Positive electrode sheet, electrode assembly, battery cell, battery, and electric device

Abstract

The embodiment of the present application provides a positive pole piece, an electrode assembly, a battery cell, a battery and an electric device. The positive pole piece is provided with a flat part and a to-be-bent part; at least one side of the positive current collector of at least part of the to-be-bent part is provided with a thickening layer, the thickening layer is arranged between the positive current collector and the positive active material layer, the positive active material layer covering the surface of the thickening layer is a first positive active material layer, the positive active material layer located in the flat part is a second positive active material layer; the thickness ratio of the first positive active material layer to the second positive active material layer is 20-80%. By arranging the thickening layer on at least one side of the positive current collector of the to-be-bent part, the coating quality of the positive active material coated on the surface of the thickening layer is reduced when the positive active material is coated on the surface of the positive current collector, so that the positive active material capacity of the region is less than the corresponding negative active material capacity, and then the occurrence of lithium precipitation is reduced or avoided, and the safety of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode sheet, electrode assembly, battery cell, battery, and power device. Background Technology

[0002] Energy conservation and emission reduction are key to the sustainable development of the automotive industry, and electric vehicles, due to their energy-saving and environmentally friendly advantages, have become an important component of this sustainable development. For electric vehicles, battery technology is a crucial factor in their development.

[0003] Lithium plating is a common abnormal phenomenon in lithium batteries, which can affect the charging efficiency and energy density of lithium ions. In severe cases, lithium plating can also form lithium crystals, which can puncture the separator and cause short circuits and thermal runaway within the battery cell, seriously endangering battery safety. Summary of the Invention

[0004] In view of the above problems, this application provides a positive electrode sheet, electrode assembly, battery cell, battery and power device, which can reduce or avoid lithium plating and improve battery safety.

[0005] In a first aspect, this application provides a positive electrode sheet, comprising: a positive current collector and a positive active material layer; the positive current collector has a positive active material layer disposed on at least one side in the thickness direction, and the positive electrode sheet is configured with a straight portion and a bending portion; at least a portion of the bending portion of the positive current collector has a thickening layer disposed on at least one side in the thickness direction, the thickening layer being disposed between the positive current collector and the positive active material layer, the positive active material layer covering the surface of the thickening layer being a first positive active material layer, and the positive active material layer located in the straight portion and connected to the first positive active material layer being a second positive active material layer; the ratio of the thickness of the first positive active material layer to the thickness of the second positive active material layer is 20% to 80%.

[0006] In the technical solution of this application embodiment, by providing a thickening layer on at least one side of the positive current collector of the part to be bent, when coating the positive active material on the surface of the positive current collector, the coating quality of the positive active material coated on the surface of the thickening layer is reduced, thereby ensuring that the capacity of the positive active material in this area is less than the capacity of the corresponding negative active material, thereby reducing or avoiding the occurrence of lithium plating and improving the safety and service life of the battery.

[0007] In some embodiments, the thickness ratio of the first positive electrode active material layer to the thickness ratio of the second positive electrode active material layer is 30-60%. In the positive electrode sheet of this application embodiment, the thickness ratio of the first positive electrode active material layer to the thickness ratio of the second positive electrode active material layer cannot be too high or too low. In this way, the energy density of the battery can be guaranteed, and lithium plating can be reduced or avoided.

[0008] In some embodiments, the thickness ratio of the first positive electrode active material layer to the thickness ratio of the second positive electrode active material layer is 45-55%. In the positive electrode sheet of this application embodiment, the thickness ratio of the first positive electrode active material layer to the thickness ratio of the second positive electrode active material layer cannot be too high or too low. This ensures the energy density of the battery while reducing or avoiding lithium plating.

[0009] In some embodiments, the ratio of the thickness of the second positive electrode active material layer to the sum of the thicknesses of the first positive electrode active material layer and the thickening layer is 1:0.9 to 1.1. In the positive electrode sheet of the embodiments of this application, the thickness of the second positive electrode active material layer is substantially equal to the sum of the thicknesses of the first positive electrode active material layer and the thickening layer, but a certain error value is also allowed.

[0010] In some embodiments, the ratio of the thickness of the second positive electrode active material layer to the sum of the thicknesses of the first positive electrode active material layer and the thickening layer is 1:0.95 to 1.05. In the positive electrode sheet of the embodiments of this application, the thickness of the second positive electrode active material layer is substantially equal to the sum of the thicknesses of the first positive electrode active material layer and the thickening layer, but a certain error value is also allowed.

[0011] In some embodiments, the positive electrode current collector has a positive electrode active material layer on both sides in the thickness direction. Having a positive electrode active material layer on both sides of the positive electrode current collector is beneficial for improving the energy density of the battery.

[0012] In some embodiments, the thickened layer has multiple porous regions, each containing positive electrode active material that connects the positive electrode current collector and the first positive electrode active material layer. By providing porous regions in the thickened layer, some of the positive electrode active material can pass through the porous regions during the coating process and adhere tightly to the positive electrode current collector, thereby strengthening the overall adhesion of the positive electrode active material and ensuring that it does not detach during manufacturing and long-term use.

[0013] In some embodiments, the surface where the thickened layer bonds to the first positive electrode active material layer is called the bonding surface, and the area of ​​the multiple pore regions distributed on the bonding surface is 20% to 50% of the area of ​​the bonding surface. In the positive electrode sheet of this application embodiment, the area of ​​the multiple pore regions distributed on the bonding surface is neither too large nor too small. This strengthens the overall adhesion of the positive electrode active material, ensuring that the positive electrode active material does not detach during manufacturing and long-term use. It also ensures that the capacity of the positive electrode active material disposed on the side with the thickened layer is much smaller than the capacity of the corresponding negative electrode active material, reducing or avoiding lithium plating and improving the safety and lifespan of the battery.

[0014] In some embodiments, the thickened layer has pores that penetrate the thickened layer, and the positive electrode active material fills the pores, with an inner diameter of 100–5000 μm. In the positive electrode sheet of this application embodiment, the inner diameter of the pores cannot be too large or too small, so that the positive electrode active material can pass through the pores during the coating process, while also ensuring the stability of the thickened layer.

[0015] In some embodiments, the thickening layer is made of an insulating material. The thickening layer does not need to be conductive, and insulating materials are inexpensive, readily available, and lightweight, making them a good material choice for manufacturing the thickening layer.

[0016] In some embodiments, the thickening layer is made of acrylic resin and / or polyolefin resin; the acrylic resin includes any one or more of acrylic-methacrylic acid copolymer, acrylic-butenoic acid copolymer, acrylic-itaconic acid copolymer, acrylic-maleic acid copolymer, acrylic-methyl methacrylate copolymer, acrylic-ethyl methacrylate copolymer, acrylic-n-butyl methacrylate copolymer, and acrylic-isobutyl methacrylate copolymer; the polyolefin resin includes any one or more of polypropylene, polyethylene, polybutadiene rubber, ethylene-propylene acetate copolymer, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, maleic anhydride modified polyolefin, and poly(butadiene-acrylonitrile), styrene-maleic anhydride copolymer. Acrylic resin and / or polyolefin resin are both common insulating materials that do not dissolve in electrolytes.

[0017] In some embodiments, the thickened layer is bonded to the positive current collector and the first positive active material layer, respectively. The thickened layer can bond to the positive current collector and the first positive active material layer through its own adhesiveness.

[0018] Secondly, this application provides an electrode assembly, including: a negative electrode sheet and the aforementioned positive electrode sheet, wherein the positive electrode sheet and the negative electrode sheet are wound or folded to form a bending region and a straight region, and the straight region is connected to the bending region; the portion to be bent is wound or folded to form a bending portion, the bending portion is located in the bending region, and the straight portion is located in the straight region.

[0019] In the technical solution of this application embodiment, a thickening layer is provided between the positive current collector in the partial bending region and the first positive active material layer. When the positive active material is coated on the surface of the positive current collector, the coating quality of the positive active material coated on the surface of the thickening layer is reduced, thereby ensuring that the capacity of the positive active material in the partial bending region is less than the capacity of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the positive electrode sheet in the active material layer in the partial bending region, and improving the safety and service life of the battery.

[0020] In some embodiments, the positive and negative electrode sheets are wound to form a wound structure. The positive current collector at the bend has an inner side and an outer side, and at least a portion of the positive current collector at the bend has a thickened layer on its inner side. For the wound electrode assembly, the inner side of the positive current collector is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy. However, by having a thickened layer on the inner side of the positive current collector at least a portion of the bend, the positive active material capacity on the inner side of the positive current collector at least a portion of the bend can be reduced, thereby ensuring that the positive active material capacity in this region is less than the corresponding negative active material capacity. This weakens or prevents the delithiation reaction of the active material layer of the positive electrode sheet in the partially bent region, improving the safety and lifespan of the battery.

[0021] In some embodiments, the positive and negative electrode sheets are wound to form a wound structure. The positive electrode sheet has an innermost first bend, and the positive current collector of the first bend has a thickened layer on at least one side in the thickness direction. The first bend, located at the innermost part of the electrode assembly, is the region most prone to lithium plating. The thickened layer on at least one side of the positive current collector in the first bend ensures that the capacity of the positive active material in this region is less than that of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet in this region, and improving the safety and lifespan of the battery.

[0022] In some embodiments, the positive current collector of the first bend is configured with an inner side and an outer side, and a thickened layer is provided on the inner side of the positive current collector of the first bend. For the wound electrode assembly, the inner side of the positive current collector is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy. However, by providing a thickened layer on the inner side of the positive current collector of the first bend, the positive active material capacity on the inner side of the positive current collector of the first bend can be reduced, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the delithiation reaction of the active material layer of the positive electrode sheet in part of the bend area, improving the safety and service life of the battery.

[0023] In some embodiments, along the winding direction, the positive electrode sheet has a second bend adjacent to the first bend, and the positive current collector of the second bend has a thickened layer on at least one side in the thickness direction. The second bend located inside the electrode assembly is a second region where lithium plating reaction is more likely to occur. The thickened layer on at least one side of the positive current collector in the second bend ensures that the capacity of the positive active material in this region is less than the capacity of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet in this region, improving the safety and lifespan of the battery, while ensuring the energy density of the battery.

[0024] In some embodiments, the positive current collector of the second bend is configured with an inner side and an outer side, and a thickening layer is provided on the inner side of the positive current collector of the second bend. For the wound electrode assembly, the inner side of the positive current collector is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy. However, by providing a thickening layer on the inner side of the positive current collector of the second bend, the positive active material capacity on the inner side of the positive current collector of the second bend can be reduced, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the delithiation reaction of the active material layer of the positive electrode sheet in part of the bend area, improving the safety and service life of the battery.

[0025] In some embodiments, along the winding direction, the positive electrode sheet has a third bend adjacent to the second bend, and the positive current collector of the third bend has a thickened layer on at least one side in the thickness direction. The third bend located inside the electrode assembly is a third region where lithium plating reaction is more likely to occur. The thickened layer on at least one side of the positive current collector in the third bend ensures that the capacity of the positive active material in this region is less than the capacity of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet in this region, improving the safety and lifespan of the battery, while ensuring the energy density of the battery.

[0026] In some embodiments, the positive current collector of the third bend is configured with an inner side and an outer side, and a thickened layer is provided on the inner side of the positive current collector of the third bend. For the wound electrode assembly, the inner side of the positive current collector is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy. However, by providing a thickened layer on the inner side of the positive current collector of the third bend, the positive active material capacity on the inner side of the positive current collector of the third bend can be reduced, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the delithiation reaction of the active material layer of the positive electrode sheet in the partial bend area, improving the safety and service life of the battery.

[0027] In some embodiments, along the winding direction, the positive electrode sheet has a fourth bend adjacent to the third bend, and the positive current collector of the fourth bend has a thickened layer on at least one side in the thickness direction. The fourth bend located inside the electrode assembly is a fourth region where lithium plating reaction is likely to occur. The thickened layer on at least one side of the positive current collector in the fourth bend ensures that the capacity of the positive active material in this region is less than the capacity of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet in this region, improving the safety and lifespan of the battery, while ensuring the energy density of the battery.

[0028] In some embodiments, the positive current collector of the fourth bend is configured with an inner side and an outer side, and a thickening layer is provided on the inner side of the positive current collector of the fourth bend. For the wound electrode assembly, the inner side of the positive current collector is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy. However, by providing a thickening layer on the inner side of the positive current collector of the fourth bend, the positive active material capacity on the inner side of the positive current collector of the fourth bend can be reduced, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the delithiation reaction of the active material layer of the positive electrode sheet in part of the bend area, improving the safety and service life of the battery.

[0029] In some embodiments, the positive and negative electrode sheets are folded to form a stacked structure. The positive electrode sheet has a fifth bend that covers the negative electrode sheet. The positive current collector in the fifth bend has a thickened layer on at least one side in the thickness direction. The fifth bend in the stacked structure is a region where lithium plating is likely to occur. The thickened layer on at least one side of the positive current collector in the fifth bend ensures that the capacity of the positive active material in this region is less than the capacity of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet in this region, improving the safety and lifespan of the battery, while ensuring the energy density of the battery.

[0030] In some embodiments, the positive current collector of the fifth bend is configured with an inner side and an outer side, and a thickening layer is provided on the inner side of the positive current collector of the fifth bend. For the stacked electrode assembly, the inner side of the positive current collector is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy. However, by providing a thickening layer on the inner side of the positive current collector of the fifth bend, the positive active material capacity on the inner side of the positive current collector of the fifth bend can be reduced, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the delithiation reaction of the active material layer in the part of the bend of the positive electrode sheet, improving the safety and service life of the battery.

[0031] Thirdly, this application provides a battery cell including the aforementioned electrode assembly.

[0032] Fourthly, this application provides a battery, including: the aforementioned battery cell.

[0033] Fifthly, this application provides an electrical device, including: the battery described above, the battery being used to provide electrical energy. Attached Figure Description

[0034] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0035] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0036] Figure 2 Exploded views of batteries provided in some embodiments of this application;

[0037] Figure 3 for Figure 2The exploded view of the battery cell shown;

[0038] Figure 4 This is a cross-sectional view of a first type of positive electrode sheet according to some embodiments of this application;

[0039] Figure 5 Schematic diagram of the structure of the positive current collector after a thickened layer is provided in some embodiments of this application;

[0040] Figure 6 This is a cross-sectional view of a second type of positive electrode sheet according to some embodiments of this application;

[0041] Figure 7 This is a cross-sectional view of a third type of positive electrode sheet according to some embodiments of this application;

[0042] Figure 8 This is a partial structural diagram of some embodiments of this application;

[0043] Figure 9 This is a schematic diagram of the structure of a first electrode assembly according to some embodiments of this application;

[0044] Figure 10 This is a schematic diagram of the structure of a second type of electrode assembly according to some embodiments of this application;

[0045] Figure 11 This is a schematic diagram of the structure of a third electrode assembly according to some embodiments of this application;

[0046] Figure 12 This is a schematic diagram of a first partial structure of a first type of electrode assembly according to some embodiments of this application;

[0047] Figure 13 This is a schematic diagram of a second partial structure of a first electrode assembly according to some embodiments of this application;

[0048] Figure 14 This is a schematic diagram of a third partial structure of a first electrode assembly according to some embodiments of this application;

[0049] Figure 15 This is a schematic diagram of a fourth partial structure of a first electrode assembly according to some embodiments of this application;

[0050] Figure 16 This is a schematic diagram of the structure of a fourth electrode assembly according to some embodiments of this application;

[0051] Figure 17 This is a schematic diagram of the structure of a fifth electrode assembly according to some embodiments of this application;

[0052] Figure 18 This is a schematic diagram of the structure of a sixth electrode assembly according to some embodiments of this application;

[0053] Figure 19 This is a partial structural schematic diagram of a second type of electrode assembly according to some embodiments of this application;

[0054] Figure 20 This is a partial structural schematic diagram of a third electrode assembly according to some embodiments of this application.

[0055] The reference numerals in the detailed embodiments are as follows:

[0056] 1000 - Vehicles;

[0057] 100 - Battery; 200 - Controller; 300 - Motor;

[0058] 10-Box body; 11-First part; 12-Second part; 13-Accommodation space;

[0059] 20-Battery cell; 21-Casing; 22-Electrode assembly; 23-Electrode terminal; 24-Pressure relief structure;

[0060] 211-Shell; 212-Cover; 213-Sealed space;

[0061] 400 - Positive electrode sheet; 401 - Straight portion; 402 - Part to be bent; 410 - Positive current collector; 420 - First positive electrode active material layer; 430 - Thickened layer; 431 - Pore area; 432 - Bonding surface; 440 - Second positive electrode active material layer; 451 - First bending portion; 452 - Second bending portion; 453 - Third bending portion; 454 - Fourth bending portion;

[0062] 500 - Electrode assembly; 501 - Straight region; 502 - Bending region; 600 - Negative electrode sheet; 700 - Separator membrane. Detailed Implementation

[0063] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0065] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0066] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0067] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0068] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0069] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0070] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0071] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0072] The inventors of this application have noted that during charging, lithium ions are extracted from the positive electrode and inserted into the negative electrode; during discharging, lithium ions are extracted from the negative electrode and inserted into the positive electrode. During charging, lithium-ion batteries may experience abnormal situations leading to lithium plating. For example, insufficient space for lithium insertion at the negative electrode, excessive resistance to lithium ion insertion into the negative electrode, or excessively rapid extraction of lithium ions from the positive electrode can cause lithium ions to fail to insert into the negative electrode active material layer in equal quantities. These uninserted lithium ions can only gain electrons on the negative electrode surface, forming silvery-white metallic lithium, a phenomenon known as lithium plating. Lithium plating not only degrades lithium-ion battery performance and significantly shortens cycle life but also limits the fast-charging capacity of lithium-ion batteries. Furthermore, when lithium plating occurs, the deposited lithium metal is highly reactive and reacts with the electrolyte, causing a decrease in the battery's self-heating initiation temperature and an increase in the self-heating rate, seriously jeopardizing battery safety. Furthermore, when lithium plating is severe, the deintercalated lithium ions can form lithium crystals on the surface of the negative electrode. These lithium crystals can pierce the separator, causing short circuits and thermal runaway between adjacent positive and negative electrodes.

[0073] The applicant's research found that lithium plating often occurs in the bending area of ​​the electrode assembly. During the winding or folding process of the positive and negative electrode sheets, the negative active material of the negative electrode sheet in the bending area is easily detached. This results in the number of lithium intercalation sites in the negative active material layer of the negative electrode sheet being less than the number of lithium ions that the positive active material layer of the adjacent positive electrode sheet can provide. As a result, lithium plating is more likely to occur when the lithium-ion battery is being charged.

[0074] To mitigate the lithium desorption problem, the applicant attempted to place a barrier layer between the positive electrode current collector and the positive electrode active material layer in the bending region. This barrier layer was intended to block electron transport between the two layers, thereby weakening or preventing the delithiation reaction in the positive electrode active material layer at the bending point, with the hope of minimizing or eliminating lithium ion deintercalation. However, further research revealed that this barrier layer cannot prevent lithium ion deintercalation from the surface of the positive electrode active material. This is because the positive electrode active materials are connected in parallel, forming an equipotential structure. Electrons can be transferred between the active materials through surrounding binders or conductive agents, a process that can be accompanied by lithium ion deintercalation. Therefore, the material of the barrier layer has limited impact on mitigating lithium desorption.

[0075] The applicant unexpectedly discovered that when the thickness of the barrier layer reaches a certain range, it has a significant effect on slowing lithium desorption. Based on the above considerations, in order to alleviate the problem of excessive lithium ion deintercalation in the positive electrode active material layer in the bending region, the inventors, after in-depth research, designed a positive electrode sheet, including: a positive electrode current collector and a positive electrode active material layer; the positive electrode current collector has a positive electrode active material layer on at least one side in the thickness direction, and the positive electrode sheet is configured with a straight portion and a bending portion; at least a portion of the positive electrode current collector in the bending portion has a thickening layer on at least one side in the thickness direction, the thickening layer is disposed between the positive electrode current collector and the positive electrode active material layer, the positive electrode active material layer covering the surface of the thickening layer is the first positive electrode active material layer, and the positive electrode active material layer located in the straight portion and connected to the first positive electrode active material layer is the second positive electrode active material layer; the thickness ratio of the first positive electrode active material layer to the second positive electrode active material layer is 20% to 80%.

[0076] When this positive electrode sheet is used to make an electrode assembly, since at least one side of the positive current collector in the bending section is provided with a thickened layer, when the positive active material is coated on the surface of the positive current collector, the coating quality of the positive active material coated on the surface of the thickened layer is reduced, thereby ensuring that the capacity of the positive active material in this area is less than the capacity of the corresponding negative active material, thereby reducing or avoiding the occurrence of lithium plating and improving the safety and service life of the battery.

[0077] Even if the negative electrode active material in the bending area of ​​the electrode assembly falls off, the capacity of the positive electrode active material in that area is less than the corresponding capacity of the negative electrode active material. In this case, the negative electrode active material layer of the negative electrode sheet can still provide enough lithium intercalation sites for the positive electrode active material layer of its adjacent positive electrode sheet, thereby reducing or avoiding the occurrence of lithium plating.

[0078] The battery mentioned in the embodiments of this application refers to a single physical module comprising one or more battery cells to provide higher voltage and capacity. A battery generally includes a battery housing for encapsulating one or more battery cells, which prevents liquids or other foreign matter from affecting the charging or discharging of the battery cells.

[0079] Battery cells can include lithium-ion rechargeable battery cells, lithium-ion primary battery cells, lithium-sulfur battery cells, sodium-lithium-ion battery cells, sodium-ion battery cells, or magnesium-ion battery cells, etc., and this application embodiment is not limited to these. Battery cells can be cylindrical, flat, cuboid, or other shapes, etc., and this application embodiment is not limited to these either. Battery cells are generally classified into three types according to their packaging method: cylindrical battery cells, prismatic battery cells, and pouch battery cells.

[0080] A single battery cell includes an electrode assembly and an electrolyte. The electrode assembly consists of a positive electrode, a negative electrode, and a separator. The battery cell primarily functions by the movement of metal ions between the positive and negative electrodes. The positive electrode includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector, and the uncoated positive current collector protrudes beyond the coated one, serving as the positive electrode tab. Taking a lithium-ion battery as an example, the positive current collector can be made of aluminum, and the positive active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The negative electrode includes a negative current collector and a negative active material layer. The negative active material layer is coated on the surface of the negative current collector, and the uncoated negative current collector protrudes beyond the coated one, serving as the negative electrode tab. The negative electrode current collector can be made of copper, and the negative electrode active material can be carbon or silicon, etc. To ensure that a large current can pass through without melting, there are multiple positive electrode tabs stacked together, and there are multiple negative electrode tabs stacked together. The separator can be made of polypropylene (PP) or polyethylene (PE), etc. Furthermore, the electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to these.

[0081] The battery cell also includes a current collector, which is used to electrically connect the tabs and electrode terminals of the battery cell to deliver electrical energy from the electrode assembly to the electrode terminals, and then to the outside of the battery cell via the electrode terminals. Multiple battery cells are electrically connected through a current collector to realize series, parallel or mixed connection of multiple battery cells.

[0082] The battery also includes sampling terminals and a battery management system. The sampling terminals are connected to the busbar and are used to collect information from individual battery cells, such as voltage or temperature. The sampling terminals transmit the collected information from individual battery cells to the battery management system. When the battery management system detects that the information from a battery cell exceeds the normal range, it limits the battery's output power to achieve safety protection.

[0083] It is understood that the power devices applicable to the use of batteries described in the embodiments of this application can take many forms, such as mobile phones, portable devices, laptops, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0084] The battery cells and batteries described in the embodiments of this application are not limited to the electrical devices described above, but can also be applied to all electrical devices that use battery cells and batteries. However, for the sake of brevity, the following embodiments are all illustrated using electric vehicles as an example.

[0085] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0086] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0087] See Figure 2 , Figure 2This is an exploded view of a battery 100 provided in some embodiments of this application. The battery 100 may include a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 is used to house the battery cell 20 and may have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, defining a receiving space 13 for housing the battery cell 20. The second portion 12 may be a hollow structure open at one end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 to form a housing 10 with the receiving space 13; alternatively, the first portion 11 and the second portion 12 may both be hollow structures open on one side, with the open side of the first portion 11 covering the open side of the second portion 12 to form a housing 10 with the receiving space 13. Of course, the first portion 11 and the second portion 12 may have various shapes, such as cylinders, cuboids, etc.

[0088] In battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells 20 is housed in housing 10. Alternatively, multiple battery cells 20 can first be connected in series, in parallel, or in a mixed configuration to form a battery module, and then multiple battery modules can be connected in series, in parallel, or in a mixed configuration to form a whole assembly, which is then housed in housing 10. Battery 100 may also include other structures. For example, multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed configurations of multiple battery cells 20.

[0089] Each battery cell 20 can be a secondary battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0090] Please see Figure 3 , Figure 3 for Figure 2 The diagram shows an exploded view of battery cell 20. Battery cell 20 refers to the smallest unit that makes up battery 100. Figure 3 The battery cell 20 may include a housing 21 and an electrode assembly 22, the electrode assembly 22 being housed within the housing 21. In some embodiments, the housing 21 may also be used to house an electrolyte, such as an electrolyte solution. The housing 21 may have various structural forms.

[0091] The outer casing 21 may include a housing 211 and a cover 212.

[0092] The housing 211 is an assembly used to fit the cover 212 to form an internal sealed space 213 of the battery cell 20. The formed sealed space 213 can accommodate the electrode assembly 22, electrolyte, and other components. The housing 211 and cover 212 can be independent components, with openings on the housing. The cover 212 closes the opening to form the internal environment of the battery cell 20. Alternatively, the cover 212 and housing 211 can be integrated. Specifically, the cover 212 and housing 211 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 211, the cover 212 closes the housing 211. The housing 211 can have various shapes and sizes, such as cuboid, cylindrical, or hexagonal prism. Specifically, the shape of the housing 211 can be determined according to the specific shape and size of the electrode assembly 22. The shell 211 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special restrictions on this.

[0093] The cover 212 refers to a component that covers the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 can be adapted to the shape of the housing 211 to fit it. In some embodiments, the cover 212 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the cover 212 is less prone to deformation under pressure and impact, allowing the battery cell 20 to have higher structural strength and improved safety performance. The material of the cover 212 can also be other, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating member can also be provided on the inner side of the cover 212. The insulating member can be used to isolate the electrical connection components inside the housing 211 from the cover 212 to reduce the risk of short circuit. For example, the insulating member can be plastic, rubber, etc.

[0094] Functional components such as electrode terminals 23 may be provided on the cover 212. The electrode terminals 23 are mounted on the cover 212. The electrode terminals 23 are electrically connected to the electrode assembly 22 to output the electrical energy generated by the battery cell 20. For example, the electrode terminals 23 and the electrode assembly 22 can be electrically connected via an adapter (not shown).

[0095] The battery cell 20 may also include a pressure relief structure 24, which is used to release the internal pressure of the battery cell 20 when the internal pressure or temperature reaches a predetermined value. For example, the pressure relief structure 24 may be a component such as an explosion-proof valve, an explosion-proof disc, a gas valve, a pressure relief valve, or a safety valve.

[0096] When assembling the battery cell 20, the electrode assembly 22 can be placed into the housing 211 first, and the electrolyte can be filled into the housing 211. Then, the cover 212 can be placed over the opening of the housing 211.

[0097] According to some embodiments of this application, please refer to Figures 4-7 , Figure 4 This is a cross-sectional view of a first positive electrode 400 according to some embodiments of this application. Figure 5 This is a schematic diagram of the structure of the positive current collector 410 after the thickening layer 430 is provided in some embodiments of this application. Figure 6 This is a cross-sectional view of a second type of positive electrode 400 according to some embodiments of this application. Figure 7 This is a cross-sectional view of a third positive electrode 400 according to some embodiments of this application.

[0098] This application provides a positive electrode sheet 400, including: a positive current collector 410 and a positive active material layer; the positive current collector 410 has a positive active material layer disposed on at least one side in the thickness direction, and the positive electrode sheet 400 is configured with a straight portion 401 and a bending portion 402; at least a portion of the bending portion 402 has a thickening layer 430 disposed on at least one side in the thickness direction of the positive current collector 410, the thickening layer 430 is disposed between the positive current collector 410 and the positive active material layer, the positive active material layer covering the surface of the thickening layer 430 is a first positive active material layer 420, and the positive active material layer located in the straight portion 401 and connected to the first positive active material layer 420 is a second positive active material layer 440; the ratio of the thickness (H1) of the first positive active material layer 420 to the thickness (H2) of the second positive active material layer 440 is 20-80%.

[0099] The straight section 401 is the part of the positive electrode plate 400 that forms the straight region 501 after being wound or bent.

[0100] The bending section 402 is the part of the positive electrode sheet 400 that has been wound or bent to form the bending area 502.

[0101] The thickened layer 430 is a layered structure disposed on at least one side of the positive electrode current collector 410 and in which the active material cannot be released.

[0102] In the process of manufacturing the positive electrode sheet 400, a thickening layer 430 is first set on the surface of the positive current collector 410, and then the positive active material slurry is coated. Since the thickening layer 430 occupies part of the space, when coating the positive active material slurry, the positive active material slurry on the surface of the thickening layer 430 is significantly less than the positive active material slurry on the surface without the thickening layer 430, so that the thickness of the first positive active material layer 420 is significantly less than the thickness of the second positive active material layer 440.

[0103] As an example, the positive current collector 410 may have a positive active material layer on both sides in the thickness direction, or a positive active material layer on only one side in the thickness direction.

[0104] Please see Figure 5 In some embodiments of this application, the positive current collector 410 is provided with a positive active material layer on both sides in the thickness direction, and at least a portion of the positive current collector 410 of the portion to be bent 402 is provided with a thickening layer 430 on one side in the thickness direction.

[0105] Please see Figure 6 In some embodiments of this application, the positive current collector 410 is provided with a positive active material layer on both sides in the thickness direction, and at least a portion of the positive current collector 410 of the portion to be bent 402 is provided with a thickening layer 430 on both sides in the thickness direction.

[0106] Please see Figure 7 In some embodiments of this application, the positive current collector 410 has a positive active material layer on one side in the thickness direction, and at least a portion of the positive current collector 410 of the portion to be bent 402 has a thickening layer 430 on one side in the thickness direction.

[0107] As an example, the ions released by the positive electrode active material are lithium ions.

[0108] As an example, the ratio of the thickness of the first positive electrode active material layer 420 to the thickness of the second positive electrode active material layer 440 can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%.

[0109] Some embodiments of this application provide a thickened layer 430 on at least one side of the positive current collector 410 in the bending portion 402. When the positive active material is coated on the surface of the positive current collector 410, the coating quality of the positive active material coated on the surface of the thickened layer 430 is reduced, thereby ensuring that the capacity of the positive active material in this area is less than the capacity of the corresponding negative active material, thereby reducing or avoiding lithium plating and improving the safety and service life of the battery.

[0110] According to some embodiments of this application, optionally, the thickness ratio of the first positive electrode active material layer 420 to the thickness ratio of the second positive electrode active material layer 440 is 30-60%.

[0111] In the positive electrode 400 of this application embodiment, the ratio of the thickness of the first positive electrode active material layer 420 to the thickness of the second positive electrode active material layer 440 cannot be too much or too little. In this way, the energy density of the battery can be guaranteed, and lithium plating can be reduced or avoided.

[0112] According to some embodiments of this application, optionally, the thickness ratio of the first positive electrode active material layer 420 to the thickness ratio of the second positive electrode active material layer 440 is 45-55%.

[0113] In the positive electrode 400 of this application embodiment, the ratio of the thickness of the first positive electrode active material layer 420 to the thickness of the second positive electrode active material layer 440 cannot be too much or too little. In this way, the energy density of the battery can be guaranteed, and lithium plating can be reduced or avoided.

[0114] Optionally, the thickness ratio of the first positive electrode active material layer 420 to the thickness ratio of the second positive electrode active material layer 440 is 50%.

[0115] According to some embodiments of this application, optionally, the ratio of the thickness of the second positive electrode active material layer 440 to the sum of the thicknesses (H3) of the first positive electrode active material layer 420 and the thickening layer 430 is 1:0.9 to 1.1.

[0116] As an example, the ratio of the thickness of the second positive electrode active material layer 440 to the sum of the thicknesses of the first positive electrode active material layer 420 and the thickening layer 430 can be 1:0.9, 1:0.95, 1:1, 1:1.05 or 1:1.1.

[0117] In the positive electrode 400 of this application embodiment, the thickness of the second positive electrode active material layer 440 is basically equal to the thickness of the first positive electrode active material layer 420 and the thickening layer 430, but a certain error value is also allowed.

[0118] According to some embodiments of this application, optionally, the ratio of the thickness of the second positive electrode active material layer 440 to the sum of the thicknesses of the first positive electrode active material layer 420 and the thickening layer 430 is 1:0.95 to 1.05.

[0119] In the positive electrode 400 of this application embodiment, the thickness of the second positive electrode active material layer 440 is basically equal to the thickness of the first positive electrode active material layer 420 and the thickening layer 430, but a certain error value is also allowed.

[0120] Optionally, the thickness of the second positive electrode active material layer 440 is in a ratio of 1:1 to the sum of the thicknesses of the first positive electrode active material layer 420 and the thickened layer 430.

[0121] According to some embodiments of this application, optionally, the positive current collector 410 has a positive active material layer on both sides in the thickness direction.

[0122] Having positive electrode active material layers on both sides of the positive electrode current collector 410 is beneficial to improving the energy density of the battery.

[0123] According to some embodiments of this application, optionally, please refer to... Figure 8 , Figure 8 This is a partial structural diagram of some embodiments of this application. The thickened layer 430 has a plurality of pore regions 431 distributed therein, and the pore regions 431 have positive electrode active material connecting the positive electrode current collector 410 and the first positive electrode active material layer 420.

[0124] The pore region 431 is the area on the surface of the thickened layer 430 where pores are formed. The pore region 431 allows the positive electrode active material to pass through and contact the positive electrode current collector 410.

[0125] If the adhesion of the thickened layer 430 is weak and the thickened layer 430 has no pores, the positive electrode active material coated on the surface of the thickened layer 430 is easy to fall off. This can easily cause excessive positive electrode active material in local areas of other locations. Furthermore, the fallen positive electrode active material may directly puncture the separator 700, causing a short circuit in the battery cell. It may also cause lithium plating on the negative electrode in the opposite location, thus creating a safety hazard.

[0126] Some embodiments of this application provide a porous region 431 in the thickened layer 430, allowing some of the positive electrode active material to pass through the porous region 431 during the coating process and adhere tightly to the positive electrode current collector 410, thereby strengthening the overall adhesion of the positive electrode active material and ensuring that the positive electrode active material does not fall off during manufacturing and long-term use.

[0127] Optionally, multiple perforated areas 431 are arranged in an array.

[0128] According to some embodiments of this application, optionally, the surface where the thickened layer 430 is bonded to the first positive electrode active material layer 420 is the bonding surface 432, and the area of ​​the multiple pore regions 431 distributed on the bonding surface 432 is 20% to 50% of the area of ​​the bonding surface 432.

[0129] The bonding surface 432 is the outer surface of the thickened layer 430 along its thickness direction, and the inner surface is used to bond the positive current collector 410.

[0130] The area of ​​the multiple hole areas 431 is the same as the area of ​​the holes provided on the mating surface 432.

[0131] As an example, the ratio of the area of ​​the multiple hole regions 431 distributed on the mating surface 432 to the area of ​​the mating surface 432 can be 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0132] In the positive electrode sheet 400 of this application embodiment, the area of ​​the multiple pore regions 431 distributed on the bonding surface 432 should not be too much or too little compared with the area of ​​the bonding surface 432. In this way, the overall adhesion of the positive electrode active material can be strengthened, ensuring that the positive electrode active material does not fall off during manufacturing and long-term use. It can also ensure that the capacity of the positive electrode active material disposed on the side with the thickened layer 430 is much smaller than the capacity of the corresponding negative electrode active material, thereby reducing or avoiding lithium plating and improving the safety and service life of the battery.

[0133] According to some embodiments of this application, optionally, the pore region 431 of the thickened layer 430 is distributed with pores penetrating the thickened layer 430, and the positive electrode active material is filled in the pores, the inner diameter of the pores being 100 to 5000 μm.

[0134] The shape of the hole can be a cylinder, cuboid, cube, or other shapes, and this application embodiment is not limited to this.

[0135] As an example, the inner diameter of the hole can be 100μm, 200μm, 500μm, 800μm, 1000μm, 1500μm, 2000μm, 2500μm, 3000μm, 3500μm, 4000μm, 4500μm or 5000μm.

[0136] The inner diameters of the multiple holes in the multiple hole region 431 may be the same or different. For example, the inner diameter of all the multiple holes may be 1000 μm; or the inner diameter of some holes may be 500 μm and the inner diameter of some holes may be 2000 μm. This application embodiment does not limit this.

[0137] In the positive electrode sheet 400 of this application embodiment, the inner diameter of the hole cannot be too large or too small. This allows the positive active material to pass through the hole during the coating process while ensuring the stability of the thickened layer 430.

[0138] According to some embodiments of this application, the thickened layer 430 may optionally be made of an insulating material.

[0139] The thickened layer 430 does not need to be conductive, and the insulating material is inexpensive, readily available, and lightweight, making it a better material choice for making the thickened layer 430.

[0140] According to some embodiments of this application, optionally, the material of the thickening layer 430 includes acrylic resin and / or polyolefin resin; the acrylic resin includes any one or more of acrylic acid-methacrylic acid copolymer, acrylic acid-butenoic acid copolymer, acrylic acid-itaconic acid copolymer, acrylic acid-maleic acid copolymer, acrylic acid-methyl methacrylate copolymer, acrylic acid-ethyl methacrylate copolymer, acrylic acid-n-butyl methacrylate copolymer, and acrylic acid-isobutyl methacrylate copolymer; the polyolefin resin includes any one or more of polypropylene, polyethylene, polybutadiene rubber, ethylene-propylene acetate copolymer, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, maleic anhydride modified polyolefin, and poly(butadiene-acrylonitrile), styrene-maleic anhydride copolymer.

[0141] Acrylic resins and / or polyolefin resins are common insulating materials that do not dissolve in electrolytes.

[0142] According to some embodiments of this application, optionally, the thickened layer 430 is bonded to the positive electrode current collector 410 and the first positive electrode active material layer 420, respectively.

[0143] The thickened layer 430 can be bonded to the positive electrode current collector 410 and the first positive electrode active material layer 420 respectively by its own adhesiveness.

[0144] According to some embodiments of this application, please refer to Figures 9-11 , Figure 9 This is a schematic diagram of the structure of a first electrode assembly 500 according to some embodiments of this application. Figure 10 This is a schematic diagram of the structure of a second type of electrode assembly 500 according to some embodiments of this application. Figure 11 This is a schematic diagram of the structure of a third electrode assembly 500 according to some embodiments of this application.

[0145] This application provides an electrode assembly 500, including: a negative electrode 600 and the aforementioned positive electrode 400. The positive electrode 400 and the negative electrode 600 are wound or folded to form a bending region 502 and a straight region 501. The straight region 501 is connected to the bending region 502. The bending portion 402 is wound or folded to form a bending portion. The bending portion is located in the bending region 502, and the straight portion 401 is located in the straight region 501.

[0146] Please see Figure 9 The positive electrode 400, negative electrode 600, and separator 700 are wound together to form an electrode assembly 500 with a wound structure. The middle part of the electrode assembly 500 is a straight region 501, and the two ends of the straight region 501 are bending regions 502. The closer the positive electrode 400 and negative electrode located in the bending region 502 are to the center of the wound structure, the greater the curvature of the curve formed after winding.

[0147] Please see Figure 10 A stacked electrode assembly 500 is formed by folding a positive electrode 400, a negative electrode 600, and a separator 700. The electrode assembly 500 has a flat region 501 in the middle, and multiple bending regions 502 at both ends. Each bending region 502 includes an inner electrode and an outer electrode. The curves formed by the folding of the inner positive electrode 400 and the negative electrode 600 have the same curvature, and the curves formed by the folding of the outer positive electrode 400 and the negative electrode 600 in the bending region 502 also have the same curvature.

[0148] Please see Figure 11 The positive electrode 400 and the separator 700 are folded to form multiple insertion slots. Multiple negative electrode 600s are inserted into the insertion slots one by one to form a stacked electrode assembly 500. The middle part of the electrode assembly 500 is a flat region 501, and the two ends of the flat region 501 are multiple bending regions 502. Each bending region 502 includes a negative electrode 600 located on the inner side and a positive electrode 400 located on the outer side. The curvature of the curve formed after each positive electrode 400 located on the outer side of the bending region 502 is the same.

[0149] In the technical solution of this application embodiment, a thickening layer 430 is provided between the positive current collector 410 and the first positive active material layer 420 in the partial bending region 502. When the positive active material is coated on the surface of the positive current collector 410, the coating quality of the positive active material coated on the surface of the thickening layer 430 is reduced, thereby ensuring that the capacity of the positive active material in the partial bending region 502 is less than the corresponding capacity of the negative active material, thereby weakening or preventing the delithiation reaction of the positive electrode 400 in the active material layer of the partial bending region 502, and improving the safety and service life of the battery.

[0150] According to some embodiments of this application, optionally, the positive electrode 400 and the negative electrode 600 are wound to form a wound structure, the positive current collector 410 of the bent portion has an inner side and an outer side, and at least part of the positive current collector 410 of the bent portion has a thickened layer 430 on the inner side.

[0151] For the wound electrode assembly 500, the inner side of the positive current collector 410 is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector 410 being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy to occur. However, a thickened layer 430 is provided on the inner side of the positive current collector 410 at least in the bend portion, which can reduce the positive active material capacity on the inner side of the positive current collector 410 at least in the bend portion, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the lithium delithiation reaction of the active material layer of the positive electrode sheet 400 in the partially bend region 502, improving the safety and service life of the battery.

[0152] According to some embodiments of this application, optionally, please refer to... Figure 9 , 12 ~15, Figure 12 This is a schematic diagram of a first partial structure of a first type of electrode assembly 500 according to some embodiments of this application. Figure 13 This is a schematic diagram of a second partial structure of a first electrode assembly 500 according to some embodiments of this application. Figure 14 This is a schematic diagram of a third partial structure of a first electrode assembly 500 according to some embodiments of this application. Figure 15 This is a schematic diagram of a fourth partial structure of a first electrode assembly 500 according to some embodiments of this application. The positive electrode 400 and the negative electrode 600 are wound to form a wound structure. The positive electrode 400 has an innermost first bend 451. The positive current collector 410 of the first bend 451 has a thickened layer 430 on at least one side in the thickness direction.

[0153] The first bending section 451 is the structure with the largest bending curvature of the positive electrode sheet 400.

[0154] Please see Figure 12 The first bending portion 451 includes a positive current collector 410, a second positive active material layer 440 located outside the positive current collector 410, and a thickened layer 430 and a first positive active material layer 420 located inside the positive current collector 410.

[0155] Please see Figure 13 The first bending portion 451 includes a positive electrode current collector 410, a thickened layer 430 located on both sides of the positive electrode current collector 410, and a first positive electrode active material layer 420.

[0156] Please see Figure 14 The first bending portion 451 includes a positive current collector 410, a thickened layer 430 located inside the positive current collector 410, and a first positive active material layer 420.

[0157] Please see Figure 15The first bending portion 451 includes a positive electrode current collector 410, a thickened layer 430 located outside the positive electrode current collector 410, and a first positive electrode active material layer 420.

[0158] The first bend 451, located at the innermost side of the electrode assembly 500, is the area most prone to lithium plating reaction. By providing a thickened layer 430 on at least one side of the positive current collector 410 in the first bend 451, the capacity of the positive active material in this area can be ensured to be less than the capacity of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet 400 in this area, and improving the safety and service life of the battery.

[0159] According to some embodiments of this application, optionally, as shown in the figure, the positive current collector 410 of the first bending portion 451 is configured with an inner side and an outer side, and the positive current collector 410 of the first bending portion 451 is provided with a thickening layer 430 on the inner side.

[0160] The inner side faces the center of the winding structure.

[0161] The outer side faces the opposite direction to the inner side.

[0162] For the wound electrode assembly 500, the inner side of the positive current collector 410 is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector 410 being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy to occur. However, the positive current collector 410 in the first bend 451 has a thickened layer 430 on its inner side, which can reduce the positive active material capacity on the inner side of the positive current collector 410 in the first bend 451, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the lithium delithiation reaction of the active material layer of the positive electrode sheet 400 in the partial bend area 502, improving the safety and service life of the battery.

[0163] According to some embodiments of this application, optionally, please refer to... Figure 16 , Figure 16 This is a schematic diagram of the structure of a fourth electrode assembly 500 according to some embodiments of this application. Along the winding direction, the positive electrode 400 has a second bend 452 adjacent to the first bend 451, and the positive current collector 410 of the second bend 452 has a thickened layer 430 on at least one side in the thickness direction.

[0164] The second bending portion 452 has the second largest bending curvature of the positive electrode sheet 400, and a straight portion 401 is arranged between the second bending portion 452 and the first bending portion 451.

[0165] As an example, the second bending portion 452 may include a positive current collector 410, a second positive active material layer 440 located outside the positive current collector 410, and a thickened layer 430 and a first positive active material layer 420 located inside the positive current collector 410; or the second bending portion 452 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located on both sides of the positive current collector 410; or the second bending portion 452 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located inside the positive current collector 410; or the second bending portion 452 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located outside the positive current collector 410.

[0166] The second bend 452 located inside the electrode assembly 500 is the second region where lithium plating reaction is likely to occur. The thickening layer 430 provided on at least one side of the positive current collector 410 in the second bend 452 can ensure that the capacity of the positive active material in this region is less than the capacity of the corresponding negative active material, thereby weakening or preventing the lithium delithiation reaction of the positive electrode sheet 400 in the active material layer in this region, improving the safety and service life of the battery, while ensuring the energy density of the battery.

[0167] According to some embodiments of this application, optionally, the positive current collector 410 of the second bending portion 452 is configured with an inner side and an outer side, and the positive current collector 410 of the second bending portion 452 is provided with a thickening layer 430 on the inner side.

[0168] For the wound electrode assembly 500, the inner side of the positive current collector 410 is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector 410 being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy to occur. However, the positive current collector 410 in the second bend 452 has a thickened layer 430 on its inner side, which can reduce the positive active material capacity on the inner side of the positive current collector 410 in the second bend 452, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the lithium delithiation reaction of the active material layer of the positive electrode sheet 400 in the partial bend area 502, improving the safety and service life of the battery.

[0169] According to some embodiments of this application, optionally, please refer to... Figure 17 , Figure 17 This is a schematic diagram of the structure of a fifth electrode assembly 500 according to some embodiments of this application. Along the winding direction, the positive electrode sheet 400 has a third bend 453 adjacent to the second bend 452, and the positive current collector 410 of the third bend 453 has a thickened layer 430 on at least one side in the thickness direction.

[0170] The third bending portion 453 has the third largest bending curvature of the positive electrode sheet 400, and a straight portion 401 is arranged between the third bending portion 453 and the second bending portion 452.

[0171] As an example, the third bending portion 453 may include a positive current collector 410, a second positive active material layer 440 located outside the positive current collector 410, and a thickened layer 430 and a first positive active material layer 420 located inside the positive current collector 410; or the third bending portion 453 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located on both sides of the positive current collector 410; or the third bending portion 453 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located inside the positive current collector 410; or the third bending portion 453 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located outside the positive current collector 410.

[0172] The third bend 453 located inside the electrode assembly 500 is the third region where lithium plating reaction is likely to occur. By providing a thickened layer 430 on at least one side of the positive current collector 410 in the third bend 453, the capacity of the positive active material in this region can be ensured to be less than the capacity of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet 400 in this region, improving the safety and service life of the battery, and ensuring the energy density of the battery.

[0173] According to some embodiments of this application, optionally, the positive current collector 410 of the third bend portion 453 is configured with an inner side and an outer side, and the positive current collector 410 of the third bend portion 453 is provided with a thickening layer 430 on the inner side.

[0174] For the wound electrode assembly 500, the inner side of the positive current collector 410 is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector 410 being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy to occur. However, the positive current collector 410 in the third bend 453 has a thickened layer 430 on its inner side, which can reduce the positive active material capacity on the inner side of the positive current collector 410 in the third bend 453. This ensures that the positive active material capacity in this area is less than the corresponding negative active material capacity, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet 400 in the partial bend area 502, and improving the safety and service life of the battery.

[0175] According to some embodiments of this application, optionally, please refer to... Figure 18 , Figure 18This is a schematic diagram of the structure of a sixth electrode assembly 500 according to some embodiments of this application. Along the winding direction, the positive electrode sheet 400 has a fourth bend 454 adjacent to the third bend 453, and the positive current collector 410 of the fourth bend 454 has a thickened layer 430 on at least one side in the thickness direction.

[0176] The fourth bending portion 454 has the fourth largest bending curvature of the positive electrode sheet 400, and a straight portion 401 is arranged between the fourth bending portion 454 and the third bending portion 453.

[0177] As an example, the fourth bending portion 454 may include a positive current collector 410, a second positive active material layer 440 located outside the positive current collector 410, and a thickened layer 430 and a first positive active material layer 420 located inside the positive current collector 410; or the fourth bending portion 454 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located on both sides of the positive current collector 410; or the fourth bending portion 454 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located inside the positive current collector 410; or the fourth bending portion 454 may include a positive current collector 410, thickened layers 430 and a first positive active material layer 420 located outside the positive current collector 410.

[0178] The fourth bend 454 located inside the electrode assembly 500 is the fourth region where lithium plating reaction is likely to occur. By providing a thickened layer 430 on at least one side of the positive current collector 410 in the fourth bend 454, it can be ensured that the capacity of the positive active material in this region is less than the capacity of the corresponding negative active material, thereby weakening or preventing the delithiation reaction of the active material layer of the positive electrode sheet 400 in this region, improving the safety and service life of the battery, and ensuring the energy density of the battery.

[0179] According to some embodiments of this application, optionally, the positive current collector 410 of the fourth bend portion 454 is configured with an inner side and an outer side, and the positive current collector 410 of the fourth bend portion 454 is provided with a thickening layer 430 on the inner side.

[0180] For the wound electrode assembly 500, the inner side of the positive current collector 410 is larger than the outer side of the corresponding negative current collector. This results in the positive active material capacity on the inner side of the positive current collector 410 being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy to occur. However, the positive current collector 410 in the fourth bend 454 has a thickened layer 430 on its inner side, which can reduce the positive active material capacity on the inner side of the positive current collector 410 in the fourth bend 454, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the lithium delithiation reaction of the active material layer of the positive electrode sheet 400 in the partial bend area 502, improving the safety and service life of the battery.

[0181] In addition, for the wound electrode assembly 500, the positive electrode sheet 400 may only have the thickening layer 430 in the second bend 452, the third bend 453, the fourth bend 454 or other bends, or only in the second bend 452 and the third bend 453, or only in the third bend 453 and the fourth bend 454, or only in the second bend 452, the third bend 453 and the fourth bend 454. This application does not limit this.

[0182] According to some embodiments of this application, optionally, please refer to... Figure 10 , 11 19 and 20 Figure 19 This is a partial structural schematic diagram of a second type of electrode assembly 500 according to some embodiments of this application. Figure 20 This is a partial structural schematic diagram of a third electrode assembly 500 according to some embodiments of this application. The positive electrode 400 and the negative electrode 600 are folded to form a stacked structure. The positive electrode 400 has a fifth bend that covers the negative electrode 600. The positive current collector 410 of the fifth bend has a thickened layer 430 on at least one side in the thickness direction.

[0183] Since the curvature of the curve formed by each positive electrode 400 located on the outer side of the bending region 502 of the stacked electrode assembly 500 is the same after folding, the fifth bending part can be a bending part at any position.

[0184] Please see Figure 19 and 20 The fifth bending portion includes a positive current collector 410, a second positive active material layer 440 located outside the positive current collector 410, and a thickened layer 430 and a first positive active material layer 420 located inside the positive current collector 410.

[0185] In some other embodiments of this application, the fifth bending portion may include a positive current collector 410, a thickened layer 430 located on both sides of the positive current collector 410, and a first positive active material layer 420; or the fifth bending portion may include a positive current collector 410, a thickened layer 430 located inside the positive current collector 410, and a first positive active material layer 420; or the fifth bending portion may include a positive current collector 410, a thickened layer 430 located outside the positive current collector 410, and a first positive active material layer 420.

[0186] The fifth bend in the stacked structure is a region where lithium plating is likely to occur. By providing a thickened layer 430 on at least one side of the positive current collector 410 in the fifth bend, the capacity of the positive active material in this region can be ensured to be less than the capacity of the corresponding negative active material. This weakens or prevents the delithiation reaction of the positive electrode 400 in the active material layer in this region, improves the safety and lifespan of the battery, and ensures the energy density of the battery.

[0187] According to some embodiments of this application, optionally, in some embodiments, the positive current collector 410 of the fifth bend is configured with an inner side and an outer side, and the positive current collector 410 of the fifth bend has a thickened layer 430 on the inner side.

[0188] For the stacked electrode assembly 500, the inner surface of the positive current collector 410 is larger than the outer surface of the corresponding negative current collector. This results in the positive active material capacity on the inner surface of the positive current collector 410 being greater than the corresponding negative active material capacity under normal conditions, making lithium plating reaction very easy to occur. However, a thickened layer 430 is provided on the inner surface of the positive current collector 410 at the fifth bend, which can reduce the positive active material capacity on the inner surface of the positive current collector 410 at the fifth bend, thereby ensuring that the positive active material capacity in this area is less than the corresponding negative active material capacity. This weakens or prevents the lithium delithiation reaction of the active material layer of the positive electrode sheet 400 in the partial bend area 502, improving the safety and service life of the battery.

[0189] The electrode assembly of this application will be further described in detail below with reference to the embodiments. The structure and parameters of the electrode assemblies of Embodiments 1 to 35 and Comparative Examples 1 to 9 are shown in Tables 1 and 2.

[0190] Among them, Examples 1 to 23 and Comparative Examples 1 to 3 are Figure 9 , 16 The electrode assembly with the wound structure shown in Examples 24-29 and Comparative Examples 4-6 is shown in Examples 24-29. Figure 10 The electrode assembly with the stacked structure shown in Examples 30-35 and Comparative Examples 7-9 is... Figure 11 The electrode assembly with a stacked structure is shown.

[0191] Furthermore, positive electrode active material layers are provided on both sides of the positive electrode current collector of the positive electrode sheet.

[0192] In all embodiments and comparative examples, the thickness of the second positive electrode active material layer is in a 1:1 ratio to the sum of the thicknesses of the first positive electrode active material layer and the thickening layer.

[0193] Table 1 Examples and Comparative Examples of the Wound Electrode Assembly

[0194]

[0195]

[0196] Table 2 Examples and Comparative Examples of Stacked Electrode Assemblies

[0197]

[0198]

[0199] Test case

[0200] Batteries were fabricated using the electrode assemblies of Examples 1-35 and Comparative Examples 1-9 of this application, and the capacity retention rate of the fabricated batteries was measured respectively. The results are shown in Table 3.

[0201] The battery is manufactured as follows:

[0202] (1) Preparation of negative electrode

[0203] The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were mixed in a weight ratio of graphite:acetylene black:styrene-butadiene rubber:sodium carboxymethyl cellulose = 95:2:2:1. After adding deionized water, the mixture was stirred thoroughly to form a uniform negative electrode slurry. This slurry was coated onto the negative electrode current collector copper foil, then dried and cold-pressed to obtain the negative electrode sheet, wherein the copper foil thickness was 6 μm and the total electrode sheet thickness was 158.5 μm.

[0204] (2) Preparation of positive electrode

[0205] The positive electrode active material NCM211, conductive agent acetylene black, and binder polyvinylidene fluoride were mixed in a weight ratio of 97:2:1. N-methylpyrrolidone solvent was added, and the mixture was thoroughly stirred to form a uniform positive electrode slurry. This slurry was coated onto the positive electrode current collector aluminum foil, then dried and cold-pressed to obtain the positive electrode sheet. Before coating the corner area of ​​the positive electrode sheet with the slurry, an insulating tape was first applied. The tape's height was flush with the width of the electrode sheet, and its length completely covered the corner area and extended appropriately into the larger surface area. In this case, a 24μm wide hot melt tape was used throughout.

[0206] (3) Preparation of electrolyte

[0207] In an argon atmosphere glove box with a water content of <10ppm, carbonate solvent EC and EMC are mixed in a weight ratio of 3:7 to obtain a mixed solvent. Then, fully dried lithium salt LiPF6 and additives PS and VC are dissolved in the above mixed solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 is 1mol / L and the weight ratio of PS and VC is 1%.

[0208] (4) Battery manufacturing

[0209] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging foil or metal casing, and the prepared electrolyte is injected into the dried battery. After vacuum sealing and standing, the battery is obtained.

[0210] The test method for battery capacity retention is as follows:

[0211] At 45℃, the lithium-ion secondary battery is first charged to 4.3V (other voltages are acceptable, but 4.3V corresponds to 100% SOC) at a constant current of 0.5C. Then, it is further charged at a constant voltage of 4.3V to a current of 0.025C, and finally discharged to 3.0V at a constant current of 0.5C. This constitutes one charge-discharge cycle. The discharge capacity of this cycle is denoted as Cap1. The lithium-ion secondary battery is then subjected to cyclic charge-discharge tests as described above. The discharge capacity of the 10th cycle is denoted as Cap2. The capacity retention rate (%) of the lithium-ion secondary battery after 10 cycles is calculated as M = [Cap2 / Cap1] × 100%. A larger M value indicates less capacity loss due to lithium plating and a better improvement effect.

[0212] Table 3 shows the detection results of Examples 1-35 and Comparative Examples 1-9.

[0213]

[0214]

[0215] As can be seen from Examples 1 and 2, for the wound electrode assembly, providing thickening layers on the inner or both sides of the first, second, third, and fourth bends can reduce or avoid lithium plating, allowing the battery to retain 99.8% of its capacity after 10 cycles. The battery capacity of Example 1, which only provides thickening layers on the inner side, is slightly higher than that of Example 2, which provides thickening layers on both sides. Furthermore, the fourth bend itself does not plating lithium, but considering process fluctuations, thickening layers can be provided in the first four bends.

[0216] A comparison of Examples 3-4 with Example 1 shows that for the wound electrode assembly, providing thickening layers on the inner or double sides of the first, second, and third bends can reduce or avoid lithium plating; and the fourth bend itself does not plating lithium, so the capacity retention rate of the battery after 10 cycles is basically not improved; the battery capacity of Example 3, which only provides thickening layers on the inner side, is slightly higher than that of Example 4, which provides thickening layers on both sides.

[0217] A comparison of Examples 5-6 and Example 2 shows that for the wound electrode assembly, providing a thickening layer on the inner or both sides of the first and second bends can reduce or prevent lithium plating. However, since no thickening layer is provided on the third bend, lithium plating may occur there. Therefore, the capacity retention rate of the battery after 10 cycles is 99.7%. The battery capacity of Example 5, which only provides a thickening layer on the inner side, is slightly higher than that of Example 6, which provides a thickening layer on both sides.

[0218] A comparison of Examples 7-8 and Example 3 shows that for the wound electrode assembly, providing a thickening layer only on the inner side or both sides of the first bend can reduce or avoid lithium plating; however, no thickening layer is provided on the second bend, and lithium plating may occur in the second bend, so the capacity retention rate of the battery after 10 cycles is 99.6%; the battery capacity of Example 7, which provides a thickening layer only on the inner side, is slightly higher than that of Example 8, which provides a thickening layer on both sides.

[0219] As can be seen from the comparison between Examples 9-10 and Example 1, for the wound electrode assembly, providing a thickening layer in all bending portions can reduce or avoid lithium plating; however, since the fourth bending portion and the bending portions on its outer side basically do not plating lithium or plating very little lithium, it will not affect the battery capacity retention rate. Moreover, providing a thickening layer in the bending portions on the outer side of the fourth bending portion will affect the battery capacity and reduce its capacity.

[0220] As can be seen from the comparison between Examples 11-16 and Example 1, when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is 20-80%, the capacity retention rate of the battery after 10 cycles can reach 99.3-99.8%, and the smaller the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer, the higher the capacity retention rate of the battery after 10 cycles.

[0221] A comparison of Examples 17-19 and Example 1 shows that when the area of ​​the multiple pore regions distributed on the bonding surface is 20%-50% of the total area of ​​the bonding surface, the capacity retention rate of the battery after 10 cycles can reach 99.7%-99.8%. When the area of ​​the multiple pore regions distributed on the bonding surface is less than 20%, the proportion of the pore area decreases, which may cause a decrease in conductivity, an increase in internal resistance, and a decrease in the capacity retention rate of the battery after 10 cycles. When the area of ​​the multiple pore regions distributed on the bonding surface is greater than 50%, slight lithium plating may occur, and the capacity retention rate of the battery after 10 cycles may decrease.

[0222] A comparison of Examples 20-23 and Example 1 shows that when the inner diameter of the pores is 100-5000 μm, the capacity retention rate of the battery after 10 cycles can reach 99.6-99.8%. When the inner diameter of the pores is less than 100 μm, the positive electrode active material particles may not adhere firmly due to the small inner diameter, and the particles may fall off, resulting in a decrease in the capacity retention rate of the battery after 10 cycles. When the inner diameter of the pores is greater than 5000 μm, the capacity retention rate of the battery after 10 cycles decreases.

[0223] As can be seen from the comparison between Comparative Example 1 and Example 1, the bending part of Comparative Example 1 has no thickening layer and serious lithium plating. Although the discharge capacity of the first cycle is slightly higher than that of Example 1, the capacity retention rate of the battery after 10 cycles is only 98.9%, which is far lower than the capacity retention rate of the battery after 10 cycles of Example 1.

[0224] As can be seen from the comparison between Comparative Example 2 and Example 1, when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is less than 20%, although the capacity retention rate of the battery after 10 cycles can reach 99.8%, the discharge capacity of the first cycle is low.

[0225] As can be seen from the comparison between Comparative Example 3 and Example 1, when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is greater than 80%, the capacity retention rate of the battery after 10 cycles is low.

[0226] As can be seen from Examples 24 and 25, for Figure 10 The electrode assembly with the stacked structure shown has a thickened layer on the inner side or both sides of all the fifth bends, which can reduce or avoid lithium plating, so that the capacity retention rate of the battery can reach 99.6% after 10 cycles; the battery capacity of Example 24, which has a thickened layer on only the inner side, is slightly higher than that of Example 25, which has a thickened layer on both sides.

[0227] A comparison of Examples 26-29 and Example 24 shows that when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is between 20% and 80%, the capacity retention rate of the battery after 10 cycles can reach 99.2% to 99.6%. Furthermore, the smaller the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer, the higher the capacity retention rate of the battery after 10 cycles.

[0228] As can be seen from the comparison between Comparative Example 4 and Example 24, the bending part of Comparative Example 4 has no thickening layer and serious lithium plating. Although the discharge capacity of the first cycle is higher than that of Example 24, the capacity retention rate of the battery after 10 cycles is only 99.1%, which is much lower than the capacity retention rate of the battery after 10 cycles of Example 24.

[0229] As can be seen from the comparison between Comparative Example 5 and Example 24, when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is less than 20%, although the capacity retention rate of the battery after 10 cycles can reach 99.6%, the discharge capacity of the first cycle is low.

[0230] As can be seen from the comparison between Comparative Example 6 and Example 24, when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is greater than 80%, the capacity retention rate of the battery after 10 cycles is low.

[0231] As can be seen from Examples 30 and 31, for Figure 11 The electrode assembly with the stacked structure shown has a thickened layer on the inner side or both sides of all the fifth bends, which can reduce or avoid lithium plating, so that the capacity retention rate of the battery can reach 99.5% after 10 cycles; the battery capacity of Example 30 with a thickened layer on only the inner side is slightly higher than that of Example 31 with a thickened layer on both sides.

[0232] A comparison of Examples 32-35 and Example 30 shows that when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is between 20% and 80%, the capacity retention rate of the battery after 10 cycles can reach 99% to 99.5%. Furthermore, the smaller the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer, the higher the capacity retention rate of the battery after 10 cycles.

[0233] As can be seen from the comparison between Comparative Example 7 and Example 30, the bending part of Comparative Example 7 has no thickening layer and serious lithium plating. Although the discharge capacity of the first cycle is higher than that of Example 30, the capacity retention rate of the battery after 10 cycles is only 88.8%, which is much lower than the capacity retention rate of the battery after 10 cycles of Example 30.

[0234] As can be seen from the comparison between Comparative Example 8 and Example 30, when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is less than 20%, although the capacity retention rate of the battery after 10 cycles can reach 99.6%, the discharge capacity of the first cycle is low.

[0235] As can be seen from the comparison between Comparative Example 9 and Example 30, when the ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is greater than 80%, the capacity retention rate of the battery after 10 cycles is low.

[0236] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions 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 within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode plate, wherein, include: A positive current collector and a positive active material layer, wherein the positive current collector has the positive active material layer disposed on at least one side in the thickness direction, and the positive electrode sheet is provided with a straight portion and a portion to be bent; At least a portion of the positive current collector of the portion to be bent has a thickening layer on at least one side in the thickness direction, the straight portion does not have the thickening layer, the thickening layer is disposed between the positive current collector and the positive active material layer, the positive active material layer covering the surface of the thickening layer is the first positive active material layer, and the positive active material layer located in the straight portion and connected to the first positive active material layer is the second positive active material layer; The ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is 20% to 80%. The thickened layer has multiple porous regions, and the interior of each porous region contains positive electrode active material that connects the positive electrode current collector and the first positive electrode active material layer. The surface where the thickened layer is bonded to the first positive electrode active material layer is called the bonding surface, and the area of ​​the plurality of pore regions distributed on the bonding surface is 25% to 50% of the area of ​​the bonding surface.

2. The positive electrode sheet according to claim 1, wherein, The ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is 30% to 60%.

3. The positive electrode sheet according to claim 1, wherein, The ratio of the thickness of the first positive electrode active material layer to the thickness of the second positive electrode active material layer is 45% to 55%.

4. The positive electrode sheet according to any one of claims 1 to 3, wherein, The ratio of the thickness of the second positive electrode active material layer to the sum of the thicknesses of the first positive electrode active material layer and the thickened layer is 1:0.9 to 1.

1.

5. The positive electrode sheet according to any one of claims 1 to 3, wherein, The ratio of the thickness of the second positive electrode active material layer to the sum of the thicknesses of the first positive electrode active material layer and the thickened layer is 1:0.95 to 1.

05.

6. The positive electrode sheet according to any one of claims 1 to 3, wherein, The positive electrode current collector has a positive electrode active material layer on both sides in the thickness direction.

7. The positive electrode sheet according to claim 5, wherein, The thickened layer has pores that penetrate the thickened layer, and the positive electrode active material fills the pores. The inner diameter of the pores is 100-5000 μm.

8. The positive electrode sheet according to any one of claims 1 to 3, wherein, The thickened layer is made of insulating material.

9. The positive electrode sheet according to any one of claims 1 to 3, wherein, The material of the thickening layer includes acrylic resin and / or polyolefin resin; The acrylic resin includes any one or more of the following: acrylic acid-methacrylic acid copolymer, acrylic acid-butenoic acid copolymer, acrylic acid-itaconic acid copolymer, acrylic acid-maleic acid copolymer, acrylic acid-methyl methacrylate copolymer, acrylic acid-ethyl methacrylate copolymer, acrylic acid-n-butyl methacrylate copolymer, and acrylic acid-isobutyl methacrylate copolymer. The polyolefin resin includes any one or more of polypropylene, polyethylene, polybutadiene rubber, ethylene-propylene acetate copolymer, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, maleic anhydride modified polyolefin, and poly(butadiene-acrylonitrile) and styrene-maleic anhydride copolymer.

10. The positive electrode sheet according to any one of claims 1 to 3, wherein, The thickened layer is bonded to the positive electrode current collector and the first positive electrode active material layer, respectively.

11. An electrode assembly, wherein, include: The negative electrode sheet and the positive electrode sheet according to any one of claims 1 to 3, wherein the positive electrode sheet and the negative electrode sheet are wound or folded to form a bending region and a straight region, and the straight region is connected to the bending region; The part to be bent is formed by winding or folding, the bent part is located in the bending area, and the straight part is located in the straight area.

12. The electrode assembly according to claim 11, wherein, The positive electrode and the negative electrode are wound to form a wound structure. The positive current collector of the bent portion has an inner side and an outer side, and at least a portion of the positive current collector of the bent portion has the thickened layer on the inner side.

13. The electrode assembly according to claim 11, wherein, The positive electrode and the negative electrode are wound together to form a wound structure. The positive electrode has an innermost first bend. The positive current collector of the first bend has a thickened layer on at least one side in the thickness direction.

14. The electrode assembly according to claim 13, wherein, The positive current collector of the first bend is provided with an inner side and an outer side, and the positive current collector of the first bend is provided with the thickened layer on the inner side.

15. The electrode assembly according to claim 13, wherein, Along the winding direction, the positive electrode sheet has a second bend adjacent to the first bend, and the positive current collector of the second bend has the thickened layer on at least one side in the thickness direction.

16. The electrode assembly according to claim 15, wherein, The positive current collector of the second bend is provided with an inner side and an outer side, and the thickened layer is provided on the inner side of the positive current collector of the second bend.

17. The electrode assembly of claim 15, wherein, Along the winding direction, the positive electrode sheet has a third bend adjacent to the second bend, and the positive current collector of the third bend has the thickened layer on at least one side in the thickness direction.

18. The electrode assembly according to claim 17, wherein, The positive current collector of the third bend is provided with an inner side and an outer side, and the thickened layer is provided on the inner side of the positive current collector of the third bend.

19. The electrode assembly according to claim 17, wherein, Along the winding direction, the positive electrode sheet has a fourth bend adjacent to the third bend, and the positive current collector of the fourth bend has the thickened layer on at least one side in the thickness direction.

20. The electrode assembly of claim 19, wherein, The positive current collector of the fourth bend is provided with an inner side and an outer side, and the thickened layer is provided on the inner side of the positive current collector of the fourth bend.

21. The electrode assembly of claim 11, wherein, The positive electrode and the negative electrode are folded to form a stacked structure. The positive electrode has a fifth bend that covers the negative electrode. The positive current collector of the fifth bend has a thickened layer on at least one side in the thickness direction.

22. The electrode assembly according to claim 21, wherein, The positive current collector of the fifth bend is provided with an inner side and an outer side, and the positive current collector of the fifth bend has the thickened layer on the inner side.

23. A single battery cell, wherein, Includes the electrode assembly as described in any one of claims 11 to 22.

24. A battery, wherein, Includes the battery cell described in claim 23.

25. An electrical appliance, wherein, Includes the battery of claim 24, the battery being used to provide electrical energy.

Images