Battery monomer, battery device, power utilization device and energy storage device

Abstract

The invention provides a battery monomer, a battery device, a power utilization device and an energy storage device. The compaction density of the positive electrode film layer of the battery monomer in a full discharge state is 2.3 g / cm < 3 >-2.5 g / cm < 3 >; the compaction density of the negative electrode film layer is 1.35 g / cm < 3 > to 1.55 g / cm < 3 >; the single-side coating mass of the positive electrode film layer is 0.370 g / 1540 mm < 2 > to 0.400 g / 1540 mm < 2 >; in a number cumulative distribution curve of particles obtained by the cross section of the positive electrode film layer along the thickness direction of the pole piece, the number distribution particle size D50 of the particles is 0.4-0.8 [mu] m; in a number cumulative distribution curve of particles obtained by the cross section of the negative electrode film layer along the thickness direction of the pole piece, the number distribution particle size D50 of the particles is 10-25 [mu] m, and D50 is the particle size of the corresponding particles when the cumulative number distribution of the particles reaches 50% in an exponential cumulative distribution curve.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a battery cell, a battery device, an electrical device, and an energy storage device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydro, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the further development of battery applications, higher performance requirements have also been put forward for the electrical properties of battery cells, such as energy density and cycle life. Summary of the Invention

[0003] The present application is made in view of the above problems, and its purpose is to provide a battery cell that takes into account both long cycle life and high energy density.

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

[0005] In the battery cell provided by the embodiment of the present application, the positive electrode uses positive electrode active material particles with a number - average particle size D50 of 0.4 μm - 0.8 μm, and the negative electrode uses negative electrode active material particles with a number - average particle size D50 of 10 μm - 25 μm, taking into account reducing the probability of side reactions caused by particles and the polarization phenomenon, improving the first - cycle Coulombic efficiency and cycle life of the battery cell; further controlling the compaction density of the negative electrode film layer to be 1.35 g / cm 3 - 1.55 g / cm 3 , and matching with the compaction density of the positive electrode film layer of 2.3 g / cm 3 - 2.5 g / cm 3 , so that while the negative electrode film layer has a high porosity and improved cycle life, the compaction design of the positive electrode can form a good match with the low - compaction design of the negative electrode pole piece, and can leave space for the volume expansion during the lithium de - intercalation process of the negative electrode, and take into account the particle integrity of the positive electrode active material during compaction, thereby taking into account improving the energy density and cycle life of the battery cell; further combining to control the single - side coating mass of the positive electrode film layer to be 0.370 g / 1540 mm 2 - 0.400 g / 1540 mm 2 . Through the thick - coating design, while improving the energy density, the positive electrode film layer has an appropriate lithium - ion diffusion distance and resistance, thus taking into account the cycle life. Through the matching of the positive electrode pole piece and the negative electrode pole piece, the battery cell takes into account having a long cycle life and a high energy density, meeting the performance requirements.

[0006] In any implementation manner, when the battery cell is in a fully - discharged state, the compaction density of the positive electrode film layer is 2.3 g / cm 3 - 2.45 g / cm 3 .

[0007] In any implementation manner, when the battery cell is in a fully - discharged state, the compaction density of the negative electrode film layer is 1.4 g / cm 3 - 1.5 g / cm 3 .

[0008] Controlling the compaction densities of the positive electrode film layer and the negative electrode film layer to meet the above ranges can enable the positive and negative electrodes to form a good match, leave space for the lithium - intercalation expansion of the negative electrode, further take into account the particle integrity of the positive electrode active material, and further improve the energy density and cycle life of the battery cell.

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

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

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

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

[0013] Controlling the particle size D50 of the particles in the positive and negative electrode film layers to meet the above range can reduce the probability of side reactions caused by the particles, and further improve the initial efficiency and cycle life of the battery cell.

[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] The matching design of the charge / discharge capacities of the positive and negative electrodes of the battery cell helps lithium ions to be fully inserted / extracted on the positive and negative electrode sides during the charge and discharge processes of the battery. Controlling the ratio CB of the negative electrode charging capacity to the positive electrode discharging capacity to meet the above range can enable the negative electrode to have a larger redundant capacity, which is beneficial for more lithium ions to be inserted into the negative electrode side during the first charge of the battery, preventing the situation of lithium deposition caused by the inability of lithium ions to be inserted into the negative electrode and aggregating on the negative electrode side, reducing the loss of active lithium, being beneficial for the full utilization of the battery capacity, and improving 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, and the conductive agent includes one or more of a linear conductive agent and a dot-shaped conductive agent.

[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 network conductive network inside the film layer, and at the same time enable the active material particles to be embedded in the network, improving the conductivity of the active material, being beneficial for the full utilization of the specific capacity of the active material, and also being beneficial for improving the diffusion of lithium ions, further improving the energy density and cycle life of the battery cell, especially suitable for battery systems with large particle size positive and negative active materials or thick coatings.

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

[0020] Although adding linear conductive agent to the positive electrode film layer can improve the conductivity of the positive electrode film layer, it will occupy the mass of active materials in the unit area of the film layer. Too high a mass content of the linear conductive agent 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 layer to meet the above range can ensure the amount of active materials while fully utilizing the material's gram capacity, so that the battery cell has a long cycle life while having a high energy density.

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

[0022] Controlling the electrolyte injection coefficient in the battery cell within the above range can, on the one hand, ensure that the electrolyte inside the battery cell can be fully infiltrated, and on the other hand, release a certain amount of space to accommodate more active materials, which is beneficial to improving the energy density of the battery cell; on the other hand, the electrolyte is continuously consumed during battery operation, and insufficient electrolyte in the later stage will lead to insufficient reaction of active materials, which is not conducive to maintaining a long cycle life of the battery cell. If the electrolyte injection coefficient is too high, the reserved space inside the battery will be compressed. The volume expansion and gas production of the battery during the working cycle will directly affect the battery shell, causing the shell to deform and bulge, etc., especially for soft-pack batteries, it will cause the soft-pack shell to rupture, which is not conducive to the safety performance of the battery cell. Controlling the electrolyte injection coefficient to meet the above range can ensure that there is sufficient electrolyte to support the charge and discharge reaction throughout the life cycle of the battery cell, and improve the cycle life and safety performance of the battery while improving the energy density of the battery cell.

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

[0024] The degree of graphitization reflects the completeness of the graphite crystal structure, that is, the regularity of the atomic arrangement in the material structure. The high degree of graphitization of graphite indicates that the interlayer spacing of its internal structure is small, the smaller the lattice rotation, the less scattered stacking of the layers, and the orderly arrangement, which can provide more stable lithium insertion sites, which is conducive to the embedding of active lithium ions into the negative electrode material, and is conducive to improving its gram capacity and the first effect of the battery cell, but it also shows that the interlayer bonding is tighter and the volume expansion is larger when lithium is inserted. The low degree of graphitization of graphite indicates that the interlayer spacing of the structure is large, and the expansion of the material is small when lithium is inserted, but at this time the number of stable lithium insertion sites is reduced, which is not conducive to the utilization of the gram capacity of graphite. The degree of graphitization of the negative active material in the embodiment of the present application is within the above range, and the negative active material takes into account both excellent gram capacity and low volume expansion when lithium is inserted, and the battery cell further takes into account excellent energy density, cycle life and first effect.

[0025] In any embodiment, in the X-ray diffraction pattern of the negative electrode film layer, the peak intensity ratio OI value of the diffraction peaks of the carbon 004 crystal plane and the carbon 110 crystal plane is 2-4, and can be optionally 2-2.9.

[0026] When the plane structure of graphite in the negative electrode film is perpendicular to the plane of the pole piece, it helps to reduce the expansion force of the negative electrode film along the thickness direction, and can also provide a shorter diffusion path and more embedding / de-embedding channels for active ions. In the X-ray diffraction spectrum of the negative electrode film, the diffraction peak signal of the 004 crystal plane of carbon comes from the graphite with a plane structure parallel to the plane of the pole piece, and the diffraction signal of the 110 crystal plane of carbon comes from the graphite with a plane structure perpendicular to the plane of the pole piece. The OI value of the negative electrode film meets the above range. On the one hand, it is conducive to the embedding of lithium ions on the negative electrode side and improves the lithium insertion speed of lithium ions, so that the negative electrode capacity can be more fully utilized, and the energy density of the battery cell can be further improved; on the other hand, it can effectively reduce the expansion of the negative electrode pole piece during operation, which is conducive to improving the cycle life of the battery cell.

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

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

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

[0030] In the cumulative distribution curve of the number of particles obtained from the cross section of the positive electrode film layer along the thickness direction of the electrode sheet, the number distribution particle sizes D10, D90, and D99 of the particles meet the above ranges. The particles in the positive electrode film layer can meet the particle grading theory, achieve close stacking of particles inside the film layer, and further improve the energy density of the battery cell.

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

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

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

[0034] In the cumulative number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the number-average particle sizes D10, D90, and D99 of the particles satisfy the above ranges. On the one hand, the specific surface area of the negative electrode particles is large and the activity is low, which can reduce the probability of side reactions occurring during the first charge and discharge process of the battery, further improving the initial efficiency of the battery cell; on the other hand, the distribution of the negative electrode particles is more uniform, which is beneficial to the insertion of lithium ions on the negative electrode side, effectively reducing the probability of lithium deposition, and at the same time 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, and the positive electrode active material includes lithium-containing transition metal phosphate particles at least partially coated with a carbon material on the surface. The lithium-containing transition metal phosphate particles have a composition with the following general formula: Li m Fe x P y O j Q q , where 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, Br, 0.6 ≤ m ≤ 1.15, 0 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 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, the battery using it as the positive electrode active material can maintain a high capacity retention rate during charge and discharge cycles, enabling the battery cell to have excellent cycle life.

[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] When the negative electrode active material in the battery cell adopts the above-mentioned substances, the negative electrode can have a high lithium intercalation capacity, further improving the energy density of the battery cell. In addition, the negative electrode active materials represented by artificial graphite and natural graphite have a low degree of graphitization and a low OI value, and their greater isotropy can effectively reduce the swelling of the negative electrode sheet during operation, further improving the cycle life of the battery cell.

[0039] In any embodiment, the single-sided coating mass of the negative electrode film layer is 0.170 g / 1540 mm 2 -0.200 g / 1540 mm 2 , and can be optionally 0.180 g / 1540 mm 2 -0.200 g / 1540 mm 2 .

[0040] Controlling the coating mass of the negative electrode film layer to meet the above range is beneficial to improving the charging capacity of the negative electrode sheet, can form a good match with the discharge capacity of the positive electrode sheet, realize good lithium deintercalation / insertion inside the battery, is conducive to the full play of the battery capacity, and improves the energy density of the battery cell. In addition, controlling the thick coating of the negative electrode film layer increases the proportion of the 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 single-sided positive electrode film layer is 96 μm - 113 μm; and / or, the thickness of the single-sided negative electrode film layer is 71 μm - 96 μm.

[0042] Controlling the thickness of the single-sided positive electrode film layer to meet the above range can, on the one hand, ensure the loading amount of the positive electrode active material, making the battery cell have a high energy density; on the other hand, using a reasonable space design inside the battery to give way to space for the negative electrode sheet is beneficial to improving the performance degradation caused by the swelling of the negative electrode sheet during charge and discharge occupying the positive electrode space, so that the battery cell has a good cycle life while having a high energy density. Controlling the thickness of the single-sided negative electrode film layer to meet the above range can, on the one hand, increase the proportion of the negative electrode active material relative to the current collector, improve the lithium intercalation capacity of the negative electrode sheet, and further increase the energy density of the battery cell; on the other hand, through space design, it forms a good match with the structure of the positive electrode sheet, which is beneficial to the further play of the battery's specific capacity while taking into account the improvement of the cycle life of the battery cell.

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

[0044] Using large particles for the active material is beneficial to improving the initial efficiency of the battery. However, during the processing of the electrode sheet, the large particles squeeze the current collector, resulting in damage to the current collector and breakage of the electrode sheet. In the battery cell of the embodiment of the present application, controlling the thickness of the current collector to meet the above range can effectively reduce the probability of damage to the current collector and breakage of the electrode sheet during cold pressing, and improve the yield rate of electrode sheet processing. Moreover, it can ensure that no cracks appear in the current collector during long-term cycling, improving the long-term stability and safety of the battery.

[0045] In any implementation manner, the separator includes a base film and a ceramic coating provided on at least one surface of the base film.

[0046] In any implementation manner, the ceramic coating includes ceramic particles and a binder. The ceramic particles include one or more of boehmite, aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, magnesium nitride, or barium titanate, and the binder includes polyvinylidene fluoride.

[0047] Using the above types of ceramic particles for the ceramic coating of the separator can effectively improve the wettability of the electrolyte, which is beneficial to improving the cycle life of the battery cell. Further, using the above types of binders can form a three-dimensional fibrous network in the coating, improving the uniformity of the bonding in the coating. And compared with spraying the binder particles on the surface of the ceramic particles, dissolving the binder and the ceramic particles in a solvent and mixing them by roll coating on the surface of the base film can further improve the uniformity of the binder in the coating, making the bonding between the electrode sheet and the separator more uniform, and further improving the wettability of the electrolyte and the cycle life of the battery cell.

[0048] In any implementation manner, the separator includes a base film and ceramic coatings provided on both surfaces of the base film.

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

[0050] In any implementation manner, the battery cell includes a housing, and the material of the housing includes a soft package material, and the soft package material includes an aluminum-plastic film.

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

[0052] Controlling the thickness of the soft-pack battery to meet the above range indicates that the electrode assembly has an appropriate thickness. While ensuring the energy density, it effectively reduces the swelling force of the battery cell, avoids the performance drop caused by the increase in the swelling of the negative electrode, and is beneficial to improving the cycle life of the battery. In addition, it is conducive to the rapid conduction of the heat generated inside the battery cell to the surface, direct contact with heat dissipation devices such as air or a water-cooled plate, improves the heat dissipation and cooling efficiency, reduces the decomposition of the electrolyte caused by the increase in the working temperature of the battery cell, and is beneficial to improving the cycle life and safety performance of the battery cell. When the length and width of the battery cell are within the above range, while improving the energy density, it is beneficial to take into account the wetting of the membrane layer by the electrolyte and improve the cycle life.

[0053] An embodiment of the second aspect of the present application provides a battery device, which includes the battery cell in the above embodiment.

[0054] An embodiment of the third aspect of the present application provides an electrical device, which includes the battery device in the above embodiment, and the battery device is used to provide electrical energy.

[0055] An embodiment of the fourth aspect of the present application provides an energy storage device, which includes the battery device in the above embodiment, and the battery device is used to store electrical energy.

[0056] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present application more obvious and understandable, the following specifically illustrates the specific implementation manners of the present application. Description of the Drawings

[0057] In the drawings, unless otherwise specified, the same reference numerals throughout the multiple drawings denote the same or similar components or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings only depict some embodiments disclosed according to the present application and should not be regarded as limiting the scope of the present application.

[0058] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application; Figure 2 is Figure 1 the exploded view of the battery cell according to an embodiment of the present application shown; Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application; Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 5 is Figure 4 the exploded view of the battery pack according to an embodiment of the present application shown; Figure 6It is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0059] Description of reference numerals: 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed implementation manners

[0060] Hereinafter, embodiments of the battery cell, battery device, electrical device, and energy storage device of the present application specifically disclosed will be described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0061] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, 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 understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. In addition, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0062] If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0063] If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0064] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0065] Unless otherwise specified, "including" and "comprising" mentioned in this application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0066] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0067] In the prior art, the cycle life of power batteries is generally 2000 cycles, while the market requirement for the service life of energy storage batteries has reached >5000 cycles. Currently, the main ways to improve the battery service life mainly include optimizing the structural stability of materials (such as using single-crystal cathode particles that are not easily broken, setting a coating layer on the particle surface to inhibit the dissolution of transition metal ions, etc.), but these will inevitably sacrifice the energy density of the battery. How to balance the energy density of the battery on the basis of achieving such a high battery cycle life is a technical problem that urgently needs to be solved in this field.

[0068] Based on this, an embodiment of this application provides a battery cell. The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The positive electrode plate 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 plate includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. When the battery cell is in a fully discharged state, the compaction density of the positive electrode film layer is 2.3 g / cm 3 -2.5 g / cm 3 ; the single-sided coating mass of the positive electrode film layer is 0.370 g / 1540 mm 2 -0.400 g / 1540 mm 2; In the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D50 of the particle number distribution is 0.4 μm - 0.8 μm; and, when the battery cell is in a fully discharged state, the tap density of the negative electrode film layer is 1.35 g / cm 3 -1.55 g / cm 3 ; In the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the particle size D50 of the particle number distribution is 10 μm - 25 μm, where D50 refers to the particle size corresponding to the cumulative particle number distribution reaching 50% in the cumulative particle number distribution curve.

[0069] The applicant has found through research that when the particle size D50 of the particle number distribution in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet is less than 0.4 μm or the particle size D50 of the particle number distribution in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet is less than 10 μm, the particles in the positive and negative film layers are small in size and large in specific surface area, increasing the probability of side reactions with the electrolyte, resulting in serious irreversible loss of active lithium ions in the battery and low initial efficiency, and it is difficult to meet the usage requirements that the cycle life reaches more than 6400 cycles when the discharge capacity of the subsequent battery operation decays to 80%.

[0070] When the particle size D50 of the particle number distribution in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet is greater than 0.8 μm or the particle size D50 of the particle number distribution in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet is greater than 25 μm, although it can effectively reduce the probability of side reactions occurring inside the battery caused by small particles and improve the initial efficiency of the battery cell, the too large particles make the electron transport path too long, exacerbating the polarization phenomenon of the battery and leading to the attenuation of the cycle life of the battery cell.

[0071] Moreover, the applicant's research has also found that when the tap densities of the positive electrode film layer and the negative electrode film layer are relatively high, the porosity of the film layer is relatively low, which is not conducive to the infiltration of the electrolyte into the film layer, thereby affecting the extraction / insertion of lithium ions. In particular, it is not conducive to the infiltration of the electrolyte into the negative electrode film layer and the insertion of lithium ions into the negative electrode, thereby causing lithium deposition on the surface of the negative electrode sheet and deteriorating the cycle life of the battery cell.

[0072] The applicant further found through research that the single-sided coating mass of the positive electrode film layer is less than 0.370 g / 1540 mm 2, it will result in too little active material loading in battery cells of the same volume. Although the battery cells have excellent cycle life, their energy density cannot meet the requirement of energy density above 380 Wh / L for energy storage batteries. On the contrary, although too high single-sided coating mass of the positive electrode film layer is beneficial to improving the active material loading and the energy density of the battery, it will increase the lithium ion diffusion distance and deteriorate the wettability of the electrolyte to the active material near the current collector part of the film layer, which is not conducive to the electrical performance of the battery, especially the cycle life.

[0073] In summary, in the battery cells provided by the embodiments of the present application, the positive electrode uses positive electrode active material particles with a number distribution particle size D50 of 0.4 μm - 0.8 μm, and the negative electrode uses negative electrode active material particles with a number distribution particle size D50 of 10 μm - 25 μm, taking into account reducing the probability of side reactions caused by particles and the polarization phenomenon, and improving the first-cycle Coulomb efficiency and cycle life of the battery cells; further controlling the compaction density of the negative electrode film layer to be 1.35 g / cm 3 - 1.55 g / cm 3 , in combination with the compaction density of the positive electrode film layer being 2.3 g / cm 3 - 2.5 g / cm 3 , while the negative electrode film layer has a higher porosity and improved cycle life, the compaction design of the positive electrode can form a good match with the low compaction design of the negative electrode sheet, and can leave space for the volume expansion during the lithium deintercalation process of the negative electrode, and take into account the particle integrity of the positive electrode active material during compaction, so as to take into account improving the energy density and cycle life of the battery cells; further combined with controlling the single-sided coating mass of the positive electrode film layer to be 0.370 g / 1540 mm 2 - 0.400 g / 1540 mm 2 , through the thick coating design, while improving the energy density, the positive electrode film layer has an appropriate lithium ion diffusion distance and resistance, so as to take into account the cycle life. Through the matching of the positive electrode sheet and the negative electrode sheet in the present application, the battery cells take into account having a long cycle life and a high energy density, meeting the performance requirements.

[0074] In the present application, the term "particle" refers to particles with recognizable complete boundaries in the field of view of the positive electrode film layer and / or the negative electrode film layer at a certain magnification, such as 10,000 times. There may be defects and scratches inside the particles, but no complete boundaries sufficient to divide the particles can be recognized inside the particles. It can be understood that the particles in the film layer mainly come from the active material particles. Although other additives (such as binders, additives, etc.) in the film layer preparation also have particle characteristics, their addition amount in the film layer is much smaller than that of the active material. Therefore, the number distribution particle size of the particles 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.

[0075] When used in this article, in the cross-section of the positive electrode film layer along the thickness direction, the number distribution particle size D50 of the particles can be measured by methods known in the art. As an example, the following method can be used for testing: disassemble the battery cell, take out the positive electrode sheet, perform SEM testing on the cross-section of the sheet (such as a ZEISS electron microscope, magnification 10000X), count the sizes of all particles on one SEM image, which can be counted by software or manually. The particle size is taken as the longest diameter of the particle on the picture. The longest diameter of the particle refers to the maximum value among the distances between any two points on the outer peripheral line of the particle, that is, the maximum value of the particle sizes in different directions. Arrange the particle sizes from small to large, and take the 50th percentile as the number distribution particle size D50 of the positive electrode active material particles in the cross-section of the positive electrode film layer along the thickness direction in this SEM picture; repeat the above operation multiple times, and after counting multiple different regions (such as 10) of the same electrode sheet, take the average value as the number distribution particle size D50 of the particles obtained from the cross-section of the positive electrode film layer of the sample to be tested along the thickness direction of the electrode sheet in the particle number cumulative distribution curve.

[0076] It can be understood that the number distribution particle size D50 of the particles in the film layer can be regulated by methods well-known in the art. As an example, the mechanical force of crushing and grinding processes can be utilized to process the raw materials to the target particle size distribution range to achieve the adjustment of the particle size; screening and classification equipment can be used to separate the particle sizes of the particle system to obtain the required particle size; by precisely controlling the feeding rate and adjusting the residence time and stress state of the particles in the equipment, it also helps to achieve the regulation of the particle size.

[0077] During the compaction process of the positive electrode film layer, compaction occurs in the thickness direction. Therefore, compared with the surface of the positive electrode film layer, the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet can better reflect the real compaction condition of the particles inside the film layer in the spatial scale.

[0078] It can be understood that in the prior art, a laser particle size analyzer is usually used to count the particle size of the positive electrode active material by the Malvern laser diffraction method. However, the applicant's research shows that due to the easy agglomeration of small-sized particles, the test results obtained by the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of the particle agglomerates, and cannot truly reflect the particle size of the positive electrode active material, let alone the dispersion state of the positive electrode active material in the film layer, because the dispersion degree of the positive electrode active material in the film layer will increase during the processes of pulping and film forming and rolling. The test results obtained by the Malvern laser diffraction method are affected by the particle size, specific surface area, and agglomeration degree of the positive electrode active material. Compared with the real dispersion situation in the electrode sheet, the number of large particles obtained by this test is lower than the actual value, and the number of small particles is higher than the actual value. Therefore, the particle size obtained by the Malvern laser diffraction method test cannot be equivalent to or analogized to the particle size statistically obtained in the embodiments of this application.

[0079] It is understandable that in the cumulative number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the number distribution particle size D50 of the particles can also be measured by the method for measuring the number distribution particle size D50 in the cumulative number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet described above.

[0080] When used in this article, when the battery cell is in a fully discharged state, the tap density of the positive electrode film layer can be measured by a method known in the art. As an example, the following method can be used for testing: Place the battery cell in an oven environment at 25 °C and let it stand for 2 h. Wait until the battery temperature remains at 25 °C, then discharge the battery at a constant current of 1 / 3C to 2.5V and then 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, cut it into small round pieces with an area of S, obtain its mass W1, and use a micrometer to measure the thickness T1 of the positive electrode sheet. Then wipe off the positive electrode film layer of the above-weighted electrode sheet, weigh the mass of the current collector, denoted as W2, and use a micrometer to measure the thickness T2 of the current collector. Then the tap density PD of the positive electrode film layer = (W1 - W2) / [(T1 - T2)×S]. To ensure the accuracy of the test results, multiple groups (for example, 10 groups) of samples to be tested can be tested, and the average value can be calculated as the test result.

[0081] It is understandable that when the battery cell is in a fully discharged state, the tap density of the negative electrode film layer can be measured by the method for measuring the tap density of the positive electrode film layer described above.

[0082] When used in this article, the single-sided coating mass of the positive electrode film layer has a meaning well-known in the art and can be measured by a method known in the art. For example, a positive electrode sheet can be taken from the disassembled battery cell (if it is a double-sided coated positive electrode sheet, one side of the positive electrode film layer can be wiped off first), cut into small round pieces with an area of S1, weigh its mass, and record it as M1. Then wipe off the positive electrode film layer of the above-weighted positive electrode sheet, weigh the mass of the current collector, and record it as M0. The single-sided coating mass of the positive electrode film layer = (M1 - M0) / S1. To ensure the accuracy of the test results, multiple groups (for example, 10 groups) of samples to be tested can be tested, and the average value can be calculated as the test result.

[0083] In some embodiments, in the cumulative number distribution curve of the particles obtained from the cross-section of the positive electrode film layer in the thickness direction of the electrode sheet, the number distribution particle size D50 of the particles can be selected from 0.4 μm, 0.42 μm, 0.45 μm, 0.48 μm, 0.5 μm, 0.52 μm, 0.55 μm, 0.58 μm, 0.6 μm, 0.62 μm, 0.65 μm, 0.68 μm, 0.7 μm, 0.72 μm, 0.75 μm, 0.78 μm, 0.8 μm, or any range between any two of the above values.

[0084] In some embodiments, when the battery cell is in a fully discharged state, the tap density of the positive electrode film layer can be selected from 2.3 g / cm 3 , 2.31 g / cm 3 , 2.32 g / cm 3 , 2.33 g / cm 3 , 2.34 g / cm 3 , 2.35 g / cm 3 , 2.36 g / cm 3 , 2.37 g / cm 3 , 2.38 g / 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 , 2.45 g / cm 3 , 2.46 g / cm 3 , 2.47 g / cm 3 , 2.48 g / cm 3 , 2.49 g / cm 3 , 2.5 g / cm 3 , or any range between any two of the above values.

[0085] In some embodiments, the single-sided coating mass of the positive electrode film layer can be selected from 0.370 g / 1540 mm 2 , 0.372 g / 1540 mm 2 , 0.375 g / 1540 mm 2 , 0.378 g / 1540 mm 2 , 0.380 g / 1540 mm 2 , 0.382 g / 1540 mm 2 , 0.385 g / 1540 mm 2 , 0.388 g / 1540 mm 2, 0.390 g / 1540 mm 2 , 0.392 g / 1540 mm 2 , 0.395 g / 1540 mm 2 , 0.397 g / 1540 mm 2 , 0.400 g / 1540 mm 2 , or any range between any two of the above values.

[0086] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode, the particle size D50 of the particle number distribution can be selected as 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, or any range between any two of the above values.

[0087] In some embodiments, when the battery cell is in a fully discharged state, the tap density of the negative electrode film layer can be selected as 1.35 g / cm 3 , 1.36 g / cm 3 , 1.37 g / cm 3 , 1.38 g / cm 3 , 1.39 g / cm 3 , 1.40 g / cm 3 , 1.41 g / cm 3 , 1.42 g / cm 3 , 1.43 g / cm 3 , 1.44 g / cm 3 , 1.45 g / cm 3 , 1.46 g / cm 3 , 1.47 g / cm 3 , 1.48 g / cm 3 , 1.49 g / cm 3 , 1.50 g / cm 3 , 1.51 g / cm 3 , 1.52 g / cm 3 , 1.53 g / cm 3 , 1.54 g / cm 3 , 1.55 g / cm 3 , or any range between any two of the above values.

[0088] In some embodiments, when the battery cell is in a fully discharged state, the tap density of the positive electrode film layer is 2.3 g / cm 3 - 2.45 g / cm 3 .

[0089] In some embodiments, when the battery cell is in a fully discharged state, the compaction density of the negative electrode film layer is 1.4 g / cm 3 - 1.5 g / cm 3 .

[0090] Controlling the compaction densities of the positive electrode film layer and the negative electrode film layer to meet the above ranges can enable the positive and negative electrodes to form a good match, leave space for the lithium intercalation expansion of the negative electrode, further take into account the particle integrity of the positive electrode active material, and further improve the energy density and cycle life of the battery cell.

[0091] In some embodiments, the single-sided coating mass of the positive electrode film layer is 0.380 g / 1540 mm 2 - 0.400 g / 1540 mm 2 .

[0092] Controlling the single-sided coating mass of the positive electrode film layer to meet the above range can enable lithium ions to have an appropriate diffusion distance and a high active material loading amount on the positive electrode side, and further enable the battery cell to have a high energy density and a long cycle life.

[0093] In some embodiments, in the cumulative particle number distribution curve obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D50 of the particle number distribution is 0.6 μm - 0.7 μm.

[0094] In some embodiments, in the cumulative particle number distribution curve obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the particle size D50 of the particle number distribution is 15 μm - 20 μm.

[0095] Controlling the particle size D50 of the particles in the positive and negative electrode film layers to meet the above ranges can reduce the probability of side reactions caused by the particles, and further improve the initial efficiency and cycle life of the battery cell.

[0096] In some embodiments, the ratio CB value of the negative electrode charging capacity to the positive electrode discharging capacity of the battery cell is 1.05 - 1.14.

[0097] When used in this article, the ratio CB value of the negative electrode specific capacity to the positive electrode specific capacity of the battery cell can be measured by methods known in the art. As an example, the following method can be used for testing: Step 1): Average discharge capacity test of the positive electrode single-sided active material layer. Take the disassembled positive electrode sheet, and use a punching die to obtain small round pieces containing the positive electrode single-sided active material layer. Using a lithium metal sheet as the counter electrode, a Celgard membrane as the separator, and a solution of LiPF6 (1 mol / L) in EC+DMC+DEC (ethylene carbonate, dimethyl carbonate, and diethyl carbonate with a volume ratio of 1:1:1) as the electrolyte, assemble 6 identical CR2430-type button cells in a glove box under argon protection. ① After the battery is assembled, let it stand for 12 h. ② Perform constant current charging at a charging current of 0.1C until the voltage reaches the upper cut-off voltage of 3.8V, then maintain the voltage at 3.8V for constant voltage charging until the current is 50 μA. ③ Let it stand for 5 min. ④ Perform constant current discharge at a discharge current of 0.1C until the voltage reaches the lower cut-off voltage of 2.0V. ⑤ Let it stand for 5 min. ⑥ Perform constant current discharge at a discharge current of 0.05C until the voltage reaches the lower cut-off voltage of 2.0V. ⑦ Let it stand for 5 min, repeat steps ②-⑦, and record the discharge capacity of the second cycle. The average value of the discharge capacities of the 6 button cells is the average discharge capacity of the positive electrode single-sided active material layer. Step 2): Average charge capacity test of the negative electrode single-sided active material layer. Take the negative electrode sheet after disassembling the battery, and use a punching die to obtain small round pieces with the same area as the positive electrode small round pieces in step 1) above and containing the negative electrode single-sided film layer. Using a lithium metal sheet as the counter electrode, a Celgard membrane as the separator, and a solution of LiPF6 (1 mol / L) in EC+DMC+DEC (ethylene carbonate, dimethyl carbonate, and diethyl carbonate with a volume ratio of 1:1:1) as the electrolyte, assemble 6 CR2430-type button cells in a glove box under argon protection. ① After the battery is assembled, let it stand for 12 h. ② Perform constant current discharge at a discharge current of 0.05C until the voltage reaches the lower cut-off voltage of 0.005 mV. ③ Then perform constant current discharge at a discharge current of 50 μA until the voltage reaches the lower cut-off voltage of 0.005 mV. ④ Let it stand for 5 min. ⑤ Then perform constant current discharge at a discharge current of 10 μA until the lower cut-off voltage of 0.005 mV is reached. 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 cut-off voltage of 2V. ⑧ Let it stand for 5 minutes, repeat steps ②-⑧, and record the charge capacity of the second cycle. The average value of the charge capacities of the 6 button cells is the average charge capacity of the negative electrode single-sided film layer. Step 3): Calculate the CB value according to CB value = the average charge capacity (mAh) of the above negative electrode single-sided active material layer / the average discharge capacity (mAh) of the above positive electrode single-sided active material layer.

[0098] In some embodiments, the ratio CB of the negative electrode charging capacity to the positive electrode discharging capacity of the battery cell may 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.

[0099] The matching design of the charging / discharging capacities of the positive and negative electrodes of the battery cell helps lithium ions to be fully inserted / extracted on the positive and negative electrode sides during the charging and discharging processes of the battery. Controlling the ratio CB of the negative electrode charging capacity to the positive electrode discharging capacity to meet the above range can enable the negative electrode to have a greater redundant capacity, which is beneficial for more lithium ions to be inserted into the negative electrode side during the first charge of the battery, preventing the lithium plating phenomenon caused by the inability of lithium ions to be inserted into the negative electrode and aggregating on the negative electrode side, reducing the loss of active lithium, being beneficial for the full exertion of the battery capacity, and improving the cycle life and energy density of the battery cell.

[0100] [Positive electrode tab] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector.

[0101] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0102] In some embodiments, the positive electrode film layer includes a conductive agent, and the conductive agent includes one or more of a linear conductive agent and a dot-shaped conductive agent.

[0103] As used herein, the terms "linear conductive agent, dot-shaped conductive agent" have meanings well known in the art. A linear conductive agent refers to a conductive agent having a one-dimensional fiber morphology and capable of forming a continuous conductive network in the film layer; a dot-shaped conductive agent refers to a conductive agent having a non-linear particle morphology and forming a local conductive network between the film layers through multiple point contacts.

[0104] 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.

[0105] As used herein, the terms "single-walled carbon nanotubes, multi-walled carbon nanotubes" have the meanings known in the art. Single-walled carbon nanotubes refer to carbon materials with tubular structures formed by curling around a single layer of graphene sheets; it is understood that multi-walled carbon nanotubes refer to tubular carbon materials formed by coaxial curling and nesting of multiple layers (greater than or equal to 2 layers) of graphene sheets. As used herein, "carbon nanofibers" refer to fibrous nanomaterials composed of carbon elements, which are stacked, curled or arranged in a conical spiral. Some of them may contain amorphous carbon; the layers show a certain disorder or tilted stacking, and can be prepared by catalytic pyrolysis. As used herein, "vapor-grown carbon fiber" refers to a fibrous carbon material that is directly grown in the gas phase by chemical vapor deposition (CVD) under the action of gaseous hydrocarbons (such as methane, ethylene, benzene, etc.) as carbon sources at high temperatures (800-1200°C) and catalysts (transition metals such as iron, nickel or their nanoparticles).

[0106] Adding linear conductive agent to the membrane layer can form a mesh conductive network inside the membrane layer, and at the same time can embed active material particles in the mesh network, thereby improving the conductivity of the active material, which is beneficial to fully utilize the specific capacity of the active material, and is also beneficial to improve the diffusion of lithium ions, further improving the energy density and cycle life of the battery cell, and is especially suitable for battery systems with large-particle positive and negative active materials or thick coatings.

[0107] As used herein, the linear conductive agent in the film layer can be determined using methods and instruments known in the art. As an example, a cross-sectional polishing-scanning electron microscope (CP-SEM) image of the positive electrode film layer / negative electrode film layer is taken for observation and determination.

[0108] In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the linear conductive agent is 0.5%-2%, and can be optionally 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.

[0109] Although adding linear conductive agent to the positive electrode film layer can improve the conductivity of the positive electrode film layer, it will occupy the mass of active materials in the unit area of the film layer. Too high a mass content of the linear conductive agent 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 layer to meet the above range can ensure the amount of active materials while fully utilizing the material's gram capacity, so that the battery cell has a long cycle life while having a high energy density.

[0110] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D10 of the particle number distribution is 0.1 μm - 0.4 μm, and can be optionally 0.1 μm, 0.12 μm, 0.15 μm, 0.18 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, or the range between any two of the above values.

[0111] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D90 of the particle number distribution is 0.8 μm - 1 μm, and can be optionally 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 the range between any two of the above values.

[0112] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D99 of the particle number distribution is 1 μm - 10 μm, and can be optionally 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or the range between any two of the above values.

[0113] In the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D10, D90, and D99 of the particle number distribution satisfy the above ranges, and the particles in the positive electrode film layer can satisfy the particle grading theory, realize the close packing of the particles inside the film layer, and further improve the energy density of the battery cell.

[0114] It can be understood that in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D10, D90, and D99 of the particle number distribution can be measured by the measurement method of the particle size D50 of the particle number distribution in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet described above.

[0115] In some embodiments, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes lithium-containing transition metal phosphate particles with at least part of the surface coated with a carbon material. The lithium-containing transition metal phosphate particles have the following general formula components: Li m Fex P y O j Q q , wherein, Q comprises 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, Br; 0.6 ≤ m ≤ 1.15, 0 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 0 ≤ q ≤ 1.

[0116] 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 embodiments, 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.

[0117] Lithium-containing transition metal phosphates are generally polyanionic active materials with an olivine structure. Benefiting from the intrinsically stable olivine structure, batteries using it as the cathode active material can maintain a high capacity retention rate during charge and discharge cycles, enabling the battery monomer to have excellent cycle life.

[0118] In some embodiments, the thickness of the single-sided cathode film layer is 96 μm - 113 μm, and can be selected as 96 μm, 97 μm, 98 μm, 99 μm, 100 μm, 101 μm, 102 μm, 103 μm, 104 μm, 105 μm, 106 μm, 107 μm, 108 μm, 109 μm, 110 μm, 111 μm, 112 μm, 113 μm, or a range between any two of the above values.

[0119] 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 amount of the positive electrode active material, enabling the battery cell to have a high energy density; on the other hand, using a reasonable spatial design inside the battery to allocate space for the negative electrode tab, which is beneficial to improving the performance degradation caused by the expansion of the negative electrode tab during charge and discharge and squeezing the positive electrode space, so that the battery cell has good cycle life while having a high energy density.

[0120] In some embodiments, the thickness of the positive electrode current collector is 14 μm - 16 μm, and can be optionally 14 μm, 15 μm, 16 μm, or the range between any two of the above values.

[0121] Using large particles for the active material is beneficial to improving the initial efficiency and cycle life of the battery. However, during the processing of the electrode tab, the large particles squeeze the current collector, resulting in damage to the current collector and breakage of the electrode tab. In the battery cell of the embodiment of the present application, controlling the thickness of the current collector to meet the above range can effectively reduce the probability of damage to the current collector and breakage of the electrode tab during cold pressing, and improve the yield rate of electrode tab processing. And it can ensure that no cracks appear in the current collector during long-term cycling, improving the long-term stability and safety of the battery.

[0122] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0123] In some embodiments, the positive electrode film layer may optionally further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0124] In some embodiments, the positive electrode tab can be prepared by the following method: dispersing the above components for preparing the positive electrode film layer, such as positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N - methylpyrrolidone) to form a positive electrode film layer slurry; coating the positive electrode film layer slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode tab can be obtained.

[0125] [Negative electrode tab] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0126] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0127] In some embodiments, the negative electrode film layer includes a conductive agent, and the conductive agent includes one or more of a linear conductive agent and a dot-like conductive agent.

[0128] 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.

[0129] In some embodiments, based on the total mass of the negative electrode film layer, the mass content of the linear conductive agent is 0.5% - 2%, and can be optionally 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.

[0130] Adding a linear conductive agent to the negative electrode film layer will form a network conductive structure inside the film layer, which is beneficial to improving the conductivity of the negative electrode layer and beneficial to the exertion of the charge and discharge capacity of the negative electrode. However, adding a linear conductive agent occupies the mass of the negative electrode active material in the film layer per unit area, directly affecting the insertion of lithium ions on the negative electrode side. If the mass of the negative electrode active material is too small, lithium ions cannot be inserted and lithium will be deposited on the negative electrode side, deteriorating the cycle life of the battery cell. Controlling the content of the linear conductive agent in the negative electrode film layer to meet the above range can improve the conductivity of the negative electrode film layer while enabling the battery cell to have a good cycle life.

[0131] In some embodiments, 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%, and can be 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%.

[0132] When used in this article, the degree of graphitization of the negative electrode active material has a meaning known in the art and can be measured using instruments and methods known in the art. As an example, the following method can be used for measurement: Use an X-ray diffractometer (such as Bruker D8 Discover) for testing, and the test can refer to JISK0131-1996 and JB / T4220-2011 to obtain the average interlayer spacing d002 of the C(002) crystal plane in the material crystal structure, and then calculate the degree of graphitization according to 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 crystal structure expressed in nanometers (nm). The method of obtaining the negative electrode active material includes but is not limited to disassembling the battery cell and scraping powder from the negative electrode film layer. For example, place the battery cell at 25°C, discharge the battery cell at a constant current of 0.33C to 2.0V, let it stand for 5 minutes, and then discharge it at a constant current of 0.04C to 2.0V, which is recorded as the full discharge state. Disassemble the battery cell to take out the negative electrode plate, dissolve the negative electrode plate, and centrifuge it at 3000r / min for more than 30 minutes to remove the binder in the film layer. The graphite is in the lower layer of the sediment, and the conductive agent is in the upper layer of the sediment. Take the graphite in the lower layer for graphitization test.

[0133] The degree of graphitization reflects the completeness of the graphite crystal structure, that is, the regularity of the atomic arrangement in the material structure. The high degree of graphitization of graphite indicates that the interlayer spacing of its internal structure is small, the smaller the lattice rotation, the less scattered stacking of the layers, and the orderly arrangement, which can provide more stable lithium insertion sites, which is conducive to the embedding of active lithium ions into the negative electrode material, and is conducive to improving its gram capacity and the first effect of the battery cell, but it also shows that the interlayer bonding is tighter and the volume expansion is larger when lithium is inserted. The low degree of graphitization of graphite indicates that the interlayer spacing of the structure is large, and the expansion of the material is small when lithium is inserted, but at this time the number of stable lithium insertion sites is reduced, which is not conducive to the utilization of the gram capacity of graphite. The degree of graphitization of the negative active material in the embodiment of the present application is within the above range, and the negative active material takes into account both excellent gram capacity and low volume expansion when lithium is inserted, and the battery cell further takes into account excellent energy density, cycle life and first effect.

[0134] In some embodiments, in the X-ray diffraction pattern of the negative electrode film layer, the peak intensity ratio OI value of the diffraction peak of the carbon 004 crystal plane to the carbon 110 crystal plane is 2-4, which can be 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 a range between any two of the above values. In some embodiments, in the X-ray diffraction pattern of the negative electrode film layer, the peak intensity ratio OI value of the diffraction peak of the carbon 004 crystal plane to the carbon 110 crystal plane is 2-2.9.

[0135] In this application, in the X-ray diffraction pattern of the negative electrode film layer, the peak intensity ratio OI of the diffraction peak of the 004 crystal plane of carbon to the diffraction peak of the 110 crystal plane of carbon can be tested by methods known in the art. For example, the battery cell is placed at 25 °C, and the battery cell is discharged at a constant current of 0.33C to 2.0V, left standing 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 disassembled and the negative electrode plate is taken to test the single-sided negative electrode film layer. An X-ray diffractometer (such as Bruker D8 Discover) can be used for testing. The test can refer to JISK0131-1996 and JB / T4220-2011 to obtain the X-ray diffraction pattern of the negative electrode film layer. According to the OI value = I 004 / I 110 The OI value of the negative electrode film layer is calculated. I 004 is the integrated area of the diffraction peak of the 004 crystal plane of the crystalline carbon of the material in the negative electrode film layer, and I 110 is the integrated area of the diffraction peak of the 110 crystal plane of the crystalline carbon of the material in the negative electrode film layer. In the X-ray diffraction analysis test of this application, a copper target can be used as the anode target, CuKα rays can be used as the radiation source, the ray wavelength λ = 1.5418 Å, the scanning 2θ angle range is 20° - 80°, and the scanning rate is 4° / min. It can be understood that the OI value of the negative electrode film layer can be regulated by changing the parameters in the cold pressing preparation process (such as controlling the pressure during the rolling process to be small), or by changing the type of negative electrode active material, such as using a negative electrode active material with a lower degree of graphitization (such as natural graphite, artificial graphite, etc.), or selecting a graphite raw material with a lower OI value itself.

[0136] When the planar structure of the graphite in the negative electrode film layer is perpendicular to the plane of the electrode plate, it helps to reduce the swelling force of the negative electrode film layer in the thickness direction, and can also provide a shorter diffusion path and more insertion / extraction channels for active ions. In the X-ray diffraction pattern of the negative electrode film layer, the diffraction peak signal of the 004 crystal plane of carbon comes from the graphite with a planar structure parallel to the plane of the electrode plate, and the diffraction peak signal of the 110 crystal plane of carbon comes from the graphite with a planar structure perpendicular to the plane of the electrode plate. When the OI value of the negative electrode film layer satisfies the above range, on the one hand, it is beneficial to the insertion of lithium ions on the negative electrode side, improves the lithium insertion speed of lithium ions, enables the negative electrode capacity to be exerted more fully, and further improves the energy density of the battery cell; on the other hand, it can effectively reduce the swelling of the negative electrode plate during operation, which is beneficial to improving the cycle life of the battery cell.

[0137] 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.

[0138] When the negative electrode active material in the battery cell adopts the above-mentioned substances, the negative electrode can have a high lithium intercalation capacity, further improving the energy density of the battery cell; in addition, the negative electrode active materials represented by artificial graphite and natural graphite have a low degree of graphitization and a low OI value, and their greater degree of isotropy can effectively reduce the swelling of the negative electrode sheet during operation, further improving the cycle life of the battery cell.

[0139] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the particle size D10 of the particle number distribution is 4 μm - 10 μm, and can be selected as 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or the range between any two of the above values.

[0140] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the particle size D90 of the particle number distribution is 25 μm - 45 μm, and can be selected as 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, or the range between any two of the above values.

[0141] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the particle size D99 of the particle number distribution is 40 μm - 65 μm, and can be selected as 40 μm, 42 μm, 45 μm, 48 μm, 50 μm, 52 μm, 55 μm, 58 μm, 60 μm, 62 μm, 65 μm, or the range between any two of the above values.

[0142] In the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, when the particle size D10, D90, and D99 of the particle number distribution satisfy the above ranges, on the one hand, the specific surface area of the negative electrode particles is large and the activity is low, which can reduce the probability of side reactions occurring during the first charge and discharge of the battery, further improving the first efficiency of the battery cell; on the other hand, the distribution of the negative electrode particles is more uniform, which is beneficial to the intercalation of lithium ions on the negative electrode side, effectively reducing the probability of lithium precipitation, and at the same time reducing the volume expansion on the negative electrode side, thereby improving the cycle life of the battery.

[0143] It can be understood that in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the particle size D10, D90, and D99 of the particle number distribution can be measured by the measurement method of the particle size D50 of the particle number distribution in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet described above.

[0144] In some embodiments, the coating mass of the negative electrode film layer is 0.170 g / 1540 mm 2 - 0.200 g / 1540 mm 2 , optionally 0.170 g / 1540 mm 2 、0.172 g / 1540 mm 2 、0.175 g / 1540 mm 2 、0.178 g / 1540 mm 2 、0.18 g / 1540 mm 2 、0.182 g / 1540 mm 2 、0.185 g / 1540 mm 2 、0.188 g / 1540 mm 2 、0.190 g / 1540 mm 2 、0.192 g / 1540 mm 2 、0.195 g / 1540 mm 2 、0.198 g / 1540 mm 2 、0.2 g / 1540 mm 2 ,or a range between any two of the above values.

[0145] In some embodiments, the coating mass of the negative electrode film layer is 0.180 g / 1540 mm 2 - 0.200 g / 1540 mm 2 。

[0146] Controlling the coating mass of the negative electrode film layer to meet the above range is beneficial to improving the charging capacity of the negative electrode plate, can form a good match with the discharge capacity of the positive electrode plate, realizes good extraction / insertion of lithium ions inside the battery, is conducive to the full play of the battery capacity, and improves the energy density of the battery cell; in addition, controlling the thick coating of the negative electrode film layer increases the proportion of the active material in the negative electrode plate relative to the current collector, further improving the energy density of the battery cell.

[0147] It can be understood that the coating mass of the negative electrode film layer can be measured by the coating mass measurement method of the positive electrode film layer described above.

[0148] In some embodiments, the thickness of the single-sided negative electrode film layer is 71 μm - 96 μm, optionally 71 μm, 72 μm, 73 μm, 74 μm, 75 μm, 76 μm, 77 μm, 78 μm, 79 μm, 80 μm, 81 μm, 82 μm, 83 μm, 84 μm, 85 μm, 86 μm, 87 μm, 88 μm, 89 μm, 90 μm, 91 μm, 92 μm, 93 μm, 94 μm, 95 μm, 96 μm, or a range between any two of the above values.

[0149] Controlling the thickness of the single-sided negative electrode film layer to meet the above range can, on the one hand, increase the proportion of the negative electrode active material relative to the current collector, improve the lithium intercalation capacity of the negative electrode sheet, and further increase the energy density of the battery monomer; on the other hand, through spatial design, it can form a good match with the structure of the positive electrode sheet, which is beneficial to the further utilization of the specific capacity of the battery while taking into account the improvement of the cycle life of the battery monomer.

[0150] In some embodiments, the thickness of the negative electrode current collector is 7 μm - 9 μm, and it can be selected as 7 μm, 8 μm, 9 μm, or the range between any two of the above values.

[0151] Using large particles of the active material is beneficial to improving the initial efficiency of the battery. However, during the processing of the electrode sheet, the large particles squeeze the current collector, resulting in damage to the current collector and breakage of the electrode sheet. In the battery monomer of the embodiment of the present application, controlling the thickness of the current collector to meet the above range can effectively reduce the probability of damage to the current collector and breakage of the electrode sheet during cold pressing, and improve the yield rate of electrode sheet processing. And it can ensure that no cracks appear in the current collector during long-term cycling, improving the long-term stability and safety of the battery.

[0152] As used herein, the term "breakage of the electrode sheet during cold pressing" has the meaning known in the art, which refers to the phenomenon that local defects and cracks occur in the electrode sheet during cold pressing, and breakage occurs during the cold pressing and tape-running process. The morphology of the cold-pressed electrode sheet can be observed to determine whether breakage has occurred and to count the number of breakages.

[0153] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as 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.).

[0154] In some embodiments, the negative electrode film layer may also optionally include a binder. The binder can 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).

[0155] In some embodiments, the negative electrode film layer may also optionally include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0156] In some embodiments, the negative electrode sheet can be prepared by the following method: dispersing the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0157] [Electrolyte solution] The electrolyte solution plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet.

[0158] In some embodiments, the injection coefficient of the electrolyte solution is 2.8 g / Ah - 3.2 g / Ah, and can be optionally 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 the range between any two of the above values.

[0159] When used in this application, the injection coefficient of the battery cell refers to the ratio of the mass of the electrolyte solution inside the battery cell to the battery capacity. The injection coefficient of the battery cell can be obtained by testing in any well-known manner in the art. Exemplarily, the mass of the electrolyte solution in the battery cell can be obtained by the following method: weighing the battery, and recording the mass as M0. Disassembling the battery cell and pouring out the free electrolyte solution. Taking out the internal electrode assembly and separating the positive electrode sheet, the negative electrode sheet, the separator, and the mechanical parts, soaking and cleaning the positive electrode sheet, the negative electrode sheet, the separator, and the mechanical parts with a dimethyl carbonate (DMC) solvent for 24 h - 48 h, and soaking repeatedly for more than 3 times. Placing the aforementioned positive electrode sheet, negative electrode sheet, separator, and mechanical parts in an oven at 100 °C for more than 24 h until completely dried. Weighing the dried positive electrode sheet, negative electrode sheet, separator, and mechanical parts, and recording the mass as M1. Thus, the mass of the electrolyte solution in the battery cell is (M0 - M1). The injection coefficient is calculated by (M0 - M1) / the rated capacity of the battery cell. The rated capacity is the nominal capacity of the battery, or charging at a charging rate of 0.33C to 3.65V, then charging at a constant voltage of 3.65V to 0.05C, standing for 10 min, and then discharging at a discharging rate of 0.33C to 2.0V, and taking the discharging capacity of the battery cell as the rated capacity.

[0160] Controlling the electrolyte filling coefficient in the battery cell within the above range can, on the one hand, ensure that the electrolyte inside the battery cell can be fully infiltrated, and at the same time release a certain amount of space to accommodate more active materials, which is beneficial to improving the energy density of the battery cell; on the other hand, during the operation of the battery, the electrolyte is continuously consumed, and insufficient electrolyte in the later stage will lead to insufficient reaction of the active materials, which is not conducive to the battery cell maintaining a long cycle life. However, if the electrolyte filling coefficient is too high, the reserved space inside the battery is compressed, and the volume expansion, gas generation, etc. during the working cycle of the battery will directly act on the battery case, causing the outer shell to deform, bulge, etc. Especially for soft-pack batteries, it will cause the soft-pack outer shell to rupture, etc., which is not conducive to the safety performance of the battery cell. Controlling the electrolyte filling coefficient to meet the above range can ensure that there is enough electrolyte to support the charge and discharge reactions throughout the entire life cycle of the battery cell, and improve the cycle life and safety performance of the battery on the basis of improving the energy density of the battery cell.

[0161] In some embodiments, the electrolyte includes a solvent and an electrolyte salt.

[0162] 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 bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0163] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene 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.

[0164] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0165] [Separator film] In some embodiments, the battery cell further includes a separator film.

[0166] In some embodiments, the separator film includes a base film and a ceramic coating provided on at least one surface of the base film.

[0167] In some embodiments, the ceramic coating comprises ceramic particles and a binder. The ceramic particles include one or more of boehmite, aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, magnesium nitride, or barium titanate. The binder includes polyvinylidene fluoride.

[0168] Using the above types of ceramic particles in the separator ceramic coating can effectively improve the wettability of the electrolyte, which is beneficial to improving the cycle life of the battery cell. Further, using the above types of binder can form a three-dimensional fibrous network within the coating, enhancing the uniformity of the adhesion within the coating. Moreover, compared with spraying the binder particles on the surface of the ceramic particles, dissolving the binder and the ceramic particles in a solvent and mixing them by roll coating on the surface of the base film can further improve the uniformity of the binder in the coating, making the adhesion between the electrode sheet and the separator more uniform, and further enhancing the wettability of the electrolyte and the cycle life of the battery cell.

[0169] In some embodiments, the separator includes a base film and ceramic coatings provided on both surface sides of the base film.

[0170] [Battery cell] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process. In some embodiments, the battery cell is a stacked battery or a wound battery.

[0171] In some embodiments, the battery cell includes a housing, and the material of the housing includes a soft package material, and the soft package material includes an aluminum plastic film.

[0172] In some embodiments, the aluminum plastic film includes a composite film formed by one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), polyethylene (PE) and aluminum.

[0173] In some embodiments, the battery cell has a length of L, a width of W, and a thickness of T, and the dimensions of the housing satisfy: 550 mm ≤ L ≤ 650 mm, 110 mm ≤ W ≤ 140 mm, 15 mm ≤ T ≤ 20 mm.

[0174] In some embodiments, the length L of the battery cell can be selected as 550 mm, 560 mm, 570 mm, 580 mm, 590 mm, 600 mm, 610 mm, 620 mm, 630 mm, 640 mm, 650 mm, or a range between any two of the above values.

[0175] In some embodiments, the width W of the battery cell can be selected as 110 mm, 112 mm, 115 mm, 117 mm, 120 mm, 122 mm, 125 mm, 127 mm, 130 mm, 132 mm, 135 mm, 137 mm, 140 mm, or a range between any two of the above values.

[0176] In some embodiments, the thickness T of the battery cell can be selected as 15 mm, 15.5 mm, 16 mm, 16.5 mm, 17 mm, 17.5 mm, 18 mm, 18.5 mm, 19 mm, 19.5 mm, 20 mm, or a range between any two of the above values.

[0177] Controlling the thickness of the pouch cell to meet the above range indicates that the electrode assembly has an appropriate thickness, which can effectively reduce the swelling force of the battery cell while ensuring the energy density, avoid the performance drop caused by the increase in the swelling of the negative electrode, and is beneficial to improving the cycle life of the battery; in addition, it is beneficial to quickly conduct the heat generated inside the battery cell to the surface, directly contact with heat dissipation devices such as air or a water-cooled plate, improve the heat dissipation and cooling efficiency, reduce the electrolyte decomposition caused by the increase in the working temperature of the battery cell, and is beneficial to improving the cycle life and safety performance of the battery cell.

[0178] When the length and width of the battery cell are within the above range, while improving the energy density, it is beneficial to take into account the wetting of the electrolyte on the film layer and improve the cycle life.

[0179] In some embodiments, a housing can be used to encapsulate the above electrode assembly and electrolyte.

[0180] In some embodiments, the housing of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The housing of the battery cell can also be a soft package, such as a pouch. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc. The present application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0181] In some embodiments, referring to Figure 2, the outer packaging may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate and the separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0182] [Battery device] An embodiment of the present application further provides a battery device, and the battery device includes the battery cell provided by the embodiment of the present application. In some embodiments, the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0183] In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells included in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

[0184] Figure 3 is a battery module 4 as an example. Refer to Figure 3 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0185] Optionally, the battery module 4 can further include a housing having a receiving space, and a plurality of battery cells 5 are received in the receiving space.

[0186] In some embodiments, the above battery module can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0187] Figure 4 and Figure 5 is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 , the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 and form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0188] [Electrical device] In addition, an embodiment of the present application further provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs provided by the embodiments of the present application. The battery cells, battery modules, or battery packs can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0189] As the electrical device, the battery cells, battery modules, or battery packs can be selected according to its usage requirements.

[0190] Figure 6 Take an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the electrical device for battery cells, battery packs or battery modules can be adopted.

[0191] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinness and lightness, and battery cells can be used as the power source.

[0192] Embodiment Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0193] I. Preparation Method Embodiment 1 1) Preparation of the positive electrode sheet Lithium iron phosphate (LiFePO4), conductive carbon black, polyvinylidene fluoride (PVDF), and linear conductive agent CNT (multi-walled carbon nanotube, 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 added to the solvent N-methylpyrrolidone, and stirred evenly to obtain the positive electrode slurry. The positive electrode slurry was coated on both surfaces of a positive electrode current collector aluminum foil with a thickness of 15 μm, and after drying, cold pressing, die cutting, and slitting, the positive electrode sheet was obtained.

[0194] 2) Preparation of the negative electrode sheet Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR), carboxymethyl cellulose, and CNT (multi-walled carbon nanotube, Chengdu Organic Chemicals 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 and stirred evenly to obtain the negative electrode slurry. The negative electrode slurry was coated on both surfaces of a negative electrode current collector copper foil with a thickness of 8 μm, and after drying and cold pressing, a negative electrode plate was obtained.

[0195] 3) Preparation of the separator A 7-μm polyethylene film was used as the base film. Ceramic particle boehmite and binder PVDF were dissolved in NMP solvent to form a slurry, and the slurry was coated on both sides of the base film using a gravure roll. During the coating process, the coating speed was set at 30 m / min and the coating thickness was 2 μm on each side. After the coating was completed, it was dried in an oven at a temperature of 70 °C to obtain the separator.

[0196] 4) Preparation of the electrolyte Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Then, thoroughly dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0197] 5) Assembly of the battery The negative electrode plate, separator, and positive electrode plate were placed in order, with the separator positioned between the negative electrode plate and the positive electrode plate to play an insulating role, obtaining a stacked electrode assembly. The stacked battery core was subjected to a gluing process to tightly wrap the battery core. The glued stacked electrode assembly was placed in an outer package, which was a soft package material of aluminum-plastic film composed of an inner layer of polypropylene, a middle layer of aluminum foil, and an outer layer of nylon. Among them, the aluminum-plastic film outer package was formed into the target shape and size through a punching and forming machine and trimming. Then, the aluminum-plastic film was heat-sealed, vacuum baked, and left standing. The electrolyte was injected according to an injection coefficient of 3.0 g / Ah, and then sealed. Then, hot pressing and cold pressing operations were performed on the soft package battery. Finally, through processes such as formation, vacuum exhaust, and trimming, a battery cell was obtained.

[0198] Among them, when the battery cell is in a fully discharged state, the compaction density of the positive electrode film layer is 2.36 g / cm 3 , and the compaction density of the negative electrode film layer is 1.45 g / cm 3 . The single-sided coating mass of the positive electrode film layer is 0.384 g / 1540 mm 2 ; in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the particle size D50 of the particle number distribution 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 layer is 0.185 g / 1540 mm2 In the cumulative number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the number distribution particle size D50 of the particles is 20 μm, D10 is 5 μm, D90 is 28 μm, and D99 is 50 μm; The ratio CB value of the negative electrode charging capacity to the positive electrode discharging capacity of the battery cell is 1.1; based on the total mass of the negative electrode film layer, 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 layer, the peak intensity ratio OI value of the diffraction peak of the 004 crystal plane of carbon to the diffraction peak of the 110 crystal plane of carbon is 2.9; The thickness of the single-sided positive electrode film layer is 105.7 μm; the thickness of the single-sided negative electrode film layer is 82.8 μm; The length L of the housing of the battery cell is 600 mm, the width W is 125.6 mm, and the thickness T is 17.7 mm.

[0199] Comparative Example 1-2 The battery cell of Comparative Example 1-2 was prepared in a similar manner to the battery cell in Example 1, except that the particle size of the positive / negative electrode active material particles and the compaction of the positive and negative electrode film layers were adjusted, so that when the battery cell was in a fully discharged state, the compaction density of the positive electrode film layer did not meet 2.3 g / cm 3 -2.5 g / cm 3 and the compaction density of the negative electrode film layer did not meet 1.35 g / cm 3 -1.55 g / cm 3 ; in the cumulative number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the number distribution particle size D50 of the particles did not meet 0.4 μm - 0.8 μm; and in the cumulative number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, the number distribution particle size D50 of the particles did not meet 10 μm - 25 μm. The specific preparation parameters are shown in Table 1.

[0200] Comparative Example 3 The battery cell of Comparative Example 3 was prepared in a similar manner to that in Example 1, except that the single-sided coating mass of the positive and negative electrodes was adjusted, and the single-sided coating mass of the positive electrode film layer did not meet 0.370 g / 1540 mm 2 -0.400 g / 1540 mm 2 , and the specific preparation parameters are shown in Table 1.

[0201] Examples 2-5 The battery cells of Examples 2-5 were prepared in a similar manner to that in Example 1, except that the particle size of the particles in the positive / negative electrode film layers was adjusted. The specific preparation parameters are shown in Table 1.

[0202] Examples 6-9 The battery cells of Examples 6-9 were prepared in a similar manner to that of Example 1, except that the cold pressing process for the positive electrode sheet and the negative electrode sheet was changed, and the compaction density of the positive electrode film layer / negative electrode film layer was adjusted. The specific preparation parameters are shown in Table 1.

[0203] Examples 10-13 The battery cells of Examples 10-13 were prepared in a similar manner to that of Example 1, except that the single-sided coating mass of the positive electrode film layer and the negative electrode film layer was adjusted. The specific preparation parameters are shown in Table 1.

[0204] Examples 14-15 The battery cells of Examples 14-15 were prepared in a similar manner to that of Example 1, except that negative electrode active materials with different degrees of graphitization were used, and the OI value of the negative electrode film layer was changed through the cold pressing process. The specific preparation parameters are shown in Table 1.

[0205] Examples 16-17 The battery cells of Examples 16-17 were prepared in a similar manner to that of Example 1, except that the injection coefficient of the electrolyte was adjusted. The specific preparation parameters are shown in Table 1.

[0206] Example 18 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 the linear conductive agent multi-walled carbon nanotubes in the preparation of the positive electrode film layer and the negative electrode film layer.

[0207] Example 19 The battery cell of Example 19 was prepared in a similar manner to that of Example 1, except that positive electrode current collectors and negative electrode current collectors with different thicknesses were used. The thickness of the positive electrode current collector was 13 μm, and the thickness of the negative electrode current collector was 5.5 μm.

[0208] Examples 20-21 The battery cell of Example 20 was prepared in a similar manner to that of Example 1, except that the coating method of the ceramic coating in the separator was changed. The specific preparation process was as follows: A 7-μm polyethylene film was used as the base film, and ceramic particles boehmite and binder PVDF were dissolved in NMP solvent to form a slurry. The slurry was coated on one side of the base film using a gravure roll. During the coating process, the coating speed was set at 30 m / min, and the coating thickness was 4 μm on one side. After coating, it was dried in an oven at a temperature of 70 °C to obtain the separator. During the assembly process, the side with the ceramic coating was aligned with the positive electrode sheet, and the side without the coating was aligned with the negative electrode sheet.

[0209] The battery cell of Example 21 is prepared in a similar manner to that of Example 1, except that the preparation method of the ceramic coating in the separator is changed. The specific preparation process is as follows: A 7-μm polyethylene film is used as the base film. First, the ceramic particles boehmite are dispersed in water to form a slurry, and the slurry is coated on both sides of the base film using a gravure roll. During the coating process, the coating speed is set at 30 m / min, and the coating thickness is 2 μm on each side. After the coating is completed, it is dried in an oven at a temperature of 70°C. Then, solid spherical PVDF particles are sprayed onto one surface of the separator coated with the ceramic coating to obtain the separator. Among them, the thickness of the single-sided ceramic coating is 2 μm, and the thickness of the PVDF particles sprayed to form the adhesive layer is 1 μm. During the assembly process, the adhesive layer sprayed with PVDF particles faces the negative electrode plate.

[0210] Example 22 The battery cell of Example 22 is prepared in a similar manner 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.

[0211] Table 1

[0212] II. Performance Tests 1. Test method for the frequency of cold pressing and breaking of the electrode plate Take the designed coated electrode plate and conduct a cold pressing experiment corresponding to the target compaction density. Control the cold pressing speed at 30 m / min and the cold pressing pressure at ~30 tons during the cold pressing process. Produce 10,000 m of cold-pressed electrode plates, observe the situation of belt breaking during the cold pressing process of the electrode plates, record the number of belt breakings as n, and the belt breaking frequency as n / 10 (times / km).

[0213] 2. Test method for the first-cycle Coulombic efficiency of the battery cell For the battery after injection and static placement, perform a small-current formation. Static placement for 10 min, constant-current charging at 0.05C for 14.2 min, static placement for 10 min, constant-current charging at 0.1C for 90 min, static placement for 10 min, constant-current charging at 0.2C for 42 min, static placement for 10 min. Then, for the first charge and discharge, charge at 0.33C to 3.8V, static placement for 30 min, and then charge at 0.05C to 3.8V; then discharge at 0.33C to 2.0V, static placement for 30 min, and then discharge at 0.05C to 2.0V; Add up all the capacities of the formation and capacity as the first charging capacity, add up the capacities of the two-step discharges as the first discharge capacity, and the first efficiency = first discharge capacity / first charging capacity.

[0214] 3. Test method for cycle life ①Charge the battery cell at a rate of 1.5C to a state of charge (SOC) of 40% at 25°C; ②then charge it at a rate of 1C to 60% SOC; ③then charge it at a rate of 0.8C to 80% SOC; ④finally charge it at a rate of 0.33C to 100% SOC. ⑤Discharge the battery cell at a constant current of 1C to 0% SOC, and record the discharge capacity D1 of the first cycle; ⑥Repeat steps ① to ⑤ above, and record the cycle number corresponding to when the discharge capacity Dn reaches 80% D1.

[0215] 4. Volume energy density Let the battery cell stand at 25°C for 2 h to ensure that the temperature of the lithium-ion secondary battery is 25°C. At 25°C, charge the battery cell at a rate of 0.33C until the charging cut-off voltage of 3.8V, and then continue to charge it at a constant voltage at this charging cut-off voltage until the current is 0.05C, and the charging is terminated (where C represents the rated capacity of the battery cell). After the battery cell stands at 25°C for 1 h, discharge the battery cell at a rate of 0.33C at 25°C until the discharge cut-off voltage of 2.0V, and record the total discharge energy of the battery cell as E0. Measure the length, width, and height of the battery cell, and calculate the volume value of the battery cell V0 = length × width × height. The volume energy density of the battery cell = the discharge energy E0 of the battery cell / the volume V0 of the battery cell.

[0216] III. Analysis of test results of each example and comparative example Prepare the battery cells of each example and comparative example according to the above method, and measure various performance parameters. The results are shown in the following table.

[0217] Table 2

[0218] 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 curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, if the particle size D50 of the particle number distribution is less than 0.4 μm, or in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, if the particle size D50 of the particle number distribution is less than 10 μm, it will cause an increase in side reactions caused by small particles in the positive and negative electrode film layers, resulting in serious irreversible loss of active lithium ions in the battery, low initial efficiency, poor cycle life of the battery single cell, and inability to meet the performance requirements. On the contrary, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, if the particle size D50 of the particle number distribution is greater than 0.8 μm, or in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, if the particle size D50 of the particle number distribution is greater than 25 μm, although it can effectively reduce the probability of side reactions occurring inside the battery caused by small particles and improve the initial efficiency of the battery single cell, the too large particles make the electron transport path too long, exacerbate the polarization phenomenon of the battery, and lead to the attenuation of the cycle life of the battery single cell. And from the comparison of Examples 1-22 and Comparative Examples 1 and 2, it can be seen that the compaction of the positive electrode film layer does not meet 2.3 g / cm 3 - 2.5 g / cm 3 and the negative electrode film layer does not meet 1.35 g / cm 3 - 1.55 g / cm 3 , which is not conducive to the infiltration of the electrolyte into the film layer, especially not conducive to the infiltration of the electrolyte at the negative electrode, and deteriorates the cycle life of the battery single cell. As can be seen from the results of Examples 1-22 and Comparative Example 3, if the single-sided coating mass of the positive electrode film layer does not meet 0.370 g / 1540 mm 2 - 0.400 g / 1540 mm 2 , it will result in too little active material loading in the battery single cell of the same volume. Although the battery single cell has an excellent cycle life, its energy density is too low to meet the performance requirements.

[0219] As can be seen from the comparison of Examples 1-5 in Table 2, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, when the particle size D50 of the particle number distribution is 0.4 μm - 0.8 μm, further 0.6 μm - 0.7 μm, and in the cumulative particle number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode sheet, when the particle size D50 of the particle number distribution is 10 μm - 25 μm, further 15 μm - 20 μm, it can reduce the probability of side reactions caused by particles and the polarization phenomenon, so that the battery single cell can have both high initial efficiency, long cycle life and high energy density.

[0220] As can be seen from the results of Examples 1, 6-9 in Table 2, when the battery single cell is in a fully discharged state, the compaction density of the negative electrode film layer is 1.35 g / cm3 -1.55 g / cm 3 , and further 1.4 g / cm 3 -1.5 g / cm 3 , and at the same time, the compaction density of the positive electrode film layer is 2.3 g / cm 3 -2.5 g / cm 3 , and further 2.3 g / cm 3 -2.45 g / cm 3 When it is, the negative electrode film layer has a relatively high porosity, which can improve the battery cycle life while using the compaction design of the positive electrode to form a good match with the low compaction design of the negative electrode sheet, leaving space for the volume expansion during the lithium deintercalation process of the negative electrode, and taking into account the particle integrity of the positive electrode active material during the compaction process, so as to take into account the improvement of the energy density and cycle life of the battery monomer and meet the performance requirements.

[0221] It can be seen from the results of Examples 1 and 10-13 in Table 2 that the single-sided coating mass of the positive electrode film layer is 0.370 g / 1540 mm 2 -0.400 g / 1540 mm 2 , and further 0.380 g / 1540 mm 2 -0.400 g / 1540 mm 2 , through the thick coating design of the positive electrode, the loading amount of the active material is increased. While improving the energy density of the battery monomer, the positive electrode film layer has an appropriate lithium ion diffusion distance and resistance, thus taking into account the improvement of the battery cycle life; on this basis, the single-sided coating mass of the negative electrode film layer is 0.170 g / 1540 mm 2 -0.200 g / 1540 mm 2 , and further optionally 0.180 g / 1540 mm 2 -0.200 g / 1540 mm 2 , forming a good match with the positive electrode sheet, realizing the deintercalation and intercalation of lithium ions inside the battery, facilitating the full utilization of the battery capacity, and improving the energy density of the battery monomer; in addition, controlling the thick coating of the negative electrode film layer increases the proportion of the active material in the negative electrode sheet relative to the current collector, further improving the energy density of the battery monomer.

[0222] 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 further preferably 91.5% - 92.8%. This is beneficial to improving the specific capacity of the negative electrode active material and the volume expansion during lithium intercalation, enabling the battery cell to have excellent energy density and cycle life. At the same time, in the X-ray diffraction pattern of the negative electrode film layer, when the intensity ratio OI of the diffraction peaks of the 004 crystal plane of carbon to the 110 crystal plane of carbon is 2 - 4, and further preferably 2 - 2.9, it is beneficial to the intercalation of lithium ions on the negative electrode side and the improvement of the lithium intercalation rate of lithium ions, making the negative electrode capacity more fully utilized. At the same time, it effectively reduces the expansion of the negative electrode plate during operation and further improves the cycle life and energy density of the battery cell.

[0223] As can be seen from the results of Examples 1, 16, and 17 in Table 2, the injection coefficient of the electrolyte is 2.8 g / Ah - 3.2 g / Ah, which is beneficial to improving the wettability of the electrolyte and alleviating the liquid deficiency phenomenon in the later stage of battery cycling, ensuring that there is sufficient electrolyte to support the charge and discharge reactions throughout the entire life cycle of the battery cell, and improving the cycle life of the battery while increasing the energy density of the battery cell.

[0224] As can be seen from the results of Examples 1 and 18 in Table 2, the positive electrode film layer and the negative electrode film layer include linear conductive agents, which can form a network conductive network inside the film layer, improve the conductivity of the active material, and are also beneficial to improving the diffusion of lithium ions, further improving the energy density and cycle life of the battery cell.

[0225] Table 3

[0226] 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 14 μm - 16 μm and the thickness of the negative electrode current collector is 7 μm - 9 μm, it can ensure that the current collector does not crack during long-term battery cycling, improve the cycle stability and safety of the battery cell; at the same time, it can effectively reduce the probability of damage to the current collector and cold pressing breakage of the electrode sheet, and improve the yield rate of electrode sheet processing.

[0227] From the results of Examples 1 and 21 in Table 2, it can be seen that the isolation membrane in the battery cell includes a base membrane and a ceramic coating disposed on at least one side of the base membrane, the ceramic coating includes ceramic particles of boehmite, and the binder includes polyvinylidene fluoride, which can effectively improve the wettability of the electrolyte and improve the cycle life of the battery cell; and compared with spraying the binder particles on the surface of the ceramic particles, dissolving the binder and the ceramic particles in a solvent and mixing them with a roller on the surface of the base membrane can further improve the uniformity of the binder in the coating, so that the electrode and the separator are more evenly bonded, and the cycle life of the battery cell is further improved. Furthermore, from the comparison of the results of Examples 1 and 20, it can be seen that the isolation membrane includes a base membrane and a ceramic coating disposed on the surfaces of both sides of the base membrane, which can further improve the wettability of the electrolyte, reduce battery polarization, and thus further improve the cycle life of the battery cell.

[0228] It can be seen from the results of Examples 1 and 22 in Table 2 that when the thickness T of the battery cell satisfies 15 mm ≤ T ≤ 20 mm, the expansion force of the battery cell is effectively reduced, avoiding the performance drop caused by the increase of the negative electrode expansion; in addition, controlling the thickness within the above range can help the battery cell to dissipate heat quickly, reduce the decomposition of the electrolyte caused by the increase of the working temperature of the battery cell, and is beneficial to improving the cycle life and safety performance of the battery cell.

[0229] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, the battery cell comprising an electrode assembly and an electrolyte, the electrode assembly comprising a positive electrode tab, a negative electrode tab, and a separator disposed between the positive electrode tab and the negative electrode tab, the positive electrode tab 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 tab 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 in a fully discharged state, the compaction density of the positive electrode film layer is 2.3 g / cm 3 - 2.5 g / cm 3 ; the single-sided coating mass of the positive electrode film layer is 0.370 g / 1540 mm 2 - 0.400 g / 1540 mm 2 ; in the cumulative number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the number distribution particle size D50 of the particles is 0.4 μm - 0.8 μm; and When the battery cell is in a fully discharged state, the compaction density of the negative electrode film layer is 1.35 g / cm 3 -1.55 g / cm 3 ; in the cumulative number distribution curve of the particles obtained from the cross-section of the negative electrode film layer along the thickness direction of the electrode, the particle size D50 of the particle number distribution is 10 μm - 25 μm, where D50 refers to the particle size corresponding to 50% of the cumulative particle number distribution in the cumulative number distribution curve.

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

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

4. The battery cell according to claim 1, wherein The single-sided coating mass of the positive electrode film layer is 0.380 g / 1540 mm 2 -0.400 g / 1540 mm 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 layer in the thickness direction of the tab, the particle size D50 of the particle number distribution is 0.6 μm - 0.7 μm.

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

7. The battery cell according to claim 1, wherein The ratio CB value of the negative charging capacity to the positive 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 layer and / or the negative electrode film layer comprises a conductive agent, and the conductive agent comprises one or more of a linear conductive agent and a dot-shaped conductive agent.

9. The battery cell according to claim 8, wherein The linear conductive agent comprises 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, wherein, The linear conductive agent comprises multi-walled carbon nanotubes.

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

12. The battery cell according to claim 1, characterized in that, The injection coefficient of the electrolyte is 2.8 g / Ah - 3.2 g / Ah.

13. The battery cell according to claim 1, characterized in that, The negative electrode film layer comprises a negative active material, and the graphitization degree of the negative active material is 91.5% - 95%.

14. The battery cell according to claim 13, wherein The graphitization degree of the negative active material is 91.5% - 92.8%.

15. The battery cell according to claim 1, wherein In the X-ray diffraction pattern of the negative electrode film layer, the peak intensity ratio OI value of the diffraction peak of the 004 crystal plane of carbon to the diffraction peak of the 110 crystal plane of carbon is 2 - 4.

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

9.

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

18. The battery cell according to claim 1, wherein, In the cross-section of the positive electrode film layer in the thickness direction, the particle size D90 of the particle number distribution is 0.8 μm - 1 μm.

19. The battery cell according to claim 1, wherein In the cross-section of the positive electrode film layer in the thickness direction, the particle size D99 of the particle number distribution is 1 μm - 10 μm.

20. The battery cell according to claim 1, wherein, In the cross-section of the negative electrode film layer in the thickness direction, the particle size D10 of the particle number distribution is 4 μm - 10 μm.

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

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

23. The battery cell according to claim 1, wherein, The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes lithium-containing transition metal phosphate particles at least partially coated with a carbon material on the surface. The lithium-containing transition metal phosphate particles have a composition with the following general formula: Li m Fe x P y O j Q q , where 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, Br, 0.6 ≤ m ≤ 1.15, 0 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 0 ≤ q ≤ 1.

24. The battery cell according to claim 13, characterized in that, The negative active material comprises one or more of artificial graphite, natural graphite, modified natural graphite, microcrystalline graphite, soft carbon, and hard carbon.

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

26. The battery cell according to claim 25, wherein The single-sided coating mass of the negative electrode film layer is 0.180 g / 1540 mm 2 -0.200 g / 1540 mm 2 .

27. The battery cell according to claim 1, characterized in that, The thickness of the single-sided positive electrode film layer is 96 μm - 113 μm; and / or, the thickness of the single-sided negative electrode film layer is 71 μm - 96 μm.

28. The battery cell according to claim 1, wherein, 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.

29. The battery cell according to claim 1, wherein The separator includes a base film and a ceramic coating provided on at least one surface of the base film.

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

31. The battery cell according to claim 29, wherein The separator includes a base film and ceramic coatings provided on both surfaces of the base film.

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

33. The battery cell according to claim 1, wherein The battery cell includes a housing, and the material of the housing includes a soft package material, and the soft package material includes an aluminum-plastic film.

34. The battery cell according to claim 1, wherein, The length of the battery cell is L, the width is W, and the thickness is T. The dimensions of the battery cell satisfy: 550 mm ≤ L ≤ 650 mm, 110 mm ≤ W ≤ 140 mm, 15 mm ≤ T ≤ 20 mm.

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

36. An electrical device, characterized in that, The electrical device includes the battery device according to claim 35, and the battery device is used to provide electrical energy.

37. An energy storage device, characterized in that, The energy storage device includes the battery device according to claim 35, and the battery device is used to store electrical energy.

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