Patent Description:
A rechargeable battery, also referred to as a secondary battery, is a battery that can be charged and reused by activating an active material after the battery is discharged. The rechargeable batteries are widely used in electronic devices, for example, mobile phones, laptops, battery cars, electric cars, electric planes, electric ships, electric toy cars, electric toy ships, electric toy planes, electric tools, etc..

In the development of battery technology, apart from improvement to the performance of the battery, the safety is also non-negligible because the battery cannot be used unless the safety is guaranteed. Thus, how to enhance the safety of the battery is a technical problem to be solved urgently in the battery technology.

<CIT> discloses an electrode assembly, comprising a positive electrode and a negative electrode which are stacked and an electrode edge portion that is configured in such a way that a capacity per unit area of an electrode edge portion is smaller than that of the electrode body portion.

The application provides an electrode assembly and a manufacturing method therefor, a battery cell and a battery, which may enhance safety of the battery.

In a fist aspect, the embodiment of the application provides the electrode assembly according to appended claims <NUM>-<NUM>.

When the negative active material layer includes the negative body portion and the negative edge portion, then the negative edge portion includes a first portion overlapping the positive active material layer in a stacking direction and a second portion extending beyond the positive active material layer. When the capacity per unit area of the negative body portion meets a setting requirement, that is, the capacity per unit area of the negative body portion reaches a first preset value, lithium plating is less likely to occur on the negative body portion. Since the capacity per unit area of the negative edge portion is greater than that of the negative body portion, that is, the capacity per unit area of the negative edge portion is greater than the first preset value, equivalently, the capacity per unit area of the negative edge portion is increased, a cell balance (CB) value of the negative edge portion may be increased. During cycle, even if the first portion needs to receive lithium ions separating from the positive active material layer and lithium ions diffusing from the second portion, lithium plating is less likely to occur on the first portion, thereby reducing a risk of lithium plating of the negative edge portion.

When the positive active material layer includes the positive body portion and the positive edge portion, then a portion, overlapping the positive edge portion, of the negative active material layer and a portion, extending beyond the positive active material layer, of the negative active material layer are connected. When the capacity per unit area of the positive body portion meets a setting requirement, that is, the capacity per unit area of the positive body portion reaches a second preset value, lithium plating is less likely to occur on the portion, overlapping the positive body portion, of the negative active material layer. Since the capacity per unit area of the positive edge portion is smaller than that of the positive body portion, that is, the capacity per unit area of the positive edge portion is smaller than the second preset value, equivalently, the capacity per unit area of the positive edge portion is reduced, a cell balance (CB) value of the portion, overlapping the positive edge portion, of the negative active material layer may be increased. During cycle, even if the portion, overlapping the positive edge portion, of the negative active material layer needs to receive lithium ions diffusing from the portion, extending beyond the positive active material layer, of the negative active material layer, lithium plating is less likely to occur on the portion, overlapping the positive edge portion, of the negative active material layer.

According to the invention, a weight ratio of an active material in the negative edge portion to the negative edge portion is greater than that of an active material in the negative body portion to the negative body portion, such that the capacity per unit area of the negative edge portion is greater than that of the negative body portion. By adding the active material in the negative edge portion, the weight ratio of the active material in the negative edge portion is increased, and the capacity per unit area of the negative edge portion is increased, such that the capacity per unit area of the negative edge portion is greater than that of the negative body portion.

In some embodiments, per gram capacity of the active material in the negative edge portion is greater than that of the active material in the negative body portion. By increasing the gram capacity of the active material in the negative edge portion, the capacity per unit area of the negative edge portion may be increased, such that the capacity per unit area of the negative edge portion is greater than that of the negative body portion.

In some embodiments, the negative edge portion includes a first negative coating and a second negative coating which are stacked in the stacking direction. A weight ratio of an active material in the second negative coating to the second negative coating is greater than that of an active material in the first negative coating to the first negative coating. By adding the active material in the second negative coating, the weight ratio of the active material in the second negative coating is increased, and then the capacity per unit area of the negative edge portion is increased, such that the capacity per unit area of the negative edge portion is greater than that of the negative body portion. In another embodiment, the gram capacity of the active material in the second negative coating is greater than that of the active material in the first negative coating. By of increasing the gram capacity of the active material in the second negative coating, the capacity per unit area of the negative edge portion is increased, such that the capacity per unit area of the negative edge portion is greater than that of the negative body portion.

In some embodiments, a particle size of the active material in the negative edge portion is smaller than that of the active material in the negative body portion. During charge and discharge, the lithium ions are likely to diffuse in the negative edge portion, are distributed in the negative edge portion more uniformly, and are less likely to locally gather in the negative edge portion, thereby reducing the risk of lithium plating.

In some embodiments, the negative pole piece includes a negative current collector including a negative coating region and a negative tab, the negative coating region being coated with at least part of the negative active material layer, the negative tab being connected to an end, in a first direction, of the negative coating region, and the first direction being perpendicular to the stacking direction. At least two negative edge portions are positioned on two sides, in the first direction, of the negative body portion respectively. By means of the two negative edge portions, lithium plating is less likely to occur on the negative active material layer.

In some embodiments, in the two negative edge portions, a thickness of at least part of the negative edge portion close to the negative tab is smaller than that of the negative body portion, and a thickness of the negative edge portion far away from the negative tab is equal to that of the negative body portion.

In some embodiments, a size of the portion, overlapping the positive active material layer in the stacking direction, of the negative edge portion is greater than <NUM> in the first direction, so as to reduce the risk of lithium plating of the negative active material layer.

In some embodiments, the negative edge portion is arranged around the negative body portion. In this way, a range of the negative edge portion may be expanded, and lithium plating is less likely to occur on the negative active material layer.

According to the invention, a weight ratio of an active material in the positive edge portion to the positive edge portion is smaller than that of an active material in the positive body portion to the positive body portion, such that the capacity per unit area of the positive edge portion is smaller than that of the positive body portion. By reducing the active material in the positive edge portion, the weight ratio of the active material in the positive edge portion is reduced, and the capacity per unit area of the positive edge portion is reduced, such that the capacity per unit area of the positive edge portion is smaller than that of the positive body portion.

In some embodiments, per gram capacity of the active material in the positive edge portion is smaller than that of the active material in the positive body portion. By reducing the gram capacity of the active material in the positive edge portion, the capacity per unit area of the positive edge portion may be reduced, such that the capacity per unit area of the positive edge portion is smaller than that of the positive body portion.

In some embodiments, the positive edge portion includes a first positive coating and a second positive coating which are stacked in the stacking direction. A weight ratio of an active material in the second positive coating to the second positive coating is smaller than that of an active material in the first positive coating to the first positive coating. By reducing the active material in the second positive coating, the weight ratio of the active material in the second positive coating is reduced, and then the capacity per unit area of the positive edge portion is reduced, such that the capacity per unit area of the positive edge portion is smaller than that of the positive body portion. In some other embodiments, the gram capacity of the active material in the second positive coating is smaller than that of the active material in the first positive coating. By reducing the gram capacity of the active material in the second positive coating, the capacity per unit area of the positive edge portion is reduced, such that the capacity per unit area of the positive edge portion is smaller than that of the positive body portion.

In some embodiments, a particle size of the active material in the positive edge portion is greater than that of the active material in the positive body portion. During charge and discharge, the lithium ions are less likely to diffuse in the positive edge portion, a rate of the lithium ions in the positive body portion diffusing into the positive edge portion is reduced, and a rate of the lithium ions separating from the positive edge portion is also reduced, such that a risk that the lithium ions gather in the portion, overlapping the positive edge portion, of the negative active material layer may be reduced, and lithium plating is less likely to occur on the negative active material layer.

In some embodiments, the positive pole piece includes a positive current collector including a positive coating region and a positive tab, the positive coating region being coated with at least part of the positive active material layer, the positive tab being connected to an end, in the first direction, of the positive coating region, and the first direction being perpendicular to the stacking direction. At least two positive edge portions are positioned on two sides, in the first direction, of the positive body portion respectively. By means of the two positive edge portions, lithium plating is less likely to occur on the positive active material layer.

In some embodiments, in the two positive edge portions, a thickness of at least part of the positive edge portion close to the positive tab is smaller than that of the positive body portion, and a thickness of the positive edge portion far away from the positive tab is equal to that of the positive body portion.

In some embodiments, the size of the positive edge portion is greater than <NUM> in the first direction. In this way, the risk of lithium plating of the portion, overlapping the positive body portion, of the negative active material layer may be reduced.

In some embodiments, the first positive edge portion is arranged around the positive body portion. In this way, the portion, overlapping the positive edge portion, of the negative active material layer may be expanded, and lithium plating is less likely to occur on the negative active material layer.

In a second aspect, the embodiment of the application provides the battery cell including a case and the electrode assembly provided in any embodiment of the first aspect, the electrode assembly being accommodated in the case.

In a third aspect, the embodiment of the application provides a battery including a box and the battery cell provided in any embodiment of the second aspect, the battery cell being accommodated in the box.

In a fourth aspect, the embodiments of the application provide an electric apparatus including the battery provided in any embodiment of the third aspect, the battery being used for supplying electrical energy.

The application also provides a manufacturing method for an electrode assembly, according to appended claim <NUM>.

In order to describe the technical solutions in the embodiments of the application more clearly, the accompanying drawings required for describing the embodiments are briefly described below. Obviously, the accompanying drawings in the following description show merely some embodiments of the present disclosure, and a person of ordinary skill in the art would also be able to derive other accompanying drawings from these accompanying drawings without creative efforts.

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

To make the objectives, technical solutions, and advantages of the embodiments of the application clearer, the following will clearly describe the technical solutions in the embodiments of the application with reference to the accompanying drawings in the embodiments of the application. Apparently, the described embodiments are some rather than all of the embodiments of the application. Based on the embodiments of the application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the application.

Unless otherwise defined, all technical and scientific terms used in the application have the same meanings as those commonly understood by those who belong to the technical field of the present application. In the application, the terms used in the specification of the application are merely for the purpose of describing specific embodiments, and are not intended to limit the application. The terms "including" and "having" and any variations thereof in the specification and claims of the application and the above accompanying drawings are intended to cover non-exclusive inclusion. The terms "first", "second", etc. in the specification and claims of the application or the above accompanying drawings are used to distinguish different objects, but not to describe a specific order or primary and secondary relationship.

Reference to an "embodiment" in the application means that a specific feature, structure or characteristic described in conjunction with an embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

In the description of the application, it should be noted that, unless otherwise explicitly specified and defined, the terms "mounting", "connecting", "connection" and "attachment" should be understood in a broad sense, for example, they may be a fixed connection, a detachable connection, or an integrated connection; and may be a direct connection, or an indirect connection via an intermediate medium, or communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the application could be understood according to specific circumstances.

As used herein, the term "and/or" is merely used to describe an associated relationship between associated objects and means three relationships, for example, A and/or B may mean A alone, A and B together, and B alone. In addition, the character "/" in the application generally indicates that the associated objects are an "or" relationship.

In the embodiments of the application, the same reference numerals refer to same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that a thickness, a length, a width and other dimensions of various components and an overall thickness, length, width and other dimensions of an integrated device shown in the accompanying drawings in the embodiments of the application are merely exemplary, and should not constitute any limitation on the application.

The term "plurality" in the application means two or more.

In the application, battery cells may include a lithium ion secondary battery cell, a lithium ion primary battery cell, a lithium-sulfur battery, a sodium lithium-ion battery cell, a sodium ion battery cell, a magnesium ion battery cell, etc., which are not limited by the embodiments of the application. The battery cell may be in cylindrical, flat, cuboid or other shapes, which is not limited by the embodiments of the application. Generally, the battery cells are divided into three types according to packaging manners: cylindrical battery cells, square battery cells and pouch battery cells, which are not limited by the embodiments of the application.

The battery mentioned in the embodiments of the application refers to a single physical module which includes one or a plurality of battery cells and therefore provides a higher voltage and capacity. For example, the battery mentioned in the application may include a battery module or a battery pack, etc. Generally, the battery includes a box for packaging one or a plurality of battery cells. The box may prevent liquid or other foreign matter from affecting charging or discharging of the battery cell.

The battery cell includes an electrode assembly and an electrolyte, the electrode assembly being composed of a positive pole piece, a negative pole piece and a separator film. The battery cell works mainly depending on movement of metal ions between the positive pole piece and the negative pole piece. The positive pole piece includes a positive current collector and a positive active material layer, a surface of the positive current collector is coated with the positive active material layer, a portion, not coated with the positive active material layer, of the positive current collector protrudes out of a portion, coated with the positive active material layer, of the positive current collector, and the portion, not coated with the positive active material layer, of the positive current collector serves as a positive tab. With a lithium ion battery as an example, a positive current collector may be made from aluminum, and the positive active material may be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganate, etc. The negative pole piece includes a negative current collector and a negative active material layer, a surface of the negative current collector is coated with the negative active material layer, a portion, not coated with the negative active material layer, of the negative current collector protrudes out of a portion, coated with the negative active material layer, of the negative current collector, and the portion, not coated with the negative active material layer, of the negative current collector serves as a negative tab. The negative current collector may be made from copper, and the negative active material may be carbon, silicon, etc. In order to guarantee fusing does not occur during large current flow, a plurality of positive tabs are stacked together, and a plurality of negative tabs are stacked together. The separator film may be made from polypropylene (PP), polyethylene (PE), etc. In addition, the electrode assembly may be in a winding structure or a laminated structure, which is not limited in the embodiments of the application.

When the battery cell is charged by an external power source, electrons e on a positive electrode run to a negative electrode via an external circuit, lithium ions Li+ separate from active material particles in the positive active material layer and enter an electrode liquid, pass through micro pores on the separator film and move to the negative electrode, and are combined with electrons which have run over for a long time to enter active material particles in the negative active material layer. If the negative active material layer does not have space for the lithium ions, the lithium ions will be deposited on the surface of the negative active material layer to form lithium dendrites, so as to puncture the separator film, cause a short circuit in the battery cell, and cause thermal runaway. Thus, when the electrode assembly is designed, it is necessary to guarantee that the negative active material layer is excessive to reduce a risk of lithium plating.

In view of assembly accuracy of the electrode assembly, etc. an end of the negative active material lay needs to extend beyond the positive active material layer, so as to reduce a risk that the negative active material layer cannot completely cover the positive active material lay due to assembly errors. The negative active material layer has an overlapping region overlapping the positive active material layer and an overhang region extending beyond the positive active material layer. The inventors have found that the lithium ions may diffuse to and remain in the overhang region, especially if in a charged state, the lithium ions are stored for a long time, and by applying a small current for constant voltage discharge after discharge, the residual lithium ions in the overhung region can diffuse back to the overlapping region to play a role. However, diffusion of the lithium ions between the overlapping region and the overhang region will also cause the risk of lithium plating.

In view of this, the embodiment of the application provides an electrode assembly including a positive pole piece and a negative pole piece which are stacked, where a positive active material layer of the positive pole piece and a negative active material layer of the negative pole piece are arranged oppositely, and an end of the negative active material layer extends beyond the positive active material layer. The negative active material layer includes a negative body portion and a negative edge portion connected thereto, one end, away from the negative body portion, of the negative edge portion extends beyond the positive active material layer, in a stacking direction of the positive pole piece and the negative pole piece, at least part of the negative edge portion overlaps the positive active material layer, and the negative active material layer is configured in such a way that a capacity per unit area of the negative edge portion is greater than that of the negative body portion; and/or the positive active material layer includes a positive body portion and a positive edge portion connected thereto, and the positive edge portion is configured in such a way that a capacity per unit area of the positive edge portion is smaller than that of the positive body portion. This structure may reduce the risk of lithium plating and enhance safety of the battery.

The technical solution described in the embodiments of the application is applicable to a battery and an electric apparatus using the battery.

The electric apparatus may be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, etc. The vehicles may be fuel vehicles, gas vehicles or new energy vehicles, and the new energy vehicles may be battery electric vehicles, hybrid electric vehicles, extended-range vehicles, etc. The spacecrafts include airplanes, rockets, space shuttles, spaceships, etc. The electric toys include fixed or mobile electric toys, such as game machines, electric car toys, electric ship toys and electric airplane toys. The electric tools include metal cutting electric tools, electric grinding tools, electric assembling tools and electric tools for railways, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators, electric planers, etc. The embodiments of the application do not make special restrictions on the above electric apparatuses.

In the following embodiments, the vehicle is taken as an example of the electric apparatus for the convenience of description.

With reference to <FIG> is a structural schematic diagram of a vehicle <NUM> provided in some embodiments of the application. A battery <NUM> is arranged inside the vehicle <NUM> and may be arranged at a bottom portion, a head portion or a tail portion of the vehicle <NUM>. The battery <NUM> may be used for supplying electricity to the vehicle <NUM>, for example, the battery <NUM> may be used as an operating power source for the vehicle <NUM>.

The vehicle <NUM> may further include a controller <NUM> and a motor <NUM>, where the controller <NUM> is used for controlling the battery <NUM> to supply electricity to the motor <NUM> to be used for, for example, operating electricity requirements during start-up, navigation and running of the vehicle <NUM>.

In some embodiments of the application, the battery <NUM> may not only serve as the operating power source for the vehicle <NUM>, but also serve as a driving power source for the vehicle <NUM>, so as to replace or partially replace fuel or natural gas to provide driving power for the vehicle <NUM>. With reference to <FIG> is an exploded view of a battery <NUM> provided in some embodiments of the application. The battery <NUM> includes a box <NUM> and a battery cell (not shown in <FIG>), the battery cell being accommodated in the box <NUM>.

The box <NUM> is used for accommodating the battery cell and may be of various structures. In some embodiments, the box <NUM> may include a first box portion <NUM> and a second box portion <NUM>, the first box portion <NUM> and the second box portion <NUM> may cover each other, and the first box portion <NUM> and the second box portion <NUM> define an accommodating space <NUM> for accommodating the battery cell together. The second box portion <NUM> may be of a hollow structure with an opening end, the first box portion <NUM> is of a plate-like structure, and the first box portion <NUM> covers an opening side of the second box portion <NUM> so as to form the box <NUM> with the accommodating space <NUM>. The first box portion <NUM> and the second box portion <NUM> may be both of hollow structures with opening sides, and an opening side of the first box portion <NUM> covers the opening side of the second box portion <NUM> so as to form the box <NUM> with the accommodating space <NUM>. Of course, the first box portion <NUM> and the second box portion <NUM> may be in various shapes, such as a cylinder or a cuboid.

In order to improve sealability after the first box portion <NUM> and the second box portion <NUM> are connected, a seal, such as a sealant or a seal ring, may be arranged between the first box portion <NUM> and the second box portion <NUM>.

Assuming that the first box portion <NUM> covers a top portion of the second box portion <NUM>, the first box portion <NUM> may also be referred to as an upper box cover, and the second box portion <NUM> may also be referred to as a lower box.

There may be one or more battery cells in the battery <NUM>. If there are a plurality of battery cells, the plurality of battery cells may be connected in series, in parallel, or in a series-parallel manner. The plurality of battery cells may be directly connected in series, in parallel, or in a series-parallel manner, and then a whole formed by the plurality of battery cells is accommodated in the box <NUM>. Of course, the plurality of battery cells may be connected in series, in parallel, or in a series-parallel manner first to form a battery module <NUM>, and then a plurality of battery modules <NUM> are connected in series, in parallel, or in a series-parallel manner to form a whole to be accommodated in the box <NUM>.

In some embodiments, with reference to <FIG> is a structural schematic diagram of the battery module <NUM> shown in <FIG>. The plurality of battery cells are connected in series, in parallel, or in a series-parallel manner first to form the battery module <NUM>. The plurality of battery modules <NUM> are connected in series, in parallel, or in a series-parallel manner to form the whole to be accommodated in the box.

The plurality of battery cells <NUM> in the battery module <NUM> may be electrically connected to each other by means of bus components, so as to be connected in series, in parallel, or in a series-parallel manner.

With reference to <FIG> is an exploded view of the battery cell <NUM> shown in <FIG>. The battery cell <NUM> provided in the embodiment of the application includes an electrode assembly <NUM> and a case <NUM>, the electrode assembly <NUM> being accommodated in the case <NUM>.

In some embodiments, the case <NUM> may also be used for accommodating an electrolyte, such as an electrolytic solution. The case <NUM> may be of various structures.

In some embodiments, the case <NUM> may include a casing <NUM> and an end cover <NUM>, the casing <NUM> is of a hollow structure with an opening side, and the end cover <NUM> covers an opening of the casing <NUM> to form a sealed connection, so as to form a sealed space for accommodating the electrode assembly <NUM> and the electrolyte.

When the battery cell <NUM> is assembled, the electrode assembly <NUM> may be placed in the casing <NUM> first, then the end cover <NUM> covers the opening of the casing <NUM>, and the electrolyte is injected into the casing <NUM> by means of an electrolyte injection port in the end cover <NUM>.

The casing <NUM> may be in various shapes, such as a cylinder or a cuboid. The shape of the casing <NUM> may be determined according to a specific shape of the electrode assembly <NUM>. For example, if the electrode assembly <NUM> is of a cylindrical structure, a cylindrical casing may be selected and used. If the electrode assembly <NUM> is of a cuboid structure, a cuboid casing may be selected and used. Of course, the end cover <NUM> may also be of various structures, for example, the end cover <NUM> may be of a plate-like structure or a hollow structure with an opening end. Illustratively, in <FIG>, the casing <NUM> is of a cuboid structure, the end cover <NUM> is of a plate-like structure, and the end cover <NUM> covers an opening at a top portion of the casing <NUM>.

In some embodiments, the battery cell <NUM> may further include a positive electrode terminal <NUM>, a negative terminal <NUM> and a pressure relief mechanism <NUM>, all of which are arranged on the end cover <NUM>. The positive terminal <NUM> and the negative terminal <NUM> are both used for being electrically connected to the electrode assembly <NUM>, so as to output electrical energy generated by the electrode assembly <NUM>. The pressure relief mechanism <NUM> is used for relieving a pressure inside the battery cell <NUM> when an internal pressure or temperature of the battery cell <NUM> reaches a predetermined value.

Illustratively, the pressure relief mechanism <NUM> is positioned between the positive electrode terminal <NUM> and the negative terminal <NUM> and may be components such as an explosion-proof valve, an explosion-proof sheet, an air valve, a pressure relief valve, or a safety valve.

Of course, in some embodiments, the case <NUM> may also be of other structures, for example, the case <NUM> includes the casing <NUM> and two end covers <NUM>, the casing <NUM> is a hollow structure with two opposite opening sides, and one end cover <NUM> covers one opening of the casing <NUM> correspondingly to form a sealed connection, so as to form a sealed space for accommodating the electrode assembly <NUM> and the electrolyte. In this structure, the positive electrode terminal <NUM> and the negative electrode terminal <NUM> may be arranged on the same end cover <NUM>, or may be arranged on different end covers <NUM>. The pressure relief mechanism <NUM> may be arranged on one end cover <NUM>, or the pressure relief mechanisms <NUM> may be arranged on both of the end covers <NUM>.

It should be noted that in the battery cell <NUM>, there may be one or more electrode assemblies <NUM> accommodated in the case <NUM>. Illustratively, in <FIG>, there are two electrode assemblies <NUM>. Next, a specific structure of the electrode assembly <NUM> will be described in detail with reference to the accompanying drawings.

<FIG> is a structural schematic diagram of an electrode assembly in one embodiment of the application, and <FIG> is a partial section view made of the electrode assembly shown in <FIG> along line A-A.

As shown in <FIG>, the electrode assembly <NUM> includes a positive pole piece <NUM> and a negative pole piece <NUM> which are stacked, a positive active material layer <NUM> of the positive pole piece <NUM> and a negative active material layer <NUM> of the negative pole piece <NUM> are arranged oppositely, and an end of the negative active material layer <NUM> extends beyond the positive active material layer <NUM>. A region, overlapping the positive active material layer <NUM> in a stacking direction X, of the negative active material layer <NUM> is an overlapping region S1, and a region, extending beyond the positive active material layer <NUM>, of the negative active material layer <NUM> is an overhang region S2.

In some embodiments, the positive pole piece <NUM> includes a positive current collector <NUM> and the positive active material layers <NUM> with which two surfaces of the positive current collector <NUM> are coated. The negative pole piece <NUM> includes a negative current collector <NUM> and the negative active material layers <NUM> with which two surfaces of the negative current collector <NUM> are coated. The positive current collector <NUM> includes a positive coating region <NUM> and a positive tab <NUM>, positive coating region <NUM> being coated with at least partial positive active material layer <NUM>, the positive tab <NUM> being connected to an end of the positive coating region <NUM> and protruding out of the positive coating region <NUM>, and the positive tab <NUM> being at least partially uncoated with the positive active material layer <NUM> and used for being electrically connected to the positive electrode terminal <NUM> (with reference to <FIG>). The negative current collector <NUM> includes a negative coating region <NUM> and a negative tab <NUM>, the negative coating region <NUM> being coated with at least partial negative active material layer <NUM>, the negative tab <NUM> being connected to an end of the negative coating region <NUM> and protruding out of the negative coating region <NUM>, and the negative tab <NUM> being at least partially uncoated with the negative active material layer <NUM> and used for being electrically connected to the negative electrode terminal <NUM> (with reference to <FIG>).

The electrode assembly <NUM> further includes a separator film <NUM> for separating the positive pole piece <NUM> from the negative pole piece <NUM>. The separator film <NUM> is provided with a large number of through micropores, which can guarantee free passage of electrolyte ions and has good penetrability for lithium ions. The separator film <NUM> may be made of polypropylene (PP), polyethylene (PE), etc..

In some embodiments, the positive pole piece <NUM> and the negative pole piece <NUM> are wound around a winding axis to form a wound structure. In the wound structure, the positive pole piece <NUM> and the negative pole piece <NUM> are stacked in a direction perpendicular to the winding axis. In other words, the positive pole piece <NUM> and the negative pole piece <NUM> are wound in a plurality of turns in a winding direction Z, the winding direction Z being a direction in which the positive pole piece <NUM> and the negative pole piece <NUM> are circumferentially wound from the inside to the outside. In <FIG>, the winding direction Z is counterclockwise.

In some embodiments, the positive tab <NUM> is connected to an end, in a first direction Y, of the positive coating region <NUM>, and the negative tab <NUM> is connected to an end, in the first direction Y, of the negative coating region <NUM>, the first direction Y being perpendicular to the winding direction Z and parallel to the winding axis of the electrode assembly <NUM>.

In some embodiments, the positive tab <NUM> and the negative tab <NUM> are positioned on the same side, in the first direction Y, of the electrode assembly <NUM>. In some other embodiments, the positive tab <NUM> and the negative tab <NUM> may also be positioned on two sides, in the first direction Y, of the electrode assembly <NUM>.

The electrode assembly <NUM> with the wound structure includes a straight region B and bent regions C positioned at two ends of the straight region B. The straight region B is a region with a parallel structure in the wound structure, that is, the negative pole piece <NUM>, the positive pole piece <NUM> and the separator film <NUM> in the flat region B are substantially parallel to each other, that is, a surface of each layer of the negative pole piece <NUM>, the positive pole piece <NUM> and the separator film <NUM> of the electrode assembly <NUM> in the straight region B is planar. The bent region C is a region with a bent structure in the wound structure, that is, the negative pole piece <NUM>, the positive pole piece <NUM> and the separator film <NUM> in the bent region C are all bent, that is, a surface of each layer of the negative pole piece <NUM>, the positive pole piece <NUM> and the separator film <NUM> of the electrode assembly <NUM> in the bent region C is curved.

In some embodiments, an end of the negative active material layer <NUM> extends beyond the positive active material layer <NUM>. Specifically, two ends, in the first direction Y, of the negative active material layer <NUM> extend beyond the positive active material layer <NUM>, a start end, in the winding direction Z, of the negative active material layer <NUM> extends beyond the positive active material layer <NUM>, and a tail end, in the winding direction Z, of the negative active material layer <NUM> extends beyond the positive active material layer <NUM>. In this way, in the stacking direction X, the negative active material layer <NUM> may completely cover the positive active material layer <NUM>, so as to reduce the risk of lithium plating.

<FIG> is a schematic diagram of the positive pole piece <NUM> and the negative pole piece <NUM>, in an unfolded state, shown in <FIG>. As shown in <FIG>, after the wound structure is unwound, the positive pole piece <NUM> and the negative pole piece <NUM> are substantially in long-strip shapes. In such a condition, the positive pole piece <NUM> and the negative pole piece <NUM> are stacked. In a length direction L of the negative pole piece <NUM>, a length of the negative active material layer <NUM> is greater than that of the positive active material layer <NUM>, and two ends of the negative active material layer <NUM> extend beyond the positive active material layer <NUM>. In a width direction W of the negative pole piece <NUM>, a width of the negative active material layer <NUM> is greater than that of the positive active material layer <NUM>, and the two ends of the negative active material layer <NUM> extend beyond the positive active material layer <NUM>.

<FIG> is a structural schematic diagram of an electrode assembly <NUM> in another embodiment of the application. <FIG> is a structural schematic diagram of the positive pole piece <NUM> and the negative pole piece <NUM> of the electrode assembly <NUM> shown in <FIG>. As shown in <FIG>, in some embodiments, the electrode assembly <NUM> includes a plurality of positive pole pieces <NUM> and a plurality of negative pole pieces <NUM>, which are alternately stacked in the stacking direction X. The stacking direction X is parallel to a thickness direction of the positive pole piece <NUM> and a thickness direction of the negative pole piece <NUM>. The positive pole piece <NUM> and the negative pole piece <NUM> are both substantially in flat-plate shapes.

In a direction perpendicular to the stacking direction X, an end of the negative active material layer <NUM> extends beyond the positive active material layer <NUM>. In some embodiments, the negative active material layer <NUM> and the positive active material layer <NUM> are both substantially rectangular. In the length direction of the negative active material layer <NUM>, two ends of the negative active material layer <NUM> extend beyond the positive active material layer <NUM>. In the width direction of the negative active material layer <NUM>, two ends of the negative active material layer <NUM> extend beyond the positive active material layer <NUM>.

Through research, the inventors have found that the overhang region may cause the risk of lithium plating.

Specifically, <FIG> are schematic diagrams of lithium ions migrating between the positive pole piece <NUM> and the negative pole piece <NUM>. As shown in <FIG>, the negative active material layer <NUM> includes an overlapping region S1 and an overhang region S2, the overlapping region S1 overlapping the positive active material layer <NUM> in the stacking direction X, and the overhang region S2 being a region, extending beyond the positive active material layer <NUM>, of the negative active material layer <NUM>. During charge, lithium ions Li+ separate from the positive active material layer <NUM> and are embedded into the overlapping region S1, and as shown in <FIG>, the lithium ions are substantially embedded into the overlapping region S1 in the fully charged state.

During self-discharge standing after charge, the lithium ions self-diffuse and are distributed in the negative active material layer <NUM> relatively uniformly, where the negative active material layer <NUM> includes the overhang region S2, that is, as shown in <FIG>, some of the lithium ions diffuse from the overlapping region S1 to the overhang region S2. Especially, the lithium ions are stored for a long time if in the charged state more obviously.

After discharge for a period of time, as shown in <FIG>, the lithium ions separate from the overlapping region S1 and are embedded in the positive active material layer <NUM>.

A diffusion rate of the lithium ions in the positive active material layer <NUM> is greater than that of the lithium ions in the negative active material layer <NUM>. After standing for a period of time, as shown in <FIG>, the lithium ions in the positive active material layer <NUM> diffuse to be distributed in the positive active material layer <NUM> uniformly. However, since the diffusion rate of the lithium ions in the negative active material layer <NUM> is relatively low, the lithium ions in the overhang region S2 only diffuse to a portion, close to the overhang region S2, of the overlapping region S1.

During recharge, the lithium ions in the positive active material layer <NUM> separate from the positive active material layer <NUM> and are embedded in the overlapping region S1. The portion, close to the overhang region S2, of the overlapping region S1 receives the lithium ions diffusing from the overhang region S2 and the lithium ions separating from the positive active material layer <NUM>. As shown in <FIG>, after a plurality of charge and discharge cycles, the portion, close to the overhang region S2, of the overlapping region S1 may not completely receive the lithium ions, thereby causing the risk of lithium plating.

In view of this, the inventors have made further improvements in a structure of the electrode assembly <NUM>.

<FIG> is a partial section view of an electrode assembly <NUM> in one embodiment of the application, <FIG> is a partial section view of an electrode assembly <NUM> in another embodiment of the application, <FIG> is a partial section view of an electrode assembly <NUM> in yet another embodiment of the application, <FIG> is a partial section view of an electrode assembly <NUM> in yet another embodiment of the application, and <FIG> is a partial section view of an electrode assembly <NUM> in yet another embodiment of the application.

As shown in <FIG>, in some embodiments, the negative active material layer <NUM> includes a negative body portion <NUM> and a negative edge portion <NUM> connected thereto, one end, away from the negative body portion <NUM>, of the negative edge portion <NUM> extends beyond the positive active material layer <NUM>, in a stacking direction of the positive pole piece <NUM> and the negative pole piece <NUM>, at least part of the negative edge portion <NUM> overlaps the positive active material layer <NUM>, and the negative active material layer <NUM> is configured in such a way that a capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>; and/or the positive active material layer <NUM> includes a positive body portion <NUM> and a positive edge portion <NUM> connected thereto, and the positive edge portion <NUM> is configured in such a way that a capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>.

If the negative active material layer <NUM> includes the negative body portion <NUM> and the negative edge portion <NUM>, then the negative edge portion <NUM> includes a first portion overlapping the positive active material layer <NUM> in the stacking direction X and a second portion extending beyond the positive active material layer <NUM> (that is, the second portion is at least part of the overhang region). When the capacity per unit area of the negative body portion <NUM> meets a setting requirement, that is, the capacity per unit area of the negative body portion <NUM> reaches a first preset value, lithium plating is less likely to occur on the negative body portion <NUM>. Since the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>, that is, the capacity per unit area of the negative edge portion <NUM> is greater than the first preset value, equivalently, the capacity per unit area of the negative edge portion <NUM> is increased such that a cell balance (CB) value of the negative edge portion <NUM> may be increased. During cycle, even if the first portion needs to receive lithium ions separating from the positive active material layer <NUM> and lithium ions diffusing from the second portion, lithium plating is less likely to occur on the first portion, thereby reducing a risk of lithium plating of the negative edge portion <NUM>.

If the positive active material layer <NUM> includes the positive body portion <NUM> and the positive edge portion <NUM>, then a portion, overlapping the positive edge portion <NUM>, of the negative active material layer <NUM> and a portion, extending beyond the positive active material layer <NUM>, of the negative active material layer <NUM> are connected. When the capacity per unit area of the positive body portion <NUM> meets a setting requirement, that is, the capacity per unit area of the positive body portion <NUM> reaches a second preset value, lithium plating is less likely to occur on the portion, overlapping the positive body portion <NUM>, of the negative active material layer <NUM>. Since the capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>, that is, the capacity per unit area of the positive edge portion <NUM> is smaller than the second preset value, equivalently, the capacity per unit area of the positive edge portion <NUM> is reduced such that a cell balance (CB) value of the portion, overlapping the positive edge portion <NUM>, of the negative active material layer <NUM> is increased. During cycle, even if the portion, overlapping the positive edge portion <NUM>, of the negative active material layer <NUM> needs to receive lithium ions diffusing from the portion, extending beyond the positive active material layer <NUM>, of the negative active material layer <NUM>, lithium plating is less likely to occur on the portion, overlapping the positive edge portion <NUM>, of the negative active material layer <NUM>.

The cell balance (CB) value is a ratio of the capacity per unit area of the negative active material layer <NUM> to that of the positive active material layer <NUM>. For example, if the negative active material layer <NUM> includes the negative body portion <NUM> and the negative edge portion <NUM>, the CB value of the negative body portion <NUM> equals Q1/Q2, the CB value of the negative edge portion <NUM> equals Q3/Q4, the capacity per unit area of the negative body portion <NUM> is Q1, the capacity per unit area of the portion, overlapping the negative body portion <NUM>, of the positive active material layer <NUM> is Q2, the capacity per unit area of the negative edge portion <NUM> is Q3, and the capacity per unit area of the portion, overlapping the negative edge portion <NUM>, of the positive active material layer <NUM> is Q4. For another example, when the positive active material layer <NUM> includes the positive body portion <NUM> and the positive edge portion <NUM>, the CB value of the portion, overlapping the positive body portion <NUM>, of the negative active material layer <NUM> equals Q5/Q6, and the CB value of the portion, overlapping the positive edge portion <NUM>, of the negative active material layer <NUM> equals Q7/Q8, where the capacity per unit area of the portion, overlapping the positive body portion <NUM>, of the negative active material layer <NUM> is Q5, the capacity per unit area of the positive body portion <NUM> is Q6, the capacity per unit area of the portion, overlapping the positive edge portion <NUM>, of the negative active material layer <NUM> is Q7, and the capacity per unit area of the positive edge portion <NUM> is Q8.

If the negative active material layer <NUM> includes the negative body portion <NUM> and the negative edge portion <NUM>, the negative edge portion <NUM> is arranged along an edge of the negative active material layer <NUM>, and an end, away from the negative body portion <NUM>, of the negative edge portion <NUM> is a free end of the negative active material layer <NUM>. If the positive active material layer <NUM> includes the positive body portion <NUM> and the positive edge portion <NUM>, the positive edge portion <NUM> is arranged along an edge of the positive active material layer <NUM>, and an end, away from the positive body portion <NUM>, of the positive edge portion <NUM> is a free end of the positive active material layer <NUM>.

In the embodiments of the application, the negative active material layers <NUM> are provided on two sides of the negative current collector <NUM>, the negative active material layer <NUM> described in the application is the negative active material layer <NUM> on one side, and the capacity per unit area of the negative active material layer <NUM> is the capacity per unit area of the negative active material layer <NUM> on one side of the negative pole piece <NUM>. Similarly, the positive active material layers <NUM> are provided on two sides of the positive current collector <NUM>, the positive active material layer <NUM> described in the application is the positive active material layer <NUM> on one side, and the capacity per unit area of the positive active material layer <NUM> is the capacity per unit area of the positive active material layer <NUM> on one side of the positive pole piece <NUM>. In the embodiments of the application, the capacity per unit area of the negative body portion <NUM> is a ratio of an active material capacity of the negative body portion <NUM> to an area of a portion, covered with the negative body portion <NUM>, of the negative current collector <NUM>, and the capacity per unit area of the negative edge portion <NUM> is a ratio of an active material capacity of the negative edge portion <NUM> to an area of a portion, covered with the negative edge portion <NUM>, of the negative current collector <NUM>. Similarly, the capacity per unit area of the positive body portion <NUM> is a ratio of an active material capacity of the positive body portion <NUM> to an area of a portion, covered with the positive body portion <NUM>, of the positive current collector <NUM>, and the capacity per unit area of the positive edge portion <NUM> is a ratio of the active material capacity of the positive edge portion <NUM> to the area of a portion, covered with the positive edge portion <NUM>, of the positive current collector <NUM>.

In some embodiments, as shown in <FIG>, the negative active material layer <NUM> includes the negative body portion <NUM> and the negative edge portion <NUM> connected thereto, one end, away from the negative body portion <NUM>, of the negative edge portion <NUM> extends beyond the positive active material layer <NUM>, in a stacking direction of the positive pole piece <NUM> and the negative pole piece <NUM>, at least part of the negative edge portion <NUM> overlaps the positive active material layer <NUM>, and the negative active material layer <NUM> is configured in such a way that the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>.

With the same thickness, all the portions, of the positive active material layer <NUM> feature the same capacity per unit area. Specifically, the positive active material layer <NUM> is entirely formed by performing coating with single active slurry.

In the case where the negative active material layer <NUM> is provided with the negative body portion <NUM> and the negative edge portion <NUM> which have different capacities per unit area, the positive active material layer <NUM> may be formed by performing coating with the single active slurry, so as to simplify a manufacturing process for the positive pole piece <NUM>.

In the application, positions and the number of the negative edge portions <NUM> may be set according to requirements.

In some embodiments, there is one negative edge portion <NUM>, and the negative edge portion <NUM> is positioned at one side, in the first direction Y, of the negative body portion <NUM>, that is, the negative edge portion <NUM> and the negative body portion <NUM> are arranged in the first direction Y, and a size, in the first direction Y, of the negative edge portion <NUM> is smaller than a size, in the first direction Y, of the negative body portion <NUM>. In some embodiments, the negative edge portion <NUM> is positioned on a side, in the first direction Y away from the negative tab <NUM>, of the negative body portion <NUM>. In some embodiments, the negative edge portion <NUM> and the negative body portion <NUM> feature the same thickness.

In some other embodiments, at least two negative edge portions <NUM> are positioned on two sides, in the first direction, of the negative body portion <NUM> respectively. By means of the two negative edge portions <NUM>, lithium plating is less likely to occur on the negative active material layer <NUM>.

In a forming process of the negative pole piece <NUM>, the negative current collector <NUM> is coated with negative active slurry first, and then is rolled to form the negative active material layer <NUM>. Due to fluidity and surface tension of the negative active slurry, after the negative active material layer <NUM> is formed, a thin layer region having a small thickness is formed at the end, close to the negative tab <NUM>, of the negative active material layer <NUM>. In the embodiments of the application, the negative edge portion <NUM> is arranged at one end, close to the negative tab <NUM>, of the negative active material layer <NUM>. Even if the negative edge portion <NUM> is thinned in the forming process, a requirement of the negative edge portion <NUM> on the CB value may be satisfied, and the risk of lithium plating may be reduced. In this way, in the two negative edge portions <NUM>, a thickness of at least part of the negative edge portion <NUM> close to the negative tab <NUM> is smaller than that of the negative body portion <NUM>. In some embodiments, the thickness of the negative edge portion <NUM> far away from the negative tab <NUM> is equal to that of the negative body portion <NUM>.

In the forming process of the positive pole piece <NUM>, the positive current collector <NUM> is coated with positive active slurry first and then is rolled to form the positive active material layer <NUM>. Due to fluidity and surface tension of the positive active slurry, after the positive active material layer <NUM> is formed, a thin layer region having a small thickness is formed at the end, close to the positive tab <NUM>, of the positive active material layer <NUM>.

In some embodiments, the positive pole piece <NUM> further includes an insulating layer <NUM>, the positive electrode coating region <NUM> is coated with part of the insulating layer <NUM>, and a root portion, close to the positive coating region <NUM>, of the positive tab <NUM> is coated with another part of the insulating layer <NUM>. The insulating layer <NUM> may reduce burrs in a cutting process of the positive tab <NUM>, improve insulating performance of the positive tab <NUM>, and reduce a risk of electric connection between the root portion of the positive tab <NUM> and the negative pole piece <NUM>.

The lithium ions in the second portion may diffuse to the first portion, and if the size, in the first direction Y, of the first portion is too small, the lithium ions in the second portion may diffuse to the negative body portion <NUM>, and the capacity per unit area of the negative body portion <NUM> is smaller than that of the first portion, such that the risk of the negative body portion <NUM> is likely to occur. Therefore, in order to reduce the risk of lithium plating, in some embodiments, the size of the first portion is greater than <NUM> in the first direction Y, that is, the size of the portion, overlapping the positive active material layer <NUM> in the stacking direction X, of the negative edge portion <NUM> is greater than <NUM> in the first direction Y. In the embodiments of the application, it can be achieved in a variety of ways that the capacity per unit area of the negative edge portion <NUM> may be greater than that of the negative body portion <NUM>.

In some embodiments, a weight ratio of an active material in the negative edge portion <NUM> to the negative edge portion <NUM> is greater than that of an active material in the negative body portion <NUM> to the negative body portion <NUM>, such that the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>. The negative edge portion <NUM> and the negative body portion <NUM> each include the active material, an adhesive and a conductive agent. By adding the active material in the negative edge portion <NUM>, the weight ratio of the active material in the negative edge portion <NUM> is increased, and the capacity per unit area of the negative edge portion <NUM> is increased, such that the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>.

In some examples, the weight ratio of the active material in the negative edge portion <NUM> to the negative edge portion <NUM> is greater than that of the active material in the negative body portion <NUM> to the negative body portion <NUM> by <NUM>%-<NUM>%, optionally, <NUM>%-<NUM>%. Optionally, the active material in the negative edge portion <NUM> is the same as the active material in the negative body portion <NUM>. The active material in the negative edge portion <NUM> and the active material in the negative body portion <NUM> is the same and may be a compound of graphite, silicon, etc..

In the embodiment, the thickness of the negative edge portion <NUM> may be set according to positions. For example, the thickness of the negative edge portion <NUM> close to the negative tab <NUM> is smaller than that of the negative body portion <NUM>, and the thickness of the negative edge portion <NUM> far away from the negative tab <NUM> is equal to that of the negative body portion <NUM>.

In other embodiments, per gram capacity of the active material in the negative edge portion <NUM> is greater than that of the active material in the negative body portion <NUM>. By increasing the gram capacity of the active material in the negative edge portion <NUM>, the capacity per unit area of the negative edge portion <NUM> may be increased such that the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>.

The gram capacity is a ratio of capacitance released by the active material to mass of the active material.

In the embodiment, the active material in the negative edge portion <NUM> is different from that in the negative body portion <NUM>, for example, the active material in the negative edge portion <NUM> is a compound of silicon, but the active material in the negative body portion <NUM> is graphite.

Optionally, the gram capacity of the active material in the negative edge portion <NUM> is greater than that of the active material in the negative body portion <NUM> by <NUM>%-<NUM>%. Illustratively, the gram capacity of the active material in the negative edge portion <NUM> is greater than that of the active material in the negative body portion <NUM> by <NUM>%-<NUM>%.

Optionally, the weight ratio of the active material in the negative edge portion <NUM> to the negative edge portion <NUM> is equal to that of the active material in the negative body portion <NUM> to the negative body portion <NUM>.

With reference to <FIG>, in some embodiments, the negative edge portion <NUM> includes a first negative coating 1212a and a second negative coating 1212b which are stacked in a stacking direction X. Optionally, the second negative coating 1212b is connected between the first negative coating 1212a and the negative current collector <NUM>. The first negative coating 1212a and the second negative coating 1212b are both active coatings containing active materials.

In some embodiments, the active material in the first negative coating 1212a is the same as that in the negative body portion <NUM>. A weight ratio of the active material in the first negative coating 1212a to the first negative coating 1212a is equal to that of the active material in the negative body portion <NUM> to the negative body portion <NUM>. Optionally, the first negative coating 1212a and the negative body portion <NUM> feature the same component, that is, the first negative coating 1212a and the negative body portion <NUM> may be formed of the same negative active slurry, which may simplify a manufacturing process for the negative pole piece <NUM>.

In some embodiments, a weight ratio of active material in the second negative coating 1212b to the second negative coating 1212b is greater than that of active material in the first negative coating 1212a to the first negative coating 1212a. By adding the active material in the second negative coating 1212b, the weight ratio of the active material in the second negative coating 1212b is increased, and the capacity per unit area of the negative edge portion <NUM> is increased, such that the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>.

Optionally, the active material in the second negative coating 1212b is the same as that in the first negative coating 1212a. The active material in the second negative coating 1212b and the active material in the first negative coating 1212a is the same and may be a compound of graphite, silicon, etc..

In other embodiments, per gram capacity of the active material in the second negative coating 1212b is greater than that of the active material in the first negative coating 1212a. By increasing the gram capacity of the active material in the second negative coating 1212b, the capacity per unit area of the negative edge portion <NUM> is increased, such that the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>.

In the application, in addition to increase in the capacity per unit area of the negative edge portion <NUM>, the risk of lithium plating of the negative edge portion <NUM> may be reduced by improving kinetic performance of the negative edge portion <NUM>. For example, the smaller the particle size of the active material is, the more likely the lithium ion is to diffuse, and the less likely the lithium ions are to locally gather. In some embodiments, the particle size of the active material in the negative edge portion <NUM> is smaller than that of the active material in the negative body portion <NUM>. In this way, during charge and discharge, the lithium ions are likely to diffuse in the negative edge portion <NUM>, are distributed in the negative edge portion <NUM> more uniformly, and are less likely to locally gather in the negative edge portion <NUM>, so as to reduce the risk of lithium plating.

With reference to <FIG>, in some embodiments, the positive active material layer <NUM> includes the positive body portion <NUM> and the positive edge portion <NUM> connected thereto, and the positive edge portion <NUM> is configured in such a way that a capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>. With the same thickness, all the portions of the negative active material layer <NUM> feature the same capacity per unit area. Specifically, the negative active material layer <NUM> is entirely formed by performing coating with single active slurry.

In the case where the positive active material layer <NUM> is provided with the positive body portion <NUM> and the positive edge portion <NUM> which feature different capacities per unit area, the negative active material layer <NUM> may be formed by performing coating with the single active slurry, so as to simplify a manufacturing process for the negative pole piece <NUM>.

In the application, positions and the number of the positive edge portions <NUM> may be set according to requirements.

In some embodiments, there is one positive edge portion <NUM>, and the positive edge portion <NUM> is positioned at one side, in the first direction Y, of the positive body portion <NUM>, that is, the positive edge portion <NUM> and the positive body portion <NUM> are arranged in the first direction Y, and a size, in the first direction Y, of the positive edge portion <NUM> is smaller than a size, in the first direction Y, of the positive body portion <NUM>. In some embodiments, the positive edge portion <NUM> is positioned on a side, in the first direction Y away from the positive tab <NUM>, of the positive body portion <NUM>. In some embodiments, the positive edge portion <NUM> and the positive body portion <NUM> feature the same thickness.

In some other embodiments, at least two positive edge portions <NUM> are positioned on two sides, in the first direction Y, of the positive body portion <NUM>. By means of the two positive edge portions <NUM>, lithium plating is less likely to occur on the positive active material layer <NUM>.

In the two positive edge portions <NUM>, a thickness of at least part of the positive edge portion <NUM> close to the positive tab <NUM> is smaller than that of the positive body portion <NUM>. A portion, with a thickness smaller than that of the positive body portion <NUM>, of the positive edge portion <NUM> is a thin layer region of the positive active material layer <NUM>. In some embodiments, the thickness of the positive edge portion <NUM> far away from the positive tab <NUM> is equal to that of the positive body portion <NUM>.

The lithium ions in the portion, extending beyond the positive active material layer <NUM>, of the negative active material layer <NUM> may diffuse into the portion, overlapping the positive edge portion <NUM>, of the negative active material. If the size, in the first direction Y, of the positive edge portion <NUM> is too small, the size of the portion, overlapping the positive edge portion <NUM>, of the negative active material may also be too small in the first direction Y, then the lithium ions may diffuse to a portion, overlapping the positive body portion <NUM>, of the negative active material. Since the capacity per unit area of the positive body portion <NUM> is greater than that of the positive edge portion <NUM>, lithium plating may occur in the portion, overlapping the positive body portion <NUM>, of the negative active material. Therefore, in order to reduce the risk of lithium plating, the size of the portion, overlapping the positive edge portion <NUM>, of the negative active material in the first direction Y is greater than <NUM>, that is, the size of the positive edge portion <NUM> in the first direction Y is greater than <NUM>.

In the embodiments of the application, it can be achieved in a variety of ways that the capacity per unit area of the positive edge portion <NUM> may be greater than that of the positive body portion <NUM>.

In some embodiments, a weight ratio of an active material in the positive edge portion <NUM> to the positive edge portion <NUM> is smaller than that of an active material in the positive body portion <NUM> to the positive body portion <NUM>, such that the capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>. The positive edge portion <NUM> and the positive body portion <NUM> each include the active material, an adhesive and a conductive agent. By adding the active material in the positive edge portion <NUM>, the weight ratio of the active material in the positive edge portion <NUM> is reduced, and the capacity per unit area of the positive edge portion <NUM> is reduced, such that the capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>.

In some examples, the weight ratio of the active material in the positive edge portion <NUM> to the positive edge portion <NUM> is smaller than that of the active material in the positive body portion <NUM> to the positive body portion <NUM> by <NUM>%-<NUM>%, optionally, <NUM>%-<NUM>%. Optionally, the active material in the positive edge portion <NUM> is the same as that in the positive body portion <NUM>. The active material in the positive edge portion <NUM> is the same as that in the positive body portion <NUM> and may be lithium iron phosphate, lithium manganate, ternary lithium, lithium cobaltate, etc..

In the embodiment, the thickness of the positive edge portion <NUM> may be set according to positions. For example, the thickness of the positive edge portion <NUM> close to the positive tab <NUM> is smaller than that of the positive body portion <NUM>, and the thickness of the positive edge portion <NUM> far away from the positive tab <NUM> is equal to that of the positive body portion <NUM>.

In some other embodiments, per gram capacity of the active material in the positive edge portion <NUM> is smaller than that of the active material in the positive body portion <NUM>. By increasing the gram capacity of the active material in the positive edge portion <NUM>, the capacity per unit area of the positive edge portion <NUM> may be reduced, such that the capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>.

In the embodiment, the active material in the positive edge portion <NUM> is different from that in the positive body portion <NUM>, for example, the active material in the positive edge portion <NUM> is lithium iron phosphate, but the active material in the positive body portion <NUM> is ternary lithium.

Optionally, the gram capacity of the active material in the positive edge portion <NUM> is smaller than that of the active material in the positive body portion <NUM> by <NUM>%-<NUM>%. Illustratively, the gram capacity of the active material in the positive edge portion <NUM> is smaller than that of the active material in the positive body portion <NUM> by <NUM>%-<NUM>%.

Optionally, the weight ratio of the active material in the positive edge portion <NUM> to the positive edge portion <NUM> is equal to that of the active material in the positive body portion <NUM> to the positive body portion <NUM>.

With reference to <FIG>, in some embodiments, the positive edge portion <NUM> includes a first positive coating 1112a and a second positive coating 1112b which are stacked in the stacking direction X. Optionally, the second positive coating 1112b is connected between the first positive coating 1112a and the positive current collector <NUM>.

In some embodiments, the active material in the first positive coating 1112a is the same as that in the positive body portion <NUM>. A weight ratio of the active material in the first positive coating 1112a to the first positive coating 1112a is equal to that of the active material in the positive body portion <NUM> to the positive body portion <NUM>. Optionally, the first positive coating 1112a and the positive body portion <NUM> feature the same components, that is, the first positive coating 1112a and the positive body portion <NUM> may be formed of the same negative active slurry, which may simplify a manufacturing process for the positive pole piece <NUM>.

The second positive coating 1112b may be a pure conductive coating, for example, the second positive coating 1112b may be a pure conductive coating composed of an adhesive and a conductive agent. The second positive coating 1112b may also be an active coating containing lithium ions, for example, the second positive coating 1112b is an active coating containing lithium ions and composed of a lithium-rich material, an adhesive and a conductive agent. The second positive coating 1112b may be an inactive coating containing lithium ions, for example, the second positive coating 1112b may be an inactive coating containing lithium ions composed of an adhesive, a conductive agent, and lithium powder coated with lithium carbonate.

In some embodiments, a weight ratio of active material in the second positive coating 1112b to the second positive coating 1112b is smaller than that of active material in the first positive coating 1112a to the first positive coating 1112a. By decreasing the active material in the second positive coating 1112b, the weight ratio of the active material in the second positive coating 1112b is reduced, and then the capacity per unit area of the positive edge portion <NUM> is reduced, such that the capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>. Optionally, the second positive coating 1112b does not contain active material, that is, the weight ratio of the active material in the second positive coating 1112b to the second positive coating 1112b is <NUM>.

In some other embodiments, per gram capacity of the active material in the second positive coating 1112b is smaller than that of the active material in the first positive coating 1112a. By reducing the gram capacity of the active material in the second positive coating 1112b, the capacity per unit area of the positive edge portion <NUM> is reduced, such that the capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>. In the application, in addition to reduction in the capacity per unit area of the positive edge portion <NUM>, the risk of lithium plating of the negative active material layer <NUM> may be reduced by adjusting kinetic performance of the positive edge portion <NUM>. In some embodiments, a particle size of the active material in the positive edge portion <NUM> is greater than that of the active material in the positive body portion <NUM>. In this way, during charge and discharge, lithium ions are less likely to diffuse in the positive edge portion <NUM>, a rate of the lithium ions in the positive body portion <NUM> diffusing into the positive edge portion <NUM> is reduced, and a rate of the lithium ions separating from the positive edge portion <NUM> is also reduced such that a risk that the lithium ions gather in the portion, overlapping the positive edge portion <NUM>, of the negative active material layer <NUM> may be reduced, and lithium plating is less likely to occur on the negative active material layer <NUM>.

In some embodiments, as shown in <FIG>, the negative active material layer <NUM> includes the negative body portion <NUM> and the negative edge portion <NUM> connected thereto, one end, away from the negative body portion <NUM>, of the negative edge portion <NUM> extends beyond the positive active material layer <NUM>, in the stacking direction of the positive pole piece <NUM> and the negative pole piece <NUM>, at least part of the negative edge portion <NUM> overlaps the positive active material layer <NUM>, and the negative active material layer <NUM> is configured in such a way that the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>. The positive active material layer <NUM> includes the positive body portion <NUM> and the positive edge portion <NUM> connected thereto, and the positive edge portion <NUM> is configured in such a way that a capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>.

In the embodiments of the application, by increasing the weight ratio or the gram capacity of the active material in the negative edge portion <NUM>, etc., the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>. Similarly, by reducing the weight ratio or the gram capacity of the active material in the positive edge portion <NUM>, etc., the capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>.

In some embodiments, the positive edge portion <NUM> and the negative edge portion <NUM> at least partially overlap in the stacking direction X. In some embodiments, part of the positive edge portion <NUM> and the negative body portion <NUM> overlap in the stacking direction X. When the capacity per unit area of the negative body portion <NUM> and the capacity per unit area of the positive body portion <NUM> satisfy requirements, the capacity per unit area of the negative edge portion <NUM> is greater than that of the negative body portion <NUM>, and the capacity per unit area of the positive edge portion <NUM> is smaller than that of the positive body portion <NUM>. In this way, the CB value of the negative edge portion <NUM> and the CB value of the portion, overlapping the positive edge portion <NUM>, of the negative body portion <NUM> may be increased, and lithium plating is less likely to occur in the negative active material layer <NUM>. <FIG> is a schematic diagram of a top view of the negative pole piece <NUM> of the electrode assembly <NUM> in one embodiment of the application. As shown in <FIG>, in some embodiments, the negative edge portion <NUM> is arranged around the negative body portion <NUM> such that a range of the negative edge portion <NUM> may be increased, and lithium plating is less likely to occur on the negative active material layer <NUM>.

<FIG> is a schematic diagram of a top view of the positive pole piece <NUM> of the electrode assembly <NUM> in one embodiment of the application. As shown in <FIG>, in some embodiments, the positive edge portion <NUM> is arranged around the positive body portion <NUM>, such that the portion, overlapping the positive edge portion <NUM>, of the negative active material layer <NUM> may be expanded, and lithium plating is less likely to occur in the negative active material layer <NUM>.

Test steps for the capacity per unit area and the CB value are as follow:.

<FIG> is a schematic flowchart of a manufacturing method for an electrode assembly provided in some embodiments of the application. As shown in <FIG>, in some embodiments, the manufacturing method for an electrode assembly includes:.

The negative active material layer includes a negative body portion and a negative edge portion connected thereto, one end, away from the negative body portion, of the negative edge portion extends beyond the positive active material layer, in a stacking direction of the positive pole piece and the negative pole piece, at least part of the negative edge portion overlaps the positive active material layer, and the negative active material layer is configured in such a way that a capacity per unit area of the negative edge portion is greater than that of the negative body portion; and/or the positive active material layer includes a positive body portion and a positive edge portion connected thereto, and the positive edge portion is configured in such a way that a capacity per unit area of the positive edge portion is smaller than that of the positive body portion.

It should be noted that for related structures of the electrode assembly manufactured by the above manufacturing method, it may refer to the electrode assembly provided in the above embodiments.

When the electrode assembly is assembled on the basis of the above-described manufacturing method for the electrode assembly, it is not necessary to perform the above-described steps sequentially, that is, the steps may be performed in the order mentioned in the embodiments, may be performed in a different order from that mentioned in the embodiments, or may be performed simultaneously. For example, steps S100 and S200 may be performed in no particular order, and may be performed simultaneously.

With reference to <FIG> is a schematic block diagram of a manufacturing system for an electrode assembly provided in some embodiments of the application. The manufacturing system for an electrode assembly includes a first supply device <NUM> for supplying a positive pole piece; a second supply device <NUM> for supplying a negative pole piece; and an assembly device <NUM> for stacking the positive pole piece and the negative pole piece, such that a positive active material layer of the positive pole piece and a negative active material layer of the negative pole piece are arranged oppositely, and an end of the negative active material layer extends beyond the positive active material layer.

In some embodiments, the manufacturing system further includes a third supply device (not shown) for supplying the separator film separating the positive pole piece from the negative pole piece. The assembly device is used for stacking the positive pole piece, the separator film and the negative pole piece.

For related structures of the electrode assembly manufactured by the above manufacturing system, it may refer to the electrode assembly provided in the above embodiments.

Claim 1:
An electrode assembly (<NUM>), comprising a positive pole piece (<NUM>) and a negative pole piece (<NUM>) which are stacked, characterized in that a positive active material layer (<NUM>) of the positive pole piece (<NUM>) and a negative active material layer (<NUM>) of the negative pole piece (<NUM>) are arranged oppositely, and an end of the negative active material layer (<NUM>) extends beyond the positive active material layer (<NUM>);
the negative active material layer (<NUM>) comprises a negative body portion (<NUM>) and a negative edge portion (<NUM>) connected thereto, one end, away from the negative body portion (<NUM>), of the negative edge portion (<NUM>) extends beyond the positive active material layer (<NUM>), in a stacking direction of the positive pole piece (<NUM>) and the negative pole piece (<NUM>), at least part of the negative edge portion (<NUM>) overlaps the positive active material layer (<NUM>), and the negative active material layer (<NUM>) is configured in such a way that a capacity per unit area of the negative edge portion (<NUM>) is greater than that of the negative body portion (<NUM>); wherein a weight ratio of an active material in the negative edge portion (<NUM>) to the negative edge portion (<NUM>) is greater than that of an active material in the negative body portion (<NUM>) to the negative body portion (<NUM>), such that the capacity per unit area of the negative edge portion (<NUM>) is greater than that of the negative body portion (<NUM>);
and/or the positive active material layer (<NUM>) comprises a positive body portion (<NUM>) and a positive edge portion (<NUM>) connected thereto, and the positive edge portion (<NUM>) is configured in such a way that a capacity per unit area of the positive edge portion (<NUM>) is smaller than that of the positive body portion (<NUM>); wherein a weight ratio of an active material in the positive edge portion (<NUM>) to the positive edge portion (<NUM>) is smaller than that of an active material in the positive body portion (<NUM>) to the positive body portion (<NUM>), such that the capacity per unit area of the positive edge portion (<NUM>) is smaller than that of the positive body portion (<NUM>).