Battery cell, battery device, electric device and energy storage device

Abstract

A battery cell, a battery device, an electric device and an energy storage device. The battery cell comprises an electrode assembly and an electrolyte. The electrode assembly comprises a positive electrode sheet. The positive electrode sheet comprises a positive current collector and a positive film layer arranged on at least one side of the positive current collector. The positive film layer comprises a positive active material. In the battery cell, the coating area of the positive film layer is greater than or equal to 11 m2; the positive film layer comprises a one-dimensional conductive agent. The electrolyte comprises fluoroethylene carbonate; on the basis of the total mass of the electrolyte, the mass content of fluoroethylene carbonate is 0.05%-5%.

Description

Battery cells, battery packs, electrical devices and energy storage devices

[0001] Cross-references

[0002] This application incorporates, in its entirety, patent application number PCT / CN2025 / 085988, filed on March 28, 2025, entitled “Lithium-ion secondary battery, battery device, power device, method for preparing positive electrode active material and method for preparing positive electrode sheet”, which is hereby incorporated by reference.

[0003] This application incorporates, in its entirety, patent application number PCT / CN2025 / 140513, filed on December 5, 2025, entitled “Battery cell, battery device, power consumption device and energy storage device”. Technical Field

[0004] This application relates to the field of battery technology, and in particular to a battery cell, battery device, power supply device, and energy storage device. Background Technology

[0005] In recent years, the application of high-capacity battery cells in energy storage devices has become increasingly widespread. In various energy storage application scenarios, high capacity and long cycle life have become key indicators for evaluating the performance of energy storage batteries. This is especially true for large-scale energy storage power stations, whose large-scale, long-term operation places higher demands on battery cycle life. To effectively delay battery performance degradation and reduce replacement frequency and maintenance costs, there is an urgent need to further develop battery cells that combine high capacity and long cycle life. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell with high capacity and good cycle performance.

[0007] An embodiment of the first aspect of this application provides a battery cell, the battery cell including an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a positive electrode active material, and the coating area of ​​the positive electrode film layer in the battery cell being greater than or equal to 11m². 2 The positive electrode film layer includes a one-dimensional conductive agent, and the electrolyte includes fluoroethylene carbonate. Based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate is 0.05%-5%.

[0008] Unlike power batteries, energy storage batteries need to operate in conjunction with power station systems to meet the requirements of constant power charging. This means that the charging current of an energy storage battery does not decrease as its capacity decays throughout its entire lifespan. Power batteries, on the other hand, are typically charged at a constant rate, meaning the charging current is adapted to the battery capacity. As the capacity of individual battery cells decreases during use, the charging current of the power battery also decreases accordingly. This fundamental difference forces energy storage batteries to withstand higher charging rates after capacity decay, making them prone to performance degradation after long-term cycling. Increasing the coating area of ​​the positive electrode active material in a battery cell further increases the differences in electron transport paths, causing uneven current density distribution, triggering concentration polarization within the battery, increasing the probability of lithium plating in individual cells, and limiting further improvements in the cycle life of energy storage batteries.

[0009] The applicant's research found that the positive electrode film contains a one-dimensional conductive agent, which can form a linearly intersecting mesh conductive network inside the positive electrode film. This is beneficial to improving the conductivity of the positive electrode sheet, improving the uniformity of current distribution in a large-area coated positive electrode film, and improving the cycle performance of the battery cell.

[0010] However, research shows that the conductive network formed by one-dimensional conductive agents has a rigid structure, which restricts the volume change of the positive electrode active material in the battery cell during cycling. This makes the positive electrode active material prone to particle pulverization and cracking under large expansion forces in the middle and later stages of the battery's long cycle life. The exposed fresh material interface will undergo side reactions with the electrolyte, exacerbating lithium consumption and limiting further improvement in the cycle life of the battery cell in the later stages of long-cycle operation. The battery cell provided in this application further adds 0.05%-5% fluoroethylene carbonate to the electrolyte, which further improves the cycle life of the battery cell, including the positive electrode film layer with a large coating area, meeting the long-term cycle reliability requirements of energy storage power systems. Although the mechanism is not yet clear, it is speculated that fluoroethylene carbonate can form an electrolyte interface film (CEI film) rich in F element on the exposed interface of the positive electrode active material, which helps to reduce the probability of side reactions between the fresh interface exposed by the active material particles due to pulverization and cracking and the electrolyte, thereby reducing lithium consumption and achieving further improvement in the cycle life of the battery cell.

[0011] In any embodiment, the coating area of ​​the positive electrode film in the battery cell is 11m². 2 -150m 2 In any embodiment, the coating area of ​​the positive electrode film in the battery cell is 11m². 2 -120m 2 In any embodiment, the coating area of ​​the positive electrode film in the battery cell is 11m². 2 -100m2 .

[0012] In any embodiment, the mass content of the fluoroethylene carbonate is 0.1%-0.5% based on the total mass of the electrolyte.

[0013] The mass content of fluoroethylene carbonate in the electrolyte meets the above range, which is conducive to the formation of a positive electrode interface CEI film with a suitable thickness on the surface of the positive electrode particles. This reduces the probability of phenomena such as excessive CEI film thickness and increased lithium-ion transport impedance, thereby improving the uniformity of current distribution in the positive electrode film layer and further enhancing the cycle performance of the energy storage battery cell.

[0014] In any embodiment, the capacity of the battery cell is greater than or equal to 400Ah.

[0015] In any embodiment, the capacity of the battery cell is 400Ah-3000Ah. In any embodiment, the capacity of the battery cell is 500Ah-1500Ah. In any embodiment, the capacity of the battery cell is 600Ah-1000Ah.

[0016] In any embodiment, the dimension of the battery cell along the first direction is T, the dimension of the battery cell along the second direction is H, and the dimension of the battery cell along the third direction is L, where 50mm≤T≤100mm, 200mm≤H≤240mm, and 250mm≤L≤350mm, and the first direction, the second direction, and the third direction are perpendicular to each other.

[0017] In any embodiment, the dimension T of the battery cell along the first direction satisfies 60mm≤T≤90mm.

[0018] In any embodiment, the dimension H of the battery cell along the second direction satisfies 210mm≤H≤230mm.

[0019] In any embodiment, the dimension L of the battery cell along a third direction satisfies 260mm≤L≤290mm.

[0020] Large-size, high-capacity battery cells have a high active material load, which helps meet the high-capacity requirements of energy storage systems. However, during the later stages of cycling, under constant power charging, the differences in electron transport paths within the positive electrode film are amplified, exacerbating the uneven current density distribution and increasing the probability of lithium plating, which is detrimental to further improving cycle life. The technical solution provided in this application is particularly suitable for large-size, high-capacity battery cells, effectively improving the uniformity of current distribution in the large-area positive electrode film, reducing the probability of lithium metal deposition, and further improving the cycle performance of the battery cells.

[0021] In any implementation, the second direction is parallel to the direction of gravity.

[0022] The second direction is parallel to the direction of gravity of the battery cell in use. It can be understood that when the energy storage device is placed on a horizontal surface, the direction of gravity of the battery cell is parallel to the first direction, which is parallel to the height direction of the battery cell when it is loaded into the energy storage device.

[0023] In any embodiment, the specific surface area of ​​the one-dimensional conductive agent is 100 m². 2 / g-220m 2 / g.

[0024] In any embodiment, the oil absorption value of the one-dimensional conductive agent is 100mL / 100g-200mL / 100g.

[0025] The fact that the specific surface area and oil absorption value of the one-dimensional conductive agent meet the above range indicates that the one-dimensional conductive agent has a suitable pore structure, which effectively reduces the probability of the one-dimensional conductive agent agglomerating and entangled in the positive electrode film, thereby forming a good conductive network. This is beneficial to improving the conductivity of the positive electrode sheet, improving the uniformity of current distribution in the large-area positive electrode film, reducing the probability of lithium plating, and further improving the cycle performance of the battery cell.

[0026] In any embodiment, the powder resistivity of the one-dimensional conductive agent is less than or equal to 50 mΩ·cm.

[0027] The resistivity of the one-dimensional conductive agent powder meets the above range, which is beneficial to improve the conductivity of the positive electrode sheet, thereby improving the uniformity of current distribution in the large-area coated positive electrode film, reducing the probability of lithium plating, and improving the cycle performance of the battery cell.

[0028] In any embodiment, the mass content of the one-dimensional conductive agent is 0.1%-2% based on the total mass of the positive electrode film.

[0029] In any embodiment, the mass content of the one-dimensional conductive agent is 0.2%-1% based on the total mass of the positive electrode film.

[0030] The content of one-dimensional conductive agent in the positive electrode film layer that meets the above range can form a good conductive network in the positive electrode film layer with a large coating area, improve the conductivity of the positive electrode sheet and the uniformity of current distribution, reduce the probability of lithium plating, and further improve the cycle performance of the battery cell; at the same time, it can also effectively reduce the excessive space occupied by the introduced one-dimensional conductive agent in the positive electrode active material, while also improving the battery capacity.

[0031] In any embodiment, the one-dimensional conductive agent includes one or more of single-arm carbon nanotubes, multi-arm carbon nanotubes, and carbon nanofibers.

[0032] The positive electrode film layer includes the above-mentioned types, which can form a good conductive network in the positive electrode film layer with a large coating area, improve the conductivity of the positive electrode sheet and the uniformity of current distribution, and further improve the cycle performance of the battery cell.

[0033] In any embodiment, the electrolyte comprises vinylene carbonate, and the mass content of the vinylene carbonate is 0.5%-8% based on the total mass of the electrolyte.

[0034] In any embodiment, the mass content of vinylene carbonate is 0.6%-4% based on the total mass of the electrolyte.

[0035] The electrolyte includes vinylene carbonate, which can be oxidized when the battery charging voltage increases to form a positive electrode interface film. This helps to alleviate the direct contact between the fresh interface exposed by the pulverization and cracking of the positive electrode active material particles and the electrolyte, thereby reducing the occurrence of internal side reactions, lowering lithium consumption, and further improving the cycle performance of the battery cell. At the same time, vinylene carbonate can form an SEI film on the surface of the negative electrode active material particles, reducing the probability of side reactions between the electrolyte and the negative electrode during battery cycling, and further improving the cycle performance of the battery cell.

[0036] In any embodiment, the electrolyte comprises a third cyclic carbonate, which includes one or more of ethylene carbonate, propylene carbonate, butenyl carbonate, hexenyl carbonate, and γ-butyrolactone.

[0037] In any embodiment, the mass content of the third cyclic carbonate is 1%-10% based on the total mass of the electrolyte.

[0038] In any embodiment, the mass content of the third cyclic carbonate is 3%-7% based on the total mass of the electrolyte.

[0039] The electrolyte contains the aforementioned types of third cyclic carbonates, and the mass content of the third cyclic carbonates meets the above-mentioned range. This enables the electrolyte to have suitable viscosity and ionic conductivity, improves the uniformity of current density distribution in the large-area positive electrode film, reduces the probability of lithium plating, and further enhances the cycle performance of the battery cell.

[0040] In any embodiment, the electrolyte includes a lithium salt, which includes lithium sulfonamide salt, and the mass content of the lithium sulfonamide salt is 1%-10% based on the total mass of the electrolyte.

[0041] In any embodiment, the mass content of the lithium sulfonamide salt is 2%-7% based on the total mass of the electrolyte.

[0042] The electrolyte contains lithium sulfonylimide salt and the mass content of lithium sulfonylimide salt within the above-mentioned range, which enables the electrolyte to have suitable ionic conductivity. This helps to improve the uniformity of current distribution in the large-area coated positive electrode film and enhance the cycle performance of the battery cell. Simultaneously, it reduces the probability of corrosion reaction between sulfonylimide anions and the current collector metal, further improving the cycle performance of the battery cell.

[0043] In any embodiment, the lithium salt further includes lithium hexafluorophosphate, and the mass ratio of the lithium hexafluorophosphate to the lithium sulfonamide salt in the electrolyte is 1-10.

[0044] In any embodiment, the mass ratio of lithium hexafluorophosphate to lithium sulfonamide salt in the electrolyte is 2-4.

[0045] When the mass ratio of lithium sulfonylimide salt to lithium hexafluorophosphate in the electrolyte meets the above-mentioned range, the electrolyte can have a suitable ionic conductivity, improve the uniformity of current distribution in the large-area coated positive electrode film, and thus enhance the cycle performance of the battery cell.

[0046] In any embodiment, the lithium sulfonamide salt includes one or more of lithium bisfluorosulfonamide and lithium bistrifluoromethanesulfonate.

[0047] Electrolytes containing the aforementioned types of sulfonylimide lithium salts exhibit higher lithium-ion mobility, enabling the electrolyte to possess suitable ionic conductivity. This helps improve the uniformity of current distribution in large-area coated positive electrode films, further enhancing the cycle performance of individual battery cells.

[0048] In any embodiment, the electrode assembly includes a negative electrode sheet, the negative electrode sheet includes 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 includes a negative electrode active material, and the graphitization degree of the negative electrode active material is 90%-93%.

[0049] In any embodiment, the degree of graphitization of the negative electrode active material is 91%-92%.

[0050] During the charge-discharge cycle of a battery cell, lithium ions insert and extract between the negative electrode materials, causing the negative electrode material to expand and contract in volume. In the later stages of long-term operation of the energy storage battery, under the influence of large expansion forces, the negative electrode active material is prone to cracking, film shedding, and powdering, leading to a sharp drop in battery performance and hindering further improvement in cycle performance. In this application, the negative electrode active material with a graphitization degree meeting the above-mentioned range is used. It has a suitable interlayer spacing, which helps reduce the volume expansion of the negative electrode after lithium insertion, thereby alleviating the expansion of the battery cell in the later stages of cycling and further improving the cycle performance of the battery cell.

[0051] In any embodiment, the half-width at half-maximum (WHM) of the negative electrode active material at the position of the 002 diffraction peak of graphite in the X-ray diffraction pattern is 0.15°-0.5°, wherein the 002 diffraction peak of graphite is a diffraction peak at 26.6°-27.2°.

[0052] In any embodiment, the full width at half maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak of graphite in the X-ray diffraction pattern measured by an X-ray diffractometer is 0.25°-0.35°.

[0053] In X-ray diffraction patterns, the 002 diffraction peak of graphite represents its layered stacking structure and the degree of order within the layered material. The full width at half maximum (FWHM) of the 002 diffraction peak reflects the integrity of the crystal structure stacking in the vertical direction. A smaller FWHM indicates a sharper 002 diffraction peak, a more ordered layered stacking structure, and greater volume expansion after lithium intercalation. Conversely, a larger FWHM indicates a more disordered layered stacking structure, and less volume expansion after lithium intercalation. The battery cells in this embodiment utilize negative electrode active materials with FWHMs of the 002 diffraction peak meeting the above-mentioned range. This leverages the relatively disordered interlayer stacking structure to reduce volume expansion during lithium-ion intercalation, thereby alleviating expansion in the later stages of cycling and further improving the cycle performance of the battery cells.

[0054] In any embodiment, the compacted density of the positive electrode active material at 3T is 2.2 g / cm³. 3 -3.2g / cm 3 .

[0055] In any embodiment, the powder compaction density of the positive electrode active material at 3T is 2.5 g / cm³. 3 -2.9g / cm 3 .

[0056] Meeting the above-mentioned range of powder compaction density of positive electrode active material is beneficial to improving the compaction density of positive electrode film, increasing the loading of active material in positive electrode film with large coating area, thereby further improving the capacity of battery cell.

[0057] In any embodiment, the compaction density of the positive electrode film is 2.4 g / cm³. 3 -3.0g / cm 3 .

[0058] In any embodiment, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.8g / cm 3 .

[0059] Meeting the above-mentioned range in terms of compaction density of the positive electrode film layer is beneficial to increasing the loading of active materials in the large-area positive electrode film layer, thereby further improving the capacity of the battery cell.

[0060] In any embodiment, the positive electrode active material comprises a lithium-containing transition metal phosphate with an olivine structure, the lithium-containing transition metal phosphate comprising a dopant element Q, the dopant element Q comprising one or more of Ti, V, Al, Mg, W, Na, K, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, B, S, Si, N, F, Cl, Br, and Zr.

[0061] Lithium-containing transition metal phosphates with an olivine structure exhibit excellent cycle life, thermal stability, and safety performance. The use of lithium-containing transition metal phosphates as the positive electrode active material in the battery cells of this application embodiment helps improve the reliability of the battery cells during long-term cycle operation in energy storage scenarios. Doping the lithium-containing transition metal phosphate with element Q can improve the stability of the crystal structure and the rate performance of the positive electrode active material, which is beneficial for improving the uniformity of the current density distribution in a large-area positive electrode film, reducing the probability of particle pulverization and cracking, and further improving the cycle life of the energy storage battery.

[0062] In any embodiment, the content of the dopant element Q is 0.01%-0.3% based on the total mass of the lithium-containing transition metal phosphate.

[0063] Doping with element Q can improve the lattice structure and rate performance of lithium-containing transition metal phosphates. However, excessive doping with Q atoms can cause lattice distortion, obstruction of lithium-ion insertion / extraction pathways, and the formation of irreversible impurity phases, which are detrimental to further improving the capacity and cycle performance of the battery cell. In the battery cells of this application, the content of doping element Q meets the above-mentioned range, thus achieving a balance between improving the cycle life and capacity of the battery cell.

[0064] In any embodiment, the dopant element Q includes Ti, and the mass content of Ti is 0.05%-0.1% based on the total mass of the lithium-containing transition metal phosphate.

[0065] In any embodiment, the dopant element Q includes element V, and the mass content of element V is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate.

[0066] Doping lithium transition metal phosphates with Ti and V elements can effectively improve the lattice stability of the material, which helps to reduce the probability of particle pulverization and cracking of the positive electrode active material under the large expansion force in the later stage of cycling, reduce the probability of side reactions in the electrolyte, reduce the consumption of active lithium ions, and further improve the cycle life of the battery cell.

[0067] In any embodiment, the dopant element Q includes Al, and the mass content of the Al element is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate.

[0068] In any embodiment, the dopant element Q includes Mg, and the mass content of Mg is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate.

[0069] Doping lithium-containing transition metal phosphates with Al and Mg elements can effectively improve the rate performance of the material, which is beneficial to improving the uniformity of current density distribution in large-area coated positive electrode films, reducing the probability of lithium ion deposition, and further improving the cycle performance of energy storage batteries.

[0070] In any embodiment, the lithium-containing transition metal phosphate has components of the following general formula:

[0071] LimFexPyOjQq,

[0072] Wherein, Q includes one or more of W, Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and Zr, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0073] In any embodiment, the median L of the sphericity in the cumulative distribution curve of the particle sphericity area obtained from the cross-section of the positive electrode film along the electrode thickness direction is... A50 It is 0.70-0.85.

[0074] In any embodiment, the median L of the sphericity in the cumulative distribution curve of the particle sphericity area obtained from the cross-section of the positive electrode film along the electrode thickness direction is... A50 It is 0.70-0.76.

[0075] In the cumulative distribution curve of the spheroidal area of ​​the particles obtained by the cross section of the positive electrode film along the thickness direction of the electrode sheet, the median of spheroidal area within the above range means that the particles occupying most of the area and space in the positive electrode film are also relatively rounded and the material morphology is relatively uniform. Under the action of external force, they can effectively slip and participate in the connection and reconstruction of the force chain, thereby helping to improve the compaction density of the positive electrode film and the capacity of the battery cell.

[0076] In any embodiment, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The value ranges from 0.98 to 1.20, where the degree of graphitization C is I. G / I D I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 The intensity of peak D at that location.

[0077] In any embodiment, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 It is 1.02-1.10.

[0078] The higher the degree of graphitization of carbon on the surface of the positive electrode active material, the higher the proportion of graphite structure carbon in the positive electrode film layer. The particles are more likely to slip during the rolling process by means of the highly graphitized carbon structure in the coating material. This can further reduce the possibility of stress concentration and increase the compaction density of the positive electrode film layer. Furthermore, the high degree of graphitization of the coating material can improve the electronic conductivity of the positive electrode sheet and improve the uniformity of current distribution in the large coating area positive electrode film layer, thereby improving the cycle performance of the battery cell.

[0079] In any embodiment, the positive current collector includes a main body and a tab, wherein the tab has a dimension of 25mm-40mm along the second direction.

[0080] In any embodiment, the size of the tab portion along a third direction is 30mm-50mm.

[0081] In a large-area positive electrode sheet, electrons in the positive current collector flow from various regions of the electrode sheet to the tab, resulting in a higher current density near the tab than at the far end of the current collector body. This causes current accumulation at the tab, leading to localized overheating and "hot spots," which is detrimental to further improving the cycle performance of the battery cell. In the battery cell of this application embodiment, the dimensions of the tab along the second and third directions meet the above-mentioned range. This increases the current-carrying area of ​​the positive electrode tab, reduces the local resistance of the tab, and effectively disperses the current density near the tab, thereby improving the uniformity of current distribution at the tab of the large-area positive electrode sheet and further enhancing the cycle performance of the battery cell.

[0082] An embodiment of the second aspect of this application provides a battery device that includes the battery cell described in the first aspect embodiment.

[0083] An embodiment of the third aspect of this application provides an electrical device that includes the battery cell described in the first aspect embodiment.

[0084] An embodiment of the fourth aspect of this application provides an energy storage device that includes the battery cell described in the first aspect embodiment above.

[0085] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0086] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0087] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0088] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 2;

[0089] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application;

[0090] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application;

[0091] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4;

[0092] 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.

[0093] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0094] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, battery assembly, power consumption device, and energy storage device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0095] 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.

[0096] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0097] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0098] 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.

[0099] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0100] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0101] In recent years, battery cells have been increasingly used in energy storage systems. To meet market demand for high capacity, it is necessary to increase the coating area of ​​the positive electrode active material in the battery cell to achieve high capacity, improve the energy storage capacity of the energy storage system, and meet the application and functional requirements of the energy storage system such as "continuous operation and energy transfer". However, the applicant has found that large-capacity energy storage batteries are prone to lithium plating in the middle and late stages of their long cycle life, making it difficult to further improve the cycle life of the energy storage battery.

[0102] Based on this, an embodiment of the first aspect of this application provides a battery cell, the battery cell including an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a positive electrode active material, and the coating area of ​​the positive electrode film layer in the battery cell being greater than or equal to 11m². 2 The positive electrode film layer includes a one-dimensional conductive agent, and the electrolyte includes fluoroethylene carbonate. Based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate is 0.05%-5%.

[0103] Unlike power batteries, energy storage batteries need to operate in conjunction with power station systems to meet the requirements of constant power charging. This means that the charging current of an energy storage battery does not decrease as its capacity decays throughout its entire lifespan. Power batteries, on the other hand, are typically charged at a constant rate, meaning the charging current is adapted to the battery capacity. As the capacity of individual battery cells decreases during use, the charging current of the power battery also decreases accordingly. This fundamental difference forces energy storage batteries to withstand higher charging rates after capacity decay, making them prone to performance degradation after long-term cycling. Increasing the coating area of ​​the positive electrode active material in a battery cell further increases the differences in electron transport paths, causing uneven current density distribution, triggering concentration polarization within the battery, increasing the probability of lithium plating in individual cells, and limiting further improvements in the cycle life of energy storage batteries.

[0104] The applicant's research found that the positive electrode film contains a one-dimensional conductive agent, which can form a linearly intersecting mesh conductive network inside the positive electrode film. This is beneficial to improving the conductivity of the positive electrode sheet, improving the uniformity of current distribution in a large-area coated positive electrode film, and improving the cycle performance of the battery cell.

[0105] However, research shows that the conductive network formed by one-dimensional conductive agents has a rigid structure, which restricts the volume change of the positive electrode active material in the battery cell during cycling. This makes the positive electrode active material prone to particle pulverization and cracking under large expansion forces in the middle and later stages of the battery's long cycle life. The exposed fresh material interface will undergo side reactions with the electrolyte, exacerbating lithium consumption and limiting further improvement in the cycle life of the battery cell in the later stages of long-cycle operation. The battery cell provided in this application further adds 0.05%-5% fluoroethylene carbonate to the electrolyte, which further improves the cycle life of the battery cell, including the positive electrode film layer with a large coating area, meeting the long-term cycle reliability requirements of energy storage power systems. Although the mechanism is not yet clear, it is speculated that fluoroethylene carbonate can form an electrolyte interface film (CEI film) rich in F element on the exposed interface of the positive electrode active material, which helps to reduce the probability of side reactions between the fresh interface exposed by the active material particles due to pulverization and cracking and the electrolyte, thereby reducing lithium consumption and achieving further improvement in the cycle life of the battery cell.

[0106] In this application, the term "positive electrode film" has the meaning known in the art, referring to the area of ​​the positive electrode active material covering the positive electrode current collector. "Coating area of ​​the positive electrode film" refers to the area calculated by multiplying the length and width of the area of ​​the positive electrode active material covering the positive electrode current collector.

[0107] Understandably, the coating area of ​​the positive electrode film in a single battery cell refers to the area of ​​the positive active material covering the positive current collector in all electrode components within the battery cell. It should be noted that for a single-sided coated positive electrode, the coating area is calculated by statistically analyzing the area of ​​the positive active material covering the positive current collector on that side; for a double-sided coated positive electrode, the coating area is calculated by summing the areas of the positive active material covering the positive current collector on both sides separately.

[0108] In some embodiments, the coating area of ​​the positive electrode film in the battery cell may be selected as 11m². 2 15m 2 18m 2 20m 2 30m 2 40m 2 50m 2 60m 2 70m 2 80m 2 90m 2 100m 2 110m 2 120m 2 130m 2 140m 2 150m 2 Or the range of values ​​between any two.

[0109] In some embodiments, the coating area of ​​the positive electrode film in the battery cell is 11m². 2 -150m 2 In some embodiments, the coating area of ​​the positive electrode film in the battery cell is 11m². 2 -120m 2 In some embodiments, the coating area of ​​the positive electrode film in the battery cell is 11m². 2 -100m 2 .

[0110] In some embodiments, based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate can be selected as 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range between the two.

[0111] When used in this document, the composition and proportion of fluoroethylene carbonate in the electrolyte can be determined using methods or instruments known in the art. As an example, the following method can be referenced: Disassemble the battery cell to obtain the electrolyte to be tested. Refer to GB / T9722-2023 "General Rules for Gas Chromatography of Chemical Reagents" for qualitative and quantitative analysis of the solvent in the electrolyte using gas chromatography to identify the composition and proportion of fluoroethylene carbonate.

[0112] In some embodiments, the mass content of the fluoroethylene carbonate is 0.1%-0.5% based on the total mass of the electrolyte.

[0113] The mass content of fluoroethylene carbonate in the electrolyte meets the above range, which is conducive to the formation of a positive electrode interface CEI film with a suitable thickness on the surface of the positive electrode particles. This reduces the probability of phenomena such as excessive CEI film thickness and increased lithium-ion transport impedance, thereby improving the uniformity of current distribution in the positive electrode film layer and further enhancing the cycle performance of the energy storage battery cell.

[0114] In some embodiments, the capacity of the battery cell is greater than or equal to 400 Ah.

[0115] In some embodiments, the capacity of the battery cell can be selected as 400Ah, 500Ah, 600Ah, 700Ah, 800Ah, 900Ah, 1000Ah, 1100Ah, 1200Ah, 1300Ah, 1400Ah, 1500Ah, 1600Ah, 1700Ah, 1800Ah, 1900Ah, 2000Ah, 2100Ah, 2200Ah, 2300Ah, 2400Ah, 2500Ah, 2600Ah, 2700Ah, 2800Ah, 2900Ah, 3000Ah, or any value range between the two.

[0116] In some embodiments, the capacity of the battery cell is 400Ah-3000Ah. In some embodiments, the capacity of the battery cell is 500Ah-1500Ah. In some embodiments, the capacity of the battery cell is 600Ah-1000Ah.

[0117] In this application, the term "capacity of a single battery cell" refers to the maximum amount of charge that a single battery cell can store.

[0118] In this application, the capacity of a single battery cell can be tested using equipment and methods known in the art. For example, at 25°C, the battery cell is discharged at a constant power of 0.5P to its discharge cutoff voltage and allowed to stand for 30 minutes. Then, the battery cell is subjected to a charge-discharge cycle test at a constant power of 0.5P: First charge-discharge cycle: The battery cell is charged at a constant power of 0.5P to its charging cutoff voltage, allowed to stand for 30 minutes, and then discharged at a constant power of 0.5P to its discharge cutoff voltage. The discharge capacity Q1 is recorded, where Q1 is the capacity of the battery cell, in Ah.

[0119] In this application, those skilled in the art can reasonably adjust the discharge cut-off voltage and charge cut-off voltage according to the different types of positive electrode active materials and the operating conditions of the battery cells. As an example, if lithium iron phosphate is used as the positive electrode active material, the discharge cut-off voltage can be set to 2.5V and the charge cut-off voltage can be set to 3.65V.

[0120] In some embodiments, the dimension of the battery cell along the first direction is T, the dimension of the battery cell along the second direction is H, and the dimension of the battery cell along the third direction is L, where 50mm≤T≤100mm, 200mm≤H≤240mm, and 250mm≤L≤350mm, and the first direction, the second direction, and the third direction are perpendicular to each other.

[0121] In some embodiments, the dimension T of the battery cell along the first direction can be selected as 50mm, 55mm, 60mm, 65mm, 70mm, 75mm, 80mm, 85mm, 90mm, 95mm, 100mm, or any value range between two of these. In some embodiments, the dimension T of the battery cell along the first direction satisfies 60mm ≤ T ≤ 90mm.

[0122] In some embodiments, the dimension H of the battery cell along the second direction can be selected as 200mm, 205mm, 210mm, 215mm, 220mm, 225mm, 230mm, 235mm, 240mm, or any value range between two of these. In some embodiments, the dimension H of the battery cell along the second direction satisfies 210mm ≤ H ≤ 230mm.

[0123] In some embodiments, the dimension L of the battery cell along a third direction can be selected as 250mm, 260mm, 270mm, 280mm, 290mm, 300mm, 310mm, 320mm, 330mm, 340mm, 350mm, or any value between two of these. In some embodiments, the dimension L of the battery cell along a third direction satisfies 260mm ≤ L ≤ 290mm.

[0124] Large-size, high-capacity battery cells have a high active material load, which helps meet the high-capacity requirements of energy storage systems. However, during the later stages of cycling, under constant power charging, the differences in electron transport paths within the positive electrode film are amplified, exacerbating the uneven current density distribution and increasing the probability of lithium plating, which is detrimental to further improving cycle life. The technical solution provided in this application is particularly suitable for large-size, high-capacity battery cells, effectively improving the uniformity of current distribution in the large-area positive electrode film, reducing the probability of lithium metal deposition, and further improving the cycle performance of the battery cells.

[0125] In some implementations, the second direction is parallel to the direction of gravity.

[0126] The second direction is parallel to the direction of gravity of the battery cell in use. It can be understood that when the energy storage device is placed on a horizontal surface, the direction of gravity of the battery cell is parallel to the first direction, which is parallel to the height direction of the battery cell when it is loaded into the energy storage device.

[0127] In some embodiments, the specific surface area of ​​the one-dimensional conductive agent is 100 m². 2 / g-220m 2 / g.

[0128] In some embodiments, the specific surface area of ​​the one-dimensional conductive agent may be selected as 100 m². 2 / g、110m 2 / g, 120m 2 / g, 130m 2 / g, 140m 2 / g, 150m 2 / g、160m 2 / g、170m 2 / g、180m 2 / g、190m 2 / g、200m 2 / g、210m 2 / g、220m 2 / g or any value between the two.

[0129] In some embodiments, the oil absorption value of the one-dimensional conductive agent is 100mL / 100g-200mL / 100g.

[0130] In some embodiments, the oil absorption value of the one-dimensional conductive agent can be selected as 100mL / 100g, 110mL / 100g, 120mL / 100g, 130mL / 100g, 140mL / 100g, 150mL / 100g, 160mL / 100g, 170mL / 100g, 180mL / 100g, 190mL / 100g, 200mL / 100g, or any value range between the two.

[0131] The fact that the specific surface area and oil absorption value of the one-dimensional conductive agent meet the above range indicates that the one-dimensional conductive agent has a suitable pore structure, which effectively reduces the probability of the one-dimensional conductive agent agglomerating and entangled in the positive electrode film, thereby forming a good conductive network. This is beneficial to improving the conductivity of the positive electrode sheet, improving the uniformity of current distribution in the large-area positive electrode film, reducing the probability of lithium plating, and further improving the cycle performance of the battery cell.

[0132] In this paper, the specific surface area of ​​one-dimensional conductive agents can be determined by any method known in the art. As an example, the following method can be used: Referring to GB / T 19587-2017, the specific surface area of ​​the one-dimensional conductive agent sample is tested using the nitrogen adsorption specific surface area analysis method, and the result is calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0133] In this paper, the oil absorption value of the one-dimensional conductive agent can be determined by any method known in the art. As an example, the following method can be used: The oil absorption value of the one-dimensional conductive agent is tested using the paraffin oil + torque method: A DABS-H model oil absorbent meter is selected, and the oil absorption value of the one-dimensional conductive agent is tested according to the national standard "Carbon Black Part 2: Determination of Oil Absorption Value" (GB / T3780.2—2007). The sample is added to the mixing tank of the oil absorbent meter, and paraffin oil is added to the sample at a rate of 4 mL / min using a titrator. As the oil absorption value of the sample increases, the mixture changes from a free-flowing state to a semi-plastic agglomerate, and the viscosity of the mixture continuously increases. This viscosity is transmitted to the torque sensing system of the oil absorbent meter. When the viscosity of the mixture reaches a predetermined torque value, the oil absorbent meter and the titrator automatically shut off simultaneously. The volume of oil added is read directly from the burette; the volume of oil absorbed per unit mass of sample is the oil absorption value of the sample.

[0134] In some embodiments, the powder resistivity of the one-dimensional conductive agent is less than or equal to 50 mΩ·cm. In some embodiments, the powder resistivity of the one-dimensional conductive agent can be selected from 5 mΩ·cm, 10 mΩ·cm, 15 mΩ·cm, 20 mΩ·cm, 25 mΩ·cm, 30 mΩ·cm, 35 mΩ·cm, 40 mΩ·cm, 45 mΩ·cm, 50 mΩ·cm, or any value range between the two.

[0135] The resistivity of the one-dimensional conductive agent powder meets the above range, which is beneficial to improve the conductivity of the positive electrode sheet, thereby improving the uniformity of current distribution in the large-area coated positive electrode film, reducing the probability of lithium plating, and improving the cycle performance of the battery cell.

[0136] In this paper, the powder resistivity of one-dimensional conductive agents can be determined by any method known in the art. As an example, the following method can be used for testing: using a PRCD1100 powder resistivity meter, referring to the national standard GB / T30835-2014.

[0137] In some embodiments, the mass content of the one-dimensional conductive agent is 0.1%-2% based on the total mass of the positive electrode film.

[0138] In some embodiments, based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive agent can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or any value range between the two.

[0139] In some embodiments, the mass content of the one-dimensional conductive agent is 0.2%-1% based on the total mass of the positive electrode film.

[0140] The content of one-dimensional conductive agent in the positive electrode film layer that meets the above range can form a good conductive network in the positive electrode film layer with a large coating area, improve the conductivity of the positive electrode sheet and the uniformity of current distribution, reduce the probability of lithium plating, and further improve the cycle performance of the battery cell; at the same time, it can also effectively reduce the excessive space occupied by the introduced one-dimensional conductive agent in the positive electrode active material, while also improving the battery capacity.

[0141] In some embodiments, the one-dimensional conductive agent includes one or more of single-arm carbon nanotubes, multi-arm carbon nanotubes, and carbon nanofibers.

[0142] The positive electrode film layer includes the above-mentioned types, which can form a good conductive network in the positive electrode film layer with a large coating area, improve the conductivity of the positive electrode sheet and the uniformity of current distribution, and further improve the cycle performance of the battery cell.

[0143] In some embodiments, the electrolyte comprises vinylene carbonate, and the mass content of vinylene carbonate is 0.5%-8% based on the total mass of the electrolyte.

[0144] In some embodiments, based on the total mass of the electrolyte, the mass content of the vinylene carbonate can be selected as 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, or any range between the two.

[0145] In some embodiments, the vinylene carbonate content is 0.6%-4% based on the total mass of the electrolyte.

[0146] The electrolyte includes vinylene carbonate, which can be oxidized when the battery charging voltage increases to form a positive electrode interface film. This helps to alleviate the direct contact between the fresh interface exposed by the pulverization and cracking of the positive electrode active material particles and the electrolyte, thereby reducing the occurrence of internal side reactions, lowering lithium consumption, and further improving the cycle performance of the battery cell. At the same time, vinylene carbonate can form an SEI film on the surface of the negative electrode active material particles, reducing the probability of side reactions between the electrolyte and the negative electrode during battery cycling, and further improving the cycle performance of the battery cell.

[0147] Understandably, the mass content of vinylene carbonate in the electrolyte can be tested using the method for determining the mass content of fluoroethylene carbonate described above.

[0148] In some embodiments, the electrolyte comprises a third cyclic carbonate, which includes one or more of ethylene carbonate, propylene carbonate, butene carbonate, hexene carbonate, and γ-butyrolactone.

[0149] In some embodiments, the mass content of the third cyclic carbonate is 1%-10% based on the total mass of the electrolyte.

[0150] In some embodiments, based on the total mass of the electrolyte, the mass content of the third cyclic carbonate can be selected as 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, or any range between the two.

[0151] In some embodiments, the mass content of the third cyclic carbonate is 3%-7% based on the total mass of the electrolyte.

[0152] The electrolyte contains the aforementioned types of third cyclic carbonates, and the mass content of the third cyclic carbonates meets the above-mentioned range. This enables the electrolyte to have suitable viscosity and ionic conductivity, improves the uniformity of current density distribution in the large-area positive electrode film, reduces the probability of lithium plating, and further enhances the cycle performance of the battery cell.

[0153] In some embodiments, the electrolyte includes a lithium salt, which includes lithium sulfonamide, and the mass content of the lithium sulfonamide is 1%-10% based on the total mass of the electrolyte.

[0154] In some embodiments, based on the total mass of the electrolyte, the mass content of the lithium sulfonamide salt can be selected as 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, or any range between the two.

[0155] In some embodiments, the mass content of the lithium sulfonamide salt is 2%-7% based on the total mass of the electrolyte.

[0156] The electrolyte contains lithium sulfonylimide salt and the mass content of lithium sulfonylimide salt within the above-mentioned range, which enables the electrolyte to have suitable ionic conductivity. This helps to improve the uniformity of current distribution in the large-area coated positive electrode film and enhance the cycle performance of the battery cell. Simultaneously, it reduces the probability of corrosion reaction between sulfonylimide anions and the current collector metal, further improving the cycle performance of the battery cell.

[0157] In this application, the mass content of lithium sulfonylimide salt in the battery cell can be determined using instruments and methods known in the art. As an example, the following method can be used for testing: disassemble the battery cell, remove the electrolyte, and perform qualitative or quantitative analysis of the inorganic components / electrolyte lithium salt in the electrolyte using ion chromatography, referring to standard JY / T 0575-2020 "General Rules for Ion Chromatography Analysis," to determine the mass content of lithium sulfonylimide.

[0158] In some embodiments, the lithium salt further includes lithium hexafluorophosphate, and the mass ratio of the lithium hexafluorophosphate to the lithium sulfonamide salt in the electrolyte is 1-10.

[0159] In some embodiments, the mass ratio of lithium hexafluorophosphate to lithium sulfonamide salt in the electrolyte can be selected as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or any range between the two.

[0160] In some embodiments, the mass ratio of lithium hexafluorophosphate to lithium sulfonamide salt in the electrolyte is 2-4.

[0161] When the mass ratio of lithium sulfonylimide salt to lithium hexafluorophosphate in the electrolyte meets the above-mentioned range, the electrolyte can have a suitable ionic conductivity, improve the uniformity of current distribution in the large-area coated positive electrode film, and thus enhance the cycle performance of the battery cell.

[0162] In some embodiments, the lithium sulfonamide salt includes one or more of lithium bisfluorosulfonamide and lithium bistrifluoromethanesulfonate.

[0163] Electrolytes containing the aforementioned types of sulfonylimide lithium salts exhibit higher lithium-ion mobility, enabling the electrolyte to possess suitable ionic conductivity. This helps improve the uniformity of current distribution in large-area coated positive electrode films, further enhancing the cycle performance of individual battery cells.

[0164] In some embodiments, the electrode assembly includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative electrode film layer 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%-93%.

[0165] In some embodiments, the degree of graphitization of the negative electrode active material can be selected as 90%, 90.2%, 90.4%, 90.6%, 90.8%, 91%, 91.2%, 91.4%, 91.6%, 91.8%, 92%, 92.2%, 92.4%, 92.6%, 92.8%, 93%, or any value range between the two.

[0166] In some embodiments, the degree of graphitization of the negative electrode active material is 91%-92%.

[0167] During the charge-discharge cycle of a battery cell, lithium ions insert and extract between the negative electrode materials, causing the negative electrode material to expand and contract in volume. In the later stages of long-term operation of the energy storage battery, under the influence of large expansion forces, the negative electrode active material is prone to cracking, film shedding, and powdering, leading to a sharp drop in battery performance and hindering further improvement in cycle performance. In this application, the negative electrode active material with a graphitization degree meeting the above-mentioned range is used. It has a suitable interlayer spacing, which helps reduce the volume expansion of the negative electrode after lithium insertion, thereby alleviating the expansion of the battery cell in the later stages of cycling and further improving the cycle performance of the battery cell.

[0168] In some embodiments, the half-width at half-maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak of graphite in the X-ray diffraction pattern is 0.15°-0.5°, wherein the 002 diffraction peak of graphite is a diffraction peak at 26.6°-27.2°.

[0169] In some embodiments, the full width at half maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak corresponding to graphite in the X-ray diffraction pattern measured by an X-ray diffractometer can be selected as 0.15°, 0.20°, 0.25°, 0.30°, 0.35°, 0.40°, 0.45°, 0.50°, or any value range between the two.

[0170] In some embodiments, the full width at half maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak of graphite in the X-ray diffraction pattern is 0.25°-0.35°.

[0171] In X-ray diffraction patterns, the 002 diffraction peak of graphite represents its layered stacking structure and the degree of order within the layered material. The full width at half maximum (FWHM) of the 002 diffraction peak reflects the integrity of the crystal structure stacking in the vertical direction. A smaller FWHM indicates a sharper 002 diffraction peak, a more ordered layered stacking structure, and greater volume expansion after lithium intercalation. Conversely, a larger FWHM indicates a more disordered layered stacking structure, and less volume expansion after lithium intercalation. The battery cells in this embodiment utilize negative electrode active materials with FWHMs of the 002 diffraction peak meeting the above-mentioned range. This leverages the relatively disordered interlayer stacking structure to reduce volume expansion during lithium-ion intercalation, thereby alleviating expansion in the later stages of cycling and further improving the cycle performance of the battery cells.

[0172] In this application, the full width at half maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak of graphite in the X-ray diffraction pattern can be tested using instruments and methods known in the art. As an example, the following method can be used for measurement: Disassemble the battery cell, remove the negative electrode sheet, scrape off the powder of the negative electrode active material to be tested, and then use an X-ray diffractometer to measure and obtain the XRD diffraction pattern. Analyze the pattern using software (e.g., Jade 6.5), remove background noise, and calibrate the graphite 002 diffraction peak located at 26.6°-27.2°. Then calculate the peak height of the 002 diffraction peak, find the two points corresponding to the left and right peak positions at the half-peak height, and calculate the difference in the horizontal coordinates to obtain the full width at half maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak of graphite in the X-ray diffraction pattern.

[0173] In some embodiments, the powder compaction density of the positive electrode active material at 3T is 2.2 g / cm³. 3 -3.2g / cm 3 .

[0174] In some embodiments, the powder compaction density of the positive electrode active material at 3T can be selected as 2.20 g / cm³. 3 2.22 g / cm 3 2.24 g / cm 3 2.26 g / cm 3 2.28g / cm 3 2.30g / cm 3 2.32 g / cm 3 2.34 g / cm 3 2.36 g / cm 3 2.38g / cm 3 2.40 g / cm 3 2.42 g / cm 3 2.44 g / cm 3 2.46 g / cm 3 2.48 g / cm 3 2.50g / cm 3 2.52g / cm 3 2.54 g / cm 3 2.56 g / cm 3 2.58g / cm 3 2.60g / cm 3 2.62 g / cm 3 2.64 g / cm 3 2.66 g / cm 3 2.68g / cm 3 2.70 g / cm 32.72 g / cm 3 2.74 g / cm 3 2.76 g / cm 3 2.78g / cm 3 2.80g / cm 3 2.82 g / cm 3 2.84 g / cm 3 2.86 g / cm 3 2.88g / cm 3 2.90g / cm 3 2.92g / cm 3 2.94 g / cm 3 2.96 g / cm 3 2.98g / cm 3 3.00g / cm 3 3.02g / cm 3 3.04 g / cm 3 3.06 g / cm 3 3.08g / cm 3 3.10 g / cm 3 3.12g / cm 3 3.14 g / cm 3 3.16 g / cm 3 3.18 g / cm 3 3.20g / cm 3 Or the range of values ​​between any two.

[0175] In some embodiments, the powder compaction density of the positive electrode active material at 3T is 2.5 g / cm³. 3 -2.9g / cm 3 .

[0176] Meeting the above-mentioned range of powder compaction density of positive electrode active material is beneficial to improving the compaction density of positive electrode film, increasing the loading of active material in positive electrode film with large coating area, thereby further improving the capacity of battery cell.

[0177] In this application, the term "powder compaction density" refers to the density of a compacted compact with a certain density and strength, formed during the external force compression process. This density is measured in g / cm³, as the powder moves and deforms, larger voids are filled, the contact area between particles increases, resulting in attractive forces between atoms and enhanced mechanical cohesion between particles. 3 .

[0178] The compacted density of the positive electrode active material powder can be measured using methods and equipment known in the art. For example, it can be measured using a compaction density instrument, referring to GB / T 24533-2009. Specifically, a certain amount of positive electrode active material is placed on a compaction mold (the mold diameter is known). The mold is hollow in the middle and has a metal disc at the top and bottom. The positive electrode active material is placed between the metal discs, and a metal cylinder is placed on top. The mold is placed on a compaction density instrument, and the pressure is set to 3T. The thickness of the positive electrode active material under 3T pressure can be read on the instrument. The compacted density of the positive electrode active material powder is ρ = m / v, where v = (S × H), m is the mass of the positive electrode active material, and S is the bottom area of ​​the mold (1.327 cm²). 2 H represents the thickness of the positive electrode active material after compaction.

[0179] In some embodiments, the compaction density of the positive electrode film is 2.4 g / cm³. 3 -3.0g / cm 3 .

[0180] In some embodiments, the compaction density of the positive electrode film layer may be selected as 2.40 g / cm³. 3 2.45g / cm 3 2.50g / cm 3 2.55g / cm 3 2.60g / cm 3 2.65g / cm 3 2.70 g / cm 3 2.75g / cm 3 2.80g / cm 3 2.85g / cm 3 2.90g / cm 3 2.95g / cm 3 3.00g / cm 3 Or the range of values ​​between any two.

[0181] In some embodiments, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.8g / cm 3 .

[0182] Meeting the above-mentioned range in terms of compaction density of the positive electrode film layer is beneficial to increasing the loading of active materials in the large-area positive electrode film layer, thereby further improving the capacity of the battery cell.

[0183] In this application, the compaction density of the positive electrode film can be determined by instruments and methods known in the art. For example, after discharging the battery cell to a fully discharged state (approximately 0% SOC), the positive electrode sheet at full discharge is disassembled, and the residual electrolyte is cleaned with an organic solvent (the organic solvent can be a conventional solvent in the art that can clean the electrolyte, including but not limited to dimethyl carbonate, etc.). After removing the residual electrolyte, the electrode sheet is dried, and the compaction density of the positive electrode film is measured. The compaction density of the positive electrode film is the density of any side of the positive electrode film measured after disassembly / the thickness of any side of the positive electrode film.

[0184] In this application, the fully discharged state refers to placing the battery cell at 25°C and letting it stand for 2 hours until the battery temperature is maintained at 25°C, then discharging the battery at a constant power of 0.5P until the discharge cutoff voltage is reached.

[0185] In this application, the density of any side of the positive electrode film layer has a meaning known in the art and can be tested using methods known in the art. For example, take a positive electrode sheet that has been coated on one side and cold-pressed, or take out the positive electrode sheet from a fully discharged battery cell (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1. Then wipe off the positive electrode film layer of the above-weighed positive electrode sheet, weigh the current collector, and record it as M0. The density of any side of the positive electrode film layer = (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, with the unit being g / 1540.25mm. 2 .

[0186] The thickness of either side of the positive electrode film layer has a meaning known in the art and can be tested using methods known in the art, such as a micrometer (e.g., a Mitutoyo 293-100 with an accuracy of 0.1 μm). It is understood that when a battery cell is fully discharged, the compaction density of the positive electrode film layer differs from the design value of the battery cell's compaction density. Due to practical operational factors, when disassembling a fully discharged battery cell to test the compaction density of the positive electrode film layer, the measured value is often slightly lower than the design value.

[0187] In some embodiments, the positive electrode active material comprises a lithium-containing transition metal phosphate with an olivine structure, wherein the lithium-containing transition metal phosphate comprises a dopant element Q, and the dopant element Q comprises one or more of Ti, V, Al, Mg, W, Na, K, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, B, S, Si, N, F, Cl, Br, and Zr.

[0188] Lithium-containing transition metal phosphates with an olivine structure exhibit excellent cycle life, thermal stability, and safety performance. The use of lithium-containing transition metal phosphates as the positive electrode active material in the battery cells of this application embodiment helps improve the reliability of the battery cells during long-term cycle operation in energy storage scenarios. Doping the lithium-containing transition metal phosphate with element Q can improve the stability of the crystal structure and the rate performance of the positive electrode active material, which is beneficial for improving the uniformity of the current density distribution in a large-area positive electrode film, reducing the probability of particle pulverization and cracking, and further improving the cycle life of the energy storage battery.

[0189] In some embodiments, the content of the dopant element Q is 0.01%-0.3% based on the total mass of the lithium-containing transition metal phosphate.

[0190] Doping with element Q can improve the lattice structure and rate performance of lithium-containing transition metal phosphates. However, excessive doping with Q atoms can cause lattice distortion, obstruction of lithium-ion insertion / extraction pathways, and the formation of irreversible impurity phases, which are detrimental to further improving the capacity and cycle performance of the battery cell. In the battery cells of this application, the content of doping element Q meets the above-mentioned range, thus achieving a balance between improving the cycle life and capacity of the battery cell.

[0191] In some embodiments, based on the total mass of the lithium-containing transition metal phosphate, the content of the dopant element Q can be selected as 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.11%, 0.13%, 0.15%, 0.17%, 0.19%, 0.21%, 0.23%, 0.25%, 0.27%, 0.29%, 0.3%, or any value range between the two.

[0192] In this application, the type and content of dopant element Q in the positive electrode active material can be tested using any method known in the art. As an example, inductively coupled plasma atomic emission spectrometry (ICP-AES) is used to test the dopant element Q and its content, referring to Appendix C of GB / T 33822-2017.

[0193] In some embodiments, the dopant element Q includes Ti, and the mass content of Ti is 0.05%-0.1% based on the total mass of the lithium-containing transition metal phosphate.

[0194] In some embodiments, the dopant element Q includes element V, and the mass content of element V is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate.

[0195] Doping lithium transition metal phosphates with Ti and V elements can effectively improve the lattice stability of the material, which helps to reduce the probability of particle pulverization and cracking of the positive electrode active material under the large expansion force in the later stage of cycling, reduce the probability of side reactions in the electrolyte, reduce the consumption of active lithium ions, and further improve the cycle life of the battery cell.

[0196] In some embodiments, the dopant element Q includes Al, and the mass content of the Al element is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate.

[0197] In some embodiments, the dopant element Q includes Mg, and the mass content of Mg is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate.

[0198] Doping lithium-containing transition metal phosphates with Al and Mg elements can effectively improve the rate performance of the material, which is beneficial to improving the uniformity of current density distribution in large-area coated positive electrode films, reducing the probability of lithium ion deposition, and further improving the cycle performance of energy storage batteries.

[0199] In some embodiments, the lithium-containing transition metal phosphate has components of the following general formula:

[0200] LimFexPyOjQq,

[0201] Wherein, Q includes one or more of W, Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and Zr, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0202] In some embodiments, m can be 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, or any value between two of these. In some embodiments, x can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any value between two of these. In some embodiments, y can be 0.95, 0.98, 1.0, or any value between two of these. In some embodiments, j can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any value between two of these. In some implementations, q can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value between the two.

[0203] In some embodiments, the median L of the spheroidal area distribution curve of the particles obtained from the cross-section of the positive electrode film along the electrode thickness direction is... A50 It is 0.70-0.85.

[0204] In some embodiments, the median L of the spheroidal area distribution curve of the particles obtained from the cross-section of the positive electrode film along the electrode thickness direction is... A50 The value can be selected as 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85 or any range between the two.

[0205] In some embodiments, the median L of the spheroidal area distribution curve of the particles obtained from the cross-section of the positive electrode film along the electrode thickness direction is... A50 It is 0.70-0.76.

[0206] In the cumulative distribution curve of the spheroidal area of ​​the particles obtained by the cross section of the positive electrode film along the thickness direction of the electrode sheet, the median of spheroidal area within the above range means that the particles occupying most of the area and space in the positive electrode film are also relatively rounded and the material morphology is relatively uniform. Under the action of external force, they can effectively slip and participate in the connection and reconstruction of the force chain, thereby helping to improve the compaction density of the positive electrode film and the capacity of the battery cell.

[0207] In this application, the term "particle" refers to a particle in the positive electrode film layer that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist inside the particle, but a complete boundary sufficient to divide the particle cannot be identified inside the particle.

[0208] The particle identification method is as follows: The positive electrode film layer is cut along the thickness direction of the electrode sheet using an argon ion beam (for example, a Leica EM TIC 3X CP device can be used, operating voltage: 6kV, operating time: 6h). After exposing the cut surface, a scanning electron microscope (SEM) is used (for example, a Hitachi SU8230 device can be used, operating voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) to observe the cut surface along the thickness direction of the electrode sheet. Images are acquired using a field emission scanning electron microscope at a non-edge location in the cut surface of the positive electrode film layer (after observing the electrode edge under the SEM, the field of view is adjusted to the center of the sample) in secondary electron mode. Electron micrographs are taken at 10kx magnification, and the particles in the electron micrographs are analyzed using ImageJ software (1.46r, win64 version). The specific steps for using ImageJ software are as follows: Load the scanning electron microscope image to be analyzed, as shown in Figure 1; use the Cellpose plugin software to identify particles, and then perform manual corrections; use ImageJ to read and analyze data. The specific method for identifying particles using the Cellpose plugin software is as follows: Set the segmentation diameter parameter (diameter in the Segmentation module) to 15 pixels, click "run cyto3" to identify particles; manually mark particles in the image that were not identified by the software, were not fully identified by the software, or had identification errors. Particles that were not identified by the software, were not fully identified by the software, or had identification errors mainly include the following: 1. Particles that are too large or have scratches on their surface, making them unidentifiable or incompletely recognizable; 2. During argon ion beam cutting, scratches may be generated on the particle surface, and the software may misjudge these scratches as particle boundaries, leading to identification errors; 3. Particles that are too small and were not successfully identified; 4. Particles located at the edge of the electron microscope's field of view, with the particle's interior penetrated by the edge, preventing a complete display of the morphology, and resulting in identification errors due to partial identification replacing the whole.For the unidentified or misidentified particles mentioned above, manual calibration is performed. The specific process is as follows: 1. Delete large particles located around the edges of the scanning electron microscope that are not fully displayed. 2. Determine if any unidentified or misidentified particles have internal cracks or scratches. If no cracks or scratches are found, classify it as a single particle and manually mark it based on the observed particle boundary. 3. If cracks or scratches are found inside the particle, determine if they penetrate the particle. If not, classify it as a single particle and manually mark it. 4. If cracks or scratches penetrate the particle, determine if they are linear or irregular. 5. If the cracks or scratches are irregular, classify them as the boundary between particles and divide the particles along this boundary. 6. If the cracks or scratches are linear, perform contrast comparison. 7. If the contrast is not obvious and there is no crack-like appearance, classify it as a scratch and mark it as a single particle. 8. If the contrast is strong and there is a crack-like appearance, classify it as the boundary between particles and mark it as two particles. After manual marking, delete information irrelevant to the particles from the automatic image processing, thus completing the particle identification and marking in the image.

[0209] The specific method for statistical analysis of particles in the positive electrode film is as follows: Images after particle identification and labeling are imported into ImageJ software for analysis. Scale settings are completed based on the scanning electron microscope (SEM) images. The particle size and area in the cross-section along the electrode thickness direction of the positive electrode film are analyzed using the "Feret Diameter," "Area," "Round," and "Solidity" analysis functions. According to the software manual (ImageJ User Guide IJ1.46r), the "Feret" parameter obtained from the analysis represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, thus characterizing the particle size. Since particles with a diameter less than 50 nm present significant errors during the statistical process and are difficult to accurately identify, and since the particle size of conductive agents is generally less than 50 nm, it will introduce significant errors into the statistical results. Therefore, in this application, particles with a diameter less than 50 nm are not counted in the particle size statistics process, and the statistical data for particles with AR, Round, or Solidity values ​​displayed as "NaN" are deleted. Following the above method, to ensure a statistically significant sample size, at least 10 non-overlapping scanning electron microscope images were acquired for each electrode, and the particle size of at least 5000 particles was statistically analyzed.

[0210] Unlike the state of the positive electrode active material in Malvern laser scattering, and also unlike the state of the positive electrode active material when directly observed by scanning electron microscopy, the particles in the positive electrode film exhibit a well-dispersed state under the action of roller pressure. Observing the positive electrode film is beneficial for effectively characterizing the particle size and distribution within it.

[0211] During the compaction process, the positive electrode film is compacted in the thickness direction. The cross-section of the positive electrode film along the thickness direction is more reflective of the actual compaction of the particles inside the film in a spatial scale than the surface of the positive electrode film.

[0212] It is understandable that the particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, especially those larger than 50 nm, mainly originate from the positive electrode active material. Therefore, the embodiments of this application can accurately and objectively reflect the distribution of lithium-containing transition metal phosphate particles in the electrode sheet by observing and statistically analyzing the particle size in the cross-section of the positive electrode film.

[0213] In this application, the median test method for the sphericity of particles obtained from the cumulative distribution curve of particle sphericity area along the thickness direction of the positive electrode film is as follows: Particles in the cross-section of the positive electrode film are identified using the method described above. While using the "Feret" function in ImageJ to identify the particle size, the "Shape Description" and "Area" analysis functions are used to analyze the morphology and area of ​​the particles in the cross-section along the thickness direction of the positive electrode film. According to the software manual (ImageJ User Guide IJ 1.46r), the "Area" parameter obtained from the analysis represents the pixel area of ​​the particle, and the "Round" parameter represents the ratio of the pixel area of ​​the particle to the area of ​​a circle with the fitted major axis as its diameter. The closer the particle is to a sphere, the closer the ratio of the pixel area to the area of ​​the circle with the fitted major axis as its diameter is to 1. Therefore, the "Round" parameter of the particle obtained from the analysis characterizes the sphericity of the particle. The sphericity of particles in the cross-section along the thickness direction of the obtained positive electrode film is arranged in ascending order. A cumulative distribution curve of the sphericity area of ​​particles in the positive electrode film is obtained with sphericity as the horizontal axis and cumulative area percentage as the vertical axis. The median sphericity refers to the sphericity corresponding to a cumulative area percentage of 50% on the vertical axis of the cumulative area distribution curve.

[0214] In some embodiments, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The value ranges from 0.98 to 1.20, where the degree of graphitization C is I. G / I D I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 The intensity of peak D at that location.

[0215] In some embodiments, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The value can be selected from 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, or any value range between the two.

[0216] In some embodiments, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 It is 1.02-1.10.

[0217] In this application, the graphitization degree C value of the positive electrode film can be obtained by surface scanning mode of a laser confocal Raman spectrometer. As an example, specifically, a laser confocal Raman spectrometer (high-precision Renishaw laser confocal Raman spectrometer) is used, with an excitation wavelength of 532 nm. An appropriate amount of the positive electrode film is taken and surface scanned on its surface or along the thickness direction of the electrode. The scanning area is 45 μm × 45 μm, divided into 10 × 10 grids, with grid vertices as test points, a step size of 5 μm, and a total of 100 scan points. Thus, the C values ​​at different sites and the cumulative distribution curve of the C values ​​in the surface scan area are obtained.

[0218] The graphitization degree C of the positive electrode film was obtained by the ratio of the peak intensities of the G-band and D-band in the Raman spectrum. The position of the G-band peak was 1580±100 cm⁻¹. -1 Its characterization of carbon sp 2 Hybrid structure; D peak position is 1350±100 cm⁻¹ -1 It characterizes a disordered structure, where disorder refers to the irregular arrangement of carbon atoms within the structure. In graphite crystals, carbon atoms in the same layer arrange themselves in an sp... 2 Hybridization forms covalent bonds, while interlayer bonding is facilitated by van der Waals forces, making the carbon in the graphite structure prone to slippage. Therefore, the C value can characterize the degree of graphitization of the cathode film. A higher C value indicates a higher degree of graphitization of the carbon material. It is understandable that the degree of graphitization in the cathode film mainly originates from the graphitized carbon material within the film, i.e., the carbon coating material of the cathode active material. Although rich in sp... 2 One-dimensional conductive agents with hybrid structures (such as carbon nanotubes) also have relatively high I0. G / I DHowever, due to its low content and small tube diameter, its addition to the positive electrode film results in an extreme value in the Raman surface scan test of the positive electrode film, and does not affect the graphitization degree C in the positive electrode film. 50 This has an impact. Therefore, the degree of graphitization of the positive electrode film can also be used to characterize the degree of graphitization of the positive electrode active material.

[0219] The higher the degree of graphitization of carbon on the surface of the positive electrode active material, the higher the proportion of graphite structure carbon in the positive electrode film layer. The particles are more likely to slip during the rolling process by means of the highly graphitized carbon structure in the coating material. This can further reduce the possibility of stress concentration and increase the compaction density of the positive electrode film layer. Furthermore, the high degree of graphitization of the coating material can improve the electronic conductivity of the positive electrode sheet and improve the uniformity of current distribution in the large coating area positive electrode film layer, thereby improving the cycle performance of the battery cell.

[0220] The cumulative distribution curve of graphitization degree C value refers to the curve obtained by arranging at least 100 C values ​​in ascending order, with graphitization degree as the horizontal axis and the cumulative percentage as the vertical axis. 50 This represents the C value corresponding to a cumulative percentage of 50% on the vertical axis of the cumulative distribution curve of graphitization degree C. The median C value of graphitization degree. 50 Compared to point values, it can reflect the overall graphitization degree of particles in the positive electrode film, i.e., the degree of slippage; compared to the mean value, it can reduce the influence of extreme values ​​during the test and improve the confidence of the test results.

[0221] Those skilled in the art can control the degree of graphitization of active material particles using any known process. As an example, adjusting the carbon source (which can be cross-linked PEG), sintering temperature, sintering time, sintering pressure, sintering atmosphere, and nucleation process can all achieve the adjustment of the degree of graphitization of active material particles.

[0222] In some embodiments, the positive current collector includes a main body and a tab, wherein the tab has a dimension of 25mm-40mm along the second direction.

[0223] In some embodiments, the tab portion has a dimension of 30mm-50mm along a third direction.

[0224] In some embodiments, the size of the tab portion along the second direction can be selected as 25mm, 27mm, 30mm, 32mm, 35mm, 38mm, 40mm or any value range between the two.

[0225] In some embodiments, the dimensions of the tab portion along a third direction can be selected as 30mm, 32mm, 34mm, 36mm, 38mm, 40mm, 42mm, 44mm, 46mm, 48mm, 50mm, or any value range between the two.

[0226] In a large-area positive electrode sheet, electrons in the positive current collector flow from various regions of the electrode sheet to the tab, resulting in a higher current density near the tab than at the far end of the current collector body. This causes current accumulation at the tab, leading to localized overheating and "hot spots," which is detrimental to further improving the cycle performance of the battery cell. In the battery cell of this application embodiment, the dimensions of the tab along the second and third directions meet the above-mentioned range. This increases the current-carrying area of ​​the positive electrode tab, reduces the local resistance of the tab, and effectively disperses the current density near the tab, thereby improving the uniformity of current distribution at the tab of the large-area positive electrode sheet and further enhancing the cycle performance of the battery cell.

[0227] [Positive electrode plate]

[0228] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0229] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0230] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0231] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0232] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components used to prepare the positive electrode film layer, such as positive electrode active material, conductive agent, binder and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0233] [Negative electrode plate]

[0234] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0235] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0236] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0237] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0238] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0239] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0240] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0241] [Isolation membrane]

[0242] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0243] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0244] [Battery cell]

[0245] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0246] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0247] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0248] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0249] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0250] [Battery Device]

[0251] This application also provides a battery device, which includes the battery cell provided in this application. In some embodiments, the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0252] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0253] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, 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 manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0254] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0255] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0256] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0257] [Electrical appliances]

[0258] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in 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.

[0259] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0260] 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.

[0261] 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.

[0262] This application also provides an energy storage device that uses a battery device as a power source. The energy storage device can be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system.

[0263] Example

[0264] 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.

[0265] I. Preparation Method

[0266] Example 1

[0267] (1) Preparation of positive electrode active material

[0268] S1, lithium carbonate, iron phosphate, glucose and titanium dioxide are added to water and mixed in a premixing tank at 1800 rpm. The mixture is demagnetized by a demagnetizing rod with a magnetic field strength of 8000-12000 Gs. The ratio of lithium carbonate to iron phosphate is such that the molar ratio of iron to phosphorus is 0.975. The mass content of glucose relative to the total amount of iron phosphate is 5.7%. The titanium dioxide doping amount is such that the mass content of titanium doped in the carbon-coated lithium iron phosphate positive electrode active material product is 5000 ppm.

[0269] S2, the mixed raw materials are subjected to two grinding-demagnetization cycles in a sand mill. The first grinding is performed using 0.6mm diameter zirconia balls at 500rpm for 1 hour, with a grinding chamber pressure of less than 0.3MPa. After the first grinding, the raw materials are demagnetized using a permanent magnet separator with a demagnetization intensity greater than or equal to 8000Gs. The demagnetized raw materials are then ground a second time to obtain a mixed slurry. The particle size D of the mixed slurry is... V50 It is 0.40μm ± 0.10μm;

[0270] S3, the mixed slurry is spray-dried to obtain precursor powder.

[0271] S4, the precursor powder is sintered to obtain lithium iron phosphate cathode material. The sintering process includes:

[0272] First sintering: The precursor powder is sintered in a nitrogen atmosphere, heated from 25°C to 760°C at a heating rate of 5°C / min, and held at that temperature for 10 hours. After cooling, the first sintered product is obtained.

[0273] Grinding and mixing: 1.5% glucose and 3.0% polyethylene glycol (by mass of the first sintered product) were added to the first sintered product; the mixture was then divided into two groups for grinding (third grinding), wherein the particle size of the first group was... V50 Grinding was stopped when the particle size reached 1.0 μm ± 0.20 μm (grinding conditions: 550 rpm ± 50 rpm, grinding time 1 h), yielding the first group of ground products; the particle size D of the second group... V50 Grinding was stopped when the particle size reached 0.38μm±0.05μm (grinding conditions: 500rpm±50rpm, grinding time 4h), and a second set of grinding products was obtained; the first set of grinding products and the second set of grinding products were mixed at a mass ratio of 70:30 to obtain a mixed intermediate product; the mixed intermediate product was spray-dried.

[0274] Second sintering: The dried mixed intermediate product is sintered in a nitrogen atmosphere, heated from 25°C to 800°C at a heating rate of 5°C / min, and held at that temperature for 10 hours. After cooling, the second sintered product is obtained.

[0275] S5. After sintering, the product is cooled to below 100°C and then crushed using an air jet milling method to obtain carbon-coated lithium iron phosphate cathode active material. The air jet milling stage frequency is 25Hz and the milling pressure is 0.55MPa.

[0276] The prepared positive electrode active material has a carbon content of 1.248% by mass and a powder compaction density of 2.62 g / cm³ under a pressure of 3T. 3 .

[0277] (2) Preparation of the positive electrode sheet:

[0278] A mixture of 97.1 wt% positive electrode active material, 0.8 wt% conductive carbon black, 0.6 wt% one-dimensional conductive agent single-arm carbon nanotubes, and 1.5 wt% PVDF was prepared by mixing, followed by the addition of N-methylpyrrolidone and stirring to disperse the mixture. This positive electrode slurry was then coated onto a 13 μm thick aluminum foil, dried, and cold-pressed to obtain a single-sided surface density of 320 mg / 1540.25 mm. 2 The compacted density is 2.68 g / cm³. 3 The positive electrode. The one-dimensional conductive agent has a specific surface area of ​​150 m². 2 / g, oil absorption value of 155mL / 100g, powder resistivity of 10mΩ·cm.

[0279] The median C of the graphitization degree of the prepared positive electrode film obtained in laser microscopy confocal Raman spectroscopy instrument scanning mode. 50The value is 1.04. In the cumulative distribution curve of the particle spheroidity area obtained from a cross-section along the electrode thickness direction, the median L of spheroidity is... A50 It is 0.725.

[0280] (3) Preparation of negative electrode sheet

[0281] The negative electrode film is formed by uniformly coating a negative electrode slurry (using deionized water as the solvent) onto the surface of a negative electrode current collector (a copper foil with a thickness of 5 μm), followed by drying and cold pressing. The negative electrode film comprises a negative electrode active material in a mass ratio of 96.1:0.7:1.2:2, a conductive agent acetylene black, a dispersant sodium carboxymethyl cellulose, and a binder styrene-butadiene rubber (SBR).

[0282] The graphitization degree of the negative electrode active material is 91.5%, and the full width at half maximum (FWHM) at the peak position of the 002 diffraction peak corresponding to graphite in the X-ray diffraction pattern is 0.3°; the single-sided density of the negative electrode film is 150 mg / 1540.25 mm. 2 When the battery cell is fully discharged, the compaction density of the negative electrode film is 1.6 g / cm³. 3 The porosity of the negative electrode sheet is 25%.

[0283] (4) Preparation of the separating membrane

[0284] The separator is made of polyethylene film with a thickness of 5μm and a porosity of 36%.

[0285] (5) Preparation of electrolyte

[0286] The electrolyte comprises 35% dimethyl carbonate (DMC), 16% ethyl methyl carbonate (EMC), 20% ethylene carbonate (EC), 10% propylene carbonate (PC), 3% lithium bis(fluorosulfonyl)imide (LiFSI), 6% lithium hexafluorophosphate (LiPF6), 2% fluoroethylene carbonate (FEC), and 8% vinylene carbonate (VC) by mass.

[0287] (6) Battery assembly

[0288] The negative electrode, separator, and positive electrode are arranged in sequence, with the separator positioned between the negative and positive electrodes to provide isolation. The bare cell is obtained by winding, placed in a casing, and filled with electrolyte. After encapsulation, formation, and venting, a battery cell is obtained. The battery cell has a capacity of 600 Ah, a length L of 271 mm, a height H of 213 mm, a thickness T of 71 mm, and a positive electrode film coating area of ​​20 m². 2 The tab portion of the positive electrode current collector in the battery cell has a dimension of 30mm along the second direction and a dimension of 45mm along the third direction.

[0289] Example 2

[0290] The preparation of the battery cell in Example 2 is similar to that in Example 1, except that the mass content of fluoroethylene carbonate (FEC) in the electrolyte is adjusted to 0.3%, the content of propylene carbonate (PC) is adjusted to 5%, and the content of vinylene carbonate (VC) is adjusted to 2%; at the same time, the content of one-dimensional conductive agent in the positive electrode film is adjusted to 0.5%.

[0291] Example 3

[0292] The preparation of the battery cell in Example 3 is similar to that in Example 2, except that the coating area of ​​the positive electrode film in the battery cell is adjusted, and the size of the battery cell is adjusted accordingly. The specific parameters are shown in Table 1.

[0293] Examples 4-7

[0294] The preparation of battery cells in Examples 4-7 is similar to that in Example 2, except that the mass content of fluoroethylene carbonate (FEC) in the electrolyte is adjusted. Specific parameters are shown in Table 1.

[0295] Examples 8-10

[0296] The preparation of battery cells in Examples 8-10 is similar to that in Example 2, except that the mass content of propylene carbonate (PC) in the electrolyte is adjusted. Specific parameters are shown in Table 1.

[0297] Examples 11-13

[0298] The preparation of the battery cells in Examples 11-13 is similar to that in Example 2, except that the mass content of the one-dimensional conductive agent in the positive electrode film is adjusted. The specific parameters are shown in Table 1.

[0299] Examples 14-16

[0300] The preparation of the battery cells in Examples 14-16 is similar to that in Example 2, except that the mass content of vinylene carbonate (VC) in the electrolyte is adjusted. The specific parameters are shown in Table 1.

[0301] Examples 17-20

[0302] The preparation of the battery cells in Examples 17-20 is similar to that in Example 2, except that the full width at half maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak corresponding to graphite in the X-ray diffraction pattern is adjusted. The specific parameters are shown in Table 2.

[0303] Examples 21-23

[0304] The preparation of the battery cells in Examples 21-23 is similar to that in Example 2, except that the preparation of the positive electrode active material is adjusted, specifically:

[0305] Example 21: In step S4, the D of the particles in the first group V50 Grinding was stopped when the particle size reached 1.50μm±0.20μm; grinding was stopped when the particle size Dv50 in the second group reached 0.50μm±0.05μm.

[0306] Example 22: In step S2, the particle size D of the mixed slurry V50 The thickness is 0.35μm ± 0.10μm; in step S4, after obtaining the first sintering product, a second sintering is performed directly, and the holding time for the second sintering is 12h.

[0307] Example 23: In step S4, the D of the particles in the first group V50 Grinding was stopped when the particle size reached 0.80μm ± 0.20μm; the D of the particles in the second group... V50 Stop grinding when the thickness reaches 0.30μm±0.05μm.

[0308] This alters the median C of the graphitization degree of the positive electrode film obtained in laser microscopy confocal Raman spectroscopy instrument scanning mode. 50 And in the cumulative distribution curve of particle spheroidity area obtained from the cross-section along the thickness direction of the positive electrode film, the median L of spheroidity is... A50 Specific parameters are shown in Table 3.

[0309] Example 24

[0310] The battery cell preparation in Example 24 is similar to that in Example 2, except that the dimensions of the positive current collector tab along the second and third directions are adjusted. Specific parameters are shown in Table 4.

[0311] Comparative Example 1

[0312] The preparation of the battery cell in Comparative Example 1 was similar to that in Example 2, except that the coating area of ​​the positive electrode film in the battery cell was adjusted to not be greater than or equal to 11 μm. 2 The coating area was controlled at 6.8m². 2 See the table for specific parameters.

[0313] Comparative Example 2

[0314] The preparation of the battery cell in Comparative Example 2 is similar to that in Example 2, except that no one-dimensional conductive agent is added to the positive electrode film of the battery cell. Specific parameters are shown in the table.

[0315] Comparative Example 3

[0316] The preparation of the battery cell in Comparative Example 3 was similar to that in Example 2, except that no fluorinated carbonate was added to the electrolyte of the battery cell. Specific parameters are shown in the table.

[0317] II. Performance Testing

[0318] 1. Cycle performance test of individual battery cells at 25℃

[0319] At 25℃, the battery cells were discharged at a constant power of 0.5P until the voltage of the battery cell reached 2.5V, and then allowed to rest for 30 minutes. Then, the battery cells were subjected to a charge-discharge cycle test at a constant power of 0.5P: First charge-discharge cycle: The battery cell was charged at a constant power of 0.5P to 3.65V, allowed to rest for 30 minutes, and then discharged at a constant power of 0.5P to 2.5V, recording the discharge capacity Q1; subsequently, after allowing the battery to rest for 30 minutes, the first charge-discharge cycle was repeated; this cycle was repeated, and the discharge capacity Qn was recorded. When the discharge capacity Qn of the battery cell decayed to 70% of Q1, the number of cycles for the battery cell was recorded.

[0320] 2. Cycle performance test of individual battery cells at 45℃

[0321] At 45℃, the battery cells were discharged at a constant power of 0.5P until the voltage of the battery cell reached 2.5V, and then allowed to rest for 30 minutes. Next, the battery cells were subjected to a charge-discharge cycle test at a constant power of 0.5P: First charge-discharge cycle: The battery cell was charged at a constant power of 0.5P to 3.65V, allowed to rest for 30 minutes, and then discharged at a constant power of 0.5P to 2.5V, recording the discharge capacity Q1. Afterward, the battery was allowed to rest for 30 minutes, and the first charge-discharge cycle was repeated. This cycle was repeated, and the discharge capacity Qn was recorded. When the discharge capacity Qn of the battery cell decreased to 70% of Q1, the number of cycles for the battery cell was recorded.

[0322] 3. Capacity testing of individual battery cells

[0323] At 25℃, the battery cell is discharged at a constant power of 0.5P to the discharge cutoff voltage of 2.5V, and then left to stand for 30 minutes. Then, the battery cell is subjected to charge-discharge cycle test at a constant power of 0.5P: First charge-discharge cycle: The battery cell is charged at a constant power of 0.5P to the charging cutoff voltage of 3.65V, left to stand for 30 minutes, and then discharged at a constant power of 0.5P to the discharge cutoff voltage. The discharge capacity Q1 is recorded. Q1 is the capacity of the battery cell, in Ah.

[0324] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0325] Battery cells for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in the table below.

[0326] Table 1

[0327] As can be seen from the results of Comparative Example 1 in Table 1, the coating area of ​​the positive electrode film in the battery cell does not meet the requirement of being greater than or equal to 11m². 2 The battery cells exhibit good cycle life due to the small differences in electron transport paths and good uniformity of current density distribution. However, the small coating area of ​​the positive electrode active material results in low cell capacity, failing to meet the application requirements of high-capacity and high energy storage in energy storage batteries. As shown in Comparative Example 2, increasing the coating area of ​​the positive electrode film can improve battery capacity, but the current distribution uniformity is poor in large-area coatings, leading to a deterioration in cell cycle life. As shown in Comparative Example 3, the one-dimensional conductive agent in the positive electrode film can improve the uniformity of current distribution in large-area coatings, but it also increases the probability of particle pulverization, cracking, and side reactions with the electrolyte in the later stages of cycling. Further addition of fluoroethylene carbonate to the electrolyte can form a film on the particle surface, reducing side reactions and further improving the cell cycle life.

[0328] As can be seen from the results of Examples 2 and 3 in Table 1, the technical solution provided by this application is particularly suitable for large-area coated positive electrode film layers and high-capacity battery cells. It can effectively improve the uniformity of current distribution in the positive electrode film layer, which is beneficial to improving battery capacity while further improving the cycle life of battery cells.

[0329] As can be seen from the results of Examples 2 and 4-7 in Table 1, the mass content of fluoroethylene carbonate in the electrolyte is 0.05%-5%, and further 0.1%-0.5%, which is beneficial to form a positive electrode interface CEI film with a suitable thickness on the surface of the positive electrode particles, reducing the probability of side reactions, and alleviating the increase in impedance caused by excessive CEI film thickness, thereby further improving the cycle life of the energy storage battery cell.

[0330] As can be seen from the results of Examples 2 and 8-10 in Table 1, when the electrolyte contains propylene carbonate and the content of propylene carbonate is 1%-10%, and further 3%-7%, it helps to improve the dissociation degree of electrolyte salt, increase the conductivity of electrolyte, reduce lithium-ion transport impedance and lithium consumption; at the same time, it alleviates the graphite peeling and pulverization caused by propylene carbonate co-intercalation into graphite, and further improves the cycle life of battery cells.

[0331] As can be seen from the results of Examples 2 and 11-13 in Table 1, when the content of one-dimensional conductive agent in the positive electrode film is 0.1%-2%, and further 0.2%-1%, a good conductive network can be formed in the positive electrode film with a large coating area, improving the conductivity of the positive electrode sheet and the uniformity of current distribution, and further improving the cycle performance of the battery cell; at the same time, it can also effectively reduce the excessive occupation of the positive electrode active material space by the introduction of one-dimensional conductive agent, while taking into account the improvement of the capacity of the energy storage battery cell.

[0332] As can be seen from the results of Examples 2 and 14-16 in Table 1, when the mass content of vinylene carbonate in the electrolyte is 0.5%-8%, and further 0.6%-4%, an SEI film and CEI film of suitable thickness can be formed on the surface of the positive electrode active material and negative electrode active material particles, reducing the probability of side reactions in the battery cell and further improving the cycle life of the battery cell.

[0333] Table 2

[0334] As can be seen from the results of Examples 2 and 17-20 in Table 2, when the full width at half maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak corresponding to graphite in the X-ray diffraction pattern is 0.15°-0.5°, and further 0.25°-0.35°, the relatively disordered stacking structure between the layers of the negative electrode active material can be utilized to reduce the volume expansion of the negative electrode, thereby alleviating the expansion of the battery cell in the later stages of cycling and further improving the cycle performance of the battery cell.

[0335] Table 3

[0336] As can be seen from the results of Examples 2 and 21-23 in Table 3, the median L of the sphericity of the particles in the positive electrode film layer is... A50 A value of 0.70-0.76 indicates that the material has a relatively uniform morphology and a near-spherical shape, which allows it to slip effectively under external forces, participate in the connection and reconstruction of the force chain, and thus help to improve the compaction density of the positive electrode film and the capacity of the battery cell. At the same time, in the later stages of battery cell cycling, the effective slippage of particles helps to alleviate the expansion of particles inside the positive electrode film, reduce the probability of particle breakage and pulverization, and further improve the cycle life of the battery cell.

[0337] Table 4

[0338] As can be seen from the results of Examples 2 and 24 in Table 4, the dimensions of the positive current collector tab along the second direction are 25mm-40mm and the dimensions along the third direction are 30mm-50mm. This is beneficial to increase the current flow area of ​​the positive current collector tab and reduce the local resistance of the tab, thereby improving the uniformity of the current distribution in the tab of the large-area positive electrode sheet and further improving the cycle performance of the battery cell.

[0339] 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, The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, which includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector. The positive electrode film includes a positive active material. The coating area of ​​the positive electrode film in the battery cell is greater than or equal to 11m². 2 The positive electrode film layer includes a one-dimensional conductive agent. The electrolyte comprises fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is 0.05%-5% based on the total mass of the electrolyte.

2. The battery cell according to claim 1, characterized in that, The coating area of ​​the positive electrode film in the battery cell is 11m². 2 -150m 2 11m is optional 2 -120m 2 Further options include 11m. 2 -100m 2 .

3. The battery cell according to claim 1 or 2, characterized in that, Based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate is 0.1%-0.5%.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The capacity of the battery cell is greater than or equal to 400Ah, and can be selected from 400Ah to 3000Ah, further selected from 500Ah to 1500Ah, and even further selected from 600Ah to 1000Ah.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The dimension of the battery cell along the first direction is T, the dimension of the battery cell along the second direction is H, and the dimension of the battery cell along the third direction is L. 50mm≤T≤100mm, 200mm≤H≤240mm, 250mm≤L≤350mm, and the first direction, the second direction, and the third direction are perpendicular to each other.

6. The battery cell according to claim 5, characterized in that, The battery cell satisfies: 60mm≤T≤90mm or 210mm≤H≤230mm or 260mm≤L≤290mm.

7. The battery cell according to claim 5 or 6, characterized in that, The second direction is parallel to the direction of gravity.

8. The battery cell according to any one of claims 1 to 7, characterized in that, The one-dimensional conductive agent satisfies one or more of the following conditions: (1) The specific surface area of ​​the one-dimensional conductive agent is 100 m². 2 / g-220m 2 / g; (2) The oil absorption value of the one-dimensional conductive agent is 100mL / 100g-200mL / 100g; (3) The resistivity of the powder of the one-dimensional conductive agent is less than or equal to 50 mΩ·cm.

9. The battery cell according to any one of claims 1 to 8, characterized in that, Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive agent is 0.1%-2%, optionally 0.2%-1%.

10. The battery cell according to any one of claims 1 to 9, characterized in that, The one-dimensional conductive agent includes one or more of single-arm carbon nanotubes, multi-arm carbon nanotubes, and carbon nanofibers.

11. The battery cell according to any one of claims 1 to 10, characterized in that, The electrolyte comprises vinylene carbonate, and the mass content of the vinylene carbonate is 0.5%-8%, optionally 0.6%-4%, based on the total mass of the electrolyte.

12. The battery cell according to any one of claims 1 to 11, characterized in that, The electrolyte comprises a third cyclic carbonate, which includes one or more of ethylene carbonate, propylene carbonate, butene carbonate, hexene carbonate, and γ-butyrolactone.

13. The battery cell according to claim 12, characterized in that, Based on the total mass of the electrolyte, the mass content of the third cyclic carbonate is 1%-10%, optionally 3%-7%.

14. The battery cell according to any one of claims 1 to 13, characterized in that, The electrolyte includes a lithium salt, which includes lithium sulfonamide salt. Based on the total mass of the electrolyte, the mass content of the lithium sulfonamide salt is 1%-10%, optionally 2%-7%.

15. The battery cell according to claim 14, characterized in that, The lithium salt further includes lithium hexafluorophosphate, and the mass ratio of the lithium hexafluorophosphate to the lithium sulfonamide salt in the electrolyte is 1-10, optionally 2-4.

16. The battery cell according to claim 14 or 15, characterized in that, The lithium sulfonylimide salt includes one or more of lithium bisfluorosulfonylimide and lithium bistrifluoromethylsulfonate imide.

17. The battery cell according to any one of claims 1 to 16, characterized in that, The electrode assembly includes a negative electrode sheet, the negative electrode sheet includes 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 includes a negative electrode active material, and the graphitization degree of the negative electrode active material is 90%-93%, optionally 91%-92%.

18. The battery cell according to claim 17, characterized in that, The half-width at half-maximum (FWHM) of the negative electrode active material at the position of the 002 diffraction peak of graphite in the X-ray diffraction pattern is 0.15°-0.5°, which can be selected as 0.25°-0.35°. The 002 diffraction peak of graphite is located at 26.6°-27.2°.

19. The battery cell according to any one of claims 1 to 18, characterized in that, The compacted density of the positive electrode active material at 3T is 2.2 g / cm³. 3 -3.2g / cm 3 2.5g / cm³ is an option. 3 -2.9g / cm 3 .

20. The battery cell according to any one of claims 1 to 19, characterized in that, The compaction density of the positive electrode film is 2.4 g / cm³. 3 -3.0g / cm 3 2.5g / cm³ is an option. 3 -2.8g / cm 3 .

21. The battery cell according to any one of claims 1 to 20, characterized in that, The positive electrode active material comprises a lithium-containing transition metal phosphate with an olivine structure, wherein the lithium-containing transition metal phosphate comprises a dopant element Q, and the dopant element Q comprises one or more of Ti, V, Al, Mg, W, Na, K, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, B, S, Si, N, F, Cl, Br, and Zr.

22. The battery cell according to claim 21, characterized in that, Based on the total mass of the lithium-containing transition metal phosphate, the content of the dopant element Q is 0.01%-0.3%.

23. The battery cell according to claim 21 or 22, characterized in that, The lithium-containing transition metal phosphate satisfies one or more of the following conditions: (1) The doping element Q includes Ti element, and the mass content of Ti element is 0.05%-0.1% based on the total mass of the lithium-containing transition metal phosphate; (2) The doping element Q includes element V, and the mass content of element V is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate; (3) The doping element Q includes Al element, and the mass content of Al element is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate; (4) The doping element Q includes Mg, and the mass content of Mg is 0.1%-0.2% based on the total mass of the lithium-containing transition metal phosphate.

24. The battery cell according to any one of claims 21 to 23, characterized in that, The lithium-containing transition metal phosphate has the following general formula: LimFexPyOjQq, Wherein, Q includes one or more of W, Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and Zr, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.

1.

25. The battery cell according to any one of claims 1 to 24, characterized in that, In the cumulative distribution curve of particle sphericity area obtained from the cross-section of the positive electrode film along the electrode thickness direction, the median L of sphericity is... A50 The value is 0.70-0.85, and can be selected as 0.70-0.

76.

26. The battery cell according to any one of claims 1 to 25, characterized in that, In the cumulative distribution curve of the graphitization degree C value of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode, the median C of the graphitization degree is... 50 The value is 0.98-1.20, and can be selected as 1.02-1.10, where the graphitization degree C value is I. G / I D I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 The intensity of peak D at that location.

27. The battery cell according to any one of claims 1 to 26, characterized in that, The positive current collector includes a main body and an electrode tab. The electrode tab has a dimension of 25mm-40mm along the second direction; and / or, The size of the tab portion along the third direction is 30mm-50mm.

28. A battery device, characterized in that, The battery device comprises the battery cell according to any one of claims 1 to 27.

29. An electrical appliance, characterized in that, The electrical device includes a battery cell as described in any one of claims 1 to 27 or a battery device as described in claim 28.

30. An energy storage device, characterized in that, The energy storage device includes a battery cell as described in any one of claims 1 to 27 or a battery device as described in claim 28.

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