Battery cell, battery device and energy storage device

Abstract

Disclosed in the present application are a battery cell, a battery device and an energy storage device. The battery cell comprises an end cover, a housing, an electrode assembly and an electrolyte, wherein the housing comprises an accommodating cavity having an opening, the end cover is used for sealing the opening, the electrode assembly and the electrolyte are arranged in the accommodating cavity of the housing, the electrode assembly comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises lithium iron phosphate particles, and the lithium iron phosphate particles comprise one or more of a titanium element and a vanadium element; the electrolyte comprises a lithium fluorosulfonylimide salt, and on the basis of the total mass of the electrolyte, the mass content of the lithium fluorosulfonylimide salt is 2-7%; the compaction density of the positive electrode film layer is greater than or equal to 2.5 g / cm3; and the sum of the coating areas of the positive electrode film layers contained in the battery cell is greater than or equal to 11 m2.

Description

Battery cells, battery devices and energy storage devices

[0001] Cross-referencing

[0002] This application incorporates, in its entirety, the following PCT patent applications filed on March 28, 2025, entitled "Lithium-ion secondary battery, battery device, electrical device, method for preparing positive electrode active material and method for preparing positive electrode sheet": PCT / CN2025 / 085902, and December 5, 2025, entitled "Battery cell, battery device and energy storage device": PCT / CN2025 / 140522, which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a battery cell, a battery device, and an energy storage device. Background Technology

[0004] In recent years, battery cells have been increasingly widely used in energy storage devices. In various energy storage application scenarios, high capacity, long cycle life, and high energy conversion efficiency 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 and long-cycle operation places higher demands on battery performance. Therefore, there is an urgent need to develop battery cells that combine high capacity, long cycle life, and high energy conversion efficiency. Summary of the Invention

[0005] This application aims to at least solve one of the technical problems existing in the background art. To this end, one object of this application is to provide a battery cell, a battery device, and an energy storage device, wherein the battery cell has high capacity, high volumetric energy density, good cycle performance, and high energy conversion efficiency.

[0006] The first aspect of this application provides a battery cell, which includes an end cap, a housing, an electrode assembly, and an electrolyte. The housing includes a receiving cavity with an opening, and the end cap is used to close the opening. The electrode assembly and the electrolyte are disposed in the receiving cavity of the housing. The electrode assembly includes a positive electrode sheet, which includes 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 includes a positive active material, which includes lithium iron phosphate particles, and the lithium iron phosphate particles include one or more of titanium and vanadium. The electrolyte includes a lithium fluorosulfonyl imide salt, and the mass content of the lithium fluorosulfonyl imide salt is 2%-7% based on the total mass of the electrolyte. The compaction density of the positive electrode film layer is greater than or equal to 2.5 g / cm³. 3 The total coating area of ​​the positive electrode film in each battery cell is greater than or equal to 11m². 2 .

[0007] To meet the demand for high-capacity energy storage batteries in energy storage devices, the total coating area of ​​the positive electrode film within the battery cell can be increased to enhance the loading area of ​​the positive electrode active material and improve the battery cell's capacity. Furthermore, increasing the compaction density of the positive electrode film can increase the loading of positive electrode active material per unit volume, while also maintaining the volumetric energy density of the battery cell. However, high compaction density positive electrode films are prone to large rebound, making the positive electrode active material more susceptible to crushing and breakage under the high expansion force of the negative electrode in the later stages of long-term cycling. This leads to the failure of the positive electrode active material, exacerbates the capacity decay of the battery cell, and deteriorates its cycle performance. Meanwhile, a larger total coating area of ​​the positive electrode film will exacerbate uneven current distribution, easily leading to excessively high current density in local areas. In high current density areas, the electrochemical reaction rate is too fast, which can easily cause an increase in ion concentration gradient and generate concentration polarization. The high density of the positive electrode will further aggravate the polarization effect, causing the battery operating voltage to deviate from the equilibrium potential. During charging, a voltage higher than the equilibrium potential needs to be applied to drive ions to overcome various resistances. During discharging, the polarization resistance causes the output voltage to be lower than the equilibrium potential, resulting in an increase in the difference between the charging and discharging voltages. This part of the electrical energy is irreversibly converted into heat dissipation during the charging and discharging process, reducing the energy efficiency of the battery cell.

[0008] By doping one or more of titanium and vanadium elements into lithium iron phosphate, the applicant can form a more stable bonding network, improve the structural stability of lithium iron phosphate, enhance its mechanical strength and structural toughness, and help it better withstand the compression caused by the expansion of the negative electrode film during long-term cycling of the battery cell. This effectively reduces the probability of microcracks or even breakage of the positive electrode active material in the high-density positive electrode film, improves the structural integrity of the positive electrode active material, and improves the cycle performance of the battery cell.

[0009] However, due to the large total coating area and high compaction density of the positive electrode film, the battery cell is prone to uneven current distribution and excessively high local current density during charging and discharging. Simultaneously, the transport resistance of lithium ions in the high compaction density positive electrode increases significantly, exacerbating the polarization effect of the battery cell and leading to increased internal heat generation and temperature. Under high-temperature conditions, transition metal elements (such as iron, titanium, and vanadium) in the doped lithium iron phosphate are more prone to dissolution, leaching into the electrolyte and being reduced and deposited at the negative electrode. Studies have shown that transition metals deposited on the negative electrode act as catalysts, catalyzing the decomposition of the solid electrolyte interphase (SEI) film, causing more active lithium to be consumed during SEI film repair, thus deteriorating the cycle performance of the battery cell.

[0010] Therefore, the applicant further added a certain amount of fluorosulfonylimide lithium salt to the electrolyte. During cycling, it preferentially decomposes on the surface of the positive electrode active material to form a stable, dense, and LiF-rich positive electrode electrolyte interphase (CEI) film. On the one hand, the stable and dense CEI film formed by the fluorosulfonylimide lithium salt helps to inhibit the dissolution of transition metal ions into the electrolyte. Its anions have a strong complexing ability and easily coordinate with transition metal ions to form stable complexes, effectively reducing the probability of transition metal ions migrating to the negative electrode, reducing irreversible lithium ion consumption caused by rebuilding the SEI film, and improving the cycle performance of the battery cell. On the other hand, the CEI film has good ionic conductivity, which helps to reduce the charge transfer impedance at the positive electrode interface and improve the transport efficiency of lithium ions at the positive electrode interface. By reducing the transport impedance, the heat consumption of the battery can be compensated, thereby improving the energy efficiency of the battery cell.

[0011] When the lithium fluorosulfonylimide content in the electrolyte is less than 2%, it is insufficient to effectively construct a stable, dense, and LiF-rich CEI film on the positive electrode surface. This makes it difficult to effectively inhibit the dissolution of transition metal ions into the electrolyte, resulting in a large proportion of transition metal ions migrating to the negative electrode and being reduced and precipitated. Lithium ions are irreversibly consumed in the reconstruction of the SEI film, which deteriorates the cycle performance of the battery cell. When the lithium fluorosulfonylimide content in the electrolyte is greater than 7%, its high content of active anions will cause severe chemical corrosion to the positive electrode current collector, such as aluminum foil, which will adversely affect the cycle stability of the battery cell.

[0012] In summary, the compaction density of the positive electrode film layer of the battery cell provided in this application embodiment is greater than or equal to 2.5 g / cm³. 3 The total coating area of ​​the positive electrode film in each battery cell is greater than or equal to 11m². 2 Simultaneously, lithium iron phosphate doped with one or more elements of titanium and vanadium is used as the positive electrode active material, and 2%-7% of fluorosulfonylimide lithium salt is added to the electrolyte. On the basis of high capacity and high volumetric energy density, the cycle performance and energy efficiency of the battery cell are further improved.

[0013] In any embodiment, the fluorosulfonylimide lithium salt includes one or more of lithium bisfluorosulfonylimide and lithium bistrifluoromethylsulfonylimide, and may be selected as lithium bisfluorosulfonylimide.

[0014] The fluorosulfonylimide lithium salt, including the aforementioned substances, facilitates the formation of a stable and dense CEI film, inhibits the dissolution of transition metal ions into the electrolyte, and readily coordinates with transition metal ions to form stable complexes. This effectively reduces the probability of transition metal ions migrating to the negative electrode and minimizes irreversible lithium ion consumption due to SEI film reconstruction. Simultaneously, the CEI film exhibits excellent ionic conductivity, which helps reduce the charge transfer impedance at the positive electrode interface and improves the lithium ion transport efficiency at the positive electrode interface. By reducing the transport impedance, it compensates for battery heat consumption, thus balancing the cycle performance and energy efficiency of the battery cell.

[0015] In any embodiment, the mass content of the fluorosulfonylimide lithium salt is 3.7%-7% based on the total mass of the electrolyte.

[0016] The mass content of lithium fluorosulfonylimide salt within the above range is beneficial to further balance the amount of CEI film formation and the negative impact of lithium fluorosulfonylimide salt on the positive electrode current collector, thereby improving the cycle stability and energy conversion efficiency of the battery cell.

[0017] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0018] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 15m². 2 -130m 2 .

[0019] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 18m². 2 -115m 2 .

[0020] If the total coating area of ​​the positive electrode film layer contained in the battery cell is within the above range, it will help to further increase the loading area of ​​the positive electrode active material and increase the capacity of the battery cell.

[0021] In any embodiment, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -3.0g / cm 3 2.5g / cm³ is an option. 3 -2.8g / cm 3 .

[0022] The compaction density of the positive electrode film is within the above range, which helps to further increase the loading of positive electrode active material per unit volume and improve the volumetric energy density of the battery cell.

[0023] In any embodiment, the lateral density of the positive electrode film layer on any side is 0.25 g / 1540.25 mm. 2 -0.40g / 1540.25mm 2 .

[0024] This application embodiment further increases the lateral density of the positive electrode film layer on either side, which is beneficial to further improve the volumetric energy density and capacity of the battery cell. However, it increases the lithium-ion transport path, increases the diffusion resistance of lithium ions in the positive electrode film layer, intensifies the heat generation of the battery cell, and increases the dissolution of transition metal elements in the positive electrode active material. By adding a certain amount of fluorosulfonylimide lithium salt to the electrolyte, it is beneficial to form a stable and dense CEI film, inhibit the dissolution of transition metal ions into the electrolyte, and also easily coordinate with transition metal ions to form stable complexes, effectively reducing the probability of transition metal ions migrating to the negative electrode and reducing the irreversible consumption of lithium ions caused by rebuilding the SEI film. On the basis of high volumetric energy density and high capacity, the cycle performance of the battery cell is improved.

[0025] In any embodiment, the lateral density of the positive electrode film layer on any side is 0.25 g / 1540.25 mm. 2 -0.35g / 1540.25mm 2 .

[0026] Having the lateral density of the positive electrode film layer on either side within the above range is beneficial for further balancing the volumetric energy density, capacity, and cycle performance of the battery cell.

[0027] In any embodiment, the lithium iron phosphate particles include titanium, and the mass content of the titanium is 0.05%-0.10% based on the total mass of the positive electrode active material.

[0028] Within a reasonable range, the titanium content helps stabilize the crystal structure of lithium iron phosphate through titanium ion doping, enhancing the strength of PO bonds and thus improving the mechanical strength and structural toughness of lithium iron phosphate. This helps the battery cell withstand the periodic expansion force transmitted from the expansion of the negative electrode film during long-term cycling, effectively reducing the probability of microcracks or even breakage of the positive electrode active material in the high-density positive electrode film, improving the structural integrity of the positive electrode active material, and improving the cycle performance of the battery cell. On the other hand, controlling the appropriate doping content can effectively reduce the dissolution rate of titanium ions, reducing the probability of titanium ions catalyzing the decomposition of the SEI film during the reduction and precipitation of titanium ions at the negative electrode, reducing the irreversible consumption of lithium ions caused by the reconstruction of the SEI film, and improving the cycle performance of the battery cell.

[0029] In any embodiment, the lithium iron phosphate particles include vanadium, and the vanadium content is 0.05%-0.15% based on the total mass of the positive electrode active material.

[0030] Within a reasonable range, the vanadium content helps stabilize the crystal structure of lithium iron phosphate through vanadium ion doping, enhancing the strength of PO bonds and thus improving the mechanical strength and structural toughness of lithium iron phosphate. This helps the battery cell withstand the periodic expansion force transmitted from the expansion of the negative electrode film during long-term cycling, effectively reducing the probability of microcracks or even breakage of the positive electrode active material in the high-density positive electrode film, improving the structural integrity of the positive electrode active material, and improving the cycle performance of the battery cell. On the other hand, controlling the appropriate doping content can effectively reduce the dissolution rate of vanadium ions, reducing the probability of vanadium ions catalyzing the decomposition of the SEI film during the reduction and precipitation of vanadium ions at the negative electrode, reducing the irreversible consumption of lithium ions caused by the reconstruction of the SEI film, and improving the cycle performance of the battery cell.

[0031] In any embodiment, the electrolyte further includes a solvent, which includes one or more of dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.

[0032] In any embodiment, the solvent comprises dimethyl carbonate, and the mass content of the dimethyl carbonate is 15%-50% based on the total mass of the electrolyte.

[0033] The solvent includes dimethyl carbonate, which helps to reduce the viscosity of the electrolyte, increase the ionic conductivity of the electrolyte, promote the rapid migration of lithium ions in the electrolyte, and improve the energy conversion efficiency of the battery cell.

[0034] When the mass content of dimethyl carbonate is within the above range, it is beneficial to improve the ionic conductivity of the electrolyte, promote the rapid migration of lithium ions in the electrolyte, and at the same time reduce the probability of increased gas production in the battery cell due to excessive dimethyl carbonate content, thus balancing the energy conversion efficiency and cycle stability of the battery cell.

[0035] In any embodiment, the mass content of dimethyl carbonate is 15%-45% based on the total mass of the electrolyte.

[0036] A mass content of dimethyl carbonate within the above range is beneficial for further balancing the energy conversion efficiency and cycle stability of battery cells.

[0037] In any embodiment, the mass content of dimethyl carbonate is 15%-36% based on the total mass of the electrolyte.

[0038] A mass content of dimethyl carbonate within the above range is beneficial for further balancing the energy conversion efficiency and cycle stability of battery cells.

[0039] In any embodiment, the solvent comprises ethyl methyl carbonate, and the ethyl methyl carbonate content is 10%-60% based on the total mass of the electrolyte.

[0040] Ethyl methyl carbonate has high ionic conductivity and good thermal stability. When the mass content of ethyl methyl carbonate is within the above range, it is beneficial to improve the ionic conductivity of the electrolyte, promote the rapid migration of lithium ions in the electrolyte, and at the same time reduce the gas production of the battery cells, thus balancing the energy conversion efficiency and cycle stability of the battery cells.

[0041] The applicant discovered through experiments that when the electrolyte includes ethyl methyl carbonate and fluoroethylene carbonate, the energy conversion efficiency of the battery cell can be further improved.

[0042] In any embodiment, the methyl ethyl carbonate content is 30%-60% based on the total mass of the electrolyte.

[0043] In any embodiment, the solvent comprises propylene carbonate, and the mass content of the propylene carbonate is 0.5%-5% based on the total mass of the electrolyte.

[0044] Propylene carbonate possesses a high dielectric constant and good low-temperature performance, which is beneficial for promoting the dissociation of lithium-containing electrolyte salts, improving the ionic conductivity of the electrolyte, facilitating the rapid migration of lithium ions in the electrolyte, and enhancing the energy conversion efficiency of individual battery cells. However, propylene carbonate readily undergoes co-intercalation reactions on the surface of negative electrode active materials such as graphite. Since the diameter of propylene carbonate is much larger than the interlayer spacing of graphite, intercalation leads to the peeling and pulverization of the graphite structure, deteriorating cycle performance. Maintaining the propylene carbonate content within the aforementioned range helps to balance the energy conversion efficiency and cycle performance of individual battery cells.

[0045] In any embodiment, the mass content of propylene carbonate is 1%-3% based on the total mass of the electrolyte.

[0046] Having a propylene carbonate content within the above range is beneficial for further balancing the energy conversion efficiency and cycle performance of individual battery cells.

[0047] In any embodiment, the electrolyte further includes lithium hexafluorophosphate; based on the total mass of the electrolyte, the mass content of lithium hexafluorophosphate is 6%-20%, optionally 8%-16%.

[0048] Lithium fluorosulfonylimide salts are prone to corroding positive electrode current collectors such as aluminum foil. Adding a certain amount of lithium hexafluorophosphate can form a more stable and denser passivation protective film on the surface of the positive electrode current collector, reducing the negative effects of lithium fluorosulfonylimide salts on the positive electrode current collector and improving the cycle stability of the battery cell.

[0049] In any embodiment, the mass ratio of the lithium hexafluorophosphate to the lithium fluorosulfonyl imide salt is 1-5, and optionally 2-4.

[0050] When the mass ratio of lithium hexafluorophosphate to lithium fluorosulfonyl imide is within the above range, it is beneficial to form a stable, dense, and LiF-rich positive electrode electrolyte interphase (CEI) film. This effectively reduces the probability of transition metal ions migrating to the negative electrode, reduces irreversible lithium ion consumption caused by SEI film reconstruction, lowers the charge transfer impedance at the positive electrode interface, improves the transport efficiency of lithium ions at the positive electrode interface, and at the same time reduces the negative impact of lithium fluorosulfonyl imide on the positive electrode current collector, such as aluminum foil, thereby improving the energy efficiency and cycle performance of the battery cell.

[0051] In any embodiment, the mass ratio of the lithium hexafluorophosphate to the lithium fluorosulfonyl imide salt is 2-3.

[0052] A mass ratio of lithium hexafluorophosphate to lithium fluorosulfonyl imide salt within the above range is beneficial for further balancing the energy efficiency and cycle stability of the battery cell.

[0053] In any embodiment, the electrolyte further includes fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is 0.05%-10% based on the total mass of the electrolyte.

[0054] Fluorinated ethylene carbonate can be preferentially reduced on the negative electrode surface to form a dense, LiF-rich solid electrolyte interphase (SEI) film with high ionic conductivity. This helps reduce the transfer resistance of lithium ions at the negative electrode interface. When combined with low-viscosity ethyl methyl carbonate, the ionic conductivity of the electrolyte is improved. The synergistic effect of the two can further improve the energy efficiency of the battery cell. At the same time, this dense, LiF-rich SEI film is not easily decomposed by transition metals, reducing the irreversible consumption of lithium ions caused by the reconstruction of the SEI film and improving the cycle performance of the battery cell.

[0055] In any embodiment, the mass content of the fluoroethylene carbonate is 2%-5% based on the total mass of the electrolyte.

[0056] In any embodiment, the mass content of the fluoroethylene carbonate is 3%-5% based on the total mass of the electrolyte.

[0057] When the mass content of fluoroethylene carbonate is within the above range, it is beneficial to form a dense solid electrolyte interphase (SEI) film rich in LiF and with high ionic conductivity. At the same time, it reduces the probability of excessively thick film due to excessive mass content of fluoroethylene carbonate, and further improves the energy efficiency of the battery cell.

[0058] In any embodiment, the area ratio of particles with a diameter greater than or equal to 1 μm in the cross-section of the positive electrode film layer along the electrode thickness direction is 30.0%-50.0%.

[0059] Particles with a diameter of 1 μm or larger can fully play a gradation role in the manufacturing process of the positive electrode sheet, effectively improving the compaction density of the positive electrode film and increasing the volumetric energy density of the battery cell. However, when the content of large-sized particles in the positive electrode film is too high, it hinders the diffusion of lithium ions into the positive electrode film and increases the diffusion path of lithium ions in the particles, resulting in severe local polarization of the positive electrode sheet and increasing the impedance of the battery cell. When the area ratio of particles with a diameter of 1 μm or larger in the cross-section of the positive electrode film along the thickness direction is within the above range, it is beneficial to improve the compaction density of the positive electrode film, while reducing the diffusion path of lithium ions in the particles, reducing the probability of local polarization, and balancing the volumetric energy density and energy conversion efficiency of the battery cell.

[0060] In any embodiment, the area ratio of particles with a diameter of 1μm-5μm in the cross-section of the positive electrode film along the thickness direction of the electrode sheet is 30.0%-50.0%.

[0061] In any embodiment, the area ratio of particles with a diameter of 1μm-5μm in the cross-section of the positive electrode film along the thickness direction of the electrode sheet is 30.0%-45.0%.

[0062] In the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a diameter of 1μm-5μm is within the above range, which is beneficial to further improve the compaction density of the positive electrode film, while reducing the diffusion path of lithium ions in the particles, reducing the probability of local polarization, and taking into account the volumetric energy density and energy conversion efficiency of the battery cell.

[0063] In any embodiment, the mass percentage of magnetic material in the positive electrode film is 20ppm-1980ppm.

[0064] This application embodiment helps to reduce the dissolution of transition metal ions and their catalytic effect on the SEI film surface by controlling the mass ratio of magnetic materials in the positive electrode film layer within the above range, thereby reducing lithium consumption caused by rebuilding the SEI film and improving the cycle performance of the battery cell.

[0065] In any embodiment, the mass percentage of magnetic material in the positive electrode film is 20ppm-300ppm.

[0066] In any embodiment, the mass percentage of magnetic material in the positive electrode film is 20ppm-200ppm.

[0067] When the mass percentage of magnetic material in the positive electrode film is within the above range, it helps to further reduce the dissolution of transition metal ions and their catalytic effect on the SEI film surface, thereby reducing the lithium consumption caused by rebuilding the SEI film and improving the cycle performance of the battery cell.

[0068] In any embodiment, the magnetic material includes one or more of Fe, Fe2P, FeP, γ-Fe2O3, and Fe2P2O7.

[0069] In any embodiment, the positive electrode film layer further includes a conductive agent, the conductive agent comprising carbon nanotubes, wherein the mass content of the carbon nanotubes is 0.1%-1.5% based on the total mass of the positive electrode film layer.

[0070] Carbon nanotubes can construct a three-dimensional network structure with a shorter electron transport path. Their one-dimensional structure can directly connect the current collector and the positive electrode active material, reducing the interfacial resistance between the traditional conductive agent and the positive electrode active material. This helps to reduce the impedance of the positive electrode film and improve the energy conversion efficiency of the battery cell. At the same time, carbon nanotubes can provide mechanical support for the positive electrode active material, reduce the probability of the positive electrode active material falling off, and improve the cycle stability of the battery cell.

[0071] In any embodiment, the conductive agent further includes conductive carbon black.

[0072] Conductive carbon black has a small size and adheres to the surface of the positive electrode active material particles and fills the gaps between the particles, forming dense point-like conductive contacts. By using carbon nanotubes and conductive carbon black in combination, both long-range and short-range conductivity can be achieved, which is beneficial to further improve the conductive network in the positive electrode film, reduce the impedance of the positive electrode film, and improve the energy conversion efficiency of the battery cell.

[0073] In any embodiment, the housing includes a first side plate, the first side plate including a first plate portion and a second plate portion disposed along a first direction, the second plate portion being disposed on the side of the first plate portion near the opening of the receiving cavity, the second plate portion being used to weld to the end cap to form a weld portion, the thickness of the second plate portion being greater than the thickness of the first plate portion; wherein, the first side plate is disposed opposite to the positive electrode sheet.

[0074] As the number of cycles of a battery cell increases, the negative electrode active material expands and contracts repeatedly, and the solid electrolyte membrane is continuously formed and reconstructed, which increases the internal expansion of the battery cell. This expansion force is periodically transmitted to the positive electrode film layer. That is, during the charging process of the battery cell, the electrode assembly will expand and squeeze the first plate, causing the first side plate to swing back and forth with the welded part as the base point. The first side plate is prone to cracking under the action of swing stress.

[0075] Increasing the overall thickness of the first side plate helps to mitigate the risk of cracking of the first side plate, but it will reduce the energy density of the battery cell. In this embodiment, the thickness of the second plate near the opening is increased to ensure the strength of the first side plate in the area near the weld, reduce the risk of cracking of the first side plate, improve the safety performance of the battery cell, and take into account the energy density of the battery cell.

[0076] In any embodiment, the thickness ratio of the second plate portion to the first plate portion is 1.05-3.

[0077] The thickness ratio of the second plate to the first plate is within the above range. The second plate has higher strength, which helps to improve the safety performance of the battery cell while taking into account the energy density of the battery cell.

[0078] In any embodiment, the thickness of the first plate portion is 0.5mm-1.2mm, and can be selected as 0.6mm-1.0mm.

[0079] The thickness of the first plate is within the aforementioned range, which can take into account the energy density of the battery cell while also withstanding the periodic expansion force of the electrode assembly during the charging process of the battery cell, reducing the probability of cracking of the first plate and improving the safety performance of the battery cell.

[0080] In any embodiment, the capacity of the battery cell is 400Ah-3000Ah.

[0081] The capacity of individual battery cells is within the above range, which helps to further meet the capacity requirements of energy storage devices for energy storage batteries.

[0082] In any embodiment, the capacity of the battery cell is 500Ah-1500Ah.

[0083] In any embodiment, the capacity of the battery cell is 600Ah-1000Ah.

[0084] An embodiment of the second aspect of this application provides a battery device that includes the battery cell provided in the first aspect of this application.

[0085] An embodiment of the third aspect of this application provides an energy storage device, which includes the battery device provided in the second aspect of this application, the battery device being used to store electrical energy.

[0086] 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

[0087] 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.

[0088] Figure 1 is an exploded view of a battery cell according to an embodiment of this application;

[0089] Figure 2 is a cross-sectional view of a battery cell according to an embodiment of this application;

[0090] Figure 3 is an enlarged schematic diagram of the battery cell of one embodiment of the present application shown in Figure 2 at the circular frame C;

[0091] Figure 4 is a schematic diagram of a battery device according to an embodiment of this application.

[0092] Explanation of reference numerals in the attached drawings: 2 Battery assembly; 5 Housing; 5a First housing section; 5b Second housing section; 5c Receiving space; 6 Battery module; 7 Battery cell; 10 Electrode assembly; 20 Housing; 21 First side plate; 211 First plate section; 212 Second plate section; 212a Base section; 212b Transition section; 20a Opening; 30 End cap; W Welding section; X First direction; Z Second direction; Y Thickness direction of the first side plate. Detailed Implementation

[0093] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, battery device, and energy storage device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially 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.

[0094] 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.

[0095] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

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

[0097] 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 mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0098] 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.

[0099] 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).

[0100] Energy storage batteries are primarily used in scenarios requiring long-term storage and release of electrical energy, such as working with energy storage power stations to store or release electrical energy in emergencies, and playing roles in frequency regulation and emergency backup within the power grid. This necessitates that energy storage batteries store more electrical energy within limited resources and space to continuously and stably provide a large amount of power, thereby ensuring the reliable operation of energy storage devices and the efficient utilization of energy. However, research shows that increasing the capacity and volumetric energy density of energy storage batteries often exacerbates the degradation of battery cycle life and energy loss, leading to a decrease in energy conversion efficiency. How to further improve the volumetric energy density of high-capacity battery cells while maintaining high cycle performance and energy conversion efficiency is a pressing technical problem that needs to be solved in this field.

[0101] To address the aforementioned problems, this application provides a battery cell 7, as shown in Figure 1. The battery cell 7 includes an end cap 30, a housing 20, an electrode assembly 10, and an electrolyte. The housing 20 includes a receiving cavity with an opening 20a. The end cap 30 is used to close the opening 20a. The electrode assembly 10 and the electrolyte are disposed in the receiving cavity 20a of the housing 20. The electrode assembly includes a positive electrode sheet, which includes 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 includes a positive active material, which includes lithium iron phosphate particles. The lithium iron phosphate particles include one or more elements selected from titanium and vanadium. The electrolyte includes a lithium fluorosulfonyl imide salt, and the mass content of the lithium fluorosulfonyl imide salt is 2%-7% based on the total mass of the electrolyte. The compaction density of the positive electrode film layer is greater than or equal to 2.5 g / cm³. 3 The total coating area of ​​the positive electrode film in each battery cell is greater than or equal to 11m². 2 .

[0102] To meet the demand for high-capacity energy storage batteries in energy storage devices, the total coating area of ​​the positive electrode film within the battery cell can be increased to enhance the loading area of ​​the positive electrode active material and improve the battery cell's capacity. Furthermore, increasing the compaction density of the positive electrode film can increase the loading of positive electrode active material per unit volume, while also maintaining the volumetric energy density of the battery cell. However, high compaction density positive electrode films are prone to large rebound, making the positive electrode active material more susceptible to crushing and breakage under the high expansion force of the negative electrode in the later stages of long-term cycling. This leads to the failure of the positive electrode active material, exacerbates the capacity decay of the battery cell, and deteriorates its cycle performance. Meanwhile, a larger total coating area of ​​the positive electrode film will exacerbate uneven current distribution, easily leading to excessively high current density in local areas. In high current density areas, the electrochemical reaction rate is too fast, which can easily cause an increase in ion concentration gradient and generate concentration polarization. The high density of the positive electrode will further aggravate the polarization effect, causing the battery operating voltage to deviate from the equilibrium potential. During charging, a voltage higher than the equilibrium potential needs to be applied to drive ions to overcome various resistances. During discharging, the polarization resistance causes the output voltage to be lower than the equilibrium potential, resulting in an increase in the difference between the charging and discharging voltages. This part of the electrical energy is irreversibly converted into heat dissipation during the charging and discharging process, reducing the energy efficiency of the battery cell.

[0103] By doping one or more of titanium and vanadium elements into lithium iron phosphate, the applicant can form a more stable bonding network, improve the structural stability of lithium iron phosphate, enhance its mechanical strength and structural toughness, and help it better withstand the compression caused by the expansion of the negative electrode film during long-term cycling of the battery cell. This effectively reduces the probability of microcracks or even breakage of the positive electrode active material in the high-density positive electrode film, improves the structural integrity of the positive electrode active material, and improves the cycle performance of the battery cell.

[0104] However, due to the large total coating area and high compaction density of the positive electrode film, the battery cell is prone to uneven current distribution and excessively high local current density during charging and discharging. Simultaneously, the transport resistance of lithium ions in the high compaction density positive electrode increases significantly, exacerbating the polarization effect of the battery cell and leading to increased internal heat generation and temperature. Under high-temperature conditions, transition metal elements (such as iron, titanium, and vanadium) in the doped lithium iron phosphate are more prone to dissolution, leaching into the electrolyte and being reduced and deposited at the negative electrode. Studies have shown that transition metals deposited on the negative electrode act as catalysts, catalyzing the decomposition of the solid electrolyte interphase (SEI) film, causing more active lithium to be consumed during SEI film repair, thus deteriorating the cycle performance of the battery cell.

[0105] Therefore, the applicant further added a certain amount of fluorosulfonylimide lithium salt to the electrolyte. During cycling, it preferentially decomposes on the surface of the positive electrode active material to form a stable, dense, and LiF-rich positive electrode electrolyte interphase (CEI) film. On the one hand, the stable and dense CEI film formed by the fluorosulfonylimide lithium salt helps to inhibit the dissolution of transition metal ions into the electrolyte. Its anions have a strong complexing ability and easily coordinate with transition metal ions to form stable complexes, effectively reducing the probability of transition metal ions migrating to the negative electrode, reducing irreversible lithium ion consumption caused by rebuilding the SEI film, and improving the cycle performance of the battery cell. On the other hand, the CEI film has good ionic conductivity, which helps to reduce the charge transfer impedance at the positive electrode interface and improve the transport efficiency of lithium ions at the positive electrode interface. By reducing the transport impedance, the heat consumption of the battery can be compensated, thereby improving the energy efficiency of the battery cell.

[0106] When the lithium fluorosulfonylimide content in the electrolyte is less than 2%, it is insufficient to effectively construct a stable, dense, and LiF-rich CEI film on the positive electrode surface. This makes it difficult to effectively inhibit the dissolution of transition metal ions into the electrolyte, resulting in a large proportion of transition metal ions migrating to the negative electrode and being reduced and precipitated. Lithium ions are irreversibly consumed in the reconstruction of the SEI film, which deteriorates the cycle performance of the battery cell. When the lithium fluorosulfonylimide content in the electrolyte is greater than 7%, its high content of active anions will cause severe chemical corrosion to the positive electrode current collector, such as aluminum foil, which will adversely affect the cycle stability of the battery cell.

[0107] In summary, the compaction density of the positive electrode film layer of the battery cell provided in this application embodiment is greater than or equal to 2.5 g / cm³. 3 The total coating area of ​​the positive electrode film in each battery cell is greater than or equal to 11m². 2 Simultaneously, lithium iron phosphate doped with one or more elements of titanium and vanadium is used as the positive electrode active material, and 2%-7% of fluorosulfonylimide lithium salt is added to the electrolyte. On the basis of high capacity and high volumetric energy density, the cycle performance and energy efficiency of the battery cell are further improved.

[0108] In this application, the type of positive electrode active material can be detected by any method known in the art. For example, it can be detected by X-ray diffraction and energy dispersive spectroscopy. It is understood that lithium iron phosphate particles refer to particles whose phase conforms to that of lithium iron phosphate, including lithium iron phosphate and its doped and modified materials, and lithium iron phosphate and its coated and modified materials.

[0109] In this application, the types and contents of elements in lithium iron phosphate 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 elements and their contents, referring to Appendix C of GB / T33822-2017.

[0110] In this application, the types and mass contents of each component in the electrolyte can be obtained by detecting the electrolyte using any method known to those skilled in the art. For example, the composition and content of the electrolyte can be characterized using one or more of the following methods: gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectrometry (GC-MS). For example, referring to GB / T-9722-2023 "General Rules for Gas Chromatography of Chemical Reagents" and / or GB / T6041-2020 "General Rules for Mass Spectrometry Analysis Methods", gas chromatography and mass spectrometry are coupled. After gas chromatography separates the components in the sample, the components are broken into ion fragments in mass spectrometry and separated according to mass-to-charge ratio (m / z) to form specific mass spectra, obtaining qualitative analysis of each organic component in the electrolyte. Then, the organic components in the electrolyte are separated in the chromatographic column, and detection signal spectra of each component are generated. The retention time is used for component qualitative analysis, and the peak area is corrected by standardization to achieve quantification, obtaining quantitative analysis of the organic components in the electrolyte. Referring to JY / T-020, the types of anions of electrolyte salts in the electrolyte are detected by ion chromatography and quantitatively analyzed. Referring to JY / T 0578-2020, nuclear magnetic resonance spectroscopy (NMR) is used to obtain qualitative and quantitative analysis of the components in the electrolyte.

[0111] The electrolyte referred to in this application can be either fresh electrolyte or electrolyte obtained by disassembling a battery cell. The electrolyte obtained by disassembling a battery cell can be either the free electrolyte in the battery casing or the electrolyte obtained by centrifugation from the electrode.

[0112] In this application, the compaction density of the positive electrode film can be tested using methods known in the art. As an example, the battery is placed in a 25°C oven environment and left to stand for 2 hours. After the battery temperature is maintained at 25°C, the battery is discharged to 2.5V at a constant power of 0.5P. The battery is then disassembled to obtain the positive electrode sheet. The residual electrolyte is treated with dimethyl carbonate solvent, the electrode sheet is dried, and it is cut into small circular pieces with an area of ​​S. The weight is recorded as W1, and the thickness T1 of the positive electrode sheet is measured using a micrometer. Then, the positive electrode film layer of the weighed electrode sheet is wiped off, the weight of the current collector is measured and recorded as W2, and the thickness T2 of the current collector is measured using a micrometer. Then, the compaction density of the positive electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0113] In some embodiments, the compaction density of the positive electrode film can be selected as 2.50 g / cm³. 3 2.51g / cm 3 2.52g / cm 3 2.53g / cm 3、2.54g / cm 3 、2.55g / cm 3 、2.56g / cm 3 、2.57g / cm 3 、2.58g / cm 3 、2.59g / cm 3 、2.60g / cm 3 、2.61g / cm 3 、2.62g / cm 3 、2.63g / cm 3 、2.64g / cm 3 、2.65g / cm 3 、2.66g / cm 3 、2.67g / cm 3 、2.68g / cm 3 、2.69g / cm 3 、2.70g / cm 3 、2.71g / cm 3 、2.72g / cm 3 、2.73g / cm 3 、2.74g / cm 3 、2.75g / cm 3 、2.76g / cm 3 、2.77g / cm 3 、2.78g / cm 3 、2.79g / cm 3 、2.80g / cm 3 、2.81g / cm 3 、2.82g / cm 3 、2.83g / cm 3 、2.84g / cm 3 、2.85g / cm 3 、2.86g / cm 3 、2.87g / cm 3 、2.88g / cm 3 、2.89g / cm 3 、2.90g / cm 3 、2.91g / cm 3 、2.92g / cm 3 、2.93g / cm 3 、2.94g / cm 3 、2.95g / cm 3 、2.96g / cm 3 、2.97g / cm 3 、2.98g / cm 3 、2.99g / cm3 3.00g / cm 3 Or the range of values ​​between any two of the above.

[0114] In this application, the total coating area of ​​the positive electrode film layer contained in a single battery cell can be tested using the following method: Disassemble the battery cell, remove the electrode assembly (which can be one or more), remove the positive electrode sheet contained in the electrode assembly, measure the length and width of the positive electrode film layer on each positive electrode sheet, and calculate the coating area of ​​each positive electrode sheet. It can be understood that when the positive electrode sheet is coated on one side, only the coating area of ​​that side needs to be calculated; when the positive electrode sheet is coated on both sides, the coating areas of both sides need to be calculated separately and summed. The total coating area of ​​the positive electrode film layer contained in the single battery cell can be obtained by summing the coating areas of all positive electrode sheets.

[0115] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell may be selected as 11m². 2 15m 2 20m 2 25m 2 30m 2 35m 2 40m 2 45m 2 50m 2 55m 2 60m 2 65m 2 70m 2 75m 2 80m 2 85m 2 90m 2 95m 2 100m 2 105m 2 110m 2 115m 2 120m 2 125m 2 130m 2 135m 2 140m 2 145m 2 150m 2 Or the range of values ​​between any two of the above.

[0116] In some embodiments, based on the total mass of the electrolyte, the mass content of the fluorosulfonylimide lithium salt can be selected as 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, etc. 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, or any range of two of the above.

[0117] In some embodiments, the fluorosulfonylimide lithium salt includes one or more of lithium bisfluorosulfonylimide and lithium bistrifluoromethylsulfonylimide, with lithium bisfluorosulfonylimide being the preferred choice.

[0118] The fluorosulfonylimide lithium salt, including the aforementioned substances, facilitates the formation of a stable and dense CEI film, inhibits the dissolution of transition metal ions into the electrolyte, and readily coordinates with transition metal ions to form stable complexes. This effectively reduces the probability of transition metal ions migrating to the negative electrode and minimizes irreversible lithium ion consumption due to SEI film reconstruction. Simultaneously, the CEI film exhibits excellent ionic conductivity, which helps reduce the charge transfer impedance at the positive electrode interface and improves the lithium ion transport efficiency at the positive electrode interface. By reducing the transport impedance, it compensates for battery heat consumption, thus balancing the cycle performance and energy efficiency of the battery cell.

[0119] In some embodiments, the mass content of the fluorosulfonylimide lithium salt is 3.7%-7% based on the total mass of the electrolyte.

[0120] The mass content of lithium fluorosulfonylimide salt within the above range is beneficial to further balance the amount of CEI film formation and the negative impact of lithium fluorosulfonylimide salt on the positive electrode current collector, thereby improving the cycle stability and energy conversion efficiency of the battery cell.

[0121] In some embodiments, the total coating area of ​​the positive electrode film layers contained in the battery cell is 11m². 2 -150m 2 .

[0122] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 15m². 2 -130m 2 .

[0123] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 18m². 2 -115m 2 .

[0124] If the total coating area of ​​the positive electrode film layer contained in the battery cell is within the above range, it will help to further increase the loading area of ​​the positive electrode active material and increase the capacity of the battery cell.

[0125] In some embodiments, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -3.0g / cm 3 2.5g / cm³ is an option. 3 -2.8g / cm 3 .

[0126] The compaction density of the positive electrode film is within the above range, which helps to further increase the loading of positive electrode active material per unit volume and improve the volumetric energy density of the battery cell.

[0127] In some embodiments, the lateral density of the positive electrode film layer on any one side is 0.25 g / 1540.25 mm². 2 -0.40g / 1540.25mm 2 .

[0128] In this application, the lateral density of the positive electrode film layer on any side has a meaning known in the art and can be tested using methods known in the art. For example, take a positive electrode sheet coated on one side and compacted (if it is a positive electrode sheet coated on both sides, 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 lateral density of the positive electrode film layer = (M1-M0) / S1. To ensure the accuracy of the test results, multiple sets (e.g., 10 sets) of test samples can be tested, and the average value can be calculated as the test result.

[0129] In some embodiments, the lateral density of the positive electrode film layer on either side may be selected as 0.25 g / 1540.25 mm. 2 0.26g / 1540.25mm 2 0.27g / 1540.25mm 2 0.28g / 1540.25mm 2 0.29g / 1540.25mm 2 0.30g / 1540.25mm 2 0.31g / 1540.25mm 2 0.32g / 1540.25mm 20.33g / 1540.25mm 2 0.34g / 1540.25mm 2 0.35g / 1540.25mm 2 0.36g / 1540.25mm 2 0.37g / 1540.25mm 2 0.38g / 1540.25mm 2 0.39g / 1540.25mm 2 0.40g / 1540.25mm 2 Or the range of values ​​between any two of the above.

[0130] This application embodiment further increases the lateral density of the positive electrode film layer on either side, which is beneficial to further improve the volumetric energy density and capacity of the battery cell. However, it increases the lithium-ion transport path, increases the diffusion resistance of lithium ions in the positive electrode film layer, intensifies the heat generation of the battery cell, and increases the dissolution of transition metal elements in the positive electrode active material. By adding a certain amount of fluorosulfonylimide lithium salt to the electrolyte, it is beneficial to form a stable and dense CEI film, inhibit the dissolution of transition metal ions into the electrolyte, and also easily coordinate with transition metal ions to form stable complexes, effectively reducing the probability of transition metal ions migrating to the negative electrode and reducing the irreversible consumption of lithium ions caused by rebuilding the SEI film. On the basis of high volumetric energy density and high capacity, the cycle performance of the battery cell is improved.

[0131] In some embodiments, the lateral density of the positive electrode film layer on any one side is 0.25 g / 1540.25 mm². 2 -0.35g / 1540.25mm 2 .

[0132] Having the lateral density of the positive electrode film layer on either side within the above range is beneficial for further balancing the volumetric energy density, capacity, and cycle performance of the battery cell.

[0133] In some embodiments, the lithium iron phosphate particles include titanium, and the titanium content is 0.05%-0.10% based on the total mass of the positive electrode active material.

[0134] In some embodiments, based on the total mass of the positive electrode active material, the mass content of titanium can be selected as 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, or any value range between the two above.

[0135] Within a reasonable range, the titanium content helps stabilize the crystal structure of lithium iron phosphate through titanium ion doping, enhancing the strength of PO bonds and thus improving the mechanical strength and structural toughness of lithium iron phosphate. This helps the battery cell withstand the periodic expansion force transmitted from the expansion of the negative electrode film during long-term cycling, effectively reducing the probability of microcracks or even breakage of the positive electrode active material in the high-density positive electrode film, improving the structural integrity of the positive electrode active material, and improving the cycle performance of the battery cell. On the other hand, controlling the appropriate doping content can effectively reduce the dissolution rate of titanium ions, reducing the probability of titanium ions catalyzing the decomposition of the SEI film during the reduction and precipitation of titanium ions at the negative electrode, reducing the irreversible consumption of lithium ions caused by the reconstruction of the SEI film, and improving the cycle performance of the battery cell.

[0136] In some embodiments, the lithium iron phosphate particles include vanadium, and the vanadium content is 0.05%-0.15% based on the total mass of the positive electrode active material.

[0137] In some embodiments, based on the total mass of the positive electrode active material, the mass content of vanadium can be selected as 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, or any value range between the above two.

[0138] Within a reasonable range, the vanadium content helps stabilize the crystal structure of lithium iron phosphate through vanadium ion doping, enhancing the strength of PO bonds and thus improving the mechanical strength and structural toughness of lithium iron phosphate. This helps the battery cell withstand the periodic expansion force transmitted from the expansion of the negative electrode film during long-term cycling, effectively reducing the probability of microcracks or even breakage of the positive electrode active material in the high-density positive electrode film, improving the structural integrity of the positive electrode active material, and improving the cycle performance of the battery cell. On the other hand, controlling the appropriate doping content can effectively reduce the dissolution rate of vanadium ions, reducing the probability of vanadium ions catalyzing the decomposition of the SEI film during the reduction and precipitation of vanadium ions at the negative electrode, reducing the irreversible consumption of lithium ions caused by the reconstruction of the SEI film, and improving the cycle performance of the battery cell.

[0139] In some embodiments, the electrolyte further includes a solvent, which includes one or more of dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.

[0140] In some embodiments, the solvent comprises dimethyl carbonate, and the mass content of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte.

[0141] In some embodiments, based on the total mass of the electrolyte, the mass content of dimethyl carbonate can be selected as 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any range between the above.

[0142] The solvent includes dimethyl carbonate, which helps to reduce the viscosity of the electrolyte, increase the ionic conductivity of the electrolyte, promote the rapid migration of lithium ions in the electrolyte, and improve the energy conversion efficiency of the battery cell.

[0143] When the mass content of dimethyl carbonate is within the above range, it is beneficial to improve the ionic conductivity of the electrolyte, promote the rapid migration of lithium ions in the electrolyte, and at the same time reduce the probability of increased gas production in the battery cell due to excessive dimethyl carbonate content, thus balancing the energy conversion efficiency and cycle stability of the battery cell.

[0144] In some embodiments, the dimethyl carbonate content is 15%-45% based on the total mass of the electrolyte.

[0145] A mass content of dimethyl carbonate within the above range is beneficial for further balancing the energy conversion efficiency and cycle stability of battery cells.

[0146] In some embodiments, the dimethyl carbonate content is 15%-36% based on the total mass of the electrolyte.

[0147] A mass content of dimethyl carbonate within the above range is beneficial for further balancing the energy conversion efficiency and cycle stability of battery cells.

[0148] In some embodiments, the solvent comprises ethyl methyl carbonate, and the ethyl methyl carbonate content is 10%-60% based on the total mass of the electrolyte.

[0149] In some embodiments, based on the total mass of the electrolyte, the mass content of methyl ethyl carbonate can be selected as 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, or any range between the above.

[0150] Ethyl methyl carbonate has high ionic conductivity and good thermal stability. When the mass content of ethyl methyl carbonate is within the above range, it is beneficial to improve the ionic conductivity of the electrolyte, promote the rapid migration of lithium ions in the electrolyte, and at the same time reduce the gas production of the battery cells, thus balancing the energy conversion efficiency and cycle stability of the battery cells.

[0151] The applicant discovered through experiments that when the electrolyte includes ethyl methyl carbonate and fluoroethylene carbonate, the energy conversion efficiency of the battery cell can be further improved.

[0152] In some embodiments, the methyl ethyl carbonate content is 30%-60% based on the total mass of the electrolyte.

[0153] In some embodiments, the solvent comprises propylene carbonate, and the propylene carbonate content is 0.5%-5% based on the total mass of the electrolyte.

[0154] In some embodiments, based on the total mass of the electrolyte, the mass content of propylene 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%, or any range between the above.

[0155] Propylene carbonate possesses a high dielectric constant and good low-temperature performance, which is beneficial for promoting the dissociation of lithium-containing electrolyte salts, improving the ionic conductivity of the electrolyte, facilitating the rapid migration of lithium ions in the electrolyte, and enhancing the energy conversion efficiency of individual battery cells. However, propylene carbonate readily undergoes co-intercalation reactions on the surface of negative electrode active materials such as graphite. Since the diameter of propylene carbonate is much larger than the interlayer spacing of graphite, intercalation leads to the peeling and pulverization of the graphite structure, deteriorating cycle performance. Maintaining the propylene carbonate content within the aforementioned range helps to balance the energy conversion efficiency and cycle performance of individual battery cells.

[0156] In some embodiments, the propylene carbonate content is 1%-3% based on the total mass of the electrolyte.

[0157] Having a propylene carbonate content within the above range is beneficial for further balancing the energy conversion efficiency and cycle performance of individual battery cells.

[0158] In some embodiments, the electrolyte further includes lithium hexafluorophosphate; the mass content of lithium hexafluorophosphate is 6%-20% based on the total mass of the electrolyte, optionally 8%-16%.

[0159] In some embodiments, based on the total mass of the electrolyte, the mass content of lithium hexafluorophosphate can be selected as 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any range between the above.

[0160] Lithium fluorosulfonylimide salts are prone to corroding positive electrode current collectors such as aluminum foil. Adding a certain amount of lithium hexafluorophosphate can form a more stable and denser passivation protective film on the surface of the positive electrode current collector, reducing the negative effects of lithium fluorosulfonylimide salts on the positive electrode current collector and improving the cycle stability of the battery cell.

[0161] In some embodiments, the mass ratio of the lithium hexafluorophosphate to the lithium fluorosulfonyl imide salt is 1-5, and optionally 2-4.

[0162] In some embodiments, the mass ratio of the lithium hexafluorophosphate to the fluorosulfonylimide lithium salt can be selected as 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.5, 5.0 or any value range between the two.

[0163] When the mass ratio of lithium hexafluorophosphate to lithium fluorosulfonyl imide is within the above range, it is beneficial to form a stable, dense, and LiF-rich positive electrode electrolyte interphase (CEI) film. This effectively reduces the probability of transition metal ions migrating to the negative electrode, reduces irreversible lithium ion consumption caused by SEI film reconstruction, lowers the charge transfer impedance at the positive electrode interface, improves the transport efficiency of lithium ions at the positive electrode interface, and at the same time reduces the negative impact of lithium fluorosulfonyl imide on the positive electrode current collector, such as aluminum foil, thereby improving the energy efficiency and cycle performance of the battery cell.

[0164] In some embodiments, the mass ratio of the lithium hexafluorophosphate to the lithium fluorosulfonyl imide salt is 2-3.

[0165] A mass ratio of lithium hexafluorophosphate to lithium fluorosulfonyl imide salt within the above range is beneficial for further balancing the energy efficiency and cycle stability of the battery cell.

[0166] In some embodiments, the electrolyte further includes fluoroethylene carbonate, wherein the fluoroethylene carbonate content is 0.05%-10% based on the total mass of the electrolyte.

[0167] 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%, 0.5%, 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%, 8.5%, 9.0%, 9.5%, 10.0%, or any range between the above.

[0168] Fluorinated ethylene carbonate can be preferentially reduced on the negative electrode surface to form a dense, LiF-rich solid electrolyte interphase (SEI) film with high ionic conductivity. This helps reduce the transfer resistance of lithium ions at the negative electrode interface. When combined with low-viscosity ethyl methyl carbonate, the ionic conductivity of the electrolyte is improved. The synergistic effect of the two can further improve the energy efficiency of the battery cell. At the same time, this dense, LiF-rich SEI film is not easily decomposed by transition metals, reducing the irreversible consumption of lithium ions caused by the reconstruction of the SEI film and improving the cycle performance of the battery cell.

[0169] In some embodiments, the mass content of the fluoroethylene carbonate is 2%-5% based on the total mass of the electrolyte.

[0170] In some embodiments, the mass content of the fluoroethylene carbonate is 3%-5% based on the total mass of the electrolyte.

[0171] When the mass content of fluoroethylene carbonate is within the above range, it is beneficial to form a dense solid electrolyte interphase (SEI) film rich in LiF and with high ionic conductivity. At the same time, it reduces the probability of excessively thick film due to excessive mass content of fluoroethylene carbonate, and further improves the energy efficiency of the battery cell.

[0172] In some embodiments, the area ratio of particles with a diameter greater than or equal to 1 μm in the cross-section of the positive electrode film layer along the electrode thickness direction is 30.0%-50.0%.

[0173] The specific method for identifying particles in the positive electrode film is as follows: The positive electrode film is cut along the thickness direction of the electrode using an argon ion beam (for example, a Leica EM TIC 3X CP 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 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 positive electrode film. Images are acquired in secondary electron mode at non-edge locations within the cut surface of the positive electrode film using a field emission scanning electron microscope (after observing the electrode edge under the SEM, the field of view is adjusted to the center of the sample). 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 usage of ImageJ software is as follows: Load the scanning electron microscope image to be analyzed, use the Cellpose plugin to identify particles, and then perform manual correction; use ImageJ to read and analyze data. The specific method for identifying particles using the Cellpose plugin 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 were identified incorrectly. Particles that were not identified by the software, were not fully identified by the software, or were identified incorrectly mainly include the following: 1. Particles that are too large or have scratches on their surface, making them unidentifiable or incompletely identifiable; 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 field of view, with the interior of the particle 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.

[0174] During the compaction process, the positive electrode film undergoes compaction along its thickness direction. Therefore, compared to the surface of the positive electrode film, the cross-section along the thickness direction provides a more accurate reflection of the actual compaction of the particles within the film on a spatial scale. In the cross-section along the thickness direction, the area ratio of particles with a diameter greater than or equal to 1 μm directly reflects the ratio of the area of ​​some particles in that size range to the total area of ​​the particles, thus indicating the size of the particles in that range.

[0175] 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 phosphate particles in the electrode sheet by observing and statistically analyzing the particle area in the cross-section of the positive electrode film.

[0176] The specific method for testing the area ratio of particles with a diameter greater than or equal to 1 μm in the cross-section of the positive electrode film along the electrode thickness direction is as follows: Particles in the positive electrode film are identified using the method described above in this application. The images after particle identification and labeling are imported into ImageJ software for analysis. A scale is set based on the scanning electron microscope image. The particle diameter and area in the cross-section of the positive electrode film along the electrode thickness direction are statistically analyzed using the "Feret" and "Area" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the obtained "Feret" parameter represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, thus characterizing the particle diameter; the obtained "Area" parameter represents the pixel area of ​​the particle. Since particles with a diameter less than 50 nm have a large error in the statistical process and are difficult to accurately identify, and the particle diameter of conductive agents is generally less than 50 nm, which will produce a large error in the statistical results, particles with a diameter less than 50 nm are not counted in the particle diameter statistics process in this application, and the particle statistics corresponding to Area displaying "NaN" are deleted. The sum of the "Area" parameters for particles with a diameter greater than or equal to 1 μm and the sum of the "Area" parameters for all particles are calculated, and these are used as the area of ​​particles with a diameter greater than or equal to 1 μm and the total area of ​​the statistically analyzed particles, respectively. The sum of the areas of particles with a diameter greater than or equal to 1 μm divided by the total area of ​​the statistically analyzed particles is used as the percentage of the area of ​​particles with a diameter greater than or equal to 1 μm in the cross-section of the positive electrode film along the thickness direction of the electrode sheet.

[0177] Those skilled in the art can control the area ratio of particles using any known process. For example, particle size distribution can be adjusted through the scientific gradation of particles of different sizes; the mechanical force of crushing and grinding processes can be used to process raw materials to the target particle size distribution range, thus adjusting particle size and concentration; particle size separation can be achieved by using screening and grading equipment to obtain a particle size distribution that meets the requirements; and precise control of the feed rate can also help control particle concentration by adjusting the residence time and stress state of particles within the equipment.

[0178] In some embodiments, the area percentage of particles with a diameter greater than or equal to 1 μm in the cross-section of the positive electrode film along the thickness direction of the electrode sheet can be selected as 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any value range between the above two.

[0179] Particles with a diameter of 1 μm or larger can fully play a gradation role in the manufacturing process of the positive electrode sheet, effectively improving the compaction density of the positive electrode film and increasing the volumetric energy density of the battery cell. However, when the content of large-sized particles in the positive electrode film is too high, it hinders the diffusion of lithium ions into the positive electrode film and increases the diffusion path of lithium ions in the particles, resulting in severe local polarization of the positive electrode sheet and increasing the impedance of the battery cell. When the area ratio of particles with a diameter of 1 μm or larger in the cross-section of the positive electrode film along the thickness direction is within the above range, it is beneficial to improve the compaction density of the positive electrode film, while reducing the diffusion path of lithium ions in the particles, reducing the probability of local polarization, and balancing the volumetric energy density and energy conversion efficiency of the battery cell.

[0180] In some embodiments, the area ratio of particles with a diameter of 1μm-5μm in the cross-section of the positive electrode film along the thickness direction of the electrode sheet is 30.0%-50.0%.

[0181] In some embodiments, the area percentage of particles with a diameter of 1μm-5μm in the cross-section of the positive electrode film along the thickness direction of the electrode sheet can be selected as 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any value range between the above two.

[0182] In the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a diameter of 1μm-5μm can be tested with reference to the area ratio of particles with a diameter greater than or equal to 1μm mentioned above.

[0183] In some embodiments, the area ratio of particles with a diameter of 1μm-5μm in the cross-section of the positive electrode film along the thickness direction of the electrode sheet is 30.0%-45.0%.

[0184] In the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a diameter of 1μm-5μm is within the above range, which is beneficial to further improve the compaction density of the positive electrode film, while reducing the diffusion path of lithium ions in the particles, reducing the probability of local polarization, and taking into account the volumetric energy density and energy conversion efficiency of the battery cell.

[0185] In some embodiments, the mass percentage of magnetic material in the positive electrode film is 20ppm-1980ppm.

[0186] In this application, "magnetic material" refers to a substance that can generate magnetism when subjected to a magnetic field.

[0187] The "mass content of magnetic material in the positive electrode film" mentioned in this article can be measured through the following steps. Disassemble the battery to obtain the positive electrode sheet, soak it in dimethyl carbonate solvent for 8 hours, dry it, and then sinter the positive electrode sheet at 600°C for 2 hours under a nitrogen atmosphere. During the sintering process, the positive current collector on the positive electrode sheet will detach. Crush the sintered electrode sheet with a mortar and pestle, and pass it through a 200-mesh sieve to obtain positive electrode material powder. Step 1: Weigh 80g of the positive electrode material powder obtained by the reverse method above, place it in a plastic bucket, add 6L of deionized water, and cover it with a plastic tube. A magnetic rod (magnetic induction intensity of 6000GS) is used. It is then heat-sealed using heat-sealing clamps and placed inside a plastic bucket. The bucket is then sealed, and the drum mixer is set to a speed of 60 rpm and a stirring time of 15 minutes. The sealed bucket is placed on the drum mixer for stirring. Step 2: Prepare another clean plastic bucket and add 5±0.2L of deionized water. Pour the magnetic material from the plastic tube into the bucket until the surface of the magnetic rod has no area greater than or equal to 0.5 cm². 2After removing the slurry clumps, place the magnetic rod into a clean plastic bucket. Cover the bucket with a clean lid and place the bucket back into the drum mixer. Set the drum mixer speed to 60 rpm and the mixing time to 15 minutes. Place the sealed bucket on the equipment for mixing. Repeat step 2 at least twice to ensure the accuracy of the magnetic material extraction. Step 3: Prepare a clean 500mL beaker. Remove the magnetic rod from the bucket and place it in the beaker. Use a rinsing bottle to rinse all the magnetic material from the plastic tube head into the beaker. Use demagnetized scissors to cut open both sides of the heat shrink tubing head and fold the upper edge of the heat shrink tubing 90°. Remove the magnetic rod and place it in the magnetic rod placement area. Use a rinsing bottle to rinse the heat shrink tubing from top to bottom in a Z-shape (rinse at least three times on each side) to rinse the magnetic material into the beaker until there are no particles remaining on the surface of the heat shrink tubing (if there are clumps that are difficult to rinse, scrape them off with the back of a clean ceramic knife and rinse any impurities adhering to the ceramic knife into the beaker). Lift the sleeve and rinse the bottom of the sleeve at least three times to ensure that all adsorbed magnetic particles are collected. Step 4: ① Place the small magnetic block at the bottom of the beaker and rotate it clockwise at least three times from the outside to the inside, then rotate it counterclockwise at least three times from the outside to the inside of the beaker to adsorb. ② Repeat step ① three times, each time adsorbing for at least 10 seconds. ③ Fix the small magnetic block in the center of the bottom of the beaker with your palm, let it stand for more than 2 seconds, then slowly tilt and pour out the solution. ④ Stand the beaker upright and rinse the walls of the beaker with a rinsing bottle to ensure that all the adsorbed magnetic particles are put into the solvent. The amount of solution added is 100-150 mL. ⑤ Repeat step ③ rinsing 2-4 times until the liquid in the beaker is clear (no need to add solvent after the last rinse). Step 5: First, add 70 mL of deionized water to the beaker using one syringe, then slowly add 70 mL of 36%-38% hydrochloric acid to the beaker using another syringe. After the hydrochloric acid dilution is completed, transfer it to a fluorinated bottle with a sealed cap for storage. Step 6: ① Inject 15±2 mL of the hydrochloric acid solution prepared in Step 5 into the beaker containing the extracted magnetic material using a syringe, and then seal the beaker opening with sealing film. Place it in an ultrasonic bath and sonicate for 2 minutes (power 200 W / frequency 53 kHz). After sonication, inject 100±10 mL of deionized water into the beaker for rinsing, repeating the rinsing operation twice. Inject 100-150 mL of deionized water into the beaker for filtration. Use a filter membrane with a pore size of 0.45 μm to collect the magnetic material particles. Place the filter membrane with the magnetic material particles on its surface on a slide of a cleanliness microscope and place it in an oven to dry at 45℃ for (15±2) minutes. Weigh the dried filter membrane (containing magnetic material particles) using an electronic balance and subtract the mass of the blank filter membrane to obtain the mass of the magnetic material. Calculate the mass content of the magnetic material relative to the mass of the cathode material powder sample, as the mass percentage of the magnetic material in the cathode film layer, in ppm.

[0188] In some embodiments, the mass percentage of the magnetic material in the positive electrode film can be selected as 20ppm, 50ppm, 150ppm, 250ppm, 350ppm, 450ppm, 550ppm, 650ppm, 750ppm, 850ppm, 950ppm, 1050ppm, 1150ppm, 1250ppm, 1350ppm, 1450ppm, 1550ppm, 1650ppm, 1750ppm, 1850ppm, 1950ppm, 1980ppm, or any value range between the above two.

[0189] This application embodiment helps to reduce the dissolution of transition metal ions and their catalytic effect on the SEI film surface by controlling the mass ratio of magnetic materials in the positive electrode film layer within the above range, thereby reducing lithium consumption caused by rebuilding the SEI film and improving the cycle performance of the battery cell.

[0190] In some embodiments, the mass percentage of magnetic material in the positive electrode film is 20ppm-300ppm.

[0191] In some embodiments, the mass percentage of magnetic material in the positive electrode film is 20ppm-200ppm.

[0192] When the mass percentage of magnetic material in the positive electrode film is within the above range, it helps to further reduce the dissolution of transition metal ions and their catalytic effect on the SEI film surface, thereby reducing the lithium consumption caused by rebuilding the SEI film and improving the cycle performance of the battery cell.

[0193] In some embodiments, the magnetic material includes one or more of Fe, Fe2P, FeP, γ-Fe2O3, and Fe2P2O7.

[0194] In some embodiments, the positive electrode film further includes a conductive agent comprising carbon nanotubes, wherein the mass content of the carbon nanotubes is 0.1%-1.5% based on the total mass of the positive electrode film.

[0195] In some embodiments, based on the total mass of the positive electrode film, the mass content of the carbon nanotubes 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%, or any value range between the above two.

[0196] Carbon nanotubes can construct a three-dimensional network structure with a shorter electron transport path. Their one-dimensional structure can directly connect the current collector and the positive electrode active material, reducing the interfacial resistance between the traditional conductive agent and the positive electrode active material. This helps to reduce the impedance of the positive electrode film and improve the energy conversion efficiency of the battery cell. At the same time, carbon nanotubes can provide mechanical support for the positive electrode active material, reduce the probability of the positive electrode active material falling off, and improve the cycle stability of the battery cell.

[0197] In some embodiments, the conductive agent further includes conductive carbon black.

[0198] Conductive carbon black has a small size and adheres to the surface of the positive electrode active material particles and fills the gaps between the particles, forming dense point-like conductive contacts. By using carbon nanotubes and conductive carbon black in combination, both long-range and short-range conductivity can be achieved, which is beneficial to further improve the conductive network in the positive electrode film, reduce the impedance of the positive electrode film, and improve the energy conversion efficiency of the battery cell.

[0199] In some embodiments, referring to Figures 1 to 3, the housing 20 includes a first side plate 21, which includes a first plate portion 211 and a second plate portion 212 disposed along a first direction X. The second plate portion 212 is disposed on the side of the first plate portion 211 near the opening 20a of the receiving cavity. The second plate portion 212 is used to weld to the end cap 30 to form a weld portion W. The thickness of the second plate portion 212 is greater than the thickness of the first plate portion 211. The first side plate 21 is disposed opposite to the positive electrode sheet.

[0200] As the number of cycles of a battery cell increases, the negative electrode active material expands and contracts repeatedly, and the solid electrolyte membrane is continuously formed and reconstructed, which increases the internal expansion of the battery cell. This expansion force is periodically transmitted to the positive electrode film layer. That is, during the charging process of the battery cell, the electrode assembly will expand and squeeze the first plate, causing the first side plate to swing back and forth with the welded part as the base point. The first side plate is prone to cracking under the action of swing stress.

[0201] Increasing the overall thickness of the first side plate helps to mitigate the risk of cracking of the first side plate, but it will reduce the energy density of the battery cell. In this embodiment, the thickness of the second plate near the opening is increased to ensure the strength of the first side plate in the area near the weld, reduce the risk of cracking of the first side plate, improve the safety performance of the battery cell, and take into account the energy density of the battery cell.

[0202] It is understandable that the first direction X is parallel to the thickness direction of the end cap 30, and the second direction Z is perpendicular to the first direction X and the thickness direction Y of the first side plate.

[0203] In some embodiments, the second plate portion 212 includes a base portion 212a and a first transition portion 212b, the first transition portion 212b being connected between the base portion 212a and the first plate portion 211. The thickness of the first transition portion 212b gradually decreases along the direction away from the base portion 212a.

[0204] By providing a first transition section, the embodiments of this application can achieve a smooth transition at the junction of the first plate and the second plate, reduce stress concentration, lower the risk of cracking of the first side plate, and improve the safety performance of the battery cell.

[0205] In some embodiments, the thickness ratio of the second plate portion to the first plate portion is 1.05-3.

[0206] In some embodiments, the thickness ratio of the second plate portion to the first plate portion can be selected as 1.05, 1.1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 or any value between the two.

[0207] The thickness ratio of the second plate to the first plate is within the above range. The second plate has higher strength, which helps to improve the safety performance of the battery cell while taking into account the energy density of the battery cell.

[0208] In some embodiments, the thickness of the first plate portion is 0.5mm-1.2mm, and optionally 0.6mm-1.0mm.

[0209] In some embodiments, the thickness of the first plate portion can be selected as 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm or any value range between the two.

[0210] The thickness of the first plate is within the aforementioned range, which can take into account the energy density of the battery cell while also withstanding the periodic expansion force of the electrode assembly during the charging process of the battery cell, reducing the probability of cracking of the first plate and improving the safety performance of the battery cell.

[0211] In some embodiments, the housing 20 is a hollow structure, with an internal cavity for accommodating the electrode assembly 10 and the electrolyte. The housing 20 can be of various shapes, such as a cylinder or a cuboid. The shape of the housing 20 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, a cylindrical housing can be used; if the electrode assembly 10 is a cuboid structure, a cuboid housing can be used.

[0212] In some embodiments, the end cap 30 is sealingly connected to the housing 20 to form a sealed space for accommodating the electrode assembly 10 and the electrolyte. Exemplarily, the end cap 30 is connected to the housing 20 by welding. Welding can simultaneously achieve a seal and secure connection between the end cap 30 and the housing 20.

[0213] In some embodiments, the housing 20 may include one or more first side plates 21. For example, for a cuboid housing 20, there may be two first side plates 21, which are arranged opposite to each other. For a cylindrical housing 20, there may be one first side plate 21, which is generally cylindrical in shape.

[0214] In some embodiments, the capacity of the battery cell is 400Ah-3000Ah.

[0215] 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 charged at a constant power of 0.5P until the charging cutoff voltage is reached, and then discharged at a constant power of 0.5P until the discharging cutoff voltage is reached. This constitutes one charge-discharge cycle, and the capacity of the first discharge is calculated as the capacity of the single battery cell.

[0216] 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.

[0217] 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 above two.

[0218] The capacity of individual battery cells is within the above range, which helps to further meet the capacity requirements of energy storage devices for energy storage batteries.

[0219] In some embodiments, the capacity of the battery cell is 500Ah-1500Ah.

[0220] In some embodiments, the capacity of the battery cell is 600Ah-1000Ah.

[0221] A second aspect of this application provides a battery device, which includes the battery cell provided in this application.

[0222] In some implementations, the battery device is one or more of a battery module and a battery pack.

[0223] As shown in Figure 4, the battery device 2 includes a housing 5 and battery cells (not shown in Figure 4), with the battery cells housed inside the housing 5.

[0224] The housing 5 is used to house individual battery cells, and the housing 5 can have various structures. In some embodiments, the housing 5 may include a first housing portion 5a and a second housing portion 5b, which overlap each other, and together define a housing space 5c for housing the individual battery cells. The second housing portion 5b may be a hollow structure with one end open, and the first housing portion 5a may be a plate-like structure, with the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c; alternatively, both the first housing portion 5a and the second housing portion 5b may be hollow structures with one side open, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as cylinders, cuboids, etc.

[0225] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0226] In battery device 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells are connected in both series and parallel. Multiple battery cells can be directly connected in series, parallel, or in a mixed manner, and then the whole assembly of multiple battery cells is housed in housing 5. Alternatively, multiple battery cells can first be connected in series, parallel, or in a mixed manner to form battery module 6, and then multiple battery modules 6 can be connected in series, parallel, or in a mixed manner to form a whole assembly, which is then housed in housing 5.

[0227] A third aspect of this application also provides an energy storage device, which includes the battery cell or battery device provided in this application.

[0228] 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.

[0229] Energy storage devices can be used in energy storage power stations, wind power generation systems, solar power generation systems, mobile power systems, or temporary power supply systems. Energy storage devices can store electrical energy as needed and output it when appropriate. For example, energy storage devices can store electrical energy during off-peak hours and provide power to relevant users or electrical equipment during peak hours.

[0230] Example

[0231] 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.

[0232] Example 1

[0233] (1) Preparation of positive electrode sheet

[0234] Preparation of positive electrode active materials:

[0235] Lithium carbonate, iron phosphate, titanium dioxide, glucose, and polyethylene glycol were added to water and mixed in a premixing tank at 1400 rpm. The mixture was demagnetized by a demagnetizing rod with a magnetic field strength of 10000 Gs. The ratio of lithium carbonate to iron phosphate was such that the molar ratio of lithium to iron was 1.03:1.0. The mass content of glucose was 6% of the total raw materials, and the mass content of polyethylene glycol was 5% of the total raw materials. After uniform mixing, a mixed raw material with a solid content of 40% was obtained.

[0236] Among them, the number of magnetic particles in lithium carbonate is less than or equal to 500 pcs / kg, and the particle size D is... V10 ≥1μm, particle size D V50 The particle size is 6 μm, and the particle size D is... V90 The magnetic particle size is less than or equal to 40 μm; the number of magnetic particles in ferric phosphate is less than or equal to 95 pcs / kg, and the morphology is quasi-spherical; the number of magnetic particles in glucose is less than or equal to 500 pcs / kg; the molecular weight of polyethylene glycol is 1500, and the number of magnetic particles is less than or equal to 150 pcs / kg.

[0237] The mixed raw materials were subjected to two grinding-demagnetization cycles in a sand mill. After coarse grinding for 1 hour, the coarsely ground raw materials were demagnetized using a permanent magnet separator with a demagnetization intensity greater than or equal to 8000 Gs. The demagnetized raw materials were then finely ground, with the slurry temperature controlled below 40℃ during the grinding process to obtain a mixed slurry. The solid particle size D in the mixed slurry was... VThe particle size was 0.35 μm. After spray drying, the precursor powder was obtained, and the D50 after drying was 55.0 μm; the magnetic material content was less than 70 pcs / kg.

[0238] The precursor powder was subjected to a two-stage heating sintering process in a nitrogen atmosphere to obtain lithium iron phosphate cathode material: the temperature was increased from 25℃ to 450℃ at a heating rate of 2℃ / min (first heating stage), and held for 3 hours; the temperature was then increased from 450℃ to 780℃ at a heating rate of 5℃ / min (second heating stage), and held for 12 hours; the air flow rate in the heating stage was greater than that in the isothermal stage, with a ratio of 1.5:1, and the total air flow rate was 1350 cm³. 3 / h, after which cooling is completed; D is obtained by airflow pulverization. V 50 is a lithium iron phosphate material with 1.0μm-2.0μm carbon coating.

[0239] The prepared carbon-coated lithium iron phosphate material contains 0.07% titanium by mass.

[0240] The above-mentioned positive electrode active materials lithium iron phosphate, carbon nanotubes, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:1:2:2, and then N-methylpyrrolidone solvent was added and stirred evenly to obtain a positive electrode slurry. This positive electrode slurry was transferred and coated onto a current collector aluminum foil, dried, hot-pressed, die-cut, and slit to obtain the positive electrode sheet. The transfer coating speed was 20 m / min.

[0241] The hot pressing process includes three hot roller pressing processes, with the hot roller pressing pressure increasing sequentially to 40 tons, 60 tons, and 80 tons. The hot roller temperature is 60℃. Before the first hot roller compaction, the electrode sheet is heated to 40℃.

[0242] In the positive electrode film layer, particles with a diameter of 1μm-5μm account for 30% of the area of ​​the cross-section along the thickness direction of the electrode sheet; the magnetic material in the positive electrode film layer accounts for 20ppm by mass; and the compaction density of the positive electrode film layer is 2.51g / cm³. 3 The lateral density of the positive electrode film layer on any side is 0.27 g / 1540.25 mm². 2 .

[0243] (2) Preparation of negative electrode sheet

[0244] The negative electrode active material graphite, conductive agent SP, and binder PVDF are mixed in a ratio of 96:2:2, and deionized water is added and stirred to disperse and prepare a negative electrode slurry. The negative electrode slurry is then coated on both sides of a Cu foil. After both sides are coated, the foil is dried, compacted, slit, and sheeted to prepare the negative electrode sheet.

[0245] (3) Separating membrane

[0246] A 5μm thick polyethylene film was used as the base film. An alumina ceramic coating was first sprayed on both sides of the base film, and after drying, a polyvinylidene fluoride coating was sprayed on.

[0247] (4) Preparation of electrolyte

[0248] Based on the mass of the electrolyte, the electrolyte contains 32% dimethyl carbonate, 40% ethyl methyl carbonate, 10.5% ethylene carbonate, 12.5% ​​lithium hexafluorophosphate, and 5% lithium difluorosulfonamide.

[0249] (5) Preparation of battery cells

[0250] The positive electrode, separator, and negative electrode are stacked and wound sequentially, with the separator acting as a separator between the positive and negative electrodes, resulting in a wound electrode assembly. The electrode assembly is placed in an open cavity within a housing, with an end cap covering the opening. The housing includes a first side plate, comprising a first plate portion and a second plate portion arranged along a first direction. The second plate portion is located on the side of the first plate portion near the opening of the cavity. The first plate portion has a thickness of 0.8 mm, and the second plate portion has a thickness of 1.0 mm. The electrolyte is then injected and the assembly is sealed. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. The total coating area of ​​the positive electrode film layer in the battery cell is 22 m². 2 The capacity of a single battery cell is 600 Ah. The volumetric energy density of a single battery cell is 430 Wh / L.

[0251] The preparation of the battery cells in Examples 2 to 4 is similar to that in Example 1, except that the types or mass contents of doping elements in the positive electrode active material of the positive electrode sheet are different, as shown in Table 1.

[0252] The preparation of the battery cells in Examples 5 to 13 is similar to that in Example 1, except that the electrolyte formulations are different, as shown in Table 1.

[0253] The preparation of the battery cells in Examples 14 to 16 is similar to that in Example 1, except that the mass content of magnetic material in the positive electrode film is different, as shown in Table 2.

[0254] Example 14

[0255] The preparation method of the positive electrode active material in Example 14 is basically the same as that in Example 1, except that the sintering process of the positive electrode active material is different, specifically:

[0256] The precursor powder was subjected to a two-stage heating sintering process in a nitrogen atmosphere to obtain lithium iron phosphate cathode material: the temperature was increased from 25℃ to 450℃ at a heating rate of 2℃ / min (first heating stage), and held for 3 hours; the temperature was then increased from 450℃ to 800℃ at a heating rate of 5℃ / min (second heating stage), and held for 12 hours; the air volume in the heating stage was greater than that in the isothermal stage, with a ratio of 1.5:1, and the total air volume was 1350 cm³. 3 / h, after which cooling is completed; D is obtained by airflow pulverization. V 50 is a lithium iron phosphate material with 1.0μm-2.0μm carbon coating.

[0257] Example 15

[0258] The preparation method of the positive electrode active material in Example 15 is basically the same as that in Example 1, except that the sintering process of the positive electrode active material is different, specifically:

[0259] The precursor powder was subjected to a two-stage heating sintering process in a nitrogen atmosphere to obtain lithium iron phosphate cathode material: the temperature was increased from 25℃ to 450℃ at a heating rate of 2℃ / min (first heating stage), and held for 3 hours; the temperature was then increased from 450℃ to 820℃ at a heating rate of 5℃ / min (second heating stage), and held for 12 hours; the air flow rate in the heating stage was greater than that in the isothermal stage, with a ratio of 1.5:1, and the total air flow rate was 1350 cm³. 3 / h, after which cooling is completed; D is obtained by airflow pulverization. V 50 is a lithium iron phosphate material with 1.0μm-2.0μm carbon coating.

[0260] Example 16

[0261] The preparation method of the positive electrode active material in Example 16 is basically the same as that in Example 1, except that the preparation process of the positive electrode active material is slightly different. The differences are as follows:

[0262] (1) The carbon source in the mixed raw materials is only glucose, and the mass of glucose is 5.7 wt% compared to the mass of iron phosphate;

[0263] (2) The heating and sintering processes are different. The precursor powder is sintered at least twice in a nitrogen atmosphere. The first sintering temperature is 750℃ and the holding time is 8 hours to obtain the initial sintered product.

[0264] 1.5 wt% (based on the mass of the initial calcined product) of glucose, 3.0 wt% (based on the mass of the initial calcined product) of polyethylene glycol and titanium source were added to the initial calcined product. After homogenization, the mixture was divided into two groups for secondary grinding. The grinding parameters for the two groups were different, and the particle size distribution (D) of the particles after the first group of grinding was controlled. V 50 is 2.0μm, and the D of the particles after the second group of grinding is... V50 represents 0.35 μm. The ground particles from the first and second groups were mixed at a mass ratio of 30:70, spray-dried, and then subjected to a second sintering. The second sintering temperature was 800℃, and the temperature was maintained for 10 hours.

[0265] The preparation of the battery cells in Comparative Examples 1 to 4 was similar to that in Example 1, except that the positive electrode active material in the positive electrode sheet of Comparative Example 1 was different, and the electrolyte formulations of Comparative Examples 2 to 4 were different, as shown in Table 1.

[0266] II. Battery Performance Testing

[0267] (1) Battery cycle performance test

[0268] At 25℃, the battery cells were left to stand for 5 hours, then discharged at a constant power of 0.5P to 2.5V. After standing for 30 minutes, the battery cells were charged at a constant power of 0.5P to 3.65V (cutoff). After standing for 10 minutes, the cells were discharged again at a constant power of 0.5P to 2.5V (cutoff), and then stood for 10 minutes. The cycle discharge capacity was recorded. This constituted one cycle. The discharge capacity of each cycle was recorded, as well as the number of cycles in which the capacity decayed to 80% of the initial cycle discharge capacity.

[0269] (2) Battery energy conversion efficiency test

[0270] At 25℃, the battery cell was left to stand for 5 hours, then discharged at a constant power of 0.5P to 2.5V. After standing for 30 minutes, the battery cell was charged at a constant power of 0.5P to 3.65V. After standing for 10 minutes, the charging energy was recorded. Then, the battery cell was discharged at a constant power of 0.5P to 2.5V. After standing for 10 minutes, the discharge energy was recorded. The energy conversion efficiency of the battery was calculated using the formula: Discharge energy / Charging energy.

[0271] (3) Battery volumetric energy density test

[0272] At 25°C, the battery cell is charged at a constant power of 0.5P to 3.65V cutoff. After resting for 10 minutes, it is discharged at a constant power of 0.5P to 2.5V cutoff. The total discharge energy of the battery cell after discharge is recorded as E0.

[0273] Measure the length, width, and height of the battery cell, and calculate the volume of the battery cell, V0 = length × width × height. The volumetric energy density of the battery cell = discharge energy of the battery cell E0 / volume of the battery cell V0.

[0274] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0275] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below.

[0276] Table 1

[0277] As can be seen from the comparison of the embodiments and comparative examples of this application, the positive electrode active material includes lithium iron phosphate particles, which include one or more of titanium and vanadium elements; the electrolyte includes lithium fluorosulfonyl imide salt, and the mass content of lithium fluorosulfonyl imide salt is 2%-7% based on the total mass of the electrolyte; the compaction density of the positive electrode film layer is greater than or equal to 2.5 g / cm³. 3 The total coating area of ​​the positive electrode film in each battery cell is greater than or equal to 11m². 2 At that time, based on the high capacity and high volumetric energy density of the battery cells, the cycle performance and energy conversion efficiency of the battery cells were further improved.

[0278] As can be seen from the comparison between Examples 5 and 6 and Examples 1, 7 and 8, when the mass content of lithium fluorosulfonylimide salt is 3.7%-7%, the battery cell has high capacity and high volumetric energy density, and further improves the cycle performance and energy conversion efficiency of the battery cell.

[0279] As can be seen from the comparison between Example 11 and Examples 9 and 12, the electrolyte also includes fluoroethylene carbonate. Based on the total mass of the electrolyte, when the mass content of fluoroethylene carbonate is 3%-5%, the battery cell has high capacity, high volumetric energy density and good cycle performance, and the energy conversion efficiency of the battery cell is further improved.

[0280] As can be seen from the comparison between Example 9 and Example 13, when the solvent includes propylene carbonate, the battery cell not only has high capacity, high volumetric energy density and good cycle performance, but also further improves the energy conversion efficiency of the battery cell.

[0281] Table 2

[0282] As can be seen from the comparison between Examples 15 and 16 and Examples 1 and 14, when the mass percentage of magnetic material in the positive electrode film is 20ppm-200ppm, the battery cell not only has high capacity, high volumetric energy density and high energy conversion efficiency, but also further improves the cycle performance of the battery cell.

[0283] 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 end cap, a housing, an electrode assembly, and an electrolyte. The housing includes a receiving cavity with an opening, and the end cap is used to close the opening. The electrode assembly and the electrolyte are disposed within the receiving cavity of the housing. The electrode assembly includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes lithium iron phosphate particles, and the lithium iron phosphate particles include one or more of titanium and vanadium. The electrolyte comprises a lithium fluorosulfonyl imide salt, and the mass content of the lithium fluorosulfonyl imide salt is 2%-7% based on the total mass of the electrolyte; The compaction density of the positive electrode film layer is greater than or equal to 2.5 g / cm³. 3 ; The total coating area of ​​the positive electrode film in the battery cell is greater than or equal to 11m². 2 .

2. The battery cell according to claim 1, characterized in that, The fluorinated sulfonyl imide lithium salt includes one or more of lithium bisfluorosulfonyl imide and lithium bistrifluoromethylsulfonyl imide, and may be selected as lithium bisfluorosulfonyl imide.

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 fluorosulfonylimide lithium salt is 3.7%-7%.

4. The battery cell according to any one of claims 1-3, characterized in that, The total coating area of ​​the positive electrode film in the battery cell is 11m². 2 -150m 2 15m is optional 2 -130m 2 Further options include 18m. 2 -115m 2 .

5. The battery cell according to any one of claims 1-4, characterized in that, The compaction density of the positive electrode film is 2.5 g / cm³. 3 -3.0g / cm 3 .

6. The battery cell according to any one of claims 1-5, characterized in that, The compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.8g / cm 3 .

7. The battery cell according to any one of claims 1-6, characterized in that, The lateral density of the positive electrode film layer on either side is 0.25 g / 1540.25 mm². 2 -0.40g / 1540.25mm 2 Available in 0.25g / 1540.25mm. 2 -0.35g / 1540.25mm 2 .

8. The battery cell according to any one of claims 1-7, characterized in that, The lithium iron phosphate particles include titanium, and the mass content of titanium is 0.05%-0.10% based on the total mass of the positive electrode active material.

9. The battery cell according to any one of claims 1-8, characterized in that, The lithium iron phosphate particles include vanadium, and the vanadium content is 0.05%-0.15% based on the total mass of the positive electrode active material.

10. The battery cell according to any one of claims 1-9, characterized in that, The electrolyte also includes a solvent, which includes one or more of dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.

11. The battery cell according to claim 10, characterized in that, The solvent includes dimethyl carbonate, and the mass content of the dimethyl carbonate is 15%-50% based on the total mass of the electrolyte, optionally 15%-45%, and further optionally 15%-36%.

12. The battery cell according to claim 10, characterized in that, The solvent includes ethyl methyl carbonate, and the ethyl methyl carbonate content is 10%-60% based on the total mass of the electrolyte, optionally 30%-60%.

13. The battery cell according to claim 10, characterized in that, The solvent includes propylene carbonate, and the mass content of propylene carbonate is 0.5%-5% based on the total mass of the electrolyte, optionally 1%-3%.

14. The battery cell according to any one of claims 1-13, characterized in that, The electrolyte also includes lithium hexafluorophosphate; based on the total mass of the electrolyte, the mass content of lithium hexafluorophosphate is 6%-20%, optionally 8%-16%.

15. The battery cell according to claim 14, characterized in that, The mass ratio of lithium hexafluorophosphate to lithium difluorosulfonyl imide is 1-5, optionally 2-4, and further optionally 2-3.

16. The battery cell according to any one of claims 1-15, characterized in that, The electrolyte also includes fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is 0.05%-10% based on the total mass of the electrolyte, optionally 2%-5%, and further optionally 3%-5%.

17. The battery cell according to any one of claims 1-16, characterized in that, In the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of particles with a diameter greater than or equal to 1 μm is 30.0%-50.0%.

18. The battery cell according to claim 17, characterized in that, In the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of particles with a particle size of 1μm-5μm is 30.0%-50.0%, and can be selected as 30.0%-45.0%.

19. The battery cell according to any one of claims 1-18, characterized in that, The mass percentage of magnetic material in the positive electrode film is 20ppm-1980ppm, optionally 20ppm-300ppm, and further optionally 20ppm-200ppm.

20. The battery cell according to claim 19, characterized in that, The magnetic material includes one or more of Fe, Fe2P, FeP, γ-Fe2O3, and Fe2P2O7.

21. The battery cell according to any one of claims 1-20, characterized in that, The positive electrode film layer also includes a conductive agent, which includes carbon nanotubes, and the mass content of the carbon nanotubes is 0.1%-1.5% based on the total mass of the positive electrode film layer.

22. The battery cell according to any one of claims 1-21, characterized in that, The housing includes a first side plate, which includes a first plate portion and a second plate portion disposed along a first direction. The second plate portion is disposed on the side of the first plate portion near the opening of the receiving cavity. The second plate portion is used to weld to the end cap to form a weld portion. The thickness of the second plate portion is greater than the thickness of the first plate portion. The first side plate is disposed opposite to the positive electrode sheet.

23. The battery cell according to claim 22, characterized in that, The thickness ratio of the second plate portion to the first plate portion is 1.05-3.

24. The battery cell according to claim 22 or 23, characterized in that, The thickness of the first plate portion is 0.5mm-1.2mm, and can be selected as 0.6mm-1.0mm.

25. The battery cell according to any one of claims 1-24, characterized in that, The capacity of the battery cell is 400Ah-3000Ah, optionally 500Ah-1500Ah, and further optionally 600Ah-1000Ah.

26. A battery device, characterized in that, The battery device comprises the battery cell according to any one of claims 1-25.

27. An energy storage device, characterized in that, The energy storage device includes a battery cell as described in any one of claims 1-25 or a battery device as described in claim 26.

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