Battery cell, battery apparatus, and electric device

Abstract

The present application provides a battery cell, a battery apparatus, and an electric device. The battery cell comprises a casing and an electrode assembly accommodated in the casing. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet, the negative electrode sheet, and the separator are wound to form a straight region and a bent region. The positive electrode sheet comprises a positive electrode current collector and a first positive electrode active substance layer. The first positive electrode active substance layer is arranged on the inner surface of the positive electrode current collector. The first positive electrode active substance layer comprises a first portion and a second portion that are arranged along the winding direction of the electrode assembly, wherein the thickness of the second portion is less than that of the first portion, at least part of the first portion is arranged in the straight region, and at least part of the second portion is arranged in the bent region. The negative electrode sheet comprises a negative electrode current collector and a first negative electrode active substance layer. The first negative electrode active substance layer is arranged on the outer surface of the negative electrode current collector. In the bent region, a gap is formed between the second portion and the first negative electrode active substance layer.

Description

Battery cells, battery devices and electrical equipment Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a battery cell, a battery device, and an electrical appliance. Background Technology

[0002] Battery cells are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools, etc.

[0003] In the development of battery technology, improving the reliability of individual battery cells is a key research direction. Summary of the Invention

[0004] This application provides a battery cell, a battery device, and an electrical appliance that can improve reliability.

[0005] In a first aspect, embodiments of this application provide a battery cell, comprising a casing and an electrode assembly, at least a portion of which is housed within the casing. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet, negative electrode sheet, and separator are wound together to form a straight region and a bent region, the bent region being connected to the straight region. The positive electrode sheet includes a positive current collector and a first positive active material layer. The first positive active material layer is disposed on the inner surface of the positive current collector and includes a first portion and a second portion arranged along the winding direction of the electrode assembly. The thickness of the second portion is less than the thickness of the first portion. At least a portion of the first portion is disposed in the straight region, and at least a portion of the second portion is disposed in the bent region. The negative electrode sheet includes a negative current collector and a first negative active material layer, the first negative active material layer being disposed on the outer surface of the negative current collector. In the bent region, a gap is provided between the second portion and the first negative active material layer.

[0006] In this embodiment, the second portion has a smaller thickness than the first portion. By placing at least a portion of the second portion in the bending region, the amount of ions released from the first positive electrode active material layer located in the bending region can be reduced. Thinning the second portion reduces the need for ion embedding space in the first negative electrode active material layer located inside the second portion, thus reducing the risk of metal ion deposition. The gap provides space for the expansion of the first negative electrode active material layer, reducing the pressure between the second portion and the first negative electrode active material layer. This reduces the compression of the electrolyte in the internal pores of the second portion and the first negative electrode active material layer, decreasing internal resistance, reducing the risk of metal ion deposition, and improving the reliability of the battery cell.

[0007] In some embodiments, the gap has a dimension greater than or equal to 50 μm and less than or equal to 600 μm in the thickness direction of the second portion.

[0008] In this embodiment, the gap size is set to be greater than or equal to 50 μm to provide space for the expansion of the first negative electrode active material layer, reduce the pressure between the second part and the first negative electrode active material layer, thereby reducing the compression of the electrolyte in the internal pores of the second part and the electrolyte in the internal pores of the first negative electrode active material layer, and reducing internal resistance. In this embodiment, the gap size is set to be less than or equal to 600 μm to reduce the ion migration path between the second part and the first negative electrode active material layer, reduce the risk of metal ion deposition, and improve the reliability of the battery cell.

[0009] In some embodiments, the gap has a dimension greater than or equal to 100 μm and less than or equal to 300 μm in the thickness direction of the second portion, which can further reduce internal resistance, reduce the risk of metal ion precipitation, reduce heat generation, and improve the reliability of the battery cell.

[0010] In some embodiments, the thickness of the first portion is t1, the thickness of the second portion is t2, and k = (t1-t2) / t1 × 100%. 5% ≤ k ≤ 90%. In the embodiments of the application, k is set to be greater than or equal to 5% to reduce ions released from the second portion, lower the risk of metal ion precipitation, and improve the reliability of the battery cell. Setting k to be less than or equal to 90% reduces the impact of thinning the second portion on the capacity of the battery cell.

[0011] In some embodiments, 20% ≤ k ≤ 65%. In this application embodiment, k is set to be greater than or equal to 20% to reduce ions released from the second portion, lower the risk of metal ion precipitation, and improve the reliability of the battery cell. In this application embodiment, k is set to be less than or equal to 65% to reduce the thinning degree of the second portion and reduce the impact of thinning the second portion on the capacity of the battery cell.

[0012] In some embodiments, 65% ≤ k ≤ 90%, the dimension of the gap in the thickness direction of the second portion is less than or equal to 500 μm.

[0013] In some embodiments, 55% ≤ k ≤ 65%, the dimension of the gap in the thickness direction of the second portion is less than or equal to 350 μm.

[0014] In some embodiments, 45% ≤ k ≤ 55%, the dimension of the gap in the thickness direction of the second portion is less than or equal to 300 μm.

[0015] In some embodiments, 40% ≤ k ≤ 45%, the gap dimension in the thickness direction of the second portion is less than or equal to 200 μm.

[0016] In some embodiments, 35% ≤ k ≤ 40%, the gap dimension in the thickness direction of the second portion is less than or equal to 150 μm.

[0017] In some embodiments, 25% ≤ k ≤ 35%, the gap dimension in the thickness direction of the second portion is less than or equal to 120 μm.

[0018] In some embodiments, 20% ≤ k ≤ 25%, the gap dimension in the thickness direction of the second portion is less than or equal to 100 μm.

[0019] In some embodiments, 5% ≤ k ≤ 20%, the dimension of the gap in the thickness direction of the second portion is less than or equal to 60 μm.

[0020] In some embodiments, the positive electrode sheet includes a plurality of positive electrode bends disposed along the winding direction, each positive electrode bend being disposed in a bend region. At least a portion of the second portion is formed in the first positive electrode bend of the positive electrode sheet along the winding direction; and / or, at least a portion of the second portion is formed in the second positive electrode bend of the positive electrode sheet along the winding direction.

[0021] In this embodiment, at least a portion of the second part is formed at the first positive electrode bend and / or the second positive electrode bend to reduce the number of ions released, lower the risk of metal ion precipitation in the first negative electrode active material layer, and improve the reliability of the battery cell.

[0022] In some embodiments, both ends of the second portion are located in the straight region along the winding direction. The second portion passes through at least one bending region along the winding direction.

[0023] The second part passes through at least one bending zone, thereby reducing the number of ions released from the first positive electrode active material layer located in the bending zone, lowering the risk of metal ion precipitation in the first negative electrode active material layer, and improving the reliability of the battery cell. Positioning both ends of the second part in the straight zone along the winding direction reduces the risk of excessively increasing the gap between the second part and the first negative electrode active material layer due to the first part extending into the bending zone near the second part. This reduces the ion migration path between the second part and the first negative electrode active material layer, lowering the risk of metal ion precipitation and improving the reliability of the battery cell.

[0024] In some embodiments, the second portion passes through at least two bending regions along the winding direction. The second portion can reduce the risk of metal ion precipitation problems in the two bending regions, improving the reliability of the battery cell. This application ensures that the second portion passes through at least two bending regions, which can reduce the number of second portions and simplify the forming process of the positive electrode sheet.

[0025] In some embodiments, the first positive electrode active material layer includes a plurality of second portions, which are spaced apart along the winding direction. A first portion is disposed between two adjacent second portions along the winding direction. The electrode assembly includes two bending regions, which are respectively connected to the two ends of the straight region, and two adjacent second portions are respectively disposed corresponding to the two bending regions. Embodiments of this application can reduce the size of a single second portion along the winding direction, reduce the number of times a single second portion passes through bending regions, reduce the total size of multiple second portions along the winding direction, and reduce the impact of multiple second portions on the capacity of the battery cell.

[0026] In some embodiments, the positive electrode sheet has a winding start end and a winding end end at its two ends along the winding direction, respectively. The winding start end is located in the flat region, and the second part extends from the winding start end along the winding direction. Embodiments of this application can reduce the number of the first and second parts, reduce the number of thickness changes in the first positive electrode active material layer during the coating process, and simplify the forming process of the positive electrode sheet.

[0027] In some embodiments, in the bending region, the number of layers of the separator disposed between the second portion and the first negative electrode active material layer is greater than or equal to 2. In the embodiments of this application, even if metal ion precipitation and metal dendrites are formed in the first negative electrode active material layer, the multilayer separator can still block the metal dendrites to a certain extent, reduce the risk of metal dendrites contacting the second portion, and improve the reliability of the battery cell.

[0028] In some embodiments, the first positive electrode active material layer further includes a third portion, which is connected between the first portion and the second portion. The third portion gradually decreases in size along the direction from the first portion to the second portion. The third portion can smoothly transition between the first and second portions, thereby reducing abrupt changes in thickness, reducing stress concentration, reducing metal ion deposition caused by stress concentration, and improving the cycle performance of the battery cell.

[0029] In some embodiments, the first positive electrode active material layer further includes a fourth portion, which is disposed along the winding axis and the first portion, the winding axis being perpendicular to the winding direction. The dimension of the fourth portion along the winding axis is smaller than the dimension of the first portion along the winding axis. The fourth portion gradually decreases in size along the direction from the first portion to the fourth portion.

[0030] By incorporating the fourth portion in this embodiment, stress concentration at the edge of the first positive electrode active material layer along the winding axis can be reduced, thereby lowering the risk of cracking of the positive electrode current collector and the risk of edge collapse of the first positive electrode active material layer along the winding axis, and improving reliability. The fourth portion also facilitates electrolyte wetting, improving the cycle performance of the battery cell.

[0031] In some embodiments, the minimum thickness of the fourth portion is greater than or equal to the thickness of the second portion. Along the winding axis, the end of the fourth portion furthest from the first portion is flush with one end of the second portion. Since the thickness of the second portion is less than or equal to the minimum thickness of the fourth portion, the second portion experiences less rolling pressure during the rolling of the positive electrode sheet, making it less prone to edge collapse. The smaller thickness of the second portion helps reduce the risk of metal ion precipitation and improves the reliability of the battery cell.

[0032] In some embodiments, the minimum thickness of the fourth portion is less than the thickness of the second portion. The first positive electrode active material layer further includes a fifth portion, which is disposed along the winding axis with the second portion, and the dimension of the fifth portion along the winding axis is smaller than the dimension of the second portion along the winding axis. The fifth portion gradually decreases in size along the direction from the second portion to the fifth portion. The fifth portion is connected to the fourth portion, and the fifth portion and the fourth portion are disposed along the winding direction.

[0033] Setting the thickness of the second part to be greater than the minimum thickness of the fourth part reduces the thinning degree of the second part and decreases its impact on the capacity of the battery cell. By setting the fifth part, stress concentration at the edge of the first positive electrode active material layer along the winding axis can be reduced, lowering the risk of cracking of the positive electrode current collector and the risk of edge collapse of the first positive electrode active material layer along the winding axis, thus improving reliability.

[0034] Secondly, embodiments of this application provide a battery device comprising a plurality of battery cells provided in any of the embodiments of the first aspect.

[0035] Thirdly, embodiments of this application provide an electrical device that includes a battery device provided in any of the embodiments of the second aspect, the battery device being used to provide electrical energy. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0037] Figure 1 is a structural schematic diagram of a vehicle provided in some embodiments of this application;

[0038] Figure 2 is a schematic diagram of a battery device provided in some embodiments of this application;

[0039] Figure 3 is a schematic diagram of the battery module shown in Figure 2;

[0040] Figure 4 is an explosion diagram of a single battery cell in some embodiments of this application;

[0041] Figure 5 is a cross-sectional schematic diagram of an electrode assembly provided in some embodiments of this application;

[0042] Figure 6 is an enlarged schematic diagram of a partial structure in Figure 5;

[0043] Figure 7 is a schematic diagram of the positive electrode sheet of the electrode assembly provided in some embodiments of this application in a flattened state;

[0044] Figure 8 is a cross-sectional view along the AA direction shown in Figure 7;

[0045] Figure 9 is a cross-sectional view along the BB direction shown in Figure 7;

[0046] Figure 10 is a cross-sectional view along the CC direction shown in Figure 7;

[0047] Figure 11 is a schematic diagram of the positive electrode sheet of a battery cell provided in some other embodiments of this application in a flattened state;

[0048] Figure 12 is a schematic cross-sectional view along the DD direction shown in Figure 11;

[0049] Figure 13 is a cross-sectional schematic diagram of the electrode assembly of a battery cell provided in some other embodiments of this application;

[0050] Figure 14 is a schematic diagram of the positive electrode sheet of a battery cell provided in some other embodiments of this application in a flattened state;

[0051] Figure 15 is a partial schematic diagram of the electrode assembly of a battery cell provided in some other embodiments of this application.

[0052] The reference numerals in the attached figures are as follows: 1. Vehicle; 2. Battery unit; 3. Controller; 4. Motor; 5. Housing; 5a. First housing; 5b. Second housing; 6. Battery module; 7. Battery cell; 10. Electrode assembly; 11. Positive electrode sheet; 111. Positive current collector; 1111. Current collector body; 1112. Positive electrode tab; 111a. Inner surface of the positive current collector; 111b. Outer surface of the positive current collector; 112. First positive electrode active material layer; 1121. First part; 1122. Second part; 1123. Third part; 1123a. First segment; 1123b. Second segment; 1124. Fourth part; 1125. Fifth part; 1126. Recess; 113. Second positive electrode active material layer; 114. Insulating layer; 11a. Positive electrode bend; 11b. Positive electrode straight part; 12. Negative electrode sheet; 121. Negative electrode current collector; 121a. Outer surface of negative electrode current collector; 121b. Inner surface of negative electrode current collector; 122. First negative electrode active material layer; 123. Second negative electrode active material layer; 12a. Negative electrode bending portion; 12b. Negative electrode straight portion; 13. Separator; 20. Outer shell; 21. Housing; 22. End cap; 30. Electrode terminal; 40. Pressure relief mechanism; E1. Winding start end; E2. Winding end; G. Gap; G1. First gap; G2. Second gap; Q1. Straight region; Q2. Bending region; V. Winding direction; X. Length direction; Y. Width direction; Z. Winding axis. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0054] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms "comprising" and "having," and any variations thereof, in the description, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the description, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy.

[0055] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0056] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0057] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0058] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0059] In this application, "multiple" means two or more (including two).

[0060] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in aerospace and other fields. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0061] A single battery cell can be a rechargeable battery, which refers to a battery cell that can be recharged after being discharged to activate the active materials and continue to be used.

[0062] A battery device typically refers to a single physical module comprising multiple battery cells to provide higher voltage and capacity. A battery cell can be the smallest unit that makes up a battery device.

[0063] A single battery cell typically includes an electrode assembly and a housing to house the electrode assembly. The electrode assembly typically includes a positive electrode, a negative electrode, and a separator, which separates the positive and negative electrodes. During the charging and discharging process of the battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0064] During the charging process of a battery cell, ions are extracted from the positive active material layer of the positive electrode and inserted into the negative active material layer of the negative electrode. When there is insufficient space for insertion into the negative active material layer, excessive resistance to ion insertion, or excessively rapid extraction of ions from the positive active material layer, the amount of ions extracted from the positive active material layer cannot be equally inserted into the negative active material layer. Ions that cannot be inserted can only gain electrons on the surface of the negative active material layer and form elemental lithium. Taking a lithium-ion battery cell as an example, lithium ions that cannot be inserted into the negative active material layer can only gain electrons on the surface of the negative active material layer and form elemental lithium; this phenomenon is called lithium plating. As elemental lithium accumulates, lithium dendrites gradually form inside the electrode assembly. These dendrites can easily pierce the separator and conduct electricity between the positive and negative electrodes, thus posing a risk of short circuit in the electrode assembly, leading to thermal runaway in the battery cell and affecting its reliability.

[0065] Electrode assemblies with wound structures typically form bending regions. In these bending regions, the radius of the inner positive electrode active material layer is larger than the radius of the inner negative electrode active material layer, making it prone to metal ion deposition due to insufficient embedding space in the negative electrode active material layer. Furthermore, the negative electrode active material layer may experience active material detachment during bending due to stress concentration, which can also lead to insufficient embedding space. Additionally, during charging, the negative electrode active material layer expands due to ion embedding, increasing the pressure between the positive and negative electrode active material layers. This causes the electrolyte in the pores of both layers to be squeezed out, increasing internal resistance and also increasing the risk of metal ion deposition.

[0066] In view of this, the present application provides a technical solution that reduces the thickness of the positive active material layer on the inner side of the positive electrode sheet in the bending area and sets a gap between the positive active material layer and the negative active material layer, thereby reducing the ions released from the positive active material layer, reducing the pressure on the positive and negative active material layers, reducing the risk of metal ion precipitation, and improving the reliability of the battery cell.

[0067] The battery cells described in this application are applicable to battery devices and electrical equipment using battery devices. Electrical equipment can be devices that use battery devices as a power source or various energy storage systems that use battery devices as energy storage elements. Electrical equipment can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0068] For ease of explanation, the following embodiments use a vehicle as an example of electrical equipment.

[0069] Figure 1 is a schematic diagram of the structure of a vehicle provided in some embodiments of this application.

[0070] As shown in Figure 1, a battery device 2 is installed inside the vehicle 1. The battery device 2 can be located at the bottom, front, or rear of the vehicle 1. The battery device 2 can be used to power the vehicle 1; for example, the battery device 2 can serve as the operating power source for the vehicle 1.

[0071] The vehicle 1 may also include a controller 3 and a motor 4. The controller 3 is used to control the battery device 2 to supply power to the motor 4, for example, for the power needs of the vehicle 1 during starting, navigation and driving.

[0072] In some embodiments of this application, the battery device 2 can not only serve as the operating power source for the vehicle 1, but also as the driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0073] Figure 2 is a schematic diagram of a battery device provided in some embodiments of this application.

[0074] In some embodiments, the battery device 2 may include one or more battery cell assemblies for providing voltage and capacity.

[0075] A battery cell assembly may include multiple battery cells (not shown in Figure 2), which are connected in series, parallel, or mixed connection via a busbar. Mixed connection refers to multiple battery cells being connected in both series and parallel connections.

[0076] A battery cell can be a rechargeable battery cell, which refers to a battery cell that can be recharged after being discharged to activate the active materials and continue to be used.

[0077] As an example, a single battery cell can be a lithium-ion battery cell, a sodium-ion battery cell, a sodium-lithium-ion battery cell, a lithium metal battery cell, a sodium metal battery cell, a lithium-sulfur battery cell, a magnesium-ion battery cell, a nickel-metal hydride battery cell, a nickel-cadmium battery cell, a lead-acid battery cell, etc.

[0078] As an example, a battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic battery cells, such as hexagonal prismatic battery cells.

[0079] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells; as an example, a battery cell assembly can be a battery module 6, which is formed by arranging and fixing multiple battery cells into a single module. As an example, a battery module 6 can be formed by bundling multiple battery cells together with cable ties.

[0080] In some embodiments, the battery device 2 may be a battery pack, which includes a housing 5 and one or more battery cell assemblies housed within the housing 5. As an example, the battery cell assembly may be a battery module 6, which can be housed within the housing by securing the battery module 6 to the housing. Alternatively, the battery cell assembly may be housed within the housing by directly securing multiple battery cells to the housing.

[0081] In some embodiments, the housing 5 is used to house individual battery cells, and the housing 5 can have various structures.

[0082] In some embodiments, the housing 5 may include a first housing 5a and a second housing 5b. The first housing 5a and the second housing 5b are fastened together to form a closed space inside the housing 5 to house the battery cell assembly. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first housing may be a top cover or a bottom plate.

[0083] In some embodiments, the housing 5 may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are respectively connected to the frame, forming an enclosed space inside the housing to accommodate individual battery cells. As an example, the frame may include multiple side beams.

[0084] In some embodiments, the housing 5 may be part of the vehicle's chassis structure. For example, a portion of the housing 5 may be at least a portion of the vehicle's floor, or a portion of the housing 5 may be at least a portion of the vehicle's crossbeams and longitudinal beams.

[0085] In some embodiments, the battery device 2 may be an energy storage device.

[0086] Energy storage devices can be used in energy storage power stations, wind power generation systems, solar power generation systems, mobile power systems, or temporary power supply systems. Energy storage devices can store electrical energy as needed and output it when appropriate. For example, energy storage devices can store electrical energy during off-peak hours and provide power to relevant users or electrical equipment during peak hours.

[0087] In some embodiments, the energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0088] Figure 3 is a schematic diagram of the battery module shown in Figure 2.

[0089] In some embodiments, as shown in FIG3, there are multiple battery cells 7, which are first connected in series, parallel, or mixed to form a battery module 6. The multiple battery modules 6 are then connected in series, parallel, or mixed to form a whole and housed in a casing.

[0090] Multiple battery cells 7 in battery module 6 can be electrically connected through a busbar to achieve parallel, series, or mixed connection of multiple battery cells 7 in battery module 6. There can be one or more busbars, each used to electrically connect at least two battery cells 7.

[0091] Figure 4 is an exploded schematic diagram of a battery cell in some embodiments of this application.

[0092] Referring to Figure 4, the battery cell 7 includes a housing 20 and an electrode assembly 10, at least a portion of which is housed within the housing 20.

[0093] In some embodiments, the outer casing 20 can be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc.

[0094] In some embodiments, the housing 20 can be a sealed structure or a non-sealed structure. As an example, when the housing 20 is a non-sealed structure, it serves to protect the electrode assembly 10, and a sealing bag is included between the housing 20 and the electrode assembly 10. The sealing bag is used to encapsulate the electrode assembly 10 and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating component or an aluminum-plastic film. When the housing 20 is a sealed structure, it is used to encapsulate the electrode assembly 10 and the electrolyte, among other components.

[0095] In some embodiments, the casing 20 of the battery cell 7 is a cylindrical casing, a square casing, a prismatic casing, or a casing of other shapes.

[0096] In some embodiments, the housing 20 includes a housing 21 and an end cap 22, the housing 21 having an opening, and the end cap 22 being connected to the housing 21 and covering the opening.

[0097] The housing 21 is a component used to fit the end cap 22 to form the internal cavity of the battery cell 7. The formed internal cavity can be used to accommodate the electrode assembly 10, the electrolyte, and other components.

[0098] The housing 21 and the end cap 22 can be separate components. For example, an opening can be provided on the housing 21, and the end cap 22 can be used to close the opening to form an internal cavity for the battery cell 7.

[0099] The housing 21 can be of various shapes and sizes, such as cuboid or cylindrical. Specifically, the shape of the housing 21 can be determined according to the specific shape and size of the electrode assembly 10. The housing 21 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc.

[0100] The shape of the end cap 22 can be adapted to the shape of the housing 21 to fit the housing 21. The material of the end cap 22 can be the same as or different from the material of the housing 21. Optionally, the end cap 22 can be made of a material with a certain hardness and strength (such as copper, iron, aluminum, stainless steel, aluminum alloy, etc.), so that the end cap 22 is not easily deformed when subjected to compression and impact, so that the battery cell 7 can have higher structural strength and improve reliability.

[0101] The end cap 22 is connected to the housing 21 by welding, bonding, snap-fitting or other means.

[0102] The housing 21 may be open at one end or open at both ends. In some examples, the housing 21 may be a structure with an opening on one side, and one end cap 22 is provided to cover the housing 21. In other examples, the housing 21 may also be a structure with openings on both sides, and two end caps 22 are provided, with the two end caps 22 respectively covering the two openings of the housing 21.

[0103] In some embodiments, the electrode assembly 10 is a component in the battery cell 7 where an electrochemical reaction occurs. The housing 20 may contain one or more electrode assemblies 10. Optionally, the electrode assembly 10 is housed within the housing 20.

[0104] In some embodiments, the electrode assembly 10 is provided with tabs that can conduct current from the electrode assembly 10. The tabs include a positive tab and a negative tab.

[0105] In some embodiments, the battery cell 7 further includes an electrode terminal 30, which is disposed on the housing 20 and electrically connected to the tab.

[0106] The electrode terminal 30 can be disposed on the end cap 22 or on the housing 21.

[0107] The electrode terminal 30 can be directly connected to the electrode tab, or it can be indirectly connected to the electrode tab through the current collector.

[0108] In some embodiments, a pressure relief mechanism 40 is provided on the housing 20. The pressure relief mechanism 40 is used to release the internal gas of the battery cell 7.

[0109] As an example, the internal pressure or temperature of the battery cell 7 is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell 7 reaches the predetermined threshold, the pressure relief mechanism 40 is activated or a weak structure provided in the pressure relief mechanism 40 is destroyed, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell 7.

[0110] As an example, the pressure relief mechanism 40 can be integrally formed with the housing 20.

[0111] As an example, the pressure relief mechanism 40 can also be separately configured and connected to the housing 20.

[0112] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0113] In some embodiments, when the housing 20 is a non-sealed structure, the pressure relief mechanism 40 can be configured as a through hole for discharging gas inside the battery cell 7.

[0114] The emissions from battery cell 7 mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0115] In some embodiments, the battery cell 7 further includes an electrolyte housed within the housing 20.

[0116] In some embodiments, the liquid electrolyte includes an electrolyte salt and a solvent.

[0117] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0118] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0119] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0120] In some embodiments, the gel electrolyte comprises a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0121] In some embodiments, the solid electrolyte includes a polymer solid electrolyte, an inorganic solid electrolyte, and a composite solid electrolyte.

[0122] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0123] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium germanium phosphorus sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0124] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0125] Figure 5 is a cross-sectional schematic diagram of an electrode assembly provided in some embodiments of this application; Figure 6 is an enlarged schematic diagram of a partial structure of Figure 5; Figure 7 is a schematic diagram of the positive electrode sheet of an electrode assembly provided in some embodiments of this application in a flattened state; Figure 8 is a cross-sectional schematic diagram of Figure 7 taken along the AA direction; Figure 9 is a cross-sectional schematic diagram of Figure 7 taken along the BB direction; Figure 10 is a cross-sectional schematic diagram of Figure 7 taken along the CC direction.

[0126] Referring to Figures 5 to 10, an embodiment of this application provides an electrode assembly 10, which includes a positive electrode 11, a negative electrode 12 and an insulating member 13. The positive electrode 11, the negative electrode 12 and the insulating member 13 are wound together to form a straight region Q1 and a bent region Q2, and the bent region Q2 is connected to the straight region Q1.

[0127] The bending region Q2 is the area in the electrode assembly 10 that has a bending structure. In the bending region Q2, the positive electrode 11, the negative electrode 12, and the separator 13 are all bent. For example, the portion of the positive electrode 11 located in the bending region Q2 is generally bent into an arc shape, and the portion of the negative electrode 12 located in the bending region Q2 is also generally bent into an arc shape.

[0128] The flat region Q1 is the area of ​​the electrode assembly 10 with a flat structure. The portions of the positive electrode 11 and the negative electrode 12 located in the flat region Q1 are substantially flat. Exemplarily, the surface of each layer of positive electrode 11 and the surface of each layer of negative electrode 12 located in the flat region Q1 are substantially planar.

[0129] In some embodiments, there are two bending regions Q2, which are respectively connected to the two ends of the straight region Q1.

[0130] In some embodiments, the positive electrode 11 includes a positive current collector 111 and a first positive active material layer 112, the first positive active material layer 112 being disposed on the inner surface 111a of the positive current collector.

[0131] The positive electrode current collector 111 has an inner surface and an outer surface that are arranged opposite to each other along its own thickness direction, and the first positive electrode active material layer 112 can be disposed on the inner surface 111a of the positive electrode current collector.

[0132] In some examples, the first positive electrode active material layer 112 may be directly disposed on the inner surface 111a of the positive electrode current collector. For example, the first positive electrode active material layer 112 may be coated on the inner surface 111a of the positive electrode current collector. In other examples, other coatings, such as conductive coatings, may be provided between the first positive electrode active material layer 112 and the inner surface 111a of the positive electrode current collector.

[0133] As an example, the positive current collector 111 can be made of metal foil, conductive polymer material, carbon material, or composite current collector. For example, as a metal foil, pure metal, alloy, or surface-treated metal can be used, including but not limited to stainless steel, copper, aluminum, nickel, nickel alloy, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0134] As an example, the first positive electrode active material layer 112 may include a positive electrode active material, which may include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphate may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 LiNi 0.9 Co 0.05 Mn 0.05O2, LiNi 0.92 Co 0.03 Mn 0.05 O2, LiNi 0.95 Co 0.02 Mn 0.03 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0135] In some embodiments, the positive electrode 11 may further include a second positive electrode active material layer 113, which may be disposed on the outer surface 111b of the positive electrode current collector.

[0136] The first positive electrode active material layer 112 and the second positive electrode active material layer 113 can be made of the same positive electrode active material or different positive electrode active materials. Optionally, the first positive electrode active material layer 112 and the second positive electrode active material layer 113 are coatings made of the same slurry.

[0137] The thickness of the first positive electrode active material layer 112 and the thickness of the second positive electrode active material layer 113 can be the same or different.

[0138] In some embodiments, the positive current collector 111 includes a current collector body 1111 and a positive electrode tab 1112, at least a portion of the first positive electrode active material layer 112 is disposed on the current collector body 1111, at least a portion of the second positive electrode active material layer 113 is disposed on the current collector body 1111, and at least a portion of the positive electrode tab 1112 is not disposed on the first positive electrode active material layer 112 and the second positive electrode active material layer 113.

[0139] In some embodiments, a first positive electrode active material layer 112 is disposed on the inner surface of the current collector 1111, and a second positive electrode active material layer 113 is disposed on the outer surface of the current collector 1111. The positive electrode tab 1112 is not provided with the first positive electrode active material layer 112 and the second positive electrode active material layer 113.

[0140] In some embodiments, the current collector 1111 and the positive electrode tab 1112 are arranged along the winding axis Z, which is perpendicular to the winding direction V of the electrode assembly 10.

[0141] In some embodiments, there may be one or more positive tabs 1112. Exemplarily, there may be multiple positive tabs 1112, which are spaced apart along the winding direction V.

[0142] In some embodiments, along the winding direction V, the sum of the dimensions of all positive tabs 1112 is less than the dimension of the current collector 1111.

[0143] In some embodiments, the positive electrode 11 further includes two insulating layers 114. At least a portion of one insulating layer 114 is disposed on the inner surface of the current collector 1111 and is located on the side of the first positive electrode active material layer 112 facing the positive electrode tab 1112. At least a portion of the other insulating layer 114 is disposed on the outer surface of the current collector 1111 and is located on the side of the second positive electrode active material layer 113 facing the positive electrode tab 1112.

[0144] In some embodiments, the insulating layer 114 comprises ceramic particles.

[0145] In some embodiments, the negative electrode 12 includes a negative electrode current collector 121 and a first negative electrode active material layer 122, the first negative electrode active material layer 122 being disposed on the outer surface 121a of the negative electrode current collector.

[0146] The negative electrode current collector 121 has an inner surface and an outer surface that are arranged opposite to each other along its own thickness direction, and the first negative electrode active material layer 122 can be disposed on the outer surface 121a of the negative electrode current collector.

[0147] In some examples, the first negative electrode active material layer 122 can be directly disposed on the outer surface 121a of the negative electrode current collector. For example, the first negative electrode active material layer 122 can be coated on the outer surface 121a of the negative electrode current collector. In other examples, other coatings, such as conductive coatings, can be provided between the first negative electrode active material layer 122 and the outer surface 121a of the negative electrode current collector.

[0148] As an example, the negative electrode current collector 121 can be made of metal foil, conductive polymer material, carbon material, or composite current collector. For example, as a metal foil, pure metal, alloy, or surface-treated metal can be used, including but not limited to stainless steel, copper, aluminum, nickel, nickel alloy, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0149] As an example, the first negative electrode active material layer 122 includes a negative electrode active material, which may be a negative electrode active material known in the art for use in battery cell 7. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cell 7 may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0150] In some embodiments, the negative electrode 12 may further include a second negative electrode active material layer 123, which may be disposed on the inner surface 121b of the negative electrode current collector.

[0151] The first negative electrode active material layer 122 and the second negative electrode active material layer 123 can be made of the same negative electrode active material or different negative electrode active materials. Optionally, the first negative electrode active material layer 122 and the second negative electrode active material layer 123 are coatings formed by coating the same slurry.

[0152] The thickness of the first negative electrode active material layer 122 and the thickness of the second negative electrode active material layer 123 can be the same or different. Optionally, the thickness of the first negative electrode active material layer 122 and the thickness of the second negative electrode active material layer 123 are the same.

[0153] In some embodiments, the first positive electrode active material layer 112 and the first negative electrode active material layer 122 are disposed opposite to each other, and the ions extracted from the first positive electrode active material layer 112 can be embedded into the first negative electrode active material layer 122.

[0154] The second positive electrode active material layer 113 and the second negative electrode active material layer 123 are disposed opposite to each other, and the ions extracted from the second positive electrode active material layer 113 can be inserted into the second negative electrode active material layer 123.

[0155] In some embodiments, the positive current collector 111 may be made of aluminum, and the negative current collector 121 may be made of copper.

[0156] In some embodiments, the separator 13 includes a separator membrane. The separator membrane of this application can be any known porous membrane with good chemical and mechanical stability.

[0157] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0158] Inorganic particle coating, organic particle coating, or organic / inorganic composite coating can also be applied to the surface of the separator.

[0159] The separator 13 can be a single component located between the positive electrode 11 and the negative electrode 12, or it can be attached to the surface of the positive electrode 11 or the surface of the negative electrode 12.

[0160] In some embodiments, the separator 13 is a solid electrolyte. The solid electrolyte is disposed between the positive electrode 11 and the negative electrode 12, and serves to both transport ions and isolate the positive and negative electrodes.

[0161] This application provides an electrode assembly 10, which includes a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are wound together to form a straight region Q1 and a bent region Q2, with the bent region Q2 connected to the straight region Q1. The positive electrode 11 includes a positive current collector 111 and a first positive active material layer 112. The first positive active material layer 112 is disposed on the inner surface 111a of the positive current collector. The first positive active material layer 112 includes a first portion 1121 and a second portion 1122 arranged along the winding direction V of the electrode assembly 10. The thickness of the second portion 1122 is less than the thickness of the first portion 1121. At least a portion of the first portion 1121 is disposed in the straight region Q1, and at least a portion of the second portion 1122 is disposed in the bent region Q2. The negative electrode sheet 12 includes a negative electrode current collector 121 and a first negative electrode active material layer 122, the first negative electrode active material layer 122 being disposed on the outer surface 121a of the negative electrode current collector. In the bending region Q2, a gap G is provided between the second portion 1122 and the first negative electrode active material layer 122.

[0162] The winding direction V of the electrode assembly 10 can be the direction in which the positive electrode 11, negative electrode 12, and separator 13 are wound from the inside to the outside circumferential direction. For example, in FIG5, the winding direction V is clockwise.

[0163] The first part, 1121, can be one or more. The second part, 1122, can be one or more.

[0164] In some examples, the first part 1121 and the second part 1122 are both one. The positive electrode 11 has a winding start end E1 and a winding end end E2 at its two ends along the winding direction V; along the winding direction V, the second part 1122 may be located on the side of the first part 1121 closer to the winding start end E1, or it may be located on the side of the first part 1121 away from the winding start end E1.

[0165] In other examples, there is one first part 1121 and two second parts 1122, with the first part 1121 located between the two second parts 1122 along the winding direction V.

[0166] In some other examples, there are two first parts 1121 and one second part 1122, with the second part 1122 located between the two first parts 1121 along the winding direction V.

[0167] In some other examples, there are multiple first portions 1121 and multiple second portions 1122. The multiple first portions 1121 and multiple second portions 1122 are alternately arranged along the winding direction V.

[0168] The first part 1121 can be entirely set in the straight area Q1, or it can be partially set in the straight area Q1. For example, a part of the first part 1121 can be set in the straight area Q1, and another part can be set in the bending area Q2.

[0169] The second part 1122 can be entirely located in the bending area Q2, or it can be partially located in the bending area Q2. For example, a portion of the first part 1121 can be located in the bending area Q2, and another portion can be located in the straight area Q1.

[0170] The end of the second part 1122 along the winding direction V can be located in the straight region Q1 or the bending region Q2. In some examples, both ends of the second part 1122 along the winding direction V are located in the bending region Q2; in other examples, one end of the second part 1122 along the winding direction V is located in the bending region Q2 and the other end is located in the straight region Q1; in still other examples, both ends of the second part 1122 along the winding direction V are located in the straight region Q1.

[0171] In some examples, the first portion 1121 and the second portion 1122 can be directly connected. In other examples, the first portion 1121 and the second portion 1122 are indirectly connected through other portions of the first positive electrode active material layer 112.

[0172] There may be two bend regions Q2. In some examples, at least a portion of the second portion 1122 is located in one bend region Q2, and the second portion 1122 does not extend into the other bend region Q2. In other examples, a portion of the second portion 1122 is located in one bend region Q2, and another portion of the second portion 1122 is located in the other bend region Q2.

[0173] The dimension of the second part 1122 along the winding axis Z can be the same as or different from the dimension of the first part 1121 along the winding axis Z. The winding axis Z is perpendicular to the winding direction V. For example, the positive electrode 11 and the negative electrode 12 are wound around the winding axis, which can be parallel to the winding axis Z.

[0174] As an example, the gap G can be the space located between the second part 1122 and the first negative electrode active material layer 122 that is not filled by the separator 13.

[0175] In this embodiment, the second portion 1122 has a smaller thickness than the first portion 1121. By placing at least a portion of the second portion 1122 in the bending region Q2, the amount of ions released from the first positive electrode active material layer 112 located in the bending region Q2 can be reduced. Thinning the second portion 1122 reduces the need for ion embedding space in the first negative electrode active material layer 122 located inside the second portion 1122, thus reducing the risk of metal ion deposition. The gap G provides space for the expansion of the first negative electrode active material layer 122, reducing the pressure between the second portion 1122 and the first negative electrode active material layer 122. This reduces the compression of the electrolyte in the internal pores of the second portion 1122 and the first negative electrode active material layer 122, decreasing internal resistance, reducing the risk of metal ion deposition, and improving the reliability of the battery cell.

[0176] In some embodiments, the gap G has a dimension greater than or equal to 50 μm and less than or equal to 600 μm in the thickness direction of the second portion 1122.

[0177] In the bending region Q2, the second part 1122 is bent; the thickness direction of the second part 1122 can also be different at different positions. As an example, the bending region Q2 can be semi-circular, and the dimension of the gap G in the thickness direction of the second part 1122 can be the dimension of the gap G in the radial direction of the bending region Q2.

[0178] As an example, the dimension of the gap G along the thickness direction of the second part 1122 can be measured as follows:

[0179] Discharge the individual battery cells to the lower cutoff voltage (e.g., 2.5V);

[0180] Using CT (Computed Tomography) technology, X-rays are used to obtain cross-sectional images of the battery cell, which are perpendicular to the winding axis of the electrode assembly and pass through the second part;

[0181] Based on this image, a virtual straight line is defined, which can pass through the center of the bend and intersect with the second part;

[0182] Based on the image and the virtual line, the first intersection point between the virtual line and the inner surface of the second part is obtained, and the second intersection point between the virtual line and the outer surface of the first negative electrode active material layer is obtained. The second intersection point is located inside the first intersection point, and there are no positive or negative electrode plates between the first and second intersection points.

[0183] Measure the distance between the first intersection point and the second intersection point;

[0184] Repeat the above steps to set up 10 different virtual lines, measure 10 spacing values, and calculate the average value D1 of the 10 spacing values;

[0185] Disassemble the battery cell and unfold the positive electrode, negative electrode and separator; select 10 positions on the separator and measure 10 thickness values, then calculate the average of the 10 thickness values, which can be the thickness D2 of the separator;

[0186] The dimension W of the gap in the thickness direction of the second part can be D1-D2.

[0187] As an example, the dimension of the gap G in the thickness direction of the second part 1122 can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 120μm, 130μm, 150μm, 180μm, 200μm, 220μm, 230μm, 250μm, 280μm, 300μm, 320μm, 330μm, 350μm, 380μm, 400μm, 420μm, 430μm, 450μm, 480μm, 500μm, 520μm, 530μm, 550μm, 580μm or 600μm.

[0188] In this embodiment, the gap G is set to a size greater than or equal to 50 μm to provide space for the expansion of the first negative electrode active material layer 122, reducing the pressure between the second part 1122 and the first negative electrode active material layer 122. This reduces the compression of the electrolyte in the internal pores of the second part 1122 and the first negative electrode active material layer 122, thereby reducing internal resistance. In this embodiment, the gap G is set to a size less than or equal to 600 μm to reduce the ion migration path between the second part 1122 and the first negative electrode active material layer 122, reducing the risk of metal ion deposition and improving the reliability of the battery cell 7.

[0189] By setting the reduction range to 50μm-600μm, the wettability of the electrolyte and the ion migration path can be balanced to a certain extent, thereby reducing the internal resistance.

[0190] In some embodiments, when winding the positive electrode 11, the separator 13 and the negative electrode 12, the tightness of the electrode assembly 10 after winding is adjusted by controlling the tension or other parameters of the three components, thereby reducing the size of the gap G.

[0191] In some embodiments, the gap G includes a first gap G1 and a second gap G2. The first gap G1 may be formed between the inner surface of the second portion 1122 and the separator 13, and the second gap G2 may be formed between the outer surface of the first negative electrode active material layer 122 and the separator 13.

[0192] As an example, in the thickness direction of the second part 1122, the size of the first gap G1 can be W1, and the size of the second gap G2 can be W2; the size of the gap G in the thickness direction of the second part 1122 is W = W1 + W2.

[0193] In some embodiments, the dimension W of the gap G in the thickness direction of the second portion 1122 is greater than or equal to 60 μm and less than or equal to 500 μm.

[0194] Setting the gap G to a size greater than or equal to 60 μm provides more space for the expansion of the first negative electrode active material layer 122, reducing the pressure between the second part 1122 and the first negative electrode active material layer 122. This reduces the compression of the electrolyte in the internal pores of the second part 1122 and the first negative electrode active material layer 122, thereby reducing internal resistance. In this embodiment, setting the gap G to a size less than or equal to 500 μm further reduces the ion migration path between the second part 1122 and the first negative electrode active material layer 122, reducing the risk of metal ion deposition, lowering the internal resistance of the battery cell 7, reducing heat generation, and improving the reliability of the battery cell 7.

[0195] In some embodiments, the gap G has a dimension in the thickness direction of the second portion 1122 that is greater than or equal to 100 μm and less than or equal to 300 μm.

[0196] Setting the gap G to be greater than or equal to 100 μm provides more space for the expansion of the first negative electrode active material layer 122, reducing the pressure between the second part 1122 and the first negative electrode active material layer 122. This reduces the compression of the electrolyte in the internal pores of the second part 1122 and the first negative electrode active material layer 122, thereby reducing internal resistance. In this embodiment, setting the gap G to be less than or equal to 300 μm further reduces the ion migration path between the second part 1122 and the first negative electrode active material layer 122, reducing the risk of metal ion deposition, lowering the internal resistance of the battery cell 7, reducing heat generation, and improving the reliability of the battery cell 7.

[0197] In some embodiments, the thickness of the first portion 1121 is t1, and the thickness of the second portion 1122 is t2. k = (t1 - t2) / t1 × 100%; 5% ≤ k ≤ 90%.

[0198] As an example, discharge the battery cell to the lower cutoff voltage (e.g., 2.5V), disassemble the battery cell, and unfold the positive electrode, negative electrode, and separator.

[0199] Remove the second positive electrode active material layer of the positive electrode sheet. Then, in the region corresponding to the first part, arbitrarily select 10 positions and measure 10 thickness values. Then calculate the average value T1 of the 10 thickness values. In the region corresponding to the second part, arbitrarily select 10 positions and measure 10 thickness values. Then calculate the average value T2 of the 10 thickness values.

[0200] Remove the first positive electrode active material layer of the positive electrode sheet, arbitrarily select 10 positions on the positive electrode current collector, measure 10 thickness values, and then calculate the average value T3 of the 10 thickness values;

[0201] The thickness of the first part is t1 = T1 - T3, and the thickness of the second part is t2 = T2 - T3.

[0202] As an example, k is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0203] As an example, k can be used to represent the degree to which the second part 1122 is thinned relative to the first part 1121.

[0204] In the embodiments of the application, k is set to be greater than or equal to 5% to reduce ions released from the second portion 1122, thereby reducing the risk of metal ion precipitation and improving the reliability of the battery cell 7. k is set to be less than or equal to 90% to reduce the impact of thinning the second portion 1122 on the capacity of the battery cell 7.

[0205] In some embodiments, 65% ≤ k ≤ 90%, the dimension W of the gap G in the thickness direction of the second portion 1122 is less than or equal to 500 μm.

[0206] The embodiments of this application can balance the thinning degree of the second part 1122 and the size of the gap G, thereby reducing the risk of metal ion precipitation and taking into account the capacity and reliability of the battery cell to a certain extent.

[0207] Exemplarily, the size W of the gap G may be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 130 μm, 150 μm, 180 μm, 200 μm, 220 μm, 2 30μm, 250μm, 280μm, 300μm, 320μm, 330μm, 350μm, 380μm, 400μm, 420μm, 430μm, 450μm, 480μm or 500μm.

[0208] In some embodiments, 65% ≤ k ≤ 90%, 50 μm ≤ W ≤ 500 μm; alternatively, 350 μm ≤ W ≤ 500 μm.

[0209] This embodiment of the application, by increasing the thinning degree of the second portion 1122, reduces the number of ions released from the second portion 1122, lowers the requirements for the ion migration path between the second portion 1122 and the first negative electrode active material layer 122, and allows the gap G to have a larger size. A larger gap G provides more space for the expansion of the first negative electrode active material layer, reducing the pressure between the second portion and the first negative electrode active material layer, thereby reducing the compression of the electrolyte in the internal pores of the second portion and the first negative electrode active material layer, and reducing internal resistance.

[0210] In some embodiments, 55% ≤ k ≤ 65%, and the gap G has a dimension of less than or equal to 350 μm in the thickness direction of the second portion 1122.

[0211] The embodiments of this application can balance the thinning degree of the second part 1122 and the size of the gap G, thereby reducing the risk of metal ion precipitation and taking into account the capacity and reliability of the battery cell to a certain extent.

[0212] As an example, the size W of the gap G can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 120μm, 130μm, 150μm, 180μm, 200μm, 220μm, 230μm, 250μm, 280μm, 300μm, 320μm, 330μm or 350μm.

[0213] In some embodiments, 55% ≤ k ≤ 65%, 50 μm ≤ W ≤ 350 μm. Optionally, 300 μm ≤ W ≤ 350 μm.

[0214] In some embodiments, 45% ≤ k ≤ 55%, and the gap G has a dimension of less than or equal to 300 μm in the thickness direction of the second portion 1122.

[0215] The embodiments of this application can balance the thinning degree of the second part 1122 and the size of the gap G, thereby reducing the risk of metal ion precipitation and taking into account the capacity and reliability of the battery cell to a certain extent.

[0216] For example, the size W of the gap G can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 120μm, 130μm, 150μm, 180μm, 200μm, 220μm, 230μm, 250μm, 280μm or 300μm.

[0217] In some embodiments, 45% ≤ k ≤ 55%, 50 μm ≤ W ≤ 300 μm. Optionally, 200 μm ≤ W ≤ 300 μm.

[0218] In some embodiments, 40% ≤ k ≤ 45%, and the dimension of the gap G in the thickness direction of the second portion 1122 is less than or equal to 200 μm.

[0219] The embodiments of this application can balance the thinning degree of the second part 1122 and the size of the gap G, thereby reducing the risk of metal ion precipitation and taking into account the capacity and reliability of the battery cell to a certain extent.

[0220] For example, the size W of the gap G can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 120μm, 130μm, 150μm, 160μm, 180μm, or 200μm.

[0221] In some embodiments, 40% ≤ k ≤ 45%, 50 μm ≤ W ≤ 200 μm. Optionally, 150 μm ≤ W ≤ 200 μm.

[0222] In some embodiments, 35% ≤ k ≤ 40%, the gap G has a dimension of less than or equal to 150 μm in the thickness direction of the second portion 1122.

[0223] The embodiments of this application can balance the thinning degree of the second part 1122 and the size of the gap G, thereby reducing the risk of metal ion precipitation and taking into account the capacity and reliability of the battery cell to a certain extent.

[0224] For example, the size W of the gap G can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm or 150μm.

[0225] In some embodiments, 35% ≤ k ≤ 40%, 50 μm ≤ W ≤ 150 μm. Optionally, 120 μm ≤ W ≤ 150 μm.

[0226] In some embodiments, 25% ≤ k ≤ 35%, and the gap G has a dimension of less than or equal to 120 μm in the thickness direction of the second portion 1122.

[0227] The embodiments of this application can balance the thinning degree of the second part 1122 and the size of the gap G, thereby reducing the risk of metal ion precipitation and taking into account the capacity and reliability of the battery cell to a certain extent.

[0228] For example, the size W of the gap G can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm or 120 μm.

[0229] In some embodiments, 25% ≤ k ≤ 35%, 50 μm ≤ W ≤ 120 μm. Optionally, 10 μm ≤ W ≤ 120 μm.

[0230] In some embodiments, 20% ≤ k ≤ 25%, and the gap G has a dimension of less than or equal to 100 μm in the thickness direction of the second portion 1122.

[0231] The embodiments of this application can balance the thinning degree of the second part 1122 and the size of the gap G, thereby reducing the risk of metal ion precipitation and taking into account the capacity and reliability of the battery cell to a certain extent.

[0232] For example, the size W of the gap G can be 50μm, 60μm, 70μm, 80μm, 90μm, or 100μm.

[0233] In some embodiments, 5% ≤ k ≤ 20%, and the dimension of the gap G in the thickness direction of the second portion 1122 is less than or equal to 60 μm.

[0234] The embodiments of this application can balance the thinning degree of the second part 1122 and the size of the gap G, thereby reducing the risk of metal ion precipitation and taking into account the capacity and reliability of the battery cell to a certain extent.

[0235] For example, the size W of the gap G can be 50μm, 51μm, 52μm, 53μm, 54μm, 55μm, 56μm, 57μm, 58μm, 59μm or 60μm.

[0236] In this embodiment, k is set to be greater than or equal to 5% to reduce ions released from the second portion 1122, thereby reducing the risk of metal ion precipitation and improving the reliability of the battery cell 7. Setting k to be less than or equal to 20% can further reduce the thinning degree of the second portion 1122, reducing the impact of thinning the second portion 1122 on the capacity of the battery cell 7. Setting the size of the gap G to be less than or equal to 60 μm further reduces the ion migration path between the second portion 1122 and the first negative electrode active material layer 122, thereby reducing the risk of metal ion precipitation and improving the reliability of the battery cell 7 while maintaining a large thickness in the second portion 1122.

[0237] In some embodiments, 20% ≤ k ≤ 65%. Optionally, 25% ≤ k ≤ 55%. In this application embodiment, k is set to be greater than or equal to 20% to reduce ions released from the second portion 1122, thereby reducing the risk of metal ion precipitation and improving the reliability of the battery cell. In this application embodiment, k is set to be less than or equal to 65% to reduce the thinning degree of the second portion 1122 and reduce the impact of thinning the second portion on the capacity of the battery cell.

[0238] In some embodiments, 50 μm ≤ W ≤ 200 μm. Optionally, 100 μm ≤ W ≤ 150 μm.

[0239] In this embodiment, setting W to less than or equal to 200 μm reduces the ion migration path between the second part 1122 and the first negative electrode active material layer 122, lowers the risk of metal ion deposition, and improves the reliability of the battery cell 7. Setting W to greater than or equal to 50 μm provides space for the expansion of the first negative electrode active material layer 122, reduces the pressure between the second part 1122 and the first negative electrode active material layer 122, thereby reducing the compression of the electrolyte in the internal pores of the second part 1122 and the first negative electrode active material layer 122, and reducing internal resistance. Setting W to greater than or equal to 50 μm also reduces the requirements for the winding process and improves the winding efficiency of the electrode assembly 10.

[0240] In some embodiments, during the manufacturing process of the electrode assembly 10, the flat region Q1 of the electrode assembly 10 can be hot-pressed to reduce the gap between the first positive electrode active material layer 112 and the first negative electrode active material layer 122 located in the flat region Q1, thereby shortening the ion migration path.

[0241] In some embodiments, the active material capacity C2 per unit area of ​​the second portion 1122 is less than the active material capacity C1 per unit area of ​​the first portion 1121.

[0242] In the embodiments of this application, "capacity" includes charging capacity and discharging capacity. In the embodiments of this application, the charging capacity per unit area of ​​active material in the second part 1122 may be less than the charging capacity per unit area of ​​active material in the first part 1121; alternatively, the discharging capacity per unit area of ​​active material in the second part 1122 may be less than the discharging capacity per unit area of ​​active material in the first part 1121.

[0243] This application embodiment reduces the thickness of the second part 1122, thereby reducing the active material capacity per unit area of ​​the second part 1122 and reducing the number of ions released from the second part 1122 during charging.

[0244] In some embodiments, C2 / t2 may be equal to C1 / t1.

[0245] In some embodiments, the positive electrode sheet 11 further includes a second positive electrode active material layer 113 disposed on the outer surface 111b of the positive electrode current collector, wherein the thickness of the region of the second positive electrode active material layer 113 corresponding to the first portion 1121 is equal to the thickness of the first portion 1121.

[0246] For example, the region corresponding to the second positive electrode active material layer 113 and the first portion 1121 can be: the region of the second positive electrode active material layer 113 that overlaps with the first portion 1121 in the thickness direction of the positive electrode sheet 11 after the positive electrode sheet 11 is flattened.

[0247] In some embodiments, the thickness of the region corresponding to the second positive electrode active material layer 113 and the second portion 1122 is greater than the thickness of the second portion 1122.

[0248] The region corresponding to the second positive electrode active material layer 113 and the second part 1122 can be: the region where the second positive electrode active material layer 113 overlaps with the second part 1122 in the thickness direction of the positive electrode sheet 11 after the positive electrode sheet 11 is flattened.

[0249] The embodiments of this application can increase the capacity of the battery cell 7.

[0250] In some embodiments, the thickness of the region corresponding to the second positive electrode active material layer 113 and the second portion 1122 is equal to the thickness of the first portion 1121.

[0251] Compared to the first positive electrode active material layer 112, the second positive electrode active material layer 113 can have a relatively uniform thickness, thereby simplifying the molding process of the second positive electrode active material layer 113.

[0252] In some embodiments, the thickness of the insulating layer 114 is less than or equal to the thickness of the second portion 1122.

[0253] In some embodiments, the positive electrode sheet 11 includes a plurality of positive electrode bending portions 11a disposed along the winding direction V, and each positive electrode bending portion 11a is disposed in the bending region Q2.

[0254] For example, the positive electrode bending portion 11a is generally arc-shaped.

[0255] The electrode assembly 10 includes two bending regions Q2. Exemplarily, two adjacent positive electrode bending portions 11a of the positive electrode sheet 11 along the winding direction V are respectively disposed in the two bending regions Q2.

[0256] In some embodiments, the positive electrode 11 further includes a plurality of positive electrode straight portions 11b disposed in the straight region Q1. The plurality of positive electrode straight portions 11b are stacked.

[0257] For example, along the winding direction V, a plurality of positive electrode straight portions 11b and a plurality of positive electrode bent portions 11a are alternately arranged. Two adjacent positive electrode bent portions 11a along the winding direction V are connected by a positive electrode straight portion 11b.

[0258] In some embodiments, the negative electrode sheet 12 includes a plurality of negative electrode bending portions 12a disposed along the winding direction V, and each negative electrode bending portion 12a is disposed in the bending region Q2.

[0259] For example, the negative electrode bending portion 12a is generally arc-shaped.

[0260] For example, two adjacent negative electrode bends 12a along the winding direction V of the negative electrode sheet 12 are respectively disposed in two bend regions Q2.

[0261] In some embodiments, the negative electrode 12 further includes a plurality of negative electrode straight portions 12b disposed in the straight region Q1. The plurality of negative electrode straight portions 12b are stacked.

[0262] For example, along the winding direction V, a plurality of negative electrode straight portions 12b and a plurality of negative electrode bent portions 12a are alternately arranged. Two adjacent negative electrode bent portions 12a along the winding direction V are connected by a negative electrode straight portion 12b.

[0263] In some embodiments, at least a portion of the second portion 1122 is formed in the first positive electrode bend 11a of the positive electrode sheet 11 along the winding direction V.

[0264] The first positive electrode bending portion 11a can be the portion of the positive electrode sheet 11 that is bent for the first time during the winding process along the winding direction V.

[0265] For example, a negative electrode bending portion 12a is provided inside the first positive electrode bending portion 11a, and a gap G is formed between the portion of the second portion 1122 formed in the first positive electrode bending portion 11a and the first negative electrode active material layer 122 formed in the negative electrode bending portion 12a.

[0266] The first positive electrode bend 11a of the positive electrode sheet 11 has a large curvature. Correspondingly, the portion of the first negative electrode active material layer 122 located inside the first positive electrode bend 11a also has a large curvature. This makes the portion of the first negative electrode active material layer 122 located inside the first positive electrode bend 11a more prone to active material shedding during bending. In this embodiment, at least a portion of the second part 1122 is formed in the first positive electrode bend 11a to reduce the number of released ions, lower the risk of metal ion deposition in the portion of the first negative electrode active material layer 122 located inside the first positive electrode bend 11a, and improve the reliability of the battery cell 7.

[0267] In some embodiments, the first negative electrode bend 12a of the negative electrode sheet 12 along the winding direction V is located inside the first positive electrode bend 11a.

[0268] In some embodiments, at least a portion of the second portion 1122 is formed in the second positive electrode bend 11a of the positive electrode sheet 11 along the winding direction V.

[0269] The second positive electrode bending portion 11a can be the portion of the positive electrode sheet 11 that is bent for the second time during the winding process along the winding direction V.

[0270] The first positive electrode bending portion 11a and the second positive electrode bending portion 11a can be respectively provided in the two bending regions Q2 of the electrode assembly 10.

[0271] The second positive electrode bend 11a of the positive electrode sheet 11 has a larger curvature. Correspondingly, the portion of the first negative electrode active material layer 122 located inside the second positive electrode bend 11a also has a larger curvature. This makes the portion of the first negative electrode active material layer 122 located inside the second positive electrode bend 11a more prone to active material shedding during bending. In this embodiment, at least a portion of the second part 1122 is formed in the second positive electrode bend 11a to reduce the number of released ions, lower the risk of metal ion deposition in the portion of the first negative electrode active material layer 122 located inside the second positive electrode bend 11a, and improve the reliability of the battery cell 7.

[0272] In some embodiments, the second negative electrode bend 12a of the negative electrode sheet 12 along the winding direction V is located inside the second positive electrode bend 11a.

[0273] In some embodiments, at least a portion of the second portion 1122 is formed in the first positive electrode bend 11a of the positive electrode sheet 11 along the winding direction V; at least a portion of the second portion 1122 is formed in the second positive electrode bend 11a of the positive electrode sheet 11 along the winding direction V.

[0274] The second portion 1122 formed in the first positive electrode bending portion 11a and the second portion 1122 formed in the second positive electrode bending portion 11a can be the same continuously arranged second portion 1122, or two second portions 1122 can be arranged at intervals along the winding direction V.

[0275] In this embodiment, at least a portion of the second part 1122 is formed on the first positive electrode bending portion 11a and the second positive electrode bending portion 11a to reduce the number of ions released, reduce the risk of metal ion precipitation in the first negative electrode active material layer 122, and improve the reliability of the battery cell 7.

[0276] In some embodiments, both ends of the second portion 1122 are located in the straight region Q1 along the winding direction V. The second portion 1122 passes through at least one bending region Q2 along the winding direction V.

[0277] The second part 1122 may pass through one, two, three or more bending zones Q2. For example, if there are two bending zones Q2, and the second part 1122 extends one revolution along the winding direction V, then it passes through two bending zones Q2, that is, it passes through two bending zones Q2.

[0278] For example, each time the second portion 1122 passes through the bending region Q2, a portion of the second portion 1122 is formed in a positive electrode bending portion 11a.

[0279] In this embodiment, the second portion 1122 passes through the bending region Q2 at least once, thereby reducing the number of ions released from the first positive electrode active material layer 112 located in the bending region Q2, reducing the risk of metal ion precipitation in the first negative electrode active material layer 122, and improving the reliability of the battery cell 7. By placing both ends of the second portion 1122 along the winding direction V in the straight region Q1, the risk of excessive increase in the gap G between the second portion 1122 and the first negative electrode active material layer 122 due to the first portion 1121 extending near the end of the second portion 1122 into the bending region Q2 can be reduced. This reduces the ion migration path between the second portion 1122 and the first negative electrode active material layer 122, reduces the risk of metal ion precipitation, and improves the reliability of the battery cell 7.

[0280] In some embodiments, the flat region Q1 of the electrode assembly 10 undergoes a hot pressing process during the molding process. Hot pressing can reduce the gap between the second part 1122 located in the flat region Q1 and the first negative electrode active material layer 122.

[0281] In some embodiments, along the winding direction V, the second portion 1122 passes through a bending zone Q2.

[0282] In some embodiments, the first positive electrode active material layer 112 includes a plurality of second portions 1122, which are spaced apart along the winding direction V. A first portion 1121 is disposed between two adjacent second portions 1122 along the winding direction V.

[0283] Along the winding direction V, each second part 1122 can pass through the bending zone Q2 once or multiple times.

[0284] The number of times that two adjacent second parts 1122 pass through the bending zone Q2 can be the same or different.

[0285] In some embodiments, after the positive electrode 11 is flattened, a plurality of second portions 1122 and a plurality of first portions 1121 are alternately arranged along the length direction X of the positive electrode 11. After the positive electrode 11 is flattened, the winding axis Z is parallel to the width direction Y of the positive electrode 11.

[0286] In some embodiments, a recess 1126 is provided on the side of the first positive electrode active material layer 112 away from the positive electrode current collector 111, and the bottom wall of the recess 1126 includes a second portion 1122. In this embodiment, the second portion 1122 is thinned by providing the recess 1126.

[0287] In some embodiments, the electrode assembly 10 includes two bending regions Q2, which are respectively connected to the two ends of the straight region Q1, and two adjacent second portions 1122 are respectively disposed corresponding to the two bending regions Q2.

[0288] As an example, the two bending regions Q2 can be defined as a first bending region and a second bending region, respectively. In two adjacent second portions 1122, at least a portion of one second portion 1122 is formed in the first bending region and the one second portion 1122 does not extend into the second bending region, and at least a portion of the other second portion 1122 is formed in the second bending region and the other second portion 1122 does not extend into the first bending region.

[0289] The embodiments of this application can reduce the size of a single second part 1122 along the winding direction V, reduce the number of times a single second part 1122 passes through the bending area Q2, reduce the total size of multiple second parts 1122 along the winding direction V, and reduce the impact of setting multiple second parts 1122 on the capacity of the battery cell 7.

[0290] In some embodiments, in two adjacent second portions 1122, at least a portion of one second portion 1122 is formed in the first positive electrode bend 11a, and at least a portion of the other second portion 1122 is formed in the second positive electrode bend 11a.

[0291] In some embodiments, the first positive electrode active material layer 112 further includes a third portion 1123, which is connected between the first portion 1121 and the second portion 1122. The third portion 1123 gradually decreases in size along the direction from the first portion 1121 to the second portion 1122.

[0292] The third part, 1123, can be one or multiple.

[0293] The third part 1123 can smoothly transition between the first part 1121 and the second part 1122, thereby reducing abrupt changes in thickness, reducing stress concentration, reducing metal ion precipitation caused by stress concentration, and improving the cycle performance of the battery cell 7.

[0294] In some embodiments, the average thickness of the third portion 1123 is less than the thickness of the first portion 1121 and greater than the thickness of the second portion 1122.

[0295] In some embodiments, the thickness of the connection between the third portion 1123 and the first portion 1121 is equal to the thickness of the first portion 1121, and the thickness of the connection between the third portion 1123 and the second portion 1122 is equal to the thickness of the second portion 1122.

[0296] In some embodiments, the first positive electrode active material layer 112 further includes a fourth portion 1124, which is disposed along the winding axis Z with the first portion 1121, and the winding axis Z is perpendicular to the winding direction V. The dimension of the fourth portion 1124 along the winding axis Z is smaller than the dimension of the first portion 1121 along the winding axis Z. The fourth portion 1124 gradually decreases in size along the direction from the first portion 1121 to the fourth portion 1124.

[0297] In some examples, the first portion 1121 has a fourth portion 1124 on one side along the winding axis Z. In other examples, the first portion 1121 has a fourth portion 1124 on both sides along the winding axis Z.

[0298] The minimum thickness of part 1124 can be greater than, equal to or less than the thickness of part 1122.

[0299] During the forming process of the positive electrode sheet 11, it is usually necessary to roll-press the positive electrode sheet 11 to increase the compaction density of the first positive electrode active material layer 112. In this embodiment, by providing the fourth portion 1124, the stress concentration at the edge of the first positive electrode active material layer 112 along the winding axis Z can be reduced, thereby lowering the risk of cracking of the positive electrode current collector 111 and the risk of collapse at the edge of the first positive electrode active material layer 112 along the winding axis Z, and improving reliability. Providing the fourth portion 1124 also facilitates electrolyte wetting, improving the cycle performance of the battery cell 7.

[0300] In some embodiments, the minimum thickness of the fourth portion 1124 is greater than or equal to the thickness of the second portion 1122.

[0301] The thickness of the second part 1122 is less than or equal to the minimum thickness of the fourth part 1124. When rolling the positive electrode sheet 11, the second part 1122 experiences less rolling pressure, and the second part 1122 is less prone to edge collapse. The smaller thickness of the second part 1122 helps reduce the risk of metal ion precipitation and improves the reliability of the battery cell 7.

[0302] In some embodiments, along the winding axis Z, one end of the fourth portion 1124 away from the first portion 1121 is flush with one end of the second portion 1122.

[0303] The second part 1122 has a larger dimension in the winding axis Z, thereby effectively reducing the risk of metal ion precipitation.

[0304] In some embodiments, along the winding axis Z, one end of the first portion 1121 away from the fourth portion 1124 is flush with the other end of the second portion 1122.

[0305] For example, in the winding axis Z, the sum of the dimensions of the first portion 1121 and the fourth portion 1124 is equal to the dimension of the second portion 1122.

[0306] In some embodiments, the third portion 1123 includes a first segment 1123a and a second segment 1123b arranged along the winding axis Z, the first segment 1123a connecting the first portion 1121 and the second portion 1122, and the second segment 1123b connecting the fourth portion 1124 and the second portion 1122.

[0307] Optionally, the average thickness of the first segment 1123a is greater than the average thickness of the second segment 1123b.

[0308] In some embodiments, FIG11 is a schematic diagram of the positive electrode sheet of a battery cell provided in other embodiments of the present application in a flattened state; FIG12 is a cross-sectional schematic diagram of FIG11 along the DD direction.

[0309] Referring to Figures 11 and 12, in some embodiments, the minimum thickness of the fourth portion 1124 is less than the thickness of the second portion 1122. The first positive electrode active material layer 112 further includes a fifth portion 1125, which is disposed along the winding axis Z with the second portion 1122. The dimension of the fifth portion 1125 along the winding axis Z is smaller than the dimension of the second portion 1122 along the winding axis Z. The fifth portion 1125 gradually decreases in size along the direction from the second portion 1122 to the fifth portion 1125. The fifth portion 1125 is connected to the fourth portion 1124, and the fifth portion 1125 and the fourth portion 1124 are disposed along the winding direction V.

[0310] In some examples, the second portion 1122 has a fifth portion 1125 on one side along the winding axis Z. In other examples, the second portion 1122 has a fifth portion 1125 on both sides along the winding axis Z.

[0311] Setting the thickness of the second portion 1122 to be greater than the minimum thickness of the fourth portion 1124 reduces the thinning degree of the second portion 1122, thus reducing the impact of thinning the second portion 1122 on the capacity of the battery cell 7. By setting the fifth portion 1125, the stress concentration on the edge of the first positive electrode active material layer 112 along the winding axis Z can be reduced, thereby reducing the risk of cracking of the positive electrode current collector 111 and the risk of collapse of the edge of the first positive electrode active material layer 112 along the winding axis Z, and improving reliability.

[0312] In some embodiments, the end of the fifth portion 1125 away from the second portion 1122 is flush with the end of the fourth portion 1124 away from the first portion 1121.

[0313] In some embodiments, the thickness of the end of the fifth portion 1125 away from the second portion 1122 is equal to the thickness of the end of the fourth portion 1124 away from the first portion 1121.

[0314] In some embodiments, the fifth portion 1125 is smaller than the fourth portion 1124 in the winding axis Z.

[0315] In some embodiments, the third portion 1123 includes a first segment 1123a and a second segment 1123b arranged along the winding axis Z, the first segment 1123a connecting the first portion 1121 and the second portion 1122, and the second segment 1123b connecting the fourth portion 1124 and the fifth portion 1125.

[0316] Figure 13 is a cross-sectional schematic diagram of the electrode assembly of a battery cell provided in some other embodiments of this application; Figure 14 is a schematic diagram of the positive electrode sheet of a battery cell provided in some other embodiments of this application in a flattened state.

[0317] Referring to Figures 13 and 14, in some embodiments, both ends of the second portion 1122 are located in the straight region Q1 along the winding direction V. Along the winding direction V, the second portion 1122 passes through at least two bending regions Q2.

[0318] The second part 1122 can reduce the risk of metal ion precipitation in the two bending regions Q2 and improve the reliability of the battery cell 7. This application ensures that the second part 1122 passes through at least the two bending regions Q2, which can reduce the number of second parts 1122 and simplify the forming process of the positive electrode sheet 11.

[0319] In some embodiments, a portion of the second portion 1122 is formed in the first positive electrode bend 11a, and another portion of the second portion 1122 is formed in the second positive electrode bend 11a.

[0320] In some embodiments, the second portion 1122 is configured as one, which can simplify the forming process of the positive electrode 11.

[0321] In some embodiments, the positive electrode 11 has a winding start end E1 and a winding end end E2 at its two ends along the winding direction V, with the winding start end E1 located in the straight region Q1. The second portion 1122 extends from the winding start end E1 along the winding direction V.

[0322] The embodiments of this application can reduce the number of the first part 1121 and the second part 1122, reduce the number of thickness changes of the first positive electrode active material layer 112 during the coating process, and simplify the forming process of the positive electrode sheet 11.

[0323] In some embodiments, the second portion 1122 extends from the winding start end E1 along the winding direction V and passes through two bending zones Q2.

[0324] In some embodiments, the thickness of the second portion 1122 is less than or equal to the minimum thickness of the fourth portion 1124.

[0325] Figure 15 is a partial schematic diagram of the electrode assembly of a battery cell provided in some other embodiments of this application.

[0326] Referring to FIG15, in some embodiments, in the bending region Q2, the number of layers of the separator 13 disposed between the second portion 1122 and the first negative electrode active material layer 122 is greater than or equal to 2.

[0327] For example, in the bending region Q2, the number of layers of the separator 13 disposed between the second portion 1122 and the first negative electrode active material layer 122 can be 2-8. For example, the number of layers of the separator 13 disposed between the second portion 1122 and the first negative electrode active material layer 122 can be 2, 3, 4, 5, 6, 7 or 8.

[0328] In this embodiment, even if metal ions are deposited and metal dendrites are formed in the first negative electrode active material layer 122, the multilayer separator 13 can block the metal dendrites to a certain extent, reduce the risk of metal dendrites contacting the second part 1122, and improve the reliability of the battery cell 7.

[0329] This application also provides a battery device including multiple battery cells according to any of the above embodiments.

[0330] According to some embodiments of this application, this application also provides an electrical device, including a battery cell from any of the above embodiments, wherein the battery cell is used to provide electrical energy to the electrical device. The electrical device can be any of the aforementioned devices or systems that utilize battery cells.

[0331] Referring to Figures 4 to 10, an embodiment of this application provides a battery cell 7, which includes a housing 20 and an electrode assembly 10, the electrode assembly 10 being housed within the housing 20.

[0332] The electrode assembly 10 includes a positive electrode 11, a negative electrode 12, and an insulating member 13. The positive electrode 11, the negative electrode 12, and the insulating member 13 are wound together to form a straight region Q1 and two bent regions Q2. The two bent regions Q2 are respectively connected to the two ends of the straight region Q1.

[0333] The positive electrode 11 includes a positive current collector 111, a first positive active material layer 112 and a second positive active material layer 113. The first positive active material layer 112 is disposed on the inner surface 111a of the positive current collector, and the second positive active material layer 113 is disposed on the outer surface 111b of the positive current collector.

[0334] The negative electrode sheet 12 includes a negative electrode current collector 121, a first negative electrode active material layer 122 and a second negative electrode active material layer 123. The first negative electrode active material layer 122 is disposed on the outer surface 121a of the negative electrode current collector, and the second negative electrode active material layer 123 is disposed on the inner surface 121b of the negative electrode current collector.

[0335] The positive electrode 11 includes a plurality of positive electrode bending portions 11a arranged along the winding direction V, and each positive electrode bending portion 11a is disposed in the bending region Q2. The negative electrode 12 includes a plurality of negative electrode bending portions 12a arranged along the winding direction V, and each negative electrode bending portion 12a is disposed in the bending region Q2.

[0336] The first positive electrode active material layer 112 includes a first portion 1121 and a second portion 1122 arranged along the winding direction V of the electrode assembly 10. The thickness of the second portion 1122 is less than the thickness of the first portion 1121. At least a portion of the first portion 1121 is disposed in the straight region Q1, and at least a portion of the second portion 1122 is disposed in the bending region Q2.

[0337] The second part 1122 is located in the straight section Q1 at both ends along the winding direction V. Along the winding direction V, the second part 1122 passes through the bending section Q2.

[0338] At least two second parts 1122 are provided. A portion of one second part 1122 is provided in the first positive electrode bend 11a, and a portion of the other second part 1122 is provided in the second positive electrode bend 11a.

[0339] The thickness of the first part 1121 is t1, and the thickness of the second part 1122 is t2. k = (t1-t2) / t1; 20% ≤ k ≤ 65%. In the bending region Q2, the gap G between the second part 1122 and the first negative electrode active material layer 122 is greater than or equal to 100 μm and less than or equal to 350 μm in the thickness direction of the second part 1122.

[0340] Example

[0341] The following embodiments describe the contents disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosures in this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0342] Example 1

[0343] 1. Preparation of positive electrode sheet

[0344] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is located on both sides of the positive current collector. The positive current collector is an aluminum foil. The positive active material layer is a film formed by uniformly coating a positive electrode slurry (solvent being N-methylpyrrolidone, NMP) onto the surface of the aluminum foil, followed by drying and cold pressing. The positive active material layer includes positive active material, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) in a weight ratio of 97:1:2. The positive active material includes materials with the molecular formula LiNi. 0.8 Co 0.1 Mn 0.1 O2(NCM 811 Layered transition metal oxides.

[0345] The positive electrode active material layer located on the positive electrode current collector side includes a first part and a second part. The thickness of the first part is 70 μm, and the thickness of the second part is 7 μm. The second part extends one turn from the starting end of the positive electrode sheet.

[0346] 2. Preparation of negative electrode sheet

[0347] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is located on both sides of the negative electrode current collector. The negative electrode current collector is a copper foil. The negative electrode active material layer is a film layer formed by uniformly coating the surface of the negative electrode current collector copper foil with negative electrode slurry (solvent is deionized water), and then drying and cold pressing. The negative electrode active material layer includes graphite, conductive agent Super-p, and binder styrene-butadiene rubber (SBR) in a weight ratio of 97:2:1.

[0348] The areal density of the negative electrode active material layer is 9.0 mg / cm³. 2 The porosity is 22.1%, and the compacted density is 1.7 g / cm³. 3 .

[0349] 3. Isolation components

[0350] We provide PE (polyethylene) based films.

[0351] 4. Preparation of electrolyte

[0352] The electrolyte consists of an organic solvent and a lithium salt. Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0353] 5. Preparation of battery cells

[0354] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. The positive electrode, separator, and negative electrode are then wound to obtain an electrode assembly. The electrode assembly is placed in a square-structured shell, dried, and then injected with electrolyte. After processes such as welding, formation, and aging, a battery cell is obtained.

[0355] Example 2-12

[0356] Examples 2-12 were prepared using a method similar to that of Example 1. The difference from Example 1 was that the thickness of the second part was adjusted, and the tension was changed during the winding of the positive electrode, separator, and negative electrode to adjust the size of the gap between the second part and the negative electrode active material layer of the negative electrode.

[0357] Comparative Example 1

[0358] Comparative Example 1 used a similar method to Example 1 to prepare a lithium-ion battery. The difference from Example 1 was that the thickness of the positive electrode active material layer in Comparative Example 1 was uniform, specifically, the thickness of both the first and second portions was 70 μm.

[0359] Performance testing

[0360] 1. Parameter measurement of individual battery cells

[0361] At 25°C, the prepared battery cell was charged to 4.25V at 0.33C, then discharged to 2.5V at 0.33C, and then discharged to 2.5V at 0.1C.

[0362] Using CT (Computed Tomography) technology, X-rays are used to obtain cross-sectional images of the battery cell, which are perpendicular to the winding axis of the electrode assembly and pass through the second and first parts;

[0363] Based on this image, a virtual straight line is defined, which can pass through the center of the bend and intersect with the second part;

[0364] Based on the image and the virtual line, the first intersection point between the virtual line and the inner surface of the second part is obtained, and the second intersection point between the virtual line and the outer surface of the first negative electrode active material layer is obtained. The second intersection point is located inside the first intersection point, and there are no positive or negative electrode plates between the first and second intersection points.

[0365] Measure the distance between the first intersection point and the second intersection point;

[0366] Repeat the above steps to set up 10 different virtual lines, measure 10 spacing values, and calculate the average value D1 of the 10 spacing values;

[0367] Disassemble the battery cell and unfold the positive electrode, negative electrode and separator; select 10 positions on the separator and measure 10 thickness values, then calculate the average of the 10 thickness values, which can be the thickness D2 of the separator;

[0368] The dimension W of the gap in the thickness direction of the second part can be D1-D2.

[0369] 2. Lithium plating test of individual battery cells

[0370] The lithium plating test was conducted at 25°C. The lithium-ion batteries prepared in the examples and comparative examples were fully charged to 4.25V at 4C and then fully discharged to 2.5V at 1C, repeated 10 times. Afterward, the battery cells were fully charged at 4C, and the negative electrode was disassembled to observe the lithium plating on the innermost two rings. The test results showed that a lithium plating area of ​​less than 5% on the negative electrode surface (i.e., the lithium plating area of ​​the innermost two rings of the negative electrode / the total area of ​​the innermost two rings of the negative electrode < 5%) was considered slight lithium plating; a lithium plating area of ​​5%-40% was considered moderate lithium plating; and a lithium plating area of ​​more than 40% was considered severe lithium plating.

[0371] The test results are shown in Table 1.

[0372] Table 1

[0373] Referring to Examples 1-12 and Comparative Example 1 in Table 1, this application can reduce the risk of lithium plating by locally thinning the positive electrode active material layer.

[0374] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0375] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

A battery cell includes a housing and an electrode assembly, at least a portion of which is housed within the housing; The electrode assembly includes a positive electrode, a negative electrode, and an insulating element. The positive electrode, the negative electrode, and the insulating element are wound together to form a straight region and a bent region. The bent region is connected to the straight region. The positive electrode sheet includes a positive current collector and a first positive active material layer. The first positive active material layer is disposed on the inner surface of the positive current collector. The first positive active material layer includes a first part and a second part arranged along the winding direction of the electrode assembly. The thickness of the second part is less than the thickness of the first part. At least a portion of the first part is disposed in the straight region, and at least a portion of the second part is disposed in the bent region. The negative electrode sheet includes a negative electrode current collector and a first negative electrode active material layer, wherein the first negative electrode active material layer is disposed on the outer surface of the negative electrode current collector; in the bending region, a gap is provided between the second portion and the first negative electrode active material layer. According to claim 1, the battery cell, wherein, In the bending region, the gap has a dimension greater than or equal to 50 μm and less than or equal to 600 μm in the thickness direction of the second portion. According to claim 2, the battery cell, wherein, The gap has a dimension in the thickness direction of the second part that is greater than or equal to 100 μm and less than or equal to 300 μm. The battery cell according to any one of claims 1-3, wherein, The thickness of the first part is t1, the thickness of the second part is t2, and k = (t1-t2) / t1 × 100%. 5% ≤ k ≤ 90%; optionally, 20% ≤ k ≤ 65%. The battery cell according to claim 4 satisfies one of the following conditions (1) to (8): (1) 65% ≤ k ≤ 90%, the dimension of the gap in the thickness direction of the second part is less than or equal to 500 μm; (2) 55% ≤ k ≤ 65%, the dimension of the gap in the thickness direction of the second part is less than or equal to 350 μm; (3) 45% ≤ k ≤ 55%, the dimension of the gap in the thickness direction of the second part is less than or equal to 300 μm; (4) 40% ≤ k ≤ 45%, the dimension of the gap in the thickness direction of the second part is less than or equal to 200 μm; (5) 35% ≤ k ≤ 40%, the dimension of the gap in the thickness direction of the second part is less than or equal to 150 μm; (6) 25% ≤ k ≤ 35%, the dimension of the gap in the thickness direction of the second part is less than or equal to 120 μm; (7) 20% ≤ k ≤ 25%, the dimension of the gap in the thickness direction of the second part is less than or equal to 100 μm; (8) 5% ≤ k ≤ 20%, the gap in the thickness direction of the second part is less than or equal to 60 μm. The battery cell according to any one of claims 1-5, wherein, The positive electrode sheet includes a plurality of positive electrode bending portions arranged along the winding direction, and each of the positive electrode bending portions is disposed in the bending area; At least a portion of the second part is formed at the first positive electrode bend of the positive electrode sheet along the winding direction; and / or, at least a portion of the second part is formed at the second positive electrode bend of the positive electrode sheet along the winding direction. The battery cell according to any one of claims 1-6, wherein, Both ends of the second part along the winding direction are located in the straight area; Along the winding direction, the second portion passes through the bending zone at least once. According to claim 7, the battery cell, wherein, Along the winding direction, the second portion passes through the bending zone at least twice. The battery cell according to any one of claims 1-7, wherein, The first positive electrode active material layer includes a plurality of second portions, which are spaced apart along the winding direction; Along the winding direction, the first portion is disposed between two adjacent second portions; The electrode assembly includes two bending regions, which are respectively connected to the two ends of the straight region, and two adjacent second parts are respectively provided corresponding to the two bending regions. The battery cell according to any one of claims 1-9, wherein, The positive electrode sheet has a winding start end and a winding end end at both ends along the winding direction. The winding start end is located in the straight region, and the second part extends from the winding start end along the winding direction. The battery cell according to any one of claims 1-10, wherein, In the bending region, the number of layers of the separator disposed between the second part and the first negative electrode active material layer is greater than or equal to 2. The battery cell according to any one of claims 1-11, wherein, The first positive electrode active material layer further includes a third part, which is connected between the first part and the second part; Along the direction from the first part to the second part, the third part gradually decreases in size. The battery cell according to any one of claims 1-12, wherein, The first positive electrode active material layer further includes a fourth part, which is disposed along the winding axis with the first part, and the winding axis is perpendicular to the winding direction; The dimension of the fourth portion along the winding axis is smaller than the dimension of the first portion along the winding axis; Along the direction from the first part to the fourth part, the fourth part gradually decreases in size. According to claim 13, the battery cell, wherein, The minimum thickness of the fourth part is greater than or equal to the thickness of the second part; Along the winding axis, the end of the fourth portion away from the first portion is flush with the end of the second portion. According to claim 13, the battery cell, wherein, The minimum thickness of the fourth part is less than the thickness of the second part; The first positive electrode active material layer further includes a fifth portion, which is disposed along the winding axis with the second portion, and the dimension of the fifth portion along the winding axis is smaller than the dimension of the second portion along the winding axis. Along the direction from the second part to the fifth part, the fifth part gradually decreases in size; The fifth part is connected to the fourth part, and the fifth part and the fourth part are arranged along the winding direction. A battery device comprising a plurality of battery cells according to any one of claims 1-15. An electrical device includes a battery device according to claim 16, the battery device being used to provide electrical energy.

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