Battery cell, battery apparatus and electric apparatus

Abstract

A battery cell, a battery apparatus and an electric apparatus. The battery cell comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode coating layer arranged on at least one side of a surface of the positive electrode current collector; the positive electrode current collector comprises a positive electrode current collecting portion and a positive electrode tab arranged on at least one side of a side face of the positive electrode current collecting portion; the width of the positive electrode current collecting portion is 62-98 mm; and the lithium-ion conductivity of the electrolyte is 10-25 mS / cm.

Description

Battery cells, battery packs, and electrical devices

[0001] Cross-references

[0002] This application incorporates Chinese Patent Application No. 202411605958.3, filed on November 12, 2024, entitled “Battery cell, battery device and power consumption device”, which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of battery cell technology, and more particularly to a battery cell, a battery device, and an electrical device. Background Technology

[0004] In recent years, battery cells have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0005] With the market demanding both increased energy density and fast-charging cycle life of battery cells, how to simultaneously achieve both has become a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell that has both good cycle life and fast charge cycle stability.

[0007] The first aspect of this application provides a battery cell, which includes a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the surface of the positive current collector. The positive current collector includes a positive current collection portion and a positive electrode tab disposed on at least one side of the positive current collection portion. The width of the positive current collection portion is 62mm-98mm. Along the width direction of the positive current collection portion, the size of the positive electrode film layer is 63mm-90mm. The lithium-ion conductivity of the electrolyte is 10mS / cm-25mS / cm.

[0008] Electrolytes with lithium-ion conductivity within the aforementioned range exhibit high lithium-ion transport rates, reducing the internal resistance of individual battery cells. This, in turn, decreases the temperature rise of the battery cells during fast charging, reduces internal temperature differences within the cells, and mitigates the negative impact of inconsistent internal temperature rise on the fast-charging cycle life. Furthermore, it allows for a wider positive electrode current collector while maintaining a uniform internal temperature difference within the battery cell. In the embodiments of this application, the combination of the electrolyte and the positive electrode current collector improves the fast-charging cycle life of the battery cells while maintaining good energy density.

[0009] In any embodiment, the battery cell includes a stacked cell, and the lithium-ion conductivity of the electrolyte is 10mS / cm-20mS / cm.

[0010] In any embodiment, the electrolyte comprises a solvent and an electrolyte salt, wherein the solvent comprises a chain carboxylic acid ester solvent, and the chain carboxylic acid ester solvent accounts for more than or equal to 5% of the total mass of the electrolyte, and is optionally 7%-75%.

[0011] The addition of chain-like carboxylic acid ester solvents to the electrolyte not only improves the lithium-ion conductivity of the electrolyte but also reduces its viscosity, improves the wetting between the electrolyte and the electrode, and enhances the electrolyte flow across the electrode width. This further increases the lithium-ion transport rate at the solid-liquid interface of the battery cell, reduces the internal resistance of the battery cell, decreases the temperature rise during fast charging, and narrows the internal temperature difference within the battery cell. This allows the battery cell to support a wider positive electrode current collector at the same temperature rise. In the embodiments of this application, the battery cell achieves a balance between fast-charging cycle life and energy density through the cooperation of the electrolyte and the positive electrode current collector.

[0012] In any embodiment, the chain carboxylic acid ester solvent accounts for 7%-60% of the total mass of the electrolyte.

[0013] Chain-like carboxylic acid ester solvents exhibit high reactivity and readily undergo side reactions with negative electrode materials, increasing battery gas production and negatively impacting battery safety. Chain-like carboxylic acid ester solvents within the aforementioned mass content range can control side reactions within a reasonable range, allowing battery cells to achieve both good fast-charge cycle life and energy density while maintaining low gas production levels, thus ensuring battery safety.

[0014] In any embodiment, the electrolyte salt comprises lithium bisfluorosulfonylimide, and the mass percentage of lithium bisfluorosulfonylimide is 5%-60%, optionally 10%-50%, based on the total mass of the electrolyte salt in the electrolyte.

[0015] Lithium difluorosulfonylimide readily dissociates in electrolyte solvents, which is beneficial for improving cell kinetics, reducing internal resistance, and further decreasing heat generation and temperature rise during fast charging, thus mitigating the inconsistent internal temperature rise of cells during fast charging. However, lithium difluorosulfonylimide readily undergoes side reactions with LiC6 formed during deep lithium intercalation at the negative electrode, reducing reversible lithium capacity and negatively impacting the retention of cell capacity during cycling. Electrolytes containing lithium difluorosulfonylimide within the aforementioned mass range can both reduce inconsistent internal temperature rise of cells and maintain side reactions with the negative electrode material at reasonable levels, comprehensively improving the battery's fast-charging cycle life.

[0016] In any embodiment, the mass percentage of lithium bis(fluorosulfonyl)imide is 1%-10% based on the total mass of the electrolyte, and optionally 1%-8%.

[0017] When the mass content of lithium difluorosulfonylimide in the electrolyte is within the above range, the fast-charging cycle life of the battery cells can be further improved while taking into account the energy density of the battery cells.

[0018] In any embodiment, the lithium bisfluorosulfonylimide accounts for 3%-6% of the total mass of the electrolyte.

[0019] When the mass content of lithium difluorosulfonylimide in the electrolyte is within the above range, the battery cell can better balance fast-charging cycle life and low gas production level while maintaining good energy density, thus achieving a balance between fast-charging life and safety performance.

[0020] In any embodiment, the chain carboxylic acid ester solvent includes one or more of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

[0021] The small molecular size of the aforementioned chain-like carboxylic acid ester solvents helps to reduce the viscosity of the electrolyte, increase the wetting rate of the electrolyte, improve electrolyte dynamics, increase the transport rate of charge carriers inside the battery cell, reduce the inconsistency of current density inside the battery, further reduce the phenomenon of inconsistent internal temperature rise of the battery cell during fast charging, and improve the fast charging cycle life of the battery cell.

[0022] In any embodiment, the chain carboxylic acid ester solvent includes one or more of ethyl acetate and methyl acetate, and the total mass percentage of ethyl acetate and methyl acetate is 5%-80% based on the total mass of the solvent.

[0023] Compared to other chain carboxylic acid ester solvents, ethyl acetate and methyl acetate have both relatively high kinetic activity and relatively low gas production levels, which is beneficial for further improving the lithium-ion transport rate and reducing the side reaction level of the electrolyte. This reduces the internal temperature difference of the battery cell during fast charging, balances the fast charging cycle life of the battery cell with low gas production levels, and achieves a balance between fast charging life and safety performance.

[0024] In any embodiment, the chain carboxylic acid ester solvent includes methyl acetate, and the methyl acetate content is 5%-80% based on the total mass of the solvent, optionally 5%-50%.

[0025] In any embodiment, the size of the positive electrode film layer along the width direction of the positive electrode current collector is 60mm-97mm, and can be selected as 63mm-90mm.

[0026] The size of the positive electrode film layer is within the above range, and matching the size of the positive electrode current collector can further balance the energy density of the battery cell.

[0027] In any embodiment, the positive current collector comprises an aluminum foil with a thickness of 10 μm to 16 μm.

[0028] With the aluminum foil thickness within the aforementioned range, it will not occupy too large a proportion of the battery's mass, nor will it cause excessive internal resistance due to a reduction in the overcurrent area. This reduces heat generation and temperature rise during fast charging, alleviates the inconsistent temperature rise of individual battery cells during fast charging, and balances the energy density and fast charging cycle life of individual battery cells.

[0029] In any embodiment, the thickness of the aluminum foil is 12μm-14μm.

[0030] With the aluminum foil thickness within the aforementioned range, the battery cells further improve the fast-charging cycle life while maintaining energy density.

[0031] In any embodiment, the positive electrode film layer includes a positive electrode active material, which includes lithium iron phosphate and its modified materials.

[0032] In any embodiment, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The projection of the positive electrode film layer along the thickness direction falls within the range of the negative electrode film layer, and along the width direction of the negative current collector, the distance between the edge of the negative electrode film layer and the projected edge of the adjacent positive electrode film layer is 1mm-4mm.

[0033] During fast charging, significant polarization at the negative electrode can easily cause the lithium intercalation potential to drop below 0V, leading to lithium metal deposition on the negative electrode surface. This deposited lithium metal readily reacts with the electrolyte to form high-resistivity inorganic salts, reducing battery capacity. Ensuring that the projection of the positive electrode film along its thickness falls within the range of the negative electrode film reduces the risk of lithium deposition in individual cells during discharge, improving fast charging performance. Furthermore, it helps control capacity loss caused by excessive lithium ion diffusion into the negative electrode, thus balancing fast charging cycle life.

[0034] In any embodiment, the negative current collector comprises a copper foil with a thickness of 4μm-6μm.

[0035] With the copper foil thickness within the aforementioned range, it will not occupy too large a proportion of the battery's mass, nor will it cause excessive temperature rise during fast charging, making it difficult for heat to dissipate. This approach can further balance the energy density of individual battery cells and the fast charging cycle life.

[0036] In any embodiment, the one-sided density of the negative electrode film is 0.08 g / 1540.25 mm. 2 -0.20g / 1540.25mm 2 Available in 0.10g / 1540.25mm. 2 -0.16g / 1540.25mm 2 .

[0037] Battery cells with a single-sided density of the negative electrode film within the above range can reduce the transport distance of lithium ions in the negative electrode film, match the electrolyte with high conductivity, reduce concentration polarization during fast charging, and improve the fast charging cycle life of the battery cell while taking into account the energy density of the battery cell.

[0038] In any embodiment, the compaction density of the negative electrode sheet is 1.2 g / cm³. 3 -1.9g / cm 3 1.2g / cm³ is an option. 3 -1.65g / cm 3 .

[0039] Negative electrode sheets with a compaction density within the above range have suitable porosity, which can be matched with electrolytes with high conductivity, facilitate the transport of lithium ions in the negative electrode, reduce concentration polarization during fast charging, and help improve the fast charging cycle life of battery cells while taking into account the energy density of battery cells.

[0040] In any embodiment, the compaction density of the negative electrode sheet is 1.35 g / cm³. 3 -1.6g / cm 3 .

[0041] In any embodiment, the average thickness of the negative electrode film layer on one side is 30μm-150μm, and can be selected as 30μm-80μm.

[0042] Battery cells with an average thickness of the negative electrode film on one side within the above range can reduce the transport distance of lithium ions in the negative electrode film, match the electrolyte with high conductivity, reduce concentration polarization during fast charging, and improve the fast charging cycle life of the battery cell while taking into account the energy density of the battery cell.

[0043] In any embodiment, the porosity of the negative electrode sheet is 20%-60%, optionally 25%-40%.

[0044] Negative electrode sheets with porosity within the above range can be matched with electrolytes with high conductivity, improving the diffusion rate of lithium ions in the negative electrode, reducing concentration polarization generated by the battery cell during fast charging, and helping to improve the fast charging cycle life of the battery cell while taking into account the energy density of the battery cell.

[0045] In any embodiment, the porosity of the separator is 25%-55%, optionally 28%-42%.

[0046] Separator membranes with porosity within the aforementioned range are beneficial for improving the liquid phase transport rate of lithium ions and reducing the liquid phase transport resistance of lithium ions, thereby reducing battery impedance, minimizing temperature rise and temperature inconsistency, and allowing for further increases in current collector width and energy density. Simultaneously, the reduced temperature rise can decrease the degree of side reactions between the electrolyte and the negative electrode active material, and reduce gas production. Porosity within the aforementioned range also provides the separator with a certain mechanical strength, while reducing the probability of lithium dendrites piercing the separator and causing short circuits, thus comprehensively improving the fast-charging cycle life of individual battery cells.

[0047] In any embodiment, the porosity of the isolation membrane is 30%-42%.

[0048] Separators with porosity within the above range are beneficial for further reducing the temperature rise of the battery and the phenomenon of inconsistent temperature rise, alleviating the technical problems of severe local polarization of the battery and increased risk of lithium plating, and further improving the fast charging cycle life of the battery cells while maintaining certain mechanical properties of the separator.

[0049] In any embodiment, the Gurley value G of the separator is 50s-620s, optionally 250s-610s. The Gurley value refers to the time required for 100mL of air to pass through a 1 square inch separator under a pressure of 1.22kPa when the separator is placed in an air permeability tester. The unit is seconds.

[0050] Separators with Gurley values ​​within the aforementioned range are beneficial for reducing the impedance of individual battery cells, minimizing temperature rise and inconsistencies, and allowing for a further increase in the width of the current collector and energy density. Simultaneously, the reduced temperature rise decreases the degree of side reactions between the electrolyte and the negative electrode active material, reducing gas production. A Gurley value within this range also provides the separator with a certain mechanical strength, reducing the probability of lithium dendrites piercing the separator and causing short circuits, thus comprehensively improving the fast-charge cycle life of individual battery cells.

[0051] In any embodiment, the battery cell includes a wound cell, wherein at least one turn of the positive electrode sheet of the wound cell includes at least two positive electrode tabs.

[0052] In any embodiment, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative current collector includes a negative current collection portion and a negative electrode tab disposed on at least one side of the negative current collection portion. At least one turn of the negative electrode sheet of the wound cell includes at least two negative electrode tabs.

[0053] In the prior art, the positive or negative electrode in a wound cell is typically provided with one tab per turn. This application's embodiment reduces overcurrent at the tabs and decreases temperature rise at the tabs by providing at least two tabs on at least one turn of the wound cell electrode. This alleviates the uneven current density distribution on the electrode and the inconsistent temperature rise within the battery cell during fast charging, thereby improving the fast charging cycle life of the battery cell.

[0054] In any embodiment, the wound cell includes a large surface area and a bending area. The positive electrode tab is disposed in the large surface area of ​​the wound cell. The number of positive electrode layers in the wound cell is defined according to the rule that the number of positive electrode layers in the large surface area increases sequentially along the winding direction from the inside to the outside. The positive electrode of the wound cell has at least two consecutive layers, each of which is provided with a positive electrode tab.

[0055] In existing technologies, the tabs in wound battery cells are generally located on layers N, N+2, N+4, etc., with a maximum of one tab every two layers in the electrode sheet. This application's embodiment addresses this by having tabs continuously placed on at least two consecutive layers of the electrode sheet, i.e., on layers N and N+1. This reduces overcurrent and temperature rise at the tabs, mitigating uneven current density distribution on the electrode sheet and inconsistent temperature rise within the battery cell during fast charging, thus improving the fast charging cycle life of the battery cell.

[0056] In any embodiment, the battery cell includes a stacked cell, wherein the length of the positive current collector in the stacked cell is 100mm-700mm, and can be selected as 200mm-600mm.

[0057] During their research, the applicant discovered that the length of the current collector in a laminated battery cell has a crucial impact on the current uniformity and temperature rise consistency during fast charging. Maintaining the length of the positive current collector within the aforementioned range can further improve the inconsistent temperature rise during fast charging and increase the fast charging cycle life of the battery cells.

[0058] In any embodiment, the electrolyte injection coefficient of the battery cell is 2.5g / Ah-3.1g / Ah, and can be selected as 2.6g / Ah-2.9g / Ah.

[0059] Battery cells with an electrolyte injection coefficient within the above range can improve the wettability between the electrolyte and the electrode, reduce the battery interface resistance, and decrease the battery impedance. This alleviates the phenomenon of inconsistent temperature rise in the current collector during fast charging, and the width of the current collector can be further increased. At the same time, the increase in gas production caused by the side reaction of the electrolyte solvent can be kept within a controllable range, further balancing the battery's fast charging cycle performance, energy density, and safety performance.

[0060] In any implementation, at 25°C, the number of battery cells in the corresponding fast charging window is 2530-2980 cycles.

[0061] The second aspect of this application provides a battery device including the battery cell provided in the first aspect of this application, the battery device including at least one of a battery module, a battery pack, and an energy storage battery.

[0062] A third aspect of this application also provides an electrical device, which includes a single battery cell provided in the first aspect of this application or a battery device provided in the second aspect of this application. Attached Figure Description

[0063] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0064] Figure 2 is a schematic diagram of a battery module according to an embodiment of this application;

[0065] Figure 3 is a schematic diagram of a battery pack according to an embodiment of this application;

[0066] Figure 4 is an exploded view of the battery pack shown in Figure 3;

[0067] Figure 5 is an exploded view of a single battery cell according to an embodiment of this application;

[0068] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0069] Figure 7 is a partial schematic diagram of a battery cell according to an embodiment of this application;

[0070] Figure 8 is a schematic diagram of the positive electrode sheet according to one embodiment of this application;

[0071] Figure 9 is a schematic diagram of a wound battery cell according to an embodiment of this application.

[0072] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 6 Winded cell; 61 Large surface area; 62 Bending area; 10 Battery cell; 101 Positive electrode; 102 Negative electrode; 103 Separator; 1011 Positive current collector; 1012 Positive film layer; 10111 Positive current collector; 10112 Positive electrode tab; 1021 Negative current collector; 1022 Negative film layer; 1023 Negative electrode tab. Detailed Implementation

[0073] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0074] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0075] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0076] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0077] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0078] In this application, the terms "multiple" or "various" refer to two or more kinds of things.

[0079] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0080] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0081] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0082] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, and the embodiments of this application are not limited to this. Figure 1 shows a cuboid battery cell 5 as an example.

[0083] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0084] In some implementations, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0085] In some implementations, individual battery cells can be assembled into a battery module. The number of battery cells in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2 is a schematic diagram of a battery module 4 as an example. As shown in Figure 2, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0086] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0087] In some implementations, the aforementioned battery modules and individual battery cells can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0088] Figures 3 and 4 are schematic diagrams of a battery pack 1 as an example. As shown in Figures 3 and 4, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 and forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0089] The battery provided in this application embodiment may include a lithium-ion battery.

[0090] A single battery cell includes electrode components and an electrolyte.

[0091] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0092] In some embodiments, as shown in FIG5, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be adjusted as needed.

[0093] Electrode assemblies typically include positive and negative electrodes. The negative electrode is the electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharging. The positive electrode is the electrode that absorbs or delithiates lithium ions during charging and absorbs or lithiates lithium during discharging.

[0094] Currently, the charging time for lithium-ion batteries in pure electric vehicles is generally over 1 hour, about 20 times longer than the time it takes to fill up a regular gasoline car. Therefore, charging speed has become one of the most pressing concerns for consumers, and improving battery fast-charging performance is a common goal in the industry. While fast-charging technology has improved the charging rate and shortened the charging time, it still faces challenges such as rapid reversible capacity degradation and low cycle life during fast charging.

[0095] The applicant's research found that the low cycle life of fast-charging batteries is closely related to the high current density, rapid temperature rise of the cell, and large temperature rise amplitude during fast charging. During battery charging, the current first converges at the tabs and then is transmitted to the current collector. Due to the time required for electron transport, there is a difference in current density between the tabs and the current collector, and the difference in current density between the current collector and the tab varies at different points on the current collector. Generally, the difference in current density between the current collector and the tab increases with the increase in distance between them, and also with the increase in current density. In other words, the inconsistency in current density on the current collector is more pronounced during high-rate charging and discharging, i.e., fast charging. According to Joule's law, the inconsistency in current density at different points on the current collector further leads to inconsistent temperature rises in different parts of the battery, increasing the temperature gradient on the current collector. This results in uneven lithium-ion transport rates within the cell, increasing the risk of battery polarization and localized lithium plating, and reducing the cycle life of individual battery cells. Reducing the maximum distance between the bottom edge of the current collector (the side furthest from the tab) and the tab, i.e. reducing the width of the current collector, can alleviate the phenomenon of inconsistent temperature rise inside the battery cell during fast charging and improve the cycle stability of the battery cell during fast charging. However, reducing the width of the battery current collector will lead to a decrease in battery energy density.

[0096] Based on the above problems, this application provides a battery cell. Please refer to Figures 7 and 8. The battery cell 10 includes a positive electrode 101, a negative electrode 102, an electrolyte (not shown in the figures), and a separator 103 disposed between the positive electrode 101 and the negative electrode 102. The positive electrode 101 includes a positive current collector 1011 and a positive electrode film 1012 disposed on at least one side of the surface of the positive current collector 1011. The positive current collector 1011 includes a positive current collector portion 10111 and a positive electrode tab 10112 disposed on at least one side of the positive current collector portion 10111. The width L1 of the positive current collector portion 10111 is 62mm-98mm. Along the width direction of the positive current collector portion, the size of the positive electrode film is 63mm-90mm. The lithium-ion conductivity of the electrolyte is 10mS / cm-25mS / cm.

[0097] Please refer to Figure 8. The width L1 of the positive current collector 10111 refers to the dimension of the positive current collector 10111 in the direction perpendicular to the rolling of the positive electrode film layer 1012 in the positive electrode sheet 101. It also refers to the dimension of the positive current collector 10111 in the direction perpendicular to the connection between the positive electrode tab 10112 and the positive current collector 10111 (i.e., the X direction in Figure 8).

[0098] Among them, the surface of the positive current collector refers to the surface defined by the length and width of the positive current collector; the side surface of the positive current collector refers to the surface defined by the dimension in the thickness direction of the positive current collector.

[0099] In some implementations, the width L1 of the positive current collector can be selected as 62mm, 64mm, 66mm, 68mm, 70mm, 72mm, 74mm, 76mm, 78mm, 80mm, 82mm, 84mm, 86mm, 88mm, 90mm, 92mm, 94mm, 96mm, 98mm or any value range between the two.

[0100] The material of the positive electrode current collector is not particularly limited, as long as it does not cause chemical changes in the battery cell and is conductive. Current collectors include metal foils with a pure metal content of 95% or higher, such as at least one of copper, aluminum, stainless steel, titanium, and nickel foils. They also include alloy foils with at least two main metals, for example, alloy foils made from at least two main elements of copper, aluminum, nickel, titanium, and iron. Furthermore, they can include copper, aluminum-cadmium alloys, iron, or stainless steel with surface treatments using carbon, nickel, titanium, silver, copper, etc. In addition, the bonding force with the negative electrode active material can be enhanced by forming micro-uneven surfaces, and they can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0101] In this application, the lithium-ion conductivity of the electrolyte describes the ability of dissociated ions in the electrolyte solution to conduct electricity through the directional movement of these ions in an electric field, and can be tested using any method known in the art. As an example, a battery cell is disassembled, and approximately 100 mL of electrolyte sample is taken in a dry, clean, corrosion-resistant sample bottle. This sample is then sealed and placed in a constant-temperature water bath, with occasional shaking, until the temperature reaches 25°C (deviation ±0.5°C). After the sample temperature stabilizes, its conductivity is tested using a commercially available conductivity meter. The conductivity meter is thoroughly dried with calibration solution and then vertically immersed in the liquid to be tested. The test is started, and the results are recorded after the data has stabilized for at least 10 seconds. It is understood that the lithium-ion conductivity of the electrolyte is closely related to the solvent, lithium-containing electrolyte salt, additives, and other components and formulations in the electrolyte.

[0102] In some embodiments, the lithium-ion conductivity of the electrolyte can be selected from 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 19 mS / cm, 20 mS / cm, 21 mS / cm, 22 mS / cm, 23 mS / cm, 24 mS / cm, 25 mS / cm, or any value range between the two.

[0103] Electrolytes with lithium-ion conductivity within the aforementioned range exhibit high lithium-ion transport rates, reducing the internal resistance of individual battery cells. This, in turn, decreases the temperature rise of the battery cells during fast charging, reduces internal temperature differences within the cells, and mitigates the negative impact of inconsistent internal temperature rise on the fast-charging cycle life. Furthermore, it allows for a wider positive electrode current collector while maintaining a uniform internal temperature difference within the battery cell. In the embodiments of this application, the combination of the electrolyte and the positive electrode current collector improves the fast-charging cycle life of the battery cells while maintaining good energy density.

[0104] In some embodiments, the battery cell includes a stacked cell, and the electrolyte has a lithium-ion conductivity of 10 mS / cm to 20 mS / cm.

[0105] In some embodiments, the electrolyte includes a solvent and an electrolyte salt, the solvent including a chain carboxylic acid ester solvent, wherein the chain carboxylic acid ester solvent accounts for more than or equal to 5% of the total mass of the electrolyte, and is optionally 7%-75%.

[0106] In this application, chain carboxylic acid esters refer to linear organic solvents containing carboxylic acid ester groups, including but not limited to one or more of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

[0107] In this paper, the types and mass contents of each component in the electrolyte can be obtained by any method known to those skilled in the art. As an example, the composition and content of the electrolyte can be characterized by one or more of the following methods: gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectrometry (GC-MS). For example, referring to GB / T-9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" and / or GB / T6041-2002 "General Rules for Mass Spectrometry Analysis Methods", gas chromatography and mass spectrometry are coupled. After gas chromatography separates the components in the sample, the components are broken into ion fragments in mass spectrometry and separated according to mass-to-charge ratio (m / z) to form specific mass spectra, obtaining qualitative analysis of each organic component in the electrolyte. Then, the organic components in the electrolyte are separated in the chromatographic column, and detection signal spectra of each component are generated. Component qualitative analysis is performed using retention time, and quantitative analysis is performed by standardizing and correcting peak area, obtaining quantitative analysis of the organic components in the electrolyte. Referring to JY / T-020, the types of anions of electrolyte salts in the electrolyte are detected by ion chromatography and quantitatively analyzed. Referring to JY / T0578-2020, nuclear magnetic resonance spectroscopy (NMR) is used to obtain qualitative and quantitative analysis of the components in the electrolyte.

[0108] In this document, based on the total mass of the electrolyte, the mass content of the chain-like carboxylic acid ester solvent can be calculated by dividing the mass of the detected chain-like carboxylic acid ester solvent by the total mass of the electrolyte sample. The electrolyte referred to in this document can be either fresh electrolyte or electrolyte obtained from the disassembly of a battery cell. Electrolyte obtained from the disassembly of a battery cell can be either the free electrolyte within the battery casing or the electrolyte obtained by centrifugation from the electrodes.

[0109] In some embodiments, based on the total mass of the electrolyte, the mass content of the chain carboxylic acid ester solvent can be selected as 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or any range between the two.

[0110] The addition of chain-like carboxylic acid ester solvents to the electrolyte not only improves the lithium-ion conductivity of the electrolyte but also reduces its viscosity, improves the wetting between the electrolyte and the electrode, and enhances the electrolyte flow across the electrode width. This further increases the lithium-ion transport rate at the solid-liquid interface of the battery cell, reduces the internal resistance of the battery cell, decreases the temperature rise during fast charging, and narrows the internal temperature difference within the battery cell. This allows the battery cell to support a wider positive electrode current collector at the same temperature rise. In the embodiments of this application, the battery cell achieves a balance between fast-charging cycle life and energy density through the cooperation of the electrolyte and the positive electrode current collector.

[0111] In some embodiments, the chain carboxylic acid ester solvent accounts for 7%-60% of the total mass of the electrolyte.

[0112] Chain-like carboxylic acid ester solvents exhibit high reactivity and readily undergo side reactions with negative electrode materials, increasing battery gas production and negatively impacting battery safety. Chain-like carboxylic acid ester solvents within the aforementioned mass content range can control side reactions within a reasonable range, allowing battery cells to achieve both good fast-charge cycle life and energy density while maintaining low gas production levels, thus ensuring battery safety.

[0113] In some embodiments, the electrolyte salt comprises lithium bis(fluorosulfonyl)imide (LiFSI), wherein the mass percentage of lithium bis(fluorosulfonyl)imide is 5%-60% based on the total mass of the electrolyte salt in the electrolyte, and optionally 10%-50%.

[0114] In some embodiments, the mass content of lithium difluorosulfonylimide can be selected as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any range between the two, based on the total mass of electrolyte salts in the electrolyte.

[0115] Lithium difluorosulfonylimide readily dissociates in electrolyte solvents, which is beneficial for improving cell kinetics, reducing internal resistance, and further decreasing heat generation and temperature rise during fast charging, thus mitigating the inconsistent internal temperature rise of cells during fast charging. However, lithium difluorosulfonylimide readily undergoes side reactions with LiC6 formed during deep lithium intercalation at the negative electrode, reducing reversible lithium capacity and negatively impacting the retention of cell capacity during cycling. Electrolytes containing lithium difluorosulfonylimide within the aforementioned mass range can both reduce inconsistent internal temperature rise of cells and maintain side reactions with the negative electrode material at reasonable levels, comprehensively improving the battery's fast-charging cycle life.

[0116] In some embodiments, the mass percentage of the lithium bisfluorosulfonylimide (LiFSI) is 1%-10% based on the total mass of the electrolyte, and optionally 1%-8%.

[0117] In some embodiments, based on the total mass of the electrolyte, the mass content percentage of lithium bisfluorosulfonylimide (LiFSI) can be selected as 1%, 1.5%, 2%, 2.5%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any value range between the two.

[0118] When the mass content of lithium bisfluorosulfonylimide (LiFSI) in the electrolyte is within the above-mentioned range, the fast-charging cycle life of the battery cells can be further improved while taking into account the energy density of the battery cells.

[0119] In some embodiments, the lithium bisfluorosulfonylimide (LiFSI) accounts for 3%-6% of the total mass of the electrolyte.

[0120] When the mass content of lithium bisfluorosulfonylimide (LiFSI) in the electrolyte is within the above range, the battery cell can better balance fast-charging cycle life and low gas production level while maintaining good energy density, thus achieving a balance between fast-charging life and safety performance.

[0121] In some embodiments, the chain carboxylic acid ester solvent includes one or more of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

[0122] The small molecular size of the aforementioned chain-like carboxylic acid ester solvents helps to reduce the viscosity of the electrolyte, increase the wetting rate of the electrolyte, improve electrolyte dynamics, increase the transport rate of charge carriers inside the battery cell, reduce the inconsistency of current density inside the battery, further reduce the phenomenon of inconsistent internal temperature rise of the battery cell during fast charging, and improve the fast charging cycle life of the battery cell.

[0123] In some embodiments, the chain-like carboxylic acid ester solvent includes one or more of ethyl acetate and methyl acetate.

[0124] Compared to other chain carboxylic acid ester solvents, ethyl acetate and methyl acetate have both relatively high kinetic activity and relatively low gas production levels, which is beneficial for further improving the lithium-ion transport rate and reducing the side reaction level of the electrolyte. This reduces the internal temperature difference of the battery cell during fast charging, balances the fast charging cycle life of the battery cell with low gas production levels, and achieves a balance between fast charging life and safety performance.

[0125] In some embodiments, the total mass percentage of ethyl acetate and methyl acetate is 5%-80% based on the total mass of the solvent.

[0126] In some embodiments, the total mass percentage of ethyl acetate and methyl acetate, based on the total mass of the solvent, can be selected as 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any range between the two.

[0127] In some embodiments, the chain carboxylic acid ester solvent includes methyl acetate.

[0128] In some embodiments, the methyl acetate content is 5%-80% based on the total mass of the solvent, optionally 5%-50%.

[0129] In some embodiments, the mass content of methyl acetate, based on the total mass of the solvent, can be selected as 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any range between the two.

[0130] In some embodiments, referring to Figures 7 and 8, the size L2 of the positive electrode film layer 1012 along the width direction X of the positive electrode current collector is 60mm-97mm, and can be 63mm-90mm.

[0131] In some embodiments, the size L2 of the positive electrode film layer 1012 along the width direction X of the positive electrode current collector can be selected as 60mm, 61mm, 62mm, 63mm, 64mm, 65mm, 66mm, 67mm, 70mm, 74mm, 77mm, 80mm, 84mm, 87mm, 90mm, 94mm, 97mm or any value range between the two.

[0132] The size of the positive electrode film layer is within the above range, and matching the size of the positive electrode current collector can further balance the energy density of the battery cell.

[0133] In some embodiments, the positive current collector comprises an aluminum foil with a thickness of 10 μm-16 μm.

[0134] In some embodiments, the thickness of the aluminum foil can be selected as 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm or any value range between the two.

[0135] With the aluminum foil thickness within the aforementioned range, it will not occupy too large a proportion of the battery's mass, nor will it cause excessive internal resistance due to a reduction in the overcurrent area. This reduces heat generation and temperature rise during fast charging, alleviates the inconsistent temperature rise of individual battery cells during fast charging, and balances the energy density and fast charging cycle life of individual battery cells.

[0136] In some embodiments, the thickness of the aluminum foil is 12μm-14μm.

[0137] With the aluminum foil thickness within the aforementioned range, the battery cells further improve the fast-charging cycle life while maintaining energy density.

[0138] In some embodiments, the positive electrode film layer includes a positive electrode active material, which includes lithium iron phosphate and its modified materials.

[0139] In some embodiments, the modified materials for lithium iron phosphate include one or more of lithium iron phosphate coating materials and lithium iron phosphate doping materials.

[0140] In some embodiments, referring to FIG7, the negative electrode 102 includes a negative current collector 1021 and a negative electrode film layer 1022 disposed on at least one side of the negative current collector 1021. The projection of the positive electrode film layer 1012 along the thickness direction Z falls within the range of the negative electrode film layer 1022, and along the width direction X of the negative current collector 1021, the distance L3 between the edge of the negative electrode film layer 1022 and the projected edge of the adjacent positive electrode film layer 1012 is 1mm-4mm.

[0141] In some embodiments, the negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil. Examples of three-dimensional porous current collectors include copper mesh, nickel mesh, copper foam, nickel foam, and aluminum foam. A composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, aluminum, aluminum alloys, silver, and silver alloys. Examples of polymer material substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0142] In some embodiments, the distance between the edge of the negative electrode film and the projected edge of the adjacent positive electrode film along the width direction of the negative electrode current collector can be selected as 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm or any value range between the two.

[0143] During fast charging, significant polarization at the negative electrode can easily cause the lithium intercalation potential to drop below 0V, leading to lithium metal deposition on the negative electrode surface. This deposited lithium metal readily reacts with the electrolyte to form high-resistivity inorganic salts, reducing battery capacity. Ensuring that the projection of the positive electrode film along its thickness falls within the range of the negative electrode film reduces the risk of lithium deposition in individual cells during discharge, improving fast charging performance. Furthermore, it helps control capacity loss caused by excessive lithium ion diffusion into the negative electrode, thus balancing fast charging cycle life.

[0144] In some embodiments, the negative current collector comprises a copper foil with a thickness of 4 μm-6 μm.

[0145] In some embodiments, the thickness of the copper foil may be selected from 4μm, 4.1μm, 4.2μm, 4.3μm, 4.4μm, 4.5μm, 4.6μm, 4.7μm, 4.8μm, 4.9μm, 5μm, 5.1μm, 5.2μm, 5.3μm, 5.4μm, 5.5μm, 5.6μm, 5.7μm, 5.8μm, 5.9μm, 6μm, or any value range between the two.

[0146] With the copper foil thickness within the aforementioned range, it will not occupy too large a proportion of the battery's mass, nor will it cause excessive temperature rise during fast charging, making it difficult for heat to dissipate. This approach can further balance the energy density of individual battery cells and the fast charging cycle life.

[0147] In some embodiments, the one-sided density of the negative electrode film is 0.08 g / 1540.25 mm. 2 -0.20g / 1540.25mm 2 Available in 0.10g / 1540.25mm. 2 -0.16g / 1540.25mm 2 .

[0148] In this application, the areal density of the film layer has a meaning known in the art and can be tested using methods known in the art. For example, take an electrode sheet that has been coated on one side and cold-pressed (if it is a double-sided coated electrode sheet, the film layer on one side can be wiped off first), cut it into small circular pieces with an area of ​​S1, weigh them, and record their weight as M1. Then wipe off the film layer of the electrode sheet after weighing, weigh the current collector, and record it as M0. The areal density of the film layer on one side = (M1-M0) / S1. To ensure the accuracy of the test results, multiple sets (e.g., 10 sets) of samples can be tested, and the average value can be calculated as the test result.

[0149] In some embodiments, the density of the negative electrode film layer on one side can be selected as 0.08 g / 1540.25 mm. 2 0.09g / 1540.25mm 2 0.10g / 1540.25mm 2 0.11g / 1540.25mm 2 0.12g / 1540.25mm 2 0.13g / 1540.25mm 2 0.14g / 1540.25mm 2 0.15g / 1540.25mm 2 0.16g / 1540.25mm 2 0.17g / 1540.25mm 2 0.18g / 1540.25mm 2 0.19g / 1540.25mm 2 0.20g / 1540.25mm 2 Or the range of values ​​between any two.

[0150] It is understandable that the density of the negative electrode film is tested on the negative electrode sheet, and the density of the positive electrode film is tested on the positive electrode sheet.

[0151] Battery cells with a single-sided density of the negative electrode film within the above range can reduce the transport distance of lithium ions in the negative electrode film, match the electrolyte with high conductivity, reduce concentration polarization during fast charging, and improve the fast charging cycle life of the battery cell while taking into account the energy density of the battery cell.

[0152] In some embodiments, the compaction density of the negative electrode sheet is 1.2 g / cm³. 3 -1.9g / cm 3 1.2g / cm³ is an optional value. 3 -1.65g / cm 3 .

[0153] In this application, the compaction density of the negative electrode sheet has a meaning known in the art and can be tested using methods known in the art. The negative electrode sheet is removed from the lithium-ion battery, and a certain area of ​​the electrode sheet is taken. The mass and thickness of the electrode sheet and the current collector after the film layer has been removed are measured respectively. The compaction density of the electrode sheet is calculated according to the following formula: Compaction density of the electrode sheet = (Electrode sheet mass - Current collector mass) / [(Electrode sheet thickness - Current collector thickness) × Electrode sheet area].

[0154] In some embodiments, the compaction density of the negative electrode sheet can be selected as 1.2 g / cm³. 3 1.3g / cm 3 1.35g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 Or the range of values ​​between any two.

[0155] Negative electrode sheets with a compaction density within the above range have suitable porosity, which can be matched with electrolytes with high conductivity, facilitate the transport of lithium ions in the negative electrode, reduce concentration polarization during fast charging, and help improve the fast charging cycle life of battery cells while taking into account the energy density of battery cells.

[0156] In some embodiments, the compaction density of the negative electrode sheet is 1.35 g / cm³. 3 -1.6g / cm 3 .

[0157] In some embodiments, the average thickness of the negative electrode film on one side is 30μm-150μm, and can be selected as 30μm-80μm.

[0158] In some embodiments, the average thickness of one side of the negative electrode film can be selected as 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm or any value range between the two.

[0159] Battery cells with an average thickness of the negative electrode film on one side within the above range can reduce the transport distance of lithium ions in the negative electrode film, match the electrolyte with high conductivity, reduce concentration polarization during fast charging, and improve the fast charging cycle life of the battery cell while taking into account the energy density of the battery cell.

[0160] In some embodiments, the porosity of the negative electrode sheet is 20%-60%, optionally 25%-40%.

[0161] In this application, the porosity of the electrode can be tested using methods known in the art. For example, based on the national standard GB / T24586-2009, the electrode is immersed in ethyl methyl carbonate (EMC) for cleaning; the porosity is determined using a true density meter (American AccuPycII1340) based on the gas displacement method. The porosity is the percentage of pore volume to the total volume of the electrode, calculated using the formula: Porosity = (V - V0) / V × 100%, where V0 is the true volume and V is the apparent volume.

[0162] In some embodiments, the porosity of the negative electrode sheet can be selected as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any value range between the two.

[0163] Negative electrode sheets with porosity within the above range can be matched with electrolytes with high conductivity, improving the diffusion rate of lithium ions in the negative electrode, reducing concentration polarization generated by the battery cell during fast charging, and helping to improve the fast charging cycle life of the battery cell while taking into account the energy density of the battery cell.

[0164] In some embodiments, the porosity of the separator is 25%-55%, optionally 28%-42%.

[0165] In this application, the porosity of the separator can be determined using methods known in the art. As an example, the gas displacement method is used for measurement in accordance with GB / T24586. Porosity ε=(V1-V2) / V1*100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample.

[0166] In some embodiments, the porosity of the isolation membrane may be selected as 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 50%, 55%, or any range between the two.

[0167] Separator membranes with porosity within the aforementioned range are beneficial for improving the liquid phase transport rate of lithium ions and reducing the liquid phase transport resistance of lithium ions, thereby reducing battery impedance, minimizing temperature rise and temperature inconsistency, and allowing for further increases in current collector width and energy density. Simultaneously, the reduced temperature rise can decrease the degree of side reactions between the electrolyte and the negative electrode active material, and reduce gas production. Porosity within the aforementioned range also provides the separator with a certain mechanical strength, while reducing the probability of lithium dendrites piercing the separator and causing short circuits, thus comprehensively improving the fast-charging cycle life of individual battery cells.

[0168] In some embodiments, the porosity of the separator is 30%-42%.

[0169] Separators with porosity within the above range are beneficial for further reducing the temperature rise of the battery and the phenomenon of inconsistent temperature rise, alleviating the technical problems of severe local polarization of the battery and increased risk of lithium plating, and further improving the fast charging cycle life of the battery cells while maintaining certain mechanical properties of the separator.

[0170] In some embodiments, the Gurley value G of the separator is 50s-620s, optionally 250s-610s.

[0171] In this application, the term "Gurley value" is used to characterize the air permeability of the separator membrane, which refers to the time required for 100 mL of air to pass through a 1 square inch separator membrane at a pressure of 1.22 kPa, measured in seconds.

[0172] In this application, the Gurley value of the separator can be tested using any known method. As an example, the time required for 100 mL of air to pass through a 1 square inch separator under a pressure of 1.22 kPa in an air permeability tester is the Gurley value. The average of the test results from multiple (e.g., 3) parallel samples can be taken as the Gurley value of the separator.

[0173] In some embodiments, the Gurley value G of the separator can be selected as 50s, 100s, 150s, 200s, 250s, 260s, 270s, 280s, 290s, 300s, 310s, 320s, 330s, 340s, 350s, 360s, 370s, 380s, 390s, 400s, 410s, 420s, 430s, 440s, 450s, 460s, 470s, 480s, 490s, 500s, 510s, 520s, 530s, 540s, 550s, 560s, 570s, 580s, 590s, 600s, 610s, 620s, or any value range between the two.

[0174] Separators with Gurley values ​​within the aforementioned range are beneficial for reducing the impedance of individual battery cells, minimizing temperature rise and inconsistencies, and allowing for a further increase in the width of the current collector and energy density. Simultaneously, the reduced temperature rise decreases the degree of side reactions between the electrolyte and the negative electrode active material, reducing gas production. A Gurley value within this range also provides the separator with a certain mechanical strength, reducing the probability of lithium dendrites piercing the separator and causing short circuits, thus comprehensively improving the fast-charge cycle life of individual battery cells.

[0175] In some embodiments, the material of the separator may include, but is not limited to, one or more of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0176] In some embodiments, as shown in FIG9, the battery cell includes a wound cell 6, wherein at least one turn of the positive electrode sheet 101 of the wound cell 6 includes at least two positive electrode tabs.

[0177] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative current collector includes a negative current collection portion and a negative electrode tab 1023 disposed on at least one side of the negative current collection portion. At least one turn of the negative electrode sheet of the wound cell includes at least two negative electrode tabs.

[0178] The tabs are connected to the battery casing or external module structure, and current must flow through the tabs to connect to the outside of the battery.

[0179] In some implementations, the tab extending along the width of the current collector means that the tab is located at the end in the height direction of the cell.

[0180] In some embodiments, the wound cell 6, as shown in Figure 9, is a square wound cell.

[0181] In some embodiments, the wound cell 6 is a cylindrical wound cell.

[0182] Please continue to refer to Figure 9. Whether in a square or cylindrical wound cell, one turn of the positive electrode plate refers to the free inward and outward winding direction starting from any point A on the positive electrode plate. That is, after winding around the winding needle in a clockwise direction as shown in Figure 9, the next turn is wound to the point B that is closest to point A.

[0183] In some embodiments, the positive electrode 101 of the wound cell 6 includes at least two, three, four or more consecutive turns, each turn of which includes at least two tabs.

[0184] In the prior art, the positive or negative electrode sheet in the wound cell is usually provided with one tab per turn. The embodiments of this application reduce the overcurrent at the tab by providing at least two tabs on at least one turn of the wound cell electrode sheet, reduce the temperature rise at the tab, and alleviate the phenomenon of uneven current density distribution on the electrode sheet and inconsistent temperature rise inside the battery cell during fast charging, thereby improving the fast charging cycle life of the battery cell.

[0185] In some embodiments, the wound cell 6 is shown in FIG9. The wound cell 6 includes a large surface area 61 and a bending area 62. The positive electrode tab 10112 is disposed in the large surface area 61 of the wound cell 6. The number of positive electrode layers in the wound cell is defined according to the rule that the number of positive electrode layers in the large surface area increases sequentially along the winding direction from the inside to the outside (clockwise direction in FIG9). The positive electrode of the wound cell 6 has at least two consecutive layers, each of which is provided with a positive electrode tab.

[0186] As an example, take the first layer of the large surface area of ​​the positive electrode 101 as the Nth layer of the positive electrode. Following the winding direction from the inside out (clockwise as shown in Figure 9), the positive electrode 101 is wound through the bending area 62 to the large surface area on the opposite side of the Nth layer. This layer of the positive electrode is recorded as the N+1 layer. The winding continues in the winding direction from the inside out. After passing through the bending area on the other side, the positive electrode is wound to the N+2 layer on the same side as the Nth layer. This process is repeated to define the number of layers of the positive electrode 101.

[0187] In some embodiments, the positive electrode sheet of the wound cell has at least three, four, five, six or more consecutive layers, each of which is provided with a positive electrode tab.

[0188] In existing technologies, the tabs in wound battery cells are generally located on layers N, N+2, N+4, etc., with a maximum of one tab every two layers in the electrode sheet. This application's embodiment addresses this by having tabs continuously placed on at least two consecutive layers of the electrode sheet, i.e., on layers N and N+1. This reduces overcurrent and temperature rise at the tabs, mitigating uneven current density distribution on the electrode sheet and inconsistent temperature rise within the battery cell during fast charging, thus improving the fast charging cycle life of the battery cell.

[0189] It is understandable that the tabs in the negative electrode can be set up in the same way as those in the positive electrode.

[0190] In some embodiments, the negative electrode sheet of the wound cell has at least two, three, four, five, six or more consecutive layers, each of which is provided with a negative electrode tab.

[0191] In some embodiments, the battery cell includes a stacked cell, wherein the length of the positive current collector in the stacked cell is 100mm-700mm, and optionally 200mm-600mm.

[0192] In some embodiments, the battery cell includes a stacked cell, wherein the length of the positive current collector in the stacked cell is 100mm, 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, 450mm, 500mm, 550mm, 600mm, 650mm, 700mm or any value between the two.

[0193] During their research, the applicant discovered that the length of the current collector in a laminated battery cell has a crucial impact on the current uniformity and temperature rise consistency during fast charging. Maintaining the length of the positive current collector within the aforementioned range can further improve the inconsistent temperature rise during fast charging and increase the fast charging cycle life of the battery cells.

[0194] In some embodiments, the electrolyte injection coefficient of the battery cell is 2.5g / Ah-3.1g / Ah, and can be optionally 2.6g / Ah-2.9g / Ah.

[0195] The electrolyte filling coefficient of a battery cell refers to the ratio of the mass of electrolyte inside the battery cell to the battery capacity. The electrolyte filling coefficient of a battery cell can be obtained by any method known in the art. For example, the battery cell is weighed, and its mass is denoted as M0. The battery cell is disassembled, and the free electrolyte is poured out. The internal electrode assembly is removed, and the positive electrode, negative electrode, separator, and mechanical parts are separated. The positive electrode, negative electrode, separator, and mechanical parts are immersed and cleaned using dimethyl carbonate (DMC) solvent for 24-48 hours, repeated at least three times. The aforementioned positive electrode, negative electrode, separator, and mechanical parts are placed in a 100°C oven for at least 24 hours until completely dried. The dried positive electrode, negative electrode, separator, and mechanical parts are weighed, and their mass is denoted as M1. Thus, the mass of electrolyte in the battery cell is (M0-M1). The electrolyte filling coefficient is calculated by (M0-M1) / the rated capacity of the battery cell. The rated capacity of a single battery cell is the nominal capacity of the battery, or it can be determined by charging the battery at a 0.33C rate to 3.65V, then charging it at a constant voltage of 3.65V to 0.05C, letting it stand for 10 minutes, and then discharging it at a 0.33C rate to 2.0V. The rated capacity is then determined by the discharge capacity of the single battery cell. It is understandable that, to improve the accuracy of the electrolyte filling coefficient test, it is best to use freshly shipped batteries for testing.

[0196] In some embodiments, the electrolyte injection coefficient of the battery cell can be selected as 2.5g / Ah, 2.6g / Ah, 2.7g / Ah, 2.8g / Ah, 2.9g / Ah, 3g / Ah, 3.1g / Ah or any value range between the two.

[0197] Battery cells with an electrolyte injection coefficient within the above range can improve the wettability between the electrolyte and the electrode, reduce the battery interface resistance, and decrease the battery impedance. This alleviates the phenomenon of inconsistent temperature rise in the current collector during fast charging, and the width of the current collector can be further increased. At the same time, the increase in gas production caused by the side reaction of the electrolyte solvent can be kept within a controllable range, further balancing the battery's fast charging cycle performance, energy density, and safety performance.

[0198] In some implementations, at 25°C, the number of battery cells cycling within the corresponding fast charging window is 2530-2980 cycles.

[0199] The number of battery cycles within the corresponding fast charging window can be obtained by any method known in the art. For example, the fast charging window must first be obtained: the batteries of the above embodiments and comparative examples are charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, this includes: charging the battery at a constant current rate of 1C to a voltage of 3.65V at 35°C, then charging at a constant voltage to a current ≤0.05C, letting it stand for 5 minutes, and then discharging at a constant current rate of 0.33C to a voltage of 2.5V, recording its actual capacity as C0. Then, the battery was sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 until the full battery charging cutoff voltage of 3.65V or the negative terminal cutoff potential of 0V (whichever comes first). After each charging, the battery was discharged at 1C0 until the full battery discharge cutoff voltage of 2.1V. The state of charge (SOC) was recorded at different charging rates until 10%, 20%, 30%, ..., 80%. Charge, or State of Charge, refers to the negative electrode potential at which the battery is fully discharged (SOC = 0) and fully charged (SOC = 100%). By plotting the charge rate-negative electrode potential curves for different SOC states and performing linear fitting, the charge rate corresponding to a negative electrode potential of 0V under different SOC states is obtained. This charge rate is the charging window for that SOC state, denoted as C(10% SOC), C(20% SOC), C(30% SOC), C(40% SOC), C(50% SOC), C(60% SOC), C(70% SOC), and C(80% SOC). The maximum charge rate corresponding to this state of charge is then obtained, i.e., the fast charging window.

[0200] At 25℃, charging was performed using the obtained fast charging window distribution. The charging process involved charging at C(10% SOC) to 10% SOC, C(20% SOC) to 20% SOC, C(30% SOC) to 30% SOC, C(40% SOC) to 40% SOC, C(50% SOC) to 50% SOC, C(60% SOC) to 60% SOC, C(70% SOC) to 70% SOC, and C(80% SOC) to 80% SOC. The charge was then increased to 100% SOC at 0.33C. After resting for 10 minutes, the charge was increased to 2.1V at 0.33C DC. The discharge capacity at this point was recorded as C1. The temperature rise at the tab was monitored during this charging process. The above process was repeated, and the discharge capacity for each cycle was recorded as Cn. The cycle capacity retention rate was calculated as Cn / C1. The number of cycles when the cycle capacity retention rate dropped to 80% SOH was recorded.

[0201] In some implementations, at 25°C, the number of battery cell cycles under the corresponding fast charging window can be selected as 2530 cycles, 2580 cycles, 2620 cycles, 2690 cycles, 2700 cycles, 2750 cycles, 2780 cycles, 2810 cycles, 2850 cycles, 2890 cycles, 2960 cycles, 2980 cycles, or any value range between the two.

[0202] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2530.

[0203] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2580.

[0204] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2620.

[0205] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2690.

[0206] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2700.

[0207] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2750.

[0208] In some implementations, at 25°C, the number of battery cell cycles under the corresponding fast charging window is 2780.

[0209] In some implementations, at 25°C, the number of battery cells cycling within the corresponding fast charging window is 2810.

[0210] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2850.

[0211] In some implementations, at 25°C, the number of battery cell cycles under the corresponding fast charging window is 2890.

[0212] In some implementations, at 25°C, the number of battery cell cycles under the corresponding fast charging window is 2960.

[0213] In some implementations, at 25°C, the number of battery cell cycles under the corresponding fast charging window is 2980.

[0214] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0215] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0216] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0217] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include, but are not limited to, thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0218] 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 negative electrode active materials, negative electrode conductive agents, negative electrode binders, 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.

[0219] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0220] In some embodiments, the positive electrode current collector includes a positive electrode active material. The positive electrode active material may be any positive electrode active material known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0221] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0222] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resins, 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).

[0223] 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.

[0224] In some embodiments, the lithium-containing electrolyte salt may also include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0225] In some embodiments, the solvent may include, but is not limited to, one or more of ester solvents, sulfone solvents, and ether solvents. As an example, the solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0226] In some embodiments, the electrolyte may optionally include other additives.

[0227] The second aspect of this application provides a battery device including the battery cell provided in the first aspect of this application, the battery device including at least one of a battery module, a battery pack, and an energy storage battery.

[0228] Furthermore, a third aspect of this application provides an electrical device, which includes a battery cell provided in the first aspect of this application or a battery device provided in the second aspect of this application. The battery cell, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0229] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0230] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the individual battery cells, a battery pack or battery module can be used.

[0231] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0232] Example

[0233] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0234] I. Preparation Method

[0235] Example 1

[0236] (1) Preparation of negative electrode sheet

[0237] Artificial graphite (negative electrode active material), sodium carboxymethyl cellulose (thickener), styrene-butadiene rubber (SBR) (negative electrode binder), and Super P (negative electrode conductive agent) were mixed in a mass ratio of 96.9:1.1:1.5:0.5. Deionized water was added as a solvent, and the mixture was stirred uniformly under vacuum to prepare a negative electrode slurry. The negative electrode slurry was uniformly coated once or multiple times onto both sides of a copper foil (negative electrode current collector), with a copper foil thickness of 4.5 μm. After drying, a negative electrode film was obtained. The projection of the positive electrode film along its thickness direction fell within the area of ​​the negative electrode film. Along the width direction of the negative electrode current collector, the distance between the edge of the negative electrode film and the projected edge of the adjacent positive electrode film was 3 mm. The film was then cold-pressed and slit to obtain negative electrode sheets. The thickness of the negative electrode film on one side of the negative electrode current collector was 53 μm, and the density of the negative electrode film on one side was 0.131 g / 1540.25 mm². 2 The compaction density of the negative electrode sheet is 1.6 g / cm³. 3 The porosity of the negative electrode sheet is 30%.

[0238] (2) Preparation of positive electrode sheet

[0239] Lithium iron phosphate cathode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to solvent N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5. After thorough mixing, a cathode slurry (solid content 67%) was obtained. The cathode slurry was then uniformly coated onto both sides of a cathode current collector aluminum foil, with a foil thickness of 13 μm and a single-sided coating weight of approximately 350 mg / 1540.25 mm. 2 After drying, a positive electrode film is obtained. The size of the positive electrode film is 84 mm along the width direction of the positive electrode current collector. The film is then cold-pressed and the tabs are cut out on the aluminum foil. The width of the current collector is 87 mm, thus obtaining the positive electrode sheet.

[0240] (3) Preparation of electrolyte

[0241] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl acetate were mixed thoroughly at a mass ratio of 3:2:5, and then additives were added. The additives included vinylene carbonate (VC), fluoroethylene carbonate (FEC), lithium difluorooxalate borate (LiDFOB), and 1,3-propylsulfonate lactone (PS). Based on the total mass of the electrolyte, the mass percentages of VC, FEC, LiDFOB, and PS were 2%, 1%, 0.5%, and 1%, respectively.

[0242] After mixing thoroughly, lithium hexafluorophosphate (LiPF6) and LiFSI are added to dissolve them in the organic solvent. Based on the total mass of the electrolyte, the mass percentage of LiPF6 is 9% and the mass percentage of LiFSI is 5%. The mixture is stirred thoroughly to obtain the electrolyte.

[0243] (4) Preparation of the separating membrane

[0244] Commercially available polyethylene film is used as the separator. The surface of the separator facing the positive electrode is coated with a ceramic coating containing Al2O3 and PVDF binder. The separator has a porosity of 36% and a Gurley value of 601s.

[0245] (5) Preparation of battery cells

[0246] The positive electrode (current collector width 87mm, length 270mm), the separator (width 98mm), and the negative electrode (current collector width 90mm) are stacked in sequence, so that the separator is placed between the positive and negative electrodes to play a role in isolation. Then, the electrode is wound to obtain the battery cell, so that each layer of the positive and negative electrodes in the wound battery cell is provided with tabs.

[0247] The battery cell is placed in the battery casing, dried, and then injected with electrolyte. The lithium-ion battery is then produced through processes such as formation and settling.

[0248] The capacity and electrolyte mass of the prepared lithium-ion battery were tested, and the electrolyte injection coefficient was calculated to be 3.0 g / Ah.

[0249] The preparation methods of Examples 2-11 are basically the same as those of Example 1, except that the corresponding parameters of the battery cells are adjusted, as shown in Table 1.

[0250] In Example 2, the width of the positive current collector is 63 mm, the width of the positive electrode film is 60 mm, the width of the negative current collector is 63 mm, and the width of the negative electrode film is 63 mm.

[0251] In Example 3, the width of the positive current collector is 97 mm, the width of the positive electrode film is 94 mm, the width of the negative current collector is 97 mm, and the width of the negative electrode film is 97 mm.

[0252] In Example 4, the electrolyte solvents were ethylene carbonate (EC), ethyl methyl carbonate (EMC), and ethyl acetate, with a solvent mass ratio of 3:2:5.

[0253] In Example 5, the electrolyte solvent was ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl acetate in a mass ratio of 3:6:1.

[0254] In Example 6, the electrolyte solvent was ethylene carbonate (EC) and methyl acetate in a mass ratio of 24:76.

[0255] In Example 7, the electrolyte salt content in the electrolyte was adjusted so that, based on the total mass of the electrolyte, the mass content of LIFSI was 1% and the mass content of LiPF6 was 13%.

[0256] In Example 8, the electrolyte salt content in the electrolyte was adjusted so that, based on the total mass of the electrolyte, the mass content of LIFSI was 8% and the mass content of LiPF6 was 6%.

[0257] In Example 9, the number of tabs is adjusted so that one tab is provided for every two layers of the positive and negative electrode sheets in the wound cell.

[0258] In Example 10, the thickness of the aluminum foil in the positive current collector was adjusted to 10 μm.

[0259] In Example 11, the porosity of the separator was adjusted to 28%.

[0260] The preparation method of Comparative Example 1 is basically the same as that of Example 9, except that methyl acetate solvent is not added to the electrolyte.

[0261] The preparation method of Comparative Example 2 is basically the same as that of Example 9, except that the corresponding parameters of the battery cell are adjusted. The width of the positive current collector is 110 mm and the length is 270 mm. The width of the positive electrode film is 107 mm. The width of the negative current collector is 110 mm and the width of the negative electrode film is 110 mm.

[0262] II. Performance Testing

[0263] 1) Battery fast charging temperature rise and fast charging cycle life test

[0264] First, a fast charging window needs to be obtained: The batteries of the above embodiments and comparative examples are charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, at 35°C, the battery is charged at a constant current rate of 1C to a voltage of 3.65V, then charged at a constant voltage rate to a current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.5V. Its actual capacity is recorded as C0. Then, the battery was sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 until the full battery charging cutoff voltage of 3.65V or the negative terminal cutoff potential of 0V (whichever comes first). After each charging, the battery was discharged at 1C0 until the full battery discharge cutoff voltage of 2.1V. The state of charge (SOC) was recorded at different charging rates until 10%, 20%, 30%, ..., 80%. Charge, or State of Charge, refers to the negative electrode potential at which the battery is fully discharged (SOC = 0) and fully charged (SOC = 100%). By plotting the charge rate-negative electrode potential curves for different SOC states and performing linear fitting, the charge rate corresponding to a negative electrode potential of 0V under different SOC states is obtained. This charge rate is the charging window for that SOC state, denoted as C(10% SOC), C(20% SOC), C(30% SOC), C(40% SOC), C(50% SOC), C(60% SOC), C(70% SOC), and C(80% SOC). The maximum charge rate corresponding to this state of charge is then obtained, i.e., the fast charging window.

[0265] At 25℃, charging was performed using the obtained fast charging window distribution. The charging process involved charging at C(10% SOC) to 10% SOC, C(20% SOC) to 20% SOC, C(30% SOC) to 30% SOC, C(40% SOC) to 40% SOC, C(50% SOC) to 50% SOC, C(60% SOC) to 60% SOC, C(70% SOC) to 70% SOC, and C(80% SOC) to 80% SOC. The charge was then increased to 100% SOC at 0.33C. After resting for 10 minutes, the charge was increased to 2.1V at 0.33C DC. The discharge capacity at this point was recorded as C1. The temperature rise at the tab was monitored during this charging process. The above process was repeated, and the discharge capacity for each cycle was recorded as Cn. The cycle capacity retention rate was calculated as Cn / C1. The number of cycles when the cycle capacity retention rate dropped to 80% SOH was recorded.

[0266] 2) Battery thermal chamber safety test

[0267] The battery cell is first fully charged to its designed upper limit voltage of 3.65V. The cell, with its clamp, is then charged, and its mass (m1) is recorded. The cell is placed in a temperature chamber, and the temperature is increased from room temperature at a rate of 2°C / min until it reaches 100°C. This temperature is maintained for 1 hour, then increased at a rate of 5°C / min, maintaining each 5°C temperature for 30 minutes, until the cell fails (smoke or fire upon valve opening). The test is then stopped, and the cell is allowed to cool to room temperature. The mass (m2) of the cell at this point is recorded. The weight loss rate of the cell is calculated as 1 - (m2 / m1). A higher weight loss rate indicates a greater amount of easily ejected byproducts from the cell, resulting in poorer safety performance.

[0268] Table 1

[0269] As can be seen from the comparison of the examples and comparative examples, the width of the positive electrode current collector in the battery cell is 62mm-98mm, and the lithium-ion conductivity of the electrolyte is 10mS / cm-25mS / cm, which is beneficial to improving the fast-charging cycle life of the battery while maintaining a good energy density.

[0270] Table 2

[0271] As can be seen from the comparison of Examples 1 and 4-6, based on the total mass of the electrolyte, when the mass content of the chain carboxylic acid ester solvent is 7%-60%, the battery cell can achieve both energy density and fast-charging cycle life while also having a low gas production level and high safety performance.

[0272] Table 3

[0273] As can be seen from the comparison of Examples 1 and 7-8, based on the total mass of the electrolyte, when the mass ratio of lithium bisfluorosulfonylimide (LiFSI) is 3%-6%, the battery cell can better balance fast-charging cycle life and low gas production level while maintaining good energy density, thus achieving a balance between fast-charging life and safety performance.

[0274] Table 4

[0275] As can be seen from the comparison of Examples 1 and 10, when the thickness of the aluminum foil is 12μm-14μm, the battery cell can further improve the fast charging cycle life while maintaining a certain energy density.

[0276] Table 5

[0277] As can be seen from the comparison of Examples 1 and 11, when the porosity of the separator is 30%-42%, the battery cells can further improve the fast charging cycle life while maintaining high safety.

[0278] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized by, It includes a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode; The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the surface of the positive current collector. The positive current collector includes a positive current collector portion and a positive electrode tab disposed on at least one side of the positive current collector portion. The width of the positive current collector portion is 62mm-98mm. The lithium-ion conductivity of the electrolyte is 10 mS / cm-25 mS / cm.

2. The battery cell of claim 1, wherein, The battery cell includes stacked cells, and the lithium-ion conductivity of the electrolyte is 10mS / cm-20mS / cm.

3. The battery cell according to claim 1 or 2, characterized in that, The electrolyte comprises a solvent and an electrolyte salt. The solvent includes a chain-like carboxylic acid ester solvent, and the chain-like carboxylic acid ester solvent accounts for more than or equal to 5% of the total mass of the electrolyte.

4. The battery cell according to any one of claims 1 to 3, characterized in that, Based on the total mass of the electrolyte, the chain carboxylic acid ester solvent accounts for 7%-75% of the total mass.

5. The battery cell according to any one of claims 1 to 4, characterized in that, Based on the total mass of the electrolyte, the chain carboxylic acid ester solvent accounts for 7%-60% of the total mass.

6. The battery cell of claim 3, wherein, The electrolyte salt includes lithium bisfluorosulfonylimide, and the mass percentage of lithium bisfluorosulfonylimide is 5%-60% based on the total mass of the electrolyte salt in the electrolyte.

7. The battery cell of claim 6, wherein, Based on the total mass of electrolyte salts in the electrolyte, the mass percentage of lithium difluorosulfonyl imide is 10%-50%.

8. The battery cell according to claim 6 or 7, characterized in that Based on the total mass of the electrolyte, the mass percentage of lithium bisfluorosulfonamide is 1%-10%.

9. The battery cell of any one of claims 6 to 8, wherein, Based on the total mass of the electrolyte, the mass percentage of the lithium bis(fluorosulfonyl)imide is 1%-8%.

10. The battery cell according to any one of claims 6 to 9, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the lithium bis(fluorosulfonyl)imide is 3%-6%.

11. The battery cell of claim 3, wherein, The chain-like carboxylic acid ester solvents include one or more of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

12. The battery cell of claim 3, wherein, The chain-like carboxylic acid ester solvent includes one or more of ethyl acetate and methyl acetate, and the total mass percentage of ethyl acetate and methyl acetate is 5%-80% based on the total mass of the solvent.

13. The battery cell of claim 3, wherein, The chain-like carboxylic acid ester solvent includes methyl acetate, and the methyl acetate content is 5%-80% based on the total mass of the solvent.

14. The battery cell of claim 13, wherein, The methyl acetate content is 5%-50% based on the total mass of the solvent.

15. The battery cell of any one of claims 1 to 14, wherein, Along the width direction of the positive current collector, the size of the positive electrode film is 60mm-97mm.

16. The battery cell of claim 15, wherein, Along the width direction of the positive current collector, the size of the positive electrode film is 63mm-90mm.

17. The battery cell of any one of claims 1 to 16, wherein, The positive current collector includes an aluminum foil with a thickness of 10μm-16μm.

18. The battery cell of claim 17, wherein, The thickness of the aluminum foil is 12μm-14μm.

19. The battery cell of any one of claims 1-18, wherein, The positive electrode film layer includes a positive electrode active material, which includes lithium iron phosphate and its modified materials.

20. The battery cell of any one of claims 1-19, wherein, The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The projection of the positive electrode film layer along the thickness direction falls within the range of the negative electrode film layer, and along the width direction of the negative current collector, the distance between the edge of the negative electrode film layer and the projected edge of the adjacent positive electrode film layer is 1mm-4mm.

21. The battery cell of claim 20, wherein, The negative electrode current collector includes a copper foil with a thickness of 4μm-6μm.

22. The battery cell of claim 20, wherein, The single side surface density of the negative electrode film layer is 0.08 g / 1540.25 mm 2 -0.20 g / 1540.25 mm 2 .

23. The battery cell of claim 20, wherein, The single side surface density of the negative electrode film layer is 0.10 g / 15 40.25 mm 2 -0.16 g / 15 40.25 mm 2 .

24. The battery cell of any one of claims 1-23, wherein, The compacted density of the negative electrode sheet is 1.2 g / cm 3 -1.9 g / cm 3 .

25. The battery cell of any one of claims 1-24, wherein, The compacted density of the negative electrode sheet is 1.2 g / cm 3 -1.65 g / cm 3 .

26. The battery cell of any one of claims 1-25, wherein, The compacted density of the negative electrode sheet is 1.35 g / cm 3 -1.6 g / cm 3 .

27. The battery cell of claim 20, wherein, The average thickness of the negative electrode film on one side is 30μm-150μm.

28. The battery cell of claim 20, wherein, The average thickness of the negative electrode film on one side is 30μm-80μm.

29. The battery cell of any one of claims 1-28, wherein, The porosity of the negative electrode sheet is 20%-60%.

30. The battery cell of any one of claims 1-29, wherein, The porosity of the negative electrode sheet is 25%-40%.

31. The battery cell of any one of claims 1-30, wherein, The porosity of the isolation membrane is 25%-55%.

32. The battery cell of any one of claims 1-31, wherein, The porosity of the isolation membrane is 28%-42%.

33. The battery cell of any one of claims 1-32, wherein, The porosity of the isolation membrane is 30%-42%.

34. The battery cell of any one of claims 1-33, wherein, The Gurley value G of the separator is 50s-620s. The Gurley value refers to the time required for 100mL of air to pass through a 1 square inch separator under a pressure of 1.22kPa when the separator is placed in an air permeability tester. The unit is seconds.

35. The battery cell of claim 34, wherein, The Gurley value G of the isolation membrane is 250s-610s.

36. The battery cell of claim 1, wherein, The battery cell includes a wound cell, and at least one turn of the positive electrode sheet of the wound cell includes at least two positive electrode tabs.

37. The battery cell of claim 36, wherein, The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative current collector includes a negative current collection portion and a negative electrode tab disposed on at least one side of the negative current collection portion. At least one turn of the negative electrode sheet of the wound cell includes at least two negative electrode tabs.

38. The battery cell of claim 36 or 37, wherein, The wound cell includes a large surface area and a bending area. The positive electrode tab is disposed in the large surface area of ​​the wound cell. The number of positive electrode layers in the wound cell is defined according to the rule that the number of positive electrode layers in the large surface area increases sequentially along the winding direction from the inside to the outside. The positive electrode of the wound cell has at least two consecutive layers, each of which is provided with a positive electrode tab.

39. The battery cell of claim 1, wherein, The battery cell includes a stacked cell, and the length of the positive current collector in the stacked cell is 100mm-700mm.

40. The battery cell of claim 39, wherein, The length of the positive current collector in the laminated cell is 200mm-600mm.

41. The battery cell of any one of claims 1-40, wherein, The electrolyte injection coefficient of the battery cell is 2.5 g / Ah-3.1 g / Ah.

42. The battery cell of any one of claims 1-41, wherein, The electrolyte injection coefficient of the battery cell is 2.6 g / Ah-2.9 g / Ah.

43. The battery cell of any one of claims 1-42, wherein, At 25℃, the number of battery cells in the corresponding fast charging window is 2530-2980 cycles.

44. A battery device, comprising: The battery device includes any one of the battery cells according to claims 1 to 43, and the battery device includes at least one of the following: battery module, battery pack, and energy storage battery.

45. An electrical device, comprising: Includes the battery cell according to any one of claims 1 to 43 or the battery device according to claim 44.

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