Battery cell, battery device, and energy storage device

Abstract

The present application discloses a battery cell, a battery device, and an energy storage device. The battery cell comprises a casing, an electrode assembly, and an electrolyte; the casing comprises a shell and an end cover; one end of the shell is provided with an opening; the electrode assembly and the electrolyte are provided in the shell; the end cover covers the opening of the shell; the end cover is provided with a pressure relief mechanism; the electrode assembly comprises a positive electrode sheet, and the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided 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 titanium and vanadium; the electrolyte comprises a lithium fluorosulfonylimide salt, and based on the total mass of the electrolyte, the mass content of the lithium fluorosulfonylimide salt is 2%-7%; and the battery cell further comprises at least one support member arranged between the end cover and the electrode assembly and an insulating member arranged between the support member and the electrode assembly, and the melting point of the support member is greater than that of the insulating member.

Description

Battery cells, battery devices and energy storage devices

[0001] Cross-references

[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, the application of individual battery cells in energy storage devices has become increasingly widespread. In various energy storage application scenarios, long cycle life, high energy conversion efficiency, and high safety performance have become key indicators for evaluating the performance of energy storage batteries. This is especially true for large-scale energy storage power stations, whose large-scale, long-cycle operation places higher demands on battery performance. Therefore, there is an urgent need to develop individual battery cells that combine long cycle life, high energy conversion efficiency, and high safety performance. Summary of the Invention

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

[0006] The first aspect of this application provides a battery cell, which includes a casing, an electrode assembly, and an electrolyte. The casing includes a housing and an end cap, one end of which has an opening. The electrode assembly and the electrolyte are disposed within the housing. The end cap covers the opening of the housing and is provided with a pressure relief mechanism. The electrode assembly includes a positive electrode plate, 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 battery cell also includes at least one support member disposed between the end cap and the electrode assembly, and an insulating member disposed between the support member and the electrode assembly. The melting point of the support member is greater than the melting point of the insulating member.

[0007] By doping one or more of titanium and vanadium elements into lithium iron phosphate, a more stable bonding network can be formed, improving the structural stability, mechanical strength, and structural toughness of lithium iron phosphate. This helps the lithium iron phosphate withstand the compression caused by the expansion of the negative electrode film during long-term cycling of the battery cell, 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.

[0008] However, as the internal heat generation and temperature of the battery cell increase during cycling, the 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 the transition metals deposited at the negative electrode act as catalysts, catalyzing the decomposition of the solid electrolyte interphase (SEI) film. This results in more active lithium being consumed during the SEI film repair process, deteriorating the cycle performance of the battery cell.

[0009] The applicant adds a certain amount of fluorosulfonylimide lithium salt to the electrolyte. During cycling, it preferentially decomposes on the surface of the positive electrode active material, forming 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 the reconstruction of 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, improve the transport efficiency of lithium ions at the positive electrode interface, and compensate for the heat consumption of the battery by reducing the transport impedance, thereby improving the energy efficiency of the battery cell.

[0010] 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.

[0011] Adding 2%-7% (by mass) of fluorosulfonylimide lithium salt to the electrolyte can improve the cycle stability of individual battery cells. However, the decomposition temperature of fluorosulfonylimide lithium salt is essentially the same as the thermal runaway temperature of the battery. This exacerbates the instantaneous heat generation in battery cells during abnormal situations such as short circuits or collisions. The high temperature and heat generation in battery cells under abnormal conditions can cause the insulation between the end cap and electrode assembly to soften or even melt, gradually losing its original support and isolation function. Simultaneously, the high temperature significantly accelerates the decomposition and side reactions of the electrolyte, resulting in a substantial increase in gas production within the battery cell. This rise in internal gas pressure makes the electrode assembly prone to upward movement, potentially blocking the pressure relief channels on the end cap and causing them to fail. Because the internal gas cannot be released in a timely and directional manner, the internal pressure of the battery cell will continue to accumulate, significantly increasing the probability of non-directional pressure relief and the risk of cascading failures in surrounding battery cells, thus deteriorating the overall safety performance of the battery.

[0012] The applicant discovered that at least one support member is provided between the end cap and the electrode assembly, with an insulating member located between the support member and the electrode assembly, and the melting point of the support member is higher than that of the insulating member. This support member can continue to provide mechanical support after thermal runaway of the battery cell and when the insulating member melts due to heat, effectively suppressing the upward movement of the electrode assembly under internal pressure, reducing the probability of it blocking the pressure relief mechanism on the end cap. Gas inside the battery cell can still be effectively released through a pre-set pressure relief channel, reducing the risk of non-directional pressure relief in the battery cell.

[0013] In summary, the battery cell provided in this application uses lithium iron phosphate doped with one or more of titanium and vanadium elements as the positive electrode active material, and adds 2%-7% by mass of fluorosulfonylimide lithium salt to the electrolyte. The battery cell has good cycle performance and energy efficiency. At the same time, the battery cell also includes at least one support member disposed between the end cap and the electrode assembly, and an insulating member disposed between the support member and the electrode assembly. The melting point of the support member is higher than that of the insulating member, which reduces the probability of non-directional pressure leakage in the battery cell and thus causing thermal runaway of adjacent battery cells, improves the reliability of the battery cell, and improves the safety performance of the battery.

[0014] In any embodiment, the support member includes one or more of ceramic and metal components.

[0015] The support components include the aforementioned materials, which have high melting points and high rigidity. They are not easily melted when the battery cell experiences thermal runaway and can continue to perform the function of mechanical support. This effectively suppresses the upward movement of the electrode assembly under internal pressure, reduces the probability of it blocking the pressure relief mechanism on the end cap, reduces the risk of non-directional pressure relief in the battery cell leading to thermal runaway of adjacent battery cells, improves the reliability of the battery cell, and enhances the safety performance of the battery.

[0016] In any embodiment, the metal part includes one or more of aluminum parts, aluminum alloy parts, and steel parts.

[0017] The metal parts, including the aforementioned materials, all have high melting points and are not easily melted when the battery cell experiences thermal runaway. They can continue to perform the function of mechanical support, effectively suppress the upward movement of the electrode assembly under internal pressure, reduce the probability of it blocking the pressure relief mechanism on the end cap, reduce the risk of non-directional pressure relief in the battery cell leading to thermal runaway of adjacent battery cells, improve the reliability of the battery cell, and improve the safety performance of the battery.

[0018] In any embodiment, the insulating element includes one or more of plastic elements and rubber elements.

[0019] In any embodiment, the fluorosulfonylimide lithium salt includes one or more of lithium bisfluorosulfonylimide and lithium bistrifluoromethylsulfonylimide, and may be selected as lithium bisfluorosulfonylimide.

[0020] 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.

[0021] In any embodiment, the mass content of the fluorosulfonylimide lithium salt is 3.7%-7% based on the total mass of the electrolyte.

[0022] 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.

[0023] 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.

[0024] 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, improving the structural integrity of the positive electrode active material, and enhancing 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, lower the probability of titanium ions catalyzing the decomposition of the SEI film during the reduction and precipitation of titanium ions at the negative electrode, reduce the irreversible consumption of lithium ions caused by the reconstruction of the SEI film, and improve the cycle performance of the battery cell.

[0025] 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.

[0026] Within a reasonable range, the vanadium content helps stabilize the crystal structure of lithium iron phosphate through vanadium ion doping, enhances the strength of PO bonds, and thus improves 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 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, reduce the probability of vanadium ions catalyzing the decomposition of the SEI film during the reduction and precipitation of vanadium ions at the negative electrode, reduce the irreversible consumption of lithium ions caused by the reconstruction of the SEI film, and improve the cycle performance of the battery cell.

[0027] In any embodiment, the electrolyte further includes a solvent, which includes one or more of dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] In any embodiment, the mass content of dimethyl carbonate is 15%-45% based on the total mass of the electrolyte.

[0032] A mass content of dimethyl carbonate within the above range is beneficial for further balancing the energy conversion efficiency and cycle stability of individual battery cells.

[0033] In any embodiment, the mass content of dimethyl carbonate is 15%-36% based on the total mass of the electrolyte.

[0034] A mass content of dimethyl carbonate within the above range is beneficial for further balancing the energy conversion efficiency and cycle stability of individual battery cells.

[0035] 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.

[0036] 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.

[0037] The applicant discovered through experiments that the energy conversion efficiency of a single battery cell can be further improved when the electrolyte includes ethyl methyl carbonate and fluoroethylene carbonate.

[0038] In any embodiment, the methyl ethyl carbonate content is 30%-60% based on the total mass of the electrolyte.

[0039] 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.

[0040] Propylene carbonate possesses a high dielectric constant and good low-temperature performance, which is beneficial for promoting the dissociation of lithium-containing electrolyte salts, increasing the ionic conductivity of the electrolyte, facilitating the rapid migration of lithium ions in the electrolyte, and improving the energy conversion efficiency of battery cells. However, propylene carbonate readily undergoes a co-intercalation reaction 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 battery cells.

[0041] In any embodiment, the mass content of propylene carbonate is 1%-3% based on the total mass of the electrolyte.

[0042] 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.

[0043] 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%.

[0044] 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.

[0045] In any embodiment, the mass ratio of the lithium hexafluorophosphate to the lithium fluorosulfonyl imide salt is 1-5, and optionally 2-4.

[0046] 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.

[0047] In any embodiment, the mass ratio of the lithium hexafluorophosphate to the lithium fluorosulfonyl imide salt is 2-3.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] In any embodiment, the mass content of the fluoroethylene carbonate is 2%-5% based on the total mass of the electrolyte.

[0052] In any embodiment, the mass content of the fluoroethylene carbonate is 3%-5% based on the total mass of the electrolyte.

[0053] 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.

[0054] 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%.

[0055] 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.

[0056] 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%.

[0057] 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%.

[0058] 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.

[0059] In any embodiment, the mass percentage of magnetic material in the positive electrode film is 20ppm-1980ppm.

[0060] 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 the lithium consumption caused by rebuilding the SEI film and improving the cycle performance of the battery cell.

[0061] In any embodiment, the mass percentage of magnetic material in the positive electrode film is 20ppm-300ppm.

[0062] In any embodiment, the mass percentage of magnetic material in the positive electrode film is 20ppm-200ppm.

[0063] 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 lithium consumption caused by rebuilding the SEI film and improving the cycle performance of the battery cell.

[0064] In any embodiment, the magnetic material includes one or more of Fe, Fe2P, FeP, γ-Fe2O3, and Fe2P2O7.

[0065] 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.

[0066] 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.

[0067] In any embodiment, the conductive agent further includes conductive carbon black.

[0068] 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.

[0069] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0070] 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.

[0071] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 15m². 2 -130m 2 .

[0072] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 18m². 2 -115m 2 .

[0073] 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 .

[0074] 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.

[0075] 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 .

[0076] The embodiments of this application further increase 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.

[0077] 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 .

[0078] In any embodiment, the capacity of the battery cell is 400Ah-3000Ah.

[0079] 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.

[0080] In any embodiment, the capacity of the battery cell is 500Ah-1500Ah.

[0081] In any embodiment, the capacity of the battery cell is 600Ah-1000Ah.

[0082] 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.

[0083] 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.

[0084] 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

[0085] 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.

[0086] Figure 1 is an exploded view of a battery cell according to an embodiment of this application;

[0087] Figure 2 is a schematic diagram showing the end cap, insulating component, and supporting component of a battery cell according to an embodiment of this application.

[0088] Figure 3 is a schematic diagram of a battery device according to an embodiment of this application.

[0089] 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; 9 Battery cell; 1121 Housing; 1122 End cap; 1123 First wall; 111 Electrode assembly; 115 Pressure relief mechanism; 116 Pressure relief area; 120 Support member; 1201 First support member; 1202 Second support member; 121 First part; 122, Second part; 1221, First sub-part; 1222, Second sub-part; 123, Connecting part; 1231, Chamfer; 124, First notch; 130 Insulating member. Detailed Implementation

[0090] 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 detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0091] 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.

[0092] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0093] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0094] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0095] 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.

[0096] 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).

[0097] Energy storage batteries are typically used for applications such as power storage, load balancing, and emergency backup power. They have long charge-discharge cycles and operate under relatively light loads, but this places higher demands on their cycle life and energy conversion efficiency. However, with continuous improvements and optimizations to the electrode components within battery cells, the cycle life and energy conversion efficiency of individual cells are constantly increasing. At the same time, the thermal runaway response of battery cells is becoming more severe, causing a rapid increase in pressure and temperature within the cell, leading to significant safety risks. How to improve the cycle performance and energy conversion efficiency of battery cells while simultaneously enhancing their safety performance is a pressing technical problem that needs to be solved in this field.

[0098] To address the aforementioned problems, the first aspect of this application provides a battery cell. Referring to Figure 1, the battery cell 9 includes a casing 112, an electrode assembly 111, and an electrolyte. The casing 112 includes a housing 1121 and an end cap 1122. One end of the housing 1121 has an opening. The electrode assembly 111 and the electrolyte are disposed within the housing 1121. The end cap 1122 covers the opening of the housing 1121 and is provided with a pressure relief mechanism 115. The electrode assembly includes a positive electrode plate, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The electrode film layer includes a positive electrode active material, which includes lithium iron phosphate particles, and the lithium iron phosphate particles include one or more of titanium and vanadium elements; 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; referring to Figure 2, the battery cell 9 also includes at least one support member 120 disposed between the end cap 1122 and the electrode assembly 111 and an insulating member 130 disposed between the support member 120 and the electrode assembly 111, wherein the melting point of the support member 120 is greater than the melting point of the insulating member 130.

[0099] By doping one or more of titanium and vanadium elements into lithium iron phosphate, a more stable bonding network can be formed, improving the structural stability, mechanical strength, and structural toughness of lithium iron phosphate. This helps the lithium iron phosphate withstand the compression caused by the expansion of the negative electrode film during long-term cycling of the battery cell, 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.

[0100] However, as the internal heat generation and temperature of the battery cell increase during cycling, the 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 the transition metals deposited at the negative electrode act as catalysts, catalyzing the decomposition of the solid electrolyte interphase (SEI) film. This results in more active lithium being consumed during the SEI film repair process, deteriorating the cycle performance of the battery cell.

[0101] The applicant adds a certain amount of fluorosulfonylimide lithium salt to the electrolyte. During cycling, it preferentially decomposes on the surface of the positive electrode active material, forming 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 the reconstruction of 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, improve the transport efficiency of lithium ions at the positive electrode interface, and compensate for the heat consumption of the battery by reducing the transport impedance, thereby improving the energy efficiency of the battery cell.

[0102] 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.

[0103] Adding 2%-7% (by mass) of fluorosulfonylimide lithium salt to the electrolyte can improve the cycle stability of individual battery cells. However, the decomposition temperature of fluorosulfonylimide lithium salt is essentially the same as the thermal runaway temperature of the battery. This exacerbates the instantaneous heat generation in battery cells during abnormal situations such as short circuits or collisions. The high temperature and heat generation in battery cells under abnormal conditions can cause the insulation between the end cap and electrode assembly to soften or even melt, gradually losing its original support and isolation function. Simultaneously, the high temperature significantly accelerates the decomposition and side reactions of the electrolyte, resulting in a substantial increase in gas production within the battery cell. This rise in internal gas pressure makes the electrode assembly prone to upward movement, potentially blocking the pressure relief channels on the end cap and causing them to fail. Because the internal gas cannot be released in a timely and directional manner, the internal pressure of the battery cell will continue to accumulate, significantly increasing the probability of non-directional pressure relief and the risk of cascading failures in surrounding battery cells, thus deteriorating the overall safety performance of the battery.

[0104] The applicant discovered that at least one support member is provided between the end cap and the electrode assembly, with an insulating member located between the support member and the electrode assembly, and the melting point of the support member is higher than that of the insulating member. This support member can continue to provide mechanical support after thermal runaway of the battery cell and when the insulating member melts due to heat, effectively suppressing the upward movement of the electrode assembly under internal pressure, reducing the probability of it blocking the pressure relief mechanism on the end cap. Gas inside the battery cell can still be effectively released through a pre-set pressure relief channel, reducing the risk of non-directional pressure relief in the battery cell.

[0105] In summary, the battery cell provided in this application uses lithium iron phosphate doped with one or more of titanium and vanadium elements as the positive electrode active material, and adds 2%-7% by mass of fluorosulfonylimide lithium salt to the electrolyte. The battery cell has good cycle performance and energy efficiency. At the same time, the battery cell also includes at least one support member disposed between the end cap and the electrode assembly, and an insulating member disposed between the support member and the electrode assembly. The melting point of the support member is higher than that of the insulating member, which reduces the probability of non-directional pressure leakage in the battery cell and thus causing thermal runaway of adjacent battery cells, improves the reliability of the battery cell, and improves the safety performance of the battery.

[0106] 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.

[0107] 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.

[0108] 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, separated according to their 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, generating detection signal spectra for each component. Component qualitative analysis is performed using retention time, and quantitative analysis is achieved by standardizing and correcting peak areas, obtaining quantitative analysis of the organic components in the electrolyte. Referring to JY / T-020, ion chromatography is used to detect and quantify the types of anions of electrolyte salts in the electrolyte. Referring to JY / T0578-2020, nuclear magnetic resonance spectroscopy (NMR) is used to obtain qualitative and quantitative analysis of the components in the electrolyte.

[0109] 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.

[0110] 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.

[0111] In some implementations, the support includes one or more of ceramic or metal components.

[0112] The support components include the aforementioned materials, which have high melting points and high rigidity. They are not easily melted when the battery cell experiences thermal runaway and can continue to perform the function of mechanical support. This effectively suppresses the upward movement of the electrode assembly under internal pressure, reduces the probability of it blocking the pressure relief mechanism on the end cap, reduces the risk of non-directional pressure relief in the battery cell leading to thermal runaway of adjacent battery cells, improves the reliability of the battery cell, and enhances the safety performance of the battery.

[0113] In some embodiments, the metal part includes one or more of aluminum parts, aluminum alloy parts, and steel parts.

[0114] The metal parts, including the aforementioned materials, all have high melting points and are not easily melted when the battery cell experiences thermal runaway. They can continue to perform the function of mechanical support, effectively suppress the upward movement of the electrode assembly under internal pressure, reduce the probability of it blocking the pressure relief mechanism on the end cap, reduce the risk of non-directional pressure relief in the battery cell leading to thermal runaway of adjacent battery cells, improve the reliability of the battery cell, and improve the safety performance of the battery.

[0115] In some embodiments, the insulating element includes one or more of plastic and rubber components.

[0116] In some embodiments, the battery cell further includes a housing 112, which includes the housing 1121 and the end cap 1122.

[0117] For ease of description, the wall of the end cap 1122 with the pressure relief mechanism 115 is defined as the first wall 1123. The pressure relief mechanism 115 is provided with a pressure relief area 116, which may be located at the middle of the first wall 1123 along its own length.

[0118] In this application, the pressure relief mechanism 115 is used to release the internal gas of the battery cell 9.

[0119] As an example, the internal pressure or temperature of the battery cell 9 is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell 9 reaches the predetermined threshold, the pressure relief mechanism 115 is activated or a weak structure provided in the pressure relief mechanism 115 is destroyed, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell 9.

[0120] In some embodiments, the support member 120 includes a first part 121 and at least two second parts 122, the first part 121 being disposed between the end cap 1122 and the insulator 130, one end of the at least two second parts 122 being connected to the first part 121, and at least one second part 122 being connected to the end cap 1122.

[0121] The support member 120 can have a certain supporting strength so that it can support the electrode assembly 111 within the housing 1121. One or more support members 120 can be provided. When multiple support members 120 are provided, they can be spaced apart and dispersed. The structures of the multiple support members 120 can be the same or different.

[0122] One end of the second part 122 can be connected to the first part 121 in various ways, such as welding, bonding, interference fit, snap-fit, one-piece molding connection, etc.

[0123] Optionally, the other ends of the plurality of second portions 122 extend away from the electrode assembly 111 and are spaced apart. That is, the second portions 122 can extend from the end connected to the first portion 121 in a direction away from the electrode assembly 111, and the ends of the plurality of second portions 122 away from the electrode assembly 111 (which are also the ends away from the first portion 121) are spaced apart. The direction in which the second portions 122 are away from the electrode assembly 111 is also the direction in which the second portions 122 are away from the first portion 121. The spaced-apart arrangement of the ends of the plurality of second portions 122 away from the electrode assembly 111 can be understood as a gap between any two adjacent ends of the second portions 122 away from the first portion 121. Specifically, a gap can be formed between the ends of adjacent two second portions 122 away from the first portion 121, opening towards the inner wall surface of the outer casing 112 (refer to the surface of the first wall 1123 facing the electrode assembly 111). When the support member 120 is assembled to the battery cell 9, the ends of the second portions 122 away from the first portion 121 can... The support member 120 is directly in contact with or connected to the inner wall surface of the outer casing 112 (refer to the surface of the first wall 1123 facing the electrode assembly 111). The gap between two adjacent second parts 122 can extend from the first part 121 to the inner wall surface of the outer casing 112 facing the support member 120 (refer to the surface of the first wall 1123 facing the electrode assembly 111). Before the support member 120 is assembled into the battery cell 9, the ends of the two adjacent second parts 122 of the completed support member 120 that are away from the first part 121 can be relatively independent free ends.

[0124] The gap between two adjacent second parts 122 can serve as a notch for the discharge of pollutants. For ease of description, this notch is defined as the first notch 124, which can connect to the pressure relief zone 116. Specifically, the first notch 124 can connect the area inside the housing 112 where the electrode assembly 111 is located with the area inside the housing 112 corresponding to the pressure relief zone 116. When the pressure relief mechanism 115 is actuated, the first notch 124 can connect the area where the electrode assembly 111 is located with the opening or channel formed by the pressure relief mechanism 115. In this way, when the battery cell 9 experiences thermal runaway, the pollutants can flow to the pressure relief zone 116 through the first notch 124. Furthermore, one end of the second part 122 of the support member 120 is connected to the first part 121, and the second part 122 is spaced apart from the end of the electrode assembly 111. Each spaced second part 122 can form a first notch 124, which reduces the processing difficulty of the second part 122, makes the support member 120 easy to form, improves the processing convenience of the support member 120, and enables the support member 120 to be mass-produced in the industrial sector, which improves processing efficiency, saves consumables, and reduces the production cost of the battery cell 9.

[0125] Optionally, the first wall 1123 is provided with an injection hole 1124, which is used to inject electrolyte into the outer shell 112, and the support member 120 is provided to avoid the injection hole 1124.

[0126] For example, along the length of the first wall 1123, a support member 120 is provided on one or both sides of the injection hole 1124, and the support member 120 is spaced apart from the injection hole 1124.

[0127] The insulating component 130 may be located between the first wall 1123 (e.g., end cap 1122) and the electrode assembly 111. The insulating component 130 may be a plastic component, which may be pre-molded as a single piece of plastic or assembled from various plastic parts, and the material may be an insulating material. The insulating component 130 may also be a component made of other materials, such as rubber. The insulating component 130 has two main functions: first, it can isolate the electrical connection components inside the housing 112 from the housing 112 (specifically, the end cap 1122) to reduce the risk of short circuits; second, it can effectively support the end face of the electrode assembly 111. After the electrode assembly 111 is installed in the housing and the end cap 1122 is welded, the internal core of the electrode assembly 111 is under slight pressure. Moreover, the electrode assembly 111 will be in a vibrating environment during vehicle use. If the electrode assembly 111 is not sufficiently restrained, it will easily affect the life of the core or cause a short circuit. Therefore, the insulating component 130 needs to effectively support the end face of the core to reduce the possibility of the electrode assembly 111 moving up and down.

[0128] According to some embodiments of this application, optionally, continuing to refer to FIG2, the wall of the outer shell 112 where the pressure relief area 116 is provided is a first wall 1123, and at least one second part 122 is a first sub-part 1221, with one end of the first sub-part 1221 opposite to the first part 121 connected to the first wall 1123.

[0129] Each first sub-part 1221 is one of a plurality of second parts 122. The first sub-part 1221 is a defining description for the convenience of description.

[0130] The first sub-part 1221 can be provided one, two or more. The first sub-part 1221 can be connected and fixed to the first part 121 by welding, bonding or other methods.

[0131] During normal use of the battery cell 9, when the battery cell 9 shakes or moves, the support member 120 is connected to the first wall 1123 via the first sub-part 1221. This fixes the support member 120 relative to the housing 1121, reducing the impact on the reliability of the battery cell 9 caused by friction debris (e.g., metal support members 120 may generate metal wires or metal fragments due to friction) generated by the movement of the support member 120 relative to the housing 1121. Simultaneously, the first sub-part 1221 is connected to the first wall 1123 via its end facing away from the first part 121, further fixing the support member 120 relative to the housing 1121. This connection operation is convenient, and during the assembly process of the first sub-part 1221 and the first wall 1123, the assembly operation is less likely to interfere with the electrode assembly 111, thus affecting the reliability of the battery cell 9.

[0132] Optionally, according to some embodiments of this application, referring to FIG2, the first sub-part 1221 is provided with a connecting part 123 at one end opposite to the first part 121. The connecting part 123 extends along the extending direction of the first wall 1123, and the first sub-part 1221 is connected to the first wall 1123 through the connecting part 123.

[0133] The extension direction of the first wall 1123 refers to the extension direction of the plane in which the first wall 1123 is located, that is, any direction perpendicular to the arrangement direction of the electrode assembly 111 and the first wall 1123. The connecting part 123 extends along the extension direction of the first wall 1123, which can be roughly understood as the connecting part 123 extending from the end connected to the first sub-part 1221 in a direction parallel to the first wall 1123.

[0134] According to some embodiments of this application, optionally, referring to FIG2, there are at least two first sub-parts 1221, wherein the two first sub-parts 1221 are respectively located on both sides of the first part 121.

[0135] That is, the first sub-parts 1221 are respectively provided on the opposite sides of the first part 121. The opposite sides of the first part 121 are two sides in any direction of the plane in which the first part 121 is located.

[0136] In the same support member 120, there are at least two second parts 122 that serve as first sub-parts 1221 respectively, and a portion of the first sub-parts 1221 are located on one side of the first part 121, while another portion of the first sub-parts 1221 are located on the other side of the first part 121.

[0137] It should be noted that one or more first sub-parts 1221 can be provided on the same side of the first part 121. That is, at least one of the one or more second parts 122 located on the same side of the first part 121 can be used as a first sub-part 1221.

[0138] According to some embodiments of this application, optionally, as shown in FIG2, at least one of the second parts 122 is a second sub-part 1222, and the second sub-part 1222 is disposed abutting against or spaced from the outer casing 112.

[0139] The second sub-part 1222 may be abutted against or spaced apart from any wall of its adjacent outer casing 112.

[0140] The limitation that the second sub-part 1222 is abutted or spaced from the outer casing 112 refers to the limitation when the battery cell 9 is in a normal state. When the battery cell 9 shakes, the spaced second sub-part 1222 may also abut against the outer casing 112.

[0141] For example, as shown in FIG2, one end of the second sub-part 1222 connected to the first part 121 and the first part 121 are disposed in the receiving groove of the insulating member 130. The end of the second sub-part 1222 away from the first part 121 can abut against the first wall 1123, or the second sub-part 1222 and the first wall 1123 are spaced apart.

[0142] For example, in some embodiments, the furthest position of the second sub-part 1222 away from the first part 121 is set closer to the first part 121 than the position where the first sub-part 1221 is connected to the first wall 1123, so as to reduce the interference of the second sub-part 1222 on the connection operation when the first sub-part 1221 is connected to the first wall 1123 due to its higher setting, and improve the convenience of the connection operation between the first sub-part 1221 and the first wall 1123.

[0143] For example, when the same support member 120 is provided with multiple first sub-parts 1221, one or more second sub-parts 1222 can be provided between any adjacent first sub-parts 1221 along the arrangement direction of the multiple second sub-parts 122.

[0144] For example, the number of second sub-parts 1222 of the same support member 120 is equal to or greater than the number of first sub-parts 1221.

[0145] The support member 120 may have at least one first sub-part 1221 and one second sub-part 1222. The first sub-part 1221 is used to connect and fix the outer shell 112 to the support member 120. Based on the first sub-part 1221, the support member 120 is also provided with a second sub-part 1222, which can improve the strength of the support member 120. The second sub-part 1222 may only have a supporting and reinforcing function, reducing the number of connection positions between the support member 120 and the outer shell 112. In this way, while improving the supporting strength of the support member 120, the complexity of the connection operation between the support member 120 and the outer shell 112 can be reduced, and the assembly efficiency of the support member 120 and the outer shell 112 can be improved.

[0146] In some embodiments, at least one support member 120 is a first support member 1201. The first support member 1201 may have a first sub-part 1221 on opposite sides along the width direction of the first wall 1123. The first sub-part 1221 is connected to the first wall 1123.

[0147] In some embodiments, at least one support member 120 is a second support member 1202. The second support member 1202 may have a first sub-part 1221 provided on opposite sides along the length direction of the first wall 1123. The first sub-part 1221 is connected to the first wall 1123.

[0148] In some embodiments, the fluorosulfonylimide lithium salt includes one or more of lithium bisfluorosulfonylimide and lithium bistrifluoromethylsulfonylimide, with lithium bisfluorosulfonylimide being the preferred choice.

[0149] 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.

[0150] In some embodiments, the mass content of the fluorosulfonylimide lithium salt is 3.7%-7% based on the total mass of the electrolyte.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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, improving the structural integrity of the positive electrode active material, and enhancing 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, lower the probability of titanium ions catalyzing the decomposition of the SEI film during the reduction and precipitation of titanium ions at the negative electrode, reduce the irreversible consumption of lithium ions caused by the reconstruction of the SEI film, and improve the cycle performance of the battery cell.

[0155] 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.

[0156] 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.

[0157] Within a reasonable range, the vanadium content helps stabilize the crystal structure of lithium iron phosphate through vanadium ion doping, enhances the strength of PO bonds, and thus improves 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 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, reduce the probability of vanadium ions catalyzing the decomposition of the SEI film during the reduction and precipitation of vanadium ions at the negative electrode, reduce the irreversible consumption of lithium ions caused by the reconstruction of the SEI film, and improve the cycle performance of the battery cell.

[0158] In some embodiments, the electrolyte further includes a solvent, which includes one or more of dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] In some embodiments, the dimethyl carbonate content is 15%-45% based on the total mass of the electrolyte.

[0164] A mass content of dimethyl carbonate within the above range is beneficial for further balancing the energy conversion efficiency and cycle stability of individual battery cells.

[0165] In some embodiments, the dimethyl carbonate content is 15%-36% based on the total mass of the electrolyte.

[0166] A mass content of dimethyl carbonate within the above range is beneficial for further balancing the energy conversion efficiency and cycle stability of individual battery cells.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] The applicant discovered through experiments that the energy conversion efficiency of a single battery cell can be further improved when the electrolyte includes ethyl methyl carbonate and fluoroethylene carbonate.

[0171] In some embodiments, the methyl ethyl carbonate content is 30%-60% based on the total mass of the electrolyte.

[0172] 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.

[0173] 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.

[0174] Propylene carbonate possesses a high dielectric constant and good low-temperature performance, which is beneficial for promoting the dissociation of lithium-containing electrolyte salts, increasing the ionic conductivity of the electrolyte, facilitating the rapid migration of lithium ions in the electrolyte, and improving the energy conversion efficiency of battery cells. However, propylene carbonate readily undergoes a co-intercalation reaction 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 battery cells.

[0175] In some embodiments, the propylene carbonate content is 1%-3% based on the total mass of the electrolyte.

[0176] 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.

[0177] 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%.

[0178] 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.

[0179] 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.

[0180] In some embodiments, the mass ratio of the lithium hexafluorophosphate to the lithium fluorosulfonyl imide salt is 1-5, and optionally 2-4.

[0181] 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.

[0182] 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.

[0183] In some embodiments, the mass ratio of the lithium hexafluorophosphate to the lithium fluorosulfonyl imide salt is 2-3.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] In some embodiments, the mass content of the fluoroethylene carbonate is 2%-5% based on the total mass of the electrolyte.

[0189] In some embodiments, the mass content of the fluoroethylene carbonate is 3%-5% based on the total mass of the electrolyte.

[0190] 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.

[0191] 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%.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] 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%.

[0200] 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.

[0201] 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.

[0202] 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%.

[0203] 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.

[0204] In some embodiments, the mass percentage of magnetic material in the positive electrode film is 20ppm-1980ppm.

[0205] In this application, "magnetic material" refers to a substance that can generate magnetism when subjected to a magnetic field.

[0206] 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.

[0207] 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.

[0208] 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 the lithium consumption caused by rebuilding the SEI film and improving the cycle performance of the battery cell.

[0209] In some embodiments, the mass percentage of magnetic material in the positive electrode film is 20ppm-300ppm.

[0210] In some embodiments, the mass percentage of magnetic material in the positive electrode film is 20ppm-200ppm.

[0211] 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 lithium consumption caused by rebuilding the SEI film and improving the cycle performance of the battery cell.

[0212] In some embodiments, the magnetic material includes one or more of Fe, Fe2P, FeP, γ-Fe2O3, and Fe2P2O7.

[0213] 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.

[0214] 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.

[0215] 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.

[0216] In some embodiments, the conductive agent further includes conductive carbon black.

[0217] 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.

[0218] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0219] 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.

[0220] 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 80m2 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.

[0221] 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.

[0222] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 15m². 2 -130m 2 .

[0223] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 18m². 2 -115m 2 .

[0224] 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 .

[0225] 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 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 weighed 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].

[0226] 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 32.96 g / cm 3 2.97g / cm 3 2.98g / cm 3 2.99g / cm 3 3.00g / cm 3 Or the range of values ​​between any two of the above.

[0227] 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.

[0228] 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 .

[0229] 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.

[0230] 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 2 0.33g / 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 / 1540.25mm2 0.39g / 1540.25mm 2 0.40g / 1540.25mm 2 Or the range of values ​​between any two of the above.

[0231] The embodiments of this application further increase 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.

[0232] 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 .

[0233] In some embodiments, the capacity of the battery cell is 400Ah-3000Ah.

[0234] 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.

[0235] 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.

[0236] 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.

[0237] 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.

[0238] In some embodiments, the capacity of the battery cell is 500Ah-1500Ah.

[0239] In some embodiments, the capacity of the battery cell is 600Ah-1000Ah.

[0240] A second aspect of this application provides a battery device, which includes the battery cell provided in this application.

[0241] In some implementations, the battery device is one or more of a battery module and a battery pack.

[0242] As shown in Figure 3, the battery device 2 includes a housing 5 and battery cells (not shown in Figure 3), with the battery cells housed inside the housing 5.

[0243] 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.

[0244] 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.

[0245] 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.

[0246] A third aspect of this application also provides an energy storage device, which includes the battery cell or battery device provided in this application.

[0247] 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.

[0248] 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.

[0249] Example

[0250] 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.

[0251] Example 1

[0252] (1) Preparation of positive electrode sheet

[0253] Preparation of positive electrode active materials:

[0254] 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.

[0255] Among them, the number of magnetic material particles in lithium carbonate is less than or equal to 500 pcs / kg, and the particle size D of the material 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.

[0256] 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.

[0257] 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.

[0258] The prepared carbon-coated lithium iron phosphate material contains 0.07% titanium by mass.

[0259] 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.

[0260] 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℃.

[0261] 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 mm. 2 .

[0262] (2) Preparation of negative electrode sheet

[0263] 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.

[0264] (3) Separating membrane

[0265] 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.

[0266] (4) Preparation of electrolyte

[0267] 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.

[0268] (5) Preparation of battery cells

[0269] The positive electrode, separator, and negative electrode are stacked and wound in sequence, 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 a housing with an opening at one end. An end cap covers the opening and includes a pressure relief mechanism. As shown in Figure 2, the battery cell also includes at least one support component between the end cap and the electrode assembly, and an insulating component between the support component and the electrode assembly. The support component is made of aluminum with a melting point of 660°C, and the insulating component is made of plastic with a melting point of 165°C. The battery cell is then injected with the electrolyte and encapsulated. After vacuum encapsulation, settling, formation, and shaping processes, the 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.

[0270] 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.

[0271] 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.

[0272] The preparation of the battery cell in Example 14 is similar to that in Example 1, except that the type of support for the battery cell is different, as shown in Table 2.

[0273] The preparation of the battery cells in Examples 15 to 17 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.

[0274] Example 15

[0275] 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:

[0276] 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.

[0277] Example 16

[0278] The preparation method of the positive electrode active material in Example 16 is basically the same as that in Example 1, except that the sintering process of the positive electrode active material is different, specifically:

[0279] 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.

[0280] Example 17

[0281] The preparation method of the positive electrode active material in Example 17 is basically the same as that in Example 1, except that the preparation process of the positive electrode active material is slightly different. The specific differences include the following two points:

[0282] (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;

[0283] (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.

[0284] 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. V50 is 2.0μm, and the D of the particles after the second group of grinding is... V 50 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.

[0285] 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.

[0286] The preparation of the battery cell in Comparative Example 5 was similar to that in Example 1, except that the battery cell did not have a support structure, as detailed in Table 2.

[0287] II. Battery Performance Testing

[0288] (1) Battery cycle performance test

[0289] 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.

[0290] (2) Battery energy conversion efficiency test

[0291] 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.

[0292] (3) Test to determine whether the pressure relief is directional

[0293] The battery cells were left to stand at 25°C for 5 hours, then charged to 3.65V with a constant power of 0.5P, left to stand for 2 hours, and then placed in a thermal runaway test device. A 1000W heating element was placed on the surface of the battery cell, and the temperature sampling period was set to 1 second. The criteria for thermal runaway were set as three consecutive temperature rise rate values ​​greater than or equal to 3°C / s, or fire or explosion. The battery cells were charged with a constant current of 0.5C while heating was started. Charging and heating were stopped when the criteria for thermal runaway were triggered, the temperature reached 300°C, or the test time reached 4 hours. The cells were observed for 1 hour, and the time, voltage, temperature, temperature rise rate, and test phenomena were recorded. The battery cells were observed. If any crack was found in the welds of the main surface, side, bottom, top cover, or shell, the battery cell was judged to have non-directional pressure relief. If no cracks were found in any of the above locations, the battery cell was judged to have directional pressure relief.

[0294] (4) Battery volumetric energy density test

[0295] 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.

[0296] 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.

[0297] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0298] 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.

[0299] Table 1

[0300] Table 2

[0301] Studies have shown that the battery cells in Examples 2-17 all exhibited directional pressure relief in safety performance tests. The battery cell in Example 14 showed similar data to Example 1 in terms of the number of cycles with its capacity decaying to 80% at 25°C and its energy conversion efficiency.

[0302] 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 battery cell also includes at least one support member disposed between the end cap and the electrode assembly, and an insulating member disposed between the support member and the electrode assembly. When the melting point of the support member is greater than the melting point of the insulating member, the battery cell has good cycle performance, high energy conversion efficiency, and good safety performance.

[0303] As can be seen from the comparison between Examples 5 and 6 and Examples 1, 7 and 8, when the mass content of lithium fluorosulfonyl imide salt is 3.7%-7%, the battery cell has good safety performance, and the cycle performance and energy conversion efficiency of the battery cell are further improved.

[0304] 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 good safety performance and cycle performance, and the energy conversion efficiency of the battery cell is further improved.

[0305] 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 good safety performance and cycle performance, but also further improves the energy conversion efficiency of the battery cell.

[0306] Table 3

[0307] As can be seen from the comparison between Examples 16 and 17 and Examples 1 and 15, when the mass percentage of magnetic material in the positive electrode film is 20ppm-200ppm, the battery cell not only has good safety performance and high energy conversion efficiency, but also further improves the cycle performance of the battery cell.

[0308] 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 a casing, an electrode assembly, and an electrolyte. The casing includes a housing and an end cap. One end of the housing has an opening. The electrode assembly and the electrolyte are disposed inside the housing. The end cap covers the opening of the housing and is provided with a pressure relief mechanism. 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 battery cell further includes at least one support member disposed between the end cap and the electrode assembly, and an insulating member disposed between the support member and the electrode assembly, wherein the melting point of the support member is greater than the melting point of the insulating member.

2. The battery cell according to claim 1, characterized in that, The support component includes one or more of ceramic and metal components.

3. The battery cell according to claim 2, characterized in that, The metal parts include one or more of aluminum parts, aluminum alloy parts, and steel parts.

4. The battery cell according to any one of claims 1-3, characterized in that, The insulating component includes one or more of plastic and rubber components.

5. The battery cell according to any one of claims 1-4, 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.

6. The battery cell according to any one of claims 1-5, characterized in that, Based on the total mass of the electrolyte, the mass content of the fluorosulfonylimide lithium salt is 3.7%-7%.

7. The battery cell according to any one of claims 1-6, 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.

8. The battery cell according to any one of claims 1-7, 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.

9. The battery cell according to any one of claims 1-8, characterized in that, The electrolyte also includes a solvent, which includes one or more of dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.

10. The battery cell according to claim 9, 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%.

11. The battery cell according to claim 9, 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%.

12. The battery cell according to claim 9, 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%.

13. The battery cell according to any one of claims 1-12, 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%.

14. The battery cell according to claim 13, characterized in that, The mass ratio of lithium hexafluorophosphate to lithium difluorosulfonyl imide is 1-5, optionally 2-4, and further optionally 2-3.

15. The battery cell according to any one of claims 1-14, 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%.

16. The battery cell according to any one of claims 1-15, 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%.

17. The battery cell according to claim 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 particle size of 1μm-5μm is 30.0%-50.0%, and can be selected as 30.0%-45.0%.

18. The battery cell according to any one of claims 1-17, 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.

19. The battery cell according to claim 18, characterized in that, The magnetic material includes one or more of Fe, Fe2P, FeP, γ-Fe2O3, and Fe2P2O7.

20. The battery cell according to any one of claims 1-19, 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.

21. The battery cell according to any one of claims 1-20, 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 A further option is 18m. 2 -115m 2 .

22. The battery cell according to any one of claims 1-21, characterized in that, The compaction density of the positive electrode film is 2.5 g / cm³. 3 -3.0g / cm 3 .

23. The battery cell according to any one of claims 1-22, characterized in that, The compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.8g / cm 3 .

24. The battery cell according to any one of claims 1-23, 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 .

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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