0314] In some embodiments, the electrolyte salt includes lithium hexafluorophosphate and lithium sulfonylimide salt, wherein the molar concentration of lithium hexafluorophosphate is less than or equal to 0.9 mol / L, for example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, or any range of the above values.

[0315] When the molar concentration of lithium hexafluorophosphate is within the above range, it can further reduce the corrosive effect on the casing and improve the reliability and cycle performance of cylindrical battery cells.

[0316] Optionally, the molar concentration of lithium hexafluorophosphate is from 0.2 mol / L to 0.8 mol / L.

[0317] In some embodiments, the electrolyte salt comprises lithium hexafluorophosphate and lithium sulfonylimide, wherein the molar ratio of the lithium sulfonylimide to the lithium hexafluorophosphate is 0.06 to 6, for example, it can be 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, or any range of the above values.

[0318] When the ratio of the molar concentration of lithium sulfonamide to the molar concentration of lithium hexafluorophosphate is within the above range, the electrolyte salt exhibits excellent thermal stability and is less prone to thermal decomposition leading to an increase in electrolyte acidity. Furthermore, the electrolyte salt also exhibits excellent electrochemical stability, which can further enhance the stability of the electrolyte salt and improve the reliability and cycle performance of cylindrical battery cells.

[0319] In some embodiments, the molar concentration of the electrolyte salt is from 0.5 mol / L to 2 mol / L, for example, it can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, or any range of the above values.

[0320] When the molar concentration of the electrolyte salt is within the above range, it is beneficial to further improve the stability of the electrolyte salt and to improve the conductivity and ion migration rate of the electrolyte, thereby improving the cycle performance and kinetic performance of the cylindrical battery cell.

[0321] Optionally, the molar concentration of the electrolyte salt is from 0.8 mol / L to 1.3 mol / L.

[0322] In some embodiments, lithium sulfonamide salts comprise anion represented by formula A. Formula A, In formula A, R1 and R2 each independently include a halogen atom or a C1 to C6 haloalkyl group.

[0323] The sulfonylimide lithium salts described above exhibit excellent thermal stability, which helps reduce the corrosion of the casing by the electrolyte salt and improves the reliability and cycle performance of cylindrical battery cells.

[0324] Optionally, C1 to C6 haloalkyl groups include C1 to C6 fluoroalkyl groups.

[0325] Alternatively, R1 and R2 each independently include a fluorine atom or a C1 to C3 fluoroalkyl group.

[0326] The aforementioned sulfonamide lithium salt readily dissociates into lithium ions, and the electrolyte salt has a relatively low viscosity, which is beneficial for improving the ion migration rate of the electrolyte and enhancing the electrolyte wettability and cycle performance of the cylindrical battery cell.

[0327] Optionally, the anion represented by formula A includes one or more of the anions represented by formulas A-1 to A-5.

[0328] Optionally, the anion represented by formula A includes one or more of the anions represented by formulas A-1 to A-2.

[0329] In some embodiments, the organic solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), butylene carbonate (BC), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl sulfone (EMS), and diethyl sulfone (ESE).

[0330] Alternatively, the organic solvent may also include at least one of ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC).

[0331] The conductivity of the electrolyte can be tested using a conductivity meter (e.g., Mettler Toledo S700). During testing, first, the standard solution and the test solution are kept at a constant temperature of 25°C. Then, calibration is performed using potassium chloride at 12.88 mS / cm. The test electrode is rinsed 2-3 times with alcohol and pure water, dried, and then vertically immersed in the test solution. The reading is taken after the value stabilizes.

[0332] The types and contents of electrolyte salts in the electrolyte can be qualitatively and quantitatively analyzed by ion chromatography, referring to JY / T 020-1996. The types and contents of organic components (e.g., organic solvents) in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography, referring to GB / T9722-2006.

[0333] In the embodiments of this disclosure, freshly prepared electrolyte can be used as a sample, or a fully discharged (0% SOC) cylindrical battery cell can be disassembled in reverse, and the centrifuged electrolyte obtained from the cylindrical battery cell can be used as a sample. An exemplary method for obtaining centrifuged electrolyte from a cylindrical battery cell includes the following steps: discharging the cylindrical battery cell to the lower limit cutoff voltage and then disassembling it; centrifuging the electrode assembly (including the positive electrode, negative electrode, and separator) at a speed greater than 10,000 rpm; repeatedly collecting the centrifuged electrolyte until no obvious liquid remains after centrifugation.

[0334] The outer diameter of the outer casing 20 is 30mm to 80mm, for example, it can be 30mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 65mm, 70mm, 75mm, 80mm, or any range of the above values. The outer diameter refers to the outer diameter of the outer casing 20.

[0335] Setting the outer diameter of the casing 20 to be greater than or equal to 30 mm can increase the capacity and energy density of the cylindrical battery cell 7. Setting the outer diameter of the casing 20 to be less than or equal to 80 mm can reduce the risk of the casing 20 cracking due to the expansion of the electrode assembly 10, thereby improving the reliability of the cylindrical battery cell 7.

[0336] Optionally, the outer diameter of the housing 20 is 40 mm to 60 mm.

[0337] In some embodiments, the dimension of the housing 20 along the axial direction Z of the cylindrical battery cell 7 is 50mm to 150mm, for example, it can be 50mm, 55mm, 60mm, 65mm, 70mm, 75mm, 80mm, 85mm, 90mm, 95mm, 100mm, 105mm, 110mm, 115mm, 120mm, 125mm, 130mm, 135mm, 140mm, 145mm, 150mm, or any range of the above values.

[0338] Setting the dimension of the cylindrical battery cell 7 along the axial direction Z to be greater than or equal to 50 mm can improve the capacity and energy density of the cylindrical battery cell 7. Setting the dimension of the cylindrical battery cell 7 along the axial direction Z to be less than or equal to 150 mm can reduce the difficulty of electrolyte wetting into the middle region of the electrode assembly 10 and improve the electrolyte wettability of the electrode assembly 10.

[0339] Optionally, the housing 20 has a dimension of 70 mm to 100 mm along the axial direction Z of the cylindrical battery cell 7.

[0340] In some embodiments, the outer diameter of the housing 20 is 30 mm to 80 mm, and the axial dimension Z of the housing 20 along the cylindrical battery cell 7 is 50 mm to 150 mm. When the housing 20 meets the above dimensional requirements, it has high structural stability and can improve the reliability of the cylindrical battery cell 7.

[0341] In some embodiments, the housing 20 includes a housing 21 and an end cap 22. The housing 21 includes a sidewall 212 and an end wall 211 connected to the sidewall 212, the sidewall 212 surrounding the electrode assembly 10. As an example, the sidewall 212 is cylindrical. The housing 21 has an opening, the end cap 22 is connected to the sidewall 212 and closes the opening, and the end cap 22 and the end wall 211 are opposite each other along the axial direction Z of the cylindrical battery cell 7.

[0342] In some embodiments, the base material of the sidewall 212 is steel. The base material of the sidewall 212 refers to the material that accounts for the largest proportion of the mass in the sidewall 212.

[0343] Steel has high mechanical strength. Using steel sidewalls 212 can improve the structural stability of sidewalls 212, reduce the deformation of sidewalls 212, and improve the reliability of cylindrical battery cells 7.

[0344] In some embodiments, the base material of the sidewall 212 is stainless steel.

[0345] In some embodiments, the sidewall 212 includes a sidewall body and a protective layer disposed inside the sidewall body. The sidewall body is made of steel, and the base element of the protective layer is nickel. Nickel can improve the acid corrosion resistance to friction.

[0346] As an example, the nickel content in the protective layer is 70% to 100% by mass, and can be 80% to 95%.

[0347] In some embodiments, the base material of the sidewall 212 is steel, and the thickness of the sidewall 212 is 0.2 mm to 0.6 mm, for example, it can be 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm, or any range of the above values.

[0348] The thickness of the sidewall 212 is set to be greater than or equal to 0.2 mm to improve the mechanical strength of the sidewall 212, reduce the deformation of the sidewall 212 when the electrode assembly 10 expands, reduce the risk of the sidewall 212 breaking, and improve the reliability of the cylindrical battery cell 7. The thickness of the sidewall 212 is set to be less than or equal to 0.6 mm to reduce the mass proportion of the sidewall 212 in the cylindrical battery cell 7 and increase the energy density of the cylindrical battery cell 7.

[0349] Optionally, the thickness of the sidewall 212 is 0.3 mm to 0.5 mm, or 0.35 mm to 0.45 mm.

[0350] The thickness of the sidewall can be measured using a micrometer or vernier caliper.

[0351] In some embodiments, the dimension of the housing 20 along the axial direction Z of the cylindrical battery cell 7 is 1.3 to 2.6 times the outer diameter of the housing 20, for example, it can be 1.3 times, 1.5 times, 1.7 times, 1.9 times, 2.1 times, 2.3 times, 2.6 times, or any range of the above values. When the housing 20 meets the above dimensional requirements, it can effectively constrain the volume expansion of the electrode assembly 10, making the compressive force on the housing 20 more evenly distributed, and the housing 20 is less prone to deformation, thereby improving the reliability of the cylindrical battery cell 7.

[0352] Example The following examples describe the contents of this disclosure in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0353] Example 1 Preparation of positive electrode sheet Single-crystal LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 O2, polyvinylidene fluoride, carbon nanotubes, and carbon black SP were added to NMP solvent in a mass ratio of 98:1:0.2:0.8 and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto both surfaces of the positive electrode current collector aluminum foil, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet. The positive electrode sheet consists of a positive electrode current collector and a positive electrode film layer, located on both sides of the current collector. The positive electrode film layer is formed from the positive electrode slurry, and its single-sided density is 250 mg / 1540.25 mm². 2 The carbon nanotubes are 5 μm long.

[0354] Preparation of negative electrode sheet Artificial graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and carbon black SP were added to deionized water in a mass ratio of 90:2:3:5 and stirred evenly to obtain the first slurry.

[0355] Natural graphite, artificial graphite, silicon oxide materials, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and carbon black SP were added to deionized water in a mass ratio of 20:10:50:3:15:2 and stirred evenly to obtain the second slurry.

[0356] The first slurry is evenly coated on both surfaces of the negative electrode current collector copper foil. After drying, the second slurry is coated. Then, after drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0357] The negative electrode sheet includes a negative current collector and a negative electrode film layer. The negative electrode film layer is located on both sides of the negative current collector, and the density of one side of the negative electrode film layer is 150mg / 1540.25mm. 2 The negative electrode film layer includes a first film layer and a second film layer. The first film layer is located on the surface of the negative electrode current collector, and the second film layer is located on the surface of the first film layer. The first film layer is formed from a first slurry, and the second film layer is formed from a second slurry. In the entire negative electrode film layer, the average particle size of all silicon-based materials is 7 μm, and the mass percentage of Si is 2.5%. In the second film layer, the mass percentage of Si is 25%.

[0358] Preparation of the isolation component An alumina slurry is coated on both sides of a porous polyethylene (PE) polymer film, dried, and then coated with polyvinylidene fluoride polymer binder granules. After drying again, a release film is obtained.

[0359] Preparation of electrolyte The electrolyte comprises an organic solvent, an electrolyte salt, and additives. The components of the organic solvent are mixed, and then lithium salt and additives are added to form the electrolyte. The organic solvent comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1; the electrolyte salt comprises 1 mol / L lithium hexafluorophosphate; and the additive comprises 5% fluoroethylene carbonate (FEC), based on the total mass of the electrolyte.

[0360] Preparation of cylindrical battery cells The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. The positive electrode, separator, and negative electrode are then wound to form an electrode assembly. This assembly is placed in a cylindrical outer shell, dried, and then injected with electrolyte. After settling and formation processes, a cylindrical battery cell is obtained. The outer shell includes a housing and end caps. The housing includes integrally formed sidewalls and end walls. The sidewalls surround the electrode assembly, and the end caps and end walls are axially opposite each other. The sidewalls are made of nickel-plated steel. The outer diameter of the housing is 46 mm, and the axial dimension of the housing is 95 mm.

[0361] Examples 2 to 6, Comparative Example 1 Cylindrical battery cells were prepared using a method similar to that in Example 1, except that the compaction density of the negative electrode film and the positive electrode film was changed.

[0362] The test methods for the compaction density of the negative electrode film and the positive electrode film are described above and will not be repeated here.

[0363] Performance testing (1) Energy density test of cylindrical battery cells At 25°C, a cylindrical battery cell is charged at a constant current rate of 0.33C to 4.25V, and then charged at a constant voltage rate of 4.25V until the current is less than or equal to 0.05C. After resting for 10 minutes, the cylindrical battery cell is discharged at a constant current rate of 0.33C to 2.5V and then rested for 10 minutes. The total discharge capacity C0 and the total discharge energy E0 are recorded. The ratio of the total discharge energy E0 to the volume V0 of the cylindrical battery cell is the volumetric energy density of the cylindrical battery cell.

[0364] (2) Cyclic battery cell cycle performance test Before the cycle performance test, the cylindrical battery cells were first charged at 25℃ with a constant current of 0.33C to 4.25V, and then charged at 4.25V with a constant voltage until the current was less than or equal to 0.05C. After resting for 10 minutes, the cylindrical battery cells were considered to be at 100% SOC. Then, the cylindrical battery cells were discharged at a constant current of 0.33C to 2.5V and rested for 10 minutes. After resting for 10 minutes, the cylindrical battery cells were considered to be at 0% SOC. Then, through voltage and capacity calibration, the voltages corresponding to 3% SOC, 10% SOC, 80% SOC, and 97% SOC were obtained.

[0365] The cylindrical battery cells were adjusted to 3% SOC and allowed to rest for 10 minutes before undergoing cycle performance testing. The cycle performance test was conducted as follows: At 35℃, the cylindrical battery cells were charged at a constant current rate of 0.33C from the voltage corresponding to 3% SOC to the voltage corresponding to 10% SOC. Then, they were charged at an equivalent rate of 2.2C to the voltage corresponding to 80% SOC, and then charged at a constant current rate of 0.33C to the voltage corresponding to 97% SOC. After resting for 10 minutes, the cylindrical battery cells were discharged at a constant current rate of 1C to the voltage corresponding to 3% SOC, and allowed to rest for 10 minutes. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as the discharge capacity of the first cycle. The above charge-discharge cycle steps were repeated, and the discharge capacity after each cycle was recorded until the capacity retention rate after cycling reached 80%. The test was then stopped, and the number of cycles was recorded. The capacity retention rate after N cycles = discharge capacity of N cycles / discharge capacity of the first cycle × 100%.

[0366] (3) Storage performance test of cylindrical battery cells At 25℃, the cylindrical battery cells were charged at a constant current rate of 0.33C to 4.25V, and then charged at a constant voltage rate of 4.25V until the current was less than or equal to 0.05C. After resting for 5 minutes, the cylindrical battery cells were discharged at a constant current rate of 0.33C to 2.5V and then rested for 10 minutes to obtain the discharge capacity before storage. Then, the cylindrical battery cells were charged at a constant current rate of 0.33C to 4.25V, and then charged at a constant voltage rate of 4.25V until the current was less than or equal to 0.05C. Finally, the cylindrical battery cells were discharged... The cylindrical battery cells were stored in a 60℃ constant temperature chamber. After a period of storage, they were removed and placed in a 25℃ constant temperature environment. Once the temperature of the individual cylindrical battery cells dropped to 25℃, they were discharged at a constant current of 0.33C to 2.5V, allowed to stand for 10 minutes, and then charged at a constant current of 0.33C to 4.25V. They were then charged at a constant voltage at 4.25V until the current was less than or equal to 0.05C, allowed to stand for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V, allowed to stand for 10 minutes. The discharge capacity after storage was obtained. The number of storage days corresponding to an 80% capacity retention rate was recorded. The capacity retention rate after d days of storage = (discharge capacity after d days of storage / discharge capacity before storage) × 100%.

[0367] (4) Initial DCR test of cylindrical battery cells At 35℃, the cylindrical battery cell is charged at a constant current rate of 0.33C to 4.25V, and then charged at a constant voltage rate of 4.25V until the current is less than or equal to 0.05C. After resting for 10 minutes, the cylindrical battery cell is at 100% SOC. The battery cell is then discharged at a constant current rate of 0.33C and the cylindrical battery cell is adjusted to 50% SOC. After resting for 30 minutes, the voltage of the cylindrical battery cell is recorded as U1. The cylindrical battery cell is then discharged at 1C for 30 seconds, and the voltage at the end of the discharge is recorded as U2 using a 0.1-second sampling time. The initial DCR of the cylindrical battery cell is calculated as (U1-U2) / discharge current.

[0368] Table 1

[0369] The test results above show that by including carbon nanotubes in the positive electrode film, making the average particle size of the silicon-based material 1μm to 12μm, and making the mass percentage of Si element above 0.5%, the compaction density of the negative electrode film is 1g / cm³. 3 Up to 1.65 g / cm 3 This enables cylindrical battery cells to possess high energy density, good cycle performance, good storage performance, and good kinetic performance.

[0370] In Comparative Example 1, the negative electrode film has a high compaction density and provides less expansion space for silicon-based material particles. This will intensify the mutual compression of negative electrode active material particles, exacerbate the volume expansion of the negative electrode sheet, and result in poor interfacial film stability. Furthermore, the negative electrode sheet, separator, and positive electrode sheet are in closer contact, and stress is easily transmitted rapidly along the tightly contacted interlayer interface. The stress cannot be effectively released through the pores of the negative electrode film, which in turn leads to the continuous accumulation of internal residual stress. It will also affect the electrolyte wetting and reflux, thereby affecting the cycle performance, storage performance, and kinetic performance of the cylindrical battery cell.

[0371] Example 1-1 Cylindrical battery cells were prepared using a method similar to that in Example 1, except that the preparation process of the negative electrode sheet was changed.

[0372] Preparation of negative electrode sheet Artificial graphite, silicon oxide materials, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and carbon black SP were added to deionized water in a mass ratio of 91:5:1.2:1.8:1 and stirred until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both surfaces of the negative electrode current collector copper foil, followed by drying, cold pressing, and slitting to obtain the negative electrode sheet. The negative electrode sheet consists of a negative electrode current collector and a negative electrode film layer, located on both sides of the negative electrode current collector. The negative electrode film layer is formed from the negative electrode slurry, and its single-sided density is 150 mg / 1540.25 mm². 2 Throughout the entire negative electrode film, the average particle size of all silicon-based materials is 7 μm, and the mass percentage of Si is 2.5%.

[0373] Table 2

[0374] The test results above show that by placing silicon-based materials in the second film layer away from the negative electrode current collector, the cycle performance, storage performance, and kinetic performance of cylindrical battery cells can be improved.

[0375] Examples 2-1 to 2-5 Cylindrical battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass percentage of Si in the entire negative electrode film and the compaction density of the negative electrode film were changed. The mass percentage of Si in the entire negative electrode film was altered by changing the thickness ratio of the first and second films. The NP ratio (negative electrode capacity per unit area / positive electrode capacity per unit area) of the battery cell remained unchanged.

[0376] Table 3

[0377] The test results above show that by further adjusting the mass ratio of Si in the entire negative electrode film, it is possible to better combine high energy density with good cycle performance, storage performance and kinetic performance in cylindrical battery cells.

[0378] Increasing the mass percentage of Si in the negative electrode film increases the energy density of a cylindrical battery cell. If the mass percentage of Si in the negative electrode film exceeds 10%, the cylindrical battery cell can achieve even higher energy density, but cycle performance, storage performance, and kinetic performance will decrease.

[0379] Examples 3-1 to 3-2 Cylindrical battery cells were prepared using a method similar to that of Example 1, except that the composition of the positive electrode film was changed.

[0380] In the positive electrode film layer of Example 3-1, LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 The mass ratio of O2, polyvinylidene fluoride, carbon nanotubes, and carbon black SP is 98:1:0.05:0.95.

[0381] In the positive electrode film layer of Example 3-2, LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 The mass ratio of O2, polyvinylidene fluoride, carbon nanotubes, and carbon black SP is 98:1:0.5:0.5.

[0382] Table 4

[0383] The test results above show that by further adjusting the mass ratio of carbon nanotubes in the positive electrode film, cylindrical battery cells can better combine high energy density with good cycle performance, storage performance and kinetic performance.

[0384] Examples 4-1 to 4-4, Comparative Example 2 Cylindrical battery cells were prepared using a method similar to that in Example 1, except that the average particle size of the silicon-based material in the entire negative electrode film was changed.

[0385] Table 5

[0386] The test results above show that by including carbon nanotubes in the positive electrode film, making the average particle size of the silicon-based material 1μm to 12μm, and making the mass percentage of Si element above 0.5%, the compaction density of the negative electrode film is 1g / cm³. 3 Up to 1.65 g / cm3 This allows cylindrical battery cells to possess high energy density, good cycle performance, good storage performance, and good kinetic performance. Further adjustment of the average particle size of the silicon-based material in the negative electrode film helps cylindrical battery cells to better achieve a balance between good cycle performance, storage performance, and kinetic performance.

[0387] In Comparative Example 2, the silicon-based material has a large average particle size and poor ion transport performance, resulting in a large initial DCR and poor kinetic performance of the cylindrical battery cell.

[0388] Example 5-1 Cylindrical battery cells were prepared using a method similar to that in Example 1, except that the mixture of natural and artificial graphite in the second film layer of the negative electrode was replaced with artificial graphite.

[0389] The second film layer is formed by the second slurry. The preparation process of the second slurry is as follows: artificial graphite, silicon oxide material, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and carbon black SP are added to deionized water in a mass ratio of 30:50:3:15:2 and stirred evenly to obtain the second slurry.

[0390] Example 5-2 Cylindrical battery cells were prepared using a method similar to that in Example 1, except that the mixture of natural and artificial graphite in the second film layer of the negative electrode was replaced with natural graphite.

[0391] The second film layer is formed by the second slurry. The preparation process of the second slurry is as follows: natural graphite, silicon oxide material, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and carbon black SP are added to deionized water in a mass ratio of 30:50:3:15:2 and stirred evenly to obtain the second slurry.

[0392] Table 6

[0393] The test results above show that by including both natural and artificial graphite in the second film layer, it is helpful to improve the cycle performance, storage performance and kinetic performance of cylindrical battery cells.

[0394] Examples 6-1 to 6-2 Cylindrical battery cells were prepared using a method similar to that in Example 1, except that the unilateral density of the positive and negative electrode films was changed.

[0395] Table 7

[0396] The test results above show that adjusting the unilateral density of the positive and negative electrode films helps to improve the cycle performance, storage performance, and kinetic performance of cylindrical battery cells.

[0397] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. 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, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A cylindrical battery cell, characterized in that, include: The housing includes a metal body, the outer diameter of the housing is 30 mm to 80 mm, and the dimension of the housing along the axial direction of the cylindrical battery cell is 1.3 to 2.6 times the outer diameter of the housing; Electrode assembly, housed within the housing; The electrode assembly includes a negative electrode and a positive electrode. The negative electrode includes a negative current collector and a negative electrode film. The negative electrode film is disposed on at least one side of the negative current collector. The negative electrode film includes a negative electrode active material, which includes a silicon-based material and a graphite material. The silicon-based material includes Si element. Based on the mass of the negative electrode film, the mass percentage of Si element is 0.5% or more. The positive electrode includes a positive current collector and a positive electrode film. The positive electrode film is disposed on at least one side of the positive current collector. The positive electrode film includes a positive electrode active material, which includes a lithium transition metal oxide. The lithium transition metal oxide includes a single-crystal lithium transition metal oxide. The positive electrode film also includes carbon nanotubes. The average particle size of the silicon-based material is 1 μm to 12 μm. The compaction density of the negative electrode film is 1 g / cm³. 3 Up to 1.65 g / cm 3 .

2. The cylindrical battery cell according to claim 1, characterized in that, Based on the mass of the positive electrode film, the mass percentage of carbon nanotubes in the positive electrode film is 0.05% to 0.5%.

3. The cylindrical battery cell according to claim 1, characterized in that, In the positive electrode film, the length of the carbon nanotubes is 5 μm to 10 μm.

4. The cylindrical battery cell according to claim 1, characterized in that, In the positive electrode film layer, at least a portion of the carbon nanotubes are located on the surface of the positive electrode active material.

5. The cylindrical battery cell according to claim 1, characterized in that, The average particle size of the positive electrode active material is 1.5 μm to 7.5 μm; and / or, Based on the total number of lithium transition metal oxides, the proportion of lithium transition metal oxides with single crystal morphology is 80%-100%.

6. The cylindrical battery cell according to claim 1, characterized in that, The compaction density of the positive electrode film is 3.1 g / cm³. 3 Up to 3.6 g / cm 3 ; and / or, The single-sided density of the positive electrode film is 155 mg / 1540.25 mm². 2 Up to 320mg / 1540.25mm 2 .

7. The cylindrical battery cell according to claim 1, characterized in that, The compaction density of the positive electrode film is 3.3 g / cm³. 3 Up to 3.5g / cm 3 ; and / or, The single-sided density of the positive electrode film is 220 mg / 1540.25 mm². 2 Up to 280mg / 1540.25mm 2 .

8. The cylindrical battery cell according to claim 1, characterized in that, The positive electrode active material includes a lithium transition metal oxide, which comprises a non-lithium metal element, including Ni. Based on the mass of the positive electrode film, the mass percentage of Ni element is 44% to 55.5%; and / or, Based on the total molar amount of the non-lithium metal elements, the molar percentage of Ni is 75% to 95%.

9. The cylindrical battery cell according to claim 8, characterized in that, Based on the mass of the positive electrode film, the mass percentage of Ni element is 48% to 55%; and / or, Based on the total molar amount of the non-lithium metal elements, the molar percentage of Ni is 80% to 93%.

10. The cylindrical battery cell according to claim 1, characterized in that, Based on the mass of the negative electrode film, the mass percentage of Si element is 0.5% to 20%.

11. The cylindrical battery cell according to claim 1, characterized in that, Based on the mass of the negative electrode film, the mass percentage of Si is 0.5% to 5%, and the compaction density of the negative electrode film is 1.3 g / cm³. 3 Up to 1.65 g / cm 3 ; Alternatively, based on the mass of the negative electrode film, the mass percentage of Si element is greater than 5% and less than or equal to 10%, and the compaction density of the negative electrode film is 1.2 g / cm³. 3 Up to 1.55 g / cm 3 ; Alternatively, based on the mass of the negative electrode film, the mass percentage of Si element is greater than 10% and less than or equal to 20%, and the compaction density of the negative electrode film is 1 g / cm³. 3 Up to 1.45 g / cm 3 .

12. The cylindrical battery cell according to claim 1, characterized in that, The single-sided density of the negative electrode film is 85 mg / 1540.25 mm². 2 Up to 180mg / 1540.25mm 2 .

13. The cylindrical battery cell according to claim 1, characterized in that, The silicon-based material includes one or more of elemental silicon, silicon-carbon materials, and silicon-oxygen materials; and / or, The graphite material includes one or more of natural graphite and artificial graphite.

14. The cylindrical battery cell according to claim 1, characterized in that, The silicon-based material includes one or more of silicon-carbon materials and silicon-oxygen materials; and / or, The graphite material includes natural graphite and artificial graphite.

15. The cylindrical battery cell according to claim 14, characterized in that, Based on the mass of the negative electrode film, the mass percentage of natural graphite is less than the mass percentage of artificial graphite.

16. The cylindrical battery cell according to claim 1, characterized in that, The average particle size of the graphite material is 10 μm to 18 μm.

17. The cylindrical battery cell according to claim 1, characterized in that, The negative electrode film layer includes a first film layer and a second film layer stacked along the thickness direction. The first film layer is located between the negative electrode current collector and the second film layer. The negative electrode active material in the second film layer includes silicon-based material and graphite material, and the negative electrode active material in the first film layer includes graphite material.

18. The cylindrical battery cell according to claim 17, characterized in that, The first film layer does not contain Si.

19. The cylindrical battery cell according to claim 17, characterized in that, The negative electrode active material in the first film layer also includes a silicon-based material, which includes Si element, and the mass percentage of Si element in the first film layer is less than the mass percentage of Si element in the second film layer based on the mass of the second film layer.

20. The cylindrical battery cell according to claim 19, characterized in that, Based on the mass meter of the first film layer, the mass percentage of Si element in the first film layer is greater than 0 and less than or equal to 1%; and / or, Based on the mass of the first film layer, the mass percentage of silicon-based material in the first film layer is greater than 0 and less than or equal to 2%.

21. The cylindrical battery cell according to claim 17, characterized in that, Based on the mass of the second film layer, the mass percentage of Si element in the second film layer is 10% to 40%; and / or, Based on the mass of the second film layer, the mass percentage of silicon-based material in the second film layer is 20% to 80%.

22. The cylindrical battery cell according to claim 17, characterized in that, The compaction density of the second film layer is less than that of the first film layer; and / or, The porosity of the second membrane layer is greater than that of the first membrane layer.

23. The cylindrical battery cell according to claim 1, characterized in that, The cylindrical battery cell also includes an electrolyte, wherein the mass ratio of the electrolyte to the capacity of the cylindrical battery cell is from 1.2 g / Ah to 2.1 g / Ah.

24. The cylindrical battery cell according to claim 23, characterized in that, The electrolyte includes a chain ester solvent, and the chain ester solvent accounts for 25.5% to 76.5% of the mass of the electrolyte.

25. The cylindrical battery cell according to claim 24, characterized in that, The chain ester solvents include chain carbonates. The chain carbonate in the electrolyte comprises 4% to 70% by mass; and / or, The chain carbonates include compounds represented by Formula I. Equation I, In formula I, R 11 and R 12 Each independently includes C1 to C3 alkyl or C1 to C3 haloalkyl.

26. The cylindrical battery cell according to claim 24, characterized in that, The chain-like ester solvents also include chain-like carboxylic acid esters. The chain-like carboxylic ester accounts for 4% to 70% of the mass in the electrolyte; and / or, The chain carboxylic acid esters include compounds represented by Formula II. Formula II, In Equation II, R 21 Includes hydrogen atoms, halogen atoms, C1 to C3 alkyl groups, or C1 to C3 haloalkyl groups; R 22 Includes C1 to C3 alkyl or C1 to C3 haloalkyl.

27. The cylindrical battery cell according to claim 23, characterized in that, The electrolyte comprises an electrolyte salt, which includes one or more of lithium hexafluorophosphate and lithium sulfonamide; and / or the molar concentration of the electrolyte salt is from 0.5 mol / L to 2 mol / L.

28. The cylindrical battery cell according to claim 27, characterized in that, The lithium sulfonamide salt includes the anion shown in formula A. Formula A, In formula A, R1 and R2 each independently include a halogen atom or a C1 to C6 haloalkyl group.

29. The cylindrical battery cell according to claim 1, characterized in that, The housing includes a shell and an end cap. The shell includes a side wall and an end wall connected to the side wall. The shell has an opening. The end cap is connected to the side wall and covers the opening. The end cap and the end wall are opposite each other along the axial direction of the cylindrical battery cell.

30. The cylindrical battery cell according to claim 29, characterized in that, The base material of the sidewall is steel, and the thickness of the sidewall is 0.2 mm to 0.6 mm; and / or, The outer casing has a dimension of 50 mm to 150 mm along the axial direction of the cylindrical battery cell; and / or, The outer diameter of the outer shell is 40mm to 60mm.

31. A battery device, characterized in that, It includes the cylindrical battery cell as described in any one of claims 1-30.

32. An electrical appliance, characterized in that, Includes the cylindrical battery cell according to any one of claims 1-30 or the battery device according to claim 31.

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