Electrode assembly, battery and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to an electrode assembly, a battery and an electric device. The electrode assembly comprises a negative pole piece, an isolating membrane and a positive pole piece, wherein the negative pole piece, the isolating membrane and the positive pole piece are wound around a winding axis to form the electrode assembly; wherein the positive pole piece comprises a first positive pole film layer and a second positive pole film layer which are respectively positioned on the current collector along the winding direction; the first positive electrode film layer comprises first positive electrode active particles, and the second positive electrode film layer comprises second positive electrode active particles; the median diameter Dv150 of the first positive electrode active particles is greater than the median diameter Dv250 of the second positive electrode active particles; the positive pole piece further comprises a bending area formed by extending from the winding starting end to the winding tail end in the winding direction, the bending area comprises a plurality of bending parts, and at least part of the bending part arranged close to the winding axis is provided with a first positive pole film layer. The electrode assembly designed by the invention is beneficial to relieving the problem of cracking of the electrode plates.

Description

Technical Field

[0001] The present application relates to the field of batteries, and particularly to an electrode assembly, a battery, and an electrical device. Background Art

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their outstanding features such as light weight, pollution-free, and no memory effect. Among them, lithium-ion batteries are very widely used in the fields of portable electronic devices, electric vehicles, etc.

[0003] With the increasingly wide application range of secondary batteries, the requirements for battery performance are getting higher and higher, the energy density of secondary batteries is also getting higher and higher, and the problem of pole piece cracking is becoming increasingly prominent. Summary of the Invention

[0004] In view of the above problems, the present application provides an electrode assembly, a battery, and an electrical device, and the electrode assembly designed in the present application is beneficial to alleviating the problem of pole piece cracking.

[0005] In a first aspect, the present application provides an electrode assembly, including:

[0006] A negative electrode pole piece;

[0007] A separator;

[0008] A positive electrode pole piece;

[0009] The negative electrode pole piece, the separator, and the positive electrode pole piece are wound together around a winding axis to form the electrode assembly;

[0010] The positive electrode pole piece includes a first positive electrode film layer and a second positive electrode film layer that are respectively located on a current collector along the winding direction;

[0011] The first positive electrode film layer includes first positive electrode active particles, and the second positive electrode film layer includes second positive electrode active particles;

[0012] The median particle size Dv150 of the first positive electrode active particles is greater than the median particle size Dv250 of the second positive electrode active particles;

[0013] The positive electrode pole piece further includes a bending region that extends from the winding starting end along the winding direction to the winding ending end; the bending region includes a plurality of bending parts distributed from the inside to the outside;

[0014] At least some of the bending parts close to the winding axis have the first positive electrode film layer.

[0015] In some embodiments of the present application, the Dv150 of the first positive electrode active particles and the Dv250 of the second positive electrode active particles satisfy:

[0016] 0 < (Dv150 - Dv250) < 20 μm;

[0017] Preferably, 4.9 μm < (Dv150 - Dv250) < 20 μm;

[0018] Preferably, the Dv150 of the first positive electrode active particles satisfies: 6 μm ≤ Dv150 ≤ 25 μm;

[0019] Preferably, the Dv150 of the first positive electrode active particles satisfies: 10 μm ≤ Dv150 ≤ 25 μm.

[0020] In some embodiments of the present application, the Dv190 and Dv110 of the first positive electrode active particles satisfy:

[0021] 0 < Dv190 - Dv110 < 50 μm;

[0022] Preferably, 10 μm < Dv190 - Dv110 ≤ 37 μm.

[0023] In some embodiments of the present application, the first positive electrode film layer is disposed on at least one surface of the current collector, and the first positive electrode film layer includes a first head end and a first tail end;

[0024] The second positive electrode film layer is disposed on at least one surface of the current collector, and the second positive electrode film layer includes a second head end and a second tail end;

[0025] The first head end is connected to the second tail end or the first tail end is connected to the second head end.

[0026] In some embodiments of the present application, the bending region includes a first bending portion formed along the winding direction starting from the winding start end, and the first bending portion is close to the winding axis;

[0027] The first bending portion has a first positive electrode film layer.

[0028] In some embodiments of the present application, the bending region includes a first bending portion and a second bending portion formed in sequence along the winding direction starting from the winding start end, and the first bending portion is closer to the winding axis than the second bending portion;

[0029] Both the first bending portion and the second bending portion have a first positive electrode film layer.

[0030] In some embodiments of the present application, the first positive electrode film layer is continuously distributed on the current collector along the winding direction starting from the winding start end.

[0031] In some embodiments of the present application, starting from the winding starting end, the first positive electrode film layer and the second positive electrode film layer are alternately distributed on the current collector along the winding direction.

[0032] In some embodiments of the present application, the length of the first positive electrode film layer from the winding starting end along the winding direction to the winding end is a1;

[0033] The length of the positive electrode tab from the winding starting end along the winding direction to the winding end is L;

[0034] Satisfy: a1 < L.

[0035] In some embodiments of the present application, the length of the first positive electrode film layer from the winding starting end along the winding direction to the winding end is a1;

[0036] The length of the positive electrode tab from the winding starting end along the winding direction to the winding end is L;

[0037] The negative electrode tab, the separator and the positive electrode tab together wind around the winding needle to form the electrode assembly. The winding needle has a winding needle circumference, and the winding needle circumference is less than 1 / 2 × L;

[0038] The a1 is less than the winding needle circumference.

[0039] In some embodiments of the present application, the compaction density of the first positive electrode film layer is not lower than that of the second positive electrode film layer.

[0040] In some embodiments of the present application, the compaction density of the first positive electrode film layer is ρ1, the compaction density of the second positive electrode film layer is ρ2, and ρ1 and ρ2 satisfy: ρ1 / ρ2 = 1.0 to 1.1, preferably: ρ1 / ρ2 = 1.0 to 1.05.

[0041] In some embodiments of the present application, the thickness difference between the first positive electrode film layer and the second positive electrode film layer after cold pressing is less than 40 μm;

[0042] Preferably, it is less than or equal to 30 μm.

[0043] In some embodiments of the present application, the areal capacity of the first positive electrode film layer is Q1, the areal capacity of the second positive electrode film layer is Q2, and Q1 and Q2 satisfy: Q1 / Q2 = 1.0 to 1.05;

[0044] Preferably, Q1 / Q2 = 1.0 to 1.03.

[0045] In some embodiments of the present application, the mass percentage content of the first positive electrode active particles in the first positive electrode film layer is w1, and the mass percentage content of the second positive electrode active particles in the second positive electrode film layer is w2, and w1 and w2 satisfy: w1 / w2 = 0.95 to 1.05;

[0046] Preferably, w1 / w2 = 1.0 to 1.03.

[0047] A second aspect of the present application is to provide a battery, including the electrode assembly described in the first aspect.

[0048] A third aspect of the present application is to provide an electrical device, including the electrode assembly described in the first aspect or the battery described in the second aspect.

[0049] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present application more obvious and understandable, the specific embodiments of the present application are specifically given below. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present application. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0051] Figure 1 is a schematic diagram of the battery structure of some embodiments of the present application;

[0052] Figure 2 is a schematic exploded view of the battery of some embodiments of the present application;

[0053] Figure 3 is a schematic diagram of the vehicle structure of some embodiments of the present application;

[0054] Figure 4 is a schematic diagram of the battery pack structure of some embodiments of the present application;

[0055] Figure 5 is a schematic diagram of the battery assembly structure of some embodiments of the present application;

[0056] Figure 6 is a schematic diagram of the battery assembly structure of some embodiments of the present application;

[0057] Figure 7A is a schematic diagram of the structure of a positive electrode tab of some embodiments of the present application;

[0058] Figure 7BAnother schematic diagram of the positive electrode sheet structure according to some embodiments of the present application;

[0059] Figure 7C Another schematic diagram of the positive electrode sheet structure according to some embodiments of the present application;

[0060] Figure 8A A schematic diagram of the structure of a battery assembly according to some embodiments of the present application;

[0061] Figure 8B Another schematic diagram of the structure of a battery assembly according to some embodiments of the present application;

[0062] Figure 8C Another schematic diagram of the structure of a battery assembly according to some embodiments of the present application;

[0063] Figure 8D Another schematic diagram of the structure of a battery assembly according to some embodiments of the present application;

[0064] Figure 8E Another schematic diagram of the structure of a battery assembly according to some embodiments of the present application;

[0065] Figure 8F Another schematic diagram of the structure of a battery assembly according to some embodiments of the present application;

[0066] Figure 9A A schematic diagram of the positive electrode sheet structure according to some embodiments of the present application;

[0067] Figure 9B Another schematic diagram of the positive electrode sheet structure according to some embodiments of the present application;

[0068] Figure 9C Another schematic diagram of the positive electrode sheet structure according to some embodiments of the present application;

[0069] Figure 9D Another schematic diagram of the positive electrode sheet structure according to some embodiments of the present application;

[0070] Figure 9E Another schematic diagram of the positive electrode sheet structure according to some embodiments of the present application;

[0071] The reference numerals in the specific embodiments are as follows:

[0072] 10000, vehicle;

[0073] 1000, battery; 2000, controller; 3000, motor;

[0074] 100, battery cell;

[0075] 200, box body; 210, first part; 220, second part;

[0076] 10. Secondary battery;

[0077] 101. Housing; 102. Electrode assembly; 103. Cover plate;

[0078] 1021. Negative electrode tab; 1022. Separator; 1023. Positive electrode tab; 1024. Current collector; 1025. Bent region;

[0079] 1023a. Winding start end; 1023b. Winding end; 1023c. Bent portion; 1023d. First positive electrode tab; 1023e. Second positive electrode tab;

[0080] 10231. First positive electrode film layer; 10232. Second positive electrode film layer;

[0081] X-axis direction: Length direction of the positive electrode tab;

[0082] Z-axis direction: Thickness direction of the positive electrode tab. Detailed implementation manners

[0083] Hereinafter, embodiments of the electrode assembly, battery, and electrical device of the present application are specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0084] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0085] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0086] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0087] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0088] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean only including or comprising the listed components.

[0089] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0090] Unless otherwise specified, in this application, terms such as "first", "second", etc. are only used to distinguish different objects, and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features.

[0091] Unless otherwise specified, in this application, the term "plurality" means two or more (including two). Similarly, "multiple groups" means two or more groups (including two groups), and "multiple pieces" means two or more pieces (including two pieces).

[0092] Unless otherwise specified, for technical terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of this application and simplifying the description, rather than indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation on the embodiments of this application.

[0093] As the application scope of secondary batteries becomes wider and wider, the requirements for battery performance are getting higher and higher, and the energy density of secondary batteries is also getting higher and higher. Among them, the energy density formula of the battery is as follows:

[0094] Mass energy density (W·h / kg) = Capacity that can be exerted by the positive electrode active material (A·h / kg) × Mass of the positive electrode active material (kg) × Nominal voltage of the battery (V) / Mass of the battery (kg);

[0095] Volume energy density (W·h / L) = Capacity that can be exerted by the positive electrode active material (A·h / kg) × Mass of the positive electrode active material (kg) × Nominal voltage of the battery (V) / Volume of the battery (L);

[0096] In previous studies, improving the energy density of batteries has mainly focused on developing new main materials (such as using high-capacity electrode materials like high-nickel ternary layered materials, high-capacity lithium-rich manganese-based materials, silicon-based anode materials, and lithium metal anodes) and increasing the working voltage of the battery. The methods listed above require changing the chemical system of the battery. In addition, without changing the chemical system of the battery, starting from the battery structure design, the proportion of active materials in the unit mass or unit volume of the battery can be increased, such as thick coating to increase the loading. Research shows that the microstructure and internal stress inside the coating are the main reasons for the change in the elastic modulus of the coating when the coating thickness is different. When preparing the coating, the thicker the coating, the higher the compaction density, and the stronger the brittleness of the material, the greater the internal stress. The uneven release of stress accumulation is more likely to cause the electrode sheet to crack, and the cracking of the electrode sheet poses a potential safety hazard to the battery, such as the lap short circuit caused by the shedding of active materials from the current collector.

[0097] The assembly process of secondary batteries includes the stacking process and the winding process. Among them, the winding process has been more widely used in actual applications due to its high production efficiency and fast speed. For a wound battery cell with high energy density, the inner pressure is greater at the position closer to the winding axis during hot pressing, and the probability of cracking or even breaking is higher.

[0098] In the past, to solve the problem of electrode sheet cracking, plasticizers or softeners were usually added during the pulping process to increase the flexibility of the electrode sheet. However, this method still has the following problems:

[0099] 1. Additional conveying pipelines are required to convey the plasticizer; 2. The addition amount of the plasticizer is not easy to control. If too much is added, the electrical performance will deteriorate; 3. During the high-speed thick coating process, some plasticizers have strong hydrophilicity, with a high residual amount in the electrode sheet and it is impossible to ensure the dryness of the electrode sheet.

[0100] If the brittleness of the electrode sheet of the wound battery cell can be reduced and its toughness can be improved, it will be beneficial to reduce the probability of the electrode sheet cracking or even breaking.

[0101] Based on the above considerations, to solve the problem of electrode sheet cracking in secondary batteries, an electrode assembly, a battery, and an electrical device are obtained according to the above design concept and through relevant experimental explorations.

[0102] First, the present application discloses an electrode assembly, which includes a negative electrode sheet, a separator, and a positive electrode sheet. The negative electrode sheet, the separator, and the positive electrode sheet are wound together around a winding axis to form the above-mentioned electrode assembly; wherein, the positive electrode sheet includes a first positive electrode film layer and a second positive electrode film layer respectively located on the current collector along the winding direction; the first positive electrode film layer includes first positive electrode active particles, and the second positive electrode film layer includes second positive electrode active particles; the median particle size Dv150 of the first positive electrode active particles is greater than the median particle size Dv250 of the second positive electrode active particles.

[0103] The positive electrode tab includes a bent region formed by extending from the winding starting end along the winding direction to the winding ending end. The bent region includes a plurality of bent portions, and at least some of the bent portions disposed near the winding axis have a first positive electrode film layer.

[0104] In the present application, at least one surface of the positive electrode tab and the negative electrode tab constituting the electrode assembly is designed with a coating process during preparation. The negative electrode tab and the positive electrode tab are wound together around the winding axis to form a wound battery cell. The wound battery cell includes a bent region formed by winding around the winding axis. The bent region includes a plurality of bent portions, and each bent portion is distributed from the inside to the outside of the wound battery cell. Among them, the bent portion located inside the winding axis is closer to the winding axis than the bent portion located outside the winding axis.

[0105] When the wound battery cell formed by the winding process in the present application is hot-pressed, the degree of bending inside the wound battery cell is greater than that outside. At the same time, the inside also restricts the compaction density of the positive electrode tab to a relatively large extent. During design, in order to obtain the highest possible volume density, the designed compaction density of the positive electrode tab is often relatively large. Limited by the greater degree of bending and relatively larger compaction density inside the wound battery cell compared to the outside, cracking and even fragment breakage are more likely to occur inside the wound battery cell. This phenomenon not only affects the battery performance, such as the performance of various properties including specific capacity and cycle performance of the battery, but also more easily leads to internal short circuit during the use of the battery, thus bringing safety problems. To reduce the probability of cracking of the positive electrode tab inside the wound battery cell, in the present application, a first positive electrode film layer is selected to be provided on at least some of the bent portions disposed near the winding axis, and a second positive electrode film layer is provided at other positions. The particle size of the active particles in the first positive electrode film layer is larger than the particle size of the active particles in the second positive electrode film layer. Among them, the active particles with a relatively larger particle size require a relatively smaller pressure to reach the same or even higher compaction density as the active particles with a relatively smaller particle size during the cold pressing process. During cold pressing, when reaching the same compaction density, the positive electrode tab with active particles having a relatively larger particle size requires less pressure than other positive electrode tabs with active particles having a relatively smaller particle size. Therefore, the ductility of the substrate (such as conventional aluminum foil) at the position of the positive electrode tab with active particles having a relatively larger particle size is correspondingly reduced, which is beneficial to improving the toughness of the electrode tab of the wound battery cell and reducing the probability of cracking and even breakage of the electrode tab of the wound battery cell.

[0106] The electrode assembly provided by the present application can improve battery performance, such as capacity and cycle performance, etc., on the one hand, by reducing the probability of thermal pressing cracking of the wound battery core electrode sheets, and on the other hand, can also increase the safety of the battery. The electrode assembly is made into a battery. The battery may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte. The outer package of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0107] The present application has no particular limitation on the shape of the battery, and it can be cylindrical, square or any other shape. For example, Figure 1 is a secondary battery 10 with a square structure as an example.

[0108] In some embodiments of the present application, with reference to Figure 2 , the outer package may include a housing 101 and a cover plate 103. Among them, the housing 101 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 101 has an opening communicating with the receiving cavity, and the cover plate 103 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can form an electrode assembly 102 through a winding process or a stacking process. The electrode assembly 102 is encapsulated in the receiving cavity. The electrolyte infiltrates into the electrode assembly 102. The number of electrode assemblies 102 contained in the secondary battery 10 can be one or more, and those skilled in the art can select according to specific actual needs.

[0109] The electrode assembly provided by the present application is beneficial to improving battery performance when applied to a battery. The battery can be used as a power source of an electrical device or an energy storage unit of an electrical device. The electrical device is applied to the power field, such as mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but not limited to the above fields.

[0110] In some embodiments of the present application, for the convenience of description, the electrical device is taken as an example of a vehicle for description.

[0111] Please refer to Figure 3 , Figure 3Schematic structural diagram of vehicle 10000 provided by some embodiments of the present application. Vehicle 10000 can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, an extended-range vehicle, etc. A battery 1000 is disposed inside vehicle 10000, and the battery 1000 can be disposed at the bottom, head, or tail of vehicle 10000. The battery 1000 can be used for power supply of vehicle 10000. For example, the battery 1000 can serve as the operating power source of vehicle 10000. Vehicle 10000 may further include a controller 2000 and a motor 3000. The controller 2000 is used to control the battery 1000 to supply power to the motor 3000. For example, it is used for the working power requirements during the start, navigation, and driving of vehicle 10000.

[0112] In some embodiments of the present application, the battery 1000 can not only serve as the operating power source of vehicle 10000, but also serve as the driving power source of vehicle 10000, replacing or partially replacing fuel or natural gas to provide driving power for vehicle 10000.

[0113] Please refer to Figure 4 , Figure 4 Explosion diagram of battery 1000 provided by some embodiments of the present application. The battery 1000 includes a box body 200 and battery cells 100. Conventional battery cells include primary batteries or secondary batteries. In the present application, secondary batteries are specifically protected. The battery cells 100 are accommodated in the box body 200. Among them, the box body 200 is used to provide an accommodation space for the battery cells 100, and the box body 200 can adopt various structures.

[0114] In some embodiments, the box body 200 may include a first part 210 and a second part 220. The first part 210 and the second part 220 are covered with each other, and the first part 210 and the second part 220 jointly define an accommodation space for accommodating the secondary battery 100. The second part 220 can be a hollow structure with one end open, and the first part 210 can be a plate-like structure. The first part 210 covers the open side of the second part 220 so that the first part 210 and the second part 220 jointly define an accommodation space; the first part 210 and the second part 220 can also both be hollow structures with one side open, and the open side of the first part 210 covers the open side of the second part 220. Of course, the box body 200 formed by the first part 210 and the second part 220 can be of various shapes, such as a cylinder, a cuboid, etc.

[0115] In the battery 1000, there may be multiple battery cells 100. The multiple battery cells 100 can be connected in series, parallel, or in a combined series-parallel connection. A combined series-parallel connection means that there are both series and parallel connections among the multiple battery cells 100. The multiple battery cells 100 can be directly connected in series, parallel, or in a combined series-parallel connection together, and then the whole formed by the multiple battery cells 100 is accommodated in the box body 200. Of course, the battery 1000 can also be in the form of multiple battery cells 100 first connected in series, parallel, or in a combined series-parallel connection to form a battery 1000 module, and then multiple battery 1000 modules are connected in series, parallel, or in a combined series-parallel connection to form a whole and are accommodated in the box body 200. The battery 1000 can also include other structures. For example, the battery 1000 can also include a busbar component for realizing the electrical connection among the multiple battery cells 100.

[0116] Electrode assembly

[0117] In some embodiments of the present application, an electrode assembly is disclosed, such as Figure 5 shown, the electrode assembly 102 includes a negative electrode tab 1021, a separator 1022, and a positive electrode tab 1023. The negative electrode tab 1021, the separator 1022, and the positive electrode tab 1023 are wound together around a winding axis to form the above-mentioned electrode assembly 102. As Figure 6 shown, among them, the positive electrode tab 1023 extends from the winding start end 1023a along the winding direction to the winding end 1023b to form a bending region 1025. The bending region 1025 includes multiple bending parts 1023c, and at least some of the bending parts 1023c close to the winding axis have a first positive electrode film layer 10231.

[0118] As Figure 6 、 Figure 7A 、 Figure 7B 、 Figure 7C shown, the positive electrode tab 1023 includes a first positive electrode film layer 10231 and a second positive electrode film layer 10232. The first positive electrode film layer 10231 and the second positive electrode film layer 10232 are respectively distributed on at least one surface of the current collector 1024 along the winding direction; the first positive electrode film layer 10321 includes first positive electrode active particles; the second positive electrode film layer 10232 includes second positive electrode active particles; the median particle size Dv150 of the first positive electrode active particles is greater than the median particle size Dv250 of the second positive electrode active particles.

[0119] The winding axis in the present application includes the conventional concepts in the art. For example, generally, the negative electrode tab, the separator, and the positive electrode tab are wound together around a winding needle to form an electrode assembly, and the winding axis includes the central axis of the winding needle, etc.

[0120] At least part of the present application includes one or more bending portions. For the positive electrode sheet, after being wound to form an electrode assembly, a plurality of flat portions and a plurality of bending portions are formed. Each flat portion is connected by a bending portion, or each bending portion is connected by a flat portion, so as to form a continuous structure. As described above, the bending portion of the positive electrode sheet close to the winding axis in the wound battery cell has a relatively high compaction density during design, and during hot pressing, the bending degree of the bending portion of the positive electrode sheet close to the winding axis is greater than that at other positions, so the probability of cracking or even fragmenting is relatively higher.

[0121] In the present application, by specifically selecting active particles with relatively large particle sizes for the bending portion of the positive electrode sheet close to the winding axis in the electrode assembly to prepare the positive electrode film layer, during cold pressing, at the same compaction density, the positive electrode sheet with relatively large active particles requires less pressure than the positive electrode sheet with relatively small active particles. Therefore, the ductility of the base material (such as conventional aluminum foil) at the position of the positive electrode sheet with relatively large active particles is correspondingly reduced, which is beneficial to improving the toughness of the wound battery cell electrode sheet and reducing the probability of cracking or even breaking of the wound battery cell electrode sheet.

[0122] In the present application, the first positive electrode film layer and the second positive electrode film layer are respectively located on the current collector along the winding direction, including that along the winding direction, the head or tail end of the first positive electrode film layer is connected to the tail or head end of the second positive electrode film layer, and the first positive electrode film layer and / or the second positive electrode film layer can be located on at least one side surface of the current collector, specifically as Figures 7A to 7C shown, where Figure 7A shows that the first positive electrode film layer 10231 is simultaneously located on two side surfaces of the current collector 1024 to form the first positive electrode sheet 1023d, and the second positive electrode film layer 10232 is simultaneously located on two side surfaces of the current collector 1024 to form the second positive electrode sheet 1023e. Among them, the first positive electrode film layer 10231 and the second positive electrode film layer 10232 are connected end to end.

[0123] Figure 7B shows that the first positive electrode film layer 10231 is located on one partial side surface of the current collector 1024, and the remaining side surfaces of the current collector 1024 all form the second positive electrode film layer 10232. This design method can not only reduce the probability of cracking or even breaking of the wound battery cell electrode sheet, but also reduce the influence of the second positive electrode film layer on other battery performances.

[0124] Figure 7CThe first positive electrode film layer 10231 is located on one side of the current collector 1024 to form the first positive electrode tab 1023d, and the second positive electrode film layer 10232 is located on one side of the current collector 1024 to form the second positive electrode tab 1023e, and the first positive electrode film layer 10231 and the second positive electrode film layer 10232 are located on the same side of the current collector 1024.

[0125] Combined with Figures 7A to 7C it can be known that the first positive electrode film layer includes a first head end and a first tail end; the second positive electrode film layer includes a second head end and a second tail end; the first head end is connected to the second tail end or the first tail end is connected to the second head end, that is, the first positive electrode film layer and the second positive electrode film layer are connected in a head-to-tail manner.

[0126] In this application, the positive electrode film layer can adopt the arrangement mode shown in FIG. 7 above. No matter which design mode is adopted, the problem of tab cracking can be alleviated. However, from the perspective of the positive electrode tab having as high an energy density as possible, this application preferably Figure 7A or Figure 7B the design mode. Further, from the perspective of the preparation process of this application, this application preferably Figure 7A the design mode, and mainly adopts Figure 7A the design mode to explain the first positive electrode film layer in the bending area in the following drawings. The formation mode of the positive electrode film layer in this application includes any conventional form in the art, such as but not limited to coating, deposition, etc.

[0127] The median particle size Dv50 in this application means that the volume of particles larger than it accounts for 50%, and the volume of particles smaller than it also accounts for 50%. It is also called the median diameter and is usually used to represent the average particle size of particles. The test method for the median particle size Dv50 includes the conventional measurement methods in the art, such as measuring the particle size distribution by a particle size analysis instrument and then obtaining it through statistics. In these embodiments of this application, it is selected to refer to the laser diffraction particle size analysis method for determination. Specifically, referring to the standard GB / T19077-2016, the particle size distribution diagrams of the first positive electrode active particles and the second positive electrode active particles are obtained respectively, and then calculated.

[0128] This application selects that the particle size of the active particles in the first positive electrode film layer is larger than the particle size of the active particles in the second positive electrode film layer. Among them, the active particles with relatively larger particle size require relatively less pressure to reach the same or even higher compaction density as the active particles with relatively smaller particle size during the cold pressing process. When reaching the same compaction density, the positive electrode tab containing the active particles with relatively larger particle size requires less pressure than the positive electrode tab containing the active particles with relatively smaller particle size. By reducing the extension of the substrate (conventional aluminum foil, etc.) at the position of the positive electrode tab with relatively larger active particle size, the toughness (flexibility) of the tab is improved, and thus the probability of thermal pressing cracking is reduced.

[0129] In some embodiments of the present application, the relationship between Dv150 of the first positive electrode active particles and Dv250 of the second positive electrode active particles is specifically given as: 0 < (Dv150 - Dv250) < 20 μm.

[0130] Since the present application also needs to ensure the uniformity of the entire electrode sheet during the preparation of the positive electrode sheet, there should not be a large difference between Dv150 of the first positive electrode active particles and Dv250 of the second positive electrode active particles. The present application selects 0 < (Dv150 - Dv250) < 20 μm, which can not only effectively improve the cracking of the electrode sheet (inner circle), but also ensure the uniformity of the electrode sheet.

[0131] In some embodiments of the present application, the difference between Dv150 and Dv250 satisfies any one of 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 12.5 μm, 13.0 μm, 13.5 μm, 14.0 μm, 14.5 μm, 15.0 μm, 15.0 μm, 15.5 μm, 16.0 μm, 16.5 μm, 17.0 μm, 17.5 μm, 18.0 μm, 18.5 μm, 19.0 μm, 19.5 μm, 19.8 μm or satisfies any one of the above range values.

[0132] In some embodiments of the present application, the relationship between Dv150 of the first positive electrode active particles and Dv250 of the second positive electrode active particles further satisfies: 4.9 μm < (Dv150 - Dv250) < 20 μm.

[0133] First positive electrode active particles Second positive electrode active particles In some embodiments of the present application, Dv150 of the first positive electrode active particles satisfies: 6 μm ≤ Dv150 ≤ 25 μm.

[0134] In the present application, Dv150 of the first positive electrode active particles and Dv250 of the second positive electrode active particles can be flexibly adjusted according to actual needs and the supply relationship of suppliers.

[0135] In some embodiments of the present application, the Dv150 of the first positive electrode active particles is any one of 6 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 12.5 μm, 13.0 μm, 13.5 μm, 14.0 μm, 14.5 μm, 15.0 μm, 15.5 μm, 16.0 μm, 16.5 μm, 17.0 μm, 17.5 μm, 18.0 μm, 18.5 μm, 19.0 μm, 19.5 μm, 20.0 μm, 20.5 μm, 21.0 μm, 21.5 μm, 22.0 μm, 22.5 μm, 23.0 μm, 24.5 μm, 24.0 μm, 24.5 μm, 25.0 μm or satisfies any one of the above range values.

[0136] In some embodiments of the present application, the Dv150 of the first positive electrode active particles satisfies: 10 μm ≤ Dv150 ≤ 25 μm.

[0137] In some embodiments of the present application, the Dv190 and Dv110 of the first positive electrode active particles satisfy: 0 μm < Dv190 - Dv110 < 50 μm.

[0138] In the present application, Dv190 includes that the particle volume smaller than it accounts for 90%, and Dv110 includes that the particle volume smaller than it accounts for 10%. Whether it is Dv190 or Dv110, the test method thereof includes the conventional measurement methods in the art, such as measuring the particle size distribution by a particle size analysis instrument and then obtaining it through statistics.

[0139] Based on Dv150, the present application further defines the relationship between Dv190 and Dv110, elaborates on the particle size distribution of the first positive electrode active particles in detail to establish the relationship between Dv150 of the first positive electrode active particles and Dv250 of the second positive electrode active particles, and reduces the probability of thermal pressing cracking of the electrode sheet.

[0140] In some embodiments of the present application, the difference between Dv190 and Dv110 of the first positive electrode active particles satisfies any one of 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 12.0 μm, 15.0 μm, 17.0 μm, 20.0 μm, 22.0 μm, 25.0 μm, 27.0 μm, 30.0 μm, 32.0 μm, 35.0 μm, 38.0 μm, 40.0 μm, 42.0 μm, 45.0 μm, 48.0 μm, 49.0 μm, 49.5 μm or satisfies any one of the range values. In these embodiments of the present application, by defining that 0 < Dv190 - Dv110 < 50 μm between Dv190 and Dv110 of the first positive electrode active particles, the particle size distribution of the first positive electrode active particles is elaborated in detail and used to illustrate that the particle size distribution of the first positive electrode active particles is good in uniformity, so as to reduce the probability of thermal pressing cracking of the electrode sheet.

[0141] In some embodiments of the present application, Dv190 and Dv110 of the first positive electrode active particles satisfy: 10 μm < Dv190 - Dv110 ≤ 37 μm.

[0142] Meanwhile, as described above, at least a part of the bending part located inside the wound battery cell has the first positive electrode film layer. The following elaborates in detail the possible design methods of the first positive electrode film layer on the premise of considering the feasibility of the preparation process.

[0143] In some embodiments of the present application, a layout method of the first positive electrode film layer is provided, such as Figure 8A shown in the figure, on the first bending part formed by the positive electrode sheet 1023 along the winding direction starting from the winding starting end 1023a, there is a first positive electrode film layer 10231, and this first bending part is close to the winding axis. The present application Figure 8A shows that, compared with other bending parts, the first bending part is the closest to the winding axis; meanwhile, the first positive electrode film layer is only provided on the first bending part close to the winding starting end. Among them, assuming that the first bending part forms a semi - circle, the radius in the entire circle where this semi - circle is located can be calculated by using any conventional model or calculation formula in the art: for example, radius = the thickness of the positive electrode sheet + the thickness of two layers of separator films, etc.

[0144] In some embodiments of the present application, another layout method of the first positive electrode film layer is provided, such as Figure 8BAs shown, a first positive electrode film layer 10231 is provided on both the first bending portion and the second bending portion formed in sequence from the winding starting end 1023a of the positive electrode tab along the winding direction. The first bending portion is closer to the winding axis than the second bending portion. Based on 8A in this application, it is selected to provide the first positive electrode film layer at the positions of two bending portions inside the wound battery cell. Among them, the first bending portion is closer to the winding axis than the second bending portion.

[0145] In some embodiments of this application, another arrangement of the first positive electrode film layer is provided. The first positive electrode film layer is provided on both the first bending portion, the second bending portion, and the third bending portion formed in sequence from the winding starting end along the winding direction of the positive electrode tab. The first bending portion is closer to the winding axis than the second bending portion, and the second bending portion is closer to the winding axis than the third bending portion.

[0146] This application can also provide the first positive electrode film layer on other bending portions except the above-mentioned first bending portion, second bending portion, and third bending portion, such as the fourth bending portion and the fifth bending portion. Among them, each bending portion includes the first bending portion, the second bending portion, the third bending portion, the fourth bending portion, the fifth bending portion, etc. formed in sequence from the winding starting end along the winding direction.

[0147] Combined Figure 8A 、 Figure 8B It can be seen that the first bending portion described in these embodiments of this application includes the first bending position where the positive electrode tab forms along the winding direction from the winding starting end, while the second bending portion or the third bending portion, etc. include the second bending position or the third bending position that appear in sequence as the positive electrode tab extends along the winding direction. As described above, when the positive electrode tab of this application is hot-pressed in the manufacturing process, the tabs inside the wound battery cell are bent more severely than the external tabs, and the internal tabs are more likely to crack. In particular, the probability or phenomenon of cracking in the first bending portion is more serious. Therefore, this application first designs the first positive electrode film layer in the first bending portion. On this basis, the first positive electrode film layer can also be designed in the second bending portion and / or the third bending portion. At the same time, considering factors such as design cost, difficulty, and actual battery energy density or cycle performance, etc., this application preferably designs the first positive electrode film layer in the first bending portion and / or the second bending portion and / or the third bending portion. However, the method of designing the first positive electrode film layer in more bending portions is also within the protection scope of this application, and this application will not elaborate.

[0148] In some embodiments of this application, another arrangement of the first positive electrode film layer is provided. As Figure 8C shown, the first positive electrode film layer 10231 is continuously distributed on at least one surface of the current collector from the winding starting end 1023a until the first bending portion. The first bending portion described in these embodiments of this application is the same as the above-mentioned Figure 8AThe schematic first bending portion retains the same meaning.

[0149] In some embodiments of the present application, another arrangement of the first positive electrode film layer is provided. As Figure 8D schematically shown, the first positive electrode film layer 10231 is continuously distributed on at least one surface of the current collector from the winding starting end 1023a until the first bending portion, and the first positive electrode film layer 10231 continues to continuously extend in the winding direction from the first bending portion by a certain displacement, such as continuously or intermittently extending to the second bending portion or the third bending portion. As Figure 8B schematically shown. The first bending portion, the second bending portion, the third bending portion, etc. described in these embodiments of the present application have the same meaning as the Figure 8A 、 Figure 8B schematic first bending portion. As described above, when the positive electrode tab of the present application is hot-pressed in the manufacturing process, the tabs located inside the wound battery cell are bent more severely than the external tabs, and the internal tabs are more likely to crack. In particular, the probability or phenomenon of cracking at the first bending portion is more serious. Therefore, the present application first designs the first positive electrode film layer at the first bending portion. On this basis, the first positive electrode film layer can also be designed at the second bending portion and / or the third bending portion. At the same time, considering factors such as design cost, difficulty, and actual battery energy density or cycle performance, etc., the present application preferably designs the first positive electrode film layer at the second bending portion and / or the third bending portion. However, the method of designing the first positive electrode film layer at more bending portions is also within the protection scope of the present application, and the present application will not elaborate.

[0150] In some embodiments of the present application, another arrangement of the first positive electrode film layer is provided. As Figure 8E schematically shown, starting from the winding starting end 1023a, the first positive electrode film layer 10231 and the second positive electrode film layer 10232 are alternately and spaced apart in the winding direction on at least one surface of the current collector to respectively form a plurality of first positive electrode tabs and a plurality of second positive electrode tabs.

[0151] In some embodiments of the present application, another arrangement of the first positive electrode film layer is provided. As Figure 8F schematically shown, starting from the winding starting end 1023a, the second positive electrode film layer 10232 and the first positive electrode film layer 10231 are alternately and spaced apart in the winding direction on at least one surface of the current collector to respectively form a plurality of first positive electrode tabs and a plurality of second positive electrode tabs.

[0152] Combined with Figure 8E 、 8FIt can be known that the first positive electrode film layer 10231 is provided on the first bending portion formed by the positive electrode sheet 1023 starting from the winding starting end 1023a along the winding direction, and the first positive electrode film layer 10231 and the second positive electrode film layer 10232 are alternately distributed on at least one surface of the current collector along the winding direction until a certain position. The difference lies in the design starting from the winding starting end 1023a, which can be the first positive electrode film layer 10231 or the second positive electrode film layer 10232. At the same time, as described above, the first positive electrode film layer 10231 continuously extends along the winding direction from the first bending portion for a certain displacement, for example, continues to extend to the second bending portion or the third bending portion, or the first positive electrode film layer 10231 starts from the first bending portion and alternately extends with the second positive electrode film layer 10232 until the second bending portion or the third bending portion, and preferably the first positive electrode film layer 10231 is designed at the second bending portion or the third bending portion. The meanings of the first bending portion, the second bending portion and the third bending portion described in these embodiments of the present application are consistent with those in the above-mentioned drawings.

[0153] To better elaborate on the above Figures 8A to 8F relationship between the length of the designed first positive electrode film layer and / or the first positive electrode sheet along the winding direction and the length of the positive electrode sheet extending from the winding starting end along the winding direction to the winding end, the present application is described in Figures 9A to 9E in detail. Among them, Figure 9A is an explanation of the length of the first positive electrode film layer of Figure 8A , Figure 9B is an explanation of the length of the first positive electrode film layer of Figure 8B , Figure 9C is an explanation of the length of the first positive electrode film layer of Figure 8C , Figure 8D , Figure 9D is an explanation of the length of the first positive electrode film layer of Figure 8E , Figure 9E is an explanation of the length of the first positive electrode film layer of Figure 8F . The lengths here all include the distance between one end and the other end along the winding direction, and the specific values can be obtained by direct measurement or calculation, such as directly measuring with a ruler or tape measure with millimeter scale or other measuring devices. Combining Figure 9A , Figure 9C it can be known that the length of the first positive electrode film layer and / or the first positive electrode sheet along the winding direction is a1, and the length of the positive electrode sheet extending from the winding starting end along the winding direction to the winding end is L, satisfying: a1 < L. Combining Figure 9BIt can be known that the length of the first positive electrode film layer and / or the first positive electrode tab in the winding direction is a1, and a1 = a11 + a12 + a13. a11 and / or a12 and / or a13 are respectively the distances between one end and the other end of the first positive electrode film layer discontinuously distributed on at least one surface of the current collector in the winding direction. Combining Figure 9D It can be known that the length of the first positive electrode film layer and / or the first positive electrode tab in the winding direction is a1, and a1 = a14 + a15 + a16. a14 and / or and / or a16 are respectively the distances between one end and the other end of the first positive electrode film layer discontinuously distributed on at least one surface of the current collector in the winding direction. Combining Figure 9E It can be known that the length of the first positive electrode film layer and / or the first positive electrode tab in the winding direction is a1, and a1 = a17 + a18 + a19. a17 and / or a18 and / or a19 are respectively the distances between one end and the other end of the first positive electrode film layer discontinuously distributed on at least one surface of the current collector in the winding direction.

[0154] In some embodiments of the present application, the present application further elaborates on the relationship between the length of the first positive electrode film layer and / or the first positive electrode tab in the winding direction and the length of the positive electrode tab extending from the winding starting end along the winding direction to the winding ending end. The two satisfy a1 < 1 / 2 × L. The present application also discloses in these embodiments that the length of the positive electrode tab satisfies: 0 < L ≤ 20000 mm. In these embodiments, the length of the positive electrode tab disclosed in the present application is appropriate. Otherwise, problems such as the subsequent hot pressing and shaping not achieving the ideal effect due to the too large size of the winding core are likely to occur.

[0155] Considering from the perspective of the particle size of the positive electrode active particles and other battery performances such as kinetics, when the particle size of the positive electrode active particles increases, compared with small particle size particles, the storage life decreases. In addition, large particle size particles are prone to deteriorate the kinetics, thereby bringing the problem of low coulombic capacity and affecting the capacity of the battery cell. Therefore, the present application preferably has a1 < 1 / 2 × L.

[0156] In some embodiments of the present application, the present application further elaborates on the relationship between the length of the first positive electrode film layer and / or the first positive electrode tab in the winding direction and the circumference of the winding needle. Among them, the circumference of the winding needle is less than 1 / 2 × L, and further satisfies a1 < the circumference of the winding needle. The winding needles in these embodiments of the present application include winding needles of any conventional shape or structure in the art. For example, the present application uses an elliptical winding needle. The circumference of the elliptical winding needle includes the total length of the starting end of its outer peripheral surface. The present application further discloses in these embodiments that the circumference A of the elliptical winding needle satisfies: 0 < A ≤ 5000 mm. The present application discloses in some embodiments that the circumference of the used elliptical winding needle is 3000 mm.

[0157] In some embodiments of the present application, the negative electrode tab wraps the positive electrode tab along the winding direction. Therefore, the starting end of the negative electrode tab along its winding direction is longer than the starting end of the positive electrode tab along its winding direction, and the difference between the two is as Figure 1 shown as d. In some embodiments of the present application, it is disclosed that 0 < d ≤ 60 mm. At the same time, the ending end of the negative electrode tab along its winding direction is longer than the ending end of the positive electrode tab along its winding direction, and the difference between the two is as Figure 1 shown as e. In some embodiments of the present application, it is disclosed that 0 < e ≤ 20 mm.

[0158] In the above, the present application has described in detail the design method of the positive electrode tab including the first positive electrode film layer and the second positive electrode film layer along the winding direction to solve the problem that the positive electrode tab is prone to cracking during hot pressing. It has also been elaborated in detail that relatively larger active particles are used in the first positive electrode film layer compared to the particle size of the active particles in the second positive electrode film layer. In addition, the size relationship between the active particles and the length of the first positive electrode film layer have been defined. To reduce the difference in the compaction density between the first positive electrode film layer and the second positive electrode film layer during cold pressing, for example, the difference in the compaction density between the first positive electrode film layer and the second positive electrode film layer is not significant. In some embodiments of the present application, the compaction density, the capacity per unit area, the mass ratio of the active particles, and the thickness of the electrode tab after cold pressing of the first positive electrode film layer and the second positive electrode film layer have been elaborated in detail.

[0159] In some embodiments of the present application, the compaction density of the first positive electrode film layer is not lower than that of the second positive electrode film layer.

[0160] In the present application, since the particle size of the active particles in the first positive electrode film layer is larger, under the same cold pressing conditions, the compaction density of the first positive electrode film layer is greater than that of the second positive electrode film layer. In the manufacturing process of the positive electrode tab, if the first positive electrode film layer and the second positive electrode film layer are to have the same compaction density, the cold pressing pressure applied to the first positive electrode film layer is relatively smaller.

[0161] In some embodiments of the present application, the compaction density of the first positive electrode film layer is ρ1, and the compaction density of the second positive electrode film layer is ρ2. ρ1 and ρ2 satisfy: ρ1 / ρ2 = 1.0 - 1.1.

[0162] On the premise of meeting the above requirements for the manufacturing process of the positive electrode tab, ρ1 / ρ2 = 1.0 - 1.1.

[0163] The compaction density of the positive electrode tab of the present application has a great influence on the performance of the battery. For example, the higher the compaction density, the greater the energy density or capacity of the battery. The compaction density of the present application can be calculated with reference to GB / T5162 - 2006 to obtain the compaction density of the first positive electrode tab and the second positive electrode tab under a pressure of 3000 MPa.

[0164] In order to ensure the uniformity of the capacity or energy density of the entire positive electrode sheet including the first positive electrode sheet and the second positive electrode sheet, the compaction density ρ1 of the first positive electrode sheet and the compaction density ρ2 of the second positive electrode sheet are selected to satisfy: ρ1 / ρ2 = 1.0 to 1.1.

[0165] In some embodiments of the present application, the compaction density ρ1 of the first positive electrode film layer and the compaction density ρ2 of the second positive electrode film layer satisfy: ρ1 / ρ2 = 1.0 to 1.05.

[0166] In some embodiments of the present application, the capacity per unit area of the first positive electrode film layer is Q1, and the capacity per unit area of the second positive electrode film layer is Q2. Q1 and Q2 satisfy: Q1 / Q2 = 1.0 to 1.05.

[0167] The capacity per unit area of the electrode sheet in the present application has a relatively large correlation with the capacity of the battery. Its testing method includes using a coin cell testing method to determine the gram capacity of the active material in the positive electrode film layer; determining the mass of the active material in the positive electrode film layer per unit area; multiplying the gram capacity by the mass to obtain the capacity per unit area of the positive electrode film layer.

[0168] Coin cell testing method: The active material powder is made into a single-sided coated electrode sheet, assembled with a lithium sheet into a coin cell, and the coin cell capacity is obtained by charging and discharging at a rate of 0.1C. The upper and lower voltage limits during the charging and discharging process are: for the lithium cobalt oxide positive electrode active material: 2.5 to 4.45V. Dividing the capacity by the mass of the positive electrode sheet active material to obtain the gram capacity parameter can accurately evaluate the gram capacity parameter of the positive electrode active material.

[0169] The present application selects Q1 / Q2 = 1 to 1.05 to minimize the influence of the above design method of the first positive electrode film layer and the second positive electrode film layer on the energy density of the entire battery, and at the same time does not reduce the capacity difference between the positive electrode sheet and the negative electrode sheet. For example, by controlling the matching degree between the capacity per unit area of the oppositely facing positive electrode sheet and the negative electrode sheet to reduce the probability of electrode sheet cracking and improve the cycle performance of the battery, etc.

[0170] In some embodiments of the present application, the capacity per unit area Q1 of the first positive electrode film layer and the capacity per unit area Q2 of the second positive electrode film layer satisfy: Q1 / Q2 = 1.0 to 1.03. In these embodiments of the present application, it is disclosed that when the capacity per unit area Q1 of the first positive electrode film layer and the capacity per unit area Q2 of the second positive electrode film layer satisfy: Q1 / Q2 = 1.0 to 1.03, it is convenient to better match the capacity between the first positive electrode sheet and the second positive electrode sheet, as well as the matching between the entire positive electrode sheet and the negative electrode sheet.

[0171] In some embodiments of the present application, the mass percentage content of the first positive electrode active particles in the first positive electrode film layer is w1, and the mass percentage content of the second positive electrode active particles in the second positive electrode film layer is w2, where w1 and w2 satisfy: w1 / w2 = 0.95 - 1.05.

[0172] The positive electrode film layer of the present application is prepared by coating a slurry containing positive electrode active particles on the surface of a current collector and then drying, cold pressing, etc. Among them, the types of the first positive electrode active particles in the first positive electrode film layer and the types of the second positive electrode active particles in the second positive electrode film layer can be the same or different. In some embodiments of the present application, it is mainly described that the two are the same. The mass percentage content of each active particle includes the ratio between the mass of each active particle and the total mass of each component in the slurry. The present application selects w1 / w2 = 0.95 - 1.05 to facilitate better matching of the capacity between the first positive electrode sheet and the second positive electrode sheet.

[0173] In some embodiments of the present application, the mass percentage content w1 of the first positive electrode active particles in the first positive electrode film layer and the mass percentage content w2 of the second positive electrode active particles in the second positive electrode film layer satisfy: w1 / w2 = 1.0 - 1.03.

[0174] In some embodiments of the present application, the thickness difference between the first positive electrode film layer and the second positive electrode film layer after cold pressing is less than 40 μm.

[0175] The thickness of the positive electrode sheet of the present application after cold pressing can be obtained by using a micrometer or taking a microscopic screenshot.

[0176] When preparing the positive electrode sheet, the present application needs to perform cold pressing to improve the utilization rate of the positive electrode active particles by increasing the compaction density of the sheet. The thickness difference between the first positive electrode film layer and the second positive electrode film layer of the present application under the same cold pressing conditions is less than 40 μm, so as to improve the matching degree between the first positive electrode film layer and the second positive electrode film layer on the premise of improving the energy density of the positive electrode sheet.

[0177] In some embodiments of the present application, the thickness difference between the first positive electrode film layer and the second positive electrode film layer under the same cold pressing conditions is less than or equal to 30 μm.

[0178] In some embodiments of the present application, the thickness difference between the first positive electrode film layer and the second positive electrode film layer under the same cold pressing conditions is zero.

[0179] Positive electrode film layer

[0180] The positive electrode film layer of the present application includes a first positive electrode film layer and a second positive electrode film layer. The first positive electrode film layer and / or the second positive electrode film layer contain positive electrode active particles, positive electrode conductive agents, positive electrode binders, etc. Among them, the types and / or contents of the positive electrode active particles, positive electrode conductive agents, and positive electrode binders in the first positive electrode film layer and the second positive electrode film layer may be the same or different. For better elaboration of the inventive points of the present application, the following mainly focuses on the case where they are kept the same.

[0181] The present application does not specifically limit the specific type of the positive electrode active particles. For example, when the positive electrode sheet is applied to a lithium-ion battery, the positive electrode active particles include but are not limited to LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 CO 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 CO 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 CO 0.15 Al 0.05 O2, LiFePO4 (LFP), and one or more of LiMnPO4. The positive electrode conductive agents include but are not limited to one or more combinations of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode binders include but are not limited to one or more combinations of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0182] In some embodiments of the present application, it is disclosed that the mass ratio among the positive electrode active particles, the positive electrode conductive agents, and the positive electrode binders satisfies (90 - 95):(0 - 5):(0 - 5), and any one of the positive electrode conductive agents and the positive electrode binders is not zero.

[0183] Positive electrode current collector

[0184] The positive current collector in the present application can be a metal foil or a composite current collector. Among them, the metal foil can be an aluminum foil, and the composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0185] The thickness of the positive current collector in the present application includes any thickness conventional in the art. For example, in some embodiments of the present application, the thickness of the positive current collector is selected to be 8 μm to 30 μm.

[0186] Negative electrode sheet

[0187] The present application discloses that the negative electrode sheet includes a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector. The negative electrode film layer includes, but is not limited to, a negative electrode active material, a conductive agent, a dispersant, etc. Among them, the conductive agent in the present application includes any type conventional in the art, such as one or a combination of two or more of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0188] The dispersant in the present application also includes any type conventional in the art, such as cellulose and its salts, specifically including but not limited to methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, etc.

[0189] The negative electrode active material in the present application includes carbonaceous materials, and the carbonaceous materials include one or a combination of two or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Among them, artificial graphite, natural graphite, soft carbon, hard carbon, etc. include any form of materials conventional in the art, and include any manufacturers and models conventional in the art. At the same time, the negative electrode active material can also include silicon-based materials, and the silicon-based materials include one or two of silicon oxide materials or silicon-carbon materials. In addition, the negative electrode active material can also include silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 , Li-Al alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for lithium-ion batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0190] The negative current collector in this application can be a metal foil or a composite current collector. The metal foil can be a copper foil, and the composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0191] Separator

[0192] The separator located between the positive electrode sheet and the negative electrode sheet in this application can be any well-known porous separator with good chemical stability and mechanical stability. For example, the material of the separator can include, but is not limited to, one or a combination of two or more of the following groups: glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0193] Electrolyte

[0194] The electrolyte in this application is used to conduct ions between the positive electrode sheet and the negative electrode sheet. The electrolyte includes an electrolyte salt and a solvent. Among them, the electrolyte salt can include, but is not limited to, 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate. And the solvent can include at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, or an ether solvent such as triethylene glycol dimethyl ether, etc.

[0195] Prepare positive electrode sheet

[0196] Taking lithium cobaltate material as an example:

[0197] LiCoO₂ with different particle sizes was respectively stirred and dispersed in N-methylpyrrolidone with a conductive agent Super-P and a binder polyvinylidene fluoride in a mass ratio of (90-95):(0-5):(0-5) to prepare a first positive electrode slurry and a second positive electrode slurry with a solid content of about 60%. Each slurry was coated on both surfaces of an Al foil with a thickness of 13 μm according to the attached Figures 8A to 8F design method, where the coating method includes but is not limited to the intermittent coating method.

[0198] After being compacted by a cold press, where the cold press includes any conventional machine models in the art, the pressure was controlled at 27T to obtain a positive electrode plate, and the length L of the positive electrode plate was 10000 mm (10 m). Among them, the particle size and other parameters of the first positive electrode film layer and the second positive electrode film layer are shown in Table 1 to obtain the positive electrode plates of Examples 1 to 15.

[0199] (1) Compressive strength test of the positive electrode plate:

[0200] For each positive electrode plate (including the first positive electrode plate and the second positive electrode plate) shown in Table 1; after folding it forward, it was flattened with a 2 kg roller, and then unfolded and checked for light transmission through the gap against the light. If there was no light transmission, it was folded backward, flattened with a 2 kg roller, and checked again against the light. The test was repeated three times. If there was no light transmission phenomenon, it indicated that the positive electrode plate had a certain compressive strength.

[0201] To better reflect the compressive strength of the positive electrode plate of this application, this application also provides a comparative example. Among them, the particle size distribution of the positive electrode film layer in Comparative Example 1 satisfies: the active particle size Dv50 is 25 μm, and the particle size distribution of the positive electrode film layer in Comparative Example 2 satisfies: the active particle size Dv50 is 5.5 μm. Except for this, the others are the same as those in Example 3. After cold pressing, the compaction density of the positive electrode plate in Comparative Example 1 and the compaction density of the positive electrode plate in Comparative Example 2 are not very different, for example, it can be about 3.55 g / cm 3 or so.

[0202] The parameters and compressive strength of each example and comparative example are shown in Table 1 in detail.

[0203] Table 1 Parameter list

[0204]

[0205]

[0206] Combined with Table 1, it can be seen that the positive electrode plates designed in the examples of this application did not show light transmission after being folded three times, which indicates that the positive electrode plates prepared by the design method of this application have a certain compressive strength.

[0207] Prepare negative electrode sheet

[0208] The graphite as the negative active material, conductive carbon as the conductive agent, sodium carboxymethyl cellulose as the stabilizer, and SBR as the binder are mixed in a mass ratio of 96.7%: 0.6%: 1.2%: 1.5%, and then stirred evenly with deionized water to form a negative electrode slurry. After defoaming, the negative electrode slurry is coated on the negative electrode current collector copper foil and dried and cold-pressed to obtain a negative electrode sheet.

[0209] Select separator

[0210] PE with a thickness of 12 μm.

[0211] Select electrolyte

[0212] In a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a mass ratio of 35:65, lithium salt LiPF6 is added and mixed evenly to obtain an electrolyte, where the molar concentration of LiPF6 in the electrolyte is 1 mol / L.

[0213] Prepare lithium ion secondary battery

[0214] According to some embodiments of the present application, the prepared negative electrode sheet, separator, and positive electrode sheet are stacked in sequence, with the separator placed in the middle of the positive and negative electrode sheets to play a role in isolation, and then wound to obtain a bare battery cell. After that, it is inserted into the battery case and undergoes processes such as baking, liquid injection, standing, encapsulation, formation, and grading to obtain a square lithium-ion battery.

[0215] (2) Thermal pressing detection of the bare battery cell:

[0216] The wound bare battery cell is thermally pressed and shaped on a hot press, and it is detected whether there is any cracking of the electrode sheet inside the battery cell after thermal pressing, and the proportion of battery cells with cracked electrode sheets is counted. The hot press of the present application includes any conventional measuring instruments in the art, and the thermal pressing parameters are preferably 45 °C to 60 °C, 0.3 Mpa to 2 Mpa, and 6 s to 10 s.

[0217] The specific structure is shown in Table 2.

[0218] Table 2 Performance test list

[0219]

[0220]

[0221] Combined with the list, it can be seen that in Comparative Example 1 and Comparative Example 2 of this application, the positive electrode sheets are prepared using active particles with consistent particle sizes. However, compared with the comparative examples, the number of fractures of the positive electrode sheets after hot pressing of the bare battery cells in the design method of this application is reduced. Therefore, the design method of this application alleviates the problem of electrode sheet cracking compared with the comparative examples. Further combined with Example 1, Example 2, Example 8 and other examples of this application, it can be seen that when the difference between Dv150 of the first positive electrode active particles and Dv250 of the second positive electrode active particles is relatively small, there will still be a very small number of electrode sheet fractures (the number of fractures is reduced compared with the comparative examples). Therefore, within a certain range, when the difference between the median particle size Dv150 of the first positive electrode active particles and the median particle size Dv250 of the second positive electrode active particles is relatively large, it is beneficial to reduce the probability of electrode sheet cracking in the wound battery cell.

[0222] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, rather than to limit them; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered by the scope of the claims and the description of this application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. This application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions that fall within the scope of the claims.

Claims

1. An electrode assembly, characterized in that: Comprising: Negative electrode plate; Separator; Positive electrode plate; The negative electrode plate, the separator and the positive electrode plate are wound together around a winding axis to form the electrode assembly; The positive electrode plate includes a first positive electrode film layer and a second positive electrode film layer respectively located on a current collector along the winding direction; The first positive electrode film layer includes first positive electrode active particles, and the second positive electrode film layer includes second positive electrode active particles; The median particle size Dv150 of the first positive electrode active particles is greater than the median particle size Dv250 of the second positive electrode active particles; The positive electrode plate further includes a bending region extending from a winding start end along the winding direction to a winding end; the bending region includes a plurality of bending portions; At least some of the bending portions disposed close to the winding axis have the first positive electrode film layer.

2. The electrode assembly according to claim 1, wherein: Dv150 of the first positive electrode active particles and Dv250 of the second positive electrode active particles satisfy: 0 < (Dv150 - Dv250) < 20 μm.

3. The electrode assembly according to any one of claims 1 to 2, characterized in that: Dv150 of the first positive electrode active particles and Dv250 of the second positive electrode active particles satisfy: 4.9 μm < (Dv150 - Dv250) < 20 μm.

4. The electrode assembly according to any one of claims 1 to 3, characterized in that: Dv150 of the first positive electrode active particles satisfies: 6 μm ≤ Dv150 ≤ 25 μm.

5. The electrode assembly according to any one of claims 1 to 4, characterized in that: Dv190 and Dv110 of the first positive electrode active particles satisfy: 0 < Dv190 - Dv110 < 50 μm.

6. The electrode assembly according to any one of claims 1 to 5, characterized in that: The first positive electrode film layer is disposed on at least one surface of the current collector, and the first positive electrode film layer includes a first start end and a first end; The second positive electrode film layer is disposed on at least one surface of the current collector, and the second positive electrode film layer includes a second start end and a second end; The first start end is connected to the second end or the first end is connected to the second start end.

7. The electrode assembly according to any one of claims 1 to 6, characterized in that: The bending region includes a first bending portion formed from the winding start end along the winding direction, and the first bending portion is close to the winding axis; The first bending portion has the first positive electrode film layer.

8. The electrode assembly according to any one of claims 1 to 6, characterized in that: The bending region includes a first bending portion and a second bending portion formed in sequence from the winding start end along the winding direction, and the first bending portion is closer to the winding axis than the second bending portion; Both the first bending portion and the second bending portion have the first positive electrode film layer.

9. The electrode assembly according to any one of claims 1 to 8, characterized in that: The first positive electrode film layer is continuously distributed on the current collector from the winding start end along the winding direction.

10. The electrode assembly according to any one of claims 1 to 8, characterized in that: Starting from the winding start end, the first positive electrode film layer and the second positive electrode film layer are alternately distributed on the current collector along the winding direction.

11. The electrode assembly according to any one of claims 1 to 10, characterized in that: The length of the first positive electrode film layer from the winding start end along the winding direction to the winding end is a1; The length of the positive electrode plate from the winding start end along the winding direction to the winding end is L; Satisfying: a1 < L.

12. The electrode assembly according to any one of claims 1 to 11, characterized in that: The length of the first positive electrode film layer from the winding start end along the winding direction to the winding end is a1; The length of the positive electrode tab from the start end of winding to the end of winding along the winding direction is L; The negative electrode tab, the separator, and the positive electrode tab are wound around a winding needle to form the electrode assembly. The winding needle has a winding needle circumference, and the winding needle circumference is less than 1 / 2×L; The a1 is less than the winding needle circumference.

13. The electrode assembly according to any one of claims 1 to 12, characterized in that: The compaction density of the first positive electrode film layer is not lower than that of the second positive electrode film layer.

14. The electrode assembly according to any one of claims 1 to 13, characterized in that: The compaction density of the first positive electrode film layer is ρ1, and the compaction density of the second positive electrode film layer is ρ2. ρ1 and ρ2 satisfy: ρ1 / ρ2 = 1.0 - 1.

1.

15. The electrode assembly according to any one of claims 1 to 14, characterized in that: The thickness difference between the first positive electrode film layer and the second positive electrode film layer after cold pressing is less than 40 μm.

16. The electrode assembly according to any one of claims 1 to 15, characterized in that: The areal capacity of the first positive electrode film layer is Q1, and the areal capacity of the second positive electrode film layer is Q2. Q1 and Q2 satisfy: Q1 / Q2 = 1.0 - 1.

05.

17. The electrode assembly according to any one of claims 1 to 16, characterized in that: The mass percentage content of the first positive electrode active particles in the first positive electrode film layer is w1, and the mass percentage content of the second positive electrode active particles in the second positive electrode film layer is w2. w1 and w2 satisfy: w1 / w2 = 0.95 - 1.

05.

18. A battery, characterized in that: Comprising the electrode assembly according to any one of claims 1 to 17.

19. An electrical device, characterized in that: Comprising the electrode assembly according to any one of claims 1 to 17 or the battery according to claim 18.

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