WO2024007319A1

WO2024007319A1 - Pole piece, secondary battery, battery module, battery pack, and electrical apparatus

Info

Publication number: WO2024007319A1
Application number: PCT/CN2022/104687
Authority: WO
Inventors: 孙婧轩; 刘倩; 李全国; 陈佳华; 喻春鹏; 肖得隽; 叶永煌
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-07-08
Filing date: 2022-07-08
Publication date: 2024-01-11
Also published as: CN117941120A

Abstract

The present application provides a pole piece, a secondary battery, a battery module, a battery pack, and an electrical apparatus. The pole piece comprises: a current collector, a first active material layer, and a second active material layer. Wherein, the first active material layer and the second active material layer are disposed in different surface regions of at least one side of the current collector. A capacity retention rate KA of the first active material layer at -20℃ and a capacity retention rate KB of the second active material layer at -20℃ satisfy the following relationship: 3%≤KA-KB≤80%. The capacity retention rate KA of the first active material layer at -20℃ is higher than the capacity retention rate KA of the second active material layer at -20℃, making it so that the working temperature of each region of a battery can be more uniform, further reducing the formation of lithium dendrites and enhancing the ionic conductivity of the pole piece, and thereby making it so that the battery has good electrochemical performance and safety performance in low-temperature environments.

Description

Electrode plates, secondary batteries, battery modules, battery packs and electrical devices

Technical field

The present application relates to the field of battery technology, and in particular to an electrode pole piece, a secondary battery, a battery module, a battery pack and an electrical device.

Background technique

With the development of battery technology, it has been used in various fields to provide electrical energy, such as electric vehicles, consumer electronic equipment, etc.

In the development of battery technology, in addition to improving the performance of batteries at normal operating temperatures, it is also necessary to consider the electrochemical performance and safety performance of batteries in low-temperature environments. Therefore, how to balance the electrochemical performance and safety performance of batteries in low-temperature environments is an urgent problem in battery technology that needs to be solved.

Contents of the invention

This application provides an electrode pole piece, a secondary battery, a battery module and an electrical device, which can take into account the electrochemical performance and safety performance of the battery in a low-temperature environment.

In a first aspect, embodiments of the present application provide an electrode pole piece, including: a current collector, a first active material layer and a second active material layer. Wherein, the first active material layer and the second active material layer are disposed on different surface areas of at least one side of the current collector. The capacity retention rate K _A of the first active material layer at -20°C and the capacity retention rate K _B of the second active material layer at -20°C satisfy the following relationship: 3% ≤ K _A - K _B ≤ 80% .

In the above embodiment, the first active material layer and the second active material layer are disposed on different surface areas of at least one side of the current collector, and the capacity retention rate K _A of the first active material layer at -20° C. is equal to The capacity retention rate K _B of the second active material layer at -20° C. satisfies the following relationship: 3% ≤ K _A - K _B ≤ 80%. The capacity retention rate K _A of the first active material layer at -20°C is higher than the capacity retention rate K _B of the second active material layer at -20°C, which can make the operating temperature of each area of the battery more uniform, thereby reducing lithium The generation of dendrites and the improvement of the ionic conductivity of the electrode plates enable the battery to have good electrochemical performance and safety performance in low temperature environments.

In some embodiments of the present application, the capacity retention rate of the first active material layer at -20°C is 15% ≤ K _A ≤ 95%. And/or, the capacity retention rate of the second active material layer at -20°C is 10% ≤ K _B ≤ 90%.

In the above embodiments, the capacity retention rate of the first active material layer and the second active material layer in a low temperature environment is set within the above range, and satisfies 3% ≤ K _A - K _B ≤ 80%, so that the secondary The operating temperature in each area of the battery is more uniform, which reduces the decrease in ionic conductivity of the electrode plates and the formation of lithium dendrites caused by local low temperatures, thereby further improving the electrochemical performance and safety performance of the battery in low-temperature environments.

In some embodiments of the present application, based on the total area of the first active material layer and the second active material layer, the area ratio of the first active material layer is A, where 5%≤A≤ 90%.

In the above embodiments, the area ratio A of the first active layer satisfies the above relationship, which can not only improve the capacity retention rate of the battery in a low temperature environment, but also enable the battery to have a better energy density.

In some embodiments of the present application, the total weight W _A of the first active material layer on the current collector surface and the total weight W _B of the second active material layer on the current collector surface satisfy the following Relationship: 5%≤W _A /(W _A +W _B )≤90%.

In the above embodiments, when the total weight W _A of the first active material layer on the surface of the current collector and the total weight W _B of the second active material layer on the surface of the current collector satisfy the above relationship, it helps to reduce the loss of metal ions. Precipitation further improves the safety performance of the battery.

In some embodiments of the present application, the unit area weight W a of the first active material layer on the current collector surface is the same as the unit _area weight W _b of the second active material layer on the current collector surface. The following relationship is satisfied: 0.45≤W _a /W _b ≤2.2.

In the above embodiments, the unit area weight W _a of the first active material layer on the current collector surface and the unit area weight W _b of the second active material layer on the current collector surface satisfy the above relationship, which helps to reduce the battery internal energy consumption. The precipitation of metal ions can further reduce the occurrence of internal short circuits in the battery due to metal dendrites, thereby further improving the safety performance of the battery.

In some embodiments of the present application, the unit area weight W a of the first active material layer on the current collector surface is the same as the unit _area weight W _b of the second active material layer on the current collector surface. The following relationship is satisfied: 0.5≤W _a /W _b ≤2.0.

In the above embodiments, W _a and W _b satisfy the above relationship, which can further help reduce the precipitation of metal ions in the battery, thereby reducing the occurrence of metal dendrites that cause internal short circuits in the battery, thereby further improving the safety performance of the battery. .

In some embodiments of the present application, the thickness ta of the first active material layer and the thickness t _b of the second active material layer satisfy the following relationship: 0.8 ≤ _{t a} _/ t _b ≤ 1.2.

In the above embodiments, the thickness ta of the first active material layer and the thickness t _b of the second active material layer _satisfy the above relationship, which can not only reduce the processing difficulty of the electrode pole piece, but also shorten the distance between the active material layers. The gap is beneficial to reducing the precipitation of metal ions.

In some embodiments of the present application, the thickness ta of the first active material layer and the thickness t _b of the second active material layer satisfy the following relationship: 0.9 ≤ _{t a} _/ t _b ≤ 1.1.

In the above embodiments, ta and _{t b} _satisfy the above relationship, which can further reduce the processing difficulty of the electrode pole piece and shorten the gap between the active material layers to reduce the precipitation of metal ions.

In some embodiments of the present application, a plurality of first active material layers are provided on the surface of the current collector, and the plurality of first active material layers are spaced apart along the length direction of the electrode piece. The surface of the current collector, wherein the length L _n+1 of the n+1th first active material layer is greater than the length Ln of the nth first active material layer, and _n is an integer greater than 1.

In the above-mentioned embodiments, the lengths of adjacent first active material layers are different, which allows the battery assembled with the electrode plates to have better electrochemical performance in a low-temperature environment.

In some embodiments of the present application, a plurality of second active material layers are provided on the surface of the current collector, and the plurality of second active material layers are arranged along the length direction of the electrode pole piece, At least one second active material layer is located between two adjacent first active material layers.

In some embodiments of the present application, on the surface of the same side of the current collector, the plurality of first active material layers and the plurality of second active material layers are independently formed along the electrode pole piece. Arranged in the length direction, the weight of the first active material layer located in the middle of the plurality of first active material layers is greater than or equal to the weight of the middlemost one of the plurality of second active material layers. The weight of the second active material layer.

In some embodiments of the present application, on the surface of the same side of the current collector, the plurality of first active material layers and the plurality of second active material layers are independently formed along the electrode pole piece. arranged in the length direction, the length of the first active material layer located in the middle of the plurality of first active material layers is greater than or equal to the length of the middlemost one of the plurality of second active material layers. The length of the second active material layer.

In some embodiments of the present application, on the surface of the same side of the current collector, the plurality of first active material layers and the plurality of second active material layers are independently formed along the electrode pole piece. arranged in the length direction, the area of the first active material layer located in the middle of the plurality of first active material layers is greater than or equal to the area of the middlemost one of the plurality of second active material layers. The area of the second active material layer.

In the above embodiments, the temperature difference between various areas of the battery in a low-temperature environment can be reduced and made uniform, so that the battery has better electrochemical performance in a low-temperature environment.

In some embodiments of the present application, the first active material layer and the second active material layer are distributed along the width direction of the electrode plate, wherein the width d1 of the first active material layer is the same as the width d1 of the first active material layer. The width of the electrode pole piece is D and satisfies the following relationship: d1=(0.03-0.99)D.

In the above embodiments, the width d1 of the first active material layer and the width D of the electrode plate satisfy the above relationship, which can not only improve the capacity retention rate of the battery in a low temperature environment, but also enable the battery to have better energy. density.

In some embodiments of the present application, the first active material layer and the second active material layer are distributed along the width direction of the electrode plate, wherein the width d 1 of the first active material layer is equal to the width d ₁ of the first active material layer. The width of the electrode pole piece is D and satisfies the following relationship: d1=(0.05-0.90)D.

In the above embodiments, the width d1 of the first active material layer and the width D of the electrode plate satisfy the above relationship, which can further improve the capacity retention rate of the battery in a low-temperature environment and also improve the battery's capacity retention in a low-temperature environment. energy density.

In a second aspect, embodiments of the present application provide a secondary battery, including a positive electrode plate, a negative electrode plate, a separator and an electrolyte. A separator is disposed between the positive electrode piece and the negative electrode piece. Electrolytes. Wherein, the positive electrode piece and/or the negative electrode piece are the electrode pieces described in any of the above embodiments.

In the above-mentioned embodiments, since the electrode pole piece in any of the above-mentioned embodiments is included, the secondary battery has better electrochemical performance in a low-temperature environment.

In some embodiments of the present application, the positive electrode piece is the electrode piece.

In the above embodiments, the positive electrode piece is the electrode piece described in any one of the above embodiments, so that the battery can have better electrochemical performance in a low temperature environment.

In a third aspect, embodiments of the present application provide a battery module, including the secondary battery described in any of the above embodiments.

Since the above-mentioned embodiments include the secondary batteries in the above-mentioned embodiments, the battery module also has the technical effects of the above-mentioned secondary batteries, which will not be described again.

In some embodiments of the present application, the secondary battery is located at the edge area and/or bottom of the battery module.

In the above-mentioned embodiments, the position of the secondary battery can reduce the temperature difference between the edge area and the center area of the battery module, thereby making it have better electrochemical performance.

In a fourth aspect, embodiments of the present application provide a battery pack, including the secondary battery described in any one of the above embodiments and the battery module described in any one of the above embodiments.

In the above-mentioned embodiments, since it includes the secondary battery poles or battery modules in the above-mentioned embodiments, the battery pack also has the technical effects of the above-mentioned secondary batteries or battery modules, which will not be described again.

In some embodiments of the present application, the secondary battery is located at the edge area and/or bottom of the battery pack.

In the above-mentioned embodiments, the position of the secondary battery can reduce the temperature difference between the edge area and the central area of the battery pack, thereby making it have better electrochemical performance.

In some embodiments of the present application, the battery module is located at the edge area and/or bottom of the battery pack.

In the above-mentioned embodiments, the location of the battery module can reduce the temperature difference between the edge area and the center area of the battery pack, thereby enabling it to have better electrochemical performance.

In a fifth aspect, embodiments of the present application provide an electrical device, including the secondary battery described in any one of the above embodiments, the battery module described in any one of the above embodiments, and the battery module described in any one of the above embodiments. The battery pack described in any one of the above.

In the above-mentioned embodiments, since it includes the secondary battery pole, battery module or battery pack in the above-mentioned embodiments, the electrical device can operate normally in a low-temperature environment.

Description of the drawings

In order to explain the embodiments of the present application more clearly, the drawings required to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary people in the art, For technicians, other drawings can be obtained based on the attached drawings without any creative effort.

Figure 1 shows a schematic structural diagram of a vehicle provided by some embodiments of the present application;

Figure 2 shows an exploded view of a battery pack provided by some embodiments of the present application;

Figure 3 shows a schematic cross-sectional structural diagram of a battery pack provided by some embodiments of the present application;

Figure 4 shows an exploded schematic diagram of a secondary battery provided by some embodiments of the present application;

Figure 5 shows a schematic structural diagram of the expanded electrode pole pieces provided by some embodiments of the present application;

Figure 6 shows a schematic cross-sectional structural view of the electrode pole piece provided by some embodiments of the present application after being wound;

Figure 7 shows a schematic cross-sectional structural diagram of an electrode pole piece after being wound according to other embodiments of the present application;

Figure 8 shows a schematic cross-sectional structural diagram of an electrode pole piece after being wound according to some embodiments of the present application;;

Figure 9 shows a schematic structural diagram of the expanded electrode pole piece provided by some embodiments of the present application.

Figure 10 shows a schematic structural diagram of an expanded electrode piece provided by some other embodiments of the present application.

In the drawings, the drawings are not drawn to actual scale.

Tag description:

Vehicle 1000;

Battery pack 100, controller 200, motor 300;

Box 10, first part 11, second part 12;

secondary battery 20, case 21, electrode assembly 22, cover assembly 23;

Electrode plate 221, current collector 2211, first active material layer 2212, and second active material layer 2213.

Detailed ways

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

Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the technical field belonging to this application; the terms used herein are for the purpose of describing specific embodiments only and are not intended to be used in Limitation of this application; the terms "including" and "having" and any variations thereof in the description and claims of this application and the above description of the drawings are intended to cover non-exclusive inclusion.

In the description of the embodiments of this application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of indicated technical features. A specific order or priority relationship. In the description of the embodiments of this application, "plurality" means two or more, unless otherwise explicitly and specifically limited.

Reference herein to "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearances of this phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those skilled in the art understand, both explicitly and implicitly, that the embodiments described herein may be combined with other embodiments.

In the description of the embodiments of this application, the term "and/or" is only an association relationship describing associated objects, indicating that there can be three relationships, such as M and/or F, which can mean: M exists alone and M exists simultaneously. and F, there are three cases of F alone. In addition, the character "/" in this article generally indicates that the related objects are an "or" relationship.

It will be obvious to those skilled in the art that various modifications and changes can be made in the present application without departing from the scope of the present application. Thus, this application is intended to cover the modifications and variations of this application provided they come within the scope of the corresponding claims (the scope of protection) and their equivalents. It should be noted that the implementation modes provided in the embodiments of this application can be combined with each other if there is no contradiction.

Before elaborating on the scope of protection provided by the embodiments of the present application, in order to facilitate understanding of the embodiments of the present application, the present application first specifically explains the problems existing in the related technologies:

In the development of battery technology, in addition to improving the performance of batteries under normal operating temperatures, it is also necessary to consider the capacity retention rate and safety performance of batteries in low-temperature environments.

When the battery is in a low temperature environment, the ionic conductivity of the electrode plates will decrease, which may cause the battery's capacity retention rate to decrease rapidly. In addition, when the battery is in a low-temperature environment, metal ions will precipitate on the surface of the electrode plates. The metal ions will continue to accumulate on the surface of the electrode plates and form dendrites. These dendrites will pierce the separator and make the electrode plates electrically connected. A short circuit is formed, resulting in a decrease in the safety performance of the battery.

In view of this, embodiments of the present application provide an electrode plate, a secondary battery, a battery module, a battery pack and a power device, which can take into account the electrochemical performance and safety performance of the battery in a low-temperature environment.

In this application, the electrical device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric vehicle, a ship, a spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, spaceships, etc.

For the convenience of explanation in the following embodiments, an electric device 1000 according to an embodiment of the present application is used as an example.

Figure 1 shows a schematic structural diagram of a vehicle provided by some embodiments of the present application.

Please refer to Figure 1. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended range vehicle, etc. The battery pack 100 is disposed inside the vehicle 1000 , and the battery pack 100 may be disposed at the bottom, head, or tail of the vehicle 1000 . The battery pack 100 may be used to power the vehicle 1000 , for example, the battery pack 100 may serve as an operating power source for the vehicle 1000 . The vehicle 1000 may also include a controller 200 and a motor 300 . The controller 200 is used to control the battery pack 100 to provide power to the motor 300 , for example, to meet the power requirements for starting, navigation, and driving of the vehicle 1000 .

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

Figure 2 shows an exploded view of a battery pack provided by some embodiments of the present application. Figure 3 shows a schematic cross-sectional structural diagram of a battery pack provided by some embodiments of the present application.

The battery pack 100 in this application refers to a single physical module including one or more secondary batteries to provide higher voltage and capacity. For example, the battery mentioned in this application may include a battery module or a battery pack. Referring to FIG. 2 , the battery pack 100 includes a case 10 and a secondary battery 20 . The secondary battery 20 is accommodated in the case 10 .

The battery pack 100 includes a case 10 and a secondary battery 20 , and the secondary battery 20 is accommodated in the case 10 . Among them, the box 10 is used to provide a storage space for the secondary battery 20, and the box 10 can adopt a variety of structures. In some embodiments, the box 10 may include a first part 11 and a second part 12 , the first part 11 and the second part 12 covering each other, the first part 11 and the second part 12 jointly defining a space for accommodating the secondary battery 20 of accommodation space. The second part 12 may be a hollow structure with one end open, and the first part 11 may be a plate-like structure. The first part 11 covers the open side of the second part 12 so that the first part 11 and the second part 12 jointly define a receiving space. ; The first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 is covered with the open side of the second part 12. Of course, the box 10 formed by the first part 11 and the second part 12 can be in various shapes, such as cylinder, rectangular parallelepiped, etc.

In the battery pack 100 , there may be a plurality of secondary batteries 20 , and the plurality of secondary batteries 20 may be connected in series, in parallel, or in mixed connection. Mixed connection means that the plurality of secondary batteries 20 are connected in series and in parallel. The plurality of secondary batteries 20 can be directly connected in series or in parallel or mixed together, and then the plurality of secondary batteries 20 can be accommodated in the box 10 as a whole; of course, the battery pack 100 can also be a plurality of secondary batteries. 20 are first connected in series, parallel or mixed to form a battery module form, and then multiple battery modules are connected in series, parallel or mixed to form a whole, and are accommodated in the box 10 .

Each secondary battery 20 may be a secondary battery or a primary battery; it may also be a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, or a potassium-ion battery, but is not limited thereto. The secondary battery 20 may be in the shape of a cylinder, a flat body, a rectangular parallelepiped, or other shapes.

Please refer to FIG. 3 , which shows an exploded schematic diagram of a secondary battery provided by some embodiments of the present application. The secondary battery 20 refers to the smallest unit constituting the battery. As shown in FIG. 3 , the secondary battery 20 includes a case 21 , an electrode assembly 22 and a cover assembly 23 . The housing 21 has a chamber for accommodating the electrode assembly 22 , and the cover assembly 23 is used to close the opening of the housing 21 . The cover assembly 23 includes an end cap, and the end cap is connected with the casing 21 to form the outer casing of the secondary battery 20. The electrode assembly 22 is disposed in the casing 21, and the casing 21 is filled with electrolyte.

The end cap refers to a component that covers the opening of the case 21 to isolate the internal environment of the secondary battery 20 from the external environment. Without limitation, the shape of the end cap can be adapted to the shape of the housing 21 to fit the housing 21 . Optionally, the end cap can be made of a material with a certain hardness and strength (such as aluminum alloy). In this way, the end cap is less likely to deform when subjected to extrusion and collision, so that the secondary battery 20 can have higher structural strength. , the safety performance can also be improved. Functional components such as electrode terminals can be provided on the end cap. The electrode terminals may be used to electrically connect with the electrode assembly 22 for outputting or inputting electrical energy of the secondary battery 20 . In some embodiments, the end cap may also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the secondary battery 20 reaches a threshold value. The end cap can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which are not particularly limited in the embodiments of the present application. In some embodiments, an insulating member may also be provided inside the end cover, and the insulating member may be used to isolate the electrical connection components in the housing 21 from the end cover to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, etc.

The case 21 is a component used to cooperate with the end cap to form an internal environment of the secondary battery 20 , wherein the formed internal environment can be used to accommodate the electrode assembly 22 , the electrolyte, and other components. The casing 21 and the end cover may be independent components, and an opening may be provided on the casing 21 , and the end cover covers the opening at the opening to form the internal environment of the secondary battery 20 . Without limitation, the end cover and the housing 21 can also be integrated. Specifically, the end cover and the housing 21 can form a common connection surface before other components are inserted into the housing. When it is necessary to encapsulate the inside of the housing 21, Then the end cap is closed with the housing 21 . The housing 21 can be of various shapes and sizes, such as rectangular parallelepiped, cylinder, hexagonal prism, etc. Specifically, the shape of the housing 21 can be determined according to the specific shape and size of the electrode assembly 22 . The housing 21 can be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which are not particularly limited in the embodiments of the present application.

The electrode assembly 22 is a component in the secondary battery 20 where electrochemical reactions occur. One or more electrode assemblies 22 may be contained within the housing 21 . The electrode assembly 22 is mainly formed by winding or stacking a positive electrode piece and a negative electrode piece, and usually a separator is provided between the positive electrode piece and the negative electrode piece. The portions of the positive electrode tab and the negative electrode tab that contain active material constitute the main body of the electrode assembly 22 , and the portions of the positive electrode tab and the negative electrode tab that do not contain active material each constitute tabs. The positive electrode tab and the negative electrode tab can be located together at one end of the main body or respectively located at both ends of the main body. During the charging and discharging process of the battery, the positive active material and negative active material react with the electrolyte, and the tabs are connected to the electrode terminals to form a current loop.

Figure 5 shows a schematic structural diagram of an expanded electrode piece provided by some embodiments of the present application.

As shown in Figure 5, the embodiment of the present application provides an electrode plate 221, including: a current collector 2211, a first active material layer 2212 (the part filled with patterns in Figures 5-10 represents the first active material layer) and Second active material layer 2213 (the portion not filled with patterns in FIGS. 5-10 represents the second active material layer). Wherein, the first active material layer 2212 and the second active material layer 2213 are disposed on different surface areas of at least one side of the current collector 2211. The capacity retention rate K _A of the first active material layer 2212 at -20°C and the capacity retention rate K _B of the second active material layer 2213 at -20°C satisfy the following relationship: 3% ≤ K _A - _{K B} ≤ 80%.

The current collector 2211 is a structure or part that collects current, which can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

The current collector 2211 has a first surface and a second surface arranged oppositely along its thickness direction. The first active material layer 2212 and the second active material layer 2213 may be arranged in different areas of the first surface or may be arranged on the second surface. Different areas can also be provided in different areas of the first surface and the second surface at the same time.

In some embodiments, the first active material layer 2212 and the second active material layer 2213 are disposed in different areas of the first surface, and the number of the first active material layer 2212 and the second active material layer 2213 on the first surface may be It is one or more, which is not particularly limited in the embodiments of this application. When the number of first active material layers 2212 and the number of second active material layers 2213 is multiple, the arrangement of the first active material layer 2212 and the second active material layer 2213 on the first surface is not particularly limited. In some embodiments, the first active material layer 2212 and the second active material layer 2213 may be arranged at intervals.

The first active material layer 2212 and the second active material layer 2213 usually include active materials, conductive agents, binders, thickeners and other materials, where the active materials may be positive active materials or negative active materials. In some embodiments, the active material is a cathode active material.

When the first active material layer 2212 and the second active material layer 2213 are positive active material layers, the first active material layer 2212 includes the first positive active material, the second active material layer 2213 includes the second positive active material, and the first The positive active material is different from the second active material.

In some embodiments, the first cathode active material may be selected from a cathode material of a sodium ion battery (SIB), such as at least one of Prussian blue, layered oxide (NMO, such as Na ₂ FeO ₂ ), and polyanion. species, or lithium iron manganese phosphate material (LMFP), etc. The second cathode active material may be selected from one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt One or more of manganese oxide (NCM), lithium nickel cobalt aluminum oxide and its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (LFP), composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium iron manganese phosphate, phosphoric acid One or more of the composite materials of lithium iron manganese and carbon and its modified compounds. All of the above materials are commercially available.

In some embodiments, the surfaces of the first cathode active material and the second cathode active material may be coated with carbon.

In some embodiments, the conductive agent may be, but is not limited to, one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. ; The binder can be, but is not limited to, styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin and carboxymethyl One or more types of cellulose (CMC). The thickener may be carboxymethylcellulose (CMC).

In the manufacturing process of the electrode piece 221, the active material, conductive agent, binder, toughening agent and solvent are mixed in proportion to obtain a slurry; the above slurry is coated to form an active material layer;

The active material layer and the surface of the current collector 2211 are combined, and through processes such as drying and cutting, the electrode pole piece 221 is obtained.

In the embodiment of the present application, the capacity retention rate K _A of the first active material layer 2212 at -20°C and the capacity retention rate K _B of the second active material layer 2213 at -20°C are tested by using the first The first button cell and the second button cell of the active material layer 2212 and the second active material layer 2213 are placed in a constant temperature box at 25°C for 2 hours, discharged using a rate of 1/3C until the lower limit cut-off voltage is reached, and the capacity C is recorded. ₁ . When the battery is fully charged and placed in a -20°C thermostat for 2 hours, it is discharged at a rate of 1/3C until it reaches the lower limit cut-off voltage. The capacity C ₂ is recorded. C ₂ /C ₁ is recorded as -20°C capacity retention. Rate.

In the above embodiments, the first active material layer 2212 and the second active material layer 2213 are disposed on different surface areas of at least one side of the current collector 2211, and the capacity of the first active material layer 2212 is maintained at -20°C. The rate K _A and the capacity retention rate K _B of the second active material layer 2213 at -20°C satisfy the following relationship: 3% ≤ K _A - K _B ≤ 80%. The capacity retention rate K _A of the first active material layer 2212 at -20°C is higher than the capacity retention rate K _B of the second active material layer 2213 at -20°C, which can make the operating temperature of each area of the battery more uniform, thereby enabling The generation of lithium dendrites is reduced and the ionic conductivity of the electrode pole piece 221 is improved, so that the battery has good electrochemical performance and safety performance in a low-temperature environment. The capacity retention rate K _B of the second active material layer 2213 at -20° C. is relatively low, which allows the secondary battery to have a higher energy density in a low-temperature environment.

In some embodiments of the present application, the capacity retention rate K _A of the first active material layer 2212 at -20° C. ranges from 15% to 95%.

In the above-mentioned embodiments, the capacity retention rate of the first active material layer 2212 in a low-temperature environment is set within the above-mentioned range, which can uniformize the operating temperature of each area of the battery in a low-temperature environment, so as to reduce the edge area and central area of the battery. The temperature difference can improve the ionic conductivity of the electrode piece 221 in a low temperature environment and reduce the formation of lithium dendrites in the battery, thereby improving the electrochemical performance and safety performance of the battery.

In some embodiments of the present application, the capacity retention rate K _B of the second active material layer 2213 at -20°C ranges from 10% to 90%.

In the above embodiments, the capacity retention rate of the second active material layer 2213 in a low-temperature environment is smaller than the capacity retention rate of the first active material layer 2212 in a low-temperature environment, which can help to improve the operation of each area of the secondary battery. The temperature is more uniform, which reduces the decrease in ionic conductivity of the electrode pole piece 221 and the formation of lithium dendrites caused by excessive local temperature, thereby further improving the electrochemical performance and safety performance of the battery in low-temperature environments.

For example, the capacity retention rate K _A of the first active material layer 2212 at -20°C is 80%, and the capacity retention rate K _B of the second active material layer 2213 at -20°C is less than or equal to 77%.

In some embodiments of the present application, based on the total area of the first active material layer and the second active material layer, the area ratio of the first active material layer is A, where 5%≤A≤90%.

In some embodiments of the present application, the total weight W _A of the first active material layer 2212 on the surface of the current collector 2211 and the total weight W _B of the second active material layer 2213 on the surface of the current collector 2211 satisfy the following relationship: 5% ≤W _A /(W _A +W _B )≤90%.

In the above embodiments, the total weight W _A of the first active material layer 2212 on the surface of the current collector 2211 and the total weight W _B of the second active material layer 2213 on the surface of the current collector 2211 satisfy the above relationship, which helps to reduce the battery life. The precipitation of internal metal ions can further reduce the occurrence of metal dendrites and short circuits within the battery, thereby further improving the safety performance of the battery.

In some embodiments of the present application, the unit area weight Wa of the first active material layer 2212 on the surface of the current collector 2211 and the unit area weight W _b of the second active material layer 2213 on the surface of the current collector 2211 _satisfy the following relationship: 0.45≤W _a /W _b ≤2.2.

In the above embodiments, the unit area weight Wa of the first active material layer 2212 on the surface of the current collector 2211 and the unit area weight W _b of the second active material layer ₂₂₁₃ on the surface of the current collector 2211 satisfy the above relationship, which helps In order to reduce the precipitation of metal ions in the battery, it can also reduce the occurrence of metal dendrites that cause internal short circuits in the battery, thereby further improving the safety performance of the battery.

For example, the unit area weight W _a of the first active material layer 2212 on the surface of the current collector 2211 can range from 0.019g/cm ² to 0.024g/cm ² , and the second active material layer 2213 on the surface of the current collector 2211 The weight per unit area W _b on the surface can range from 0.02g/cm ² to 0.023g/cm ² .

In some specific embodiments, the unit area weight W a of the first active material layer 2212 on the surface of the current collector 2211 _is 0.019g/cm ² , and the unit area weight W of the second active material layer 2213 on the surface of the current collector 2211 _b is 0.02g/cm ² .

In other specific embodiments, the unit area weight W _a of the first active material layer 2212 on the surface of the current collector 2211 is 0.02g/cm ² , and the unit area weight of the second active material layer 2213 on the surface of the current collector 2211 W _b is 0.023g/cm ² .

In some embodiments of the present application, the unit area weight Wa of the first active material layer 2212 on the surface of the current collector 2211 and the unit area weight W _b of the second active material layer 2213 on the surface of the current collector 2211 _satisfy the following relationship: 0.5≤W _a /W _b ≤2.0.

In some specific embodiments, the unit area weight Wa of the first active material layer 2212 on the surface of the current collector 2211 _is 0.024g/cm ² , and the unit area weight W of the second active material layer 2213 on the surface of the current collector 2211 _b is 0.023g/cm ² .

Figure 6 shows a schematic cross-sectional structural view of the electrode pole piece after being wound according to some embodiments of the present application. Figure 7 shows a schematic cross-sectional structural diagram of an electrode pole piece after being wound according to other embodiments of the present application. FIG. 8 shows a schematic cross-sectional structural diagram of an electrode pole piece after being wound according to some embodiments of the present application.

As shown in FIGS. 6 to 8 , in some embodiments of the present application, the thickness ta of the first active material layer 2212 and the thickness _{t b} _of the second active material layer 2213 satisfy the following relationship: _0.8≤ta /t _b ≤1.2.

In the above embodiments, when the thickness _ta of the first active material layer 2212 and the thickness t _b of the second active material layer 2213 satisfy the above relationship, the electrode piece 221 is processed by hot pressing, winding, etc. , which can reduce the difficulty of processing. In addition, it can also shorten the gap between the active material layers, which is beneficial to reducing the precipitation of metal ions, thereby improving the safety performance of the battery.

In some embodiments, the thickness _ta of the first active material layer 2212 may range from 0.14mm to 0.20mm, and the thickness _tb of the second active material layer 2213 may range from 0.12mm to 0.19mm. .

In some specific embodiments, the thickness _ta of the first active material layer 2212 is 0.145 mm, and the thickness t _b of the second active material layer 2213 may be 0.19 mm.

In some embodiments of the present application, the thickness ta of the first active material layer 2212 and _{the thickness t b} _of the second active material layer 2213 satisfy the following relationship: 0.9 ≤ t _a /t _b ≤ 1.1.

In the above embodiments, ta _and t _b satisfy the above relationship, which can further reduce the processing difficulty of the electrode pole piece 221 and shorten the gap between the active material layers to reduce the precipitation of metal ions.

In some specific embodiments, the thickness ta of the first active material layer 2212 is 0.20 mm, and the thickness _{t b} _of the second active material layer 2213 may be 0.19 mm.

Figure 9 shows a schematic structural diagram of the expanded electrode pole piece provided by some embodiments of the present application. Figure 10 shows a schematic structural diagram of an expanded electrode piece provided by some other embodiments of the present application.

As shown in FIG. 9 , in some embodiments of the present application, a plurality of first active material layers 2212 are provided on the surface of the current collector 2211 , and the plurality of first active material layers 2212 are spaced apart along the length direction X of the electrode plate 221 On the surface of the current collector 2211, the length L _n+1 of the n+1th first active material layer 2212 is greater than the length _Ln of the nth first active material layer 2212, and n is an integer greater than 1.

In the above-mentioned embodiments, the adjacent first active material layers 2212 have different lengths, which allows the battery assembled with the electrode pole pieces 221 to have better electrochemical performance in a low-temperature environment.

In some embodiments of the present application, a plurality of second active material layers 2213 are provided on the surface of the current collector 2211, and the plurality of second active material layers 2213 are arranged along the length direction The two active material layers 2213 are located between two adjacent first active material layers 2212.

In some embodiments of the present application, on the surface of the same side of the current collector 2211, a plurality of first active material layers 2212 and a plurality of second active material layers 2213 are independently arranged along the length direction X of the electrode pole piece 221 The weight of the middlemost first active material layer 2212 among the plurality of first active material layers 2212 is greater than or equal to the weight of the middlemost second active material layer 2213 among the plurality of second active material layers 2213 .

In some embodiments of the present application, on the surface of the same side of the current collector 2211, a plurality of first active material layers 2212 and a plurality of second active material layers 2213 are independently arranged along the length direction X of the electrode pole piece 221 The length of the middlemost first active material layer 2212 among the plurality of first active material layers 2212 is greater than or equal to the length of the middlemost second active material layer 2213 among the plurality of second active material layers 2213 .

In some embodiments of the present application, on the surface of the same side of the current collector 2211, a plurality of first active material layers 2212 and a plurality of second active material layers 2213 are independently arranged along the length direction X of the electrode pole piece 221 The area of the middlemost first active material layer 2212 among the plurality of first active material layers 2212 is greater than or equal to the area of the middlemost second active material layer 2213 among the plurality of second active material layers 2213 .

As shown in FIG. 10 , in some embodiments of the present application, the first active material layer 2212 and the second active material layer 2213 are distributed along the width direction of the electrode plate 221 , wherein the width d1 of the first active material layer 2212 is equal to The width of the electrode piece 221 is D and satisfies the following relationship: d1=(0.03-0.99)D.

In the above embodiments, the width d ₁ of the first active material layer 2212 and the width D of the electrode plate 221 satisfy the above relationship, which can improve the capacity retention rate of the battery in a low-temperature environment and also make the battery have a higher performance. Good energy density.

In some embodiments of the present application, the first active material layer 2212 and the second active material layer 2213 are distributed along the width direction of the electrode plate 221 , wherein the width d1 of the first active material layer 2212 is equal to the width of the electrode plate 221 The following relationship is satisfied for D: d1=(0.05-0.90)D.

In the above-mentioned embodiments, the width d1 of the first active material layer 2212 and the width D of the electrode plate 221 satisfy the above relationship, which can further improve the capacity retention rate of the battery in a low-temperature environment. Energy density in the environment.

Embodiments of the present application provide a secondary battery, including a positive electrode piece, a negative electrode piece, a separator and an electrolyte. The separator is located between the positive electrode piece and the negative electrode piece. Wherein, the positive electrode piece and/or the negative electrode piece are the electrode pieces in any of the above embodiments.

In some embodiments of the present application, the positive electrode piece is an electrode piece.

In the above-mentioned embodiments, the positive electrode piece is the electrode piece in any of the above-mentioned embodiments, so that the battery can have better electrochemical performance in a low-temperature environment.

In the embodiment of the present application, the negative electrode active material is provided on the negative electrode sheet. The negative active material is not specifically limited and can be one of graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fiber, carbon nanotubes, elemental silicon, silicon oxygen compounds, silicon carbon composites, and lithium titanate. Or several.

In the embodiments of the present application, the separator is not specifically limited and can be a separator known in the art. For example, the separator may be made of one or more single-layer or multi-layer films selected from the group consisting of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

In the embodiments of the present application, there is no specific limitation on the electrolyte, and it can be an electrolyte known in the art. Exemplarily, the electrolyte includes an organic solvent and an electrolyte salt, wherein the organic solvent can be ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dicarbonate. Methyl ester (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), butyl Methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE) One or more of them; the electrolyte salt can be lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), bisfluorosulfonyl Lithium imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium difluoromethanesulfonylborate (LiBOB), difluorophosphoric acid One or more of lithium (LiPO ₂ F ₂ ), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

The above-mentioned positive electrode pieces, separators, and negative electrode pieces are stacked in order, so that the separator plays an isolation role between the positive electrode pieces and the negative electrode pieces, and an electrode assembly is obtained, or the electrode assembly can be obtained after winding; The electrode assembly is connected to the tab, and the electrode assembly is placed in the packaging shell, and then heated to remove excess water, and then the electrolyte is injected and sealed; finally, after standing, hot and cold pressing, formation, shaping, capacity testing and other processes, the result is Secondary battery of the present application.

An embodiment of the present application provides a battery module, including the secondary battery in any of the above embodiments.

In some embodiments of the present application, the secondary battery is located in the edge area and/or bottom of the battery module.

The application embodiment provides a battery pack, including the secondary battery in any of the above embodiments and the battery module in any of the above embodiments.

Since the above-mentioned embodiments include the secondary batteries or battery modules in the above-mentioned embodiments, the battery pack also has the technical effects of the above-mentioned secondary batteries or battery modules, which will not be described again.

In the embodiment of the present application, the battery pack includes an edge area and a central area, where the edge area is an area with poor thermal insulation ability, which can be understood as the surrounding and/or bottom of the battery pack, and the remaining area is the central area.

As shown in FIG. 3 , in some embodiments of the present application, the secondary battery (secondary battery 20 in FIG. 3 ) is located at the edge area and/or the bottom of the battery pack 100 .

Please continue to refer to FIG. 3 . In the secondary battery of the battery pack 100 , the surface where the first active material layer 2212 is located is opposite to the inner wall of the box 10 .

In some embodiments of the present application, the battery module is located at the edge area and/or the bottom of the battery pack.

Embodiments of the present application provide an electrical device, including the secondary battery in any of the above embodiments, the battery module in any of the above embodiments, and the battery pack in any of the above embodiments.

The electrochemical performance and safety performance of secondary batteries in low temperature environments will be described in detail below through specific examples.

Example 1

Preparation of the first positive electrode slurry

Dissolve the cathode active material Na ₂ FeO ₂ , conductive agent carbon black and binder polyvinylidene fluoride (PVDF) in the solvent N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5, and stir thoroughly to mix. After uniformity, the first positive electrode slurry is obtained.

Preparation of the second positive electrode slurry

Dissolve the carbon-coated lithium iron phosphate (LFP) as the positive electrode active material, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) in the solvent N-methylpyrrolidone at a weight ratio of 96:2:2 (NMP), stir thoroughly and mix evenly to obtain the second positive electrode slurry.

Preparation of positive electrode plates

The first positive electrode slurry and the second positive electrode slurry are evenly coated on different surface areas of the positive electrode current collector, and then dried, cold pressed, and cut to obtain positive electrode sheets.

Preparation of negative electrode plates

Dissolve the active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) in the solvent deionized water at a weight ratio of 90:4:4:2 After evenly mixing with the solvent deionized water, a negative electrode slurry is prepared; then the negative electrode slurry is evenly coated on the negative electrode current collector copper foil one or more times, dried to obtain the negative electrode diaphragm, and then cold pressed and cut to obtain Negative pole piece.

Preparation of electrolyte

In an argon atmosphere glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), mix the organic solvent EC/EMC evenly according to the volume ratio of 3/7, add 12.5% LiPF ₆ lithium salt and dissolve it in the organic solvent. Stir evenly to obtain the corresponding electrolyte.

diaphragm

Use polypropylene film as separator.

Preparation of secondary batteries

Use the positive electrode piece and the negative electrode piece prepared as above, use the polypropylene film as the isolation film, stack the positive electrode piece, the isolation film, and the negative electrode piece in order so that the isolation film is between the positive and negative electrode pieces. to the isolation function, and then wound to obtain the electrode assembly. The electrode assembly is placed in the battery case, dried and then injected with electrolyte, and then formed and left to stand to prepare a lithium-ion secondary battery as a secondary battery.

Battery pack assembly

The secondary batteries prepared in this embodiment are respectively placed at the edge area and/or the bottom of the battery pack. The secondary battery placed in the central area of the battery pack is not particularly limited.

Example 2

The preparation method of the secondary battery of Example 2 is similar to that of Example 1, and the differences are listed in Table 1.

Example 3

Preparation of the first positive electrode slurry

Lithium iron manganese phosphate (LiMn _0.6 Fe _0.4 PO ₄ (LMFP)) as the positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were dissolved in the solvent N- in a weight ratio of 96:2:2. methylpyrrolidone (NMP), stir thoroughly and mix evenly to obtain the first positive electrode slurry.

Preparation of the second positive electrode slurry

Preparation of positive electrode plates

Preparation of negative electrode plates

Dissolve the negative active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC-Na) in the solvent at a weight ratio of 95:2:2:1 In deionized water, mix evenly and prepare negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and after drying, it is cold pressed and cut to obtain negative electrode sheets. Preparation of electrolyte

Preparation of electrolyte

diaphragm

Use polypropylene film as separator.

Preparation of secondary batteries

Example 4

The preparation method of the secondary battery of Example 4 is similar to that of Example 3, and the differences are listed in Table 1.

Example 5

Preparation of the first positive electrode slurry

Preparation of the second positive electrode slurry

Dissolve the positive electrode active material sodium manganate LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811), conductive agent carbon black and polyvinylidene fluoride (PVDF) in the solvent N-methylpyrrolidone ( NMP), stir thoroughly and mix evenly to obtain the second positive electrode slurry.

Preparation of positive electrode plates

Preparation of negative electrode plates

Preparation of electrolyte

diaphragm

Use polypropylene film as separator.

Preparation of secondary batteries

Example 6

The preparation method of the secondary battery of Example 6 is similar to that of Example 5, and the differences are listed in Table 1.

Comparative Example 1-6

The preparation method of the secondary battery of Comparative Example 1-6 is similar to that of Example 1-6, and the differences are listed in Table 1.

test part

(1) Capacity retention test of the first positive electrode active material layer

Take the pole piece of the active material layer to assemble a button-type half-cell (for example, lithium-ion batteries can use lithium sheets as the counter electrode, and sodium-ion batteries can use sodium sheets as the counter electrode), let it stand for 2 hours in a 25°C thermostat, and use Discharge is performed at a rate of 1/3C until the lower limit cut-off voltage is reached, and the capacity C ₁ is recorded. When the battery is fully charged and placed in a -20°C thermostat for 2 hours, it is discharged at a rate of 1/3C until it reaches the lower limit cut-off voltage. The capacity C ₂ is recorded. C ₂ /C ₁ is recorded as -20°C capacity retention. rate, the test results are shown in Table 1.

(2) Capacity retention test of the second pole active material layer

The test method is the same as the capacity retention rate of the first positive active material layer, and the test results are shown in Table 1.

(3) Capacity retention test of secondary battery

When the secondary battery is fully charged, let it stand in a 25°C thermostat for 2 hours, discharge it at a rate of 1/3C until it reaches the lower limit cut-off voltage, and record the capacity C ₃ . When the battery pack is fully charged and placed in a -20°C thermostat for 2 hours, it is discharged at a rate of 1/3C until it reaches the lower limit cut-off voltage. The capacity C ₄ is recorded, and C ₄ /C ₃ is recorded as the -20°C capacity. Retention rate, test results are shown in Table 2.

(4)Thermal spread test

Test whether the thermal runaway of a certain secondary battery in the battery will spread to adjacent secondary batteries due to acupuncture. For a test battery module composed of two or more secondary batteries to be tested, it is necessary to determine whether to add a thermal insulation pad between the secondary batteries and the thickness of the thermal insulation pad according to the specific scenario, and determine whether to turn on the water cycle. Test that the battery module is fully charged, and select a two-piece steel plate clamp with holes to fix the test battery module. Use a high-temperature resistant stainless steel needle with a diameter of 3mm to 8mm (the needle cone angle is 20° to 60°, the surface of the steel needle is smooth and free of rust, oxide layer and oil stain), at a speed of 0.1mm/s to 40mm/s, From the direction perpendicular to the plate of the secondary battery until the first secondary battery triggers thermal runaway, observe and record the time when the adjacent second battery cell thermal runaway occurs; the secondary battery that triggers thermal runaway does not cause the corresponding If a secondary battery catches fire or explodes, it is judged that the heat spread barrier has been achieved, otherwise it is judged that heat spread has occurred. The test results are shown in Table 2.

(5)Volume energy density test of secondary batteries:

Secondary battery volumetric energy density = secondary battery initial discharge capacity × discharge voltage platform/secondary battery volume.

Among them, the initial discharge capacity of the secondary battery is the capacity that starts from the upper limit cut-off voltage at 25°C and discharges to the lower limit cut-off voltage at a rate of 1/3C.

The discharge voltage platform is the average discharge voltage starting from the upper limit cut-off voltage at 25°C and discharging at a rate of 1/3C to the lower limit cut-off voltage.

Table 1

Table 2

序号serial number	-20℃放电容量保持率-20℃ discharge capacity retention rate	热蔓延heat spread	体积能量密度(Wh/L)Volume energy density (Wh/L)
实施例1Example 1	53％53%	热蔓延阻隔heat spread barrier	403403
实施例2Example 2	42％42%	热蔓延阻隔heat spread barrier	378378
实施例3Example 3	49％49%	热蔓延阻隔heat spread barrier	433433
实施例4Example 4	59％59%	热蔓延阻隔heat spread barrier	445445
实施例5Example 5	73％73%	热蔓延阻隔heat spread barrier	664664
实施例6Example 6	75％75%	热蔓延阻隔heat spread barrier	581581
对比例1Comparative example 1	30％30%	热蔓延阻隔heat spread barrier	415415
对比例2Comparative example 2	70％70%	热蔓延heat spread	705705
对比例3Comparative example 3	76％76%	热蔓延阻隔heat spread barrier	290290
对比例4Comparative example 4	76％76%	热蔓延阻隔heat spread barrier	302.5302.5
对比例5Comparative example 5	40％40%	热蔓延heat spread	612612
对比例6Comparative example 6	23％twenty three%	热蔓延heat spread	604604

It can be seen from Table 1 and Table 2 that the capacity retention rate K _A of the first active material layer at -20°C is higher than the capacity retention rate K _B of the second active material layer at -20°C, which can ensure the operation of each area of the battery. The temperature is more uniform, which can reduce the generation of lithium dendrites and improve the ionic conductivity of the electrode plates, so that the battery has good electrochemical performance and safety performance in low temperature environments. The capacity retention rate K _B of the second active material layer at -20°C is relatively low, which enables the secondary battery to have a higher energy density in a low-temperature environment.

While the present application has been described with reference to preferred embodiments, various modifications may be made and equivalents may be substituted for components thereof without departing from the scope of the application. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any way. The application is not limited to the particular embodiments disclosed but includes all embodiments falling within the scope of the claims.

Claims

An electrode pole piece including:

current collector;

first active material layer;

a second active material layer;

Wherein, the first active material layer and the second active material layer are disposed on different surface areas of at least one side of the current collector;

The capacity retention rate K A of the first active material layer at -20°C and the capacity retention rate K B of the second active material layer at -20°C satisfy the following relationship: 3% ≤ K A - K B ≤ 80% .
The electrode pole piece according to claim 1, wherein the capacity retention rate of the first active material layer at -20°C is 15% ≤ K A ≤ 95%;

And/or, the capacity retention rate of the second active material layer at -20°C is 10% ≤ K B ≤ 90%.
The electrode pole piece according to claim 1 or 2, wherein, based on the total area of the first active material layer and the second active material layer, the area ratio of the first active material layer is A, Among them, 5%≤A≤90%.
The electrode plate according to claims 1-3, wherein the total weight W A of the first active material layer on the current collector surface is equal to the total weight W A of the second active material layer on the current collector surface. The weight W B satisfies the following relationship: 5%≤W A /(W A +W B )≤90%.
The electrode pole piece according to any one of claims 1 to 4, wherein the unit area weight W a of the first active material layer on the current collector surface is equal to the weight W a of the second active material layer on the current collector surface. The unit area weight W b on the surface of the current collector satisfies the following relationship: 0.45≤W a /W b ≤2.2.
The electrode pole piece according to any one of claims 1 to 5, wherein the unit area weight W a of the first active material layer on the current collector surface is the same as the unit area weight W a of the second active material layer on the current collector surface. The unit area weight W b on the surface of the current collector satisfies the following relationship: 0.5≤W a /W b ≤2.0.
The electrode pole piece according to any one of claims 1 to 6, wherein the thickness ta of the first active material layer and the thickness t b of the second active material layer satisfy the following relationship: 0.8≤t a /t b ≤1.2.
The electrode pole piece according to any one of claims 1 to 7, wherein the thickness ta of the first active material layer and the thickness t b of the second active material layer satisfy the following relationship: 0.9≤t a /t b ≤1.1.
The electrode pole piece according to any one of claims 1 to 8, wherein a plurality of the first active material layers are provided on the surface of the current collector, and the plurality of first active material layers are arranged along the electrode. The length direction of the pole pieces is spaced apart on the surface of the current collector, wherein the length L n+1 of the n +1 first active material layer is greater than the length L n of the nth first active material layer. , n is an integer greater than 1.
The electrode piece according to claim 8, wherein a plurality of the second active material layers are provided on the surface of the current collector, and the plurality of second active material layers are along the length direction of the electrode piece. Arranged, at least one second active material layer is located between two adjacent first active material layers.
The electrode pole piece according to claim 9, wherein on the surface of the same side of the current collector, the plurality of first active material layers and the plurality of second active material layers are independently formed along the The electrode pole pieces are arranged in the length direction, and the weight of the first active material layer located in the middle of the plurality of first active material layers is greater than or equal to the weight of the middlemost one of the plurality of second active material layers. A weight of the second active material layer.
The electrode pole piece according to claim 9 or 10, wherein on the surface of the same side of the current collector, the plurality of first active material layers and the plurality of second active material layers are independently Arranged along the length direction of the electrode pole piece, the length of the first active material layer located in the middle of the plurality of first active material layers is greater than or equal to that of the plurality of second active material layers. The length of the middlemost second active material layer.
The electrode pole piece according to any one of claims 9 to 11, wherein, on the surface of the same side of the current collector, the plurality of first active material layers and the plurality of second active material layers are The material layers are independently arranged along the length direction of the electrode plate, and the area of the first active material layer located in the middle of the plurality of first active material layers is greater than or equal to that of the first active material layer located in the plurality of first active material layers. The area of the second active material layer that is the middle one among the two active material layers.
The electrode piece according to any one of claims 1 to 7, wherein the first active material layer and the second active material layer are distributed along the width direction of the electrode piece, and wherein the third active material layer The width d1 of an active material layer and the width D of the electrode pole satisfy the following relationship: d1=(0.03-0.99)D.
The electrode piece according to any one of claims 1 to 7, wherein the first active material layer and the second active material layer are distributed along the width direction of the electrode piece, and wherein the third active material layer The width d1 of an active material layer and the width D of the electrode pole satisfy the following relationship: d1=(0.05-0.90)D.
A secondary battery including:

Positive pole piece;

Negative pole piece;

A separator located between the positive electrode piece and the negative electrode piece;

electrolytes;

Wherein, the positive electrode piece and/or the negative electrode piece is the electrode piece according to any one of claims 1-14.
The secondary battery according to claim 15, wherein the positive electrode tab is the electrode tab.
A battery module including the secondary battery described in claim 15 or 16.
The battery module according to claim 17, wherein the secondary battery is located at an edge area and/or a bottom of the battery module.
A battery pack including the secondary battery according to claim 15 or 16 and the battery module according to claim 17 or 18.
The battery pack according to claim 19, wherein the secondary battery is located at an edge area and/or a bottom of the battery pack.
The battery pack according to any one of claims 19 or 20, wherein the battery module is located at an edge area and/or a bottom of the battery pack.
An electrical device includes the secondary battery described in claim 15 or 16, the battery module described in claim 17 or 18, and the battery pack described in any one of claims 19-21.