Positive pole piece, battery and electric equipment

Abstract

The invention provides a positive pole piece, a battery and electric equipment, and relates to the field of batteries. The positive pole piece comprises a positive current collector and a positive active material layer, the positive active material layer comprises a main body region and an edge region, and the thickness of the positive active material layer in the edge region is smaller than that of the main body region; the positive electrode active material layer comprises a first positive electrode active material and a second positive electrode active material, the volume expansion rate of the first positive electrode active material is smaller than that of the second positive electrode active material, and the mass percent of the second positive electrode active material in the edge region is larger than that of the second positive electrode active material in the main body region; therefore, the volume expansion rate of the positive electrode active material in the marginal area is improved, and the technical problem of lithium precipitation in the thinned area of the negative electrode plate corresponding to the positive electrode plate is solved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a positive electrode sheet, a battery, and an electrical device. Background Art

[0002] During the preparation of the electrode, the slurry is coated on the positive electrode collector until it is completely dried. Due to the fluidity and surface tension of the liquid, the slurry will spread to the edge of the coating to form a bulge, which will cause edge cracking during the drying process of the electrode, affecting the reliability of the battery. Therefore, an edge thinning process is used during the electrode coating process so that the final formed electrode has a thinned area.

[0003] After multiple cycles, the battery containing the above-mentioned electrode has the problem of large battery capacity attenuation and poor safety. Summary of the invention

[0004] In view of the above problems, the present application proposes a positive electrode plate, a battery and an electrical device, which can improve the problem of large battery capacity attenuation and poor safety after multiple cycles of negative electrode plates with thinned areas.

[0005] In a first aspect, an embodiment of the present application provides a positive electrode plate, which includes a positive electrode collector and a positive electrode active material layer arranged on the positive electrode collector, the positive electrode active material layer includes a main area and an edge area, and the thickness of the positive electrode active material layer in the edge area is less than the thickness in the main area; the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, the volume expansion rate of the first positive electrode active material is less than the volume expansion rate of the second positive electrode active material, the mass percentage of the second positive electrode active material in the edge area is greater than the mass percentage of the second positive electrode active material in the main area, and the mass percentage of the second positive electrode active material in the main area is 20% to 70%.

[0006] In the technical solution of the embodiment of the present application, the thickness of the edge area is smaller than the thickness of the main area to alleviate the problem of edge bulging and cracking during the drying of the positive electrode plate. The volume expansion rate of the first positive electrode active material is smaller than the volume expansion rate of the second positive electrode active material, and the mass percentage of the second positive electrode active material in the edge area is greater than the mass percentage of the second positive electrode active material in the main area. The volume expansion rate of the positive electrode active material in the edge area is increased, thereby reducing the thickness difference between the main area and the edge area during charging, reducing the distance between the edge area of ​​the positive electrode plate and the edge area of ​​the negative electrode plate, reducing polarization, and thereby alleviating the problem of easy lithium deposition in the edge area of ​​the negative electrode plate corresponding to the positive electrode plate, thereby improving the capacity retention rate and safety of the battery after multiple cycles.

[0007] In some embodiments, the mass percentage of the second positive electrode active material in the main region is 20% to 70%, and the mass percentage of the second positive electrode active material in the edge region is 50% to 100%, and can be optionally 80% to 100%.

[0008] Within the above range, it is beneficial to improve the capacity retention and safety of the battery after multiple cycles.

[0009] In some embodiments, the positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer includes a first positive electrode active material, and the second positive electrode active material layer includes a second positive electrode active material.

[0010] In the process of slow lithium release, a double-layer coating structure of two positive electrode active materials is utilized to reduce the mixing amount between the two positive electrode active materials, thereby reducing the probability of the mutual influence and deterioration of the performance of the two positive electrode active materials, improving the problem of early cycle attenuation, and improving the stability of battery performance and battery life.

[0011] Optionally, the first positive electrode active material layer is disposed between the second positive electrode active material layer and the positive electrode current collector.

[0012] Since the volume expansion rate of the first positive electrode active material is smaller than the volume expansion rate of the second positive electrode active material, the above arrangement is conducive to the expansion of the edge area, reducing the distance between the edge area of ​​the positive electrode sheet and the edge area of ​​the negative electrode sheet, thereby improving the capacity retention rate and safety of the battery after multiple cycles.

[0013] In some embodiments, the first positive electrode active material layer includes 90% to 98.5% wt of the first positive electrode active material, and the second positive electrode active material layer includes 90% to 98.5% wt of the second positive electrode active material; the thickness of the first positive electrode active material layer in the main area is h1, h1>0, and the thickness of the first positive electrode active material layer at 1 / 2 of the edge area is h1', h1>h1'≥0; the thickness of the second positive electrode active material layer in the main area is h2, h2>0; the thickness of the second positive electrode active material layer at 1 / 2 of the edge area is h2', h2'>1 / 2(h2+h1).

[0014] By utilizing the fact that the mass contents of the first active material contained in the first positive electrode active material layer and the second active material contained in the second positive electrode active material layer are substantially the same, and the thickness of the second positive electrode active material layer at 1 / 2 of the edge region is greater than 1 / 2 (h2+h1), thereby increasing the volume expansion rate of the positive electrode active material in the edge region compared to that in the main region, thereby reducing the thickness difference between the main region and the edge region during charging, reducing the distance between the edge region of the positive electrode sheet and the edge region of the negative electrode sheet, reducing polarization, and thereby alleviating the problem of easy lithium deposition in the edge region of the negative electrode sheet corresponding to the positive electrode sheet, thereby improving the capacity retention rate and safety of the battery after multiple cycles.

[0015] In some embodiments, h1>h1'>0, and h2'≥h2.

[0016] That is, there is a first positive electrode active material layer in the edge area, and the thickness of the first positive electrode active material layer at 1 / 2 of the edge area is thinner than the thickness of the first active material layer in the main area. At this time, h2'≥h2 is used to make the thickness of the second active material layer at 1 / 2 of the edge area thicker than the thickness of the second active material layer in the main area, thereby increasing the volume expansion rate of the edge area compared to the main area, thereby alleviating the problem of easy lithium deposition in the edge area of ​​the negative electrode plate.

[0017] In some embodiments, h1′=0, 0.5≤h2′ / (h2+h1)<1.

[0018] Using h1'=0, that is, removing the first positive electrode active material layer located in the edge area, making the entire edge area the second positive electrode active material layer. At this time, 0.5≤h2' / (h2+h1)<1, that is, the thickness of the positive electrode active material layer at 1 / 2 of the edge area is less than the thickness of the main area and is 0.5 times or more of the thickness of the main area. This not only facilitates the production and reduces the difficulty of producing the positive electrode sheet, but also alleviates the problem of easy lithium deposition in the edge area of ​​the negative electrode sheet.

[0019] Optionally, h2' / (h2+h1)=0.5-0.8.

[0020] In some embodiments, the first positive electrode active material layer has a thickness of h1 in the main body region, where h1=40-210 μm.

[0021] Within the above range, the battery has high energy density and high safety performance.

[0022] In some embodiments, the thickness of the second positive electrode active material layer in the main body region is h2, where h1-h2=-40-180 μm.

[0023] Optionally, h1-h2=-20~120μm.

[0024] By controlling the thickness difference between the above-mentioned active materials, the problem of easy lithium deposition in the edge area of ​​the negative electrode sheet corresponding to the positive electrode sheet can be alleviated, thereby improving the capacity retention rate and safety of the battery after multiple cycles.

[0025] In some embodiments, the difference in volume expansion rate between the first positive electrode active material layer and the second positive electrode active material layer is 1% to 10%.

[0026] Within the above range, the thickness difference between the main area and the edge area can be effectively reduced during charging, alleviating the problem of easy lithium deposition in the edge area of ​​the negative electrode sheet corresponding to the positive electrode sheet.

[0027] In some embodiments, a straight-line distance from one end of the edge region close to the main region to one end away from the main region is L, and L is ≤ 10 mm.

[0028] Within the above-mentioned size range, the battery capacity can be guaranteed to meet the requirements while alleviating bulging and cracking at the edge of the positive electrode.

[0029] Optionally, L is 2 to 8 mm.

[0030] In some embodiments, along the direction from the main region to the edge region, the thickness of the positive electrode active material layer located in the edge region gradually decreases.

[0031] By setting the thickness to gradually decrease, the problem of bulging and cracking at the edge of the positive electrode can be further alleviated.

[0032] In some embodiments, the volume expansion ratio a of the first positive electrode active material is ≤2%, and the volume expansion ratio b of the second positive electrode active material is ≥2%.

[0033] By reasonably matching the volume expansion rates of the first positive electrode active material and the second positive electrode active material, the thickness difference between the main area and the edge area can be effectively reduced during charging, thereby alleviating the problem of easy lithium deposition in the edge area of ​​the negative electrode sheet corresponding to the positive electrode sheet.

[0034] In some embodiments, the first positive electrode active material includes an olivine structure phosphate material, and the second positive electrode active material includes a layered transition metal oxide.

[0035] By combining the two positive electrode active materials, the battery can effectively achieve both high safety performance and high energy density.

[0036] In some embodiments, the layered transition metal oxide comprises LiCoO 2 、LiMnO 2 、LiNiO 2 , Li a Ni x Coy M1 1-x-y O 2+d , z Li 2 MnO 3 · (1-z) LiM2O 2 At least one of the following, wherein M1 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, and M2 includes at least one of Co, Ni, and Mn, 0.5≤x≤1.0, 0≤y<0.5, x+y<1, 0.2≤a<1.2, -0.02≤d<0.02, and 0<z<1.

[0037] Optionally, the layered transition metal oxide includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium-rich material, nickel-cobalt-manganese ternary material and manganese-cobalt-aluminum ternary material. The first positive electrode active material has small volume expansion, high lattice stability, good service life, and can improve the safety performance of the battery.

[0038] In some embodiments, the olivine structure phosphate material includes Li a Fe b M 1-b P 1-m O 4-n , wherein M includes at least one of other metal elements except Fe, wherein 0<a≤1.1, 0≤b≤1, 0≤m≤0.1, 0≤n≤0.1.

[0039] Optionally, M includes at least one of Mn, Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge.

[0040] Optionally, the olivine structure phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0041] The second positive electrode active material has a large volume expansion rate, a high gram capacity, and a high voltage platform, and can improve the energy density of the battery.

[0042] In a second aspect, the present application provides a battery, which includes the positive electrode plate in the above embodiment.

[0043] In a third aspect, the present application provides an electrical device, which includes the battery in the above embodiment, and the battery is used to provide electrical energy.

[0044] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0046] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0047] Figure 2 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0048] Figure 3 A schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

[0049] Figure 4 A schematic diagram of the structure of a stacked electrode assembly in some embodiments of the present application;

[0050] Figure 5 This is a schematic diagram of the structure of the positive electrode sheet of some embodiments of the present application;

[0051] Figure 6 This is a schematic diagram of the positive electrode structure of some embodiments of the present application;

[0052] Figure 7 This is a schematic diagram of the positive electrode structure of Comparative Example 2.

[0053] The reference numerals in the specific implementation manner are as follows:

[0054] 1000-Vehicles;

[0055] 100-battery; 200-controller; 300-motor;

[0056] 10-box; 11-first part; 12-second part;

[0057] 20 - battery cell; 21 - end cap; 21a - electrode terminal; 22 - housing; 23 - electrode assembly;

[0058] 30 - diaphragm;

[0059] 40-negative electrode plate; 41-negative electrode current collector; 42-negative electrode active material layer;

[0060] 50 - positive electrode sheet; 51 - positive electrode current collector; 52 - positive electrode active material layer; 521 - main body region; 523 - edge region; 53 - first positive electrode active material layer; 54 - second positive electrode active material layer. DETAILED DESCRIPTION

[0061] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0063] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0064] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0065] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0066] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0067] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0068] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0069] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0070] In order to avoid bulging and cracking of the edge of the pole piece, the edge thinning process is used during the pole piece coating process, so that the final pole piece has a thinned area. Since the thinned areas of the positive and negative electrodes exist at the same time in the battery, lithium deposition is likely to occur in the thinned area of ​​the negative pole piece during the battery cycle, causing capacity decay and bringing great safety risks.

[0071] In order to alleviate the problem of capacity attenuation caused by lithium deposition in the thinned area of ​​the negative electrode plate, resulting in large battery capacity attenuation and poor safety after multiple cycles, the present application adopts a positive electrode active material layer including a main area and an edge area, the thickness of the positive electrode active material layer in the edge area is less than the thickness of the main area, the positive electrode active material layer is thinned in the edge area, and the problem of cracking and bulging at the edge of the positive electrode plate is reduced. On this basis, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, the volume expansion rate of the first positive electrode active material is less than the volume expansion rate of the second positive electrode active material, the mass percentage of the second positive electrode active material in the edge area is greater than the mass percentage of the second positive electrode active material in the main area, and the volume expansion rate of the edge area is increased, thereby reducing the thickness difference between the main area and the edge area during charging, reducing the distance between the edge area of ​​the positive electrode plate and the edge area of ​​the negative electrode plate, reducing polarization, and then alleviating the problem of easy lithium deposition in the edge area of ​​the negative electrode plate corresponding to the positive electrode plate, thereby improving the capacity retention rate and safety of the battery after multiple cycles.

[0072] The battery cell disclosed in the embodiment of the present application can be used, but not limited to, in electric devices such as vehicles, ships or aircraft. A power supply system comprising the battery cell, battery, etc. disclosed in the present application can be used to form the electric device, which is helpful to alleviate the problem of easy lithium deposition in the edge area of ​​the negative electrode corresponding to the positive electrode, improve the capacity retention rate and safety of the battery after multiple cycles, and improve the stability of battery performance and battery life.

[0073] The embodiment of the present application provides an electric device using a battery as a power source, and the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0074] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0075] Please refer to Figure 1 , Figure 1A schematic diagram of the structure of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery 100 may be used to power the vehicle 1000, for example, the battery 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, and the controller 200 is used to control the battery 100 to power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

[0076] In some embodiments of the present application, the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0077] In the present application, the battery 100 refers to a single physical module including one or more battery cells 20 to provide a certain voltage and capacity, which may be in the form of a battery pack, a battery module, etc. The battery 100 may also include a box 10 for encapsulating one or more battery cells 20, and the box 10 may prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0078] Please refer to Figure 2 , Figure 2 An exploded view of a battery 100 provided in some embodiments of the present application. The battery 100 includes a box 10 and a battery cell 20, and the battery cell 20 is contained in the box 10. Among them, the box 10 is used to provide a storage space for the battery cell 20, and the box 10 can adopt a variety of structures. In some embodiments, the box 10 may include a first part 11 and a second part 12, the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a storage space for accommodating the battery cell 20. The second part 12 may be a hollow structure with one end open, the first part 11 may be a plate-like structure, and the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define a storage space; the first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12. Of course, the box 10 formed by the first part 11 and the second part 12 may be in a variety of shapes, such as a cylinder, a cuboid, etc.

[0079] In the battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple battery cells 20 are both connected in series and in parallel. The multiple battery cells 20 may be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10; of course, the battery 100 may also be a battery module formed by connecting multiple battery cells 20 in series, in parallel, or in a mixed connection, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The battery 100 may also include other structures, for example, the battery 100 may also include a busbar component for realizing electrical connection between the multiple battery cells 20.

[0080] Each battery cell 20 may be a secondary battery or a primary battery. The battery cell 20 may be cylindrical, flat, rectangular or in other shapes.

[0081] Please refer to Figure 3 , Figure 3 The schematic diagram of the exploded structure of the battery cell 20 provided in some embodiments of the present application. The battery cell 20 refers to the smallest unit that constitutes the battery. Figure 3 The battery cell 20 includes an end cover 21, a shell 22, an electrode assembly 23 and other functional components.

[0082] The end cap 21 refers to a component that covers the opening of the shell 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the shell 22 to match the shell 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 21 is not easily deformed when squeezed and collided, so that the battery cell 20 can have a higher structural strength and the safety performance can also be improved. Functional components such as electrode terminals 21a can be provided on the end cap 21. The electrode terminal 21a can be used to electrically connect to the electrode assembly 23 for outputting or inputting electrical energy of the battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The material of the end cap 21 can also be a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not impose special restrictions on this. In some embodiments, an insulating member may be provided inside the end cap 21, and the insulating member may be used to isolate the electrical connection components in the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, or the like.

[0083] The shell 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20, wherein the formed internal environment can be used to accommodate the electrode assembly 23, the electrolyte and other components. The shell 22 and the end cap 21 can be independent components, and an opening can be set on the shell 22, and the internal environment of the battery cell 20 is formed by covering the opening with the end cap 21 at the opening. Without limitation, the end cap 21 and the shell 22 can also be integrated. Specifically, the end cap 21 and the shell 22 can form a common connection surface before other components are put into the shell, and when the interior of the shell 22 needs to be encapsulated, the end cap 21 covers the shell 22. The shell 22 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0084] The electrode assembly 23 is a component where an electrochemical reaction occurs in the battery cell 20. One or more electrode assemblies 23 may be contained in the housing 22.

[0085] like Figure 4 As shown, the electrode assembly 23 is mainly formed by winding or stacking the positive electrode sheet 50 and the negative electrode sheet 40, and a separator 30 is usually provided between the positive electrode sheet 50 and the negative electrode sheet 40. The parts of the positive electrode sheet 50 and the negative electrode sheet 40 with active materials constitute the main body of the electrode assembly 23, and the parts of the positive electrode sheet 50 and the negative electrode sheet 40 without active materials each constitute a tab. The positive electrode tab and the negative electrode tab can be located together at one end of the main body or at both ends of the main body respectively. During the charge and discharge process of the battery 100, the positive electrode active material and the negative electrode active material react with the electrolyte, and the tab is connected to the electrode terminal 21a to form a current loop.

[0086] like Figure 4 As shown, the negative electrode plate 40 includes a negative electrode current collector 41 and a negative electrode active material layer 42 disposed on the negative electrode current collector 41 . The negative electrode active material layer 42 includes a main region 521 and an edge thinning region. The thickness of the negative electrode active material layer 42 in the edge thinning region is less than the thickness of the main region 521 .

[0087] The edge region 523 of the negative electrode active material layer 42 refers to the region from the thickness inflection point of the negative electrode active material layer 42 to the edge of the negative electrode active material. The thickness can be measured by laser measurement or by using a micrometer.

[0088] The negative electrode active material layer 42 refers to the film layer containing the negative electrode active material for reacting with the electrolyte during the charge and discharge process of the battery 100. In addition to the negative electrode active material, the negative electrode active material layer 42 may also generally contain a binder and a conductive agent. As an example, the negative electrode active material includes at least one of graphite, silicon-based materials, tin-based materials, and hard carbon, and the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] The negative electrode current collector 41 may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] See also Figure 5 as well as Figure 6 According to some embodiments of the present application, the positive electrode plate 50 includes a positive electrode collector 51, and a positive electrode active material layer 52 arranged on the positive electrode collector 51, the positive electrode active material layer 52 includes a main area 521 and an edge area 523, the thickness of the positive electrode active material layer 52 in the edge area 523 is less than the thickness of the main area 521; the positive electrode active material layer 52 includes a first positive electrode active material and a second positive electrode active material, the volume expansion rate of the first positive electrode active material is less than the volume expansion rate of the second positive electrode active material, and the mass percentage of the second positive electrode active material in the edge area 523 is greater than the mass percentage of the second positive electrode active material in the main area 521.

[0091] in, Figure 5 as well as Figure 6 The main area 521 and the edge area 523 are divided by a dotted line. Figure 6 The first positive electrode active material layer 53 exists only in the main body region 521 .

[0092] The positive electrode current collector 51 may be a metal foil or a composite current collector. For example, as the metal foil, copper foil or aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0093] The positive electrode active material layer 52 refers to the film layer containing the positive electrode active material for reacting with the electrolyte during the charge and discharge process of the battery 100. In addition to the positive electrode active material, the positive electrode active material layer 52 may also generally contain a binder and a conductive agent. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0094] The edge region 523 of the positive electrode active material layer 52 refers to the region from the thickness inflection point of the positive electrode active material layer 52 to the edge of the positive electrode active material. The thickness of the positive electrode active material layer 52 in the edge region 523 is less than the thickness of the main region 521, that is, the edge region 523 of the positive electrode active material layer 52 is a thinned region.

[0095] In the technical solution of the embodiment of the present application, the thickness of the edge area 523 is smaller than the thickness of the main area 521 to alleviate the problem of edge bulging and cracking during the drying process of the positive electrode plate 50. The volume expansion rate of the first positive electrode active material is smaller than the volume expansion rate of the second positive electrode active material, and the mass percentage of the second positive electrode active material in the edge area 523 is greater than the mass percentage of the second positive electrode active material in the main area 521. The volume expansion rate of the positive electrode active material in the edge area 523 is increased, thereby reducing the thickness difference between the main area 521 and the edge area 523 during charging, reducing the distance between the edge area 523 of the positive electrode plate 50 and the edge area 523 of the negative electrode plate 40, reducing polarization, and thereby alleviating the problem of easy lithium deposition in the edge area 523 of the negative electrode plate 40 corresponding to the positive electrode plate 50, thereby improving the capacity retention rate and safety of the battery 100 after multiple cycles.

[0096] The positive electrode current collector 51 has two side surfaces that are arranged opposite to each other along the thickness direction. The positive electrode active material layer 52 may be arranged on at least one side surface of the positive electrode current collector 51 .

[0097] Optionally, the positive electrode active material layer 52 is disposed on both sides of the positive electrode current collector 51, and in this case, the positive electrode plate 50 has a central plane symmetrical structure in the thickness direction of the positive electrode current collector 51. The above arrangement is helpful to alleviate the problem of easy lithium deposition in the edge area 523 of the negative electrode plate 40 corresponding to the positive electrode plate 50.

[0098] According to some embodiments of the present application, the mass percentage of the second positive electrode active material in the main region 521 is 20% to 70%, and the mass percentage of the second positive electrode active material in the edge region 523 is 50% to 100%.

[0099] Within the above range, it is beneficial to improve the capacity retention rate and safety of the battery 100 after multiple cycles.

[0100] Exemplarily, the mass percentage of the second positive electrode active material in the edge region 523 is any value of 50%, 60%, 70%, 80%, 90%, 100%, or between any two values.

[0101] Optionally, the mass percentage of the second positive electrode active material in the edge region 523 is 80% to 100%.

[0102] Optionally, the first positive electrode active material and the second positive electrode active material may be directly physically mixed to form a positive electrode active material layer 52 .

[0103] See also Figure 5 as well as Figure 6 According to some embodiments of the present application, the positive electrode active material layer 52 includes a first positive electrode active material layer 53 and a second positive electrode active material layer 54 , the first positive electrode active material layer 53 includes a first positive electrode active material, and the second positive electrode active material layer 54 includes a second positive electrode active material.

[0104] It should be noted that the first positive electrode active material layer 53 includes the first positive electrode active material but does not contain the second positive electrode active material, and the second positive electrode active material layer 54 includes the second positive electrode active material but does not contain the first positive electrode active material.

[0105] That is, in the process of slow lithium release, the double-layer coating structure of the two positive electrode active materials is utilized to reduce the mixing amount between the two positive electrode active materials, reduce the probability of the performance of the two positive electrode active materials affecting each other and causing deterioration, improve the problem of early cycle attenuation, and enhance the stability of the performance of the battery 100 and the life of the battery 100.

[0106] Among them, the first positive electrode active material layer 53 can be arranged between the second positive electrode active material layer 54 and the positive electrode collector 51, or it can be arranged on the side of the second positive electrode active material layer 54 away from the positive electrode collector 51, so that the second positive electrode active material layer 54 can be arranged between the first positive electrode active material layer 53 and the positive electrode collector 51.

[0107] See also Figure 5 as well as Figure 6 In some optional examples, the first positive electrode active material layer 53 is disposed between the second positive electrode active material layer 54 and the positive electrode current collector 51 .

[0108] Since the volume expansion rate of the first positive electrode active material is smaller than the volume expansion rate of the second positive electrode active material, the above arrangement is conducive to the expansion of the edge area 523, reducing the distance between the edge area 523 of the positive electrode sheet 50 and the edge area 523 of the negative electrode sheet 40, thereby improving the capacity retention rate and safety of the battery 100 after multiple cycles.

[0109] According to some embodiments of the present application, the first positive electrode active material layer 53 includes 90% to 98.5% wt of the first positive electrode active material, and the second positive electrode active material layer 54 includes

[0110] 90% to 98.5% wt of the second positive electrode active material; the thickness of the first positive electrode active material layer 53 in the main area 521 is h1, h1>0, and the thickness of the first positive electrode active material layer 53 at 1 / 2 of the edge area 523 is h1', h1>h1'≥0; the thickness of the second positive electrode active material layer 54 in the main area 521 is h2, h2>0; the thickness of the second positive electrode active material layer 54 at 1 / 2 of the edge area 523 is h2', h2'>1 / 2(h2+h1).

[0111] The thickness at 1 / 2 of the edge region 523 refers to: on the current collector, the distance from one end of the edge region 523 close to the main region 521 to the end away from the main region 521 is Y, and 1 / 2Y from the end of the edge region 523 close to the main region 521 to the end away from the main region 521 is taken as 1 / 2 of the edge region 523. The thickness of the edge region 523 at 1 / 2Y can be measured by laser measurement or by using a micrometer.

[0112] By utilizing the fact that the mass contents of the first active material contained in the first positive electrode active material layer 53 and the second active material contained in the second positive electrode active material layer 54 are substantially the same, and the thickness of the second positive electrode active material layer 54 at 1 / 2 of the edge region 523 is greater than 1 / 2 (h2+h1), thereby increasing the volume expansion rate of the positive electrode active material in the edge region 523 compared to that in the main region 521, thereby reducing the thickness difference between the main region 521 and the edge region 523 during charging, reducing the distance between the edge region 523 of the positive electrode sheet 50 and the edge region 523 of the negative electrode sheet 40, reducing polarization, and thereby alleviating the problem of easy lithium deposition in the edge region 523 of the negative electrode sheet 40 corresponding to the positive electrode sheet 50, thereby improving the capacity retention rate and safety of the battery 100 after multiple cycles.

[0113] As an example, by mass percentage, the first positive electrode active material layer 53 includes 90% to 98.5% wt of the first positive electrode active material, 0.1% to 5% wt of the conductive agent, and 1% to 5% wt of the binder, and the second positive electrode active material layer 54 includes 90% to 98.5% wt of the second positive electrode active material, 0.1% to 5% wt of the conductive agent, and 1% to 5% wt of the binder.

[0114] Optionally, the mass percentage of the first positive electrode active material in the first positive electrode active material layer 53 is the same as the mass percentage of the second positive electrode active material in the second positive electrode active material layer 54. In this case, it is advantageous to directly adjust the mass percentage of the second positive electrode active material in the positive electrode active material layer 52 in the edge region 523 and the mass percentage of the second positive electrode active material in the positive electrode active material layer 52 in the main region 521 by thickness.

[0115] See also Figure 5 According to some embodiments of the present application, h1>h1'>0, and h2'≥h2.

[0116] That is, there is a first positive electrode active material layer 53 in the edge region 523, and the thickness of the first positive electrode active material layer 53 at 1 / 2 of the edge region 523 is thinner than the thickness of the first active material layer in the main region 521. At this time, h2'≥h2 is used to make the thickness of the second active material layer at 1 / 2 of the edge region 523 thicker than the thickness of the second active material layer in the main region 521, thereby increasing the volume expansion rate of the edge region 523 compared with the main region 521, thereby alleviating the problem of easy lithium deposition in the edge region 523 of the negative electrode plate 40, thereby improving the capacity retention rate and safety of the battery 100 after multiple cycles.

[0117] See also Figure 6 According to some embodiments of the present application, h1′=0, 0.5≤h2′ / (h2+h1)<1.

[0118] By using h1'=0, that is, removing the first positive electrode active material layer 53 located in the edge area 523, so that the edge area 523 is entirely the second positive electrode active material layer 54, at this time 0.5≤h2' / (h2+h1)<1, that is, the thickness of the positive electrode active material layer 52 at 1 / 2 of the edge area 523 is less than the thickness of the main area 521 and is 0.5 times or more of the thickness of the main area 521, which not only facilitates the production and reduces the difficulty of producing the positive electrode plate 50, but also alleviates the problem of easy lithium deposition in the edge area 523 of the negative electrode plate 40.

[0119] Exemplarily, h2' / (h2+h1) is any value of 0.5, 0.6, 0.8, 0.9, 0.99, or between any two values.

[0120] Optionally, h2′ / (h2+h1)=0.5-0.8. Within this range, the problem of easy lithium deposition in the edge area 523 of the negative electrode plate 40 can be effectively solved, and the bulging and cracking of the edge of the positive electrode plate 50 can be effectively alleviated.

[0121] According to some embodiments of the present application, the thickness of the first positive electrode active material layer 53 in the main region 521 is h1, where h1=40-210 μm.

[0122] Within the above thickness range, the battery 100 has high energy density and high safety performance.

[0123] Illustratively, the thickness of the main region 521 of the first positive active material layer 53 is any value of 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 150 μm, 160 μm, 180 μm, 200 μm, 210 μm, or between any two values.

[0124] According to some embodiments of the present application, the thickness of the second positive electrode active material layer 54 in the main region 521 is h2, where h1-h2=-40-180 μm.

[0125] By controlling the thickness difference between the above active materials, the problem of easy lithium deposition in the edge area 523 of the negative electrode sheet 40 corresponding to the positive electrode sheet 50 is alleviated, thereby improving the capacity retention rate and safety of the battery 100 after multiple cycles.

[0126] Illustratively, h1-h2=any value among -40 μm, -20 μm, 0 μm, 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 or between any two values.

[0127] Optionally, h1-h2=-20~120μm.

[0128] In some embodiments, the difference in volume expansion rate between the first positive active material layer 53 and the second positive active material layer 54 is 1% to 10%.

[0129] Within the above range, the thickness difference between the main area 521 and the edge area 523 can be effectively reduced during charging, thereby alleviating the problem of easy lithium deposition in the edge area 523 of the negative electrode sheet 40 corresponding to the positive electrode sheet 50 .

[0130] According to some embodiments of the present application, the difference between the volume expansion rates of the first positive electrode active material layer 53 and the second positive electrode active material layer 54 is 1% to 10%.

[0131] The test method of the volume expansion rate of the positive electrode active material layer 52 includes: assembling the positive electrode sheet 50 with the positive electrode active material layer 52 into a battery 100, using the state of charge (SOC) of the battery 100 to represent the available state of the remaining charge in the battery 100, and when SOC=0, it means that the battery 100 is completely discharged and is in an empty state, and when SOC=1, it means that the battery 100 is fully charged and is in a fully charged state, and the thickness of the positive electrode active material layer 52 in the empty state is obtained as H1, and the thickness of the positive electrode active material layer 52 in the fully charged state is obtained as H2, and the volume expansion rate of the positive electrode active material=(H2-H1)

[0132] / H2×100%.

[0133] Within the above range, the thickness difference between the main area 521 and the edge area 523 can be effectively reduced during charging, thereby alleviating the problem of easy lithium deposition in the edge area 523 of the negative electrode sheet 40 corresponding to the positive electrode sheet 50 .

[0134] See also Figure 6 According to some embodiments of the present application, a straight-line distance from one end of the edge region close to the main region 521 to the other end away from the main region 521 is L, and L≤10 mm.

[0135] Within the above-mentioned size range, the bulging and cracking of the edge of the positive electrode plate 50 can be alleviated while ensuring that the capacity of the battery 100 meets the requirements.

[0136] Exemplarily, L is any value of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or between any two values.

[0137] Optionally, L is 2 to 8 mm.

[0138] In the direction from the main region 521 to the edge region 523 , the thickness of the positive electrode active material layer 52 located in the edge region 523 may decrease gradually.

[0139] See also Figure 5 as well as Figure 6 According to some embodiments of the present application, along the direction from the main region 521 to the edge region 523 , the thickness of the positive electrode active material layer 52 located in the edge region 523 gradually decreases.

[0140] By setting the thickness to gradually decrease, the surface of the positive electrode active material layer 52 located in the edge area 523 can be smoothly transitioned, which can further alleviate the problem of bulging and cracking at the edge of the positive electrode sheet 50.

[0141] According to some embodiments of the present application, the volume expansion rate a of the first positive electrode active material is ≤2%, and the volume expansion rate b of the second positive electrode active material is ≥2%.

[0142] By reasonably matching the volume expansion rates of the first positive electrode active material and the second positive electrode active material, the thickness difference between the main area and the edge area can be effectively reduced during charging, thereby alleviating the problem of easy lithium deposition in the edge area of ​​the negative electrode sheet corresponding to the positive electrode sheet.

[0143] Exemplarily, the volume expansion rate a of the first positive electrode active material is any value among 0.5%, 1.0%, 1.3%, 1.5%, 1.7%, 2% or between any two values, and the volume expansion rate b of the second positive electrode active material is any value among 2%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. or between any two values.

[0144] According to some embodiments of the present application, the first positive electrode active material includes an olivine structure phosphate material, and the second positive electrode active material includes a layered transition metal oxide.

[0145] By combining the two positive electrode active materials, the battery can effectively achieve both high safety performance and high energy density.

[0146] When the first positive electrode active material and the second positive electrode active material are layered and coated with the second positive electrode active material on the surface, the transmission path of lithium ions can be effectively reduced, so that the battery has both high safety performance and high energy density.

[0147] According to some embodiments of the present application, the layered transition metal oxide includes LiCoO 2 、LiMnO 2 、LiNiO 2 , Li a Ni x Co y M1 1-x-y O 2+d , z Li 2 MnO 3 · (1-z) LiM2O2 At least one of the following, wherein M1 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, and M2 includes at least one of Co, Ni, and Mn, 0.5≤x≤1.0, 0≤y<0.5, x+y<1, 0.2≤a<1.2, -0.02≤d<0.02, and 0<z<1.

[0148] Optionally, the layered transition metal oxide includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium-rich material, nickel-cobalt-manganese ternary material and manganese-cobalt-aluminum ternary material.

[0149] The first positive electrode active material has small volume expansion, high lattice stability, and long service life, and can improve the safety performance of the battery.

[0150] According to some embodiments of the present application, the olivine structure phosphate material includes Li a Fe b M 1-b P 1-m O 4-n , wherein M includes at least one of other metal elements except Fe, wherein 0<a≤1.1, 0≤b≤1, 0≤m≤0.1, 0≤n≤0.1.

[0151] Optionally, M includes at least one of Mn, Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge.

[0152] Optionally, the olivine structure phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0153] The second positive electrode active material has a large volume expansion rate, a high gram capacity, and a high voltage platform, and can improve the energy density of the battery.

[0154] It should be noted that the battery will be accompanied by Li deintercalation and consumption during the charging and discharging process, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode material is used in the battery system, and the molar content of Li will change after the charge and discharge cycle. In the list of positive electrode materials in this application, the molar content of O is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0155] According to some embodiments of the present application, the first positive electrode active material is lithium iron phosphate, and the second positive electrode active material is lithium nickel cobalt manganese oxide.

[0156] The combination of the above-mentioned lithium iron phosphate and lithium nickel cobalt manganese oxide can improve the problem of easy lithium deposition in the edge area of ​​the negative electrode corresponding to the positive electrode, so that the battery has high energy density and high safety performance.

[0157] According to some embodiments of the present application, the present application also provides a battery, comprising a positive electrode plate of any of the above schemes.

[0158] According to some embodiments of the present application, the present application also provides an electrical device, comprising a battery according to any of the above schemes, and the battery is used to provide electrical energy to the electrical device.

[0159] The power-consuming device may be any of the aforementioned devices or systems using batteries.

[0160] According to some embodiments of the present application, see Figures 5 and 6 The present application provides a positive electrode plate 50, which includes a positive electrode collector 51, and a positive electrode active material layer 52 arranged on the positive electrode collector 51, the positive electrode active material layer 52 includes a main area 521 and an edge area 523, the thickness of the positive electrode active material layer 52 in the edge area 523 is less than the thickness of the main area 521; the positive electrode active material layer 52 includes a first positive electrode active material layer 53 and a second positive electrode active material layer 54, the first positive electrode active material layer 53 is located on the side of the second positive electrode active material layer 54 close to the positive electrode collector 51; the first positive electrode active material layer 53 includes a first positive electrode active material, and the second positive electrode active material layer 54 includes a second positive electrode active material, the first positive electrode active material is an olivine structure phosphate material, and the second positive electrode active material is a layered transition metal oxide, the volume expansion rate of the first positive electrode active material is less than the volume expansion rate of the second positive electrode active material, and the mass percentage of the second positive electrode active material in the edge area 523 is greater than the mass percentage of the second positive electrode active material in the main area 521.

[0161] Some specific embodiments are listed below to better illustrate the present application.

[0162] Example 1

[0163]

Positive electrode sheet preparation

[0164] The first positive electrode active material slurry is prepared: the first positive electrode active material, polyvinylidene fluoride, and conductive carbon black are mixed in a weight ratio of 96:2:2, dissolved in N-methylpyrrolidone, and stirred to prepare a slurry.

[0165] Preparation of second positive electrode active material slurry: The second positive electrode active material, polyvinylidene fluoride, and conductive carbon black are mixed in a weight ratio of 96:2:2, dissolved in N-methylpyrrolidone, and stirred to prepare a slurry.

[0166] The second positive electrode active material slurry and the first positive electrode active material slurry are simultaneously coated on the current collector in two layers, upper and lower, by extrusion coating, wherein the first positive electrode active material slurry coating layer is located on the side of the second positive electrode active material slurry coating layer close to the current collector, and the edge area is subjected to a thinning process. After coating, the electrode sheet is dried and cold pressed to obtain a positive electrode sheet.

[0167]

Negative electrode sheet preparation

[0168] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose are mixed in a weight ratio of graphite: acetylene black: styrene butadiene rubber: sodium carboxymethyl cellulose = 95:2:2:1, and an appropriate amount of deionized water is added and stirred to form a uniform negative electrode slurry; after coating the slurry on the negative electrode current collector copper foil, it is dried and cold pressed to obtain a negative electrode sheet.

[0169]

Electrolyte preparation

[0170] Lithium salt LiPF was added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a mass ratio of 35:65. 6 , mix evenly to obtain an electrolyte, wherein LiPF 6 The molar concentration is 1 mol / L.

[0171]

Diaphragm

[0172] A 12 μm thick polyethylene porous membrane was selected, and the surface of the diaphragm was coated with nano-aluminum trioxide with a double-sided coating thickness of 5 μm.

[0173]

Battery preparation

[0174] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play a role of isolation, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried battery, and then the battery is obtained after vacuum packaging, standing, forming, shaping and other processes.

[0175]

Battery performance test

[0176] (1) 45℃ cycle performance test includes:

[0177] At 45°C, the lithium-ion secondary battery is first charged to 4.3V at a constant current of 1C, then further charged to a current of 0.05C at a constant voltage of 4.3V, and then discharged to 2.5V at a constant current of 1C. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The battery is subjected to multiple cycle charge and discharge tests in the above manner, and the discharge capacity of the 500th cycle is detected, and the capacity retention rate of the battery after the cycle is calculated by the following formula.

[0178] Capacity retention rate of battery after 1 cycle (%) = [discharge capacity at 500th cycle / discharge capacity at 1st cycle] × 100%.

[0179] (2) After the battery is cycled, the battery is disassembled to observe and obtain the lithium deposition morphology at the edge of the negative electrode.

[0180] The surface of the edge region that is away from the current collector and exposed to the electrolyte is taken as the surface A of the edge region, and the lithium deposition area ratio = [area of ​​lithium deposition on surface A / surface A] × 100%.

[0181] The differences between Examples 1-22 are shown in Table 1. The parameters are different, and the test results are shown in Table 1.

[0182] Among them, the structures of Examples 1-21 are as follows Figure 6 As shown, the structure of Example 22 is as follows Figure 5 shown.

[0183] Comparative Example 1

[0184] The only difference between it and Example 1 is that the second positive electrode active material slurry and the first positive electrode active material slurry are physically mixed in a mass ratio of 1:4, and the mixed slurry is coated on the current collector by extrusion coating. The edge area is thinned. After coating, the electrode sheet is dried and cold pressed to obtain the positive electrode sheet.

[0185] The difference between it and Example 2 and the test results are shown in Table 1.

[0186] Comparative Example 2

[0187] The difference between the embodiment 1 and the embodiment 1 is that: L2 of the first positive electrode active material layer is equal to L1 of the first positive electrode active material layer, and the thickness of the first positive electrode active material layer at 1 / 2 of the edge region is h1'=64 μm; the thickness of the second positive electrode active material layer at 1 / 2 of the edge region is h2'=16 μm. At this time, the structure of the positive electrode sheet prepared in the comparative example 2 is as follows: Figure 7 The specific differences and test results are shown in Table 1.

[0188] Table 1 Parameters of Examples and Comparative Examples

[0189]

[0190] In Table 1, the thickness of the first positive electrode active material layer in the main area is h1, the thickness of the first positive electrode active material layer at 1 / 2 of the edge area is h1', the length of the first positive electrode active material layer located in the edge area along the direction from the main area to the edge area is L1, the thickness of the second positive electrode active material layer in the main area is h2, the thickness of the second positive electrode active material layer at 1 / 2 of the edge area is h2', and the length of the second positive electrode active material layer located in the edge area along the direction from the main area to the edge area is L2, the above thickness units are μm, and the length units of L1 and L2 are mm.

[0191] Table 2 Test results

[0192]

[0193]

[0194] According to Table 1 and Table 2, it can be seen that the positive electrode plate provided in the present application can improve the problem of lithium deposition in the negative electrode plate with a thinned area after multiple cycles, large battery capacity attenuation and poor safety.

[0195] According to Example 1 and Comparative Example 1, since Comparative Example 1 directly uses the same slurry to coat the edge area and the main area, the mass percentage of the second positive electrode active material in the edge area is the same as the mass percentage of the second positive electrode active material in the main area. Therefore, the corresponding negative electrode plate with a thinned area deposits lithium after multiple cycles, and the battery capacity decays significantly, which cannot solve the technical problem of the present application.

[0196] According to Example 1 and Comparative Example 2, although Comparative Example 2 is layered and the phase change between the first positive electrode active material and the second positive electrode active material is reduced to a certain extent, the thickness of the first positive electrode active material layer at 1 / 2 of the edge area is h1'=64μm; the thickness of the second positive electrode active material layer at 1 / 2 of the edge area is h2'=16μm, resulting in the mass percentage of the second positive electrode active material in the edge area 523 being less than the mass percentage of the second positive electrode active material in the main area 521, and the technical problem of the present application cannot be solved.

[0197] According to Examples 1 to 14, h1=40 to 210 μm, h1-h2=-40 to 180 μm, and further when h1-h2=-20 to 120 μm, the capacity retention rate of the battery after 500 cycles at 45°C is high, and the lithium plating area is effectively reduced.

[0198] According to Examples 1 and 15 to 17, the thickness of the second positive electrode active material layer at 1 / 2 of the edge region has an influence on the cycle retention rate and lithium plating. When h2'>1 / 2(h2+h1) and 0.5≤h2' / (h2+h1)<1, the capacity retention rate of the battery after 500 cycles at 45°C is high, and the lithium plating area is effectively reduced.

[0199] According to Examples 1, 18 to 20, it can be seen that the length L1 of the first positive electrode active material layer in the edge region has an influence on the cycle retention rate and lithium plating. In the range of L1≤10 mm, the cycle retention rate is good and lithium plating is effectively suppressed, thereby improving battery life and safety performance.

[0200] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer comprises a main body region and an edge region, and the thickness of the positive electrode active material layer in the edge region is less than the thickness of the main body region; The positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, the volume expansion rate of the first positive electrode active material is smaller than the volume expansion rate of the second positive electrode active material, and the mass percentage of the second positive electrode active material in the edge region is greater than the mass percentage of the second positive electrode active material in the main region.

2. The positive electrode sheet according to claim 1, characterized in that: The mass percentage of the second positive electrode active material in the main region is 20% to 70%, and the mass percentage of the second positive electrode active material in the edge region is 50% to 100%, and can be optionally 80% to 100%.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer includes a first positive electrode active material, and the second positive electrode active material layer includes a second positive electrode active material; Optionally, the first positive electrode active material layer is disposed between the second positive electrode active material layer and the positive electrode current collector.

4. The positive electrode sheet according to claim 3, characterized in that: The first positive electrode active material layer comprises 90% to 98.5% by weight of the first positive electrode active material, and the second positive electrode active material layer comprises 90% to 98.5% by weight of the second positive electrode active material; The thickness of the first positive electrode active material layer in the main area is h1, h1>0, the thickness of the first positive electrode active material layer at 1 / 2 of the edge area is h1', h1>h1'≥0; the thickness of the second positive electrode active material layer in the main area is h2, h2>0; the thickness of the second positive electrode active material layer at 1 / 2 of the edge area is h2', h2'>1 / 2(h2+h1).

5. The positive electrode sheet according to claim 4, characterized in that: h1>h1'>0, and h2'≥h2.

6. The positive electrode sheet according to claim 4, characterized in that: h1′=0, 0.5≤h2′ / (h2+h1)<1, optionally, h2′ / (h2+h1)=0.5~0.

8.

7. The positive electrode sheet according to claim 3, characterized in that: The thickness of the first positive electrode active material layer in the main body region is h1, where h1=40-210 μm.

8. The positive electrode sheet according to claim 7, characterized in that: The thickness of the second positive electrode active material layer in the main body region is h2, where h1-h2=-40 to 180 μm; Optionally, h1-h2=-20~120μm.

9. The positive electrode sheet according to any one of claims 3 to 8, characterized in that: The difference in volume expansion rate between the first positive electrode active material layer and the second positive electrode active material layer is 1% to 10%.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: A straight-line distance from one end of the edge region close to the main region to one end away from the main region is L, where L≤10 mm; optionally, L is 2-8 mm.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: Along the direction from the main region to the edge region, the thickness of the positive electrode active material layer located in the edge region gradually decreases.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The volume expansion rate a of the first positive electrode active material is ≤2%, and the volume expansion rate b of the second positive electrode active material is ≥2%.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The first positive electrode active material includes an olivine structure phosphate material, and the second positive electrode active material includes a layered transition metal oxide.

14. The positive electrode sheet according to claim 13, characterized in that: The layered transition metal oxides include LiCoO2, LiMnO2, LiNiO2, Li a Ni x Co y M1 1-x-y O 2+d , z Li2MnO3 (1-z) At least one of LiM2O2, wherein M1 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, and M2 includes at least one of Co, Ni, and Mn, 0.5≤x≤1.0, 0≤y<0.5, x+y<1, 0.2≤a<1.2, -0.02≤d<0.02, and 0<z<1; Optionally, the layered transition metal oxide includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium-rich material, nickel-cobalt-manganese ternary material and manganese-cobalt-aluminum ternary material.

15. The positive electrode sheet according to claim 13, characterized in that: The olivine structure phosphate material includes Li a Fe b M 1-b P 1-m O 4-n , wherein M includes at least one of other metal elements except Fe, wherein 0<a≤1.1, 0≤b≤1, 0≤m≤0.1, 0≤n≤0.1; Optionally, M includes at least one of Mn, Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge; Optionally, the olivine structure phosphate material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

16. A battery, characterized in that: It comprises the positive electrode sheet as described in any one of claims 1 to 15.

17. An electrical equipment, characterized in that: Comprising a battery as claimed in claim 16, the battery is used to provide electrical energy.

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