Battery cell, battery device, power consuming device, and energy storage device

Abstract

This application provides a battery cell, a battery device, an electrical device, and an energy storage device. The positive electrode film of the battery cell has a compaction density of 2.3 g / cm³ under fully discharged conditions. 3 -2.5g / cm 3 The compaction density of the negative electrode film is 1.35 g / cm³. 3 -1.55g / cm 3 The single-sided coating mass of the positive electrode film is 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2 In the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction, the particle size D50 is 0.4μm-0.8μm; in the cumulative particle number distribution curve obtained from the cross-section of the negative electrode film along the electrode thickness direction, the particle size D50 is 10μm-25μm. D50 refers to the particle size corresponding to the cumulative particle number distribution reaching 50% in the cumulative number distribution curve.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery cell, battery device, power supply device, and energy storage device. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the further development of battery applications, higher performance requirements are being placed on the energy density, cycle life, and other electrical properties of individual battery cells. Summary of the Invention

[0003] This application is made in view of the above-mentioned issues, and its purpose is to provide a battery cell that combines long cycle life and high energy density.

[0004] An embodiment of the first aspect of this application provides a battery cell, the battery cell including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. In a fully discharged state, the compaction density of the positive electrode film layer is 2.3 g / cm³. 3 -2.5g / cm 3 The single-sided coating mass of the positive electrode film is 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2 The cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the thickness direction of the electrode sheet shows a particle size D50 of 0.4 μm-0.8 μm; and the compaction density of the negative electrode film in the fully discharged state of the battery cell is 1.35 g / cm³. 3 -1.55g / cm 3 The cumulative particle number distribution curve obtained from the cross section of the negative electrode film along the electrode thickness direction has a particle size distribution D50 of 10μm-25μm, where D50 refers to the particle size corresponding to the cumulative particle number distribution reaching 50% in the cumulative number distribution curve.

[0005] The battery cells provided in this application use positive electrode active material particles with a number distribution particle size D50 of 0.4μm-0.8μm for the positive electrode and negative electrode active material particles with a number distribution particle size D50 of 10μm-25μm for the negative electrode. This approach aims to reduce the probability of particle-induced side reactions and polarization phenomena, thereby improving the first-cycle coulombic efficiency and cycle life of the battery cells. Furthermore, the compaction density of the negative electrode film is controlled to be 1.35 g / cm³. 3 -1.55g / cm 3 The positive electrode film has a compaction density of 2.3 g / cm³. 3 -2.5g / cm 3 This design allows the negative electrode film to have high porosity and improve cycle life, while the compaction design of the positive electrode can be well matched with the low compaction design of the negative electrode sheet. It also allows space for volume expansion during the lithium insertion / extraction process of the negative electrode, while maintaining the particle integrity of the positive electrode active material during compaction, thus improving both the energy density and cycle life of the battery cell. Furthermore, this is combined with controlling the single-sided coating mass of the positive electrode film to 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2 By employing a thick coating design, energy density is improved while the positive electrode film has suitable lithium-ion diffusion distance and resistance, thus ensuring cycle life. This application, through the combination of positive and negative electrode sheets, enables the battery cell to achieve both long cycle life and high energy density, meeting performance requirements.

[0006] In any embodiment, when the battery cell is fully discharged, the compaction density of the positive electrode film is 2.3 g / cm³. 3 -2.45g / cm 3 .

[0007] In any embodiment, when the battery cell is fully discharged, the compaction density of the negative electrode film is 1.4 g / cm³. 3 -1.5g / cm 3 .

[0008] Controlling the compaction density of the positive and negative electrode films to meet the above range enables the positive and negative electrodes to form a good match, leaving space for the lithium insertion expansion of the negative electrode, further taking into account the particle integrity of the positive electrode active material, and further improving the energy density and cycle life of the battery cell.

[0009] In any embodiment, the single-sided coating mass of the positive electrode film is 0.380 g / 1540 mm. 2 -0.400g / 1540mm 2 .

[0010] Controlling the single-sided coating quality of the positive electrode film to meet the above range enables lithium ions to have a suitable diffusion distance on the positive electrode side while having a high active material loading, further enabling the battery cell to have high energy density and long cycle life.

[0011] In any embodiment, the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction has a particle size D50 of 0.6 μm-0.7 μm.

[0012] In any embodiment, the cumulative distribution curve of the number of particles obtained from the cross section of the negative electrode film along the thickness direction of the electrode sheet shows that the particle size D50 is 15μm-20μm.

[0013] Controlling the number distribution and particle size of particles in the positive and negative electrode films to meet the above-mentioned range can reduce the probability of particle-induced side reactions and further improve the initial efficiency and cycle life of the battery cells.

[0014] In any embodiment, the ratio CB of the negative electrode charging capacity to the positive electrode discharging capacity of the battery cell is 1.05-1.14.

[0015] Matching the charge / discharge capacities of the positive and negative electrodes in a battery cell helps ensure that lithium ions are fully inserted / extracted from both electrodes during charging and discharging. Controlling the ratio (CB) of the negative electrode's charging capacity to the positive electrode's discharging capacity within the aforementioned range allows the negative electrode to have greater redundancy. This facilitates the insertion of more lithium ions into the negative electrode during the first charge, preventing lithium plating caused by uninserted lithium ions accumulating on the negative electrode side. This reduces active lithium loss, allows for full utilization of battery capacity, and improves the cycle life and energy density of the battery cell.

[0016] In any embodiment, the positive electrode film layer and / or the negative electrode film layer includes a conductive agent, which includes one or more of linear conductive agents and dotted conductive agents.

[0017] In any embodiment, the linear conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, and vapor-grown carbon fibers. Optionally, the linear conductive agent includes multi-walled carbon nanotubes.

[0018] Adding a linear conductive agent to the film layer can form a mesh-like conductive network inside the film layer. At the same time, it can embed the active material particles into the mesh-like network, improve the conductivity of the active material, facilitate the full utilization of the specific capacity of the active material, and also improve the diffusion of lithium ions, further improving the energy density and cycle life of the battery cell. It is especially suitable for battery systems with large-particle-size positive and negative electrode active materials or thick coatings.

[0019] In any embodiment, the mass content of the linear conductive agent is 0.5%-2% based on the total mass of the positive electrode film; and / or, the mass content of the linear conductive agent is 0.5%-2% based on the total mass of the negative electrode film.

[0020] While adding a linear conductive agent to the positive electrode film can improve the conductivity of the positive electrode film, it will reduce the mass of active material per unit area of ​​the film. If the mass content of the linear conductive agent is too high, it will be detrimental to the improvement of the energy density of the battery cell. Controlling the mass content of the linear conductive agent in the film to meet the above range can ensure the amount of active material while making full use of the material's specific capacity, so that the battery cell has a long cycle life and high energy density.

[0021] In any embodiment, the electrolyte injection coefficient is 2.8 g / Ah - 3.2 g / Ah.

[0022] Controlling the electrolyte injection coefficient within the aforementioned range ensures both sufficient electrolyte wetting of the battery cell and allows for more space to accommodate active materials, thus improving the cell's energy density. Conversely, continuous electrolyte consumption during battery operation can lead to insufficient electrolyte levels and incomplete reactions of active materials, negatively impacting the cell's cycle life. Conversely, an excessively high electrolyte injection coefficient compresses the internal space, causing volume expansion and gas generation during battery cycles to directly affect the battery casing, leading to deformation and bulging. This is particularly problematic for pouch batteries, potentially causing casing rupture and compromising the cell's safety. Maintaining the electrolyte injection coefficient within the specified range ensures sufficient electrolyte to support charge and discharge reactions throughout the cell's lifespan, improving both cycle life and safety while simultaneously enhancing the cell's energy density.

[0023] In any embodiment, the negative electrode film layer includes a negative electrode active material, and the graphitization degree of the negative electrode active material is 91.5%-95%, optionally 91.5%-92.8%.

[0024] Graphitization degree reflects the integrity of the graphite crystal structure, that is, the regularity of the atomic arrangement in the material structure. High graphitization degree of graphite indicates small interlayer spacing, smaller lattice rotation, less random stacking of layers, and more ordered arrangement, providing more stable lithium intercalation sites. This is beneficial for the intercalation of active lithium ions into the anode material, improving its specific capacity and the first-time efficiency of the battery cell. However, it also indicates tighter interlayer bonding, resulting in greater volume expansion during lithium intercalation. Low graphitization degree of graphite indicates large interlayer spacing and less material expansion during lithium intercalation. However, this reduces the number of stable lithium intercalation sites, which is detrimental to the specific capacity of graphite. In the embodiments of this application, the graphitization degree of the anode active material is within the above range. The anode active material achieves both excellent specific capacity and low volume expansion during lithium intercalation, and the battery cell further achieves excellent energy density, cycle life, and first-time efficiency.

[0025] In any embodiment, the peak intensity ratio (OI) of the diffraction peaks of the 004 and 110 crystal planes of carbon in the X-ray diffraction pattern of the negative electrode film is 2-4, and can be selected as 2-2.9.

[0026] When the planar structure of graphite in the negative electrode film is perpendicular to the electrode plane, it helps reduce the expansion force of the negative electrode film along the thickness direction, and also provides shorter diffusion paths and more insertion / extraction channels for active ions. In the X-ray diffraction pattern of the negative electrode film, the diffraction peak signal of the 004 crystal plane of carbon comes from the graphite with a planar structure parallel to the electrode plane, and the diffraction signal of the 110 crystal plane of carbon comes from the graphite with a planar structure perpendicular to the electrode plane. The OI value of the negative electrode film meets the above range, which on the one hand is conducive to the insertion of lithium ions on the negative electrode side, improves the lithium ion insertion rate, and makes the negative electrode capacity more fully utilized, further improving the energy density of the battery cell; on the other hand, it can effectively reduce the expansion of the negative electrode during operation, which is beneficial to improving the cycle life of the battery cell.

[0027] In any embodiment, the particle size D10 of the positive electrode film layer in the cross section along the thickness direction is 0.1 μm-0.4 μm.

[0028] In any embodiment, the particle size D90 of the positive electrode film layer in the cross-section along the thickness direction is 0.8 μm-1 μm.

[0029] In any embodiment, the particle size D99 of the positive electrode film layer in the cross-section along the thickness direction is 1μm-10μm.

[0030] In the cumulative distribution curve of particle number obtained by cross-section along the thickness direction of the positive electrode film, the particle number distribution particle size D10, D90, and D99 meet the above range. The particles in the positive electrode film can meet the particle gradation theory, realize the close packing of particles inside the film, and further improve the energy density of the battery cell.

[0031] In any embodiment, the particle size D10 of the particles in the cross-section along the thickness direction of the negative electrode film is 4μm-10μm.

[0032] In any embodiment, the particle size D90 of the particles in the cross-section along the thickness direction of the negative electrode film is 25μm-45μm.

[0033] In any embodiment, the particle size D99 of the particles in the cross-section along the thickness direction of the negative electrode film is 40μm-65μm.

[0034] In the cumulative distribution curve of particle number obtained from the cross-section of the negative electrode film along the thickness direction of the electrode sheet, the particle number distribution particle size D10, D90, and D99 meet the above range. On the one hand, the negative electrode particles have a large specific surface area and low activity, which can reduce the probability of side reactions occurring during the first charge and discharge process of the battery, thereby further improving the first efficiency of the battery cell. On the other hand, the distribution of negative electrode particles is more uniform, which is conducive to the insertion of lithium ions on the negative electrode side, effectively reducing the probability of lithium plating, while reducing the volume expansion on the negative electrode side, thereby improving the cycle life of the battery.

[0035] In any embodiment, the positive electrode film layer includes a positive electrode active material, which comprises lithium-containing transition metal phosphate particles with at least a portion of their surface coated with carbon material. The lithium-containing transition metal phosphate particles have the following general formula: Li m Fe x P y O j Q q Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.6≤m≤1.15, 0≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤1.

[0036] Lithium-containing transition metal phosphates are generally polyanionic active materials with an olivine structure. Thanks to the intrinsically stable olivine structure, batteries using them as positive electrode active materials can maintain a high capacity retention rate during charge and discharge cycles, resulting in excellent cycle life for individual battery cells.

[0037] In any embodiment, the negative electrode active material includes one or more of artificial graphite, natural graphite, modified natural graphite, microcrystalline graphite, soft carbon, and hard carbon.

[0038] Using the aforementioned materials as the negative electrode active material in a battery cell enables the negative electrode to have a higher lithium intercalation capacity, further improving the energy density of the battery cell. In addition, negative electrode active materials represented by artificial graphite and natural graphite have a lower degree of graphitization and a lower OI value. Their greater isotropy can effectively reduce the expansion of the negative electrode sheet during operation, thereby further improving the cycle life of the battery cell.

[0039] In any embodiment, the single-sided coating mass of the negative electrode film is 0.170 g / 1540 mm. 2 -0.200g / 1540mm 2 Available in 0.180g / 1540mm 2 -0.200g / 1540mm 2 .

[0040] Controlling the coating quality of the negative electrode film to meet the above range is beneficial to improving the charging capacity of the negative electrode sheet, which can form a good match with the discharge capacity of the positive electrode sheet, realize the good extraction / intercalation of lithium ions inside the battery, facilitate the full utilization of battery capacity, and improve the energy density of the battery cell. In addition, controlling the thickness of the negative electrode film coating increases the proportion of active material in the negative electrode sheet relative to the current collector, further improving the energy density of the battery cell.

[0041] In any embodiment, the thickness of the positive electrode film layer on one side is 96 μm-113 μm; and / or, the thickness of the negative electrode film layer on one side is 71 μm-96 μm.

[0042] Controlling the thickness of the positive electrode film layer on one side to meet the above-mentioned range ensures the loading of the positive electrode active material, resulting in high energy density in the battery cell. Furthermore, the optimized internal space design of the battery provides space for the negative electrode, mitigating the performance drop caused by the expansion of the negative electrode during charging and discharging that encroaches on the positive electrode space. This allows the battery cell to maintain both high energy density and good cycle life. Controlling the thickness of the negative electrode film layer on one side also increases the proportion of negative electrode active material relative to the current collector, improving the lithium intercalation capacity of the negative electrode and further enhancing the energy density of the battery cell. Additionally, the spatial design creates a good match with the structure of the positive electrode, facilitating further utilization of the battery's specific capacity while also improving the cycle life of the battery cell.

[0043] In any embodiment, the thickness of the positive current collector is 14 μm-16 μm; and / or, the thickness of the negative current collector is 7 μm-9 μm.

[0044] Using large particles in the active material is beneficial for improving the initial efficiency of the battery. However, during electrode processing, large particles can compress the current collector, leading to damage to the current collector and electrode breakage. In the embodiments of this application, the thickness of the current collector in the battery cell is controlled within the aforementioned range, which can effectively reduce the probability of current collector damage and electrode breakage due to cold pressing, thereby improving the yield rate of electrode processing. Furthermore, it can ensure that the current collector does not crack during long-term cycling, improving the long-term stability and safety of the battery.

[0045] In any embodiment, the isolation membrane includes a base membrane and a ceramic coating disposed on at least one side surface of the base membrane.

[0046] In any embodiment, the ceramic coating comprises ceramic particles and a binder, wherein the ceramic particles comprise one or more of boehmite, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, magnesium nitride, or barium titanate, and the binder comprises polyvinylidene fluoride.

[0047] The use of the aforementioned ceramic particles in the separator ceramic coating can effectively improve electrolyte wettability, which is beneficial to improving the cycle life of the battery cells. Furthermore, the use of the aforementioned binders can form a three-dimensional fibrous network within the coating, improving the uniformity of adhesion within the coating. Compared to spraying binder particles onto the surface of ceramic particles, dissolving the binder and ceramic particles in a solvent and rolling them onto the base film surface can further improve the uniformity of the binder in the coating, resulting in more uniform adhesion between the electrode and the separator, and further improving electrolyte wettability and the cycle life of the battery cells.

[0048] In any embodiment, the separator includes a base film and a ceramic coating disposed on both sides of the base film.

[0049] In any embodiment, the battery cell is a stacked battery or a wound battery.

[0050] In any embodiment, the battery cell includes a housing, the housing being made of a pouch material, the pouch material being an aluminum-plastic film.

[0051] In any embodiment, the length of the battery cell is L, the width is W, and the thickness is T. The dimensions of the battery cell satisfy: 550mm≤L≤650mm, 110mm≤W≤140mm, and 15mm≤T≤20mm.

[0052] Controlling the thickness of the pouch cell to meet the above-mentioned range indicates that the electrode assembly has an appropriate thickness. This ensures energy density while effectively reducing the expansion force of the individual cells, preventing performance degradation due to increased negative electrode expansion, and thus improving cycle life. Furthermore, it facilitates rapid heat transfer from the cell's interior to the surface, allowing direct contact with air or water-cooled plates, improving cooling efficiency and reducing electrolyte decomposition caused by increased operating temperature, thereby enhancing cycle life and safety. Maintaining the cell's length and width within the above-mentioned range improves energy density while also ensuring proper electrolyte wetting of the membrane layer, further improving cycle life.

[0053] An embodiment of the second aspect of this application provides a battery device that includes the battery cell described in the above embodiments.

[0054] An embodiment of the third aspect of this application provides an electrical device that includes the battery device described in the above embodiments, the battery device being used to provide electrical energy.

[0055] An embodiment of the fourth aspect of this application provides an energy storage device, which includes the battery device described in the above embodiments, the battery device being used to store electrical energy.

[0056] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0057] 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.

[0058] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0059] Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of this application is shown.

[0060] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0061] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0062] Figure 5 yes Figure 4An exploded view of a battery pack according to one embodiment of this application is shown;

[0063] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0064] Explanation of reference numerals in the attached figures:

[0065] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0066] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, battery assembly, power consumption device, and energy storage device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0067] 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.

[0068] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0069] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0070] 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.

[0071] 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.

[0072] 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).

[0073] In current technology, the cycle life of power batteries is generally around 2000 cycles, while the market demand for energy storage batteries has reached >5000 cycles. Current methods to improve battery life mainly include optimizing material structure stability (such as using less fragile single-crystal cathode particles and adding a coating layer to the particle surface to suppress the dissolution of transition metal ions), but these inevitably sacrifice battery energy density. How to achieve such a high cycle life while maintaining sufficient energy density is a pressing technical problem that needs to be solved in this field.

[0074] Based on this, this application provides a battery cell, which includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. In a fully discharged state, the compaction density of the positive electrode film layer is 2.3 g / cm³. 3 -2.5g / cm 3The single-sided coating mass of the positive electrode film is 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2 The cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the thickness direction of the electrode sheet shows a particle size D50 of 0.4 μm-0.8 μm; and the compaction density of the negative electrode film in the fully discharged state of the battery cell is 1.35 g / cm³. 3 -1.55g / cm 3 The cumulative particle number distribution curve obtained from the cross section of the negative electrode film along the electrode thickness direction has a particle size distribution D50 of 10μm-25μm, where D50 refers to the particle size corresponding to the cumulative particle number distribution reaching 50% in the cumulative number distribution curve.

[0075] The applicant's research revealed that when the cumulative particle size distribution curve obtained from the cross-section of the positive electrode film along the thickness direction of the electrode sheet shows a particle size distribution D50 of less than 0.4 μm, or when the cumulative particle size distribution curve obtained from the cross-section of the negative electrode film along the thickness direction of the electrode sheet shows a particle size distribution D50 of less than 10 μm, the particles in the positive and negative films are small in size and have a large specific surface area. This increases the probability of side reactions with the electrolyte, leading to severe irreversible loss of active lithium ions in the battery and low initial efficiency. This makes it difficult to meet the requirement of achieving a cycle life of more than 6400 cycles when the battery's working discharge capacity decays to 80%.

[0076] In the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the thickness direction of the electrode sheet, if the particle number distribution particle size D50 is greater than 0.8 μm, or in the cumulative particle number distribution curve obtained from the cross-section of the negative electrode film along the thickness direction of the electrode sheet, if the particle number distribution particle size D50 is greater than 25 μm, it can effectively reduce the probability of side reactions inside the battery caused by small particles and improve the first efficiency of the battery cell. However, excessively large particles make the electron transport path too long, aggravate the polarization phenomenon of the battery, and lead to the decay of the cycle life of the battery cell.

[0077] Furthermore, the applicant's research also found that when the compaction density of the positive and negative electrode films is high, the porosity of the films is low, which is not conducive to the wetting of the films by the electrolyte, and thus affects the extraction / intercalation of lithium ions. In particular, it is not conducive to the wetting of the negative electrode films by the electrolyte and the intercalation of lithium ions in the negative electrode, which in turn leads to lithium plating on the surface of the negative electrode sheet and deteriorates the cycle life of the battery cells.

[0078] Further research by the applicant revealed that the single-sided coating quality of the positive electrode film was less than 0.370 g / 1540 mm. 2This can lead to insufficient active material loading in a single battery cell of the same volume. Although the battery cell has excellent cycle life, its energy density cannot meet the requirements of energy storage batteries for an energy density of over 380Wh / L. Conversely, excessively high single-sided coating quality of the positive electrode film, while beneficial to increasing the active material loading and battery energy density, will increase the lithium-ion diffusion distance and reduce the wettability of the electrolyte to the active material near the current collector of the film, which is detrimental to the battery's electrical performance, especially cycle life.

[0079] In summary, the battery cells provided in this application use positive electrode active material particles with a number distribution particle size D50 of 0.4μm-0.8μm for the positive electrode and negative electrode active material particles with a number distribution particle size D50 of 10μm-25μm for the negative electrode. This approach aims to reduce the probability of particle-induced side reactions and polarization phenomena, thereby improving the first-cycle coulombic efficiency and cycle life of the battery cells. Furthermore, the compaction density of the negative electrode film is controlled to be 1.35 g / cm³. 3 -1.55g / cm 3 The positive electrode film has a compaction density of 2.3 g / cm³. 3 -2.5g / cm 3 This design allows the negative electrode film to have high porosity and improve cycle life, while the compaction design of the positive electrode can be well matched with the low compaction design of the negative electrode sheet. It also allows space for volume expansion during the lithium insertion / extraction process of the negative electrode, while maintaining the particle integrity of the positive electrode active material during compaction, thus improving both the energy density and cycle life of the battery cell. Furthermore, this is combined with controlling the single-sided coating mass of the positive electrode film to 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2 By employing a thick coating design, energy density is improved while the positive electrode film has suitable lithium-ion diffusion distance and resistance, thus ensuring cycle life. This application, through the combination of positive and negative electrode sheets, enables the battery cell to achieve both long cycle life and high energy density, meeting performance requirements.

[0080] In this application, the term "particle" refers to a particle in the positive and / or negative electrode film layers that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist within the particle, but no complete boundary sufficient to separate the particle can be identified within it. Understandably, the particles in the film layer mainly originate from the active material particles. Although other additives in the film layer preparation (such as binders and additives) also have particle characteristics, their addition amount in the film layer is much smaller than that of the active material. Therefore, the particle size distribution in the film layer is mainly contributed by the active material and can reflect the true state of the active material in the film layer.

[0081] When used in this paper, the particle size distribution (D50) of the positive electrode film layer in the cross-section along the thickness direction can be determined using methods known in the art. As an example, the following method can be used for testing: Disassemble the battery cell, remove the positive electrode sheet, and perform SEM testing on the cross-section of the electrode sheet (e.g., ZEISS electron microscope, magnification 10000X). Statistically analyze the size of all particles on a single SEM image. This can be done using software or manually. The particle size is taken as the longest diameter of the particles in the image. The longest diameter of a particle refers to the maximum distance between any two points on the outer edge of the particle, i.e., the maximum size of the particle in different directions. Arrange the particle sizes from smallest to largest and take the 50th quantile as the particle size distribution (D50) of the positive electrode active material particles in the cross-section along the thickness direction of the positive electrode film layer in the SEM image. Repeat the above operation multiple times, statistically analyzing multiple different regions (e.g., 10) of the same electrode sheet, and take the average value as the particle size distribution (D50) of the cumulative particle distribution curve obtained from the cross-section along the thickness direction of the positive electrode film layer of the sample under test.

[0082] Understandably, the particle size distribution (D50) of particles in the membrane layer can be controlled using methods known in the art. For example, the mechanical force of crushing and grinding processes can be used to process raw materials to the target particle size distribution range, thus adjusting the particle size; screening and grading equipment can be used to separate the particle system by size, thereby obtaining the required particle size; and precise control of the feed rate, adjusting the residence time and stress state of particles within the equipment, also helps to control the particle size.

[0083] During the compaction process, the positive electrode film is compacted in the thickness direction. Therefore, the cross-section of the positive electrode film along the thickness direction is more able to reflect the actual compaction status of the particles inside the film in a spatial scale than the surface of the positive electrode film.

[0084] Understandably, existing technologies typically employ laser particle size analyzers to statistically analyze the particle size of positive electrode active materials using Malvern laser diffraction. However, the applicant's research indicates that because small-sized particles are prone to agglomeration, the test results obtained using Malvern laser diffraction, based on the principle of laser scattering, often only reflect the particle size of the agglomerates. This does not accurately reflect the particle size within the positive electrode active material, nor does it reflect the dispersion state of the positive electrode active material within the film layer, as the dispersion of the positive electrode active material within the film layer increases during slurry preparation and film-forming rolling. The test results obtained by Malvern laser diffraction are affected by the particle size, specific surface area, and degree of agglomeration of the positive electrode active material. Compared to the actual dispersion within the electrode sheet, the number of large particles obtained by this test is lower than the actual value, while the number of small particles is higher. Therefore, the particle size obtained by Malvern laser diffraction cannot be equated with or analogized to the particle size statistically obtained in the embodiments of this application.

[0085] It is understandable that the particle size distribution D50 in the cumulative distribution curve of particles obtained from the cross-section of the negative electrode film along the thickness direction of the electrode sheet can also be determined using the particle size distribution D50 measurement method described above in the cumulative distribution curve of particles obtained from the cross-section of the positive electrode film along the thickness direction of the electrode sheet.

[0086] When used in this document, the compaction density of the positive electrode film layer of the battery cell in its fully discharged state can be determined using methods known in the art. As an example, the following method can be used for testing: Place the battery cell in a 25°C oven environment and let it stand for 2 hours. After the battery temperature is maintained at 25°C, discharge the battery at a constant current of 1 / 3C to 2.5V and then discharge it at a constant current of 0.1C to 2.0V. Disassemble the battery to obtain the positive electrode sheet. Treat the residual electrolyte with dimethyl carbonate solvent, dry the electrode sheet, and cut it into small circular pieces with an area of ​​S. Obtain its mass as W1 and measure the thickness T1 of the positive electrode sheet using a micrometer. Then wipe off the positive electrode film layer of the weighed electrode sheet, weigh the current collector and record it as W2, and measure the thickness T2 of the current collector using a micrometer. Then the compaction density of the positive electrode film layer PD = (W1-W2) / [(T1-T2)×S]. To ensure the accuracy of the test results, multiple groups (e.g., 10 groups) of samples can be tested, and the average value can be calculated as the test result.

[0087] It is understood that the compaction density of the negative electrode film layer in the fully discharged state of the battery cell can be determined using the positive electrode film layer compaction density measurement method described above.

[0088] In this document, the single-sided coating mass of the positive electrode film has a meaning known in the art and can be tested using methods known in the art. For example, a positive electrode sheet can be taken from a disassembled battery cell (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), cut into a small circular piece with an area of ​​S1, and its mass can be weighed and recorded as M1. Then, the positive electrode film layer of the weighed positive electrode sheet can be wiped off, and the mass of the current collector can be weighed and recorded as M0. The single-sided coating mass of the positive electrode film = (M1-M0) / S1. To ensure the accuracy of the test results, multiple sets (e.g., 10 sets) of samples can be tested, and the average value can be calculated as the test result.

[0089] In some embodiments, the particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction, wherein the particle size D50 can be selected as 0.4μm, 0.42μm, 0.45μm, 0.48μm, 0.5μm, 0.52μm, 0.55μm, 0.58μm, 0.6μm, 0.62μm, 0.65μm, 0.68μm, 0.7μm, 0.72μm, 0.75μm, 0.78μm, 0.8μm, or any range between any two of the above values.

[0090] In some embodiments, the compaction density of the positive electrode film layer in the fully discharged state of the battery cell can be selected as 2.3 g / cm³. 3 2.31 g / cm 3 2.32 g / cm 3 2.33 g / cm 3 2.34 g / cm 3 2.35g / cm 3 2.36 g / cm 3 2.37 g / cm 3 2.38g / cm 3 2.39 g / cm 3 2.40 g / cm 3 2.41 g / cm 3 2.42 g / cm 3 2.43 g / cm 3 2.44 g / cm 3 2.45g / cm 3 2.46 g / cm 3 2.47 g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.5g / cm 3 , or any range between any two of the above values.

[0091] In some embodiments, the single-sided coating weight of the positive electrode film can be selected as 0.370 g / 1540 mm. 2 0.372g / 1540mm 2 0.375g / 1540mm 2 0.378g / 1540mm 2 0.380g / 1540mm 2 0.382g / 1540mm 2 0.385g / 1540mm 2 0.388g / 1540mm 20.390g / 1540mm 2 0.392g / 1540mm 2 0.395g / 1540mm 2 0.397g / 1540mm 2 0.400g / 1540mm 2 , or any range between any two of the above values.

[0092] In some embodiments, the particle number distribution curve obtained from the cross-section of the negative electrode film layer along the electrode thickness direction, wherein the particle size D50 can be selected as 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, or any range between any two of the above values.

[0093] In some embodiments, the compaction density of the negative electrode film layer in the fully discharged state of the battery cell can be selected as 1.35 g / cm³. 3 1.36 g / cm 3 1.37g / cm 3 1.38g / cm 3 1.39 g / cm 3 1.40 g / cm 3 1.41 g / cm 3 1.42g / cm 3 1.43 g / cm 3 1.44 g / cm 3 1.45g / cm 3 1.46 g / cm 3 1.47 g / cm 3 1.48g / cm 3 1.49 g / cm 3 1.50g / cm 3 1.51g / cm 3 1.52g / cm 3 1.53g / cm 3 1.54g / cm 3 1.55g / cm 3 , or any range between any two of the above values.

[0094] In some embodiments, the compaction density of the positive electrode film layer in the fully discharged state of the battery cell is 2.3 g / cm³. 3 -2.45g / cm 3 .

[0095] In some embodiments, the compaction density of the negative electrode film layer in the fully discharged state of the battery cell is 1.4 g / cm³. 3 -1.5g / cm 3 .

[0096] Controlling the compaction density of the positive and negative electrode films to meet the above range enables the positive and negative electrodes to form a good match, leaving space for the lithium insertion expansion of the negative electrode, further taking into account the particle integrity of the positive electrode active material, and further improving the energy density and cycle life of the battery cell.

[0097] In some embodiments, the single-sided coating mass of the positive electrode film is 0.380 g / 1540 mm. 2 -0.400g / 1540mm 2 .

[0098] Controlling the single-sided coating quality of the positive electrode film to meet the above range enables lithium ions to have a suitable diffusion distance on the positive electrode side while having a high active material loading, further enabling the battery cell to have high energy density and long cycle life.

[0099] In some embodiments, the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction has a particle size D50 of 0.6 μm-0.7 μm.

[0100] In some embodiments, the cumulative particle number distribution curve obtained from the cross section of the negative electrode film along the electrode thickness direction shows that the particle size D50 is 15μm-20μm.

[0101] Controlling the number distribution and particle size of particles in the positive and negative electrode films to meet the above-mentioned range can reduce the probability of particle-induced side reactions and further improve the initial efficiency and cycle life of the battery cells.

[0102] In some embodiments, the ratio CB of the negative electrode charging capacity to the positive electrode discharging capacity of the battery cell is 1.05-1.14.

[0103] When used herein, the ratio of the negative electrode specific capacity to the positive electrode specific capacity of the battery cell, CB, can be determined using methods known in the art. As an example, the following method can be used for testing: Step 1) Average discharge capacity test of the single-sided active material layer of the positive electrode. Take the disassembled positive electrode sheet and obtain a small disc containing the single-sided active material layer of the positive electrode using a stamping die. Using a lithium metal sheet as the counter electrode, a Celgard membrane as the separator, and a solution of EC+DMC+DEC (ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1) containing LiPF6 (1 mol / L) as the electrolyte, assemble six identical CR2430 coin cells in an argon-protected glove box. ① After battery assembly, let it stand for 12 hours. ② Perform constant current charging at a charging current of 0.1C until the voltage reaches the upper limit cutoff voltage of 3.8V. Then maintain the voltage at 3.8V and perform constant voltage charging until the current is 50μA. ③ Let it stand for 5 minutes. ④ Perform constant current discharge at a discharge current of 0.1C until the voltage reaches the lower limit cutoff voltage of 2.0V. ⑤ Let it stand for 5 minutes. ⑥ Perform constant current discharge at a discharge current of 0.05C until the voltage reaches the lower limit cutoff voltage of 2.0V. ⑦ Let it stand for 5 minutes. Repeat steps ②-⑦ and record the discharge capacity of the second cycle. The average discharge capacity of the 6 coin cells is the average discharge capacity of the positive electrode single-sided active material layer. Step 2): Test the average charging capacity of the negative electrode single-sided active material layer. Take the negative electrode sheet after disassembling the battery and use a stamping die to obtain a small disc with the same area as the positive electrode disc in step 1) above, which also contains the negative electrode single-sided film layer. Six CR2430 coin cells were assembled in an argon-protected glove box using lithium metal sheets as the counter electrode, Celgard membrane as the separator, and a solution of EC+DMC+DEC (ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1) containing LiPF6 (1 mol / L) as the electrolyte. ① After battery assembly, let it stand for 12 hours. ② Perform constant current discharge at a discharge current of 0.05C until the voltage reaches the lower cutoff voltage of 0.005mV. ③ Then perform constant current discharge at a discharge current of 50μA until the voltage reaches the lower cutoff voltage of 0.005mV. ④ Let it stand for 5 minutes. ⑤ Then perform constant current discharge at a discharge current of 10μA until the lower cutoff voltage reaches 0.005mV. ⑥ Let it stand for 5 minutes. ⑦ Finally, perform constant current charging at a charging current of 0.1C until the final voltage reaches the upper cutoff voltage of 2V. ⑧ Let it stand for 5 minutes. Repeat steps ②-⑧ and record the charging capacity of the second cycle. The average charging capacity of the 6 coin cells is the average charging capacity of the negative electrode single-sided film layer. Step 3): Calculate the CB value according to the formula: CB value = average charging capacity (mAh) of the negative electrode single-sided active material layer / average discharge capacity (mAh) of the positive electrode single-sided active material layer.

[0104] In some embodiments, the ratio CB of the negative electrode charging capacity to the positive electrode discharging capacity of the battery cell can be selected as 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, or any range between any two of the above values.

[0105] Matching the charge / discharge capacities of the positive and negative electrodes in a battery cell helps ensure that lithium ions are fully inserted / extracted from both electrodes during charging and discharging. Controlling the ratio (CB) of the negative electrode's charging capacity to the positive electrode's discharging capacity within the aforementioned range allows the negative electrode to have greater redundancy. This facilitates the insertion of more lithium ions into the negative electrode during the first charge, preventing lithium plating caused by uninserted lithium ions accumulating on the negative electrode side. This reduces active lithium loss, allows for full utilization of battery capacity, and improves the cycle life and energy density of the battery cell.

[0106] [Positive electrode plate]

[0107] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0108] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0109] In some embodiments, the positive electrode film layer includes a conductive agent, which includes one or more of linear conductive agents and dotted conductive agents.

[0110] As used herein, the terms "linear conductive agent" and "dot conductive agent" have the meanings known in the art. A linear conductive agent is a conductive agent with a one-dimensional fiber morphology that can form a continuous conductive network in the film layer; a dot conductive agent is a conductive agent with a non-linear particle morphology that forms a local conductive network between the film layers through multi-point contact.

[0111] In some embodiments, the linear conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, and vapor-grown carbon fibers.

[0112] As used herein, the terms "single-walled carbon nanotubes" and "multi-walled carbon nanotubes" have their well-known meanings in the art. Single-walled carbon nanotubes refer to carbon materials with a tubular structure formed by the coiling of a single layer of graphene sheets. Multi-walled carbon nanotubes, as understood, refer to tubular carbon materials formed by the coaxial coiling and nesting of multiple layers (greater than or equal to two layers) of graphene sheets. As used herein, "carbon nanofibers" refer to fibrous nanomaterials composed of carbon elements, formed by the stacking, coiling, or conical helical arrangement of multiple layers of graphene sheets, some of which may contain amorphous carbon; the interlayers exhibit a certain degree of disorder or tilted stacking, and can be prepared by catalytic pyrolysis. As used herein, "vapor-phase grown carbon fibers" refer to fibrous carbon materials grown directly in the gas phase by chemical vapor deposition (CVD) using gaseous hydrocarbons (such as methane, ethylene, benzene, etc.) as the carbon source, under high temperature (800–1200℃) and the action of a catalyst (transition metals such as iron, nickel, or their nanoparticles).

[0113] Adding a linear conductive agent to the film layer can form a mesh-like conductive network inside the film layer. At the same time, it can embed the active material particles into the mesh-like network, improve the conductivity of the active material, facilitate the full utilization of the specific capacity of the active material, and also improve the diffusion of lithium ions, further improving the energy density and cycle life of the battery cell. It is especially suitable for battery systems with large-particle-size positive and negative electrode active materials or thick coatings.

[0114] In this document, the linear conductive agent in the film layer can be determined using methods and instruments known in the art. As an example, cross-sectional polished scanning electron microscopy (CP-SEM) images of the positive / negative electrode film layer are taken for observation and determination.

[0115] In some embodiments, based on the total mass of the positive electrode film, the mass content of the linear conductive agent is 0.5%-2%, and 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%, or a range between any two of the above values.

[0116] While adding a linear conductive agent to the positive electrode film can improve the conductivity of the positive electrode film, it will reduce the mass of active material per unit area of ​​the film. If the mass content of the linear conductive agent is too high, it will be detrimental to the improvement of the energy density of the battery cell. Controlling the mass content of the linear conductive agent in the film to meet the above range can ensure the amount of active material while making full use of the material's specific capacity, so that the battery cell has a long cycle life and high energy density.

[0117] In some embodiments, the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction has a particle size D10 of 0.1μm-0.4μm, which can be selected as 0.1μm, 0.12μm, 0.15μm, 0.18μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, or any range between any two of the above values.

[0118] In some embodiments, the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction shows that the particle size D90 is 0.8 μm-1 μm, which can be selected as 0.8 μm, 0.81 μm, 0.82 μm, 0.83 μm, 0.84 μm, 0.85 μm, 0.86 μm, 0.87 μm, 0.88 μm, 0.89 μm, 0.90 μm, 0.91 μm, 0.92 μm, 0.93 μm, 0.94 μm, 0.95 μm, 0.96 μm, 0.97 μm, 0.98 μm, 0.99 μm, 1.0 μm, or a range between any two of the above values.

[0119] In some embodiments, the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction shows that the particle size D99 is 1μm-10μm, and can be selected as 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, or a range between any two of the above values.

[0120] In the cumulative distribution curve of particle number obtained by cross-section along the thickness direction of the positive electrode film, the particle number distribution particle size D10, D90, and D99 meet the above range. The particles in the positive electrode film can meet the particle gradation theory, realize the close packing of particles inside the film, and further improve the energy density of the battery cell.

[0121] Understandably, the particle size distributions D10, D90, and D99 in the cumulative particle size distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction can be determined using the same method described above for determining the particle size distribution D50 in the cumulative particle size distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction.

[0122] In some embodiments, the positive electrode film layer includes a positive electrode active material, which comprises lithium-containing transition metal phosphate particles with at least a portion of their surface coated with carbon material. The lithium-containing transition metal phosphate particles have the following general formula: Li m Fex P y O j Q q Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.6≤m≤1.15, 0≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤1.

[0123] In some embodiments, m can be selected as 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, or a range between any two of the above values. In some embodiments, x can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or a range between any two of the above values. In some embodiments, y can be selected as 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or a range between any two of the above values. In some embodiments, j can be selected as 3.5, 3.55, 3.6, 3.65, 3.7, 3.75, 3.8, 3.85, 3.9, 3.95, 4, or a range between any two of the above values. In some implementations, q can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or a range between any two of the above values.

[0124] Lithium-containing transition metal phosphates are generally polyanionic active materials with an olivine structure. Thanks to the intrinsically stable olivine structure, batteries using them as positive electrode active materials can maintain a high capacity retention rate during charge and discharge cycles, resulting in excellent cycle life for individual battery cells.

[0125] In some embodiments, the thickness of the positive electrode film layer on one side is 96μm-113μm, and can be selected as 96μm, 97μm, 98μm, 99μm, 100μm, 101μm, 102μm, 103μm, 104μm, 105μm, 106μm, 107μm, 108μm, 109μm, 110μm, 111μm, 112μm, 113μm, or a range between any two of the above values.

[0126] Controlling the thickness of the positive electrode film layer on one side to meet the above range can, on the one hand, ensure the loading of the positive electrode active material, so that the battery cell has high energy density; on the other hand, by using the reasonable internal space design of the battery to make way for the negative electrode sheet, it is beneficial to improve the performance drop caused by the expansion of the negative electrode sheet during charging and discharging, which squeezes the positive electrode space, so that the battery cell has good cycle life while having high energy density.

[0127] In some embodiments, the thickness of the positive current collector is 14μm-16μm, and can be selected as 14μm, 15μm, 16μm, or any range between the two values ​​mentioned above.

[0128] Using large particles in the active material is beneficial for improving the battery's initial efficiency and cycle life. However, during electrode processing, large particles can compress the current collector, leading to damage and electrode breakage. In the embodiments of this application, the thickness of the current collector in the battery cell is controlled to meet the aforementioned range, which can effectively reduce the probability of current collector damage and electrode breakage due to cold pressing, thereby improving the yield rate of electrode processing. Furthermore, it can ensure that the current collector does not crack during long-term cycling, improving the long-term stability and safety of the battery.

[0129] 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.).

[0130] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0131] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode film layer, such as positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode film layer slurry; coating the positive electrode film layer slurry onto the positive electrode current collector, and obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0132] [Negative electrode plate]

[0133] The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0134] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0135] In some embodiments, the negative electrode film layer includes a conductive agent, which includes one or more of linear conductive agents and dotted conductive agents.

[0136] In some embodiments, the linear conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, and vapor-grown carbon fibers.

[0137] In some embodiments, based on the total mass of the negative electrode film, the mass content of the linear conductive agent is 0.5%-2%, and 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%, or a range between any two of the above values.

[0138] Adding a linear conductive agent to the negative electrode film forms a network conductive structure within the film, which improves the conductivity of the negative electrode layer and enhances its charge-discharge capacity. However, the addition of the linear conductive agent reduces the mass of the negative electrode active material per unit area of ​​the film, directly affecting the insertion of lithium ions into the negative electrode. If the mass of the negative electrode active material is too low, lithium ions cannot be inserted, leading to lithium deposition on the negative electrode side and deteriorating the cycle life of the battery cell. Controlling the content of the linear conductive agent in the negative electrode film to meet the above-mentioned range can improve the conductivity of the negative electrode film while ensuring a good cycle life for the battery cell.

[0139] In some embodiments, the negative electrode film layer comprises a negative electrode active material, the graphitization degree of which is 91.5%-95%, optionally 91.5%, 91.8%, 92%, 92.2%, 92.5%, 92.8%, 93%, 93.2%, 93.5%, 93.8%, 94%, 94.2%, 94.5%, 94.8%, 95%, or a range between any two of the above values. In some embodiments, the graphitization degree of the negative electrode active material is 91.5%-92.8%.

[0140] When used herein, the degree of graphitization of the negative electrode active material has a meaning known in the art and can be determined using instruments and methods known in the art. As an example, it can be determined using the following method: X-ray diffractometer (such as a Bruker D8 Discover) is used for testing, with reference to JISK0131-1996 and JB / T4220-2011, to obtain the average interlayer spacing d002 of the C(002) crystal plane in the material's crystal structure. Then, the degree of graphitization is calculated using the formula g = (0.344 - d002) / (0.344 - 0.3354) × 100%. In the above formula, d002 is the average interlayer spacing of the C(002) crystal plane in the material's crystal structure, expressed in nanometers (nm). Methods for obtaining the negative electrode active material include, but are not limited to, disassembling battery cells and scraping powder from the negative electrode film layer. For example, the battery cell is placed at 25°C and discharged at a constant current of 0.33C to 2.0V. After standing for 5 minutes, it is discharged at a constant current of 0.04C to 2.0V, which is recorded as the fully discharged state. The battery cell is disassembled and the negative electrode is taken out. The negative electrode is dissolved and centrifuged at 3000r / min for more than 30 minutes to remove the binder and other substances in the film layer. Graphite is in the lower layer of the deposit and conductive agent is in the upper layer of the deposit. The graphite in the lower layer is taken out for graphitization degree test.

[0141] Graphitization degree reflects the integrity of the graphite crystal structure, that is, the regularity of the atomic arrangement in the material structure. High graphitization degree of graphite indicates small interlayer spacing, smaller lattice rotation, less random stacking of layers, and more ordered arrangement, providing more stable lithium intercalation sites. This is beneficial for the intercalation of active lithium ions into the anode material, improving its specific capacity and the first-time efficiency of the battery cell. However, it also indicates tighter interlayer bonding, resulting in greater volume expansion during lithium intercalation. Low graphitization degree of graphite indicates large interlayer spacing and less material expansion during lithium intercalation. However, this reduces the number of stable lithium intercalation sites, which is detrimental to the specific capacity of graphite. In the embodiments of this application, the graphitization degree of the anode active material is within the above range. The anode active material achieves both excellent specific capacity and low volume expansion during lithium intercalation, and the battery cell further achieves excellent energy density, cycle life, and first-time efficiency.

[0142] In some embodiments, the peak intensity ratio (OI) of the diffraction peaks of the 004 and 110 carbon planes in the X-ray diffraction pattern of the negative electrode film is 2-4, and can be selected as 2, 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, or any range between the above two values. In some embodiments, the peak intensity ratio (OI) of the diffraction peaks of the 004 and 110 carbon planes in the X-ray diffraction pattern of the negative electrode film is 2-2.9.

[0143] In this application, the peak intensity ratio (OI) of the diffraction peaks of the carbon 004 crystal plane and the carbon 110 crystal plane in the X-ray diffraction pattern of the negative electrode film can be tested using methods known in the art. For example, the battery cell is placed at 25°C, discharged at a constant current of 0.33C to 2.0V, left to stand for 5 minutes, and then discharged at a constant current of 0.04C to 2.0V, which is recorded as the fully discharged state. The battery cell is then disassembled, and the negative electrode sheet is taken to test the single-sided negative electrode film. An X-ray diffractometer (such as a Bruker D8 Discover) can be used for testing. The testing can be performed with reference to JISK0131-1996 and JB / T4220-2011 to obtain the X-ray diffraction pattern of the negative electrode film. According to OI value = I 004 / I 110 The OI value of the negative electrode film was calculated. 004 I is the integrated area of ​​the diffraction peak of the 004 crystal plane of the crystalline carbon in the negative electrode film. 110 This represents the integrated area of ​​the diffraction peak on the 110 crystal plane of the crystalline carbon in the negative electrode film. In the X-ray diffraction analysis of this application, a copper target can be used as the anode target, with CuKα rays as the radiation source. The ray wavelength is 2 = 1.5418 Å, the scanning 2θ angle range is 20°-80°, and the scanning rate is 4° / min. It is understood that the OI value of the negative electrode film can be controlled by changing the parameters in the cold pressing process (e.g., controlling the pressure during the rolling pressing process to be relatively low), or by changing the type of negative electrode active material, such as using a negative electrode active material with a low degree of graphitization (e.g., natural graphite, artificial graphite, etc.), or by selecting graphite raw materials with inherently low OI values.

[0144] When the planar structure of graphite in the negative electrode film is perpendicular to the electrode plane, it helps reduce the expansion force of the negative electrode film along the thickness direction, and also provides shorter diffusion paths and more insertion / extraction channels for active ions. In the X-ray diffraction pattern of the negative electrode film, the diffraction peak signal of the 004 crystal plane of carbon comes from the graphite with a planar structure parallel to the electrode plane, and the diffraction peak signal of the 110 crystal plane of carbon comes from the graphite with a planar structure perpendicular to the electrode plane. The OI value of the negative electrode film meets the above range, which on the one hand is conducive to the insertion of lithium ions on the negative electrode side, improves the lithium ion insertion rate, and makes the negative electrode capacity more fully utilized, further improving the energy density of the battery cell; on the other hand, it can effectively reduce the expansion of the negative electrode during operation, which is beneficial to improving the cycle life of the battery cell.

[0145] In some embodiments, the negative electrode active material includes one or more of artificial graphite, natural graphite, modified natural graphite, microcrystalline graphite, soft carbon, and hard carbon.

[0146] Using the aforementioned materials as the negative electrode active material in a battery cell enables the negative electrode to have a higher lithium intercalation capacity, further improving the energy density of the battery cell. In addition, negative electrode active materials represented by artificial graphite and natural graphite have a lower degree of graphitization and a lower OI value. Their greater isotropy can effectively reduce the expansion of the negative electrode sheet during operation, thereby further improving the cycle life of the battery cell.

[0147] In some embodiments, the cumulative particle number distribution curve obtained from the cross-section of the negative electrode film layer along the electrode thickness direction has a particle size D10 of 4μm-10μm, which can be selected as 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, or any range between any two of the above values.

[0148] In some embodiments, the cumulative particle number distribution curve obtained from the cross-section of the negative electrode film layer along the electrode thickness direction has a particle size D90 of 25μm-45μm, which can be selected as 25μm, 28μm, 30μm, 32μm, 35μm, 38μm, 40μm, 42μm, 45μm, or any two of the above values.

[0149] In some embodiments, the cumulative particle number distribution curve obtained from the cross-section of the negative electrode film layer along the electrode thickness direction has a particle size D99 of 40μm-65μm, which can be selected as 40μm, 42μm, 45μm, 48μm, 50μm, 52μm, 55μm, 58μm, 60μm, 62μm, 65μm, or any range between any two of the above values.

[0150] In the cumulative distribution curve of particle number obtained from the cross-section of the negative electrode film along the thickness direction of the electrode sheet, the particle number distribution particle size D10, D90, and D99 meet the above range. On the one hand, the negative electrode particles have a large specific surface area and low activity, which can reduce the probability of side reactions occurring during the first charge and discharge process of the battery, thereby further improving the first efficiency of the battery cell. On the other hand, the distribution of negative electrode particles is more uniform, which is conducive to the insertion of lithium ions on the negative electrode side, effectively reducing the probability of lithium plating, while reducing the volume expansion on the negative electrode side, thereby improving the cycle life of the battery.

[0151] Understandably, the particle size distributions D10, D90, and D99 in the cumulative particle distribution curve obtained from the cross-section of the negative electrode film along the electrode thickness direction can be determined using the particle size distribution D50 measurement method described above in the cumulative particle distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction.

[0152] In some embodiments, the coating mass of the negative electrode film is 0.170 g / 1540 mm. 2 -0.200g / 1540mm 2 Available in 0.170g / 1540mm 2 0.172g / 1540mm 2 0.175g / 1540mm 2 0.178g / 1540mm 2 0.18g / 1540mm 2 0.182g / 1540mm 2 0.185g / 1540mm 2 0.188g / 1540mm 2 0.190g / 1540mm 2 0.192g / 1540mm 2 0.195g / 1540mm 2 0.198g / 1540mm 2 0.2g / 1540mm 2 , or the range between any two of the above values.

[0153] In some embodiments, the coating mass of the negative electrode film is 0.180 g / 1540 mm. 2 -0.200g / 1540mm 2 .

[0154] Controlling the coating quality of the negative electrode film to meet the above range is beneficial to improving the charging capacity of the negative electrode sheet, which can form a good match with the discharge capacity of the positive electrode sheet, realize the good extraction / intercalation of lithium ions inside the battery, facilitate the full utilization of battery capacity, and improve the energy density of the battery cell. In addition, controlling the thickness of the negative electrode film coating increases the proportion of active material in the negative electrode sheet relative to the current collector, further improving the energy density of the battery cell.

[0155] Understandably, the coating quality of the negative electrode film can be determined using the coating quality measurement method for the positive electrode film described above.

[0156] In some embodiments, the thickness of the negative electrode film layer on one side is 71μm-96μm, and can be selected as 71μm, 72μm, 73μm, 74μm, 75μm, 76μm, 77μm, 78μm, 79μm, 80μm, 81μm, 82μm, 83μm, 84μm, 85μm, 86μm, 87μm, 88μm, 89μm, 90μm, 91μm, 92μm, 93μm, 94μm, 95μm, 96μm, or a range between any two of the above values.

[0157] Controlling the thickness of the negative electrode film on one side to meet the above range can, on the one hand, increase the proportion of the negative electrode active material relative to the current collector, increase the lithium intercalation capacity of the negative electrode sheet, and further improve the energy density of the battery cell; on the other hand, through spatial design, it can form a good match with the structure of the positive electrode sheet, which is conducive to further realizing the battery's specific capacity while also improving the cycle life of the battery cell.

[0158] In some embodiments, the thickness of the negative electrode current collector is 7μm-9μm, and can be selected as 7μm, 8μm, 9μm, or any range between the two values ​​mentioned above.

[0159] Using large particles in the active material is beneficial for improving the initial efficiency of the battery. However, during electrode processing, large particles can compress the current collector, leading to damage to the current collector and electrode breakage. In the embodiments of this application, the thickness of the current collector in the battery cell is controlled within the aforementioned range, which can effectively reduce the probability of current collector damage and electrode breakage due to cold pressing, thereby improving the yield rate of electrode processing. Furthermore, it can ensure that the current collector does not crack during long-term cycling, improving the long-term stability and safety of the battery.

[0160] As used herein, the term "cold-pressed electrode breakage" has the meaning known in the art, referring to the phenomenon where local defects and cracks occur in the electrode during the cold pressing process, and the breakage occurs during the cold pressing process. Morphological observation of the cold-pressed electrode can be used to determine whether breakage has occurred, and the number of breakages can be counted.

[0161] 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.).

[0162] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive 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).

[0163] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0164] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0165] Electrolyte

[0166] The electrolyte plays a role in conducting ions between the positive and negative electrodes.

[0167] In some embodiments, the electrolyte injection coefficient is 2.8 g / Ah-3.2 g / Ah, and can be selected as 2.8 g / Ah, 2.85 g / Ah, 2.9 g / Ah, 2.95 g / Ah, 3.0 g / Ah, 3.05 g / Ah, 3.1 g / Ah, 3.15 g / Ah, 3.2 g / Ah, or any range between the above two values.

[0168] In this application, the electrolyte filling coefficient of a battery cell refers to the ratio of the mass of electrolyte inside the battery cell to the battery capacity. The electrolyte filling coefficient of a battery cell can be obtained by any method known in the art. For example, the mass of electrolyte in a battery cell can be obtained by the following method: Weigh the battery, and record the mass as M0. Disassemble the battery cell and pour out the free electrolyte. Remove the internal electrode assembly and separate the positive electrode, negative electrode, separator, and mechanical parts. Soak and clean the positive electrode, negative electrode, separator, and mechanical parts using dimethyl carbonate (DMC) solvent for 24-48 hours, repeating the soaking at least three times. Place the aforementioned positive electrode, negative electrode, separator, and mechanical parts in a 100°C oven for at least 24 hours until completely dried. Weigh the dried positive electrode, negative electrode, separator, and mechanical parts, and record the mass as M1. The mass of electrolyte in the battery cell is thus obtained as (M0-M1). The electrolyte filling coefficient is calculated by (M0-M1) / rated capacity of the battery cell. The rated capacity is the nominal capacity of the battery, or the rated capacity is obtained by charging the battery to 3.65V at a charging rate of 0.33C, then charging it to 0.05C at a constant voltage of 3.65V, letting it stand for 10 minutes, and then discharging it to 2.0V at a discharging rate of 0.33C.

[0169] Controlling the electrolyte injection coefficient within the aforementioned range ensures both sufficient electrolyte wetting of the battery cell and allows for more space to accommodate active materials, thus improving the cell's energy density. Conversely, continuous electrolyte consumption during battery operation can lead to insufficient electrolyte levels and incomplete reactions of active materials, negatively impacting the cell's cycle life. Conversely, an excessively high electrolyte injection coefficient compresses the internal space, causing volume expansion and gas generation during battery cycles to directly affect the battery casing, leading to deformation and bulging. This is particularly problematic for pouch batteries, potentially causing casing rupture and compromising the cell's safety. Maintaining the electrolyte injection coefficient within the specified range ensures sufficient electrolyte to support charge and discharge reactions throughout the cell's lifespan, improving both energy density and cycle life and safety.

[0170] In some embodiments, the electrolyte comprises a solvent and an electrolyte salt.

[0171] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0172] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0173] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0174] [Isolation membrane]

[0175] In some implementations, the battery cell also includes a separator.

[0176] In some embodiments, the separator membrane includes a base membrane and a ceramic coating disposed on at least one surface of the base membrane.

[0177] In some embodiments, the ceramic coating comprises ceramic particles and a binder, wherein the ceramic particles comprise one or more of boehmite, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, magnesium nitride, or barium titanate, and the binder comprises polyvinylidene fluoride.

[0178] The use of the aforementioned ceramic particles in the separator ceramic coating can effectively improve electrolyte wettability, which is beneficial to improving the cycle life of the battery cells. Furthermore, the use of the aforementioned binders can form a three-dimensional fibrous network within the coating, improving the uniformity of adhesion within the coating. Compared to spraying binder particles onto the surface of ceramic particles, dissolving the binder and ceramic particles in a solvent and rolling them onto the base film surface can further improve the uniformity of the binder in the coating, resulting in more uniform adhesion between the electrode and the separator, and further improving electrolyte wettability and the cycle life of the battery cells.

[0179] In some embodiments, the separator includes a base film and a ceramic coating disposed on both sides of the base film.

[0180] [Battery cell]

[0181] In some embodiments, the positive electrode, negative electrode, and separator are fabricated into an electrode assembly using a winding or stacking process. In some embodiments, the battery cell is a stacked battery or a wound battery.

[0182] In some embodiments, the battery cell includes a housing, the housing being made of a pouch material, the pouch material being an aluminum-plastic film.

[0183] In some embodiments, the aluminum-plastic film includes a composite film formed with aluminum from one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), and polyethylene (PE).

[0184] In some embodiments, the length of the battery cell is L, the width is W, and the thickness is T, and the dimensions of the casing satisfy: 550mm≤L≤650mm, 110mm≤W≤140mm, and 15mm≤T≤20mm.

[0185] In some embodiments, the length L of the battery cell can be selected as 550mm, 560mm, 570mm, 580mm, 590mm, 600mm, 610mm, 620mm, 630mm, 640mm, 650mm, or any range between any two of the above values.

[0186] In some embodiments, the width W of the battery cell can be selected as 110mm, 112mm, 115mm, 117mm, 120mm, 122mm, 125mm, 127mm, 130mm, 132mm, 135mm, 137mm, 140mm, or a range between any two of the above values.

[0187] In some embodiments, the thickness T of the battery cell can be selected as 15mm, 15.5mm, 16mm, 16.5mm, 17mm, 17.5mm, 18mm, 18.5mm, 19mm, 19.5mm, 20mm, or a range between any two of the above values.

[0188] Controlling the thickness of the pouch cell to meet the above range indicates that the electrode assembly has an appropriate thickness. This ensures energy density while effectively reducing the expansion force of the battery cells, avoiding performance degradation caused by increased negative electrode expansion, and improving the cycle life of the battery. In addition, it facilitates the rapid conduction of heat generated inside the battery cell to the surface, allowing direct contact with heat dissipation devices such as air or water cooling plates, improving heat dissipation and cooling efficiency, reducing electrolyte decomposition caused by increased operating temperature, and further improving the cycle life and safety performance of the battery cells.

[0189] When the length and width of the battery cell are within the above range, it is beneficial to improve the energy density while also ensuring the electrolyte wets the membrane layer and improves cycle life.

[0190] In some embodiments, the housing may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0191] In some embodiments, the casing of the battery cell can be a rigid casing, such as a hard plastic casing, an aluminum casing, or a steel casing. The casing of the battery cell can also be a pouch, such as a soft-pack pouch. The material of the pouch can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate. This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0192] In some implementations, refer to Figure 2The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0193] [Battery Device]

[0194] This application also provides a battery device, which includes the battery cell provided in this application. In some embodiments, the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0195] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0196] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0197] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0198] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0199] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0200] [Electrical appliances]

[0201] In addition, this application embodiment also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application embodiment. The battery cell, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0202] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0203] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0204] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0205] Example

[0206] 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.

[0207] I. Preparation Method

[0208] Example 1

[0209] 1) Preparation of positive electrode sheet

[0210] Lithium iron phosphate (LiFePO4), conductive carbon black, polyvinylidene fluoride (PVDF), and linear conductive agent CNT (multi-walled carbon nanotubes, Chengdu Organic Chemistry Co., Ltd., Chinese Academy of Sciences, TNGM5) were mixed in a mass ratio of 96.2:1:1.8:1, and then N-methylpyrrolidone solvent was added and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated on both surfaces of a 15 μm thick aluminum foil for the positive electrode current collector. After drying, cold pressing, die-cutting, and slitting, the positive electrode sheet was obtained.

[0211] 2) Preparation of negative electrode sheet

[0212] Artificial graphite, conductive carbon black, polystyrene-butadiene rubber (SBR), carboxymethyl cellulose, and CNTs (multi-walled carbon nanotubes, Chengdu Organic Chemistry Co., Ltd., Chinese Academy of Sciences, TNGM5) were mixed in a mass ratio of 97.1:0.7:1:0.6:0.6 and then added to water. The mixture was stirred until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was coated onto both surfaces of an 8 μm thick copper foil used as a negative electrode current collector. After drying and cold pressing, the negative electrode sheet was obtained.

[0213] 3) Preparation of the separating membrane

[0214] A 7μm polyethylene film was used as the base film. A slurry was formed by dissolving boehmite-ceramic binder PVDF in NMP solvent. The slurry was then applied to both sides of the base film using a gravure roller. The coating speed was set at 30 m / min, and the coating thickness was 2 μm on each side. After coating, the film was dried in an oven at 70℃ to obtain the release film.

[0215] 4) Preparation of electrolyte

[0216] Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0217] 5) Battery assembly

[0218] The negative electrode, separator, and positive electrode are arranged in sequence, with the separator positioned between the negative and positive electrodes to provide isolation, resulting in a stacked electrode assembly. The stacked cells are then coated with adhesive to tightly enclose them. The coated electrode assembly is placed in an outer packaging material, an aluminum-plastic film, composed of an inner polypropylene layer, a middle aluminum foil layer, and an outer nylon layer. The aluminum-plastic film packaging is formed and trimmed using a punching machine to achieve the desired shape and size. The aluminum-plastic film is then heat-sealed, vacuum-baked, and allowed to stand. Electrolyte is injected at a rate of 3.0 g / Ah, followed by sealing. The soft-pack battery then undergoes hot and cold pressing operations, and finally, after formation, vacuum degassing, and edge trimming, a single battery cell is obtained.

[0219] Among them, the compaction density of the positive electrode film layer in the fully discharged state of the battery cell is 2.36 g / cm³. 3 The compaction density of the negative electrode film is 1.45 g / cm³. 3 The single-sided coating mass of the positive electrode film is 0.384 g / 1540 mm. 2The cumulative particle number distribution curve obtained from the cross-section along the thickness direction of the positive electrode film shows that the particle size distribution is as follows: D50 is 0.6 μm, D10 is 0.2 μm, D90 is 0.9 μm, and D99 is 5 μm. The single-sided coating mass of the negative electrode film is 0.185 g / 1540 mm. 2 The cumulative particle number distribution curves obtained from the cross-section of the negative electrode film along the thickness direction of the electrode sheet show that the particle size distribution is as follows: D50 = 20 μm, D10 = 5 μm, D90 = 28 μm, and D99 = 50 μm.

[0220] The ratio of the negative electrode charging capacity to the positive electrode discharging capacity of the battery cell is CB, which is 1.1; based on the total mass of the negative electrode film, the mass content of the linear conductive agent is 1%; the graphitization degree of the negative electrode active material is 92.8%; in the X-ray diffraction pattern of the negative electrode film, the peak intensity ratio OI of the diffraction peaks of the 004 crystal plane of carbon and the 110 crystal plane of carbon is 2.9.

[0221] The thickness of the positive electrode film on one side is 105.7 μm; the thickness of the negative electrode film on one side is 82.8 μm.

[0222] The battery cell has a casing length L of 600mm, a width W of 125.6mm, and a thickness T of 17.7mm.

[0223] Comparative Examples 1-2

[0224] The battery cells in Comparative Examples 1-2 were prepared similarly to those in Example 1, except that the particle size of the positive / negative active material particles and the compaction of the positive and negative electrode films were adjusted so that the compaction density of the positive electrode film did not meet the requirement of 2.3 g / cm³ when the battery cell was fully discharged. 3 -2.5g / cm 3 The compaction density of the negative electrode film layer does not meet the requirement of 1.35 g / cm³. 3 -1.55g / cm 3 The cumulative distribution curve of particle number obtained from the cross section of the positive electrode film along the thickness direction of the electrode sheet shows that the particle size D50 does not meet the requirement of 0.4μm-0.8μm; and the cumulative distribution curve of particle number obtained from the cross section of the negative electrode film along the thickness direction of the electrode sheet shows that the particle size D50 does not meet the requirement of 10μm-25μm. The specific preparation parameters are shown in Table 1.

[0225] Comparative Example 3

[0226] The battery cell in Comparative Example 3 was prepared using a similar method to that in Example 1, except that the coating quality on one side of the positive and negative electrodes was adjusted. The coating quality on one side of the positive electrode film did not meet the requirement of 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2The specific preparation parameters are shown in Table 1.

[0227] Examples 2-5

[0228] The battery cells in Examples 2-5 are prepared using a similar method to those in Example 1, except that the particle size of the particles in the positive / negative electrode films is adjusted. The specific preparation parameters are shown in Table 1.

[0229] Examples 6-9

[0230] The battery cells in Examples 6-9 are prepared in a similar manner to those in Example 1, except that the cold pressing process of the positive and negative electrode sheets is changed, and the compaction density of the positive / negative electrode film is adjusted. The specific preparation parameters are shown in Table 1.

[0231] Examples 10-13

[0232] The battery cells in Examples 10-13 were prepared in a similar manner to those in Example 1, except that the coating quality of the positive and negative electrode films on one side was adjusted. The specific preparation parameters are shown in Table 1.

[0233] Examples 14-15

[0234] The battery cells in Examples 14-15 were prepared in a similar manner to those in Example 1. The difference was that negative electrode active materials with different degrees of graphitization were used, and the OI value of the negative electrode film was changed by a cold pressing process. The specific preparation parameters are shown in Table 1.

[0235] Examples 16-17

[0236] The battery cells in Examples 16-17 were prepared using a similar method to those in Example 1, except that the electrolyte injection coefficient was adjusted. The specific preparation parameters are shown in Table 1.

[0237] Example 18

[0238] The battery cell of Example 18 was prepared in a similar manner to that of Example 1, except that super P was used instead of linear conductive multi-walled carbon nanotubes in the preparation of the positive electrode film and the negative electrode film.

[0239] Example 19

[0240] The battery cell of Example 19 is prepared in a similar way to that of Example 1, except that positive current collectors and negative current collectors of different thicknesses are used. The thickness of the positive current collector is 13 μm and the thickness of the negative current collector is 5.5 μm.

[0241] Examples 20-21

[0242] The battery cell of Example 20 was prepared using a similar method to that of Example 1, except that the ceramic coating in the separator was applied differently. The specific preparation process is as follows: A 7μm polyethylene film was used as the base film. A slurry was formed by dissolving boehmite ceramic particles mixed with PVDF binder in NMP solvent. The slurry was then applied to one side of the base film using a gravure roller. The coating speed was set at 30 m / min, and the coating thickness was 4 μm on one side. After coating, the film was dried in an oven at 70°C to obtain the separator. During assembly, the side coated with the ceramic coating was aligned with the positive electrode, and the uncoated side was aligned with the negative electrode.

[0243] The battery cell in Example 21 was prepared using a similar method to that in Example 1, except that the preparation method of the ceramic coating in the separator was changed. The specific preparation process is as follows: A 7μm polyethylene film was used as the base film. First, boehmite ceramic particles were dispersed in water to form a slurry. The slurry was then coated on both sides of the base film using a gravure roller. The coating speed was set at 30m / min, and the coating thickness was 2μm on each side. After coating, the film was dried in an oven at 70℃. Then, solid spherical PVDF particles were sprayed onto one surface of the ceramic-coated separator to obtain the separator. The thickness of the ceramic coating on one side was 2μm, and the thickness of the adhesive layer formed by the sprayed PVDF particles was 1μm. During assembly, the adhesive layer coated with PVDF particles was placed facing the negative electrode.

[0244] Example 22

[0245] The battery cell of Example 22 is prepared in a similar way to that of Example 1, except that the thickness of the battery cell is changed and the thickness T of the battery cell is 35 mm.

[0246] Table 1

[0247]

[0248] II. Performance Testing

[0249] 1. Test method for frequency of electrode breakage during cold pressing

[0250] Take the designed coated electrode sheet and conduct a cold pressing experiment corresponding to the target compaction density. Control the cold pressing speed at 30m / min and the cold pressing pressure at ~30 tons during the cold pressing process. Produce 10,000m of cold-pressed electrode sheet and observe the occurrence of strip breakage during the cold pressing process. Record the number of strip breaks as n and the strip breakage frequency as n / 10 (times / km).

[0251] 2. Method for testing the first-cycle coulombic efficiency of a single battery cell

[0252] After the battery has been filled with electrolyte and allowed to stand, it undergoes low-current formation, followed by a 10-minute stand, 14.2-minute constant-current charging at 0.05C, a 10-minute stand, 90-minute constant-current charging at 0.1C, a 10-minute stand, 42-minute constant-current charging at 0.2C, and a 10-minute stand. Then, it undergoes its first charge-discharge cycle, charging at 0.33C to 3.8V, followed by a 30-minute stand, and then charging at 0.05C to 3.8V. Next, it undergoes a 0.33C discharge to 2.0V, followed by a 30-minute stand, and then a 0.05C discharge to 2.0V. The sum of the formation and initial capacity is taken as the initial charge capacity, and the sum of the discharge capacities from both cycles is taken as the initial discharge capacity. The initial efficiency is calculated as: Initial Discharge Capacity / Initial Charge Capacity.

[0253] 3. Cycle life test method

[0254] ① Charge the battery cells at 1.5C rate to 40% State of Charge (SOC) at 25℃; ② Then charge at 1C rate to 60% SOC; ③ Then charge at 0.8C rate to 80% SOC; ④ Finally charge at 0.33C rate to 100% SOC. ⑤ Discharge at a constant current of 1C to 0% SOC, and record the discharge capacity D1 of the first cycle; ⑥ Repeat steps ① to ⑤ above, and record the cycle number when the discharge capacity Dn reaches 80% D1.

[0255] 4. Volumetric energy density

[0256] The battery cells were left to stand at 25°C for 2 hours to ensure the temperature of the lithium-ion secondary battery remained at 25°C. At 25°C, the battery cells were charged at 0.33C to the charging cutoff voltage of 3.8V, and then continued to be charged at this voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of the battery cell). After leaving the battery cells to stand at 25°C for 1 hour, they were discharged at 0.33C to the discharge cutoff voltage of 2.0V at 25°C. The total discharge energy of the battery cells was recorded as E0. The length, width, and height of the battery cells were measured, and the volume of the battery cells was calculated as V0 = length × width × height. The volumetric energy density of the battery cells was calculated as: discharge energy of the battery cells E0 / volume of the battery cells V0.

[0257] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0258] Battery cells for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in the table below.

[0259] Table 2

[0260]

[0261] As can be seen from the results of Examples 1-22 and Comparative Examples 1 and 2 in Table 2, in the cumulative particle number distribution curves obtained from the cross-section along the thickness direction of the positive electrode film, if the particle size D50 is less than 0.4 μm, or in the cumulative particle number distribution curves obtained from the cross-section along the thickness direction of the negative electrode film, if the particle size D50 is less than 10 μm, it will lead to an increase in side reactions caused by small particles in the positive and negative electrode films. This results in severe irreversible loss of active lithium ions in the battery, low initial efficiency, poor cycle life of the battery cells, and failure to meet performance requirements. Conversely, in the cumulative particle number distribution curve obtained from the cross-section along the thickness direction of the positive electrode film, if the particle size D50 is greater than 0.8 μm, or in the cumulative particle number distribution curve obtained from the cross-section along the thickness direction of the negative electrode film, if the particle size D50 is greater than 25 μm, although this can effectively reduce the probability of side reactions caused by small particles inside the battery and improve the first-time efficiency of the battery cell, excessively large particles result in excessively long electron transport paths, exacerbating battery polarization and leading to a decrease in the cycle life of the battery cell. Furthermore, a comparison between Examples 1-22 and Comparative Examples 1 and 2 shows that the compaction of the positive electrode film does not meet the requirement of 2.3 g / cm³. 3 -2.5g / cm 3 And the negative electrode film layer does not meet the requirement of 1.35 g / cm³. 3 -1.55g / cm 3 This is detrimental to the wetting of the film layer by the electrolyte, especially to the wetting of the negative electrode, thus worsening the cycle life of the battery cell. As can be seen from the results of Examples 1-22 and Comparative Example 3, the single-sided coating quality of the positive electrode film layer does not meet the requirement of 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2 This will result in insufficient active material loading in a single battery cell of the same volume. Although the battery cell has excellent cycle life, its energy density is too low to meet performance requirements.

[0262] As can be seen from the comparison of Examples 1-5 in Table 2, when the particle number distribution curves obtained from the cross-section of the positive electrode film along the electrode thickness direction have a particle number distribution diameter D50 of 0.4μm-0.8μm, and further 0.6μm-0.7μm, and when the particle number distribution curves obtained from the cross-section of the negative electrode film along the electrode thickness direction have a particle number distribution diameter D50 of 10μm-25μm, and further 15μm-20μm, the probability of particle-induced side reactions and polarization phenomena can be reduced, so that the battery cell can have high initial efficiency, long cycle life and high energy density.

[0263] As can be seen from the results of Examples 1 and 6-9 in Table 2, the compaction density of the negative electrode film layer of the battery cell under fully discharged state is 1.35 g / cm³.3 -1.55g / cm 3 Further, it was 1.4 g / cm³. 3 -1.5g / cm 3 Simultaneously, the positive electrode film layer has a compaction density of 2.3 g / cm³. 3 -2.5g / cm 3 Further, it was 2.3 g / cm³. 3 -2.45g / cm 3 At that time, the negative electrode film has a high porosity, which can improve the cycle life of the battery. It can also form a good match with the low compaction design of the negative electrode by utilizing the compaction design of the positive electrode. This allows space for the volume expansion during the lithium insertion / extraction process of the negative electrode, while taking into account the particle integrity of the positive electrode active material during the compaction process. This can improve the energy density and cycle life of the battery cell and meet the performance requirements.

[0264] As can be seen from the results of Examples 1 and 10-13 in Table 2, the single-sided coating mass of the positive electrode film is 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2 Further reduced to 0.380g / 1540mm 2 -0.400g / 1540mm 2 By employing a thick coating design for the positive electrode, the loading of active materials is increased, thereby improving the energy density of the battery cell. Simultaneously, the positive electrode film possesses suitable lithium-ion diffusion distance and resistance, thus enhancing the battery's cycle life. Furthermore, the single-sided coating weight of the negative electrode film is 0.170g / 1540mm. 2 -0.200g / 1540mm 2 Further options include 0.180g / 1540mm. 2 -0.200g / 1540mm 2 It forms a good match with the positive electrode sheet, realizing the insertion and extraction of lithium ions inside the battery, which is conducive to the full utilization of battery capacity and improves the energy density of the battery cell; in addition, controlling the thickness of the negative electrode film layer increases the proportion of active material in the negative electrode sheet relative to the current collector, further improving the energy density of the battery cell.

[0265] As can be seen from the results of Examples 1, 14, and 15 in Table 2, the graphitization degree of the negative electrode active material is 91.5%-95%, and can be further selected as 91.5%-92.8%, which is beneficial to improving the specific capacity of the negative electrode active material and the volume expansion during lithium intercalation, so that the battery cell has both excellent energy density and cycle life. At the same time, in the X-ray diffraction pattern of the negative electrode film, the peak intensity ratio OI value of the diffraction peaks of the 004 crystal plane of carbon and the 110 crystal plane of carbon is 2-4, and can be further selected as 2-2.9, which is beneficial to the intercalation of lithium ions on the negative electrode side, improves the lithium intercalation rate, makes the negative electrode capacity more fully utilized, and effectively reduces the expansion of the negative electrode sheet during operation, further improving the cycle life and energy density of the battery cell.

[0266] As can be seen from the results of Examples 1, 16, and 17 in Table 2, the electrolyte injection coefficient is 2.8 g / Ah-3.2 g / Ah, which is beneficial to improve the wettability of the electrolyte and improve the liquid shortage phenomenon in the later stage of battery cycle, ensuring that there is enough electrolyte to support the charge and discharge reaction throughout the entire life cycle of the battery cell, thereby improving the cycle life of the battery while increasing the energy density of the battery cell.

[0267] As can be seen from the results of Examples 1 and 18 in Table 2, the inclusion of linear conductive agents in the positive and negative electrode films can form a mesh-like conductive network inside the film, improve the conductivity of the active material, and also help improve the diffusion of lithium ions, further improving the energy density and cycle life of the battery cell.

[0268] Table 3

[0269]

[0270] As can be seen from the comparison of Examples 1 and 19 in Table 3, when the thickness of the positive electrode current collector of the battery cell is 14μm-16μm and the thickness of the negative electrode current collector is 7μm-9μm, it can ensure that the current collector does not crack during long-term battery cycling, thereby improving the cycle stability and safety of the battery cell; at the same time, it can effectively reduce the probability of current collector damage and electrode cold pressing breakage, and improve the yield of electrode processing.

[0271] As can be seen from the results of Examples 1 and 21 in Table 2, the separator in the battery cell includes a base film and a ceramic coating disposed on at least one side of the base film. The ceramic coating includes boehmite ceramic particles, and the binder includes polyvinylidene fluoride. This effectively improves electrolyte wettability and enhances the cycle life of the battery cell. Furthermore, compared to spraying binder particles onto the surface of ceramic particles, dissolving the binder and ceramic particles in a solvent and rolling them onto the base film surface further improves the uniformity of the binder in the coating, resulting in more uniform adhesion between the electrode and the separator, further enhancing the cycle life of the battery cell. Moreover, a comparison of the results of Examples 1 and 20 shows that the separator, including a base film and ceramic coatings disposed on both sides of the base film, further improves electrolyte wettability and reduces battery polarization, thereby further enhancing the cycle life of the battery cell.

[0272] As can be seen from the results of Examples 1 and 22 in Table 2, when the thickness T of the battery cell satisfies 15mm≤T≤20mm, the expansion force of the battery cell is effectively reduced, avoiding the performance drop caused by the increase of negative electrode expansion. In addition, controlling the thickness within the above range can help the battery cell dissipate heat quickly, reduce the electrolyte decomposition caused by the increase of the battery cell operating temperature, and help to improve the cycle life and safety performance of the battery cell.

[0273] 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, the battery cell comprising an electrode assembly and an electrolyte, the electrode assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the positive electrode comprising a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the negative electrode comprising a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, characterized in that, When the battery cell is fully discharged, the compaction density of the positive electrode film is 2.3 g / cm³. 3 -2.5g / cm 3 The single-sided coating mass of the positive electrode film is 0.370 g / 1540 mm. 2 -0.400g / 1540mm 2 The cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction shows that the particle size D50 is 0.4 μm-0.8 μm. When the battery cell is fully discharged, the compaction density of the negative electrode film is 1.35 g / cm³. 3 -1.55g / cm 3 The cumulative particle number distribution curve obtained from the cross section along the thickness direction of the negative electrode film layer has a particle size D50 of 10μm-25μm, where D50 refers to the particle size corresponding to the cumulative particle number distribution reaching 50% in the cumulative number distribution curve. The negative electrode film layer includes a negative electrode active material, and the graphitization degree of the negative electrode active material is 91.5%-95%.

2. The battery cell according to claim 1, characterized in that, When the battery cell is fully discharged, the compaction density of the positive electrode film is 2.3 g / cm³. 3 -2.45g / cm 3 .

3. The battery cell according to claim 1, characterized in that, When the battery cell is fully discharged, the compaction density of the negative electrode film is 1.4 g / cm³. 3 -1.5g / cm 3 .

4. The battery cell according to claim 1, characterized in that, The single-sided coating mass of the positive electrode film is 0.380 g / 1540 mm. 2 -0.400g / 1540mm 2 .

5. The battery cell according to claim 1, characterized in that, In the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction, the particle size D50 is 0.6μm-0.7μm.

6. The battery cell according to claim 1, characterized in that, In the cumulative distribution curve of particle number obtained from the cross section along the thickness direction of the negative electrode film, the particle size D50 is 15μm-20μm.

7. The battery cell according to claim 1, characterized in that, The ratio (CB) of the negative electrode charging capacity to the positive electrode discharging capacity of the battery cell is 1.05-1.

14.

8. The battery cell according to claim 1, characterized in that, The positive electrode film and / or the negative electrode film include a conductive agent, which includes one or more of linear conductive agents and dotted conductive agents.

9. The battery cell according to claim 8, characterized in that, The linear conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, and vapor-grown carbon fibers.

10. The battery cell according to claim 9, characterized in that, The linear conductive agent includes multi-walled carbon nanotubes.

11. The battery cell according to claim 8, characterized in that, Based on the total mass of the positive electrode film, the mass content of the linear conductive agent is 0.5%-2%; and / or, Based on the total mass of the negative electrode film, the mass content of the linear conductive agent is 0.5%-2%.

12. The battery cell according to claim 11, characterized in that, The electrolyte injection coefficient is 2.8 g / Ah - 3.2 g / Ah.

13. The battery cell according to claim 1, characterized in that, The degree of graphitization of the negative electrode active material is 91.5%-92.8%.

14. The battery cell according to claim 1, characterized in that, In the X-ray diffraction pattern of the negative electrode film, the peak intensity ratio (OI) of the diffraction peaks of the 004 crystal plane of carbon and the 110 crystal plane of carbon is 2-4.

15. The battery cell according to claim 14, characterized in that, In the X-ray diffraction pattern of the negative electrode film, the peak intensity ratio (OI) of the diffraction peaks of the 004 crystal plane of carbon and the 110 crystal plane of carbon is 2-2.

9.

16. The battery cell according to claim 1, characterized in that, In the cross-section of the positive electrode film along the thickness direction, the particle size D10 is 0.1μm-0.4μm.

17. The battery cell according to claim 1, characterized in that, In the cross-section of the positive electrode film along the thickness direction, the particle size D90 is 0.8μm-1μm.

18. The battery cell according to claim 1, characterized in that, In the cross-section of the positive electrode film along the thickness direction, the particle size D99 is 1μm-10μm.

19. The battery cell according to claim 1, characterized in that, In the cross-section of the negative electrode film along the thickness direction, the particle size D10 is 4μm-10μm.

20. The battery cell according to claim 1, characterized in that, In the cross-section of the negative electrode film along the thickness direction, the particle size D90 is 25μm-45μm.

21. The battery cell according to claim 1, characterized in that, In the cross-section of the negative electrode film along the thickness direction, the particle size D99 is 40μm-65μm.

22. The battery cell according to claim 1, characterized in that, The positive electrode film layer includes a positive electrode active material, which includes lithium-containing transition metal phosphate particles with at least a portion of their surface coated with carbon material. The lithium-containing transition metal phosphate particles have the following general formula: Li m Fe x P y O j Q q Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, 0.6≤m≤1.15, 0<x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤1.

23. The battery cell according to claim 1, characterized in that, The negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

24. The battery cell according to claim 1, characterized in that, The single-sided coating mass of the negative electrode film is 0.170 g / 1540 mm. 2 -0.200g / 1540mm 2 .

25. The battery cell according to claim 24, characterized in that, The single-sided coating mass of the negative electrode film is 0.180 g / 1540 mm. 2 -0.200g / 1540mm 2 .

26. The battery cell according to claim 1, characterized in that, The thickness of the positive electrode film on one side is 96 μm-113 μm; and / or, the thickness of the negative electrode film on one side is 71 μm-96 μm.

27. The battery cell according to claim 1, characterized in that, The thickness of the positive current collector is 14μm-16μm; and / or, the thickness of the negative current collector is 7μm-9μm.

28. The battery cell according to claim 1, characterized in that, The isolation membrane includes a base membrane and a ceramic coating disposed on at least one side of the base membrane.

29. The battery cell according to claim 28, characterized in that, The ceramic coating comprises ceramic particles and a binder. The ceramic particles include one or more of boehmite, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, magnesium nitride, or barium titanate. The binder includes polyvinylidene fluoride.

30. The battery cell according to claim 28, characterized in that, The isolation membrane includes a base membrane and a ceramic coating disposed on both sides of the base membrane.

31. The battery cell according to claim 1, characterized in that, The battery cell is a stacked battery or a wound battery.

32. The battery cell according to claim 1, characterized in that, The battery cell includes a casing, and the casing is made of a soft-pack material, which includes an aluminum-plastic film.

33. The battery cell according to claim 1, characterized in that, The battery cell has a length of L, a width of W, and a thickness of T. The dimensions of the battery cell satisfy the following conditions: 550mm≤L≤650mm, 110mm≤W≤140mm, and 15mm≤T≤20mm.

34. A battery device, characterized in that, The battery device comprises the battery cell according to any one of claims 1 to 33.

35. An electrical appliance, characterized in that, The electrical device includes the battery device of claim 34, the battery device being used to provide electrical energy.

36. An energy storage device, characterized in that, The energy storage device includes the battery device of claim 34, the battery device being used to store electrical energy.

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