Positive electrode sheet, battery, and electric device

Abstract

A positive electrode sheet, a battery, and an electric device, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer, the positive electrode current collector and the positive electrode active material layer being distributed along a thickness direction of the positive electrode sheet; a plurality of specified regions at different positions in the positive electrode active material layer of the positive electrode sheet, along the thickness direction of the positive electrode sheet, 50 μm ≤ thickness of the specified region < thickness of the positive electrode active material layer, satisfying: in the two specified regions distributed along the thickness direction of the positive electrode sheet, a tortuosity of the specified region on a side away from the positive electrode current collector is T 外 , a tortuosity of the specified region on a side close to the positive electrode current collector is T 内 , and T 外 > T 内 . In the positive electrode sheet, the tortuosity of the outer specified region is greater than the tortuosity of the inner specified region, so that the inner specified region has better seepage performance, which is conducive to the infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer, thereby being able to improve the electrolyte infiltration performance of the positive electrode active material layer and being conducive to improving the rate performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode sheet, a battery and an electric device. BACKGROUND

[0002] With the increase of the requirement of energy density, some technical solutions propose to prepare thick electrodes, that is, to increase the thickness of the active material layer. The electrolyte infiltration performance of the positive electrode sheet is a factor affecting the performance of the battery. However, with the increase of the thickness of the positive active material layer, the difficulty of the electrolyte penetrating the positive active material layer increases, which easily affects the rate performance due to incomplete electrolyte infiltration. SUMMARY

[0003] In view of the above problems, the present application provides a positive electrode sheet, a battery and an electric device, which can improve the electrolyte infiltration performance of the positive active material layer, thereby facilitating the improvement of the rate performance.

[0004] The embodiments of the present application are implemented as follows:

[0005] In a first aspect, the embodiments of the present application provide a positive electrode sheet, which comprises a positive current collector and a positive active material layer, and the positive current collector and the positive active material layer are distributed along the thickness direction of the positive electrode sheet; wherein a plurality of specified regions at different positions of the positive active material layer satisfy 50 μm ≤ thickness of the specified region < thickness of the positive active material layer along the thickness direction of the positive electrode sheet, and meet: along the thickness direction of the positive electrode sheet, the tortuosity of the specified region on the side far from the positive current collector in the two specified regions is T 外 , the tortuosity of the specified region on the side close to the positive current collector is T 内 , and T 外 > T 内 .

[0006] In the technical solution of the embodiments of the present application, the tortuosity of the outer specified region is greater than that of the inner specified region with respect to the position of the positive current collector, so that the inner specified region has better seepage performance, which is conducive to the infiltration of the electrolyte from the outside to the inside of the positive active material layer, can improve the liquid absorption rate and the liquid absorption amount of the positive active material layer, thereby improving the electrolyte infiltration performance of the positive active material layer and facilitating the improvement of the rate performance.

[0007] In some embodiments, T 外 / T 内 = 1.07-1.24; optionally, T 外 / T 内 = 1.09-1.17; optionally, T 外 / T 内 = 1.09-1.16.

[0008] In these embodiments, the outer side and the inner side maintain a certain tortuosity ratio relative to the position of the positive electrode current collector, the seepage performance of the specified area of the inner side relative to the specified area of the outer side is improved to a certain extent, and the electrolyte is better infiltrated from the outside to the inside of the positive electrode active material layer.

[0009] In some embodiments, at least one of the following conditions (a1) to (a3) is met: (a1) the tortuosity of the specified area at the first position is T 表 , the first position is located at the side of the positive electrode active material layer away from the positive electrode current collector, 1.60≤T 表 ≤2.05; optionally, 1.70≤T 表 ≤1.75; (a2) the tortuosity of the specified area at the second position is T 中 , the second position passes through the midpoint of the thickness of the positive electrode active material layer, 1.50≤T 中 ≤1.65; optionally, 1.50≤T 中 ≤1.55; (a3) the tortuosity of the specified area at the third position is T 底 , the third position is located at the side of the positive electrode active material layer close to the positive electrode current collector; 1.30≤T 底 ≤1.55; optionally, 1.30≤T 底 ≤1.35.

[0010] In these embodiments, the surface, the middle and the bottom of the positive electrode active material layer have a smaller tortuosity, which is conducive to the electrolyte to infiltrate more quickly at the surface, the middle and the bottom of the positive electrode active material layer; the tortuosity of the surface, the middle and the bottom of the positive electrode active material layer gradually decreases with a suitable gradient, which is conducive to the electrolyte to infiltrate from the outside to the inside of the positive electrode active material layer.

[0011] In some embodiments, the tortuosity of the positive electrode active material layer as a whole is T 总 , 1.45≤T 总 ≤1.75; optionally, 1.50≤T 总 ≤1.70.

[0012] In these embodiments, the positive electrode active material layer as a whole has a smaller tortuosity, and the tortuosity close to 1 indicates that the transmission channel in the positive electrode active material layer extends in the thickness direction of the positive electrode tab, which is conducive to the electrolyte to infiltrate more quickly in the positive electrode active material layer as a whole.

[0013] In some embodiments, the positive electrode active material layer includes a positive electrode active material; among the two specified areas distributed in the thickness direction of the positive electrode tab, the mass fraction of the positive electrode active material in the specified area at the side away from the positive electrode current collector is C1 外C1 内 C1 外 C1 内 = 0.1% to 1.2%; optionally, C1 外 C1 内 = 0.1% to 1.0%.

[0014] In these embodiments, C1 外 is higher than C1 内 within a certain range, which is conducive to regulating T 外 , T 内 both meet a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive active material layer.

[0015] In some embodiments, at least one of the following conditions (b1) to (b3) is met: (b1) the positive active material mass percentage in the specified region at the first position is C1 表 , the first position is located at the side of the positive active material layer away from the positive current collector, 97.4%≤C1 表 ≤98.1%; optionally, 97.4%≤C1 表 ≤98.0%; (b2) the positive active material mass percentage in the specified region at the second position is C1 中 , the second position passes through the midpoint of the thickness of the positive active material layer, 96.7%≤C1 中 ≤97.3%; optionally, 97.1%≤C1 中 ≤97.2%; (b3) the positive active material mass percentage in the specified region at the third position is C1 底 , the third position is located at the side of the positive active material layer close to the positive current collector; 95.9%≤C1 底 ≤96.9%; optionally, 96.4%≤C1 底 ≤96.6%.

[0016] In these embodiments, the surface, the middle and the bottom of the positive active material layer have a larger positive active material mass percentage, which is conducive to providing a higher energy density; the positive active material mass percentage of the surface, the middle and the bottom of the positive active material layer gradually decreases in a suitable gradient, which is conducive to regulating T 表 , T 中 , T 底 gradually decreases in a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive active material layer.

[0017] In some embodiments, the positive active material layer includes a binder; in the two specified regions distributed along the thickness direction of the positive electrode plate, the binder mass percentage in the specified region away from the positive current collector is C2外 C2 内 C2 内 C2 外 = 0.05% to 0.8%; optionally, C2 内 C2 外 = 0.05% to 0.45%.

[0018] In these embodiments, C2 外 is lower than C2 内 is within a certain range, which is conducive to regulating C1 外 is higher than C1 内 is within a certain range, which is conducive to regulating T 外 , T 内 both meet a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive active material layer.

[0019] In some embodiments, at least one of the following conditions (c1) to (c3) is met: (c1) the binder mass fraction in the specified area at the first position is C2 表 , the first position is located at the side away from the positive current collector in the positive active material layer, 0.5% ≤ C2 表 ≤ 1.0%; optionally, 0.6% ≤ C2 表 ≤ 0.9%; (c2) the binder mass fraction in the specified area at the second position is C2 中 , the second position passes through the midpoint of the thickness of the positive active material layer, 1.0% ≤ C2 中 ≤ 1.3%; optionally, 1.0% ≤ C2 中 ≤ 1.1%; (c3) the binder mass fraction in the specified area at the third position is C2 底 , the third position is located at the side close to the positive current collector in the positive active material layer; 1.3% ≤ C2 底 ≤ 1.8%; optionally, 1.5% ≤ C2 底 ≤ 1.8%; optionally, 1.5% ≤ C2 底 ≤ 1.7%.

[0020] In these embodiments, the surface, the middle and the bottom of the positive active material layer have suitable binder mass fractions, which is conducive to providing better bonding performance; the binder mass fractions of the surface, the middle and the bottom of the positive active material layer gradually increase with a suitable gradient, which is conducive to regulating C1 表 , C1 中 , C1 底 gradually decrease with a suitable gradient, which is conducive to regulating T 表 , T 中 , T 底Gradually reducing with a proper gradient is conducive to better infiltration of the electrolyte from the outside to the inside of the positive active material layer, and is also conducive to improving the overall structural stability of the positive active material layer.

[0021] In some embodiments, the positive active material layer includes a conductive agent; in the two specified regions distributed along the thickness direction of the positive electrode tab, the mass fraction of the conductive agent in the specified region away from the positive current collector is C3 外 , and the mass fraction of the conductive agent in the specified region close to the positive current collector is C3 内 , C3 内 -C3 外 = 0.2% to 0.8%; optionally, C3 内 -C3 外 = 0.2% to 0.45%.

[0022] In these embodiments, C3 外 is lower than C3 内 within a certain range, which is conducive to regulating C1 外 higher than C1 内 within a certain range, thereby facilitating the regulation of T 外 , T 内 both meet a proper gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive active material layer.

[0023] In some embodiments, at least one of the following conditions (c1) to (c3) is met: (c1) the mass fraction of the conductive agent in the specified region at the first position is C3 表 , the first position is located away from the positive current collector in the positive active material layer, and 0.7%≤C3 表 ≤1.4%; optionally, 0.9%≤C3 表 ≤1.4%; optionally, 0.9%≤C3 表 ≤1.2%; (c2) the mass fraction of the conductive agent in the specified region at the second position is C3 中 , the second position passes through the midpoint of the thickness of the positive active material layer, and 1.1%≤C3 中 ≤1.7%; optionally, 1.2%≤C3 中 ≤1.7%; optionally, 1.2%≤C3 中 ≤1.3%; (c3) the mass fraction of the conductive agent in the specified region at the third position is C3 底 , the third position is located close to the positive current collector in the positive active material layer; 1.2%≤C3 底 ≤2.0%; optionally, 1.5%≤C3 底 ≤2.0%; optionally, 1.5%≤C3 底 ≤1.7%.

[0024] In these embodiments, the surface, the middle part and the bottom part of the positive electrode active material layer have a suitable mass ratio of the conductive agent, which is conducive to providing better conductivity; the mass ratio of the conductive agent in the surface, the middle part and the bottom part of the positive electrode active material layer gradually increases with a suitable gradient, which is conducive to regulating C1 表 , C1 中 , C1 底 gradually decreases with a suitable gradient, which is conducive to regulating T 表 , T 中 , T 底 gradually decreases with a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer.

[0025] In some embodiments, in the two specified regions distributed along the thickness direction of the positive electrode tab, the porosity of the specified region away from the positive electrode current collector is P 外 , and the porosity of the specified region close to the positive electrode current collector is P 内 , P 外 < P 内 ; optionally, (P 外 / P 内 ) x 100% = 91.4% to 96.9%.

[0026] In these embodiments, the porosity of the outer side is lower than that of the inner side with respect to the position of the positive electrode current collector, and optionally the outer side and the inner side maintain a certain porosity ratio, which is conducive to regulating T 外 , T 内 to meet a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer.

[0027] In some embodiments, at least one of the following conditions (d1) to (d3) is met: (d1) the porosity of the specified region at the first position is P 表 , the first position is located on the side away from the positive electrode current collector in the positive electrode active material layer, and 27.5% ≤ P 表 ≤ 28.3%; (d2) the porosity of the specified region at the second position is P 中 , the second position passes through the midpoint of the thickness of the positive electrode active material layer, and 29.2% ≤ P 中 ≤ 30.1%; (d3) the porosity of the specified region at the third position is P 底 , the third position is located on the side close to the positive electrode current collector in the positive electrode active material layer; and 30.6% ≤ P 底 ≤ 33.3%.

[0028] In these embodiments, the surface, the middle part and the bottom of the positive electrode active material layer have suitable porosities, which are beneficial to providing better seepage performance; the porosities of the surface, the middle part and the bottom of the positive electrode active material layer gradually increase with a suitable gradient, which is beneficial to regulating T 表 , T 中 , T 底 gradually decrease with a suitable gradient, which is beneficial to better infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer.

[0029] In some embodiments, the positive electrode active material in the positive electrode active material layer comprises one or more of lithium iron phosphate or modified lithium iron phosphate.

[0030] In these embodiments, the positive electrode active material adopts lithium iron phosphate, which is convenient for regulating the gradient distribution of the positive electrode active material in the positive electrode active material layer through the magnetic response of the lithium iron phosphate, is beneficial to realizing the gradient design of tortuosity, mass proportion of the positive electrode active material, mass proportion of the binder, mass of the conductive agent, etc., is beneficial to reducing the overall tortuosity of the positive electrode active material layer, and is also beneficial to improving the porosity and the uniformity of the material distribution in the positive electrode active material layer.

[0031] In a second aspect, the embodiments of the present application provide a battery comprising the positive electrode sheet in the above embodiments.

[0032] In a third aspect, the embodiments of the present application provide a use-electricity device comprising the battery in the above embodiments.

[0033] The above description is only a summary of the technical solutions of the embodiments of the present application, in order to more clearly understand the technical means of the present application, the embodiments can be implemented according to the content of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments, it should be understood that the following drawings only show some embodiments of the present application, therefore should not be regarded as a limitation on the scope, for those skilled in the art, without creative labor, other related drawings can also be obtained according to these drawings.

[0035] Figure 1 The structural schematic diagram of the vehicle is provided for some embodiments of the present application;

[0036] Figure 2 The exploded view of the battery is provided for some embodiments of the present application;

[0037] Figure 3 The exploded view of the battery monomer is provided for some embodiments of the present application;

[0038] Figure 4 A cross-sectional schematic view of a positive electrode tab provided for some embodiments of the present application;

[0039] Figure 5 A structural schematic view of a positive electrode tab provided for some embodiments of the present application;

[0040] Figure 6 Another structural schematic view of a positive electrode tab provided for some embodiments of the present application;

[0041] Figure 7 A microstructure schematic view of a positive electrode tab provided for some embodiments of the present application;

[0042] Figure 8 A structural schematic view of a battery cell provided for some embodiments and comparative examples of the present application;

[0043] Figure 9 A liquid absorption performance statistical chart when some embodiments and comparative examples of the present application are applied to a battery cell.

[0044] Icon:

[0045] 1000 - vehicle;

[0046] 100 - battery; 200 - controller; 300 - motor;

[0047] 10 - case; 11 - first part; 12 - second part; 13 - accommodation space;

[0048] 20 - battery cell; 21 - case; 22 - electrode assembly; 23 - electrode terminal; 24 - pressure relief structure;

[0049] 211 - case; 212 - cover; 213 - sealed space;

[0050] 221 - positive electrode tab; 2211 - positive electrode current collector; 2212 - positive electrode active material layer; 2212a - designated area; 2212b - first position; 2212c - second position; 2212d - third position; 2212e - transport channel; 222 - separator; 223 - negative electrode tab;

[0051] A - thickness direction of the positive electrode tab. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. If specific conditions are not specified in the embodiments, the conditions are performed according to conventional conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0053] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0054] 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 the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0055] 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.

[0056] In the description of the embodiments of the present application, the technical term "and / or", such as "feature 1 and / or feature 2", means that it can be "feature 1" alone, "feature 2" alone, or "feature 1" plus "feature 2". In addition, the character " / " in this paper generally indicates that the front and rear associated objects are in an "or" relationship.

[0057] In the description of the embodiments of the present application, unless otherwise stated, the meaning of "multiple" in "one or more" is two or more.

[0058] In this paper, the mention of "embodiments" means that the specific features, structures or properties described in conjunction with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment to other embodiments. The skilled person in the art explicitly and implicitly understands that the embodiments described herein can be combined with other embodiments.

[0059] In the embodiments of the present application, the same reference signs represent the same components, and for brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the height, length, width, etc. of various components in the embodiments of the present application shown in the drawings, and the overall height, length, width, etc. of the integrated device are only exemplary and should not constitute any limitation on the present application.

[0060] From the development of market situation, the application of power battery is more and more extensive. The power battery is not only applied to the energy storage power system of hydropower, thermal power, wind power and solar power station, but also widely applied to electric vehicles such as electric bicycles, electric motorcycles, electric vehicles and other electric vehicles, military equipment and aerospace and other fields. With the continuous expansion of the application field of power battery, the demand of its market is also increasing.

[0061] With the increase of the requirement of energy density, some technical solutions propose to prepare thick electrode, that is, to increase the thickness of the active material layer. However, the design of thick electrode has the following problems: 1. With the increase of the thickness of the active material layer, the coating process is not easy to dry, the bonding strength between the active material layer and the current collector is reduced, and the active material layer is easy to fall off; at the same time, the baking temperature of the pole piece is high, the binder and the conductive agent will float with the solvent, which is easy to cause the problems such as low peeling force of the active material layer, uneven distribution of conductive agent and uneven distribution of pores. 2. With the increase of the thickness of the active material layer, the difficulty of electrolyte penetrating the active material layer increases, which is easy to affect the rate performance of the battery due to incomplete wetting of the electrolyte in the active material layer; 3. The increase of the active material layer will prolong the transmission path of electrons and lithium ions, reduce the ion and electron conductivity, and cause the rate performance and cycle performance to be poor.

[0062] Among them, the electrolyte wetting performance of the positive pole piece is a factor affecting the performance of the battery. In order to improve the wetting performance, in some current research, the morphology of the transmission channel in the active material layer is changed to improve the overall wetting performance of the active material layer. For example, in some technical solutions, the magnetic material is directionally arranged in the high-nickel positive electrode slurry by alternately loading and removing the magnetic field, and the ice crystal effect is constructed to prepare a thick pole plate with hierarchical multi-dimensional through channels. However, the way of constructing the transmission channel is usually complex and has high process requirements.

[0063] Based on this, the application provides a positive pole piece. It is considered that in the process of electrolyte wetting the positive active material layer, the electrolyte wets from the outside to the inside, and the wetting speed is usually slower and more difficult as it goes to the inside. In the embodiments of the application, the positive active material layer is designed with a gradient, and the gradient control method is relatively easy to implement. Among them, by controlling the tortuosity of the outside to be greater than that of the inside, the seepage performance of the inside is better than that of the outside, so as to improve the wetting speed of the electrolyte in the inside, which is conducive to the wetting of the electrolyte from the outside to the inside of the positive active material layer, can improve the liquid absorption rate and liquid absorption amount of the positive active material layer, thereby improving the electrolyte wetting performance of the positive active material layer, and is conducive to improving the rate performance.

[0064] The battery cell provided by the embodiment of the application can be used in an electric device such as a vehicle, a ship or an aircraft, but is not limited thereto. The electric device provided by the embodiment of the application can be powered by a battery. The electric device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric automobile, a ship, a spacecraft and the like. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric automobile toy, an electric ship toy and an electric aircraft toy. The spacecraft can include an airplane, a rocket, a space shuttle and a spacecraft.

[0065] The following embodiments are described by taking a vehicle as an example for convenience of description.

[0066] Referring to Figure 1 , Figure 1 A structural schematic diagram of a vehicle 1000 is provided in some embodiments of the application. The vehicle 1000 can be a fuel automobile, a gas automobile or a new energy automobile. The new energy automobile can be a pure electric automobile, a hybrid electric automobile or a range extended automobile. The vehicle 1000 is internally provided with a battery 100. The battery 100 can be arranged at the bottom, the head or the tail of the vehicle 1000. The battery 100 can be used for power supply of the vehicle 1000. For example, the battery 100 can be used as an operating power source of the vehicle 1000. The vehicle 1000 can further 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 demand of the vehicle 1000 during starting, navigation and driving.

[0067] In some embodiments of the application, the battery 100 can not only be used as an operating power source of the vehicle 1000, but also be used as a driving power source of the vehicle 1000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 1000.

[0068] In the 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 can be in the form of a battery pack or a battery module. The battery 100 can include a box 10 for packaging one or more battery cells 20. The box 10 can prevent liquid or other foreign matters from affecting the charging or discharging of the battery cells 20.

[0069] Referring to Figure 2 , Figure 2An exploded view of a battery 100 is provided for some embodiments of the present application. The battery 100 includes a box 10 and a plurality of battery cells 20, which are accommodated in the box 10. The box 10 is used to accommodate the battery cells 20, and the box 10 can be of various structures. In some embodiments, the box 10 can include a first part 11 and a second part 12, the first part 11 and the second part 12 are mutually covered, and the first part 11 and the second part 12 jointly define an accommodation space 13 for accommodating the battery cells 20. The second part 12 can be a hollow structure with one end open, and the first part 11 is a plate-like structure, which is covered on the open side of the second part 12 to form the box 10 with the accommodation space 13; the first part 11 and the second part 12 can also be hollow structures with one side open, and the open side of the first part 11 is covered on the open side of the second part 12 to form the box 10 with the accommodation space 13. Of course, the first part 11 and the second part 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0070] In the battery 100, the plurality of battery cells 20 can be connected in series, in parallel, or in a mixed manner, and the mixed manner means that the plurality of battery cells 20 are connected in series and in parallel. The plurality of battery cells 20 can be directly connected in series, in parallel, or in a mixed manner, and then the plurality of battery cells 20 are accommodated in the box 10 as a whole. Alternatively, the plurality of battery cells 20 can be connected in series, in parallel, or in a mixed manner to form a module, and then a plurality of modules are connected in series, in parallel, or in a mixed manner to form a whole, which is accommodated in the box 10. The battery 100 can also include other structures, for example, the plurality of battery cells 20 can be electrically connected through a busbar to realize the parallel, series, or mixed connection of the plurality of battery cells 20.

[0071] The battery cell 20 refers to the smallest unit that constitutes a battery pack. The battery cell 20 can be a lithium ion battery, a lithium-sulfur battery, a sodium ion battery, or a magnesium ion battery, but is not limited thereto.

[0072] Referring to Figure 3 , the battery cell 20 can include a shell 21, an electrode assembly 22, and an electrolyte, and the electrode assembly 22 and the electrolyte are accommodated in the shell 21.

[0073] The shell 21 can include a shell body 211 and a cover body 212. The shell body 211 is a component for cooperating with the cover body 212 to form an internal sealed space 213 of the battery monomer 20, wherein the formed sealed space 213 can be used to accommodate the electrode assembly 22, the electrolyte and other components. The cover body 212 refers to a component that is lidded at the opening of the shell body 211 to isolate the internal environment of the battery monomer 20 from the external environment. The shape of the cover body 212 can be adapted to the shape of the shell body 211 to cooperate with the shell body 211. The cover body 212 can also be provided with functional components such as the electrode terminal 23, the pressure relief structure 24, etc. A sealing ring can be arranged between the opening of the shell body 211 and the cover body 212 to realize the sealing between the shell body 211 and the cover body 212.

[0074] The shell body 211 and the cover body 212 can be various shapes and sizes, such as rectangular parallelepiped, cylindrical, hexagonal prism, etc. Specifically, the shape of the shell body 211 and the cover body 212 can be determined according to the specific shape and size of the electrode assembly 22. The material of the shell body 211 and the cover body 212 can be various, such as but not limited to copper, iron, aluminum, stainless steel, aluminum alloy, etc. The material of the sealing ring can be various, such as but not limited to PP (polypropylene), PC (polycarbonate), PET (polyethylene terephthalate), etc. The material is resistant to electrolyte corrosion, high toughness and fatigue resistant. The outer surface of the shell body 211 can form a plating layer, and the material of the plating layer can be various, such as but not limited to Ni, Cr, etc. corrosion resistant material.

[0075] The battery monomer 20 can also be in the form of a soft package, such as a pouch type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0076] The electrode assembly 22 includes a negative electrode sheet, a separator and a positive electrode sheet 221 (see Figure 4 and Figure 5 ). The battery monomer 20 mainly relies on the movement of metal ions between the positive electrode sheet 221 and the negative electrode sheet to work. In the charging and discharging process, active ions are embedded and de-embedded between the positive electrode sheet 221 and the negative electrode sheet; the separator is arranged between the positive electrode sheet 221 and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The electrode assembly 22 can be a roll type structure or a laminated type structure, and the embodiments of the present application are not limited thereto.

[0077] The negative electrode sheet includes a negative electrode current collector, a negative electrode tab and a negative electrode active material layer, the negative electrode active material layer is arranged on at least one side of the negative electrode current collector, and a primer layer or the like can also be arranged between the negative electrode active material layer and the negative electrode current collector; the negative electrode tab protrudes from the negative electrode current collector, and the negative electrode tab is located at one end or opposite ends of the negative electrode current collector, for example.

[0078] The negative electrode current collector can be a metal foil or a composite current collector. For example, the material of the negative electrode current collector and the negative electrode tab can be copper, and the composite current collector can include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0079] The negative electrode active material in the negative electrode active material layer can be a carbon-based negative electrode active material, a silicon-based negative electrode active material, or the like. For example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, or the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material can also be used.

[0080] In some embodiments, the negative electrode active material layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0081] In some embodiments, the negative electrode active material layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0082] In some embodiments, the negative electrode active material layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0083] The separator film is between the positive electrode tab 221 and the negative electrode tab, and serves to separate the positive electrode tab 221 and the negative electrode tab. The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0084] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0085] Referring to Figure 4 The positive electrode tab 221 includes a positive electrode current collector 2211 and a positive electrode active material layer 2212, and the positive electrode active material layer 2212 is arranged on at least one side of the positive electrode current collector 2211, i.e., the positive electrode current collector 2211 can be provided with the positive electrode active material layer 2212 on one side or both sides; a primer layer or the like can also be arranged between the positive electrode active material layer 2212 and the positive electrode current collector 2211.

[0086] The positive electrode current collector 2211 can be a metal foil or a composite current collector, for example, the material of the positive electrode current collector 2211 can be aluminum. The composite current collector can include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer, and the composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0087] The design requirements of the positive electrode active material layer 2212 can be designed according to the technical solutions proposed in the embodiments of the present application, except for special instructions.

[0088] In some embodiments, the positive electrode active material layer 2212 can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0089] In some embodiments, the positive electrode active material layer 2213 can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super-conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] Next, the positive electrode tab 221 proposed in the embodiments of the present application is described in detail.

[0091] Referring to Figure 4 and Figure 5In a first aspect, the embodiments of the present application provide a positive electrode tab 221, the positive electrode tab 221 comprising a positive electrode current collector 2211 and a positive electrode active material layer 2212, the positive electrode current collector 2211 and the positive electrode active material layer 2212 being distributed along a thickness direction A of the positive electrode tab; wherein a plurality of specified regions 2212a are taken at different positions in the positive electrode active material layer 2212, along the thickness direction A of the positive electrode tab, 50 μm ≤ thickness of the specified region 2212a < thickness of the positive electrode active material layer 2212, satisfying: among the two specified regions 2212a distributed along the thickness direction A of the positive electrode tab, the tortuosity of the specified region 2212a on the side away from the positive electrode current collector 2211 is T 外 , and the tortuosity of the specified region 2212a on the side close to the positive electrode current collector 2211 is T 内 , T 外 > T 内 .

[0092] The plurality of specified regions 2212a taken at different positions in the positive electrode active material layer 2212 means that different specified regions 2212a are taken from different positions, and each specified region 2212a corresponds to a specified position. The specified region 2212a refers to a local region in the positive electrode active material layer 2212 that meets the specified thickness requirement; as an example, in a cross section perpendicular to the thickness direction A of the positive electrode tab, the size of the specified region is consistent with the size of the positive electrode active material layer 2212. The specified region 2212a is a definition of region division of the positive electrode active material layer 2212, and its position in the positive electrode active material layer 2212 is not limited, as long as it meets the specified thickness requirement; as for the two specified regions 2212a, their thicknesses can be the same or different, and they are exemplarily the same. As an example, the thickness of the specified region 2212a along the thickness direction A of the positive electrode tab is 50 μm-60 μm, for example, 50 μm.

[0093] Referring to Figure 5 In some examples, among the two specified regions 2212a distributed along the thickness direction A of the positive electrode tab, the two specified regions 2212a are sequentially arranged along the thickness direction A of the positive electrode tab, and the boundary therebetween overlaps. As an example, the opposite two surfaces of the specified region 2212a distributed along the thickness direction A of the positive electrode tab are both perpendicular to the thickness direction A of the positive electrode tab.

[0094] In the embodiments of the present application, the description of the specified area 2212a on the side of 2211 away from the positive current collector (i.e. the outer specified area 2212a) and the specified area 2212a on the side of 2211 close to the positive current collector (i.e. the inner specified area 2212a) are both relative to the position of the positive current collector 2211, which will not be repeated hereinafter. Among the two specified areas 2212a distributed along the thickness direction A of the positive electrode tab, the outer specified area 2212a refers to the specified area 2212a relatively far away from the positive current collector 2211, and the inner specified area 2212a refers to the specified area 2212a relatively close to the positive current collector 2211.

[0095] The tortuosity is a common knowledge in the art, has a meaning known in the art, and can be measured by instruments and test methods known in the art; for example, the tortuosity of the positive active material layer 2212 refers to the ratio of the length of the transmission channel 2212e in the positive active material layer 2212 to the displacement from one side surface to the other side surface. The tortuosity reflects the degree of tortuosity of the transmission channel 2212e (see Figure 7 ) in the positive active material layer 2212, and the smaller the tortuosity, the smaller the degree of tortuosity of the transmission channel 2212e, and the better the corresponding seepage performance. As an example, the test method of tortuosity includes: 1) measurement of tab thickness (d, cm), surface area (A, cm 2 ); 2) measurement of tab porosity (ε, %); 3) measurement of electrolyte ion conductivity (k, S / cm); 4) measurement of electrochemical impedance spectroscopy EIS, and high-frequency resistance and ion impedance in the pores (R ion , Ω) are obtained by extrapolation in the low-frequency region; 5) calculation of tortuosity (τ) according to the above test results, τ = ε*k*R ion *A / d.

[0096] It should be noted that in the present application, when testing the parameters related to the positive active material layer 2212, the entire positive active material layer 2212 of the positive electrode tab 2212 can be peeled off for testing, or the positive electrode tab 2212 can be cut into a small sample, and the area of the single side surface of the small sample is close to 1000mm 2 , and the entire positive active material layer 2212 on the peeled small sample is tested. When testing the parameters related to the specified area 2212a, a local area meeting the thickness requirement can be cut from the entire positive active material layer 2212 of the positive electrode tab 2212 for testing; or the positive electrode tab 2212 can be cut into a small sample, and then a local area meeting the thickness requirement can be cut from the positive active material layer 2212 of the small sample for testing.

[0097] In the technical solutions of the embodiments of the present application, the tortuosity of the specified area 2212a on the outer side is greater than the tortuosity of the specified area 2212a on the inner side relative to the position of the positive electrode current collector 2211, so that the specified area 2212a on the inner side has better seepage performance, which is conducive to the infiltration of the electrolyte from the outer side to the inner side of the positive electrode active material layer 2212, can improve the liquid absorption rate and the liquid absorption amount of the positive electrode active material layer 2212, and thus can improve the electrolyte infiltration performance of the positive electrode active material layer 2212 and improve the rate capability.

[0098] In some embodiments, T 外 / T 内 = 1.07-1.24; optionally, T 外 / T 内 = 1.09-1.17; optionally, T 外 / T 内 = 1.09-1.16.

[0099] As an example, T 外 / T 内 has a value of, for example but not limited to, any one of 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, or a range value between any two of them.

[0100] In these embodiments, the outer side and the inner side maintain a certain tortuosity ratio relative to the position of the positive electrode current collector 2211, and the seepage performance of the specified area 2212a on the inner side relative to the outer side is improved to a certain extent, which is conducive to the better infiltration of the electrolyte from the outer side to the inner side of the positive electrode active material layer 2212.

[0101] Referring to Figure 6 In some embodiments, at least one of the following conditions (a1)-(a3) is met: (a1) the tortuosity of the specified area 2212a at the first position 2212b is T 表 , the first position 2212b is located on the side of the positive electrode active material layer 2212 away from the positive electrode current collector 2211, and 1.60≤T 表 ≤2.05; optionally, 1.70≤T 表 ≤1.75; (a2) the tortuosity of the specified area 2212a at the second position 2212c is T 中 , the second position 2212c passes through the midpoint of the thickness of the positive electrode active material layer 2212, and 1.50≤T 中 ≤1.65; optionally, 1.50≤T 中≤ 1.55; (a3) the tortuosity of the specified region 2212a at the third position 2212d is T 底 , the third position 2212d is located at the side of the positive electrode active material layer 2212 close to the positive electrode current collector 2211; 1.30 ≤ T 底 ≤ 1.55; optionally, 1.30 ≤ T 底 ≤ 1.35.

[0102] In the embodiments of the present application, as an example, the specified region 2212a at the first position 2212b, whose side away from the positive electrode current collector 2211 is located at the surface of the positive electrode active material layer 2212, that is, the side away from the positive electrode current collector 2211 of the positive electrode active material layer 2212 is a side boundary of the specified region 2212a at the first position 2212b; the specified region 2212a at the second position 2212c, whose thickness midpoint is consistent with the thickness midpoint of the positive electrode active material layer 2212; the specified region 2212a at the second position 2212c, whose side close to the positive electrode current collector 2211 is located at the bottom surface of the positive electrode active material layer 2212, that is, the side close to the positive electrode current collector 2211 of the positive electrode active material layer 2212 is a side boundary of the specified region 2212a at the third position 2212d. Hereinafter, the relevant description can refer to the description here, and subsequent will not be elaborated. As an example, the specified region 2212a at the first position 2212b described in different embodiments refers to the same specified region 2212a, and the specified region 2212a at the second position 2212c and the specified region 2212a at the second position 2212c are explained with reference to the above description.

[0103] In the embodiments of the present application, the thickness midpoint of the specified structure refers to the midpoint of the specified structure in the thickness direction A of the positive electrode tab.

[0104] As an example, the value of T 表 For example but not limited to, any one of the point values 1.60, 1.65, 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.80, 1.85, 1.90, 1.95, 2.00, 2.05 or a range value between any two of them.

[0105] As an example, the value of T 中 For example but not limited to, any one of the point values 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.60, 1.65 or a range value between any two of them.

[0106] As an example, the value of T 底The value of T is, for example but not limited to, any one of the point values 1.30, 1.31, 1.32, 1.33, 1.34, 1.35, 1.40, 1.45, 1.50, 1.55 or a range value between any two of them.

[0107] In these embodiments, the surface, the middle part and the bottom of the positive electrode active material layer 2212 have a smaller tortuosity, which is conducive to the electrolyte to infiltrate more quickly on the surface, the middle part and the bottom of the positive electrode active material layer 2212; and the tortuosity of the surface, the middle part and the bottom of the positive electrode active material layer 2212 gradually decreases with a suitable gradient, which is conducive to the electrolyte to infiltrate the positive electrode active material layer 2212 from outside to inside.

[0108] In some embodiments, the tortuosity of the positive electrode active material layer 2212 as a whole is T 总 , 1.45≤T 总 ≤1.75; optionally, 1.50≤T 总 ≤1.70.

[0109] For example, the value of T 总 is, for example but not limited to, any one of the point values 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75 or a range value between any two of them.

[0110] In the embodiments of the present application, the specified area 2212a at the first position 2212b, the specified area 2212a at the second position 2212c and the specified area 2212a at the third position 2212d are sampled, for example, in the following manner: taking the surface of the positive electrode active material layer 2212 as a starting position, cutting a local area meeting the thickness requirement to obtain the specified area 2212a at the first position 2212b; scraping off the excess positive electrode active material layer 2212 downward until close to the thickness midpoint of the positive electrode active material layer 2212, then taking this position as a starting position, cutting a local area meeting the thickness requirement to obtain the specified area 2212a at the second position 2212c; and continuing to scrape off the excess positive electrode active material layer 2212 downward until close to the positive electrode current collector 2211, and then peeling off the remaining positive electrode active material layer 2212 from the positive electrode current collector 2211 to obtain the specified area 2212a at the third position 2212d.

[0111] In these embodiments, the positive electrode active material layer 2212 includes positive electrode active material; and the positive electrode active material layer 2212 as a whole has a smaller tortuosity, which is close to 1, indicating that the transmission channel 2212e in the positive electrode active material layer 2212 extends in the thickness direction A of the positive electrode tab, which is conducive to the electrolyte to infiltrate more quickly in the positive electrode active material layer 2212 as a whole.

[0112] In some embodiments, in the two specified regions 2212a distributed along the thickness direction A of the positive electrode tab, the positive electrode active material mass percentage in the specified region 2212a away from the positive electrode current collector 2211 side is C1 外 , and the positive electrode active material mass percentage in the specified region 2212a close to the positive electrode current collector 2211 side is C1 内 , C1 外 -C1 内 = 0.1% to 1.2%; optionally, C1 外 -C1 内 = 0.1% to 1.0%.

[0113] The positive electrode active material mass percentage can be measured by instruments and test methods known in the art. As an example, the sample to be tested is digested, and then the element composition type and mass fraction of the digestion solution are measured by ICP (inductively coupled plasma emission spectrometer), and the mass percentage of the positive electrode active material in the corresponding specified region 2212a is calculated according to the test results.

[0114] As an example, C1 外 minus C1 内 The result takes a value such as but not limited to any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, or a range value between any two of them.

[0115] In these embodiments, C1 外 is higher than C1 内 within a certain range, which is beneficial to regulating T 外 , T 内 Both of them meet a suitable gradient, which is beneficial to better infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer 2212.

[0116] Referring to Figure 6 In some embodiments, at least one of the following conditions (b1) to (b3) is met: (b1) the positive electrode active material mass percentage in the specified region 2212a at the first position 2212b is C1 表 , the first position 2212b is located on the side away from the positive electrode current collector 2211 in the positive electrode active material layer 2212, 97.4%≤C1 表 ≤98.1%; optionally, 97.4%≤C1 表 ≤98.0%; (b2) the positive electrode active material mass percentage in the specified region 2212a at the second position 2212c is C1 中 , the second position 2212c passes through the thickness midpoint of the positive electrode active material layer 2212, 96.7%≤C1 中≤ 97.3%; optionally, 97.1% ≤ C1 中 ≤ 97.2%; (b3) the positive electrode active material mass ratio in the specified area 2212a at the third position 2212d is C1 底 , the third position 2212d is located at the side of the positive electrode active material layer 2212 close to the positive electrode current collector 2211; 95.9% ≤ C1 底 ≤ 96.9%; optionally, 96.4% ≤ C1 底 ≤ 96.6%.

[0117] As an example, C1 表 The value is, for example but not limited to, any one of 97.4%, 97.5%, 97.6%, 97.7%, 97.8%, 97.9%, 98.0%, 98.1% point value or range value between any two.

[0118] As an example, C1 中 The value is, for example but not limited to, any one of 96.7%, 96.8%, 96.9%, 97.0%, 97.1%, 97.2%, 97.3% point value or range value between any two.

[0119] As an example, C1 底 The value is, for example but not limited to, any one of 95.9%, 96.0%, 96.1%, 96.2%, 96.3%, 96.4%, 96.5%, 96.6%, 96.7%, 96.8%, 96.9% point value or range value between any two.

[0120] In these embodiments, the surface, middle and bottom of the positive electrode active material layer 2212 have a larger positive electrode active material mass ratio, which is beneficial to provide a higher energy density; the positive electrode active material mass ratio of the surface, middle and bottom of the positive electrode active material layer 2212 gradually decreases with a suitable gradient, which is beneficial to regulate T 表 , T 中 , T 底 gradually decreases with a suitable gradient, which is beneficial to better infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer 2212.

[0121] In some embodiments, the positive electrode active material layer 2212 includes a binder; in the two specified areas 2212a distributed along the thickness direction A of the positive electrode tab, the binder mass ratio in the specified area 2212a away from the positive electrode current collector 2211 side is C2 外 , the binder mass ratio in the specified area 2212a close to the positive electrode current collector 2211 side is C2 内 , C2 内 -C2 外= 0.05%~0.8%; optionally, C2 内 = 0.05%~0.8%; optionally, C2 外 = 0.05%~0.8%; optionally, C2

[0122] The binder mass ratio can be measured by instruments and test methods known in the art. As an example, the test method of the binder mass ratio includes differential scanning calorimetry, placing the electrode in a simultaneous thermal analyzer, recording the change in sample weight during temperature rise, and calculating the binder mass ratio according to the thermogravimetric curve. As an example, the binder includes or is polyvinylidene fluoride (PVDF), and the thermogravimetric heating temperature is, for example, 350°C~390°C.

[0123] As an example, C2 内 Subtracting C2 外 The result value is, for example but not limited to, any one of 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.45%, 0.5%, 0.6%, 0.7%, 0.8%, or a range value between any two of them.

[0124] In these embodiments, C2 外 Lower than C2 内 A certain range is conducive to regulating C1 外 Higher than C1 内 A certain range is conducive to regulating T 外 , T 内 Both meet a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive active material layer 2212.

[0125] Referring to Figure 6 In some embodiments, at least one of the following conditions (c1)~(c3) is met: (c1) the binder mass ratio in the specified area 2212a at the first position 2212b is C2 表 , the first position 2212b is located on the side of the positive active material layer 2212 away from the positive current collector 2211, 0.5%≤C2 表 ≤1.0%; optionally, 0.6%≤C2 表 ≤0.9%; (c2) the binder mass ratio in the specified area 2212a at the second position 2212c is C2 中 , the second position 2212c passes through the midpoint of the thickness of the positive active material layer 2212, 1.0%≤C2 中 ≤1.3%; optionally, 1.0%≤C2 中 ≤1.1%;

[0126] (c3) the binder mass ratio in the specified area 2212a at the third position 2212d is C2 底, the third position 2212d is located at a side of the positive active material layer 2212 close to the positive current collector 2211; 1.3%≤C2 底 ≤1.8%; optionally, 1.5%≤C2 底 ≤1.8%; optionally, 1.5%≤C2 底 ≤1.7%.

[0127] As an example, C2 表 The value is, for example but not limited to, any one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% point value or range value between any two.

[0128] As an example, C2 中 The value is, for example but not limited to, any one of 1.0%, 1.1%, 1.2%, 1.3% point value or range value between any two.

[0129] As an example, C2 底 The value is, for example but not limited to, any one of 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8% point value or range value between any two.

[0130] In these embodiments, the surface, middle and bottom of the positive active material layer 2212 have a suitable binder mass ratio, which is beneficial to provide better bonding performance; the binder mass ratio of the surface, middle and bottom of the positive active material layer 2212 gradually increases with a suitable gradient, which is beneficial to regulate C1 表 , C1 中 , C1 底 gradually decreases with a suitable gradient, which is beneficial to regulate T 表 , T 中 , T 底 gradually decreases with a suitable gradient, which is beneficial to better infiltration of the electrolyte from the outside to the inside of the positive active material layer 2212, and also beneficial to improve the overall structural stability of the positive active material layer 2212.

[0131] In some embodiments, the positive active material layer 2212 includes a conductive agent; in the two specified areas 2212a distributed along the thickness direction A of the positive electrode tab, the conductive agent mass ratio in the specified area 2212a away from the positive current collector 2211 side is C3 外 , and the conductive agent mass ratio in the specified area 2212a close to the positive current collector 2211 side is C3 内 , C3 内 -C3 外 =0.2%-0.8%; optionally, C3 内 -C3 外 =0.2%-0.45%.

[0132] The mass percentage of the conductive agent can be measured by instruments and test methods known in the art. As an example, the test method for the mass percentage of the conductive agent includes: differential scanning calorimetry, placing the electrode plate in a simultaneous thermal analyzer, recording the change in sample weight during the temperature rise process, and calculating the mass percentage of the conductive agent according to the thermogravimetric curve. As an example, the conductive agent includes or is a carbon black type conductive agent, and the thermogravimetric heating temperature is, for example, 450-500°C.

[0133] As an example, C3 内 Subtracting C3 外 The result value is, for example but not limited to, any one of 0.2%, 0.3%, 0.4%, 0.45%, 0.5%, 0.6%, 0.7%, 0.8%, or a range value between any two of them.

[0134] In these embodiments, C3 外 is lower than C3 内 within a certain range, which is conducive to regulating C1 外 is higher than C1 内 within a certain range, which is conducive to regulating T 外 , T 内 satisfy a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive active material layer 2212.

[0135] Referring to Figure 6 In some embodiments, at least one of the following conditions (c1)-(c3) is satisfied: (c1) the mass percentage of the conductive agent in the specified area 2212a at the first position 2212b is C3 表 , the first position 2212b is located on the side of the positive active material layer 2212 away from the positive current collector 2211, 0.7%≤C3 表 ≤1.4%; optionally, 0.9%≤C3 表 ≤1.4%; optionally, 0.9%≤C3 表 ≤1.2%; (c2) the mass percentage of the conductive agent in the specified area 2212a at the second position 2212c is C3 中 , the second position 2212c passes through the midpoint of the thickness of the positive active material layer 2212, 1.1%≤C3 中 ≤1.7%; optionally, 1.2%≤C3 中 ≤1.7%; optionally, 1.2%≤C3 中 ≤1.3%;

[0136] (c3) the mass percentage of the conductive agent in the specified area 2212a at the third position 2212d is C3 底, the third position 2212d is located at a side of the positive electrode active material layer 2212 close to the positive electrode current collector 2211; 1.2%≤C3 底 ≤2.0%; optionally, 1.5%≤C3 底 ≤2.0%; optionally, 1.5%≤C3 底 ≤1.7%.

[0137] As an example, C3 表 takes a value, for example but not limited to, any one of the point values of 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, or a range value between any two of them.

[0138] As an example, C3 中 takes a value, for example but not limited to, any one of the point values of 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, or a range value between any two of them.

[0139] As an example, C3 底 takes a value, for example but not limited to, any one of the point values of 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or a range value between any two of them.

[0140] In these embodiments, the surface, the middle part and the bottom of the positive electrode active material layer 2212 have a suitable mass ratio of the conductive agent, which is conducive to providing better conductivity; the mass ratio of the conductive agent of the surface, the middle part and the bottom of the positive electrode active material layer 2212 gradually increases with a suitable gradient, which is conducive to regulating C1 表 , C1 中 , C1 底 gradually increases with a suitable gradient, which is conducive to regulating T 表 , T 中 , T 底 gradually decreases with a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer 2212.

[0141] In some embodiments, in the two specified areas 2212a distributed along the thickness direction A of the positive electrode tab, the porosity of the specified area 2212a away from the side of the positive electrode current collector 2211 is P 外 , and the porosity of the specified area 2212a close to the side of the positive electrode current collector 2211 is P 内 , P 外 < P 内 ; optionally, (P 外 / P 内 )×100%=91.4%-96.9%.

[0142] The porosity is a common knowledge in the art, has a meaning known in the art, and can be measured by instruments and test methods known in the art. As an example, the test method of the porosity includes: calculating the apparent volume; placing a sample cup containing the sample into a true density tester, a closed test system, and according to the program, helium is introduced, and the real volume is calculated according to the Boyle's law (PV = nRT) by detecting the pressure of the gas in the sample chamber and the expansion chamber, so as to obtain the porosity of the sample to be tested according to the real volume and the apparent volume.

[0143] As an example, (P 外 / P 内 ) × 100% has a value such as, but not limited to, any one of 91.4%, 91.9%, 92.4%, 92.9%, 93.4%, 93.9%, 94.4%, 94.9%, 95.4%, 95.9%, 96.4%, 96.9%, or a range value between any two of them.

[0144] In these embodiments, the porosity of the outer side is lower than that of the inner side relative to the position of the positive electrode current collector 2211, and optionally the outer side and the inner side maintain a certain porosity ratio, which is conducive to regulating the T 外 , T 内 Both satisfy a suitable gradient, which is conducive to better infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer 2212.

[0145] In some embodiments, at least one of the following conditions (d1) to (d3) is met: (d1) the porosity of the specified area 2212a at the first position 2212b is P 表 , the first position 2212b is located on the side of the positive electrode active material layer 2212 away from the positive electrode current collector 2211, and 27.5% ≤ P 表 ≤ 28.3%; (d2) the porosity of the specified area 2212a at the second position 2212c is P 中 , the second position 2212c passes through the midpoint of the thickness of the positive electrode active material layer 2212, and 29.2% ≤ P 中 ≤ 30.1%; (d3) the porosity of the specified area 2212a at the third position 2212d is P 底 , the third position 2212d is located on the side of the positive electrode active material layer 2212 close to the positive electrode current collector 2211; and 30.6% ≤ P 底 ≤ 33.3%.

[0146] As an example, P 表 has a value such as, but not limited to, any one of 27.5%, 27.6%, 27.7%, 27.8%, 27.9%, 28.0%, 28.1%, 28.2%, 28.3%, or a range value between any two of them.

[0147] As an example, P 中 may be any one of the point values 29.2%, 29.3%, 29.4%, 29.5%, 29.6%, 29.7%, 29.8%, 29.9%, 30.0%, 30.1% or a range value between any two of them.

[0148] As an example, P 底 may be any one of the point values 30.6%, 31.0%, 31.5%, 32.0%, 32.5%, 33.0%, 33.3% or a range value between any two of them.

[0149] In these embodiments, the surface, middle part and bottom part of the positive electrode active material layer 2212 have suitable porosities, which are beneficial to providing better seepage performance; the porosities of the surface, middle part and bottom part of the positive electrode active material layer 2212 gradually increase with a suitable gradient, which is beneficial to regulating T 表 , T 中 , T 底 gradually decrease with a suitable gradient, which is beneficial to better infiltration of the electrolyte from the outside to the inside of the positive electrode active material layer 2212.

[0150] In some embodiments, the positive electrode active material in the positive electrode active material layer 2212 includes one or more of lithium iron phosphate or modified lithium iron phosphate, lithium iron phosphate containing a doping element or lithium iron phosphate containing a coating layer.

[0151] The modification method of the modified lithium iron phosphate can be a doping modification method, can be a coating modification method, or can be a modification method of both doping and coating.

[0152] In the electrode made by the traditional granular slurry coating method, the pore distribution is uneven, and the tortuosity is high. In these embodiments, the positive electrode active material is lithium iron phosphate, which is convenient for regulating the gradient distribution of the positive electrode active material in the positive electrode active material layer 2212 through the magnetic responsiveness of the lithium iron phosphate, and is beneficial to realizing the gradient design of the tortuosity, the mass ratio of the positive electrode active material, the mass ratio of the binder, the mass of the conductive agent, etc., and is beneficial to reducing the overall tortuosity of the positive electrode active material layer 2212, and is also beneficial to improving the porosity and the uniformity of the material distribution in the positive electrode active material layer 2212.

[0153] Referring to Figure 7In some example embodiments, along the thickness direction A of the positive electrode tab, from the side of the positive electrode active material layer 2212 away from the positive electrode current collector 2211 to the side close to the positive electrode current collector 2211, the tortuosity and the proportion of the positive electrode active material mass decrease, and the proportions of the binder mass, the conductive agent mass, and the porosity increase. In the positive electrode active material layer 2212, the extension direction of the transport channel 2212e extends close to the thickness direction A of the positive electrode tab, that is, the extension direction of the transport channel 2212e is close to perpendicular to the surface of the positive electrode current collector 2211.

[0154] In the above example embodiments, the decreasing trend and the increasing trend can be a continuous change trend, that is, gradual change, or a stepwise change trend, that is, maintaining a certain value in a certain region and then changing to another value in the next region.

[0155] The example embodiments of the present application provide a preparation method of the above positive electrode tab, which comprises: using magnetic particles of the positive electrode active material to prepare a slurry for coating, and then applying an external magnetic field to make the magnetic particles move directionally to realize the gradient design of the positive electrode active material layer in the above example embodiments.

[0156] Optionally, when the external magnetic field is applied, the external magnetic field is perpendicular to the surface of the slurry layer.

[0157] Optionally, after the external magnetic field makes the magnetic particles move directionally, a phase inversion method is used to form the gradient change transport channel in the positive electrode active material layer.

[0158] For example, the second preparation method of the above positive electrode tab comprises:

[0159] S1: Preparation of magnetic nano-lithium iron phosphate.

[0160] The magnetic nanoparticles are coated with a cationic dispersant to make them have a positive charge. The operation includes: dissolving 1 part by weight of magnetic nanoparticles in 5 parts by weight of cationic dispersant, stirring in a 60°C oil bath for 2 hours, and then drying at 60°C to obtain cationic dispersant-coated magnetic nanoparticles. The magnetic nanoparticles include but are not limited to magnetic nano-Fe3O4 and gadolinium gallium garnet magnetic nanoparticles. Then, 1 part by weight of lithium iron phosphate is dispersed in 40 parts by weight of distilled water by magnetic stirring, and 0.0075 parts by weight of cationic dispersant-coated magnetic nanoparticles are diluted in 15 parts by weight of distilled water and then added to the stirring dispersion, mixed and stirred for 2 hours, the suspension is centrifuged and the magnetic nano-lithium iron phosphate particles are collected, and dried in a 90°C vacuum oven overnight.

[0161] The cationic dispersant optionally includes an ammonium salt type and / or a quaternary ammonium salt type dispersant, such as including dialkyldimethylammonium chloride, for example but not limited to (4-vinylpyridine)-acrylamide-DMC copolymer (abbreviation PVAD), styrene-acrylamide-DMC copolymer (abbreviation PSAD), styrene-(4-vinylpyridine)-DMC copolymer (abbreviation PSVD), and the like.

[0162] S2: slurry preparation.

[0163] The magnetic nanometer lithium iron phosphate, the conductive agent, and the binder are weighed and dispersed in N-methylpyrrolidone (NMP) solvent, and after uniform stirring, a slurry with good uniformity is formed.

[0164] S3: coating.

[0165] The slurry is coated on the aluminum foil substrate by a coating method such as extrusion coating, transfer coating, spraying, intermittent coating, etc., to ensure uniformity of the coated material.

[0166] S4: applied magnetic field.

[0167] After coating, an applied magnetic field in the vertical pole direction is turned on, so that the magnetic nanometer lithium iron phosphate moves directionally, forming a gradient distribution of the positive electrode active material. Optionally, the magnetic field size is 5T-10T, and the duration is 2min-5min.

[0168] S5: water bath.

[0169] The positive electrode pole is water-bathed for example 1h, and solution phase conversion occurs by phase inversion, and the organic solvent in the positive electrode pole is transferred to the flocculant pool, so that the positive electrode pole is solidified, forming a ladder-shaped vertical channel.

[0170] The flocculant is for example but not limited to water, ethanol, water / ethanol mixture, etc.

[0171] Step S6: drying.

[0172] Drying is performed by vacuum drying, displacement drying, dielectric drying, etc., to obtain a dried pole. Optionally, the environmental conditions for vacuum drying include a vacuum degree of about 1kPa, a temperature of 80℃-120℃, and a water content of within 600ppm.

[0173] Step S7: polishing.

[0174] The surface layer generated in the phase inversion process is removed by polishing means, for example Ar ion polishing.

[0175] In different embodiments, the T 外 、T 内 、C1 外 、C1 内 、C2 外 、C2 内 、C3 外 、C3 内 microstructure corresponding parameters can be controlled by adjusting 1) the coating state of the cationic dispersant on the magnetic nanoparticles; 2) the uniformity of the slurry; 3) the degree of perpendicularity of the magnetic field to the pole piece, the uniformity of the magnetic field, the size of the magnetic field force; 4) the temperature and time of the water bath, etc.

[0176] In a second aspect, the embodiments of the present application provide a battery 100 comprising the positive pole piece 221 of the above embodiments.

[0177] In a third aspect, the embodiments of the present application provide a power consumption device comprising the battery 100 of the above embodiments.

[0178] Some specific embodiments are listed below to better illustrate the present application.

[0179] I. Preparation of battery monomer

[0180]

Preparation of positive pole piece

[0181] The preparation method corresponding to the embodiments is as follows:

[0182] S1: Preparation of magnetic nano lithium iron phosphate.

[0183] The magnetic nanoparticles are coated with a cationic dispersant to make them have a positive charge; the operation includes: dissolving 1 part by weight of magnetic nanoparticles in 5 parts by weight of cationic dispersant, stirring in a 60°C oil bath for 2h, and then drying at 60°C to obtain cationic dispersant-coated magnetic nanoparticles. Among them, the cationic dispersant is PVAD, and the magnetic nanoparticles are magnetic nano Fe3O4. Then, 1 part by weight of lithium iron phosphate is dispersed in 40 parts by weight of distilled water by magnetic stirring, and 0.0075 parts by weight of cationic dispersant-coated magnetic nanoparticles are diluted in 15 parts by weight of distilled water, and then added to the stirring dispersion, mixed and stirred for 2 hours, the suspension is centrifuged and the magnetic nano lithium iron phosphate particles are collected, and dried in a 90°C vacuum oven overnight.

[0184] S2: Preparation of slurry.

[0185] The magnetic nano lithium iron phosphate, conductive carbon, and binder polyvinylidene fluoride (PVDF) are weighed according to a certain mass ratio, and a certain amount of surfactant additive polyethoxymethyl acrylate (PMA) is added and dispersed in N-methyl pyrrolidone (NMP) solvent. After uniform stirring, a slurry with good uniformity is formed.

[0186] S3: Coating.

[0187] The slurry was coated on both sides on a 13 μm aluminum foil substrate according to a coating weight of 0.314 mg / mm 2 to ensure uniformity of the coating material.

[0188] S4: External magnetic field.

[0189] After coating, an external magnetic field in the direction of the vertical pole piece was turned on, so that the magnetic nanometer lithium iron phosphate moved directionally, forming a gradient distribution of the positive electrode active material, and the binder and the conductive agent were correspondingly distributed in a gradient. At this time, with reference to Figure 7 , from the side of the positive electrode active material layer away from the positive electrode current collector to the side close to the positive electrode current collector, the proportion of the positive electrode active material in the mass decreased, the proportion of the binder in the mass, the proportion of the conductive agent in the mass, and the porosity increased, so that the tortuosity ratio decreased.

[0190] In Examples 1-5, the conditions of step S4 were slightly different. In Example 1, the magnetic field strength was 8T and the duration was 200s; in Example 2, the magnetic field strength was 8T and the duration was 175s; in Example 3, the magnetic field strength was 8T and the duration was 150s; in Example 4, the magnetic field strength was 9T and the duration was 200s; and in Example 5, the magnetic field strength was 7T and the duration was 200s.

[0191] S5: Water bath.

[0192] The positive electrode pole piece was placed in a 45°C water bath for 1h, and solution phase conversion was performed by phase inversion. The organic solvent in the positive electrode pole piece was transferred to the flocculant tank, so that the positive electrode pole piece was solidified and formed into a trapezoidal vertical channel; the flocculant was water.

[0193] Step S6: Drying.

[0194] Drying was performed by a vacuum drying method to obtain a dried positive electrode pole piece.

[0195] Step S7: Polishing.

[0196] The polishing means of the Ar ion polishing method was used to remove the surface layer generated during the phase inversion process.

[0197] Step S8: Cold pressing.

[0198] The polished positive electrode pole piece was pressed to a thickness of 150 μm by a roller pressing system, and a positive electrode pole piece with a thickness of 313 μm was obtained.

[0199] The preparation method corresponding to the comparative example is as follows:

[0200] S1: Preparation of slurry.

[0201] Lithium iron phosphate, conductive carbon, and binder polyvinylidene fluoride (PVDF) are weighed according to a certain mass ratio, and a certain amount of surfactant additive polyethoxymethyl acrylate (PMA) is added and dispersed in N-methyl pyrrolidone (NMP) solvent. After uniform stirring, a slurry with good uniformity is formed.

[0202] S2: coating.

[0203] The slurry is coated on both sides of a 13 μm aluminum foil substrate according to a coating weight of 0.314 mg / mm 2 to ensure uniformity of the coated material.

[0204] Step S3: drying.

[0205] Drying is performed by a vacuum drying method to obtain a dried positive electrode sheet.

[0206] Step S4: cold pressing

[0207] The polished positive electrode sheet is pressed to a thickness of 150 μm on each side using a roller pressing system, and a positive electrode sheet with a thickness of 313 μm is obtained.

[0208]

Preparation of negative electrode sheet

[0209] Graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon are added to a certain amount of deionized water, and the mass ratio of graphite: sodium carboxymethyl cellulose: styrene-butadiene rubber: conductive agent is 90:2:3:5. The mixture is stirred to form a uniform negative electrode slurry, and the viscosity is controlled to be 3000 Pa·S-10000 mPa·S. The negative electrode slurry is coated on a copper foil, and then dried, cold pressed, and cut to form a negative electrode sheet.

[0210]

Preparation of electrolyte

[0211] LiPF6 is contained in the electrolyte at a concentration of 1 mol / L. The solvent includes ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) at a volume ratio of 1:1:1. It also contains fluoroethylene carbonate (FEC) at a content of 5 wt% in the electrolyte.

[0212]

Preparation of separator

[0213] A porous polyethylene (PE) polymer film is used as a separator.

[0214]

Preparation of bare battery

[0215] The prepared positive electrode sheet, negative electrode sheet, and separator are stacked according to a Z-shaped stacking structure to form a corresponding battery, and a battery with a thickness of 313 μm is obtained. Figure 8The shown battery cell, wherein the plurality of positive electrode tabs 221 and the plurality of negative electrode tabs 223 are alternately distributed in the order of positive electrode tab 221, negative electrode tab 223, positive electrode tab 221, negative electrode tab 223, and the separator 222 is folded in a Z-shaped manner and is spaced between the positive electrode tab 221 and the negative electrode tab 223; the battery cell is vacuum dried at 90°C for 12h, and then the positive electrode tab and the negative electrode tab are ultrasonically welded, the positive electrode tab uses an aluminum tab, the negative electrode tab uses a nickel tab, and the positive electrode tab and the negative electrode tab are located on the same side of the battery cell.

[0216] Preparation of lithium ion battery

[0217] The battery cell after welding the tabs is packaged in an aluminum-plastic film of appropriate size for top-side sealing, the top-side sealing temperature is 145°C, electrolyte is injected, and then the battery cell is allowed to stand, formed, aged, degassed, double-sealed, and capacity tested to obtain a prepared soft-pack laminated battery cell.

[0218] II. Test method

[0219] 1. Capillary liquid absorption rate test of positive electrode tab

[0220] The capillary liquid absorption method is used for testing, and the specific process is as follows: the pre-dried tab is placed on a microscope stage, a capillary tube with a diameter of 0.3mm is used to absorb 5mm of electrolyte, the time is started when the capillary tube contacts the tab, and the time when the electrolyte is completely absorbed is recorded, and finally the capillary liquid absorption rate is calculated.

[0221] 2. Liquid absorption amount test of bare battery cell

[0222] The dry weight of the bare battery cell is weighed, and then the bare battery cell is soaked in electrolyte, and the wet weight of the soaked bare battery cell is weighed at intervals. The weight of the bare battery cell before and after soaking is recorded, and the liquid absorption amount of the bare battery cell is understood according to the change of the weight with time.

[0223] 3. Rate performance test of battery cell

[0224] The battery cell is charged at different specified temperatures (-10°C, 0°C, 25°C, 45°C), and the charging is carried out according to the charging standards of 1 / 6C, 1 / 4C, 1 / 2C and 1C. The charging rate corresponding to each specified percentage SOC (5%, 25%, 50%, 75%, 100%) when the battery cell is charged from empty state to full charge state is recorded.

[0225] III. Experimental conditions and test results

[0226] The main experimental conditions in each experimental group are shown in Table 1. For experimental conditions not recorded, refer to the above description, and this paper will not be repeated here.

[0227] Table 1. Main experimental conditions

[0228]

[0229]

[0230] In Table 1:

[0231] 1) In each of the examples and comparative examples, the positions and thicknesses of the specified regions corresponding to the surface, the middle, and the bottom surface are the same, see Figure 6 , the surface refers to a region with a thickness of 50 μm starting from the surface of the positive electrode active material layer away from the positive electrode current collector, the middle refers to a region with a thickness of 50 μm centered on the thickness midpoint of the positive electrode active material layer, and the bottom surface refers to a region with a thickness of 50 μm starting from the bottom surface of the positive electrode active material layer close to the positive electrode current collector;

[0232] 2) The mass percentage of the positive electrode active material refers to the total mass percentage of lithium iron phosphate and magnetic nanoparticles;

[0233] 3) In each of the examples and comparative examples, in the positive electrode active material layer, in addition to the positive electrode active material, the adhesive, and the conductive agent, the balance is the surface-active additive polyethoxymethyl acrylate (PMA), and the total amount of the four components is 100%.

[0234] According to Table 1, it can be seen that the examples meet T 外 > T 内 , and the comparative examples do not meet T 外 > T 内 .

[0235] 1) The capillary liquid absorption rate test results are shown in Table 2.

[0236] Table 2. Capillary liquid absorption rate test results

[0237]

[0238] In Table 2, in each of the examples and comparative examples, the thickness and area size of the five samples are consistent. Among them, the five samples are obtained by cutting small samples corresponding to different positions of the surface of the electrode piece, specifically, a sample with a size of 4 cm x 4 cm is taken at the positive center in each large fold surface of the Z-shaped lamination structure, and a total of five large fold surfaces are sampled to obtain sample 1 to sample 5.

[0239] According to Table 2, it can be seen that:

[0240] The positive electrode piece provided by the examples of the present application is compared with Comparative Example 1, and the capillary liquid absorption rate is effectively improved.

[0241] From the data in Table 1, the results are rounded to two decimal places, and T 表 / T中 =1.12 and T 中 / 底 =1.16, T in Example 3 表 / T 中 =1.08 and T 中 / 底 =1.08, T in Example 4 表 / T 中 =1.18 and T 中 / 底 =1.19. It can be seen that, compared to Example 1, T in Example 3... 外 / T 内 The value is too small, meaning the gradient of tortuosity is too small; compared with Example 1, T in Example 4 is smaller. 外 / T 内 The value is too large, meaning the gradient of tortuosity is too large. Compared with Example 3, the capillary aspiration rate of Example 1 is significantly higher; compared with Example 4, the aspiration rate of Example 1 is comparable.

[0242] Compared with Example 1, Example 5, T 表 / T 中 =1.24 and T 中 / 底 =1.08, T 表 / T 中 The value is relatively high, and the overall tortuosity of the positive electrode sheet is relatively large. Compared with Example 5, Example 1 has a higher capillary absorption rate.

[0243] 2. The corresponding test results of the liquid absorption volume of the bare battery cell are as follows: Figure 9 As shown.

[0244] according to Figure 9 As can be seen, the bare cells corresponding to Example 1 and Comparative Example 1 started absorbing liquid with the same dry weight. At the same time, the bare cell corresponding to Example 1 had a greater wet weight after absorbing liquid, indicating that the bare cell corresponding to Example 1 absorbed more liquid. It is evident that the positive electrode sheet provided in this application, compared with Comparative Example 1, effectively improves the liquid absorption capacity when applied to bare cells.

[0245] 3. The rate performance test results of the battery cells are shown in Table 3.

[0246] Table 3. Ratio Performance Test Results

[0247]

[0248] As can be seen from Table 3:

[0249] Compared with Comparative Example 1, the positive electrode sheet provided in this application embodiment effectively improves the rate performance when applied to a single battery cell.

[0250] Example 3 and Example 1, the value of T 外 / T 内 is small, i.e., the gradient of tortuosity is small; compared with Example 1, the overall tortuosity of the positive electrode plate of Example 5 is large. Compared with Example 3 and Example 5, the rate performance of Example 1 is better.

[0251] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; 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 be covered in the scope of the claims and the description of the present application. Especially, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive current collector and the positive active material layer are distributed along the thickness direction of the positive electrode sheet; In this process, multiple designated regions at different locations within the positive electrode active material layer are selected. Along the thickness direction of the positive electrode sheet, the thickness of the designated region is less than the thickness of the positive electrode active material layer, provided that 50 μm ≤ the thickness of the designated region < the thickness of the positive electrode active material layer. Furthermore, among the two designated regions distributed along the thickness direction of the positive electrode sheet, the tortuosity of the designated region on the side furthest from the positive electrode current collector is T. 外 The tortuosity of the designated region on the side closest to the positive current collector is T. 内 T 外 >T 内 .

2. The positive electrode sheet according to claim 1, characterized in that, T 外 / T 内 =1.07~1.24。 3. The positive electrode sheet according to claim 1, characterized in that, T 外 / T 内 =1.09~1.17。 4. The positive electrode sheet according to claim 1, characterized in that, T 外 / T 内 =1.09~1.16。 5. The positive electrode sheet according to any one of claims 1-4, characterized in that, At least one of the following conditions (a1) to (a3) ​​must be met: (a1) The tortuosity of the designated region located in the first position is T. 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, 1.60≤T 表 ≤2.05; (a2) The tortuosity of the designated region located in the second position is T. 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 1.50 ≤ T 中 ≤1.65; (a3) The tortuosity of the designated region located in the third position is T. 底 The third position is located in the positive electrode active material layer on the side close to the positive electrode current collector; 1.30≤T 底 ≤1.55。 6. The positive electrode sheet according to any one of claims 1-4, characterized in that, At least one of the following conditions (a1) to (a3) ​​must be met: (a1) The tortuosity of the designated region located in the first position is T. 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, 1.70≤T 表 ≤1.75; (a2) The tortuosity of the designated region located in the second position is T. 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 1.50 ≤ T 中 ≤1.55; (a3) The tortuosity of the designated region located in the third position is T. 底 The third position is located in the positive electrode active material layer on the side close to the positive electrode current collector; 1.30≤T 底 ≤1.35。 7. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The overall tortuosity of the positive electrode active material layer is T. 总 1.45≤T 总 ≤1.

75.

8. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The overall tortuosity of the positive electrode active material layer is T. 总 1.50≤T 总 ≤1.

70.

9. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The positive electrode active material layer includes positive electrode active material; in the two designated regions distributed along the thickness direction of the positive electrode sheet, the mass percentage of the positive electrode active material in the designated region on the side furthest from the positive electrode current collector is C1. 外 The mass percentage of the positive electrode active material in the designated region near the positive electrode current collector is C1. 内 C1 外 -C1 内 =0.1%~1.2%.

10. The positive electrode sheet according to claim 9, characterized in that, C1 外 -C1 内 =0.1%~1.0%.

11. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, At least one of the following conditions (b1) to (b3) must be met: (b1) The mass percentage of the positive electrode active material in the designated area located at the first position is C1. 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, with 97.4% ≤ C1. 表 ≤98.1%; (b2) The mass percentage of the positive electrode active material in the designated area located in the second position is C1. 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 96.7% ≤ C1 中 ≤97.3%; (b3) The mass percentage of the positive electrode active material in the designated region located in the third position is C1. 底 The third position is located in the positive electrode active material layer on the side closer to the positive electrode current collector; 95.9%≤C1 底 ≤96.9%.

12. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, At least one of the following conditions (b1) to (b3) must be met: (b1) The mass percentage of the positive electrode active material in the designated area located at the first position is C1. 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, with 97.4% ≤ C1. 表 ≤98.0%; (b2) The mass percentage of the positive electrode active material in the designated area located at the second position is C1. 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 97.1% ≤ C1 中 ≤97.2%; (b3) The mass percentage of the positive electrode active material in the designated region located in the third position is C1. 底 The third position is located in the positive electrode active material layer on the side close to the positive electrode current collector; 96.4%≤C1 底 ≤96.6%。 13. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The positive electrode active material layer includes a binder; in the two designated regions distributed along the thickness direction of the positive electrode sheet, the mass percentage of the binder in the designated region on the side furthest from the positive electrode current collector is C2. 外 The binder mass percentage in the designated area near the positive current collector is C2. 内 C2 内 -C2 外 =0.05%~0.8%.

14. The positive electrode sheet according to claim 13, characterized in that, C2 内 -C2 外 =0.05%~0.45%。 15. The positive electrode sheet according to claim 13, characterized in that, At least one of the following conditions (c1) to (c3) must be met: (c1) The mass percentage of the adhesive in the designated area located at the first position is C2. 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, and 0.5%≤C2 表 ≤1.0%; (c2) The mass percentage of the adhesive in the designated area located in the second position is C2. 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 1.0% ≤ C2 中 ≤1.3%; (c3) The adhesive mass percentage in the designated area located in the third position is C2. 底 The third position is located in the positive electrode active material layer on the side close to the positive electrode current collector; 1.3%≤C2 底 ≤1.8%。 16. The positive electrode sheet according to claim 13, characterized in that, At least one of the following conditions (c1) to (c3) must be met: (c1) The mass percentage of the adhesive in the designated area located at the first position is C2. 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, and 0.6%≤C2 表 ≤0.9%; (c2) The mass percentage of the adhesive in the designated area located in the second position is C2. 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 1.0% ≤ C2 中 ≤1.1%; (c3) The adhesive mass percentage in the designated area located in the third position is C2. 底 The third position is located in the positive electrode active material layer on the side close to the positive electrode current collector; 1.5%≤C2 底 ≤1.8%, or 1.5%≤C2 底 ≤1.7%.

17. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The positive electrode active material layer includes a conductive agent; in the two designated regions distributed along the thickness direction of the positive electrode sheet, the mass percentage of the conductive agent in the designated region on the side furthest from the positive electrode current collector is C3. 外 The mass percentage of the conductive agent in the designated area near the positive current collector is C3. 内 C3 内 -C3 外 =0.2%~0.8%.

18. The positive electrode sheet according to claim 17, characterized in that, C3 内 -C3 外 =0.2%~0.45%。 19. The positive electrode sheet according to claim 17, characterized in that, At least one of the following conditions (c1) to (c3) must be met: (c1) The mass percentage of the conductive agent in the designated area located at the first position is C3. 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, with 0.7% ≤ C3. 表 ≤1.4%; (c2) The mass percentage of the conductive agent in the designated area located at the second position is C3. 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 1.1% ≤ C3 中 ≤1.7%; (c3) The mass percentage of the conductive agent in the designated area located in the third position is C3. 底 The third position is located in the positive electrode active material layer on the side close to the positive electrode current collector; 1.2%≤C3 底 ≤2.0%。 20. The positive electrode sheet according to claim 17, characterized in that, At least one of the following conditions (c1) to (c3) must be met: (c1) The mass percentage of the conductive agent in the designated area located at the first position is C3. 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, and 0.9%≤C3 表 ≤1.4%; or, 0.9%≤C3 表 ≤1.2%; (c2) The mass percentage of the conductive agent in the designated area located at the second position is C3. 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 1.2% ≤ C3 中 ≤1.7%; or, 1.2%≤C3 中 ≤1.3%; (c3) The mass percentage of the conductive agent in the designated area located in the third position is C3. 底 The third position is located in the positive electrode active material layer on the side close to the positive electrode current collector; 1.5%≤C3 底 ≤2.0%; or, 1.5%≤C3 底 ≤1.7%.

21. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, In the two designated regions distributed along the thickness direction of the positive electrode sheet, the porosity of the designated region on the side furthest from the positive current collector is P. 外 The porosity of the designated region near the positive electrode current collector is P. 内 P 外 <P 内 .

22. The positive electrode sheet according to claim 20, characterized in that, (P 外 / P 内 )×100%=91.4%~96.9%。 23. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, At least one of the following conditions (d1) to (d3) must be met: (d1) The porosity of the designated region located at the first position is P 表 The first position is located on the side of the positive electrode active material layer away from the positive electrode current collector, 27.5%≤P 表 ≤28.3%; (d2) The porosity of the designated region located at the second position is P 中 The second position passes through the midpoint of the thickness of the positive electrode active material layer, and 29.2% ≤ P 中 ≤30.1%; (d3) The porosity of the designated region located at the third position is P. 底 The third position is located in the positive electrode active material layer on the side close to the positive electrode current collector; 30.6%≤P 底 ≤33.3%。 24. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The positive electrode active material in the positive electrode active material layer includes one or more of lithium iron phosphate or modified lithium iron phosphate.

25. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1 to 24.

26. An electrical appliance, characterized in that, Includes the battery as described in claim 25.

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