Battery cell, battery device, and electric device

Abstract

The present application discloses a battery cell, a battery device, and an electric device. The battery cell comprises a positive electrode sheet, a negative electrode sheet, an electrolytic solution, and a separator disposed between the positive electrode sheet and the negative electrode sheet; the electrolytic solution comprises a solvent and an electrolyte salt, the electrolyte salt comprises lithium bis(fluorosulfonyl)imide, and based on the total mass of the electrolytic solution, the mass content of the lithium bis(fluorosulfonyl)imide is 1%-6%; the solvent comprises a chain carboxylic ester solvent, and based on the total mass of the electrolytic solution, the mass content of the chain carboxylic ester solvent is 5%-75%; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the degree of graphitization of the negative electrode active material is 90%-96%.

Description

Battery cells, battery packs, and electrical devices

[0001] Cross-references

[0002] This application incorporates Chinese Patent Application No. 202411606713.2, 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 technology, and in particular 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 higher fast-charging performance, cycle performance, and safety performance of individual battery cells, how to simultaneously achieve a comprehensive improvement in battery performance 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 issues, and its purpose is to provide a battery cell that has both good fast charging performance and safety performance.

[0007] The first aspect of this application provides a battery cell, the battery cell comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode; the electrolyte comprises a solvent and an electrolyte salt, the electrolyte salt comprising lithium bisfluorosulfonylimide, the lithium bisfluorosulfonylimide comprising 1%-6% by mass based on the total mass of the electrolyte; the solvent comprises a chain-like carboxylic acid ester solvent, the chain-like carboxylic acid ester solvent comprising 5%-75% by mass based on the total mass of the electrolyte; the negative electrode comprises a negative current collector and a negative electrode film disposed on at least one side of the negative current collector, the negative electrode film comprising a negative electrode active material, the graphitization degree of the negative electrode active material being 90%-96%; the positive electrode comprises a positive current collector and a positive electrode film disposed on at least one side of the positive current collector, the positive current collector comprising an aluminum foil, the aluminum foil having a thickness of 10μm-16μm.

[0008] During the research process, the applicant discovered that negative electrode active materials with graphitization within the above-mentioned range, when combined with an electrolyte containing chain-like carboxylic acid ester solvents and lithium difluorosulfonyl imide, can reduce the probability of side reactions occurring at high temperatures between the electrolyte and the defect sites of the negative electrode active material. It can also reduce the degree of side reactions between lithium difluorosulfonyl imide and the deeply lithium-intercalated negative electrode active material. Furthermore, by achieving a certain degree of disorder in the negative electrode active material and matching the lithium-ion solid-liquid transport rate with the liquid phase transport rate through the chain-like carboxylic acid ester solvent, it can promote the rapid insertion and extraction of lithium ions in the negative electrode active material, thus achieving a balance between fast-charging performance, safety performance, and high-temperature cycle life of the battery cell.

[0009] In any embodiment, the lithium bis(fluorosulfonyl)imide accounts for 1.5%-5% of the total mass of the electrolyte.

[0010] Based on the total mass of the electrolyte, the mass ratio of lithium bis(fluorosulfonyl)imide within the above-mentioned range is beneficial to further improve battery safety while maintaining good fast-charging performance and high-temperature cycle life.

[0011] In any embodiment, the chain carboxylic acid ester solvent accounts for 10%-65% of the total mass of the electrolyte.

[0012] Based on the total mass of the electrolyte, a mass ratio of chain carboxylic acid ester solvents within the above range is beneficial for balancing the fast-charging performance and high-temperature cycle life of individual battery cells.

[0013] In any embodiment, the degree of graphitization of the negative electrode active material is 92%-95%.

[0014] In any embodiment, the mass percentage of lithium difluorosulfonylimide is 10%-50% based on the total mass of electrolyte salts in the electrolyte.

[0015] When the mass percentage of lithium difluorosulfonylimide in the electrolyte salt is within the above range, it can reduce the amount of chain carboxylic acid ester solvents to a certain extent, reduce the production of hydrogen fluoride in the battery during high-temperature cycling, and alleviate the reaction with the deeply lithium-intercalated negative electrode active material, thus working together to improve the high-temperature cycling performance and safety performance of the battery cell.

[0016] 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.

[0017] The aforementioned chain-like carboxylic acid ester solvent molecules have high lithium-ion conductivity. Compared with other chain-like carboxylic acid ester solvents, only a small amount needs to be added to achieve high lithium-ion conductivity. While improving the fast-charging performance of battery cells, it can effectively control the degree of side reactions between the electrolyte and the negative electrode active material, so that the battery cells can further improve cycle stability while maintaining good fast-charging performance.

[0018] In any embodiment, 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, optionally 10%-70%.

[0019] Ethyl acetate and methyl acetate have better kinetic activity and relatively lower gas production levels compared to other carboxylic acid ester solvents. This is beneficial for further improving the lithium-ion transport rate and reducing the level of side reactions between the electrolyte and the negative electrode at high temperatures, thus balancing the fast-charging performance and high-temperature cycle stability of the battery cells.

[0020] In any embodiment, the chain carboxylic acid ester solvent includes methyl acetate, and the methyl acetate content is 5%-80% by mass based on the total mass of the solvent, optionally 5%-50%, and further optionally 10%-40%.

[0021] In any embodiment, the solvent further includes a carbonate solvent, which includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0022] In any embodiment, the solvent comprises ethylene carbonate, and the mass content of ethylene carbonate is 15%-35% based on the total mass of the solvent.

[0023] Ethylene carbonate has a high dielectric constant, which is beneficial for improving the solubility of lithium salts in the electrolyte, increasing the lithium ion concentration in the electrolyte, improving the electrolyte conductivity, and enhancing the fast-charging performance of the battery. Simultaneously, ethylene carbonate exhibits good film-forming properties, which helps improve the quality of the SEI film on the negative electrode surface, reduce the degree of side reactions between the carboxylic acid ester and the negative electrode, and improve the cycle life of the battery.

[0024] In any embodiment, the solvent comprises dimethyl carbonate, and the mass content of dimethyl carbonate is 5%-50% based on the total mass of the solvent.

[0025] Dimethyl carbonate (DMC) exhibits good electrical conductivity and gas generation properties. Adding DMC to the electrolyte can appropriately reduce the amount of carboxylic acid esters in the electrolyte, thereby reducing the degree of side reactions between carboxylic acid esters and the negative electrode, and improving the battery's cycle life while maintaining its fast-charging performance.

[0026] In any embodiment, the negative current collector comprises a copper foil with a thickness of 4μm-6μm, optionally 4μm-5μm.

[0027] Within the aforementioned range, the thickness of the copper foil can reduce the battery's internal resistance and the heat generated by individual battery cells during fast charging by increasing the thickness of the current collector, thereby enabling individual battery cells to withstand higher charging currents and improving the battery's fast charging performance and safety performance. Furthermore, the thinner current collector can increase the battery's energy density, thus balancing the fast charging performance and energy density of individual battery cells.

[0028] 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 .

[0029] 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 the concentration polarization generated by the battery cell during fast charging, and enable the battery cell to withstand a larger charging current, which is beneficial to improving the fast charging performance and safety performance of the battery cell.

[0030] 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 optional value. 3 -1.65g / cm 3 .

[0031] Negative electrode sheets with a compaction density within the above range have suitable porosity, which can be matched with electrolytes with high conductivity, improve the diffusion rate of lithium ions in the negative electrode, reduce concentration polarization during fast charging, and enable battery cells to withstand larger charging currents, which is beneficial to improving the fast charging performance and safety performance of battery cells.

[0032] In any embodiment, the compaction density of the negative electrode sheet is 1.35 g / cm³. 3 -1.6g / cm 3 .

[0033] 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.

[0034] 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 the concentration polarization generated by the battery cell during fast charging, and enable the battery cell to withstand a larger charging current, which is beneficial to improving the fast charging performance and safety performance of the battery cell.

[0035] In any embodiment, the porosity of the negative electrode sheet is 20%-60%, optionally 25%-40%.

[0036] Negative electrode sheets with porosity within the above range can be matched with electrolytes with high conductivity, thereby increasing the diffusion rate of lithium ions in the negative electrode, reducing concentration polarization generated by the battery cell during fast charging, and enabling the battery cell to withstand a larger charging current, which is beneficial to improving the fast charging performance and safety performance of the battery cell.

[0037] In any embodiment, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, wherein the positive current collector includes an aluminum foil with a thickness of 10 μm-16 μm.

[0038] Within the aforementioned range, the thickness of the aluminum foil can reduce the battery's internal resistance and the heat generated by individual battery cells under high-rate charging and discharging by adjusting the current collector thickness, thereby improving the battery's fast-charging performance and safety performance. Furthermore, it can increase the battery's energy density by thinning the current collector, thus balancing the fast-charging performance and energy density of individual battery cells.

[0039] In any embodiment, the thickness of the aluminum foil is 11 μm-14 μm.

[0040] The thickness of the aluminum foil within the above range can further improve the current carrying capacity of the current collector, alleviate the uneven current density distribution on the electrode and the inconsistent temperature rise inside the battery cell during fast charging, so that the fast charging performance can be maintained in long-term fast charging cycles and improve the fast charging cycle life of the battery cell.

[0041] In any embodiment, the positive electrode film layer includes a positive electrode active material, which includes lithium iron phosphate and its modified materials.

[0042] In any embodiment, the porosity of the isolation membrane is 25%-55%, optionally 28%-42%.

[0043] Separating 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. Therefore, the amount of chain carboxylic acid ester solvents required to achieve the same lithium ion liquid phase transport rate can be reduced, allowing battery cells to further balance fast charging performance and cycle stability.

[0044] In any embodiment, the porosity of the isolation membrane is 28%-42%.

[0045] The porosity of the separator within the above range is beneficial to further improve the liquid phase transport rate of lithium ions, alleviate the uneven current density distribution on the electrode during fast charging and the inconsistent temperature rise inside the battery cell during fast charging, so that the fast charging performance can be maintained in long-term fast charging cycles and the fast charging cycle life of the battery cell can be improved.

[0046] In any embodiment, the Gurley value G of the separator is 50s-620s, optionally 300s-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.

[0047] Separators with Gurley values ​​within the above range are beneficial for improving the liquid phase transport rate of lithium ions, thereby reducing the amount of chain carboxylic acid ester solvents required to achieve the same liquid phase transport rate of lithium ions, allowing battery cells to further balance fast charging performance and cycle stability.

[0048] In any embodiment, the separator includes a base membrane and a ceramic coating, wherein the ceramic coating is disposed only on the positive electrode side of the base membrane.

[0049] The main component of the ceramic coating is ceramic particles. These particles are flame-retardant and have high hardness, making them resistant to deformation under heat. Therefore, the ceramic coating helps improve the mechanical strength of the separator and reduces the probability of lithium dendrites, which can easily form during fast charging, piercing the separator and causing internal short circuits and thermal runaway. Applying the ceramic coating only to the positive electrode side of the base film can balance the fast-charging performance and safety of the individual battery cells.

[0050] In any embodiment, the ceramic coating comprises ceramic particles, which include one or more of alumina, boehmite, silicon oxide, titanium oxide, magnesium oxide, calcium oxide, zinc oxide, zirconium oxide, and tin oxide, and may be selected as one or more of alumina and boehmite.

[0051] In any embodiment, the ceramic coating further includes an adhesive, which includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyacrylamide, and polyvinyl alcohol, and may be selected as polyvinylidene fluoride.

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

[0053] In any embodiment, the battery cell includes a wound cell, 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, and at least one turn of the positive electrode sheet of the wound cell includes at least two positive electrode tabs.

[0054] In existing technologies, the positive or negative electrode sheet in a wound battery cell typically has 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 sheet. This reduces the degree of side reactions between the carboxylic acid ester solvent in the electrolyte and lithium bis(fluorosulfonyl)imide and the negative electrode. Simultaneously, it allows the battery cell to withstand higher charging currents, further improving the fast-charging performance and safety of the battery cell. Furthermore, providing at least two tabs on at least one turn of the wound cell electrode sheet alleviates uneven current density distribution on the electrode sheet and inconsistent temperature rise within the battery cell during fast charging, allowing fast-charging performance to be maintained during long-term fast-charging cycles and improving the fast-charging cycle life of the battery cell.

[0055] 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.

[0056] 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. 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 at the tabs, decreases temperature rise at the tabs, and reduces the degree of side reactions between the carboxylic acid ester solvent in the electrolyte and lithium difluorosulfonylimide and the negative electrode. Simultaneously, it allows the battery cell to withstand higher charging currents, further improving the fast-charging performance and safety of the battery cell. Furthermore, placing at least two tabs on at least one turn of the wound cell electrode sheet alleviates uneven current density distribution on the electrode sheet and inconsistent temperature rise within the battery cell during fast charging, allowing fast-charging performance to be maintained during long-term fast-charging cycles and further improving the cycle life of the battery cell.

[0057] In any embodiment, the electrolyte injection coefficient of the battery cell is 2.5g / Ah-3.2g / Ah, and can be selected as 2.8g / Ah-3.0g / Ah.

[0058] Battery cells with an electrolyte injection coefficient within the above range can keep the side reactions between the chain carboxylic acid ester solvent and the negative electrode active material at a low level, thus ensuring the battery's cycle life. They can also improve the wettability between the electrolyte and the electrode, reduce the battery interface resistance, decrease the battery impedance, and further improve the battery's fast charging performance.

[0059] In any implementation, at 25°C, the number of battery cells in the corresponding fast charging window is 2620-2850 cycles.

[0060] In any embodiment, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 13.5 min to 19.9 min.

[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 schematic diagram of a wound battery cell according to an embodiment of this application.

[0070] 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; 101 Positive electrode sheet; 102 Negative electrode sheet; 10112 Positive electrode tab; 1023 Negative electrode tab. Detailed Implementation

[0071] 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 those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0077] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] In some implementations, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0083] 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.

[0084] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0085] 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.

[0086] 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.

[0087] The battery provided in this application embodiment may include a lithium-ion battery.

[0088] A single battery cell includes electrode components and an electrolyte.

[0089] 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).

[0090] 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.

[0091] 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.

[0092] To improve the kinetic performance of battery cells, it is usually necessary to add chain carboxylic acid ester solvents to the electrolyte to increase the ion transport rate of the electrolyte. However, carboxylic acid ester solvents have high reactivity and are particularly prone to side reactions with negative electrode active materials at high temperatures, which deteriorates the cycle life of the battery. How to balance the fast charging performance and cycle life of the battery is a technical problem that urgently needs to be solved in this field.

[0093] To address the aforementioned issues, this application provides a battery cell comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive and negative electrodes. The electrolyte comprises a solvent and an electrolyte salt, wherein the electrolyte salt comprises lithium bis(fluorosulfonyl)imide, and the lithium bis(fluorosulfonyl)imide comprises 1%-6% of the total mass of the electrolyte. The solvent comprises a chain-like carboxylic acid ester solvent, and the chain-like carboxylic acid ester solvent comprises 5%-75% of the total mass of the electrolyte. The negative electrode comprises a negative current collector and a negative electrode film disposed on at least one side of the negative current collector, the negative electrode film comprising a negative active material having a graphitization degree of 90%-96%. The positive electrode comprises a positive current collector and a positive electrode film disposed on at least one side of the positive current collector, the positive current collector comprising an aluminum foil having a thickness of 10μm-16μm.

[0094] 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 components and contents 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). Exemplarily, referring to GB / T-9722-2006 / GB / T6041-2002, gas chromatography and mass spectrometry are used. After separating the components in the sample by gas chromatography, each component is broken into ion fragments in mass spectrometry, separated according to mass-to-charge ratio (m / z) to form a specific mass spectrum, obtaining qualitative analysis of each organic component in the electrolyte. Then, the organic components in the electrolyte are separated in the chromatographic column, generating detection signal spectra for each component. Component qualitative analysis is performed using retention time, and quantitative analysis is achieved by standardizing and correcting peak area, obtaining quantitative analysis of the organic components in the electrolyte. Referring to JY / T-020, ion chromatography was used to detect and quantify the anions of electrolyte salts in the electrolyte. Referring to JY / T 0578-2020, nuclear magnetic resonance spectroscopy (NMR) was used to obtain qualitative and quantitative analysis of the components in the electrolyte.

[0095] In this document, based on the total mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide (LiFSI) can be calculated by dividing the detected mass of lithium bis(fluorosulfonyl)imide (LiFSI) by the total mass of the electrolyte sample. The electrolyte referred to in this document can be either fresh electrolyte or electrolyte obtained from disassembling a battery cell. Electrolyte obtained from disassembling a battery cell can be either free electrolyte within the battery casing or electrolyte obtained by centrifugation from the electrodes.

[0096] In some embodiments, based on the total mass of the electrolyte, the mass percentage of lithium bis(fluorosulfonyl)imide (LiFSI) can be selected as 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3 ... 0.2%, 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%, or any range between two of these values.

[0097] In this application, chain carboxylic acid ester solvents refer to linear organic solvents containing carboxylic acid ester groups.

[0098] In this paper, based on the total mass of the electrolyte, the mass content of the chain carboxylic acid ester solvent can be calculated by dividing the mass of the detected chain carboxylic acid ester solvent by the total mass of the electrolyte sample.

[0099] In some embodiments, based on the total mass of the electrolyte, the mass percentage of the chain carboxylic acid ester solvent can be selected as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or any range between the two.

[0100] 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).

[0101] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be a graphite negative electrode active material.

[0102] In this paper, the term "degree of graphitization" macroscopically characterizes the proportion of a material that achieves a complete graphite crystal structure; microscopically, it refers to the degree to which the carbon structure in different transition states approaches an ideal graphite crystal.

[0103] The degree of graphitization in graphite anode active materials reflects the integrity of the graphite crystal structure, that is, the regularity of the carbon atom arrangement in the graphite structure. High graphitization indicates small interlayer spacing, smaller lattice rotation, less random stacking of layers, and a more ordered arrangement, resulting in high specific capacity and facilitating the production of high-energy-density battery cells. Low graphitization indicates high graphite disorder and large interlayer spacing, which is beneficial for rapid insertion / extraction of active ions, less expansion during lithium insertion, and shallow charge / discharge effects, thus improving battery kinetic performance.

[0104] In this application, the degree of graphitization of the graphite anode active material can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be performed with reference to JISK 0131-1996 and JB / T 4220-2011, to obtain the average interlayer spacing d of the C(002) crystal plane in the material's crystal structure. 002 Then, according to the formula g = (0.344 - d) 002 The degree of graphitization is calculated as d / (0.344-0.3354)×100%. In the above formula, d... 002 It is the average interlayer spacing of the C(002) crystal plane in the material crystal structure, expressed in nanometers (nm).

[0105] In some embodiments, the degree of graphitization of the negative electrode active material can be selected as 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, or any value range between the two.

[0106] 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 electrolyte flow across the electrode width, increases the lithium-ion transport rate at the solid-liquid interface of the battery cell, reduces the internal resistance of the battery cell, and improves the battery's fast-charging performance. However, chain-like carboxylic acid ester solvents have high reactivity, especially readily reacting with the negative electrode active material at high temperatures, leading to gas generation in the battery and deteriorating its high-temperature cycle life. Lithium bis(fluorosulfonyl)imide (LiFSI) readily dissociates in the electrolyte solvent, which is beneficial for further improving the lithium-ion transport rate in the battery. Therefore, adding a certain amount of LiFSI to the chain-like carboxylic acid ester solvent can reduce the amount of chain-like carboxylic acid ester solvent used in the electrolyte while maintaining the battery's fast-charging performance, thus reducing the degree of side reactions of the chain-like carboxylic acid ester solvent. At the same time, LiFSI has better thermal stability than other electrolyte salts (such as lithium hexafluorophosphate), which can reduce the probability of electrolyte salt decomposition at high temperatures to produce hydrogen fluoride, thereby improving the battery's high-temperature cycle life. However, lithium bisfluorosulfonylimide (LiFSI) readily undergoes severe side reactions with deeply lithium-intercalated anode active materials (such as LiC6), posing a safety hazard to the battery. The lithium intercalation depth of the anode active material is correlated with its graphitization degree; the lithium intercalation depth increases with increasing graphitization degree. Reducing the graphitization degree of the anode active material can decrease the probability of forming deeply lithium-intercalated anode active materials (such as LiC6) and increase the lithium-ion transport rate at the solid-liquid interface. This allows the solid-liquid transport rate of lithium ions to match the high liquid phase transport rate of chain carboxylic acid ester solvents, which is beneficial for improving the battery's fast-charging performance. However, reducing the graphitization degree of the anode active material also exacerbates the side reactions between the chain carboxylic acid ester solvent and the anode active material, deteriorating the battery's high-temperature cycling stability.

[0107] During the research process, the applicant discovered that negative electrode active materials with graphitization within the above-mentioned range, when combined with an electrolyte containing chain-like carboxylic acid ester solvents and lithium bis(fluorosulfonyl)imide (LiFSI), can reduce the probability of side reactions occurring at high temperatures between the electrolyte and the defect sites of the negative electrode active material. It can also reduce the degree of side reactions between lithium bis(fluorosulfonyl)imide (LiFSI) and the deeply lithium-intercalated negative electrode active material. Furthermore, by achieving a certain degree of disorder in the negative electrode active material and matching the lithium-ion solid-liquid transport rate with the liquid phase transport rate through the chain-like carboxylic acid ester solvent, it can promote the rapid insertion and extraction of lithium ions in the negative electrode active material, thus achieving a balance between fast-charging performance, safety performance, and high-temperature cycle life of the battery cell.

[0108] In some embodiments, the lithium bis(fluorosulfonyl)imide accounts for 1.5%-5% of the total mass of the electrolyte.

[0109] Based on the total mass of the electrolyte, the mass ratio of lithium bis(fluorosulfonyl)imide within the above-mentioned range is beneficial to further improve battery safety while maintaining good fast-charging performance and high-temperature cycle life.

[0110] In some embodiments, the chain carboxylic acid ester solvent accounts for 10%-65% of the total mass of the electrolyte.

[0111] Based on the total mass of the electrolyte, a mass ratio of chain carboxylic acid ester solvents within the above range is beneficial for balancing the fast-charging performance and high-temperature cycle life of individual battery cells.

[0112] In some embodiments, the degree of graphitization of the negative electrode active material is 92%-95%.

[0113] In some embodiments, the mass percentage of lithium difluorosulfonylimide is 10%-50% based on the total mass of electrolyte salts in the electrolyte.

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

[0115] When the mass percentage of lithium bisfluorosulfonylimide (LiFSI) in the electrolyte salt of the electrolyte is within the above range, it can reduce the amount of chain carboxylic acid ester solvents to a certain extent, reduce the production of hydrogen fluoride in the battery during high-temperature cycling, and alleviate the reaction between LiFSI and the deeply lithium-intercalated negative electrode active material. Together, they can improve the high-temperature cycling performance and safety performance of the battery cell.

[0116] 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.

[0117] The aforementioned chain-like carboxylic acid ester solvent molecules have high lithium-ion conductivity. Compared with other chain-like carboxylic acid ester solvents, only a small amount needs to be added to achieve high lithium-ion conductivity. While improving the fast-charging performance of battery cells, it can effectively control the degree of side reactions between the electrolyte and the negative electrode active material, so that the battery cells can further improve cycle stability while maintaining good fast-charging performance.

[0118] In some embodiments, the chain-like carboxylic acid ester solvent includes one or more of ethyl acetate and methyl acetate.

[0119] Ethyl acetate and methyl acetate have better kinetic activity and relatively lower gas production levels compared to other carboxylic acid ester solvents. This is beneficial for further improving the lithium-ion transport rate and reducing the level of side reactions between the electrolyte and the negative electrode at high temperatures, thus balancing the fast-charging performance and high-temperature cycle stability of the battery cells.

[0120] In some embodiments, the total mass percentage of ethyl acetate and methyl acetate is 5%-80%, optionally 10%-70%, based on the total mass of the solvent.

[0121] 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.

[0122] In some embodiments, the chain carboxylic acid ester solvent includes methyl acetate.

[0123] In some embodiments, the methyl acetate content is 5%-80% by mass, optionally 5%-50%, and further optionally 10%-40%, based on the total mass of the solvent.

[0124] 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.

[0125] In some embodiments, the solvent further includes carbonate solvents, including one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0126] In some embodiments, the solvent comprises ethylene carbonate, and the ethylene carbonate content is 15%-35% based on the total mass of the solvent.

[0127] Ethylene carbonate has a high dielectric constant, which is beneficial for improving the solubility of lithium salts in the electrolyte, increasing the lithium ion concentration in the electrolyte, improving the electrolyte conductivity, and enhancing the fast-charging performance of the battery. Simultaneously, ethylene carbonate exhibits good film-forming properties, which helps improve the quality of the SEI film on the negative electrode surface, reduce the degree of side reactions between the carboxylic acid ester and the negative electrode, and improve the cycle life of the battery.

[0128] In some embodiments, the mass content of ethylene carbonate, based on the total mass of the solvent, can be selected as 15%, 20%, 25%, 30%, 35%, or any range between the two.

[0129] In some embodiments, the solvent comprises dimethyl carbonate, and the mass content of dimethyl carbonate is 5%-50% based on the total mass of the solvent.

[0130] In some embodiments, the mass content of dimethyl carbonate, based on the total mass of the solvent, can be selected as 5%, 10%, 20%, 30%, 40%, 50%, or any value range between the two.

[0131] Dimethyl carbonate (DMC) exhibits good electrical conductivity and gas generation properties. Adding DMC to the electrolyte can appropriately reduce the amount of carboxylic acid esters in the electrolyte, thereby reducing the degree of side reactions between carboxylic acid esters and the negative electrode, and improving the battery's cycle life while maintaining its fast-charging performance.

[0132] In some embodiments, the negative current collector comprises a copper foil with a thickness of 4μm-6μm, optionally 4μm-5μm.

[0133] 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.

[0134] Within the aforementioned range, the thickness of the copper foil can reduce the battery's internal resistance and the heat generated by individual battery cells during fast charging by increasing the thickness of the current collector, thereby enabling individual battery cells to withstand higher charging currents and improving the battery's fast charging performance and safety performance. Furthermore, the thinner current collector can increase the battery's energy density, thus balancing the fast charging performance and energy density of individual battery cells.

[0135] 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 .

[0136] 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), 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 groups (e.g., 10 groups) of samples can be tested, and the average value can be calculated as the test result.

[0137] 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.

[0138] 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.

[0139] 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 the concentration polarization generated by the battery cell during fast charging, and enable the battery cell to withstand a larger charging current, which is beneficial to improving the fast charging performance and safety performance of the battery cell.

[0140] 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 .

[0141] 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].

[0142] 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.

[0143] Negative electrode sheets with a compaction density within the above range have suitable porosity, which can be matched with electrolytes with high conductivity, improve the diffusion rate of lithium ions in the negative electrode, reduce concentration polarization during fast charging, and enable battery cells to withstand larger charging currents, which is beneficial to improving the fast charging performance and safety performance of battery cells.

[0144] In some embodiments, the compaction density of the negative electrode sheet is 1.35 g / cm³. 3 -1.6g / cm 3 .

[0145] In some embodiments, the average thickness of the negative electrode film on one side is 30μm-150μm, and can be selected as 30μm-80μm.

[0146] 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.

[0147] 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 the concentration polarization generated by the battery cell during fast charging, and enable the battery cell to withstand a larger charging current, which is beneficial to improving the fast charging performance and safety performance of the battery cell.

[0148] In some embodiments, the porosity of the negative electrode sheet is 20%-60%, optionally 25%-40%.

[0149] In this application, the porosity of the negative electrode sheet can be tested using methods known in the art. For example, based on the national standard GB / T24586-2009, the electrode sheet is immersed in ethyl methyl carbonate (EMC) for cleaning; the porosity is determined using a true density meter (AccuPyc II 1340, USA) based on the gas displacement method. The porosity is the percentage of pore volume to the total volume of the electrode sheet, calculated using the formula: Porosity = (V - V0) / V × 100%, where V0 is the true volume of the electrode sheet and V is the apparent volume of the electrode sheet.

[0150] 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.

[0151] Negative electrode sheets with porosity within the above range can be matched with electrolytes with high conductivity, thereby increasing the diffusion rate of lithium ions in the negative electrode, reducing concentration polarization generated by the battery cell during fast charging, and enabling the battery cell to withstand a larger charging current, which is beneficial to improving the fast charging performance and safety performance of the battery cell.

[0152] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive current collector includes an aluminum foil with a thickness of 10 μm-16 μm, optionally 11 μm-14 μm.

[0153] 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.

[0154] 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.

[0155] Within the aforementioned range, the thickness of the aluminum foil can reduce the battery's internal resistance and the heat generated by individual battery cells under high-rate charging and discharging by adjusting the current collector thickness, thereby improving the battery's fast-charging performance and safety performance. Furthermore, it can increase the battery's energy density by thinning the current collector, thus balancing the fast-charging performance and energy density of individual battery cells.

[0156] In some embodiments, the thickness of the aluminum foil is 11 μm-14 μm.

[0157] The thickness of the aluminum foil within the above range can further improve the current carrying capacity of the current collector, alleviate the uneven current density distribution on the electrode and the inconsistent temperature rise inside the battery cell during fast charging, so that the fast charging performance can be maintained in long-term fast charging cycles and improve the fast charging cycle life of the battery cell.

[0158] In some embodiments, the positive electrode film layer includes a positive electrode active material, which includes lithium iron phosphate and its modified materials.

[0159] 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.

[0160] In some embodiments, the porosity of the separator is 25%-55%, optionally 28%-42%.

[0161] 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.

[0162] 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.

[0163] Separating 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. Therefore, the amount of chain carboxylic acid ester solvents required to achieve the same lithium ion liquid phase transport rate can be reduced, allowing battery cells to further balance fast charging performance and cycle stability.

[0164] In some embodiments, the porosity of the separator is 30%-42%.

[0165] The porosity of the separator within the above range is beneficial to further improve the liquid phase transport rate of lithium ions, alleviate the uneven current density distribution on the electrode during fast charging and the inconsistent temperature rise inside the battery cell during fast charging, so that the fast charging performance can be maintained in long-term fast charging cycles and the fast charging cycle life of the battery cell can be improved.

[0166] In some embodiments, the Gurley value G of the separator is 50s-620s, optionally 300s-610s.

[0167] 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.

[0168] In this application, the Gurley value of the separator can be tested using any known method. As an example, the Gurley value is 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. The average of the test results from multiple (e.g., 3) parallel samples can be taken as the Gurley value of the separator.

[0169] 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.

[0170] Separators with Gurley values ​​within the above range are beneficial for improving the liquid phase transport rate of lithium ions, thereby reducing the amount of chain carboxylic acid ester solvents required to achieve the same liquid phase transport rate of lithium ions, allowing battery cells to further balance fast charging performance and cycle stability.

[0171] 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.

[0172] In some embodiments, the separator includes a base membrane and a ceramic coating, wherein the ceramic coating is disposed only on the positive electrode side of the base membrane.

[0173] The main component of the ceramic coating is ceramic particles. These particles are flame-retardant and have high hardness, making them resistant to deformation under heat. Therefore, the ceramic coating helps improve the mechanical strength of the separator and reduces the probability of lithium dendrites, which can easily form during fast charging, piercing the separator and causing internal short circuits and thermal runaway. Applying the ceramic coating only to the positive electrode side of the base film can balance the fast-charging performance and safety of the individual battery cells.

[0174] In some embodiments, the ceramic coating comprises ceramic particles, which include one or more of alumina, boehmite, silicon oxide, titanium oxide, magnesium oxide, calcium oxide, zinc oxide, zirconium oxide, and tin oxide, and may be selected from one or more of alumina and boehmite.

[0175] In some embodiments, the ceramic coating further includes an adhesive, which includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyacrylamide, and polyvinyl alcohol, and may be selected as polyvinylidene fluoride.

[0176] In some embodiments, as shown in FIG7, the battery cell includes a wound cell 6, the positive current collector includes a positive current collector portion and a positive electrode tab 10112 disposed on at least one side of the positive current collector portion, and at least one turn of the positive electrode sheet 101 of the wound cell 6 includes at least two positive electrode tabs 10112.

[0177] In some embodiments, please continue to refer to FIG7, the battery cell includes a wound cell 6, the negative current collector includes a negative current collector portion and a negative electrode tab 1023 disposed on at least one side of the negative current collector portion, and at least one turn of the negative electrode sheet 102 of the wound cell 6 includes at least two negative electrode tabs 1023.

[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 7, is a square wound cell.

[0181] In some embodiments, the wound cell 6 is a cylindrical wound cell. Please continue to refer to Figure 7. Whether it is a square wound cell or a cylindrical wound cell, one turn of the positive electrode plate refers to the winding direction from any point A on the positive electrode plate, freely from the inside out. That is, after winding around the winding needle in a clockwise direction as shown in Figure 7, it is wound to the point B that is closest to point A in the next turn.

[0182] In some embodiments, at least one turn of the positive electrode 101 of the wound cell 6 includes at least three, four, five or more tabs.

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

[0184] In existing technologies, the positive or negative electrode sheet in a wound battery cell typically has 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 sheet. This reduces the degree of side reactions between the carboxylic acid ester solvent in the electrolyte and lithium bis(fluorosulfonyl)imide and the negative electrode. Simultaneously, it allows the battery cell to withstand higher charging currents, further improving the fast-charging performance and safety of the battery cell. Furthermore, providing at least two tabs on at least one turn of the wound cell electrode sheet alleviates uneven current density distribution on the electrode sheet and inconsistent temperature rise within the battery cell during fast charging, allowing fast-charging performance to be maintained during long-term fast-charging cycles and improving the fast-charging cycle life of the battery cell.

[0185] In some embodiments, the wound cell 6 is shown in FIG7. 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 FIG7). 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 7), 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. 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 at the tabs, decreases temperature rise at the tabs, and reduces the degree of side reactions between the carboxylic acid ester solvent in the electrolyte and lithium difluorosulfonylimide and the negative electrode. Simultaneously, it allows the battery cell to withstand higher charging currents, further improving the fast-charging performance and safety of the battery cell. Furthermore, placing at least two tabs on at least one turn of the wound cell electrode sheet alleviates uneven current density distribution on the electrode sheet and inconsistent temperature rise within the battery cell during fast charging, allowing fast-charging performance to be maintained during long-term fast-charging cycles and further improving the 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 electrolyte injection coefficient of the battery cell is 2.5g / Ah-3.2g / Ah, and can be optionally 2.8g / Ah-3.0g / Ah.

[0192] 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.

[0193] 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, 3.2g / Ah, or any value range between the two.

[0194] Battery cells with an electrolyte injection coefficient within the above range can keep the side reactions between the chain carboxylic acid ester solvent and the negative electrode active material at a low level, thus ensuring the battery's cycle life. They can also improve the wettability between the electrolyte and the electrode, reduce the battery interface resistance, decrease the battery impedance, and further improve the battery's fast charging performance.

[0195] In some implementations, at 25°C, the number of battery cells cycling within the corresponding fast charging window is 2620-2850 cycles.

[0196] 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.

[0197] 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.

[0198] In some implementations, at 25°C, the number of battery cell cycles under the corresponding fast charging window can be selected as 2620 cycles, 2700 cycles, 2790 cycles, 2850 cycles, or any value range between the two.

[0199] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2620.

[0200] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2700.

[0201] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2790.

[0202] In some implementations, at 25°C, the number of battery cells cycled within the corresponding fast charging window is 2850.

[0203] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 13.5 min to 19.9 min.

[0204] If the battery is placed on a charging station, the time it takes to charge from 0% SOC to 100% SOC can be directly recorded. When the vehicle is charging at a charging station, the charging station system program will display a charging curve (this curve may be visible on the charging station's display screen, on the mobile charging control app, or in the battery monitoring backend, etc.). For example, the horizontal axis represents charging time, and the vertical axis represents charging power and battery SOC. The graph shows the battery's charging power and SOC at different times, and the charging time from 10% SOC to 80% SOC can also be read from the graph.

[0205] The charging time for a single battery cell to charge from 10% SOC to 80% SOC can be obtained by any method known in the art. For example, 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, allowed 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. The charging time from 10% to 80% is 6 / C (20% SOC) + 6 / C (30% SOC) + 6 / C (40% SOC) + 6 / C (50% SOC) + 6 / C (60% SOC) + 6 / C (70% SOC) + 6 / C (80% SOC), in minutes.

[0206] In some implementations, at 35°C, the charging time for a single battery cell to charge from 10% SOC to 80% SOC can be selected as 13.5 min, 13.9 min, 14.4 min, 15.2 min, 15.3 min, 15.6 min, 15.9 min, 17.2 min, 19.5 min, 19.9 min, or any value range between the two.

[0207] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 13.5 minutes.

[0208] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 13.9 minutes.

[0209] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 14.4 minutes.

[0210] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 15.2 minutes.

[0211] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 15.3 minutes.

[0212] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 15.6 minutes.

[0213] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 15.9 minutes.

[0214] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 17.2 minutes.

[0215] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 19.5 minutes.

[0216] In some implementations, at 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 19.9 minutes.

[0217] 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.

[0218] 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).

[0219] 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.

[0220] 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.

[0221] 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.

[0222] 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.

[0223] 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.

[0224] 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).

[0225] 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.

[0226] In some embodiments, the 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).

[0227] 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).

[0228] In some embodiments, the electrolyte may optionally include other additives.

[0229] 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.

[0230] 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.

[0231] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0232] 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.

[0233] 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.

[0234] Example

[0235] 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.

[0236] I. Preparation Method

[0237] Example 1

[0238] (1) Preparation of negative electrode sheet

[0239] 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, which was then cold-pressed and slit to obtain the negative electrode sheet. The graphitization degree of the negative electrode active material was 93%, 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 mm. 2 The compaction density of the negative electrode sheet is 1.6 g / cm³. 3 The porosity of the negative electrode sheet is 30%.

[0240] (2) Preparation of positive electrode sheet

[0241] 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, which is then cold-pressed and slit to obtain the positive electrode sheet.

[0242] (3) Preparation of electrolyte

[0243] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl acetate were mixed evenly in 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.

[0244] 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.

[0245] (4) Preparation of the separating membrane

[0246] 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.

[0247] (5) Preparation of battery cells

[0248] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. They are then wound to form a battery cell, ensuring that each layer of the positive and negative electrodes has tabs. The cell is placed in a battery casing, dried, and then injected with electrolyte. Following formation and settling processes, a lithium-ion battery is produced.

[0249] 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.

[0250] The preparation methods of Examples 2-10 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.

[0251] In Example 2, based on the total mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide was 1.5%, and the mass percentage of LiPF6 was 12.5%.

[0252] In Example 3, based on the total mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide was 5.8%, and the mass percentage of LiPF6 was 8.2%.

[0253] 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.

[0254] In Example 5, the electrolyte solvent was ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl acetate in a mass ratio of 30:62:8, resulting in a carboxylic acid ester content of 6.52% based on the total mass of the electrolyte.

[0255] In Example 6, the electrolyte solvent was ethylene carbonate (EC) and methyl acetate in a mass ratio of 2:8, so that the mass content of carboxylic acid ester was 65.2% based on the total mass of the electrolyte.

[0256] In Example 7, the graphitization degree of the negative electrode active material was 91%.

[0257] In Example 8, 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 9, the porosity of the separator was adjusted to 28%.

[0259] In Example 10, the thickness of the aluminum foil in the positive current collector was adjusted to 10 μm.

[0260] The preparation method of Comparative Example 1 is basically the same as that of Example 8, except that the content of electrolyte salts in the electrolyte is adjusted so that the mass content of LIFSI is 8% and the mass content of LiPF6 is 6% based on the total mass of the electrolyte.

[0261] The preparation method of Comparative Example 2 is basically the same as that of Example 8, except that the graphitization degree of the negative electrode active material is 88%.

[0262] The preparation method of Comparative Example 3 is basically the same as that of Example 8, except that the graphitization degree of the negative electrode active material is 98%.

[0263] II. Performance Testing

[0264] 1) Battery fast charging performance

[0265] The batteries of the above embodiments and comparative examples were 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, the batteries were charged at a constant current rate of 1C to a voltage of 3.65V at 35°C, 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. The actual capacity was 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. The charging time from 10% to 80% is 6 / C (20% SOC) + 6 / C (30% SOC) + 6 / C (40% SOC) + 6 / C (50% SOC) + 6 / C (60% SOC) + 6 / C (70% SOC) + 6 / C (80% SOC), in minutes.

[0266] 2) Number of fast charging cycles for the battery

[0267] At 25℃, charging was performed using the obtained fast charging window distribution, with the following charging rates: 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, and C(70% SOC) to 60% SOC. Charge the battery at a rate of 0.33C to 70% SOC, then at a rate of 0.33C to 80% SOC, and then at 0.33C to 100% SOC. After resting for 10 minutes, charge the battery at 0.33C DC to 2.1V and record the discharge capacity as C1. Monitor the temperature rise at the tab during this charging process. Repeat the above process and record the discharge capacity as Cn for each cycle. The cycle capacity retention rate is Cn / C1. Record the number of cycles when the cycle capacity retention rate drops to 80% SOC.

[0268] 3) Battery thermal chamber safety test

[0269] 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.

[0270] 4) High-temperature cycle life

[0271] At 60°C, the prepared battery was charged to 3.65V with a constant current of 1C, then charged at a constant voltage of 3.65V until the current dropped to 0.05C. After resting for 5 minutes, it was discharged to 2.1V with a constant current of 1C. This is the first charge / discharge cycle of the battery, and the discharge capacity of this cycle is recorded as the discharge capacity (C1) of the battery in the first cycle. The above steps were repeated for the same battery. The process capacity (Cn) of the battery after the nth cycle was recorded. The capacity retention rate after n cycles was calculated as Cn / C1 × 100%. The number of cycles in which the capacity retention rate reached 80% was recorded.

[0272] Table 1

[0273] As can be seen from the comparison of the examples and comparative examples, based on the total mass of the electrolyte, when the mass ratio of the lithium difluorosulfonylimide is 1%-6%, the mass ratio of the chain carboxylic acid ester solvent is 5%-75%, and the graphitization degree of the negative electrode active material is 90%-96%, the battery cell can achieve a balance between fast charging performance, high-temperature cycle life, and safety performance.

[0274] Table 2

[0275] As can be seen from the comparison between Example 1 and Example 8, having one tab per layer in the positive electrode of the battery cell is beneficial to improving the fast charging cycle life of the battery cell.

[0276] Table 3

[0277] As can be seen from the comparison of Examples 1 and 9, when the porosity of the separator is 30%-42%, it is beneficial to improve the fast-charging cycle life of the battery cells.

[0278] Table 4

[0279] As can be seen from the comparison of Examples 1 and 10, when the thickness of the aluminum foil is 11μm-14μm, it is beneficial to improve the fast charging cycle life of the battery cells.

[0280] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode; The electrolyte comprises a solvent and an electrolyte salt, wherein the electrolyte salt comprises lithium difluorosulfonylimide, and the mass percentage of lithium difluorosulfonylimide is 1%-6% based on the total mass of the electrolyte. The solvent includes chain-like carboxylic acid ester solvents, and the chain-like carboxylic acid ester solvents account for 5%-75% of the total mass of the electrolyte. 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 electrode film layer includes a negative electrode active material, and the graphitization degree of the negative electrode active material is 90%-96%.

2. The battery cell according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of lithium bis(fluorosulfonyl)imide is 1.5%-5%.

3. The battery cell according to claim 1, characterized in that, Based on the total mass of the electrolyte, the chain-like carboxylic acid ester solvent accounts for 10%-65% of the mass.

4. The battery cell according to claim 1, characterized in that, The graphitization degree of the negative electrode active material is 92%-95%.

5. The battery cell according to claim 1 or 2, characterized in that, Based on the total mass of electrolyte salts in the electrolyte, the mass percentage of lithium difluorosulfonamide is 10%-50%.

6. The battery cell according to claim 1, characterized in that, 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.

7. The battery cell according to claim 1, characterized in that, 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.

8. The battery cell according to claim 7, characterized in that, Based on the total mass of the solvent, ethyl acetate and methyl acetate account for 10%-70% of the total mass.

9. The battery cell according to claim 1, characterized in that, 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.

10. The battery cell according to claim 9, characterized in that, The methyl acetate content is 5%-50% based on the total mass of the solvent.

11. The battery cell according to claim 9 or 10, characterized in that, The methyl acetate content is 10%-40% based on the total mass of the solvent.

12. The battery cell according to any one of claims 1 to 11, characterized in that, The solvent also includes carbonate solvents, which include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

13. The battery cell according to claim 12, characterized in that, The solvent includes ethylene carbonate, and the ethylene carbonate content is 15%-35% based on the total mass of the solvent.

14. The battery cell according to claim 12, characterized in that, The solvent includes dimethyl carbonate, and the mass content of dimethyl carbonate is 5%-50% based on the total mass of the solvent.

15. The battery cell according to any one of claims 1 to 14, characterized in that, The negative electrode current collector includes a copper foil with a thickness of 4μm-6μm.

16. The battery cell according to claim 15, characterized in that, The thickness of the copper foil is 4μm-5μm.

17. The battery cell according to any one of claims 1 to 16, characterized in that, The negative electrode sheet satisfies at least one of the following conditions: (1) The single-sided density of the negative electrode film is 0.08 g / 1540.25 mm. 2 -0.20g / 1540.25mm 2 ; (2) The compaction density of the negative electrode sheet is 1.2 g / cm³. 3 -1.9g / cm 3 ; (3) The average thickness of the negative electrode film layer on one side is 30μm-150μm; (4) The porosity of the negative electrode sheet is 20%-60%.

18. The battery cell according to any one of claims 1 to 16, characterized in that, The negative electrode sheet satisfies at least one of the following conditions: (1) The single-sided density of the negative electrode film is 0.10 g / 1540.25 mm. 2 -0.16g / 1540.25mm 2 ; (2) The compaction density of the negative electrode sheet is 1.2 g / cm³. 3 -1.65g / cm 3 ; (3) The average thickness of the negative electrode film layer on one side is 30μm-80μm; (4) The porosity of the negative electrode sheet is 25%-40%.

19. The battery cell according to any one of claims 1 to 18, characterized in that, The compaction density of the negative electrode sheet is 1.35 g / cm³. 3 -1.6g / cm 3 .

20. The battery cell according to any one of claims 1 to 19, characterized in that, The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive current collector includes an aluminum foil with a thickness of 10μm-16μm.

21. The battery cell according to claim 20, characterized in that, The thickness of the aluminum foil is 11μm-14μm.

22. The battery cell according to claim 20 or 21, characterized in that, The positive electrode film layer includes a positive electrode active material, which includes lithium iron phosphate and its modified materials.

23. The battery cell according to any one of claims 1 to 22, characterized in that, The porosity of the isolation membrane is 25%-55%.

24. The battery cell according to claim 23, characterized in that, The porosity of the isolation membrane is 28%-42%.

25. The battery cell according to claim 23 or 24, characterized in that, The porosity of the isolation membrane is 30%-42%.

26. The battery cell according to any one of claims 1 to 25, characterized in that, 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.

27. The battery cell according to claim 26, characterized in that, The Gurley value G of the isolation membrane is 300s-610s.

28. The battery cell according to any one of claims 1 to 27, characterized in that, The separator includes a base membrane and a ceramic coating, wherein the ceramic coating is disposed only on the positive electrode side of the base membrane.

29. The battery cell according to claim 28, characterized in that, The ceramic coating comprises ceramic particles, which include one or more of the following: alumina, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, calcium oxide, zinc oxide, zirconium oxide, and tin oxide.

30. The battery cell according to claim 29, characterized in that, The ceramic particles include one or more of alumina and boehmite.

31. The battery cell according to any one of claims 28 to 30, characterized in that, The ceramic coating further includes an adhesive, which includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyacrylamide, and polyvinyl alcohol.

32. The battery cell according to claim 31, characterized in that, The adhesive includes polyvinylidene fluoride.

33. The battery cell according to any one of claims 1 to 32, characterized in that, The battery cell includes a wound cell, the negative current collector includes a negative current collector portion and a negative electrode tab disposed on at least one side of the negative current collector portion, and at least one turn of the negative electrode sheet of the wound cell includes at least two negative electrode tabs.

34. The battery cell according to any one of claims 1 to 33, characterized in that, The battery cell includes a wound cell, 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, and at least one turn of the positive electrode sheet of the wound cell includes at least two positive electrode tabs.

35. The battery cell according to claim 34, characterized in that, 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.

36. The battery cell according to any one of claims 1 to 35, characterized in that, The electrolyte injection coefficient of the battery cell is 2.5 g / Ah-3.2 g / Ah.

37. The battery cell according to claim 36, characterized in that, The electrolyte injection coefficient of the battery cell is 2.8 g / Ah-3.0 g / Ah.

38. The battery cell according to any one of claims 1 to 37, characterized in that, At 25℃, the number of battery cells in the corresponding fast charging window is 2620-2850 cycles.

39. The battery cell according to any one of claims 1 to 38, characterized in that, At 35°C, the charging time for a single battery cell from 10% SOC to 80% SOC is 13.5 min to 19.9 min.

40. A battery device, characterized in that, The battery device includes any one of the battery cells according to claims 1 to 39, and the battery device includes at least one of the following: battery module, battery pack, and energy storage battery.

41. An electrical appliance, characterized in that, Includes the battery cell according to any one of claims 1 to 39 or the battery device according to claim 40.

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