Battery cell, battery, battery pack and electric equipment

Abstract

The invention relates to the technical field of battery assembling and manufacturing, in particular to a battery cell, a battery, a battery pack and electric equipment. The battery cell comprises a positive plate, a diaphragm and a negative plate, the positive plate and the negative plate are mutually stacked, the diaphragm is arranged between the positive plate and the negative plate, the positive plate comprises a positive current collector and a positive active material layer, and the negative plate comprises a negative current collector and a negative active material layer; the edge of the negative active material layer on the negative plate exceeds the edge of the positive active material layer on the positive plate by L, the thickness of the diaphragm between the negative plate and the positive plate is T, and L and T meet the condition that T / L is greater than or equal to 0.016. The direction of an electric field line for lithium ion migration in an over-hang area is adjusted by controlling the ratio of the two, so that the lithium ions embedded in the over-hang area of the negative plate during charging can be smoothly separated out and cannot be gathered on the negative plate under the action of electric field force, the lithium separation problem is reduced, the capacity loss of the battery is reduced, and the service life of the battery is prolonged. And the safety of the battery in a fast charging and long circulation scene is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery cell, a battery, a battery pack and an electrical device. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long cycle life and no memory effect, and have been widely used in portable electronic devices, new energy vehicles, energy storage and other fields. With the development of battery technology, people have higher and higher requirements for battery fast charging capability and safety.

[0003] However, when lithium-ion batteries are used in scenarios such as fast charging and low temperatures, lithium deposition at the edges becomes increasingly serious, seriously affecting the energy density and safety performance of lithium batteries. Summary of the invention

[0004] Based on this, the present application provides a battery cell, a battery, a battery pack and an electrical device to solve the problem of lithium plating in the overhang area of ​​the electrode, thereby improving the performance of the battery.

[0005] On the one hand, the present application provides a battery cell, comprising a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet and the negative electrode sheet are stacked on each other, and the separator is disposed between the positive electrode sheet and the negative electrode sheet;

[0006] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. Along the thickness direction of the positive electrode current collector, the positive electrode active material layer is located on at least one side of the surface of the positive electrode current collector;

[0007] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, and along the thickness direction of the negative electrode current collector, the negative electrode active material layer is located on at least one side of the surface of the negative electrode current collector;

[0008] Along the stacking direction, the orthographic projection of the edge of the negative electrode active material layer on the negative electrode sheet on the surface where the positive electrode sheet is located exceeds the edge of the positive electrode active material layer on the positive electrode sheet by a dimension L, the thickness of the separator between the negative electrode sheet and the positive electrode sheet is T, and L and T satisfy: T / L≥0.016.

[0009] In a possible implementation, L and T satisfy: T / L≥0.024.

[0010] In a possible implementation, L satisfies: 0<L≤5mm.

[0011] In a possible implementation, T satisfies: 8 μm≤T≤32 μm.

[0012] In a possible implementation, the thickness of the positive electrode sheet is W1, and W1 satisfies: 40 μm≤W1≤4000 μm.

[0013] In a possible implementation, the thickness of the negative electrode sheet is W2, and W2 satisfies: 20 μm≤W2≤3000 μm.

[0014] In a possible implementation, the thickness of the positive electrode current collector is W3, and W3 satisfies: 5 μm≤W3≤25 μm; and / or,

[0015] The thickness of the negative electrode current collector is W4, and W4 satisfies: 5μm≤W4≤25μm.

[0016] In a possible implementation, the separator is a PE film or a PP film.

[0017] In a possible implementation, the positive electrode active material layer includes lithium iron phosphate or nickel-cobalt-manganese ternary material or nickel-cobalt-aluminum ternary material.

[0018] In a possible implementation, the negative electrode active material layer includes a graphite material.

[0019] In a possible implementation, the battery cell is a laminated battery cell or a wound battery cell.

[0020] On the other hand, the present application provides a battery, comprising a shell and the above-mentioned battery cell, wherein the battery cell is arranged in the shell.

[0021] On the other hand, the present application provides a battery pack including the above-mentioned battery.

[0022] On the other hand, the present application provides an electrical device, including the above-mentioned battery cell, or the above-mentioned battery, or the above-mentioned battery pack.

[0023] The battery cell, battery, battery pack and electrical equipment provided by the present application adjust the direction of the electric field lines for the migration of lithium ions in the overhang area by controlling the size of the negative electrode active material layer on the negative electrode sheet exceeding the positive electrode active material layer on the positive electrode sheet in the battery cell, that is, the size difference between the edges of the positive and negative electrode active material layers in the overhang area and the thickness of the separator between the positive and negative electrode sheets, so that under the action of the electric field force, the lithium ions embedded in the overhang area of ​​the negative electrode sheet during charging can be smoothly released, and the lithium ions embedded in the overhang area of ​​the negative electrode sheet will not gather at the edge of the overhang area of ​​the negative electrode sheet, thereby reducing the problem of lithium plating in the overhang area of ​​the negative electrode sheet, thereby reducing the capacity loss of the battery, and improving the safety of the battery in fast charging and long cycle scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 A schematic diagram of the structure of a battery cell provided in an embodiment of the present application;

[0026] Figure 2 for Figure 1 A schematic cross-sectional view of the stacked positive and negative electrode sheets of the battery cell along the AA direction;

[0027] Figure 3 for Figure 2 Schematic diagram of the diffusion of lithium ions in the battery cell during charging;

[0028] Figure 4 for Figure 2 Schematic diagram of lithium ion diffusion during discharge of the battery cell shown;

[0029] Figure 5 This is a DSC test data image of the graphite negative electrode in Example 4 of the present application.

[0030] Description of reference numerals:

[0031] 100 - battery cell; 10 - positive electrode sheet; 11 - positive electrode current collector; 12 - positive electrode active material layer; 20 - separator; 30 - negative electrode sheet; 31 - negative electrode current collector; 32 - negative electrode active material layer; 40 - positive electrode ear; 50 - negative electrode ear. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiment of the present application will be described in more detail below in conjunction with the drawings in the preferred embodiments of the present application. In the drawings, the same or similar reference numerals throughout represent the same or similar parts or parts with the same or similar functions. The described embodiments are part of the embodiments of the present application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limitations on the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application. The embodiments of the present application are described in detail below in conjunction with the drawings.

[0033] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, or it can be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0034] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are orientations or positional relationships based on the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0035] The terms "first", "second" and "third" (if any) in the specification and claims of this application and the above drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0036] In addition, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or display comprising a series of steps or elements is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to such process, method, product, or display.

[0037] Lithium-ion batteries have the advantages of high energy density, long cycle life and no memory effect, and have been widely used in portable electronic devices, new energy vehicles, energy storage and other fields. With the development of battery technology, people have higher and higher requirements for battery fast charging capability and safety.

[0038] However, when lithium-ion batteries are used in scenarios such as fast charging and low temperatures, lithium deposition at the edges becomes increasingly serious, seriously affecting the energy density and safety performance of lithium batteries.

[0039] In terms of improving edge lithium plating, currently commonly used methods include controlling the N / P ratio (battery positive and negative electrode capacity ratio), thinning the edges of the positive and negative electrode sheets or thickening the edges of the current collector, modifying the diaphragm design to avoid electrolyte drying in the overhang area, and optimizing the fast charging strategy. The overhang area refers to the part of the lithium battery design where the length and width of the negative electrode sheet are longer and wider than the positive electrode sheet, that is, the area where the negative electrode is larger than the positive electrode. The purpose is to optimize the performance and safety of the battery by controlling the size and capacity of the negative electrode. Through this design, the safety and stability of the battery can be effectively improved and the battery life can be extended. For batteries with reasonable control of N / P design, the lithium deposition problem in the overlapping area of ​​the positive and negative electrodes is effectively improved, but after long cycles, the lithium deposition problem in the overhang area is still relatively serious, and there is a safety problem; for batteries with thinned edges of the positive and negative electrode sheets and thickened edges of the current collector, the accumulation of active materials at the edges of the positive and negative electrode sheets during positive and negative electrode coating is avoided, but it can only alleviate the speed of lithium deposition during fast charging. After long cycles, the lithium deposition problem in the overhang area is more serious; the modified design of the battery separator is to solve the lithium deposition problem caused by serious electrolyte drying in the overhang area, but the lithium deposition problem caused by the offset of the electric field lines in the overhang area has not been solved, so the lithium deposition problem in this area will be aggravated after long cycles; for batteries with optimized fast charging strategies, the lithium deposition problem in the overlapping area of ​​the positive and negative electrodes or on the surface of the positive and negative electrodes is improved, but the lithium deposition problem in the overhang area is still not solved.

[0040] After repeated verification, the inventors found that in the overhang area, along the length or width direction of the electrode sheet, when the ratio of the size of the negative electrode active material layer exceeding the positive electrode active material layer in the area to the thickness of the diaphragm changes, the direction of the electric field lines of lithium ion migration in the overhang area will change. Therefore, if the ratio between the two is reasonably controlled, the direction of the electric field lines of lithium ion migration in the overhang area can be adjusted, so that under the action of the electric field force, the lithium ions embedded in the overhang area of ​​the negative electrode sheet during charging can be smoothly removed from the negative electrode sheet. Therefore, the lithium ions embedded in the overhang area of ​​the negative electrode sheet will not gather in the overhang area of ​​the negative electrode sheet, thereby significantly improving the lithium precipitation problem in the overhang area of ​​the negative electrode sheet, while also reducing the capacity loss of the battery, so that the safety of the battery in fast charging and long cycle scenarios is improved.

[0041] In view of this, the present application provides a battery cell, comprising a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet and the negative electrode sheet are stacked on each other, the separator is arranged between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, and along the thickness direction of the positive electrode current collector, the positive electrode active material layer is located on at least one side of the surface of the positive electrode current collector, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, and along the thickness direction of the negative electrode current collector, the negative electrode active material layer is located on at least one side of the surface of the negative electrode current collector;

[0042] Along the stacking direction, the orthographic projection of the edge of the negative electrode active material layer on the negative electrode sheet on the surface where the positive electrode sheet is located exceeds the edge of the positive electrode active material layer on the positive electrode sheet by a dimension L, the thickness of the separator between the negative electrode sheet and the positive electrode sheet is T, and L and T satisfy: T / L≥0.016.

[0043] By controlling the size of the negative electrode active material layer on the negative electrode sheet exceeding the positive electrode active material layer on the positive electrode sheet in the battery cell, that is, the size difference between the edges of the positive and negative electrode active material layers in the overhang area, and the thickness of the separator between the positive and negative electrode sheets, the direction of the electric field lines of lithium ion migration in the overhang area is adjusted, so that under the action of the electric field force, the lithium ions embedded in the overhang area of ​​the negative electrode sheet during charging can be smoothly released, and the lithium ions embedded in the edge area of ​​the negative electrode sheet will not gather at the edge part of the negative electrode sheet, thereby reducing the problem of lithium plating in this area on the negative electrode sheet, thereby reducing the capacity loss of the battery, and improving the safety of the battery in fast charging and long cycle scenarios.

[0044] The contents of the present application will be described in detail below in conjunction with the accompanying drawings so that those skilled in the art can understand the contents of the present application more clearly and in detail.

[0045] Figure 1 A schematic diagram of the structure of a battery cell provided in an embodiment of the present application. Figure 2 for Figure 1 The cross-sectional structure diagram of the stacked positive electrode sheet and negative electrode sheet of the battery cell along the AA direction is shown. Figure 3 for Figure 2 Schematic diagram of the diffusion of lithium ions in the battery cell during charging. Figure 4 for Figure 2 Schematic diagram of the diffusion of lithium ions in the battery cell during discharge. Figure 5 This is a Differential Scanning Calorimetry (DSC) test data image of the graphite negative electrode in Example 4 of the present application.

[0046] like Figure 1 and Figure 2As shown, the battery cell 100 provided in the embodiment of the present application includes a positive electrode sheet 10 , a separator 20 and a negative electrode sheet 30 . The positive electrode sheet 10 and the negative electrode sheet 30 are stacked on each other, and the separator 20 is disposed between the positive electrode sheet 10 and the negative electrode sheet 30 .

[0047] In a possible implementation, the battery cell 100 is a laminated battery cell.

[0048] In another possible implementation, the battery cell 100 is a winding core.

[0049] like Figure 2 As shown, the positive electrode sheet 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 is disposed on the positive electrode current collector 11. Along the thickness direction of the positive electrode current collector 11, the positive electrode active material layer 12 is located on at least one side of the surface of the positive electrode current collector 11.

[0050] In a possible implementation, positive electrode active material layers 12 are provided on both sides of the positive electrode current collector 11 in the thickness direction.

[0051] The negative electrode sheet 30 includes a negative electrode current collector 31 and a negative electrode active material layer 32. The negative electrode active material layer 32 is disposed on the negative electrode current collector 31. The negative electrode active material layer 32 is located on at least one side of the surface of the negative electrode current collector 31 along the thickness direction of the negative electrode current collector 31.

[0052] In a possible implementation, negative electrode active material layers 32 are provided on both sides of the negative electrode current collector 31 in the thickness direction.

[0053] In a possible implementation, the battery cell 100 further includes a positive electrode tab 40 and a negative electrode tab 50. The positive electrode tab 40 is disposed on the positive electrode sheet 10. The negative electrode tab 50 is disposed on the negative electrode sheet 30.

[0054] The positive electrode tab 40 is connected to one side of the positive electrode sheet 10 along the length or width direction of the positive electrode sheet 10 .

[0055] The negative electrode tab 50 is connected to one side of the negative electrode sheet 30 along the length or width direction of the negative electrode sheet 30 .

[0056] like Figure 2 As shown, along the stacking direction of the positive electrode sheet 10 and the negative electrode sheet 30 , that is, along the thickness direction of the positive electrode sheet 10 or the negative electrode sheet 30 , there is a portion at the edge of the negative electrode sheet 30 that exceeds the edge of the positive electrode sheet 10 , and this portion is the overhang area of ​​the negative electrode sheet 30 .

[0057] In the overhang area, along the stacking direction, the orthographic projection of the edge of the negative electrode active material layer 32 on the negative electrode sheet 30 on the surface where the positive electrode sheet 10 is located exceeds the size of the edge of the positive electrode active material layer 12 on the positive electrode sheet 10, and the minimum value of the difference between the length direction and the width direction of the electrode sheet is L, that is, the negative electrode active material layer 32 exists on the side of the negative electrode current collector 31 facing the positive electrode current collector 11, and the positive electrode active material layer 12 exists on the side of the positive electrode current collector 11 facing the negative electrode current collector 31, and the projection of one side of the negative electrode active material layer 32 exceeds the size of the projection of one side of the positive electrode active material layer 12, that is, in the overhang area, the size difference between the negative electrode active material layer 32 and the positive electrode active material layer 12.

[0058] Among them, in the overhang area, the negative electrode active material layer 32 on the negative electrode sheet 30 represents the negative electrode active material layer 32 that is directly opposite to the positive electrode sheet 10 on the side of the negative electrode sheet 30 facing the positive electrode sheet 10, and if a protective layer such as a ceramic layer is provided at the edge of the negative electrode sheet 30, the negative electrode active material layer 32 is represented as the portion of the negative electrode sheet 30 where no protective layer is provided; similarly, the positive electrode active material layer 12 on the positive electrode sheet 10 represents the positive electrode active material layer 12 that is directly opposite to the negative electrode sheet 30 on the side of the positive electrode sheet 10 facing the negative electrode sheet 30, and if a protective layer such as a ceramic layer is provided at the edge of the positive electrode sheet 10, the positive electrode active material layer 12 is represented as the portion of the positive electrode sheet 10 where no protective layer is provided.

[0059] In a possible implementation, there are overhang areas on both sides of the negative electrode sheet 30 along the length direction and the width direction of the negative electrode sheet 30 .

[0060] The thickness of the separator 20 between the negative electrode sheet 30 and the positive electrode sheet 10 is T.

[0061] L and T satisfy: T / L≥0.016.

[0062] Right now Figure 2 , 1 / tanθ≥0.016.

[0063] like Figure 3 As shown, during the charging process of the battery cell, the lithium ions on the positive electrode sheet 10 migrate to the negative electrode sheet 30 under the action of the electric field force. Due to the uneven distribution of local current density, lithium is embedded in the overhang area. In addition, there is a difference in the lithium embedding state in the overlapping area between the positive electrode sheet 10 and the negative electrode sheet 30, and in the overhang area. Therefore, the lithium ions will also diffuse into the overhang area.

[0064] like Figure 4As shown, during the discharge process of the battery cell, if the battery cell is designed with T / L < 0.016, that is, θ is greater than a certain angle, it is difficult for lithium ions to be deintercalated in the overhang area, especially in the outer edge of the overhang area, resulting in residual lithium in the overhang area, causing the battery cell capacity to decrease and the coulombic efficiency to be low; and after multiple cycles, when the lithium ions in the overhang area accumulate to the lithium precipitation point, metallic lithium will be precipitated.

[0065] In the design of the present application, T / L≥0.016, that is, θ is less than a certain angle. At this time, the direction of the electric field lines for the migration of lithium ions in the overhang area is adjusted, so that during the discharge process, under the action of the electric field force, the lithium ions embedded in the overhang area during charging can be smoothly released, and the lithium ions embedded in the overhang area of ​​the negative electrode sheet 30 during charging will not gather in the overhang area, thereby reducing the problem of lithium plating in the overhang area of ​​the negative electrode sheet 30 and reducing the capacity loss of the battery.

[0066] Preferably, L and T satisfy: T / L≥0.032.

[0067] In a possible implementation, L satisfies: 0<L≤5mm.

[0068] L in the overhang area cannot be too long, greater than 5mm, otherwise the lithium ions embedded in the outermost edge of the overhang area will not be able to escape smoothly, resulting in lithium plating; but if L is too short, that is, the sizes of the positive and negative electrodes are exactly the same, the positive and negative electrode alignment process is more difficult, which increases production costs and easily causes capacity loss.

[0069] In a possible implementation, T satisfies: 8 μm≤T≤32 μm.

[0070] Properly increasing the thickness of the separator 20 between the positive and negative electrodes can adjust the direction of the electric field lines of lithium ion migration, which is beneficial to improving the uneven current distribution in the overhang area and is beneficial to the normal deintercalation of lithium ions in the outermost edge part of the overhang area; however, the separator 20 should not be too thick, because a too thick separator 20 will hinder the transmission of lithium ions, and will also increase the volume of the battery cell 100, resulting in a decrease in volume energy density, and will affect the fast charging performance of the battery and increase costs.

[0071] Electrode thickness has a direct impact on battery capacity, energy density, charge and discharge performance, and cycle life.

[0072] In a possible implementation, the thickness of the positive electrode sheet 10 is W1.

[0073] W1 satisfies: 40μm≤W1≤4000μm.

[0074] If W1 is less than 40 μm during the design of the battery cell, the brittleness of the positive electrode sheet 10 will increase, making the positive electrode sheet 10 difficult to process, resulting in a reduced yield; and the thinner the positive electrode sheet 10 is, the less active material is coated on it, which will also reduce the capacity and life of the battery.

[0075] In the design of the present application, W1>4000μm, because the electrode is too thick, the internal resistance of the battery is increased, the battery charging and discharging rate is slowed down, the battery capacity and charging and discharging efficiency are reduced, and the energy density of the battery is also reduced.

[0076] In a possible implementation, the thickness of the negative electrode sheet 30 is W2.

[0077] W2 satisfies: 20μm≤W2≤3000μm.

[0078] If W2 is less than 20 μm during the design of the battery cell, the brittleness of the negative electrode sheet 30 will increase, making it difficult to process the negative electrode sheet 30, resulting in a reduced yield; and the thinner the negative electrode sheet 30 is, the less active material is coated on it, which will also reduce the capacity and life of the battery.

[0079] In the design of the present application, W2>3000μm, because the electrode is too thick, the internal resistance of the battery is increased, the battery charging and discharging rate is slowed down, the battery capacity and charging and discharging efficiency are reduced, and the energy density of the battery is also reduced.

[0080] In a possible implementation, the positive electrode sheet 10 uses aluminum foil as the positive electrode current collector 11 , and the negative electrode sheet 30 uses copper foil as the negative electrode current collector 31 .

[0081] The current collector is a key component for collecting and transmitting current inside the battery. The selection of its thickness requires comprehensive consideration of multiple factors, including the type of battery, design requirements, and the material properties of the current collector, which directly affects the performance and safety of the battery.

[0082] In a possible implementation, the thickness of the positive electrode current collector 11 is W3.

[0083] W3 satisfies: 5μm≤W3≤25μm.

[0084] If W3 is less than 5μm when designing the battery cell, the resistance will increase due to the reduction in the thickness of the current collector, causing battery overheating, which in turn will cause serious safety problems. It will also lead to insufficient conductivity, affecting the performance and life of the battery.

[0085] In the design of the present application, W3>25μm, which will increase the weight and cost of the battery and reduce the energy density of the battery.

[0086] In a possible implementation, the positive electrode active material layer 12 includes an iron-lithium system material such as lithium iron phosphate (LFP).

[0087] In another possible implementation, the positive electrode active material layer 12 may further include a ternary system material, such as a nickel-cobalt-manganese ternary material (NCM), a nickel-cobalt-aluminum ternary material (NCA), etc.

[0088] In a possible implementation, the thickness of the negative electrode current collector 31 is W4.

[0089] W4 satisfies: 5μm≤W4≤25μm.

[0090] If W4 is less than 5μm when designing the battery cell, the resistance will increase due to the reduction in the thickness of the current collector, causing battery overheating, which in turn will cause serious safety problems. It will also lead to insufficient conductivity, affecting the performance and life of the battery.

[0091] In the design of the present application, W4>25μm, which will increase the weight and cost of the battery and reduce the energy density of the battery.

[0092] In a possible implementation, the negative electrode active material layer 32 includes a graphite material.

[0093] In a possible implementation, the diaphragm 20 is a polyethylene (PE) film or a polypropylene (PP) film. It is understandable that the diaphragm 20 in the present application is a polyethylene (PE) film or a polypropylene (PP) film, which means that the base film of the diaphragm 20 is a polyethylene (PE) or polyethylene (PE) material. The case where the polyethylene (PE) base film or the polypropylene (PP) base film further includes a ceramic layer and a glue layer is also within the scope of the present application. At this time, the thickness T of the diaphragm 20 is the sum of the thickness of the base film and the ceramic layer and / or the glue layer.

[0094] The selection of the material and model of the diaphragm 20 has no significant effect on the determination of the T / L ratio range in the overhang region.

[0095] The battery cell 100 provided in the embodiment of the present application includes a positive electrode sheet 10, a separator 20 and a negative electrode sheet 30. The positive electrode sheet 10 and the negative electrode sheet 30 are stacked on each other, and the separator 20 is arranged between the positive electrode sheet 10 and the negative electrode sheet 30. The positive electrode sheet 10 includes a positive electrode collector 11 and a positive electrode active material layer 12. Along the thickness direction of the positive electrode collector 11, the positive electrode active material layer 12 is located on at least one side of the surface of the positive electrode collector 11. The negative electrode sheet 30 includes a negative electrode collector 31 and a negative electrode active material layer 32. Along the thickness direction of the negative electrode collector 31, the negative electrode active material layer 32 is located on at least one side of the surface of the negative electrode collector 31.

[0096] Along the stacking direction, the projection of the edge of the negative electrode active material layer 32 on the negative electrode sheet 30 exceeds the projection of the edge of the positive electrode active material layer 12 on the positive electrode sheet 10 by a dimension L, the thickness of the separator 20 between the negative electrode sheet 30 and the positive electrode sheet 10 is T, and L and T satisfy: T / L≥0.016.

[0097] By controlling the size of the negative electrode active material layer 32 on the negative electrode sheet 30 exceeding the positive electrode active material layer 12 on the positive electrode sheet 10 in the battery cell 100, that is, the ratio of the size difference between the edges of the positive and negative electrode active material layers in the overhang area and the thickness of the separator 20 between the positive and negative electrode sheets, the direction of the electric field lines of lithium ion migration in the overhang area is adjusted, so that under the action of the electric field force, the lithium ions embedded in the overhang area of ​​the negative electrode sheet 30 during charging can be smoothly released, and the lithium ions embedded in the overhang area of ​​the negative electrode sheet 30 will not gather at the edge of the overhang area of ​​the negative electrode sheet 30, thereby reducing the problem of lithium plating in the overhang area of ​​the negative electrode sheet 30, thereby reducing the capacity loss of the battery, and improving the safety of the battery in fast charging and long cycle scenarios.

[0098] In addition, an embodiment of the present application further provides a battery, including a shell and the above-mentioned battery cell 100, wherein the battery cell 100 is disposed in the shell.

[0099] The specific structure, working principle and function of the battery cell 100 have been described in detail in the above embodiments, and will not be repeated here. It should be noted that the following is a process for preparing batteries in multiple groups of embodiments and comparative examples.

[0100] Example 1

[0101] The soft-pack battery of the LFP-Gr (lithium iron phosphate-graphite) system is assembled, the thickness of the positive active material layer 12 on the positive electrode sheet 10 is 83μm, the thickness of the negative active material layer 32 on the negative electrode sheet 30 is 58μm, the N / P ratio is 1.08 (the N / P ratio is calculated based on the surface capacity of the positive and negative electrodes, and the capacity of the overhang area is not considered), the size L of the overhang area is 0.5mm, the thickness T of the diaphragm 20 is 24μm, and the diaphragm 20 adopts a polypropylene (PP) ceramic diaphragm, T / L=0.048. After the battery is assembled and left to stand for 8h, the upper fixture is used for formation. In the early stage of formation, the battery needs to be charged with a small current to form a stable SEI film on the surface of the negative electrode, and then the capacity is divided. The specific steps of the capacity division are listed in Tables 1 and 2 respectively. After formation, the capacity division steps are followed, and the cycle is repeated 3 times, and the discharge capacity of the last cycle is recorded, and the capacity is marked as C0.

[0102] Table 1 Battery formation steps

[0103]

[0104] Table 2 Battery capacity classification steps

[0105]

[0106] Example 2

[0107] The difference from the first embodiment is that the thickness T of the diaphragm 20 is 32 μm, and T / L=0.064. The remaining steps are the same as the first embodiment.

[0108] Example 3

[0109] The difference from the first embodiment is that the thickness T of the diaphragm 20 is 16 μm, and T / L=0.032. The remaining steps are the same as the first embodiment.

[0110] Example 4

[0111] The difference from the first embodiment is that the thickness T of the diaphragm 20 is 8 μm, and T / L=0.016. The remaining steps are the same as the first embodiment.

[0112] Example 5

[0113] The difference from Example 1 is that the size L of the overhang area is 1 mm, and T / L=0.024. The remaining steps are the same as those of Example 1.

[0114] Example 6

[0115] The difference from Example 1 is that the size L of the overhang area is 0.25 mm, and T / L=0.096. The remaining steps are the same as those of Example 1.

[0116] Example 7

[0117] The difference from the first embodiment is that the size L of the overhang area is 0.15 mm, and T / L=0.16. The remaining steps are the same as the first embodiment.

[0118] Example 8

[0119] The difference from Example 4 is that the thickness of the positive electrode active material layer 12 on the positive electrode sheet 10 is 100 μm. The remaining steps are the same as those of Example 1.

[0120] Example 9

[0121] The difference from Example 4 is that the thickness of the positive electrode active material layer 12 on the positive electrode sheet 10 is 70 μm. The remaining steps are the same as those of Example 1.

[0122] Example 10

[0123] The difference from Example 4 is that the thickness of the negative electrode active material layer 32 on the negative electrode sheet 30 is 70 μm. The remaining steps are the same as those of Example 1.

[0124] Embodiment 11

[0125] The difference from Example 4 is that the thickness of the negative electrode active material layer 32 on the negative electrode sheet 30 is 40 μm. The remaining steps are the same as those of Example 1.

[0126] Comparative Example 1

[0127] The difference from Example 1 is that the size L of the overhang area is 5 mm, and T / L=0.0048. The remaining steps are the same as those of Example 1.

[0128] Comparative Example 2

[0129] The difference from Comparative Example 1 is that the thickness T of the separator 20 is 8 μm, and T / L=0.0016. The remaining steps are the same as those of Comparative Example 1.

[0130] Comparative Example 3

[0131] The difference from Comparative Example 8 is that the thickness T of the diaphragm 20 is 16 μm, the size L of the overhang area is 1.5 mm, and T / L=0.011. The remaining steps are the same as those of Comparative Example 1.

[0132] It should be noted that the positive and negative electrode materials and N / P are the same in all embodiments and comparative examples of the present application.

[0133] The batteries prepared in Examples 1-11 and Comparative Examples 1-3 were subjected to the initial coulombic efficiency test, the capacity retention rate test after 50 cycles, the fast charge capacity test and the lithium precipitation amount test.

[0134] 1) Calculation method of the first coulombic efficiency: Based on the data recorded during the battery formation stage, the first coulombic efficiency CE is calculated. Ⅰ The calculation formula is as follows: CE Ⅰ =C3 / (C1+C2); the test results are shown in Table 3;

[0135] 2) Calculation method of capacity retention rate after 50 cycles: Charge and discharge the divided battery at a constant current of 0.33C for 50 times, and record the discharge capacity of the first and 50th cycles. The discharge capacity of the first cycle is recorded as C D1 The discharge capacity of the 50th cycle is recorded as C D50 , the capacity retention rate after 50 cycles R 50cycle The calculation formula is as follows: 50cycle =C D1 / C D50 ; The test results are shown in Table 3;

[0136] 3) The calculation method of fast charge capacity is: when the remaining power of the battery is 0-22%, the battery is charged at a 4C rate, when the remaining power of the battery is 22%-27%, the battery is charged at a 3.5C rate, when the remaining power of the battery is 27%-35%, the battery is charged at a 3C rate, when the remaining power of the battery is 35%-44%, the battery is charged at a 2.5C rate, when the remaining power of the battery is 44%-65%, the battery is charged at a 2C rate, when the remaining power of the battery is 65%-80%, the battery is charged at a 1.5C rate, and when the remaining power of the battery is 80%-100%, the battery is charged at a 0.33C rate to obtain the battery fast charge capacity; the test results are shown in Table 3;

[0137] 4) The method for calculating the amount of lithium deposition is as follows: a series of DSC tests of lithium powders of different masses are conducted in advance to obtain the endothermic values ​​of lithium powders of different masses at 180°C, and the working curve of lithium metal is plotted. After the fast charge is completed, the overhang area of ​​the negative electrode sheet 30 is cut off and placed in a 40μL standard aluminum crucible with the lithium deposition surface close to the bottom of the crucible. The sample loading amount is 8mg. The endothermic value obtained from the DSC curve of the lithium deposition sample is substituted into the working curve of lithium metal to calculate the lithium deposition mass of the sample. The test results are shown in Table 3.

[0138] Table 3 Data table of first coulombic efficiency, 50 cycle capacity retention rate, fast charge capacity and DSC test lithium precipitation amount of embodiments and comparative examples

[0139]

[0140] As shown in Table 3, the size L of the overhang area of ​​the battery in Example 1, Example 2, Example 3 and Example 4 is the same, and the thickness T of the separator 20 is different. The thickness T of the separator in Example 1 to Example 4 is 24 μm, 32 μm, 16 μm and 8 μm, respectively, and T / L is 0.048, 0.064, 0.032 and 0.016, respectively. Ⅰ is 88.63%, R 50cycle The CE in Example 3 is 99.11%. Ⅰ is 88.38%, R 50cycle The CE in Example 4 is 99.14%. Ⅰ is 87.19%, R 50cycle It is 98.87%. This shows that when the size L of the overhang area is the same, increasing the thickness T of the separator 20 and increasing the T / L value are beneficial to the deintercalation of lithium ions at the outer edge of the overhang area during charging and discharging, improving the uneven current distribution in the overhang area, reducing irreversible capacity loss, and improving the first coulombic efficiency and cycle performance. Compared with Example 1, CE in Example 2 Ⅰ is 88.81%, R 50cycle The overhang area has an irreversible lithium ion loss of 99.27%, but the thickness of the separator 20 is too thick, which will sacrifice the volume energy density of the battery and increase the cost of the battery.

[0141] The thickness T of the separator 20 of the battery in Example 1, Example 5, Example 6 and Example 7 is the same, the size L of the overhang area is 0.5 mm, 1 mm, 0.25 mm and 0.15 mm, respectively, and T / L is 0.048, 0.024, 0.096 and 0.16, respectively. Ⅰ They are 88.63%, 87.77%, 88.93% and 89.06% respectively, R 50cycle They are 99.11%, 99.02%, 99.48% and 99.52% respectively. This shows that for the same thickness T of the diaphragm 20, the larger the size L of the overhang area, the more uneven the current distribution, the more difficult it is for lithium ions at the outer edge of the overhang area to be reversibly deintercalated, and lithium deposition is more likely to occur, resulting in irreversible capacity loss. In theory, the smaller the size L of the overhang area, the less reversible lithium is lost in the edge area. In reality, it is very difficult to completely align the positive and negative electrodes. Usually, process errors are considered when designing batteries. Therefore, L≠0.

[0142] In Examples 8, 9, 10 and 11, the T / L is the same, the thickness of the positive and negative active material layers is different, and compared with Comparative Examples 1 to 3, the CE Ⅰ and R50cycle The changes in are better than those in the control examples, indicating that the thickness of the active material layer has a smaller effect on the deintercalation of lithium ions at the outer edge of the overhang area than the ratio of T / L. Compared with Example 1, the size L of the overhang area is increased by 10 times, and T / L is significantly reduced, resulting in the inability of lithium ions embedded in the edge of the overhang area of ​​the negative electrode to be released during charging, resulting in serious losses in the first coulombic efficiency and cycle capacity. Compared with Example 4, the thickness T of the diaphragm 20 is the same, and the length L of the overhang area is increased by 10 times, resulting in poor first coulombic efficiency and cycle performance. Compared with Example 4, the T / L value of Comparative Example 3 is slightly different, but the CE Ⅰ and R 50cycle The change is obvious, indicating that when T / L exceeds 0.016, the effect on the deintercalation of lithium ions at the outer edge of the overhang area is significantly increased. The size L of the overhang area of ​​the battery in Example 1, Example 2, Example 3 and Example 4 is the same, the thickness T of the separator 20 is 24μm, 32μm, 16μm and 8μm respectively, and T / L is 0.048, 0.064, 0.032 and 0.016 respectively. The DSC test data image of Example 4 is shown in FIG. Figure 5 By comparing the data of capacity and lithium precipitation during the fast charge test, it is shown that the decrease in T and the decrease in T / L will cause the transmission path to become longer and the current distribution to become more uneven when lithium ions are deintercalated in the overhang area, causing some lithium ions to precipitate in the overhang area of ​​the negative electrode, affecting the capacity of the battery, which is consistent with the results of the first coulomb efficiency and cycle data.

[0143] The thickness T of the diaphragm 20 of Example 1, Example 5, Example 6 and Example 7 is the same, the size L of the overhang area is 0.5mm, 1mm, 0.25mm, 0.15mm, respectively, and T / L is 0.048, 0.024, 0.096 and 0.16, respectively. By comparing the data of capacity and lithium precipitation during fast charging test, it is shown that as L increases and T / L decreases, when lithium ions are deintercalated in the overhang area, the transmission path becomes longer, the current distribution is uneven, and irreversible lithium loss occurs, which corresponds to the first coulomb efficiency and cycle data results.

[0144] In Example 8, Example 9, Example 10 and Example 11, T / L is the same, and the thickness of the positive and negative active material layers is different. Compared with Comparative Examples 1 to 3, the changes in capacity and lithium precipitation amount are better than those of the comparative examples, indicating that the effect of the thickness of the active material layer on the insertion and extraction of lithium ions at the outer edge of the overhang area is less than the ratio of T / L.

[0145] Compared with Example 1, the size L of the overhang area in Comparative Example 1 increases by 10 times, and T / L decreases significantly, resulting in the inability of lithium ions embedded in the edge of the negative electrode overhang area to escape during charging, resulting in serious lithium precipitation and capacity decay. Compared with Example 4, the thickness T of the diaphragm 20 is the same, the size L of the overhang area increases by 10 times, and lithium precipitation and capacity decay are serious. Compared with Example 4, the T / L value of Comparative Example 3 is slightly different, but the changes in capacity and lithium precipitation are obvious, indicating that when T / L exceeds 0.016, the effect of lithium ion extraction at the outer edge of the overhang area is significantly increased, and the capacity is significantly reduced.

[0146] The battery provided in the embodiment of the present application adjusts the direction of the electric field lines for the migration of lithium ions in the overhang area by controlling the size of the negative electrode active material layer 32 on the negative electrode sheet 30 exceeding the positive electrode active material layer 12 on the positive electrode sheet 10 in the battery cell 100, that is, the ratio of the size difference between the edges of the positive and negative electrode active material layers in the overhang area and the thickness of the separator 20 between the positive and negative electrode sheets, so that under the action of the electric field force, the lithium ions embedded in the overhang area of ​​the negative electrode sheet 30 during charging can be smoothly released, and the lithium ions embedded in the overhang area of ​​the negative electrode sheet 30 will not gather at the edge of the overhang area of ​​the negative electrode sheet 30, thereby reducing the problem of lithium plating in the overhang area of ​​the negative electrode sheet 30, thereby reducing the capacity loss of the battery, and improving the safety of the battery in fast charging and long cycle scenarios.

[0147] In addition, an embodiment of the present application also provides a battery pack, including the above-mentioned battery.

[0148] The present application also provides an electric device, including an electric device and a battery cell 100, or a battery, or a battery pack as described in any of the above embodiments. The battery cell 100, or a battery, or a battery pack is used to provide electric energy to the electric device.

[0149] The electrical equipment in the embodiments of the present application may be a vehicle, for example, a vehicle may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. Accordingly, the electrical device may be a driving mechanism of the vehicle or a control system of the vehicle.

[0150] In addition, the electrical equipment may also be other energy storage devices, such as mobile phones, portable devices, laptop computers, electric toys, electric tools, ships and spacecraft, etc., among which the spacecraft may include airplanes, rockets, space shuttles or spacecraft.

[0151] In view of the fact that the electrical device in this embodiment includes the battery cell 100, or the battery, or the battery pack described in any of the above embodiments, the structure and beneficial effects of the electrical device including the battery cell 100, or the battery, or the battery pack will not be further elaborated in this embodiment.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A battery cell, characterized in that: It comprises a positive electrode sheet (10), a separator (20) and a negative electrode sheet (30), wherein the positive electrode sheet (10) and the negative electrode sheet (30) are stacked on each other, and the separator (20) is arranged between the positive electrode sheet (10) and the negative electrode sheet (30); The positive electrode sheet (10) comprises a positive electrode current collector (11) and a positive electrode active material layer (12), and along the thickness direction of the positive electrode current collector (11), the positive electrode active material layer (12) is located on at least one side of the surface of the positive electrode current collector (11); The negative electrode sheet (30) comprises a negative electrode current collector (31) and a negative electrode active material layer (32), and along the thickness direction of the negative electrode current collector (31), the negative electrode active material layer (32) is located on at least one side of the surface of the negative electrode current collector (31); Along the stacking direction, the orthographic projection of the edge of the negative electrode active material layer (32) on the negative electrode sheet (30) on the surface where the positive electrode sheet is located exceeds the edge of the positive electrode active material layer (12) on the positive electrode sheet (10) by a dimension L, the thickness of the separator (20) between the negative electrode sheet (30) and the positive electrode sheet (10) is T, and L and T satisfy: T / L≥0.

016.

2. The battery cell according to claim 1, characterized in that: L and T satisfy: T / L≥0.

024.

3. The battery cell according to claim 1, characterized in that: L satisfies: 0<L≤5mm.

4. The battery cell according to claim 1, characterized in that: T satisfies: 8μm≤T≤32μm.

5. The battery cell according to claim 1, characterized in that: The thickness of the positive electrode sheet (10) is W1, and W1 satisfies: 40 μm≤W1≤4000 μm.

6. The battery cell according to claim 1, characterized in that: The thickness of the negative electrode sheet (30) is W2, and W2 satisfies: 20 μm≤W2≤3000 μm.

7. The battery cell according to claim 1, characterized in that: The thickness of the positive electrode current collector (11) is W3, and W3 satisfies: 5 μm≤W3≤25 μm; and / or, The thickness of the negative electrode current collector (31) is W4, and W4 satisfies: 5 μm≤W4≤25 μm.

8. The battery cell according to claim 1, characterized in that: The diaphragm (20) is a PE film or a PP film.

9. The battery cell according to claim 1, characterized in that: The positive electrode active material layer (12) comprises lithium iron phosphate or nickel-cobalt-manganese ternary material or nickel-cobalt-aluminum ternary material.

10. The battery cell according to claim 1, characterized in that: The negative electrode active material layer (32) includes a graphite material.

11. The battery cell according to claim 1, characterized in that: The battery core (100) is a laminated battery core or a wound core.

12. A battery, characterized in that: It comprises a shell and a battery cell (100) according to any one of claims 1 to 11, wherein the battery cell (100) is arranged in the shell.

13. A battery pack, characterized in that: Comprising the battery of claim 12.

14. An electrical device, characterized in that: It comprises a battery cell as claimed in any one of claims 1 to 11, or a battery as claimed in claim 12, or a battery pack as claimed in claim 13.

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