Battery cell, battery device and energy storage device

Abstract

A battery cell, a battery device and an energy storage device. The battery cell comprises an end cover assembly, a casing, an electrode assembly and an electrolyte solution, wherein the casing comprises a receiving cavity having an opening; the end cover assembly covers the opening of the casing; the electrode assembly and the electrolyte solution are provided in the receiving cavity of the casing; 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 electrolyte solution comprises propylene carbonate and fluoroethylene carbonate; on the basis of the total mass of the electrolyte solution, the mass content of propylene carbonate is 1% to 15%; on the basis of the total mass of the electrolyte solution, the mass content of fluoroethylene carbonate is 0.1% to 5%; and the total coating area of the positive electrode film layer included in the battery cell is greater than or equal to 11 m2.

Description

Battery cells, battery devices and energy storage devices

[0001] Cross-references

[0002] This application incorporates, in its entirety, PCT patent application No. PCT / CN2025 / 085940, 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”, and PCT / CN2025 / 140529, filed on December 5, 2025, which are hereby incorporated 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 large-capacity battery cells in energy storage devices has become increasingly widespread. In various energy storage application scenarios, the expansion of energy storage system scale places higher demands on the capacity of individual battery cells. The industry generally meets this requirement by increasing the size of battery cells and improving the loading of active materials. However, as the capacity of battery cells increases, their energy conversion efficiency has significantly decreased. Therefore, how to balance high capacity and energy conversion efficiency of battery cells is a problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This application aims to at least address one of the technical problems existing in the background art. Therefore, one object of this application is to provide a battery cell, battery device, and energy storage device that improves the cycle life, energy conversion efficiency, and safety performance of the battery cell.

[0006] 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 assembly. The housing includes a receiving cavity with an opening, and the end cap assembly covers the opening of the housing. The electrode assembly and the electrolyte are disposed in the receiving cavity of the housing. 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 electrolyte includes propylene carbonate and fluoroethylene carbonate. Based on the total mass of the electrolyte, the mass content of propylene carbonate is 1%-15%; the mass content of fluoroethylene carbonate is 0.1%-5% based on the total mass of the electrolyte. The total coating area of ​​the positive electrode film layer included in the battery cell is greater than or equal to 11 m². 2 .

[0007] In this embodiment, a certain amount of propylene carbonate is added to the electrolyte. Its high dielectric constant promotes lithium-ion dissociation, thereby improving the electrolyte's conductivity and the energy efficiency of large-area battery cells. However, large-capacity batteries generate a lot of heat and have poor heat dissipation, leading to excessively high local temperatures. Furthermore, propylene carbonate has poor reduction stability and is easily reduced at the negative electrode to generate flammable gases, exacerbating the risk of battery thermal runaway. Additionally, propylene carbonate has polar groups on its surface, exhibiting high affinity for graphite and readily co-intercalating with lithium ions within the graphite. Since the diameter of propylene carbonate is much larger than the interlayer spacing of graphite, this intercalation causes graphite to peel off and pulverize during long-term cycling, hindering the improvement of cycle stability.

[0008] The applicant's research found that the simultaneous addition of fluoroethylene carbonate to an electrolyte containing propylene carbonate helps reduce graphite exfoliation in the later stages of cycling, while improving the cycle stability and thermal stability of the battery. Although the mechanism is not yet clear, it is speculated that it may be closely related to the fact that fluoroethylene carbonate preferentially forms a stable and dense LiF-rich solid electrolyte membrane (SEI film) at the negative electrode compared to propylene carbonate. On the one hand, this helps reduce the probability of propylene carbonate being in direct contact with the negative electrode active material and being continuously reduced and decomposed at the negative electrode, thus reducing the risk of thermal runaway. On the other hand, the stable and dense SEI film enables the desolvation of lithium ions on the surface of the negative electrode active material, reducing the probability of propylene carbonate co-intercalating into the graphite structure.

[0009] To adapt to the power grid, energy storage batteries need to be charged in a constant power mode. In the later stages of the cycle, the battery capacity decreases, but the charging current remains at a high level, effectively increasing the current rate. This leads to an increase in local overpotential at the negative electrode, making lithium metal deposition more likely and hindering the achievement of a long cycle life for the energy storage battery. Adding fluoroethylene carbonate to an electrolyte containing propylene carbonate can further extend the battery's cycle life while reducing negative impacts.

[0010] The applicant found that the total coating area of ​​the positive electrode film was greater than or equal to 11m². 2 By controlling the mass content of propylene carbonate to 1%-15% and the mass content of fluoroethylene carbonate to 0.1%-5%, the energy efficiency of the battery cell can be improved while also taking into account the cycle life and safety performance of the battery cell.

[0011] In any embodiment, the mass content of propylene carbonate is 3%-7% based on the total mass of the electrolyte.

[0012] When the mass content of propylene carbonate is within the above range, it can further promote the dissociation of lithium ions, thereby improving the conductivity of the electrolyte, improving the energy efficiency of large-capacity battery cells, while also taking into account the cycle life and safety performance of the battery cells.

[0013] In any embodiment, the mass content of fluoroethylene carbonate is 1.5%-5.0% based on the total mass of the electrolyte.

[0014] When the mass content of fluoroethylene carbonate is within the above range, it can further improve the safety performance and cycle stability of the battery cell.

[0015] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0016] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 15m². 2 -130m 2 .

[0017] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 18m². 2 -115m 2 .

[0018] The coating area of ​​the positive electrode film in the battery cell is always within the above range, which further allows the positive electrode film to accommodate more active materials, significantly improving the capacity of the battery cell and further improving the energy conversion efficiency of the battery cell.

[0019] In any embodiment, the electrolyte further includes a first component, which includes one or more of dimethyl carbonate and ethyl methyl carbonate, and the mass content of the first component is 15%-60% based on the total mass of the electrolyte.

[0020] While dimethyl carbonate and ethyl methyl carbonate have lower dielectric constants than propylene carbonate, their viscosity is significantly lower, and they exhibit higher solvent stability. Electrolytes may also include one or more of dimethyl carbonate and ethyl methyl carbonate, which helps balance the electrolyte's viscosity and dielectric constant, improve its conductivity and stability, and take into account the energy conversion efficiency, cycle life, and safety performance of the battery cells.

[0021] In any embodiment, the electrolyte comprises dimethyl carbonate, and the mass content of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte.

[0022] Compared to ethyl methyl carbonate, dimethyl carbonate has a lower viscosity but higher reactivity. Adding a certain amount of dimethyl carbonate to the electrolyte is more conducive to improving the lithium ion conduction rate in the electrolyte, thus achieving a balance between the energy conversion efficiency and cycle stability of the battery cell.

[0023] In any embodiment, the electrolyte comprises dimethyl carbonate, and the mass content of dimethyl carbonate is 15%-45% based on the total mass of the electrolyte.

[0024] In any embodiment, the electrolyte comprises dimethyl carbonate, and the mass content of dimethyl carbonate is 36%-45% based on the total mass of the electrolyte.

[0025] Having a dimethyl carbonate content within the above range is beneficial for further improving the ionic conductivity of the electrolyte, effectively dissolving lithium salts in the electrolyte, and balancing the energy conversion efficiency, cycle life, and safety stability of the battery cells.

[0026] In any embodiment, the electrolyte comprises ethyl methyl carbonate, and the mass content of ethyl methyl carbonate is 10%-60% based on the total mass of the electrolyte.

[0027] Ethyl methyl carbonate has a higher viscosity than dimethyl carbonate, but its reactivity is lower. Adding ethyl methyl carbonate within the above-mentioned mass range to the electrolyte helps to further balance the energy conversion efficiency, cycle life, and safety stability of the battery cells.

[0028] In any embodiment, the electrolyte comprises ethyl methyl carbonate, and the mass content of ethyl methyl carbonate is 30%-40% based on the total mass of the electrolyte.

[0029] Ethyl methyl carbonate has a higher viscosity than dimethyl carbonate, but its reactivity is lower. Adding ethyl methyl carbonate within the above-mentioned mass range to the electrolyte helps to further balance the energy conversion efficiency, cycle life, and safety stability of the battery cells.

[0030] In any embodiment, the electrolyte further includes lithium difluorophosphate, the mass content of which is 0.01%-1% based on the total mass of the electrolyte.

[0031] Adding lithium difluorophosphate to the electrolyte within the above-mentioned range can help form a denser and more stable solid electrolyte interphase (SEI) film at the negative electrode. This helps reduce the interlayer spacing of propylene carbonate embedded in graphite, reduce the generation of combustible gases, and further reduce the risk of thermal runaway. Moreover, the SEI film formed by lithium difluorophosphate has good ionic conductivity, which helps reduce the charge transfer impedance at the negative electrode interface, improve the transport efficiency of lithium ions at the negative electrode interface, improve cycle performance, and balance the energy efficiency, cycle life, and safety stability of the battery cell.

[0032] In any embodiment, the electrolyte further includes lithium difluorophosphate, the lithium difluorophosphate content being 0.4%-1.0% based on the total mass of the electrolyte.

[0033] Adding lithium difluorophosphate to the electrolyte within the above-mentioned range can further facilitate the formation of a denser and more stable solid electrolyte interphase (SEI) film at the negative electrode, further reduce the interlayer spacing of propylene carbonate embedded in graphite, reduce the generation of combustible gases, further reduce the risk of thermal runaway, and the SEI film formed by lithium difluorophosphate has good ionic conductivity, which helps to reduce the charge transfer impedance at the negative electrode interface, improve the transport efficiency of lithium ions at the negative electrode interface, and balance the energy efficiency, cycle life and safety stability of the battery cell.

[0034] In any embodiment, the electrolyte further includes vinylene carbonate, with a mass content of 0.5%-8% based on the total mass of the electrolyte.

[0035] By adding vinylene carbonate to the electrolyte, it can preferentially undergo a reduction reaction at the negative electrode, which can better synergize with fluoroethylene carbonate, improve the compactness of the solid electrolyte interphase (SEI) film, reduce the probability of propylene carbonate being in direct contact with the negative electrode active material and being continuously reduced and decomposed at the negative electrode, and at the same time reduce the probability of propylene carbonate co-intercalating into the graphite structure, further improving the cycle stability of the battery cell.

[0036] In any embodiment, the electrolyte further includes vinylene carbonate, with a vinylene carbonate content of 0.6%-4% based on the total mass of the electrolyte.

[0037] The mass content of vinylene carbonate within the above range is beneficial to improve the compactness of the solid electrolyte interphase (SEI) film, reduce the probability of propylene carbonate directly contacting the negative electrode active material and being continuously reduced and decomposed at the negative electrode, and at the same time reduce the probability of propylene carbonate co-intercalating into the graphite structure, thereby further improving the cycle stability of the battery cell.

[0038] In any embodiment, the positive electrode film layer includes a positive electrode active material, which comprises lithium phosphate particles with at least a portion of their surface coated with carbon material. In the cumulative distribution curve of graphitization degree C obtained by laser microscopy confocal Raman spectroscopy in surface scanning mode, the median C of the graphitization degree is... 50 Greater than or equal to 0.95 and less than or equal to 1.20; where the degree of graphitization C is I. G / I D I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 The intensity of peak D at that location.

[0039] By controlling the median C of the graphitization degree of the positive electrode film... 50Within the aforementioned range, it is beneficial to reduce the positive electrode impedance, improve the electron conduction efficiency on the positive electrode sheet, and thus improve the energy conversion efficiency of the battery cell.

[0040] In any embodiment, the median C of the graphitization degree C value in the cumulative distribution curve of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The range is 0.98-1.13.

[0041] By controlling the median C of the graphitization degree of the positive electrode film... 50 Within the aforementioned range, the positive electrode impedance can be further reduced, and the electron conduction efficiency of the positive electrode sheet can be improved, thereby improving the energy conversion efficiency of the battery cell.

[0042] In any embodiment, in the cross-section of the positive electrode film along the electrode thickness direction, the D of the particles... A50 The range is 600nm-800nm, where D A50 It refers to the particle size at which the cumulative area distribution of particles reaches 50% in the cumulative area distribution curve of particles.

[0043] Particle size D A50 Within the aforementioned range, it indicates that the positive electrode film contains a certain number of large-sized particles. The median particle size D is controlled. A50 Within the aforementioned range, the large contact area between large-sized particles can improve the efficiency of roller pressure transmission between electrode particles, fully utilize the skeletal support of large-sized particles, enable the electrode to withstand higher roller pressure, increase the compaction density of the electrode, and improve the volumetric energy density of the battery cell. It can also reduce the degree of side reactions of the positive electrode active material through large-sized particles, and reduce the kinetic decline caused by excessive particle size. While improving the compaction density of the electrode, it can maintain the kinetic performance of the battery, thereby taking into account the energy conversion efficiency of the battery cell.

[0044] In any embodiment, in the cross-section of the positive electrode film along the electrode thickness direction, the D of the particles... A50 The range is 650nm-750nm, where D A50 It refers to the particle size at which the cumulative area distribution of particles reaches 50% in the cumulative area distribution curve of particles.

[0045] Controlling the particle size D A50 Within the aforementioned range, the large contact area between large-sized particles can further improve the efficiency of roller pressure transmission between electrode particles, enabling the electrode to withstand higher roller pressure, increasing the compaction density of the electrode, and reducing the kinetic decrease caused by excessively large particle size and increased lithium-ion transport path, thereby balancing the energy conversion efficiency and cycle life of the battery cell.

[0046] In any embodiment, the positive electrode film layer further includes a conductive agent, which includes carbon nanotubes, and the mass content of carbon nanotubes is 0.1%-1.5% based on the total mass of the positive electrode film layer.

[0047] Carbon nanotubes are added to the positive electrode film as a conductive agent. By introducing a one-dimensional conductive agent, a continuous three-dimensional conductive network is formed between the positive electrode active materials, which significantly reduces the electrode interface impedance and thus improves the energy conversion efficiency and cycle life of the battery cell.

[0048] In any embodiment, the conductive agent further includes conductive carbon black.

[0049] 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.

[0050] In any embodiment, the positive electrode film layer further includes polyvinylidene fluoride, and the mass content of polyvinylidene fluoride is 1%-3% based on the total mass of the positive electrode film layer.

[0051] Adding polyvinylidene fluoride (PVDF) as a binder to the positive electrode film can form a continuous "bonding network" through PVDF, inhibiting the shedding of the positive electrode active material and preventing structural pulverization of the positive electrode active material due to volume expansion / contraction during charge-discharge cycles. This maintains the integrity and stability of the electrode structure, thereby improving the cycle performance of the battery cell.

[0052] In any embodiment, the positive electrode film layer further includes lithium carboxymethyl cellulose, and the mass content of lithium carboxymethyl cellulose is 0.3%-1% based on the total mass of the positive electrode film layer.

[0053] Adding lithium carboxymethyl cellulose within the above range as a dispersant to the positive electrode film can give the slurry good dispersibility, making the particles of the slurry more uniformly stacked after coating and drying, thereby improving the coating uniformity of the large-area positive electrode film, reducing the problem of excessive local heat generation, and improving the energy conversion efficiency of the battery cell.

[0054] In any embodiment, the mass ratio of polyvinylidene fluoride to lithium carboxymethyl cellulose is 1-10.

[0055] By adjusting the mass ratio of polyvinylidene fluoride (PVDF) to lithium carboxymethyl cellulose (CMC) within the aforementioned range, the synergistic effect of PVDF and CMC can better balance the strength and flexibility of the electrode, thereby improving the dispersion and bonding effect of the slurry. This results in more uniform particle accumulation after coating and drying, thus improving the coating uniformity of the large-area positive electrode film, reducing the problem of excessive local heat generation, and improving the energy conversion efficiency of the battery cell.

[0056] In any embodiment, the battery cell further includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes graphite, and the graphitization degree of the negative electrode film layer is 88%-93%.

[0057] When the graphitization degree of the negative electrode film is within the above range, it is beneficial to reduce the expansion force of the negative electrode film in the later stage of long cycle, and further improve the cycle life of the battery cell.

[0058] In any embodiment, the negative electrode active material includes graphite, and the graphitization degree of the negative electrode film is 91%-92%.

[0059] When the graphitization degree of the negative electrode film is within the above range, it is beneficial to reduce the degree of side reaction while reducing the expansion force of the negative electrode film in the later stage of long cycle, thereby further improving the cycle life of the battery cell.

[0060] In any embodiment, the end cap assembly includes an end cap fitted with an explosion-proof valve, wherein the ratio of the projected area A of the explosion-proof valve along the thickness direction of the end to the capacity C of the battery cell is 0.2 mm. 2 / Ah-4mm 2 / Ah.

[0061] By adopting the above scheme, since the capacity of a single battery cell directly reflects the total amount of active material and energy storage capacity, and is positively correlated with the gas production scale during thermal runaway, limiting the ratio of the projected area of ​​the explosion-proof valve along the thickness direction of the end cap to the capacity of the single battery cell to the above range allows for the establishment of a quantitative matching standard between capacity characteristics and pressure relief performance. This enables the matching of "proportional" pressure relief channels for battery cells of different capacities. Based on this, the explosion-proof valve can have sufficient pressure relief area to cope with the relatively high gas production of large-capacity battery cells, reducing the risk of obstructed exhaust passages and uncontrolled internal pressure due to an excessively small projected area of ​​the explosion-proof valve. This improves pressure relief reliability and the operational reliability of large-capacity battery cells. Furthermore, while meeting gas discharge requirements, it reduces the over-design of the explosion-proof valve, optimizes the structure and cost, and improves structural reliability, operational reliability, and design economy.

[0062] In any embodiment, the ratio of the projected area A of the explosion-proof valve along the thickness direction of the end cap to the capacity C of the battery cell is 1.1 mm. 2 / Ah-2.5mm 2 / Ah.

[0063] By adopting the above scheme, the narrowed A / C ratio optimization range can reduce the problems of insufficient venting margin and increased venting pressure risk that may be caused by a small A / C ratio. It can also reduce the over-design of explosion-proof valves (such as weakened structural strength and increased cost) and redundant waste of pressure relief area that may be caused by a large A / C ratio. As a result, battery cells of different capacities can obtain a precisely matched pressure relief channel, and large-capacity battery cells of various capacity ranges can achieve a better balance between pressure relief reliability, structural stability and design economy, thereby further reducing the risk of thermal runaway.

[0064] In any embodiment, the projected area A of the explosion-proof valve along the thickness direction of the end cap is 800 mm². 2 -1500mm 2 .

[0065] By adopting the above solution, the explosion-proof valve can have a sufficient actual pressure relief area, providing a stable, effective, and sufficiently wide gas discharge channel to meet gas discharge requirements and achieve rapid and efficient venting. This reduces the risk of pressure relief failure, maintains the pressure relief capacity of the explosion-proof valve, and maintains and improves its pressure relief reliability. Furthermore, while meeting gas discharge requirements, the actual pressure relief area of ​​the explosion-proof valve can be constrained. This allows for the preservation of a large portion of the end cap area as a structural support region to resist impact and deformation pressure, preserving the structural strength and sealing performance of the end cap to a greater extent, and maintaining and improving the strength and sealing of the outer shell. On the other hand, it reduces the risk of excessive pressure relief and excessive splashing due to an excessively large actual pressure relief area, which could accelerate heat propagation. Therefore, it effectively improves the reliability and service life of individual battery cells, further reducing the risk of thermal runaway.

[0066] In any embodiment, the capacity of a single battery cell is 400Ah-3000Ah.

[0067] In any embodiment, the capacity of a single battery cell is 500Ah-1500Ah.

[0068] In any embodiment, the capacity of a single battery cell is 600Ah-1000Ah.

[0069] A second aspect of this application provides a battery device including the battery cell of the first aspect of this application.

[0070] A third aspect of this application provides an energy storage device, including the battery device of the second aspect of this application, the battery device being used to store electrical energy.

[0071] 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, specific embodiments of this application are given below. Attached Figure Description

[0072] 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.

[0073] Figure 1 is a perspective view of a battery cell provided in one embodiment of this application;

[0074] Figure 2 is an exploded view of the battery cell shown in Figure 1;

[0075] Figure 3 is a top view of the battery cell shown in Figure 1;

[0076] Figure 4 is an exploded structural diagram of a battery device according to an embodiment of this application.

[0077] Explanation of reference numerals in the attached drawings: 10-Battery cell, 11-Casing, 111-Housing, 112-End cap assembly, 113-End cap; 12-Electrode assembly, 121-Main body, 122-Taper, 122a-Positive electrode tab, 122b-Negative electrode tab; 13-Electrode terminal, 13a-Positive electrode terminal, 13b-Negative electrode terminal; 14-Insulating component; 15-Explosion-proof valve; 100 Battery assembly; 110 Housing; 120 First part; 130 Second part. Detailed Implementation

[0078] 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.

[0079] 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.

[0080] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0081] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0082] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0083] 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.

[0084] 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).

[0085] Energy storage batteries are commonly used in applications such as power storage, energy storage power stations, load balancing, and emergency backup power, which places higher demands on their capacity. As the capacity requirements for energy storage batteries continue to increase, large-capacity energy storage batteries require a larger total coating area of ​​the positive electrode to accommodate more active material. However, due to the large coating area of ​​the positive electrode film and the significant differences in electron transport paths, uneven current distribution is easily caused, leading to increased localized heat generation and a decrease in energy conversion efficiency. Improving the energy conversion efficiency of large-capacity energy storage batteries has become a pressing technical problem that needs to be solved in this field.

[0086] Based on this, as shown in Figure 1, the first aspect of this application provides a battery cell 10, which includes a casing 11, an electrode assembly 12, and an electrolyte. The casing 11 includes a housing 111 and an end cap assembly 112. The housing 111 includes a receiving cavity with an opening, and the end cap assembly 112 covers the opening of the housing 111. The electrode assembly 12 and the electrolyte are disposed in the receiving cavity of the housing 111. The electrode assembly 12 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 electrolyte includes propylene carbonate and fluoroethylene carbonate. Based on the total mass of the electrolyte, the mass content of propylene carbonate is 1%-15%; based on the total mass of the electrolyte, the mass content of fluoroethylene carbonate is 0.1%-5%. The total coating area of ​​the positive electrode film layer included in the battery cell is greater than or equal to 11m². 2 .

[0087] In this embodiment, a certain amount of propylene carbonate is added to the electrolyte. Its high dielectric constant promotes lithium-ion dissociation, thereby improving the electrolyte's conductivity and the energy efficiency of large-area battery cells. However, large-capacity batteries generate a lot of heat and have poor heat dissipation, leading to excessively high local temperatures. Furthermore, propylene carbonate has poor reduction stability and is easily reduced at the negative electrode to generate flammable gases, exacerbating the risk of battery thermal runaway. Additionally, propylene carbonate has polar groups on its surface, exhibiting high affinity for graphite and readily co-intercalating with lithium ions within the graphite. Since the diameter of propylene carbonate is much larger than the interlayer spacing of graphite, this intercalation causes graphite to peel off and pulverize during long-term cycling, hindering the improvement of cycle stability.

[0088] The applicant's research found that the simultaneous addition of fluoroethylene carbonate to an electrolyte containing propylene carbonate helps reduce graphite exfoliation in the later stages of cycling, while improving the cycle stability and thermal stability of the battery. Although the mechanism is not yet clear, it is speculated that it may be closely related to the fact that fluoroethylene carbonate preferentially forms a stable and dense LiF-rich solid electrolyte membrane (SEI film) at the negative electrode compared to propylene carbonate. On the one hand, this helps reduce the probability of propylene carbonate being in direct contact with the negative electrode active material and being continuously reduced and decomposed at the negative electrode, thus reducing the risk of thermal runaway. On the other hand, the stable and dense SEI film enables the desolvation of lithium ions on the surface of the negative electrode active material, reducing the probability of propylene carbonate co-intercalating into the graphite structure.

[0089] To adapt to the power grid, energy storage batteries need to be charged in a constant power mode. In the later stages of the cycle, the battery capacity decreases, but the charging current remains at a high level, effectively increasing the current rate. This leads to an increase in local overpotential at the negative electrode, making lithium metal deposition more likely and hindering the achievement of a long cycle life for the energy storage battery. Adding fluoroethylene carbonate to an electrolyte containing propylene carbonate can further extend the battery's cycle life while reducing negative impacts.

[0090] The applicant found that the total coating area of ​​the positive electrode film was greater than or equal to 11m². 2 By controlling the mass content of propylene carbonate to 1%-15% and the mass content of fluoroethylene carbonate to 0.1%-5%, the energy efficiency of the battery cell can be improved while also taking into account the cycle life and safety performance of the battery cell.

[0091] In this application, the types and mass contents of each component in the electrolyte can be obtained by detecting the electrolyte using any method known to those skilled in the art. For example, the composition and content of the electrolyte can be characterized using one or more of the following methods: gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectrometry (GC-MS). For example, referring to GB / T-9722-2023 "General Rules for Gas Chromatography of Chemical Reagents" and / or GB / T6041-2020 "General Rules for Mass Spectrometry Analysis Methods", gas chromatography and mass spectrometry are coupled. After gas chromatography separates the components in the sample, the components are broken into ion fragments in mass spectrometry and separated according to mass-to-charge ratio (m / z) to form specific mass spectra, obtaining qualitative analysis of each organic component in the electrolyte. Then, the organic components in the electrolyte are separated in the chromatographic column, and detection signal spectra of each component are generated. The retention time is used for component qualitative analysis, and the peak area is corrected by standardization to achieve quantification, obtaining quantitative analysis of the organic components in the electrolyte. Referring to JY / T-020, the types of anions of electrolyte salts in the electrolyte are detected by ion chromatography and quantitatively analyzed. Referring to JY / T 0578-2020, nuclear magnetic resonance spectroscopy (NMR) is used to obtain qualitative and quantitative analysis of the components in the electrolyte.

[0092] 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.

[0093] 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.

[0094] In some embodiments, the mass content of propylene carbonate, based on the total mass of the electrolyte, can be selected as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any range between the two.

[0095] In some embodiments, the mass content of fluoroethylene carbonate is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range thereof, based on the total mass of the electrolyte.

[0096] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell may be selected as 11m². 2 15m 2 20m 2 25m 2 30m 2 35m 2 40m 2 45m 2 50m 2 55m 2 60m 2 65m 2 70m 2 75m 2 80m 2 85m 2 90m 2 95m 2 100m 2 105m 2 110m 2 115m 2 120m 2 125m 2 130m 2 135m 2 140m 2 145m 2 150m 2 Or the range of values ​​between any two.

[0097] Referring to Figure 1, the end cap 113 is a component that covers the opening of the housing 111 to isolate the internal environment of the battery cell 10 from the external environment. In some embodiments, the shape of the end cap 113 may be adapted to the shape of the housing 111 to fit the housing 111. In some embodiments, the end cap 113 may be made of a material with a certain degree of hardness and strength, so that the end cap 113 is not easily deformed when subjected to compression or impact, enabling the battery cell 10 to have high structural strength and reliability. The material of the end cap 113 can be diverse, including copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc.

[0098] The housing 111 is a component used to cooperate with the end cap 113 to form the internal environment of the battery cell 10. The internal environment formed by the housing 111 and the end cap 113 can be used to accommodate components such as the electrode assembly 12 and the electrolyte. In some embodiments, the housing 111 and the end cap 113 can be independent components, with an opening provided on the housing 111. The end cap 113 closes the opening to form the internal environment of the battery cell 10. In some embodiments, the end cap 113 and the housing 111 can also be integrated. Specifically, the end cap 113 and the housing 111 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 111, the end cap 113 closes the housing 111. The housing 111 can be of various shapes and sizes, such as a cuboid, cylinder, or hexagonal prism. The shape of the housing 111 can be determined according to the shape and size of the electrode assembly 12. The shell 111 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, and plastic.

[0099] In some embodiments, the mass content of propylene carbonate is 3%-7% based on the total mass of the electrolyte.

[0100] When the mass content of propylene carbonate is within the above range, it can further promote the dissociation of lithium ions, thereby improving the conductivity of the electrolyte, improving the energy efficiency of large-capacity battery cells, while also taking into account the cycle life and safety performance of the battery cells.

[0101] In some embodiments, the mass content of fluoroethylene carbonate is 1.5%-5.0% based on the total mass of the electrolyte.

[0102] When the mass content of fluoroethylene carbonate is within the above range, it can further improve the safety performance and cycle stability of the battery cell.

[0103] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0104] In some embodiments, the total coating area of ​​the positive electrode film layers contained in the battery cell is 15m². 2 -130m 2 .

[0105] In some embodiments, the total coating area of ​​the positive electrode film layers contained in the battery cell is 18m². 2 -115m 2 .

[0106] The coating area of ​​the positive electrode film in the battery cell is always within the above range, which further allows the positive electrode film to accommodate more active materials, significantly improving the capacity of the battery cell and further improving the energy conversion efficiency of the battery cell.

[0107] In some embodiments, the electrolyte further includes a first component, which includes one or more of dimethyl carbonate and ethyl methyl carbonate, and the mass content of the first component is 15%-60% based on the total mass of the electrolyte.

[0108] In some embodiments, the electrolyte includes a first component, the mass content of which, based on the total mass of the electrolyte, 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%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, or any range between the two.

[0109] While dimethyl carbonate and ethyl methyl carbonate have lower dielectric constants than propylene carbonate, their viscosity is significantly lower, and they exhibit higher solvent stability. Electrolytes may also include one or more of dimethyl carbonate and ethyl methyl carbonate, which helps balance the electrolyte's viscosity and dielectric constant, improve its conductivity and stability, and take into account the energy conversion efficiency, cycle life, and safety performance of the battery cells.

[0110] In some embodiments, the electrolyte includes dimethyl carbonate, and the mass content of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte.

[0111] In some embodiments, the electrolyte includes dimethyl carbonate, and the mass content of dimethyl carbonate, based on the total mass of the electrolyte, 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 two.

[0112] Compared to ethyl methyl carbonate, dimethyl carbonate has a lower viscosity but higher reactivity. Adding a certain amount of dimethyl carbonate to the electrolyte is more conducive to improving the lithium ion conduction rate in the electrolyte, thus achieving a balance between the energy conversion efficiency and cycle stability of the battery cell.

[0113] In some embodiments, the electrolyte includes dimethyl carbonate, and the mass content of dimethyl carbonate is 15%-45% based on the total mass of the electrolyte.

[0114] In some embodiments, the electrolyte includes dimethyl carbonate, and the mass content of dimethyl carbonate is 36%-45% based on the total mass of the electrolyte.

[0115] Having a dimethyl carbonate content within the above range is beneficial for further improving the ionic conductivity of the electrolyte, effectively dissolving lithium salts in the electrolyte, and balancing the energy conversion efficiency, cycle life, and safety stability of the battery cells.

[0116] In some embodiments, the electrolyte includes ethyl methyl carbonate, and the ethyl methyl carbonate content is 10%-60% based on the total mass of the electrolyte.

[0117] In some embodiments, the electrolyte includes ethyl methyl carbonate, and the mass content of ethyl methyl carbonate, based on the total mass of the electrolyte, can be selected as 10%, 11%, 12%, 13%, 14%, 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%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, or any range between the two.

[0118] Ethyl methyl carbonate has a higher viscosity than dimethyl carbonate, but its reactivity is lower. Adding ethyl methyl carbonate within the above-mentioned mass range to the electrolyte helps to further balance the energy conversion efficiency, cycle life, and safety stability of the battery cells.

[0119] In some embodiments, the electrolyte includes ethyl methyl carbonate, and the ethyl methyl carbonate content is 30%-40% based on the total mass of the electrolyte.

[0120] Ethyl methyl carbonate has a higher viscosity than dimethyl carbonate, but its reactivity is lower. Adding ethyl methyl carbonate within the above-mentioned mass range to the electrolyte helps to further balance the energy conversion efficiency, cycle life, and safety stability of the battery cells.

[0121] In some embodiments, the electrolyte also includes lithium difluorophosphate, with the lithium difluorophosphate content being 0.01%-1% based on the total mass of the electrolyte.

[0122] In some embodiments, the electrolyte further includes lithium difluorophosphate, the mass content of which, based on the total mass of the electrolyte, can be selected as 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any range between the two.

[0123] Adding lithium difluorophosphate to the electrolyte within the above-mentioned range can help form a denser and more stable solid electrolyte interphase (SEI) film at the negative electrode. This helps reduce the interlayer spacing of propylene carbonate embedded in graphite, reduce the generation of combustible gases, and further reduce the risk of thermal runaway. Moreover, the SEI film formed by lithium difluorophosphate has good ionic conductivity, which helps reduce the charge transfer impedance at the negative electrode interface, improve the transport efficiency of lithium ions at the negative electrode interface, improve cycle performance, and balance the energy efficiency, cycle life, and safety stability of the battery cell.

[0124] In some embodiments, the electrolyte also includes lithium difluorophosphate, with the lithium difluorophosphate content being 0.4%-1.0% based on the total mass of the electrolyte.

[0125] Adding lithium difluorophosphate to the electrolyte within the above-mentioned range can further facilitate the formation of a denser and more stable solid electrolyte interphase (SEI) film at the negative electrode, further reduce the interlayer spacing of propylene carbonate embedded in graphite, reduce the generation of combustible gases, further reduce the risk of thermal runaway, and the SEI film formed by lithium difluorophosphate has good ionic conductivity, which helps to reduce the charge transfer impedance at the negative electrode interface, improve the transport efficiency of lithium ions at the negative electrode interface, and balance the energy efficiency, cycle life and safety stability of the battery cell.

[0126] In some embodiments, the electrolyte also includes vinylene carbonate, with a vinylene carbonate content of 0.5%-8% based on the total mass of the electrolyte.

[0127] In some embodiments, the electrolyte further includes vinylene carbonate, and the mass content of vinylene carbonate, based on the total mass of the electrolyte, can be selected as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 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%, 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%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%, or any range between two of these values.

[0128] By adding vinylene carbonate to the electrolyte, it can preferentially undergo a reduction reaction at the negative electrode, which can better synergize with fluoroethylene carbonate, improve the compactness of the solid electrolyte interphase (SEI) film, reduce the probability of propylene carbonate being in direct contact with the negative electrode active material and being continuously reduced and decomposed at the negative electrode, and at the same time reduce the probability of propylene carbonate co-intercalating into the graphite structure, further improving the cycle stability of the battery cell.

[0129] In some embodiments, the electrolyte also includes vinylene carbonate, with a vinylene carbonate content of 0.6%-4% based on the total mass of the electrolyte.

[0130] The mass content of vinylene carbonate within the above range is beneficial to improve the compactness of the solid electrolyte interphase (SEI) film, reduce the probability of propylene carbonate directly contacting the negative electrode active material and being continuously reduced and decomposed at the negative electrode, and at the same time reduce the probability of propylene carbonate co-intercalating into the graphite structure, thereby further improving the cycle stability of the battery cell.

[0131] In some embodiments, the positive electrode film layer includes a positive electrode active material, which comprises lithium phosphate particles with at least a portion of their surface coated with carbon material. In the cumulative distribution curve of the graphitization degree C value obtained by laser microscopy confocal Raman spectroscopy in surface scanning mode, the median C of the graphitization degree is... 50 Greater than or equal to 0.95 and less than or equal to 1.20; where the degree of graphitization C is I. G / ID I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 The intensity of peak D at that location.

[0132] In this application, the carbon coating layer disposed on at least a portion of the surface of the lithium phosphate can be detected by any method known in the art. As an example, the carbon coating layer disposed on at least a portion of the surface of the lithium phosphate can be observed by characterizing the lithium phosphate using a combination of transmission electron microscopy and energy dispersive spectroscopy. It should be noted that the elements in the carbon coating layer are not limited to carbon, but may also include other non-carbon elements. The carbon coating layer is not limited to a film-like form, but also includes island-like, irregular, or discontinuous coating layers.

[0133] In this application, lithium-containing phosphates refer to phosphate materials containing lithium, which can be detected by any method known in the art. For example, they can be detected by combining X-ray diffraction with energy dispersive spectroscopy (EDS) or inductively coupled plasma mass spectrometry (ICP-MS). As examples, lithium-containing phosphates include, but are not limited to, lithium iron phosphate, lithium iron phosphate doped and modified materials, and lithium iron phosphate coated and modified materials.

[0134] In this application, the term "particle" refers to a particle in the positive electrode film layer that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist inside the particle, but a complete boundary sufficient to divide the particle cannot be identified inside the particle.

[0135] The particle identification method is as follows: The positive electrode film layer is cut along the thickness direction of the electrode sheet using an argon ion beam (for example, a Leica EM TIC 3X CP device can be used, operating voltage: 6kV, operating time: 6h). After exposing the cut surface, a scanning electron microscope (SEM) is used (for example, a Hitachi SU8230 device can be used, operating voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) to observe the cut surface along the thickness direction of the electrode sheet. Images are acquired using a field emission scanning electron microscope at a non-edge location in the cut surface of the positive electrode film layer (after observing the electrode edge under the SEM, the field of view is adjusted to the center of the sample) in secondary electron mode. Electron micrographs are taken at 10kx magnification, and the particles in the electron micrographs are analyzed using ImageJ software (1.46r, win64 version). The specific steps for using ImageJ software are as follows: Load the scanning electron microscope image to be analyzed, as shown in Figure 1; use the Cellpose plugin software to identify particles, and then perform manual corrections; use ImageJ to read and analyze data. The specific method for identifying particles using the Cellpose plugin software is as follows: Set the segmentation diameter parameter (diameter in the Segmentation module) to 15 pixels, click "run cyto3" to identify particles, and then manually mark particles in the image that were not identified by the software, were not fully identified by the software, or had identification errors. Particles in the image that were not identified by the software, were not fully identified by the software, or had identification errors mainly include the following: 1. Particles that are too large or have scratches on their surface, making them unidentifiable or incompletely recognizable; 2. During argon ion beam cutting, scratches may be generated on the particle surface, and the software may misjudge these scratches as particle boundaries during identification, 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 particle's interior penetrated by the edge, preventing a complete display of the morphology, and resulting in identification errors due to partial identification replacing the whole.For the unidentified or misidentified particles mentioned above, manual calibration is performed. The specific process is as follows: 1. Delete large particles located around the edges of the scanning electron microscope that are not fully displayed. 2. Determine if any unidentified or misidentified particles have internal cracks or scratches. If no cracks or scratches are found, classify it as a single particle and manually mark it based on the observed particle boundary. 3. If cracks or scratches are found inside the particle, determine if they penetrate the particle. If not, classify it as a single particle and manually mark it. 4. If cracks or scratches penetrate the particle, determine if they are linear or irregular. 5. If the cracks or scratches are irregular, classify them as the boundary between particles and divide the particles along this boundary. 6. If the cracks or scratches are linear, perform contrast comparison. 7. If the contrast is not obvious and there is no crack-like appearance, classify it as a scratch and mark it as a single particle. 8. If the contrast is strong and there is a crack-like appearance, classify it as the boundary between particles and mark it as two particles. After manual marking, delete information irrelevant to the particles from the automatic image processing, thus completing the particle identification and marking in the image.

[0136] In this application, the graphitization degree C value of the positive electrode film can be obtained by surface scanning mode of a laser confocal Raman spectrometer. As an example, specifically, a laser confocal Raman spectrometer (high-precision Renishaw laser confocal Raman spectrometer) is used, with an excitation wavelength of 532 nm. An appropriate amount of the positive electrode film is taken and surface scanned on its surface or along the thickness direction of the electrode. The scanning area is 45 μm × 45 μm, divided into 10 × 10 grids, with grid vertices as test points, a step size of 5 μm, and a total of 100 scan points. Thus, the C values ​​at different sites and the cumulative distribution curve of the C values ​​in the surface scan area are obtained.

[0137] The positive electrode film in this application can be either a freshly prepared positive electrode film or a positive electrode film obtained from disassembly of a battery. The surface of a positive electrode film obtained from disassembly of a battery inevitably contains residual electrolyte salt particles. To improve testing accuracy, it is preferable to perform a surface scan on a cross-section of the positive electrode film along the electrode thickness direction to characterize the degree of graphitization of the positive electrode film.

[0138] The graphitization degree C of the positive electrode film was obtained by the ratio of the peak intensities of the G-band and D-band in the Raman spectrum. The position of the G-band peak was 1580±100 cm⁻¹. -1 Its characterization of carbon sp 2 Hybrid structure; D peak position is 1350±100 cm⁻¹ -1 It characterizes the disordered structure of carbon, where disorder refers to the irregular arrangement of carbon atoms within the structure. In graphite crystals, carbon atoms in the same layer are arranged in an sp... 2Hybridization forms covalent bonds, while interlayer bonding is facilitated by van der Waals forces, making the carbon in the graphite structure prone to slippage. Therefore, the C value can characterize the degree of graphitization of the cathode film. A higher C value indicates a higher degree of graphitization of the carbon material. It is understandable that the degree of graphitization in the cathode film mainly originates from the graphitized carbon material within the cathode film, i.e., the carbon coating layer of the cathode active material. Although rich in sp... 2 Hybridized carbon nanotube conductive agents also have relatively high I0 G / I D However, due to its low content and small tube diameter, its addition to the positive electrode film results in an extreme value in the Raman surface scan test of the positive electrode film, and does not affect the graphitization degree C in the positive electrode film. 50 It has an impact.

[0139] The cumulative distribution curve of graphitization degree C value refers to the curve obtained by arranging at least 100 C values ​​in ascending order, with graphitization degree as the horizontal axis and the cumulative percentage as the vertical axis. 50 This represents the C value corresponding to a cumulative percentage of 50% on the vertical axis of the cumulative distribution curve of graphitization degree C. The median C value of graphitization degree. 50 Compared to point values, it can reflect the overall graphitization degree of particles in the positive electrode film, i.e., the degree of slippage; compared to the mean value, it can reduce the influence of extreme values ​​during the test and improve the confidence of the test results.

[0140] Those skilled in the art can control the graphitization degree of the cathode film using any known process. For example, adjusting the carbon source, sintering temperature, sintering time, sintering pressure, and sintering atmosphere can all achieve the adjustment of the graphitization degree of the cathode film.

[0141] In some embodiments, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The value can be selected from 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, or any value range between the two.

[0142] By controlling the median C of the graphitization degree of the positive electrode film... 50 Within the aforementioned range, it is beneficial to reduce the positive electrode impedance, improve the electron conduction efficiency on the positive electrode sheet, and thus improve the energy conversion efficiency of the battery cell.

[0143] In some embodiments, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The range is 0.98-1.13.

[0144] By controlling the median C of the graphitization degree of the positive electrode film... 50 Within the aforementioned range, the positive electrode impedance can be further reduced, and the electron conduction efficiency of the positive electrode sheet can be improved, thereby improving the energy conversion efficiency of the battery cell.

[0145] In some embodiments, in the cross-section of the positive electrode film layer along the electrode thickness direction, the D of the particles... A50 The range is 600nm-800nm, where D A50 It refers to the particle size at which the cumulative area distribution of particles reaches 50% in the cumulative area distribution curve of particles.

[0146] In this application, the particle size D of the particles in the cross-section of the positive electrode film along the electrode thickness direction is... A50 The specific testing method is as follows. After particle identification and labeling according to the method described above, the images are imported into ImageJ software for analysis. The scale is set according to the scanning electron microscope image. The particle size and area in the cross-section along the thickness direction of the positive electrode film are analyzed using the "Feret" and "Area" analysis functions. According to the software manual (ImageJ User Guide IJ1.46r), the "Feret" parameter obtained from the analysis represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, thus characterizing the particle size; and the "Area" parameter represents the pixel area of ​​the particle. Since particles with a diameter less than 50nm have a large error in the statistical process and are difficult to accurately identify, and the particle size of the conductive agent is generally less than 50nm, which will produce a large error in the statistical results, particles with a diameter less than 50nm are not counted in the particle size statistics process of this application, and the particle statistics data corresponding to Area displaying "NaN" are deleted. Following the above method, to ensure a statistically significant sample size, at least 10 non-overlapping scanning electron microscope (SEM) images were acquired for each electrode, and the particle size of at least 5000 particles was statistically analyzed. The particle sizes of these at least 5000 particles were arranged in ascending order, and the cumulative area distribution curve of the particles in the positive electrode film was obtained by plotting particle size on the horizontal axis and the cumulative area percentage calculated from the particle's "area" on the vertical axis. A50 This represents the particle size value corresponding to a cumulative area ratio of 50% on the vertical axis of the cumulative area distribution curve.

[0147] In some embodiments, the particle size D is obtained from the cumulative distribution curve of the positive electrode active material particle size area obtained by slicing the positive electrode film along the thickness direction of the electrode sheet. A50The range can be 600nm, 610nm, 620nm, 630nm, 640nm, 650nm, 660nm, 670nm, 680nm, 690nm, 700nm, 710nm, 720nm, 730nm, 740nm, 750nm, 760nm, 770nm, 780nm, 790nm, 800nm, or any value range between the two.

[0148] Particle size D A50 Within the aforementioned range, it indicates that the positive electrode film contains a certain number of large-sized particles. The median particle size D is controlled. A50 Within the aforementioned range, the large contact area between large-sized particles can improve the efficiency of roller pressure transmission between electrode particles, fully utilize the skeletal support of large-sized particles, enable the electrode to withstand higher roller pressure, increase the compaction density of the electrode, and improve the volumetric energy density of the battery cell. It can also reduce the degree of side reactions of the positive electrode active material through large-sized particles, and reduce the kinetic decline caused by excessive particle size. While improving the compaction density of the electrode, it can maintain the kinetic performance of the battery, thereby taking into account the energy conversion efficiency of the battery cell.

[0149] In some embodiments, in the cross-section of the positive electrode film layer along the electrode thickness direction, the D of the particles... A50 The range is 650nm-750nm, where D A50 It refers to the particle size at which the cumulative area distribution of particles reaches 50% in the cumulative area distribution curve of particles.

[0150] Controlling the particle size D A50 Within the aforementioned range, the large contact area between large-sized particles can further improve the efficiency of roller pressure transmission between electrode particles, enabling the electrode to withstand higher roller pressure, increasing the compaction density of the electrode, and reducing the kinetic decrease caused by excessively large particle size and increased lithium-ion transport path, thereby balancing the energy conversion efficiency and cycle life of the battery cell.

[0151] In some embodiments, the positive electrode film layer further includes a conductive agent, which includes carbon nanotubes, and the mass content of carbon nanotubes is 0.1%-1.5% based on the total mass of the positive electrode film layer.

[0152] In some embodiments, based on the total mass of the positive electrode film, the mass content of 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 two.

[0153] Carbon nanotubes are added to the positive electrode film as a conductive agent. By introducing a one-dimensional conductive agent, a continuous three-dimensional conductive network is formed between the positive electrode active materials, which significantly reduces the electrode interface impedance and thus improves the energy conversion efficiency and cycle life of the battery cell.

[0154] In some embodiments, the conductive agent further includes conductive carbon black.

[0155] 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.

[0156] In some embodiments, the positive electrode film layer further includes polyvinylidene fluoride (PVDF), with the PVDF content being 1%-3% based on the total mass of the positive electrode film layer.

[0157] In some embodiments, the positive electrode film layer further includes polyvinylidene fluoride (PVDF), and the mass content of PVDF, based on the total mass of the positive electrode film layer, can be selected as 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, or any value range between the two.

[0158] Adding polyvinylidene fluoride (PVDF) as a binder to the positive electrode film can form a continuous "bonding network" through PVDF, inhibiting the shedding of the positive electrode active material and preventing structural pulverization of the positive electrode active material due to volume expansion / contraction during charge-discharge cycles. This maintains the integrity and stability of the electrode structure, thereby improving the cycle performance of the battery cell.

[0159] In some embodiments, the positive electrode film layer further includes lithium carboxymethyl cellulose, wherein the mass content of lithium carboxymethyl cellulose is 0.3%-1% based on the total mass of the positive electrode film layer.

[0160] In some embodiments, the positive electrode film layer further includes lithium carboxymethyl cellulose, and the mass content of lithium carboxymethyl cellulose, based on the total mass of the positive electrode film layer, can be selected as 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any value range between the two.

[0161] Adding lithium carboxymethyl cellulose within the above range as a dispersant to the positive electrode film can give the slurry good dispersibility, making the particles of the slurry more uniformly stacked after coating and drying, thereby improving the coating uniformity of the large-area positive electrode film, reducing the problem of excessive local heat generation, and improving the energy conversion efficiency of the battery cell.

[0162] In some embodiments, the mass ratio of polyvinylidene fluoride to lithium carboxymethyl cellulose is 1-10.

[0163] In some embodiments, the mass ratio of polyvinylidene fluoride to lithium carboxymethyl cellulose can be selected as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or any range between the two.

[0164] By adjusting the mass ratio of polyvinylidene fluoride (PVDF) to lithium carboxymethyl cellulose (CMC) within the aforementioned range, the synergistic effect of PVDF and CMC can better balance the strength and flexibility of the electrode, thereby improving the dispersion and bonding effect of the slurry. This results in more uniform particle accumulation after coating and drying, thus improving the coating uniformity of the large-area positive electrode film, reducing the problem of excessive local heat generation, and improving the energy conversion efficiency of the battery cell.

[0165] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0166] In some embodiments, the battery cell further includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes graphite, and the graphitization degree of the negative electrode film layer is 88%-93%.

[0167] In this application, the degree of graphitization of the negative electrode film has a meaning known in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (such as a Bruker D8 Discover) can be used for testing. The test can be performed with reference to JISK 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d002 of the C(002) crystal plane in the material's crystal structure. d002 is the average interlayer spacing of the C(002) crystal plane in the material's crystal structure expressed in nanometers (nm). Then, the degree of graphitization of the negative electrode film is calculated according to the formula g = (0.344 - d002) / (0.344 - 0.3354) × 100%.

[0168] In some embodiments, the negative electrode active material includes graphite, and the degree of graphitization of the negative electrode film can be selected as 88%, 88.5%, 89%, 89.5%, 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, or any value range between the two.

[0169] When the graphitization degree of the negative electrode film is within the above range, it is beneficial to reduce the expansion force of the negative electrode film in the later stage of long cycle, and further improve the cycle life of the battery cell.

[0170] In some embodiments, the negative electrode active material includes graphite, and the graphitization degree of the negative electrode film is 91%-92%.

[0171] When the graphitization degree of the negative electrode film is within the above range, it is beneficial to reduce the degree of side reaction while reducing the expansion force of the negative electrode film in the later stage of long cycle, thereby further improving the cycle life of the battery cell.

[0172] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0173] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0174] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0175] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0176] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0177] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0178] In some embodiments, referring to Figure 1, the end cap assembly 112 includes an end cap 113 on which an explosion-proof valve 15 is mounted. The ratio of the projected area A of the explosion-proof valve 15 along the thickness direction of the end cap 113 to the capacity of the battery cell is 0.2 mm. 2 / Ah-4mm 2 / Ah.

[0179] An explosion-proof valve 15 is disposed on the end cap 113 of the housing 11. The explosion-proof valve 15 can be used to release internal pressure when the internal pressure (or temperature) of the battery cell 10 reaches a threshold. In some embodiments, the explosion-proof valve 15 can be integrally formed with the end cap 113 (i.e., an integral structure). In other embodiments, the explosion-proof valve 15 can be separately formed and separately connected with the end cap 113 (i.e., a separate structure). One or more explosion-proof valves 15 may be provided. When multiple explosion-proof valves 15 are provided, all multiple explosion-proof valves 15 are disposed on the end cap 113 and arranged at intervals. The multiple explosion-proof valves 15 can be arranged regularly (e.g., in a matrix array or a circular array) or irregularly. The shapes and sizes of the multiple explosion-proof valves 15 can be the same or different. The projected shape of the explosion-proof valve 15 along the thickness direction of the end cap 113 can be, but is not limited to, circular, elliptical, polygonal, semi-circular, etc. The thickness direction of the end cap 113 is perpendicular to the outer wall surface of the end cap 113, which is the wall surface of the end cap 113 facing away from the internal space of the outer shell 11.

[0180] The projection area of the explosion-proof valve 15 along the thickness direction of the end cap 113, that is, the area of the projection region formed when the explosion-proof valve 15 is projected along the thickness direction of the end cap 113 onto a plane parallel to the end cap 113, is denoted as A, and the unit is square millimeters (mm 2 ). When there is one explosion-proof valve 15 provided, the projection area of this explosion-proof valve 15 along the thickness direction of the end cap 113 is A. When there are multiple explosion-proof valves 15 provided, the sum of the projection areas of all explosion-proof valves 15 along the thickness direction of the end cap 113 is A. The projection area A of the explosion-proof valve 15 along the thickness direction of the end cap 113 can be measured in various ways. For example, in some embodiments, A can be measured by a physical projection measurement method, and the measurement process can be referred to as follows: place the battery cell 10 on the worktable of an optical projection platform (such as an image measuring instrument), adjust the posture of the battery cell 10 so that the thickness direction of the end cap 113 is consistent with the light emission direction of the projection device; turn on the projection device, project the outline of the explosion-proof valve 15 clearly onto an imaging screen (or a computer software interface), adjust the focal length and magnification, and confirm that the projected image has no distortion and the outline edge is clear (the boundary of the explosion-proof valve 15 can be marked to eliminate the interference of non-pressure-relief areas); place a standard gauge block (such as a calibration block with an accuracy of 0.1 mm) on the projected image, record the ratio of 1 mm in the image to the actual size (that is, the "pixel-millimeter" conversion relationship), and confirm the measurement accuracy (the error can be required to be ≤ 0.05 mm); use the area measurement tool supporting the projection device (such as the contour scanning function of the image measuring instrument) to automatically trace along the projection contour of the explosion-proof valve 15, and the software will automatically calculate the projection area according to the calibrated scale, thereby A can be measured.

[0181] In the present application, the capacity of the battery cell can be tested by using equipment and methods known in the art. Illustratively, at 25°C, the battery cell is charged at a constant power of 0.5P until the charge cut-off voltage is reached, and then discharged at a constant power of 0.5P until the discharge cut-off voltage is reached. This is one charge-discharge process, and the calculated first discharge capacity is the capacity of the battery cell.

[0182] In the present application, those skilled in the art can reasonably adjust the discharge cut-off voltage and the charge cut-off voltage according to different types of positive electrode active materials, working conditions of the battery cell, and the like. 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.

[0183] In some embodiments, the ratio of the projection area A of the explosion-proof valve 15 along the thickness direction of the end cap 113 to the capacity of the battery cell can be selected as 0.2 mm 2 / Ah, 0.3 mm 2 / Ah, 0.4 mm 2 / Ah, 0.5 mm 2 / Ah, 0.6mm 2 / Ah, 0.7mm 2 / Ah, 0.8mm 2 / Ah, 1.0mm 2 / Ah, 1.2mm 2 / Ah, 1.4mm 2 / Ah, 1.6mm 2 / Ah, 1.8mm 2 / Ah, 2.0mm 2 / Ah, 2.2mm 2 / Ah, 2.4mm 2 / Ah, 2.6mm 2 / Ah, 2.8mm 2 / Ah, 3.0mm 2 / Ah, 3.2mm 2 / Ah, 3.4mm 2 / Ah, 3.6mm 2 / Ah, 3.8mm 2 / Ah, 4.0mm 2 / Ah or any numerical range between the two.

[0184] Referring to Figures 2 and 3, electrode terminal 13 is a component electrically connected to electrode assembly 12 and used for outputting or inputting electrical energy. Electrode terminal 13 includes a positive electrode terminal 13a and a negative electrode terminal 13b. Positive electrode terminal 13a is electrically connected to the positive electrode tab 122a of electrode assembly 12. Negative electrode terminal 13b is electrically connected to the negative electrode tab 122b of electrode assembly 12. Electrode terminal 13 can be mounted on housing 11 (e.g., end cap 113) and stably mounted in position and state relative to housing 11. In some embodiments, electrode terminal 13 can be mounted on housing 11 by means of flange riveting.

[0185] The battery cell 10 also includes an insulating component 14, which is a component with insulating properties. The insulating component 14 is disposed within the housing 11, particularly between the electrode assembly 12 and the wall portion of the housing 11 having electrode terminals 13 (e.g., end cap 113). Based on the electrical connection between the tabs 122 of the electrode assembly 12 and the corresponding electrode terminals 13, the insulating component 14 can be used to insulate and isolate the electrode assembly 12 and the wall portion of the housing 11 having electrode terminals 13, thereby reducing the risk of short circuits, current leakage, etc. Furthermore, the insulating component 14 can also be fixed to the wall portion of the housing 11 having electrode terminals 13 and abut against the electrode assembly 12 to fill the gap between the electrode assembly 12 and the wall portion of the housing 11, thus tightly fixing the electrode assembly 12. This prevents the electrode assembly 12 from moving or shaking relative to the battery cell 10 during use, helps maintain the structural integrity of the battery cell 10, and reduces the risk of the electrode assembly 12 loosening or deforming.

[0186] By adopting the above scheme, since the capacity of the battery cell 10 directly reflects the total amount of active material and energy storage scale, and is positively correlated with the gas production scale during thermal runaway, limiting the ratio of the projected area A of the explosion-proof valve 15 along the thickness direction of the end cap 113 to the capacity of the battery cell to the above range allows for the establishment of a quantitative matching standard between capacity characteristics and pressure relief performance. This enables the matching of "proportional" pressure relief channels for battery cells 10 with different capacities. Based on this, the explosion-proof valve 15 can have sufficient pressure relief area to cope with the relatively high gas production of large-capacity battery cells, reducing the risk of poor exhaust passage and internal pressure runaway of the casing 11 due to an excessively small projected area A of the explosion-proof valve, thus improving pressure relief reliability and the operational reliability of large-capacity battery cells 10. Furthermore, while meeting gas discharge requirements, it reduces the over-design of the explosion-proof valve 15, optimizes the structure and cost, and improves structural reliability, operational reliability, and design economy.

[0187] In some embodiments, the ratio of the projected area A of the explosion-proof valve 15 along the thickness direction of the end cap 113 to the capacity C of the battery cell is 1.1 mm. 2 / Ah-2.5mm 2 / Ah.

[0188] By adopting the above scheme, the narrowed A / C ratio optimization range can reduce the problems of insufficient venting margin and increased venting pressure risk that may be caused by a small A / C ratio. It can also reduce the over-design of the explosion-proof valve 15 (such as weakened structural strength and increased cost) and the waste of pressure relief area that may be caused by a large A / C ratio. As a result, battery cells 10 of different capacities can obtain a precisely matched pressure relief channel, and large-capacity battery cells 10 of various capacity ranges can achieve a better balance between pressure relief reliability, structural stability and design economy, thereby further reducing the risk of thermal runaway.

[0189] In some embodiments, the projected area A of the explosion-proof valve 15 along the thickness direction of the end cap 113 is 800 mm². 2 -1500mm 2 .

[0190] In some embodiments, the projected area A of the explosion-proof valve 15 along the thickness direction of the end cap 113 can be selected as 800 mm². 2 850mm 2 900mm 2 950mm 2 1000mm 2 1050mm 2 1100mm 2 1150mm 2 1200mm2 1250mm 2 1300mm 2 1350mm 2 1400mm 2 1450mm 2 1500mm 2 Or the range of values ​​between any two.

[0191] By adopting the above-mentioned scheme, the explosion-proof valve 15 can have a sufficient actual pressure relief area, providing a stable, effective, and sufficiently wide gas discharge channel to meet gas discharge requirements and achieve rapid and efficient venting. This reduces the risk of pressure relief failure, maintains the pressure relief capacity of the explosion-proof valve 15, and maintains and improves its pressure relief reliability. Furthermore, while meeting gas discharge requirements, the actual pressure relief area of ​​the explosion-proof valve 15 can be constrained. On the one hand, this allows for the preservation of a large portion of the end cap 113 as a structural support area resistant to impact and deformation pressure, preserving the structural strength and sealing performance of the end cap 113 to a greater extent, and maintaining and improving the strength and sealing of the outer casing 11. On the other hand, it reduces the risk of excessive pressure relief and excessive splashing due to an excessively large actual pressure relief area, which could accelerate heat propagation. Therefore, the reliability and service life of the battery cell 10 can be effectively improved, further reducing the risk of thermal runaway.

[0192] In some implementations, the capacity of a single battery cell is 400Ah-3000Ah.

[0193] In some implementations, the capacity of a single battery cell can be selected as 400Ah, 500Ah, 600Ah, 700Ah, 800Ah, 900Ah, 1000Ah, 1100Ah, 1200Ah, 1300Ah, 1400Ah, 1500Ah, 1600Ah, 1700Ah, 1800Ah, 1900Ah, 2000Ah, 2100Ah, 2200Ah, 2300Ah, 2400Ah, 2500Ah, 2600Ah, 2700Ah, 2800Ah, 2900Ah, 3000Ah, or any value range between the two.

[0194] In some implementations, the capacity of a single battery cell is 500Ah-1500Ah.

[0195] In some implementations, the capacity of a single battery cell is 600Ah-1000Ah.

[0196] An embodiment of the second aspect of this application provides a battery device, which includes the battery cell described in the above embodiments.

[0197] Please refer to Figure 4, which is an exploded structural diagram of a battery device provided in some embodiments of this application. The battery device 100 includes a housing 110 and a battery cell 10, with the battery cell 10 housed within the housing 110. The housing 120 provides a accommodating space for the battery cell 10, and the housing 120 can adopt various structures. In some embodiments, the housing 110 may include a first portion 120 and a second portion 130, which overlap each other, jointly defining a accommodating space for the battery cell 10. The second portion 130 may be a hollow structure with one open end, and the first portion 120 may be a plate-like structure, covering the open side of the second portion 130 so that the first portion 120 and the second portion 130 jointly define the accommodating space; alternatively, the first portion 120 and the second portion 130 may both be hollow structures with one open side, with the open side of the first portion 120 covering the open side of the second portion 130. Of course, the box 110 formed by the first part 120 and the second part 130 can be of various shapes, such as cylinder, cuboid, etc.

[0198] In the battery device 100, there can be multiple battery cells 10, which can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 10 are connected in both series and parallel connections. Multiple battery cells 10 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 10 is housed within the housing 110. Alternatively, the battery device 100 can also consist of multiple battery cells 10 first connected in series, parallel, or in a mixed configuration to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed configuration to form a whole, which is also housed within the housing 110. The battery device 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 10.

[0199] An embodiment of the third aspect of this application provides an energy storage device, which includes the battery cell or battery device in the above embodiments. The energy storage device may 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.

[0200] 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.

[0201] Example

[0202] 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.

[0203] Example 1

[0204] (1) Preparation of positive electrode sheet

[0205] Preparation of positive electrode active materials:

[0206] Lithium dihydrogen phosphate, ferrous oxalate, polyethylene glycol, and titanium dioxide were mixed evenly in a solvent and then ground. The ratio of ferrous oxalate to lithium dihydrogen phosphate was such that the molar ratio of iron to phosphorus was 0.965:1.0.

[0207] The mixed raw materials were ball-milled multiple times and demagnetized in a ball mill to obtain a mixed slurry. The number of grinding cycles and time were controlled, and the particle size Dv50 of the ground mixed slurry was 3.0 μm.

[0208] The spray-dried slurry yields a dried precursor powder, which is light yellow in appearance and uniform in color.

[0209] The precursor powder was placed in a sintering furnace and heated from 25°C to 350°C at a rate of 2°C / min under a nitrogen atmosphere and held at that temperature for 3 hours. Then, the temperature was increased to a second temperature of 770°C at a rate of 5°C / min and held at that temperature for 10 hours. After the process, the temperature was lowered and cooled.

[0210] The obtained lithium iron phosphate cathode material was crushed by air jet milling to obtain carbon-coated lithium iron phosphate cathode active material.

[0211] The above-mentioned positive electrode active materials, lithium iron phosphate, carbon nanotubes, conductive carbon black, polyvinylidene fluoride, and lithium carboxymethyl cellulose, were mixed in a mass ratio of 97:0.2:0.3:2:0.5, 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 drying temperature was 95℃, and the drying speed was 2.0 m / min.

[0212] The hot pressing process includes three hot roller pressing processes, with the hot roller pressing pressure increasing sequentially to 35 tons, 55 tons, and 75 tons. The hot roller temperature is 65℃. Before the first hot roller compaction, the electrode sheet is heated to 50℃.

[0213] Among them, the cumulative distribution curve of graphitization degree C value of the positive electrode film obtained in the laser microscopic confocal Raman spectroscopy instrument scanning mode, the median C of graphitization degree. 50 The value is 1.018. In a cross-section of the positive electrode film along the thickness direction of the electrode sheet, the particle's D... A50 It is 730nm.

[0214] (2) Preparation of negative electrode sheet

[0215] A negative electrode active material (graphite), a conductive agent (carbon black), a binder (styrene-butadiene rubber (SBR), and a thickener (sodium carboxymethyl cellulose)) were mixed in a ratio of 97.3:0.5:1.5:0.7. Deionized water was added and the mixture was stirred to disperse and prepare a negative electrode slurry. The negative electrode slurry was then coated onto both sides of a Cu foil. After coating both sides, the foil was dried, compacted, slit, and sheeted to obtain the negative electrode sheet. The graphitization degree of the negative electrode film was 91.2%.

[0216] (3) Separating membrane

[0217] 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.

[0218] (4) Preparation of electrolyte

[0219] The electrolyte contains 5% propylene carbonate (PC), 60% ethyl methyl carbonate (EMC), 24% diethyl carbonate (DEC), 1.5% fluoroethylene carbonate, and 9.5% lithium hexafluorophosphate by mass.

[0220] (5) Preparation of battery cells

[0221] 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 to obtain a wound electrode assembly. The electrode assembly is placed in a housing with an opening, and an end cap assembly covers the opening of the housing. The end cap assembly includes an end cap on which an explosion-proof valve is installed, and the projected area of ​​the explosion-proof valve along the thickness direction of the end cap is 1200 mm². 2 The electrolyte is then injected and the cells are sealed. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained. The battery cell has a capacity of 600 Ah, and the ratio of the projected area of ​​the explosion-proof valve along the thickness direction of the end cap to the battery cell's capacity is 2 mm² / Ah. The total coating area of ​​the positive electrode film in the battery cell is 16.5 m². 2 .

[0222] The preparation of the battery cells in Examples 2 to 14 is similar to that in Example 1, except that the electrolyte formulations are different, as shown in Table 1.

[0223] The preparation of the battery cells in Examples 15 to 17 is similar to that in Example 1, except that the positive electrode active materials are different, as detailed in Table 3.

[0224] The preparation method of the positive electrode active material in Example 15 is basically the same as that in Example 1, except that:

[0225] Lithium dihydrogen phosphate, ferrous oxalate, polyethylene glycol, glucose (mixed in a mass ratio of 1:3), and titanium dioxide were mixed evenly in a solvent and then ground. The ratio of lithium dihydrogen phosphate to ferrous oxalate resulted in a molar ratio of iron to phosphorus of 0.965:1.0.

[0226] The preparation method of the positive electrode active material in Example 16 is basically the same as that in Example 1, except that:

[0227] The precursor powder was placed in a sintering furnace and sintered in two stages under a nitrogen atmosphere to obtain lithium iron phosphate cathode material: the temperature was increased from 25°C to 350°C at a heating rate of 2°C / min and held for 3 hours; the temperature was increased from 350°C to 755°C at a heating rate of 5°C / min and held for 10 hours; and then the temperature was cooled.

[0228] The preparation method of the positive electrode active material in Example 17 is basically the same as that in Example 1, except that:

[0229] The precursor powder was placed in a sintering furnace and sintered in two stages under a nitrogen atmosphere to obtain lithium iron phosphate cathode material: the temperature was increased from 25°C to 350°C at a heating rate of 2°C / min and held for 3 hours; the temperature was increased from 350°C to 790°C at a heating rate of 5°C / min and held for 10 hours; and then the temperature was cooled.

[0230] The preparation of the battery cells in Comparative Examples 1 to 4 was similar to that in Example 1, except that the electrolyte formulations were different, as shown in Table 1.

[0231] The battery cell in Comparative Example 5 is similar to that in Comparative Example 1, except that the size of the positive electrode film layer in each electrode assembly of the battery cell was adjusted so that the total coating area of ​​the positive electrode film layer in the battery cell is 8.3 m². 2 See Table 2 for details.

[0232] II. Battery Performance Testing

[0233] (1) Battery cycle performance test

[0234] 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 discharge capacity of the first cycle was recorded. This constituted one cycle. The discharge capacity of 1000 cycles was recorded, and the capacity retention rate after 1000 cycles was calculated.

[0235] (2) Battery energy conversion efficiency test

[0236] 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.

[0237] (3) Battery thermal runaway safety test

[0238] At 25℃, after fully charging a single battery cell at a constant power of 0.5P, continue charging the cell at the same constant power of 0.5P while simultaneously applying external heating. This process is repeated until the judgment criteria are met or the cumulative time reaches 4 hours. During monitoring, if the temperature rise rate at the monitoring point on the negative electrode side of the battery cell is ≥3℃ / s and lasts for 3 seconds, or if fire or explosion occurs, thermal runaway is immediately determined to have occurred, and the test is terminated. After stopping, observe for 1 hour and record the experimental phenomena. If sparks or flames appear on the battery cell, the thermal runaway safety test is considered to have failed.

[0239] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0240] 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.

[0241] Table 1

[0242] Table 2

[0243] As can be seen from the comparison between Comparative Examples 1 and 5 of this application, the total coating area of ​​the positive electrode film layer contained in the battery cell is greater than or equal to 11m². 2 At that time, the battery cell has a high capacity to meet the needs of energy storage devices, but due to the increase in the coating area of ​​the positive electrode film layer contained in the battery cell, the energy conversion efficiency of the battery cell deteriorates.

[0244] As can be seen from the comparison of the embodiments and comparative examples of this application, the electrolyte includes propylene carbonate and fluoroethylene carbonate. Based on the total mass of the electrolyte, the mass content of propylene carbonate is 1%-15%; based on the total mass of the electrolyte, the mass content of fluoroethylene carbonate is 0.1%-5%; and the total coating area of ​​the positive electrode film layer contained in the battery cell is greater than or equal to 11m². 2 At that time, the battery cells have high capacity, good cycle performance, high energy conversion efficiency and good safety performance.

[0245] As can be seen from the comparison between Examples 2 and 3 and Examples 1, 4 and 5, when the mass content of propylene carbonate is 3%-7% based on the total mass of the electrolyte, the battery cell has good safety performance, while also taking into account the cycle performance and energy conversion efficiency of the battery cell.

[0246] As can be seen from the comparison between Examples 7 and 8 and Examples 1, 9 and 10, when the mass content of fluoroethylene carbonate is 1.5%-5.0% based on the total mass of the electrolyte, the battery cell has good safety performance, while also taking into account the cycle performance and energy conversion efficiency of the battery cell.

[0247] As can be seen from the comparison between Example 1 and Examples 11 and 12, when the electrolyte also includes lithium difluorophosphate, the battery cell not only has good safety performance, but also further improves the cycle performance and energy conversion efficiency of the battery cell.

[0248] As can be seen from the comparison between Example 1 and Examples 13 and 14, when the electrolyte also includes vinylene carbonate, the battery cell not only has good safety performance, but also further improves the cycle performance and energy conversion efficiency of the battery cell.

[0249] Table 3

[0250] A comparison of Example 16 with Examples 1, 15, and 17 shows that, in the cumulative distribution curve of graphitization degree C obtained by laser microscopy confocal Raman spectroscopy in instrument scanning mode, the median C of graphitization degree is... 50 With a value of 0.98-1.13, the battery cells have good safety performance, and the cycle performance and energy conversion efficiency of the battery cells can be further improved.

[0251] 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 assembly. The housing includes a receiving cavity with an opening. The end cap assembly covers the opening of the housing. The electrode assembly and the electrolyte are disposed within the receiving cavity of the housing. 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 electrolyte comprises propylene carbonate and fluoroethylene carbonate, and the mass content of propylene carbonate is 1%-15% based on the total mass of the electrolyte. Based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate is 0.1%-5%; The total coating area of ​​the positive electrode film in the battery cell is greater than or equal to 11m². 2 .

2. The battery cell according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass content of propylene carbonate is 3%-7%.

3. The battery cell according to claim 1 or 2, characterized in that, Based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate is 1.5%-5.0%.

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

5. The battery cell according to any one of claims 1-4, characterized in that, The electrolyte further includes a first component, which includes one or more of dimethyl carbonate and ethyl methyl carbonate, and the mass content of the first component is 15%-60% based on the total mass of the electrolyte.

6. The battery cell according to claim 5, characterized in that, The electrolyte comprises 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 36%-45%.

7. The battery cell according to claim 5, characterized in that, The electrolyte includes ethyl methyl carbonate, and the ethyl methyl carbonate content is 10%-60% based on the total mass of the electrolyte, optionally 30%-40%.

8. The battery cell according to any one of claims 1-7, characterized in that, The electrolyte also includes lithium difluorophosphate, and the mass content of lithium difluorophosphate is 0.01%-1% based on the total mass of the electrolyte.

9. The battery cell according to claim 8, characterized in that, Based on the total mass of the electrolyte, the lithium difluorophosphate content is 0.4%-1%.

10. The battery cell according to any one of claims 1-9, characterized in that, The electrolyte also includes vinylene carbonate, and the mass content of the vinylene carbonate is 0.5%-8%, optionally 0.6%-4%, based on the total mass of the electrolyte.

11. The battery cell according to any one of claims 1-10, characterized in that, The positive electrode film layer includes a positive electrode active material, which comprises lithium phosphate particles with at least a portion of their surface coated with carbon material. In the cumulative distribution curve of the graphitization degree C value obtained by laser microscopy confocal Raman spectroscopy in surface scanning mode, the median C of the graphitization degree is... 50 Greater than or equal to 0.95 and less than or equal to 1.20; Among them, the degree of graphitization C is I G / I D I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 The intensity of peak D at that location.

12. The battery cell according to claim 11, characterized in that, In the cumulative distribution curve of the graphitization degree C value of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode, the median C of the graphitization degree is... 50 The range is 0.98-1.

13.

13. The battery cell according to claim 11 or 12, characterized in that, In the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the D of the particles A50 The range is 600nm-800nm, where D A50 It refers to the particle size at which the cumulative area distribution of particles reaches 50% in the cumulative area distribution curve of particles.

14. The battery cell according to claim 13, characterized in that, In the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the D of the particles A50 The range is 650nm-750nm, where D A50 It refers to the particle size at which the cumulative area distribution of particles reaches 50% in the cumulative area distribution curve of particles.

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

16. The battery cell according to any one of claims 1-15, characterized in that, The positive electrode film layer also includes polyvinylidene fluoride (PVDF), and the mass content of PVDF is 1%-3% based on the total mass of the positive electrode film layer.

17. The battery cell according to claim 16, characterized in that, The positive electrode film layer also includes lithium carboxymethyl cellulose, and the mass content of lithium carboxymethyl cellulose is 0.3%-1% based on the total mass of the positive electrode film layer.

18. The battery cell according to claim 17, characterized in that, The mass ratio of the polyvinylidene fluoride to the lithium carboxymethyl cellulose is 1-10.

19. The battery cell according to any one of claims 1-18, characterized in that, The battery cell further includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes graphite. The graphitization degree of the negative electrode film layer is 88%-93%, and optionally 91%-92%.

20. The battery cell according to any one of claims 1-19, characterized in that, The end cap assembly includes an end cap fitted with an explosion-proof valve, wherein the ratio of the projected area of ​​the explosion-proof valve along the thickness direction of the end cap to the capacity of the battery cell is 0.2 mm. 2 / Ah-4mm 2 / Ah, selectable as 1.1mm 2 / Ah-2.5mm 2 / Ah.

21. The battery cell according to claim 20, characterized in that, The projected area of ​​the explosion-proof valve along the thickness direction of the end cap is 800 mm². 2 -1500mm 2 .

22. The battery cell according to any one of claims 1-21, characterized in that, The capacity of the battery cell is 400Ah-3000Ah, optionally 500Ah-1500Ah, and further optionally 600Ah-1000Ah.

23. A battery device, characterized in that, The battery device comprises the battery cell according to any one of claims 1-22.

24. An energy storage device, characterized in that, The energy storage device includes a battery cell as described in any one of claims 1-22 or a battery device as described in claim 23.

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