WO2024066624A1 - Negative electrode sheet and preparation method therefor, and electrode assembly, battery cell, battery and electric apparatus - Google Patents

Abstract

The present application relates to the technical field of batteries. Provided are a negative electrode sheet and a preparation method therefor, and an electrode assembly, a battery cell, a battery and an electric apparatus. The negative electrode sheet comprises a negative-electrode current collector, a negative-electrode active substance layer and a functional layer, wherein the negative-electrode active substance layer is arranged on at least one face of the negative-electrode current collector in the thickness direction; and the functional layer protrudes from the surface of the negative-electrode active substance layer of at least part of a portion to be bent, and the functional layer comprises a negative-electrode active substance and/or a conductive agent. The functional layer is arranged on the surface of the negative-electrode active substance layer of part of the portion to be bent, and the functional layer can increase a CB value of a corresponding area of a battery, that is, the ratio of the capacity of a negative-electrode active substance in the area to the capacity of a positive-electrode active substance in the area is increased; and/or an electronic and ionic conductive channel is provided, such that accumulated lithium ions are quickly evacuated, thereby reducing or avoiding the occurrence of lithium precipitation. The functional layer can shorten the distance between a positive electrode sheet and a negative electrode sheet, reduce the liquid-phase resistance of a battery, and improve the electrochemical reaction kinetics.

Description

Negative electrode sheet and preparation method thereof, electrode assembly, battery cell, battery and power-consuming device

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Chinese patent application No. 202211175113.6 filed on September 26, 2022, entitled “A negative electrode plate and its preparation method, electrode assembly, battery cell, battery and electrical device”, and the entire contents of that application are incorporated herein by reference.

Technical Field

The present application relates to the field of battery technology, and in particular to a negative electrode plate and a preparation method thereof, an electrode assembly, a battery cell, a battery and an electrical device.

Background technique

Lithium deposition inside the battery is one of the main factors affecting the electrical and safety performance of the battery. Once lithium deposition occurs in the battery, it will not only reduce the service life of the battery, but also as the amount of lithium deposition accumulates, dendrites are likely to form. Dendrites may pierce the diaphragm, thereby causing a short circuit in the battery, creating a safety hazard.

Summary of the invention

In view of the above problems, the present application provides a negative electrode plate and a preparation method thereof, an electrode assembly, a battery cell, a battery and an electrical device, which can reduce or avoid lithium plating and improve the safety of the battery.

In the first aspect, the present application provides a negative electrode sheet, the negative electrode sheet is configured with a straight portion and a portion to be bent, the negative electrode sheet comprises: a negative electrode current collector, a negative electrode active material layer and a functional layer, the negative electrode active material layer is arranged on at least one side of the negative electrode current collector along the thickness direction, and the functional layer is convexly arranged on the surface of at least part of the negative electrode active material layer of the portion to be bent. The functional layer comprises a negative electrode active material and/or a conductive agent.

In the technical solution of the embodiment of the present application, a functional layer is arranged on the surface of the negative electrode active material layer of the part to be bent. When the functional layer includes the negative electrode active material, the CB value of the corresponding area of the battery can be increased, that is, the ratio of the capacity of the negative electrode active material to the capacity of the positive electrode active material in the area is increased, thereby reducing or avoiding the occurrence of lithium precipitation; when the functional layer includes a conductive agent, the conductive agent can provide electron and ion conductive channels to quickly dredge the accumulated lithium ions, thereby reducing or avoiding the occurrence of lithium precipitation; when the functional layer includes the negative electrode active material and the conductive agent, it can not only increase the CB value of the corresponding area of the battery, but also quickly dredge the accumulated lithium ions, thereby reducing or avoiding the occurrence of lithium precipitation, and improving the safety and service life of the battery. In addition, the functional layer arranged on the surface of the negative electrode active material layer of the part to be bent can shorten the distance between the positive electrode sheet and the negative electrode sheet of the part to be bent, reduce the liquid phase resistance of the battery, and improve the electrochemical reaction kinetics.

In some embodiments, the functional layer further includes a film-forming material. Adding the film-forming material to the functional layer 430 can improve the bonding effect between the functional layer 430 and the negative electrode active material layer 420 .

In some embodiments, the functional layer includes 20 wt% to 99 wt% of negative electrode active material and 1 wt% to 80 wt% of film-forming material. By adjusting the proportion of negative electrode active material and film-forming material in the functional layer, the CB value of the corresponding area of the battery and the bonding effect of the functional layer can be adjusted.

In some embodiments, the functional layer includes 20 wt% to 99 wt% of a conductive agent and 1 wt% to 80 wt% of a film-forming material. By adjusting the proportion of the conductive agent and the film-forming material in the functional layer, the number of electronic and ion conductive channels and the bonding effect of the functional layer can be regulated.

In some embodiments, the functional layer includes 20wt% to 70wt% of negative electrode active material, 20wt% to 70wt% of conductive agent and 10wt% to 60wt% of film-forming material. By adjusting the proportion of negative electrode active material, conductive agent and film-forming material in the functional layer, the CB value of the corresponding area of the battery, the number of electronic and ion conductive channels and the bonding effect of the functional layer can be regulated.

In some embodiments, the negative electrode active material includes any one or more of a first carbon material, a lithiation-capable metal, a lithiation-capable metal alloy, and a lithiation-capable oxide. The first carbon material includes hard carbon, soft carbon, activated carbon, graphite, silicon oxygen carbon, and an intermediate phase. Any one or more of carbon microspheres. When the negative electrode active material is selected from the above materials, the functional layer can have more lithium ion active sites and the CB value of the corresponding area of the battery can be improved.

In some embodiments, the conductive agent includes a second carbon material and/or a conductive organic matter. The second carbon material includes any one or more of carbon fiber, conductive carbon black, carbon nanotubes and graphene. When the conductive agent is selected from the above materials, the functional layer can have multiple electronic and ion conductive channels and can quickly dredge the accumulated lithium ions.

In some embodiments, the porosity of the functional layer is 10% to 90%. By adjusting the porosity of the functional layer, the functional layer can be wetted with electrolyte and form a fast lithium ion channel.

In a second aspect, the present application provides a method for preparing the negative electrode sheet in the above embodiment, which includes: forming a negative electrode active material layer on at least one side of the negative electrode current collector along the thickness direction, and forming a functional layer on the surface of at least part of the negative electrode active material layer to be bent.

In the technical solution of the embodiment of the present application, the preparation method of the negative electrode plate of the present application is simple, and the functional layer is formed on the surface of the negative electrode active material layer of at least part of the portion to be bent after the negative electrode active material layer is formed. In the formation process of the functional layer of the present application, an intermittent coating process is not required, and the manufacturing difficulty is low.

In a third aspect, the present application provides an electrode assembly, which includes: a positive electrode sheet and a negative electrode sheet in the above embodiment, wherein the positive electrode sheet and the negative electrode sheet are wound or folded to form a bending area and a straight area, and the straight area is connected to the bending area. The portion to be bent is wound or folded to form a bending portion, the bending portion is located in the bending area, and the straight portion is located in the straight area.

In the technical solution of the embodiment of the present application, a functional layer is arranged on the surface of the negative electrode active material layer in the partial bending area, so as to increase the CB value of the corresponding area of the battery, that is, to increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in the area, and/or to provide electron and ion conductive channels to quickly guide the accumulated lithium ions, thereby reducing or avoiding the occurrence of lithium precipitation. In addition, the functional layer arranged on the surface of the negative electrode active material layer in the partial bending area can shorten the distance between the positive electrode sheet and the negative electrode sheet in the partial bending area, reduce the liquid phase resistance of the battery, and improve the electrochemical reaction kinetics.

In some embodiments, the positive electrode sheet and the negative electrode sheet are wound to form a winding structure, and a functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of at least a part of the bend. For an electrode assembly with a winding structure, the outer side of the negative electrode current collector is smaller than the inner side of the corresponding positive electrode current collector, which results in that the negative electrode active material capacity of the outer side of the negative electrode current collector is smaller than the positive electrode active material capacity of the corresponding positive electrode current collector under normal circumstances, and lithium precipitation reaction is very easy to occur. The functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of at least a part of the bend, which can increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in the region, or provide an electron and ion conductive channel in the region to quickly guide the accumulated lithium ions, thereby reducing or avoiding the lithium desorption reaction of the active material layer in the partial bend area, and improving the safety and service life of the battery.

In some embodiments, the positive electrode sheet and the negative electrode sheet are wound to form a winding structure, the negative electrode sheet has a first bend located at the innermost side of the winding structure, and a functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of the first bend. The first bend located at the innermost side of the electrode assembly is the area where lithium precipitation reaction is most likely to occur, and the functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of the first bend, which can increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in the area, or provide electron and ion conductive channels in the area to quickly guide the accumulated lithium ions, thereby reducing or avoiding the lithium desorption reaction of the active material layer in the partial bend area, and improving the safety and service life of the battery.

In some embodiments, a functional layer is provided on the surface of the negative electrode active material layer on the inner side of the negative electrode current collector of the first bend. The functional layer is provided on the surface of the negative electrode active material layer on the inner side of the negative electrode current collector of the first bend, which can reduce the curvature of the negative electrode sheet in this area and improve the powder shedding of the negative electrode sheet in this area.

In some embodiments, along the winding direction, the negative electrode sheet has a second bend, a third bend, a fourth bend and a fifth bend that are adjacent to the first bend in sequence, and the second bend, the third bend, the fourth bend and the fifth bend are all provided with a functional layer on the surface of the negative electrode active material layer on the outer side of each negative electrode current collector. The first bend, the second bend, the third bend, the fourth bend and the fifth bend located at the innermost side of the electrode assembly are the areas where lithium precipitation reaction is most likely to occur, and the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of the first bend, the second bend, the third bend, the fourth bend and the fifth bend is provided with a functional layer, which can increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in the multiple regions, or provide electronic and ion conductive channels in the multiple regions to quickly guide the accumulated lithium ions, thereby reducing or avoiding the lithium desorption reaction of the active material layer in some bend areas, and improving the safety and service life of the battery.

In some embodiments, the second bend, the third bend, the fourth bend, and the fifth bend are all provided with a functional layer on the surface of the negative electrode active material layer on the inner side of each negative electrode current collector. The functional layer is provided on the surface of the negative electrode active material layer on the inner side of the negative electrode current collector of the second bend, the third bend, the fourth bend, and the fifth bend, so that the curvature of the negative electrode sheets in the multiple regions can be reduced and the powder loss of the negative electrode sheets in the multiple regions can be improved.

In some embodiments, the positive electrode sheet and the negative electrode sheet are wound to form a winding structure having multiple bends, and the functional layers corresponding to the multiple bends are thinned in sequence along the winding direction. Along the winding direction, the possibility of the multiple bends of the electrode assembly being prone to lithium deposition is reduced in sequence, or the severity of the lithium deposition reaction is reduced in sequence, and the functional layers corresponding to the multiple bends are thinned in sequence along the winding direction, so that they can correspond to the possibility of lithium deposition or the severity of the lithium deposition reaction, which is beneficial to improving the overall energy density of the battery.

In some embodiments, along the winding direction, the thickness difference of the functional layers corresponding to two adjacent bends is 1 μm to 70 μm. Adjusting the thickness of the functional layers corresponding to the multiple bends is beneficial to both improving lithium deposition and ensuring the overall energy density of the battery.

In some embodiments, the positive electrode sheet and the negative electrode sheet are folded to form a laminate structure, the negative electrode sheet has a sixth bend covered by the positive electrode sheet, and the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of the sixth bend is provided with a functional layer. The sixth bend located in the laminate structure is an area where lithium precipitation reaction is prone to occur, and the surface of the negative electrode active material layer on the inner side of the negative electrode current collector of the sixth bend is provided with a functional layer, which can increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in the area, or provide electron and ion conductive channels in the area to quickly guide the accumulated lithium ions, thereby reducing or avoiding the lithium desorption reaction of the active material layer in the partial bend area, improving the safety and service life of the battery, and ensuring the energy density of the battery.

In some embodiments, a functional layer is provided on the surface of the negative electrode active material layer on the inner side of the negative electrode current collector of the sixth bend. The functional layer is provided on the surface of the negative electrode active material layer on the inner side of the negative electrode current collector of the sixth bend, which can reduce the curvature of the negative electrode sheet in this area and improve the powder shedding of the negative electrode sheet in this area.

In a fourth aspect, the present application provides a battery cell comprising the electrode assembly in the above embodiment.

In a fifth aspect, the present application provides a battery, which includes the battery cell in the above embodiment.

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

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

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG1 is a schematic structural diagram of a vehicle according to some embodiments of the present application;

FIG2 is a schematic diagram of an exploded structure of a battery according to some embodiments of the present application;

FIG3 is a schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

FIG4 is a top view of a negative electrode sheet according to some embodiments of the present application;

FIG5 is a cross-sectional view of a first negative electrode sheet according to some embodiments of the present application;

FIG6 is a cross-sectional view of a second negative electrode sheet according to some embodiments of the present application;

FIG7 is a cross-sectional view of a third negative electrode sheet according to some embodiments of the present application;

FIG8 is a schematic structural diagram of a first electrode assembly in some embodiments of the present application;

FIG9 is a schematic structural diagram of a second electrode assembly according to some embodiments of the present application;

FIG10 is a schematic diagram of a first partial structure of a first electrode assembly according to some embodiments;

FIG11 is a schematic diagram of a second partial structure of the first electrode assembly in some embodiments of the present application;

FIG12 is a schematic diagram of a third partial structure of the first electrode assembly according to some embodiments of the present application;

FIG. 13 is a schematic structural diagram of a third electrode assembly according to some embodiments of the present application.

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

1000-Vehicles;

100-battery; 200-controller; 300-motor;

10-box; 11-first part; 12-second part; 13-accommodating space;

20-battery cell; 21-housing; 22-electrode assembly; 23-electrode terminal; 24-pressure relief structure;

211-shell; 212-cover; 213-sealed space; 400-negative electrode plate; 401-straight portion; 402-portion to be bent; 403-first bending portion; 404-second bending portion; 405-third bending portion; 406-fourth bending portion; 407-fifth bending portion; 408-sixth bending portion; 410-negative electrode current collector; 420-negative electrode active material layer; 430-functional layer; 501-straight area; 502-bending area; 600-positive electrode plate; 700-isolation film.

Detailed ways

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

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

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

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

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

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

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

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

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

The inventor of the present application has noticed that during the cycle of lithium-ion batteries, lithium ions will be embedded and de-embedded between the cathode and anode of the battery. When lithium ions migrate from the cathode to the anode, due to the limitations of the battery structure, in the area where the cathode wraps the anode at the bend of the inner circle, the capacity ratio of the cathode and anode of the battery is insufficient, and too many lithium ions in the cathode are embedded in the anode, while the anode does not have enough capacity to meet the embedding of lithium ions, resulting in the precipitation of excess lithium ions in the area where the cathode wraps the anode in the inner circle. Lithium precipitation at the anode will seriously reduce the cycle performance of the battery. At the same time, when lithium ion batteries undergo lithium precipitation, the precipitated lithium metal is very active and will react with the electrolyte, causing the battery's self-heating starting temperature to decrease and the self-heating rate to increase, seriously endangering the safety of the battery. In addition, when lithium precipitation is severe, the de-embedded lithium ions will also form lithium crystals on the surface of the anode, and the lithium crystals can pierce the isolation membrane, causing short-circuit thermal runaway of adjacent cathodes and anodes.

The applicant's research found that lithium deposition often occurs in the bending area of the electrode assembly. During the winding or folding process of the positive and negative electrode sheets, the negative electrode active material in the bending area of the negative electrode sheet is easy to fall off, which causes the lithium insertion sites of the negative electrode active material layer of the negative electrode sheet to be further less than the number of lithium ions that can be provided by the positive electrode active material layer of the adjacent positive electrode sheet. When the lithium-ion battery is charged, lithium deposition is easy to occur.

Based on the above considerations, in order to alleviate the problem of lithium deposition in the battery, the inventor has designed a negative electrode plate after in-depth research. By setting a functional layer on the surface of the negative electrode active material layer of the part to be bent, when the functional layer includes a negative electrode active material, the CB value of the corresponding area of the battery can be increased, that is, the ratio of the capacity of the negative electrode active material to the capacity of the positive electrode active material in the area is increased, thereby reducing or avoiding the occurrence of lithium deposition; when the functional layer includes a conductive agent, the conductive agent can provide electron and ion conductive channels to quickly dredge the accumulated lithium ions, thereby reducing or avoiding the occurrence of lithium deposition; when the functional layer includes a negative electrode active material and a conductive agent, it can increase the CB value of the corresponding area of the battery, and can also quickly dredge the accumulated lithium ions, thereby reducing or avoiding the occurrence of lithium deposition, and improving the safety and service life of the battery. In addition, the functional layer set on the surface of the negative electrode active material layer of the part to be bent can shorten the distance between the positive electrode plate and the negative electrode plate of the part to be bent, reduce the liquid phase resistance of the battery, and improve the electrochemical reaction kinetics.

The battery mentioned in the embodiments of the present application refers to a single physical module including one or more battery cells to provide higher voltage and capacity. The battery generally includes a battery box for encapsulating one or more battery cells, and the battery box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.

The battery cell may include a lithium-ion battery cell. The battery cell may be cylindrical, flat, rectangular or other shapes, and the present application embodiment does not limit this. Battery cells are generally divided into three types according to the packaging method: cylindrical battery cells, square battery cells and soft-pack battery cells.

The battery cell includes an electrode assembly and an electrolyte. The electrode assembly is composed of a positive electrode sheet, a negative electrode sheet and a separator. The battery cell mainly relies on the movement of metal ions between the positive electrode sheet and the negative electrode sheet to work. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode collector. The positive electrode collector not coated with the positive electrode active material layer protrudes from the positive electrode collector coated with the positive electrode active material layer. The positive electrode collector not coated with the positive electrode active material layer serves as the positive electrode tab. Taking lithium-ion batteries as an example, the material of the positive electrode collector can be aluminum, and the positive electrode active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide. The negative electrode sheet includes a negative electrode collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode collector. The negative electrode collector not coated with the negative electrode active material layer protrudes from the negative electrode collector coated with the negative electrode active material layer. The negative electrode collector not coated with the negative electrode active material layer serves as the negative electrode tab. The material of the negative electrode current collector may be copper, and the negative electrode active material may be carbon or silicon, etc. In order to ensure that a large current passes without melting, the number of positive electrode tabs is multiple and stacked together, and the number of negative electrode tabs is multiple and stacked together. The material of the isolation film may be polypropylene (PP) or polyethylene (PE), etc. In addition, the electrode assembly may be a winding structure or a laminated structure, and the embodiments of the present application are not limited thereto.

The battery cell also includes a current collecting component, which is used to electrically connect the tabs and electrode terminals of the battery cell to transmit electrical energy from the electrode assembly to the electrode terminals and then to the outside of the battery cell through the electrode terminals; multiple battery cells are electrically connected through a current collecting component to achieve series, parallel or mixed connection of multiple battery cells.

The battery also includes a sampling terminal and a battery management system. The sampling terminal is connected to the busbar to collect information about the battery cells, such as voltage or temperature, etc. The sampling terminal transmits the collected information about the battery cells to the battery management system. When the battery management system detects that the information about the battery cells exceeds the normal range, it will limit the output power of the battery to achieve safety protection.

It can be understood that the electrical devices used by the batteries described in the embodiments of the present application can be in various forms, for example, mobile phones, portable devices, laptops, battery vehicles, electric cars, ships, spacecraft, electric toys and electric tools, etc. For example, spacecraft include airplanes, rockets, space shuttles and spacecraft, etc. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc. Electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators and electric planers.

The battery cells and batteries described in the embodiments of the present application are not limited to the electrical devices described above, but can also be applied to all electrical devices using battery cells and batteries. However, for the sake of simplicity, the following embodiments are described using electric vehicles as examples.

Please refer to Figure 1, which is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is arranged inside the vehicle 1000, and the battery 100 can be arranged at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to power the vehicle 1000. For example, the battery 100 can be used 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 100 to power the motor 300, for example, for the starting, navigation and driving power requirements of the vehicle 1000.

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

Referring to FIG. 2 , FIG. 2 is an exploded view of a battery 100 provided in some embodiments of the present application. The battery 100 may include a box body 10 and a battery cell 20, and the battery cell 20 is contained in the box body 10. Among them, the box body 10 is used to contain the battery cell 20, and the box body 10 may be a variety of structures. In some embodiments, the box body 10 may include a first part 11 and a second part 12, and the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a containing space 13 for containing the battery cell 20. The second part 12 may be a hollow structure with one end open, and the first part 11 is a plate-like structure, and the first part 11 covers the open side of the second part 12 to form a box body 10 with a containing space 13; the first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12 to form a box body 10 with a containing space 13. Of course, the first part 11 and the second part 12 may be a variety of shapes, such as a cylinder, a cuboid, etc.

In the battery 100, there can be one or more battery cells 20. If there are more than one battery cell 20, the multiple battery cells 20 can be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple battery cells 20 are both connected in series and in parallel. The multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10. Alternatively, multiple battery cells 20 can be connected in series, in parallel, or in a mixed connection to form a battery module, and the multiple battery modules are then connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The battery 100 may also include other structures. For example, the multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of the multiple battery cells 20.

Each battery cell 20 may be a secondary battery or a primary battery, or a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 20 may be cylindrical, flat, rectangular, or in other shapes.

Please refer to FIG. 3, which is an exploded view of the battery cell 20 shown in FIG. 2. The battery cell 20 refers to the smallest unit constituting the battery 100. As shown in FIG. 3, the battery cell 20 may include a housing 21 and an electrode assembly 22, and the electrode assembly 22 is accommodated in the housing 21. In some embodiments, the housing 21 may also be used to accommodate an electrolyte, such as an electrolyte. The housing 21 may be in a variety of structural forms.

The housing 21 may include a shell 211 and a cover 212 .

The shell 211 is a component used to match the cover 212 to form an internal sealed space 213 of the battery cell 20, wherein the formed sealed space 213 can be used to accommodate the electrode assembly 22, electrolyte and other components. The shell 211 and the cover 212 can be independent components, and an opening can be set on the shell, and the internal environment of the battery cell 20 is formed by covering the opening with the cover 212 at the opening. Without limitation, the cover 212 and the shell 211 can also be integrated. Specifically, the cover 212 and the shell 211 can form a common connection surface before other components are put into the shell, and when the interior of the shell 211 needs to be encapsulated, the cover 212 covers the shell 211. The shell 211 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 211 can be determined according to the specific shape and size of the electrode assembly 22. The material of the shell 211 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this.

The cover 212 is a part that covers the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. Parts. Without limitation, the shape of the cover 212 can be adapted to the shape of the shell 211 to match the shell 211. In some embodiments, the cover 212 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the cover 212 is not easily deformed when squeezed and collided, so that the battery cell 20 can have a higher structural strength and the safety performance can also be improved. The material of the cover 212 can also be other, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not impose special restrictions on this. In some embodiments, an insulating member can also be provided on the inner side of the cover 212, and the insulating member can be used to isolate the electrical connection components in the shell 211 from the cover 212 to reduce the risk of short circuit. Exemplarily, the insulating member can be plastic, rubber, etc.

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

The battery cell 20 may further include a pressure relief structure 24, which is used to release the pressure inside the battery cell 20 when the internal pressure or temperature of the battery cell 20 reaches a predetermined value. Exemplarily, the pressure relief structure 24 may be a component such as an explosion-proof valve, an explosion-proof disk, an air valve, a pressure relief valve, or a safety valve.

When assembling the battery cell 20 , the electrode assembly 22 may be placed in the housing 211 first, and the housing 211 may be filled with electrolyte, and then the cover 212 may be closed on the opening of the housing 211 .

According to some embodiments of the present application, please refer to Figures 4 to 6, Figure 4 is a top view of the negative electrode sheet 400 of some embodiments of the present application, Figure 5 is a cross-sectional view of the first negative electrode sheet 400 of some embodiments of the present application, Figure 6 is a cross-sectional view of the second negative electrode sheet 400 of some embodiments of the present application; Figure 7 is a cross-sectional view of the third negative electrode sheet 400 of some embodiments of the present application.

The present application provides a negative electrode sheet 400, which is provided with a straight portion 401 and a portion to be bent 402, and includes: a negative electrode current collector 410, a negative electrode active material layer 420 and a functional layer 430, wherein the negative electrode active material layer 420 is disposed on at least one side of the negative electrode current collector 410 in the thickness direction, and the functional layer 430 is convexly disposed on the surface of the negative electrode active material layer 420 of at least a portion of the portion to be bent 402. The functional layer 430 includes a negative electrode active material and/or a conductive agent.

The straight portion 401 is a portion of the negative electrode plate 400 that is formed into a straight region 501 after being wound or bent.

The portion to be bent 402 is a portion of the negative electrode sheet 400 that forms a bending area 502 after being wound or bent.

The functional layer 430 is a layered structure disposed on the surface of the negative electrode active material layer 420 at least partially on the portion to be bent 402 and can provide lithium ion active sites or electron and ion channels.

The negative electrode active material is a component that can serve as a lithium ion active site.

Conductive agents are components that can provide pathways for electrons and ions.

As an example, the functional layer 430 may include a negative electrode active material but not a conductive agent; or may include a conductive agent but not a negative electrode active material; or may include both a negative electrode active material and a conductive agent.

A functional layer 430 is provided on the surface of the negative electrode active material layer 420 of the part to be bent 402. When the functional layer 430 includes a negative electrode active material, the CB value of the corresponding area of the battery can be increased, that is, the ratio of the negative electrode active material capacity to the positive electrode active material capacity in the area is increased, thereby reducing or avoiding the occurrence of lithium precipitation; when the functional layer 430 includes a conductive agent, the conductive agent can provide electron and ion conductive channels to quickly dredge the accumulated lithium ions, thereby reducing or avoiding the occurrence of lithium precipitation; when the functional layer 430 includes a negative electrode active material and a conductive agent, it can increase the CB value of the corresponding area of the battery, and can also quickly dredge the accumulated lithium ions, thereby reducing or avoiding the occurrence of lithium precipitation, and improving the safety and service life of the battery. In addition, the functional layer 430 provided on the surface of the negative electrode active material layer 420 of the part to be bent 402 can shorten the distance between the positive electrode sheet 600 and the negative electrode sheet 400 of the part to be bent 402, reduce the liquid phase resistance of the battery, and improve the electrochemical reaction kinetics.

4 and 5 , the negative electrode active material layer 420 is disposed on only one side of the negative electrode current collector 410 along the thickness direction, and the functional layer 430 is disposed on the surface of a layer of the negative electrode active material layer 420 .

4 and 6 , the negative electrode active material layer 420 is disposed on both sides of the negative electrode current collector 410 along the thickness direction, and the functional layer 430 is disposed on the surface of one layer of the negative electrode active material layer 420 .

4 and 7 , the negative electrode active material layer 420 is disposed on both sides of the negative electrode current collector 410 along the thickness direction, and the functional layer 430 is disposed on the surfaces of the two negative electrode active material layers 420 .

According to some embodiments of the present application, optionally, the functional layer 430 also includes a film-forming material.

Adding a film-forming material to the functional layer can improve the bonding effect between the functional layer and the negative electrode active material layer.

According to some embodiments of the present application, optionally, the functional layer 430 includes 20 wt % to 99 wt % of negative electrode active material and 1 wt % to 80 wt % of film-forming material.

The film-forming material is a component of the solution or slurry that is conducive to the formation of a thin film structure after the solvent is removed.

Optionally, the film-forming material includes any one or more of polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polypropylene (PP), polyethylene (PE), polyacrylonitrile (PAN), polyacrylic acid (PAA) and polyvinyl alcohol (PVA).

As an example, the functional layer 430 may include 20wt% negative electrode active material and 80wt% film-forming material, or may include 30wt% negative electrode active material and 70wt% film-forming material, or may include 40wt% negative electrode active material and 60wt% film-forming material, or may include 50wt% negative electrode active material and 50wt% film-forming material, or may include 60wt% negative electrode active material and 40wt% film-forming material, or may include 70wt% negative electrode active material and 30wt% film-forming material, or may include 80wt% negative electrode active material and 20wt% film-forming material, or may include 90wt% negative electrode active material and 10wt% film-forming material, or may include 99wt% negative electrode active material and 1wt% film-forming material.

By adjusting the proportions of the negative electrode active material and the film-forming material in the functional layer 430 , the CB value of the corresponding area of the battery and the bonding effect of the functional layer 430 can be regulated.

According to some embodiments of the present application, optionally, the functional layer 430 includes 20 wt % to 99 wt % of a conductive agent and 1 wt % to 80 wt % of a film-forming material.

As an example, the functional layer 430 may include 20wt% conductive agent and 80wt% film-forming material, or may include 30wt% conductive agent and 70wt% film-forming material, or may include 40wt% conductive agent and 60wt% film-forming material, or may include 50wt% conductive agent and 50wt% film-forming material, or may include 60wt% conductive agent and 40wt% film-forming material, or may include 70wt% conductive agent and 30wt% film-forming material, or may include 80wt% conductive agent and 20wt% film-forming material, or may include 90wt% conductive agent and 10wt% film-forming material, or may include 99wt% conductive agent and 1wt% film-forming material.

By adjusting the proportions of the conductive agent and the film-forming material in the functional layer 430 , the number of electronic and ion conductive channels and the bonding effect of the functional layer 430 can be controlled.

According to some embodiments of the present application, optionally, the functional layer 430 includes 20 wt % to 70 wt % of negative electrode active material, 20 wt % to 70 wt % of conductive agent and 10 wt % to 60 wt % of film-forming material.

As an example, the functional layer 430 may include 20wt% negative electrode active material, 20wt% conductive agent and 60wt% film-forming material, or may include 30wt% negative electrode active material, 30wt% conductive agent and 40wt% film-forming material, or may include 40wt% negative electrode active material, 40wt% conductive agent and 20wt% film-forming material, or may include 70wt% negative electrode active material, 20wt% conductive agent and 10wt% film-forming material, or may include 20wt% negative electrode active material, 70wt% conductive agent and 10wt% film-forming material, or may include 50wt% negative electrode active material, 30wt% conductive agent and 20wt% film-forming material, or may include 30wt% negative electrode active material, 50wt% conductive agent and 20wt% film-forming material.

By adjusting the proportions of the negative electrode active material, the conductive agent and the film-forming material in the functional layer 430 , the CB value of the corresponding area of the battery, the number of electronic and ion conductive channels and the bonding effect of the functional layer 430 can be controlled.

According to some embodiments of the present application, optionally, the negative electrode active material includes any one or more of a first carbon material, a lithiation-capable metal, a lithiation-capable metal alloy, and a lithiation-capable oxide.

The first carbon material includes any one or more of hard carbon, soft carbon, activated carbon, graphite, silicon oxycarbon and mesophase carbon microbeads.

The lithiation-capable metal includes any one or more of Al, Mg and Zn.

The lithiation-capable metal alloys include LiAl alloys and/or MgAl alloys.

The lithiable oxide includes ZnO and/or MnO.

When the negative electrode active material is selected from the above materials, the functional layer 430 can have more lithium ion active sites and the CB value of the corresponding area of the battery can be improved.

According to some embodiments of the present application, optionally, the conductive agent includes a second carbon material and/or a conductive organic matter.

The second carbon material includes any one or more of carbon fiber, conductive carbon black, carbon nanotube and graphene.

Optionally, the carbon nanotubes include single-walled carbon nanotubes and/or multi-walled carbon nanotubes.

Optionally, the graphene includes any one or more of single-layer graphene, few-layer graphene, few-layer graphene, multi-layer graphene and three-dimensional graphene.

The conductive organic material includes polypyrrole and/or polythiophene.

When the conductive agent is selected from the above materials, the functional layer 430 can have multiple electronic and ion conductive channels and can quickly conduct the accumulated lithium ions.

According to some embodiments of the present application, optionally, the porosity of the functional layer 430 is 10% to 90%.

As an example, the porosity of the functional layer 430 may be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%.

By adjusting the porosity of the functional layer 430 , the functional layer 430 can be infiltrated with electrolyte and form a fast lithium ion channel.

According to some embodiments of the present application, the present application also provides a method for preparing the negative electrode plate 400 in the above embodiment, which includes: forming a negative electrode active material layer 420 on at least one side of the negative electrode current collector 410 along the thickness direction, and forming a functional layer 430 on the surface of the negative electrode active material layer 420 of at least part of the portion to be bent 402.

The preparation method of the negative electrode plate 400 of the present application is simple, and the functional layer 430 is formed on the surface of the negative electrode active material layer 420 of at least a portion of the bending portion 402 after the negative electrode active material layer 420 is formed. In the formation process of the functional layer 430 of the present application, an intermittent coating process is not required, and the manufacturing difficulty is low.

According to some embodiments of the present application, please refer to Figures 8 to 12, Figure 8 is a structural schematic diagram of the first electrode assembly 22 of some embodiments of the present application, Figure 9 is a structural schematic diagram of the second electrode assembly 22 of some embodiments of the present application, Figure 10 is a structural schematic diagram of the third electrode assembly 22 of some embodiments of the present application, Figure 11 is a first partial structural schematic diagram of the first electrode assembly 22 of some embodiments of the present application, and Figure 12 is a second partial structural schematic diagram of the first electrode assembly 22 of some embodiments of the present application.

The present application also provides an electrode assembly 22, which includes: a positive electrode sheet 600 and a negative electrode sheet 400 in the above embodiment, wherein the positive electrode sheet 600 and the negative electrode sheet 400 are wound or folded to form a bending area 502 and a straight area 501, and the straight area 501 is connected to the bending area 502. The portion to be bent 402 is wound or folded to form a bending portion, the bending portion is located in the bending area 502, and the straight portion 401 is located in the straight area 501.

Please refer to FIG8 , the positive electrode sheet 600, the negative electrode sheet 400 and the separator 700 are wound to form the electrode assembly 22 of the wound structure, the middle of the electrode assembly 22 is a straight area 501, and the two ends of the straight area 501 are respectively bending areas 502. And the closer the positive electrode sheet 600 and the negative electrode sheet 400 located in the bending area 502 are to the center of the wound structure, the greater the curvature of the positive electrode sheet 600 and the negative electrode sheet 400 after winding.

Please refer to FIG9 . The positive electrode sheet 600, the negative electrode sheet 400 and the separator 700 are folded to form an electrode assembly 22 of a laminated structure. The middle of the electrode assembly 22 is a straight area 501, and the two ends of the straight area 501 are respectively a plurality of bending areas 502. Each bending area 502 includes an inner electrode sheet and an outer electrode sheet. Each inner positive electrode sheet 600 and the negative electrode sheet 400 have the same curvature after folding, and each outer positive electrode sheet 600 and the negative electrode sheet 400 have the same curvature after folding in the bending area 502.

Please refer to FIG. 10 , the bent portion includes a negative electrode current collector 410 , a negative electrode active material layer 420 located only on the outer side of the negative electrode current collector 410 , and a functional layer 430 located on the surface of the negative electrode active material layer 420 .

Please refer to FIG. 11. The bent portion includes a negative electrode current collector 410, a negative electrode active electrode located on the outer side and the inner side of the negative electrode current collector 410, and a negative electrode active electrode located on the outer side and the inner side of the negative electrode current collector 410. The negative electrode active material layer 420 and the functional layer 430 are located on the surface of the negative electrode active material layer 420 on the outer side of the negative electrode current collector 410.

The functional layer 430 is provided on the surface of the negative electrode active material layer 420 of the partial bending area 502, so that the CB value of the corresponding area of the battery can be increased, that is, the ratio of the negative electrode active material capacity to the positive electrode active material capacity in the area is increased, and/or an electron and ion conductive channel is provided to quickly guide the accumulated lithium ions, thereby reducing or avoiding the occurrence of lithium precipitation. In addition, the functional layer 430 provided on the surface of the negative electrode active material layer 420 of the partial bending area 502 can shorten the distance between the positive electrode plate 600 and the negative electrode plate 400 of the partial bending area 502, reduce the liquid phase resistance of the battery, and improve the electrochemical reaction kinetics.

According to some embodiments of the present application, optionally, the positive electrode sheet 600 and the negative electrode sheet 400 are wound to form a wound structure, and a functional layer 430 is provided on the surface of the negative active material layer 420 on the outer side of the negative electrode current collector 410 of at least part of the bent portion.

The outer side surface of the negative electrode current collector 410 is a convex surface of the negative electrode current collector 410 after being bent.

For the electrode assembly 22 of the wound structure, the outer side surface of the negative electrode collector 410 is smaller than the inner side surface of the corresponding positive electrode collector, which results in that under normal circumstances, the negative electrode active material capacity of the outer side surface of the negative electrode collector 410 is smaller than the positive electrode active material capacity of the corresponding positive electrode collector, and lithium precipitation reaction is very likely to occur. A functional layer 430 is provided on the surface of the negative electrode active material layer 420 on the outer side surface of at least part of the bent portion of the negative electrode collector 410, which can increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in the area, or provide electron and ion conductive channels in the area to quickly guide the accumulated lithium ions, thereby reducing or avoiding the lithium desorption reaction of the active material layer in the partial bending area 502, thereby improving the safety and service life of the battery.

According to some embodiments of the present application, optionally, the positive electrode sheet 600 and the negative electrode sheet 400 are wound to form a winding structure, and the negative electrode sheet 400 has a first bending portion 403 located at the innermost side of the winding structure, and a functional layer 430 is provided on the surface of the negative active material layer 420 on the outer side of the negative electrode current collector 410 of the first bending portion 403.

The first bending portion 403 is a structure of the negative electrode plate 400 with the largest bending curvature.

The first bent portion 403 located at the innermost side of the electrode assembly 22 is the area most prone to lithium deposition reaction, and a functional layer 430 is provided on the surface of the negative electrode active material layer 420 on the outer side of the negative electrode current collector 410 of the first bent portion 403, which can increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in this area, or provide electron and ion conductive channels in this area to quickly guide the accumulated lithium ions, thereby reducing or avoiding the lithium desorption reaction of the active material layer in the partial bending area 502, thereby improving the safety and service life of the battery.

According to some embodiments of the present application, optionally, please refer to FIG. 12 for a third partial structural diagram of the first electrode assembly 22 of some embodiments of the present application. A functional layer 430 is disposed on the surface of the negative active material layer 420 on the inner side of the negative current collector 410 of the first bent portion 403 .

The inner side surface of the negative electrode current collector 410 is a concave surface of the negative electrode current collector 410 after being bent.

A functional layer 430 is provided on the surface of the negative active material layer 420 on the inner side of the negative current collector 410 of the first bent portion 403 , which can reduce the curvature of the negative electrode sheet 400 in this area and improve the powder shedding of the negative electrode sheet 400 in this area.

According to some embodiments of the present application, optionally, please refer to FIG. 13 , FIG. 13 is a schematic structural diagram of a third electrode assembly 22 of some embodiments of the present application. Along the winding direction, the negative electrode sheet 400 has a second bending portion 404, a third bending portion 405, a fourth bending portion 406 and a fifth bending portion 407 which are adjacent to the first bending portion 403 in sequence, and the second bending portion 404, the third bending portion 405, the fourth bending portion 406 and the fifth bending portion 407 are all provided with a functional layer 430 on the surface of the negative active material layer 420 on the outer side of the respective negative current collectors 410.

The second bending portion 404 is a structure with the second largest curvature of the negative electrode plate 400 , and a straight portion 401 is disposed between the second bending portion 404 and the first bending portion 403 .

The third bending portion 405 is a structure having the third largest curvature of the negative electrode plate 400 , and a straight portion 401 is disposed between the third bending portion 405 and the second bending portion 404 .

The fourth bending portion 406 is a structure with the fourth largest curvature of the negative electrode plate 400 , and a straight portion 401 is disposed between the fourth bending portion 406 and the third bending portion 405 .

The fifth bending portion 407 is a structure with the fifth largest curvature of the negative electrode plate 400 , and a straight portion 401 is disposed between the fifth bending portion 407 and the fourth bending portion 406 .

The first bend 403, the second bend 404, the third bend 405, the fourth bend 406 and the fifth bend 407 located at the innermost side of the electrode assembly 22 are the areas most prone to lithium deposition reactions, and a functional layer 430 is provided on the surface of the negative electrode active material layer 420 on the outer side of the negative electrode current collector 410 of the first bend 403, the second bend 404, the third bend 405, the fourth bend 406 and the fifth bend 407, which can increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in these multiple areas, or provide electron and ion conductive channels in these multiple areas to quickly guide the accumulated lithium ions, thereby reducing or avoiding the delithiation reaction of the active material layer in the partial bend area 502, thereby improving the safety and service life of the battery.

According to some embodiments of the present application, optionally, the second bend 404 , the third bend 405 , the fourth bend 406 and the fifth bend 407 are all provided with a functional layer 430 on the surface of the negative electrode active material layer 420 on the inner side of each negative electrode current collector 410 .

A functional layer 430 is provided on the surface of the negative active material layer 420 on the inner side of the negative electrode current collector 410 of the second bend 404, the third bend 405, the fourth bend 406 and the fifth bend 407, which can reduce the curvature of the negative electrode sheets 400 in these multiple regions and improve the powder shedding of the negative electrode sheets 400 in these multiple regions.

According to some embodiments of the present application, optionally, the positive electrode sheet 600 and the negative electrode sheet 400 are wound to form a winding structure having a plurality of bends, and along the winding direction, the functional layers 430 corresponding to the plurality of bends are sequentially thinned.

Along the winding direction, the possibility of lithium deposition reaction occurring at the multiple bent portions of the electrode assembly 22 decreases successively, or the severity of the lithium deposition reaction decreases successively. The functional layers 430 corresponding to the multiple bent portions are thinned successively along the winding direction, so that they can correspond to the possibility of lithium deposition reaction or the severity of lithium deposition reaction, which is beneficial to improving the overall energy density of the battery.

According to some embodiments of the present application, optionally, along the winding direction, a thickness difference of the functional layer 430 corresponding to two adjacent bending portions is 1 μm to 70 μm.

As an example, the thickness difference between the functional layer 430 corresponding to two adjacent bending portions may be 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm or 70 μm.

Adjusting the thickness of the functional layer 430 corresponding to the multiple bending portions is beneficial to both improving lithium deposition and ensuring the overall energy density of the battery.

Optionally, the thickness of the functional layer 430 is 0.1 μm to 200 μm.

As an example, the thickness of the functional layer 430 may be 0.1 μm, 5 μm, 10 μm, 20 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, or 200 μm.

According to some embodiments of the present application, optionally, the positive electrode sheet 600 and the negative electrode sheet 400 are folded to form a stacked structure, the negative electrode sheet 400 has a sixth bent portion 408 covered by the positive electrode sheet 600, and a functional layer 430 is provided on the surface of the negative active material layer 420 on the outer side of the negative electrode current collector 410 of the sixth bent portion 408.

Since the curvature of the curve formed by folding each negative electrode sheet 400 located on the outer side of the bending area 502 of the laminated structure electrode assembly 22 is the same, the sixth bending portion 408 can be a bending portion at any position.

The sixth bend 408 located in the stacked structure is an area where lithium deposition reaction is prone to occur, and a functional layer 430 is provided on the surface of the negative electrode active material layer 420 on the inner side of the negative electrode current collector 410 of the sixth bend 408, which can increase the ratio of the negative electrode active material capacity to the positive electrode active material capacity in this area, or provide electron and ion conductive channels in this area to quickly guide the accumulated lithium ions, thereby reducing or avoiding the lithium desorption reaction of the active material layer in the partial bend area 502, improving the safety and service life of the battery, while ensuring the energy density of the battery.

According to some embodiments of the present application, optionally, a functional layer 430 is provided on the surface of the negative electrode active material layer 420 on the inner side of the negative electrode current collector 410 of the sixth bent portion 408 .

A functional layer 430 is provided on the surface of the negative active material layer 420 on the inner side of the negative current collector 410 of the sixth bent portion 408 , which can reduce the curvature of the negative electrode sheet 400 in this area and improve the powder shedding of the negative electrode sheet 400 in this area.

The electrode assembly of the present application is further described in detail below in conjunction with the embodiments. The structures and parameters of the electrode assemblies of embodiments 1 to 38 and comparative examples 1 to 3 are shown in Tables 1 to 3.

Table 1 Structure and parameters of electrode assembly with negative electrode active material as functional layer

Table 2 Structure and parameters of electrode assembly with conductive agent as functional layer

Table 3 Structure and parameters of electrode assembly with negative electrode active material and conductive agent as functional layer

Test example

Batteries were made using the electrode assemblies of Examples 1 to 38 of the present application and Comparative Examples 1 to 3, and the capacity retention rate and the distance (gap) between the positive electrode sheet and the negative electrode sheet at the bending portion of the batteries were measured. The test results are shown in Tables 4 to 6.

The preparation method of the battery is as follows:

The positive electrode sheet, the negative electrode sheet and the isolation film are wound to form a battery, and the designs of the electrolyte and the aluminum-plastic film are consistent.

Using the Xinwei capacity test cabinet, the prepared battery was subjected to capacity cycle test according to the following steps: ① 0.33C full charge to the charge limit voltage, and test its initial capacity Cap0 according to the 1.0C discharge limit voltage; ② At 25℃±5℃, the battery was fully charged to the charge limit voltage at 1.5C, the cut-off current was 0.05C, and left for 5min~10min; ③ At 25℃±5℃, the battery was discharged to the discharge cut-off voltage at 1.0C, and left for 5min~10min; ④ Repeat steps ②-③ for 50 times. Compare the capacity retention rate after the cycle and the full charge disassembly interface.

The test method for the gap between the positive and negative electrodes of the battery is as follows:

Use X-ray CT to capture the gap between the positive and negative pole pieces at the bent part of the battery.

Table 4 Test results of Examples 1 to 13 and Comparative Example 1

Table 5 Test results of Examples 14 to 25 and Comparative Example 2

Table 6 Test results of Examples 26 to 38 and Comparative Example 3

As shown in Table 4, in Examples 1 to 13, a functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector at the first bend, or the first, second, third, fourth, fifth bend, or sixth bend, and the functional layer includes a negative electrode active material material, which can reduce or avoid the occurrence of lithium precipitation, so that the capacity retention rate of the battery after 50 cycles reaches more than 93%, the highest is 97%, and the Gap value is less than 50μm. Comparative Example 1 has no functional layer, and the capacity retention rate of the battery after 50 cycles is less than 90%, and the Gap value is less than 200μm.

As can be seen from Table 5, in Examples 14 to 25, a functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector at the first bend, or the first, second, third, fourth, fifth bend, or sixth bend, and the functional layer includes a conductive agent, which can reduce or avoid the occurrence of lithium precipitation, so that the capacity retention rate of the battery after 50 cycles reaches more than 91%, the highest is 95%, and the Gap value is less than 50μm. Comparative Example 2 has no functional layer, and the capacity retention rate of the battery after 50 cycles is less than 90%, and the Gap value is less than 200μm.

As shown in Table 6, in Examples 26 to 38, a functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector at the first bend, or the first, second, third, fourth, fifth bend, or sixth bend, and the functional layer includes a negative electrode active material and a conductive agent, which can reduce or avoid the occurrence of lithium precipitation, so that the capacity retention rate of the battery after 50 cycles reaches more than 91%, the highest is 95%, and the Gap value is less than 50μm. Comparative Example 3 has no functional layer, and the capacity retention rate of the battery after 50 cycles is less than 90%, and the Gap value is less than 200μm.

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

Claims (22)

1. A negative electrode sheet, wherein the negative electrode sheet is provided with a straight portion and a portion to be bent, the negative electrode sheet comprises a negative electrode current collector, a negative electrode active material layer and a functional layer, the negative electrode active material layer is arranged on at least one side of the negative electrode current collector along the thickness direction, and the functional layer is convexly arranged on the surface of at least part of the negative electrode active material layer of the portion to be bent;

   The functional layer includes a negative electrode active material and/or a conductive agent.
2. The negative electrode sheet according to claim 1, wherein the functional layer further comprises a film-forming material.
3. The negative electrode plate according to claim 1 or 2, wherein the functional layer comprises 20wt% to 99wt% of the negative electrode active material and 1wt% to 80wt% of a film-forming material.
4. The negative electrode sheet according to any one of claims 1 to 3, wherein the functional layer comprises 20wt% to 99wt% of the conductive agent and 1wt% to 80wt% of the film-forming material.
5. The negative electrode sheet according to any one of claims 1 to 4, wherein the functional layer comprises 20wt% to 70wt% of the negative electrode active material, 20wt% to 70wt% of the conductive agent and 10wt% to 60wt% of the film-forming material.
6. The negative electrode sheet according to any one of claims 1 to 5, wherein the negative electrode active material comprises any one or more of a first carbon material, a lithiation-capable metal, a lithiation-capable metal alloy, and a lithiation-capable oxide;

   Wherein, the first carbon material includes any one or more of hard carbon, soft carbon, activated carbon, graphite, silicon oxygen carbon and mesophase carbon microspheres.
7. The negative electrode sheet according to any one of claims 1 to 6, wherein the conductive agent comprises a second carbon material and/or a conductive organic matter;

   Wherein, the second carbon material includes any one or more of carbon fiber, conductive carbon black, carbon nanotube and graphene.
8. The negative electrode sheet according to any one of claims 1 to 7, wherein the porosity of the functional layer is 10% to 90%.
9. A method for preparing a negative electrode sheet according to any one of claims 1 to 8, wherein the method for preparing the negative electrode sheet comprises: forming the negative electrode active material layer on at least one side of the negative electrode current collector along the thickness direction, and forming the functional layer on the surface of the negative electrode active material layer of at least part of the portion to be bent.
10. An electrode assembly, wherein the electrode assembly comprises: a positive electrode sheet and a negative electrode sheet according to any one of claims 1 to 8, wherein the positive electrode sheet and the negative electrode sheet are wound or folded to form a bending area and a straight area, and the straight area is connected to the bending area;

    The portion to be bent is wound or folded to form a bent portion, the bent portion is located in the bending zone, and the straight portion is located in the straight zone.
11. The electrode assembly according to claim 10, wherein the positive electrode sheet and the negative electrode sheet are wound to form a winding structure, and a functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of at least part of the bent portion.
12. The electrode assembly according to claim 10 or 11, wherein the positive electrode sheet and the negative electrode sheet are wound to form a winding structure, the negative electrode sheet has a first bent portion located at the innermost side of the winding structure, and the functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of the first bent portion.
13. The electrode assembly according to claim 12, wherein the functional layer is provided on the surface of the negative electrode active material layer on the inner side of the negative electrode current collector of the first bent portion.
14. According to the electrode assembly according to claim 12 or 13, wherein, along the winding direction, the negative electrode sheet has a second bend portion, a third bend portion, a fourth bend portion and a fifth bend portion which are adjacent to the first bend portion in sequence, and the second bend portion, the third bend portion, the fourth bend portion and the fifth bend portion are all provided with the functional layer on the surface of the negative electrode active material layer on the outer side surface of each negative electrode current collector.
15. The electrode assembly according to claim 14, wherein the second bent portion, the third bent portion, the fourth bent portion and the fifth bent portion are all provided with the functional layer on the surface of the negative electrode active material layer on the inner side surface of each negative electrode current collector.
16. According to the electrode assembly according to any one of claims 10 to 15, the positive electrode sheet and the negative electrode sheet are wound to form a winding structure having a plurality of the bending portions, and along the winding direction, the functional layers corresponding to the plurality of the bending portions are thinned sequentially.
17. The electrode assembly according to claim 16, wherein, along the winding direction, the thickness difference between the functional layers corresponding to two adjacent bending portions is 1 μm to 70 μm.
18. The electrode assembly according to any one of claims 10 to 17, wherein the positive electrode sheet and the negative electrode sheet are folded to form a stacked structure, the negative electrode sheet has a sixth bend portion covered by the positive electrode sheet, and the functional layer is provided on the surface of the negative electrode active material layer on the outer side of the negative electrode current collector of the sixth bend portion.
19. The electrode assembly according to claim 18, wherein the functional layer is provided on the surface of the negative electrode active material layer on the inner side of the negative electrode current collector of the sixth bent portion.
20. A battery cell, wherein the battery cell comprises the electrode assembly according to any one of claims 10 to 19.
21. A battery, wherein the battery comprises the battery cell according to claim 20.
22. An electrical device, wherein the electrical device comprises the battery according to claim 21, and the battery is used to provide electrical energy.