Patent Description:
An electrochemical device is a device that converts external energy into electrical energy for being stored internally so that the stored electrical energy can be supplied to an external device (such as a portable electronic device) when necessary. Generally, an electrochemical device includes a housing, an electrode assembly accommodated in the housing, and tabs. The electrode assembly includes a first electrode plate, a second electrode plate, and a separator. The first electrode plate and the second electrode plate are of opposite polarities, and are separated by a separator in between. One end of a tab is connected to the first electrode plate, and the other end of the tab protrudes from the housing. A plurality of conductive sheets protrude from the edge of the second electrode plate, and the plurality of conductive sheets are stacked. One end of the other tab is welded to the stacked conductive sheets, and the other end of the other tab protrudes from the housing.

In the process of working out this application, the applicant of this application finds that: during the use of an electrochemical device, polarization increases and consistency is deficient between an active material layer of a first electrode plate and an active material layer of a second electrode plate. This disadvantage results in low cycle performance of the electrochemical device, especially a low cycle capacity retention rate.

This application aims to provide an electrochemical device and an electronic device to alleviate the problem of the low cycle performance caused by poor consistency between the active material layer of the first electrode plate and the active material layer of the second electrode plate.

According to a first aspect, an embodiment of this application provides an electrochemical device. The electrochemical device includes a housing, an electrode assembly, a first tab, and a second tab. The electrode assembly is accommodated in the housing, the electrode assembly includes a first electrode plate, a second electrode plate, and a separator disposed between the first electrode plate and the second electrode plate. The first electrode plate, the second electrode plate, and the separator are stacked and then wound. The first electrode plate includes a first current collector. The second electrode plate includes a second current collector and a plurality of conductive sheets disposed together with the second current collector in one piece. The plurality of conductive sheets protrude from the second current collector along a first direction. The plurality of conductive sheets are stacked in a thickness direction of the electrode assembly to form a collection portion. The first direction is perpendicular to the thickness direction. The first tab is connected to the first current collector and protrudes out of the housing. The second tab is connected to the collection portion and protrudes out of the housing. A conductivity of the first tab is g<NUM> S/mm, a cross-sectional area of the first tab is s<NUM> mm<NUM>, a conductivity of the plurality of conductive sheets is g<NUM> S/mm, a sum of cross-sectional areas of the plurality of conductive sheets s<NUM> mm<NUM>, and the electrochemical device satisfies <NUM> ≤ (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) ≤ <NUM>.

Because the first electrode plate accepts or donates electrons through a directly connected first tab while the second electrode plate accepts or donates electrons through a plurality of conductive sheets, the temperature increment differs between the first tab and the conductive sheets. In the related art, the temperature increments of both the first tab and the conductive sheets of the electrochemical device are usually high. The inconsistency between the temperature increment of the first tab and the temperature increment of the conductive sheets reduces the consistency between the first active material layer and the second active material layer, and in turn, deteriorates the performance of the electrochemical device, for example, reduces the cycle capacity retention rate of the electrochemical device.

By contrast, in an embodiment of this application, the electrochemical device satisfies: <NUM> ≤ (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) ≤ <NUM>. In this case, the temperature increment difference between the first tab and the second tab is relatively small, and therefore, the consistency between the active material layer of the first electrode plate and the active material layer of the second electrode plate is still relatively high after charge-and-discharge cycles, and the cycle capacity retention rate of the electrochemical device is still relatively high. In other words, the electrochemical device according to this embodiment of this application alleviates the problem of poor consistency between the active material layer of the first electrode plate and the active material layer of the second electrode plate.

In some embodiments, the first tab is welded to the first current collector, a conductivity of the first current collector is g<NUM> S/mm, a welding area between the first tab and the first current collector is a<NUM> mm<NUM>, and the electrochemical device satisfies min(g<NUM>, g<NUM>) × a<NUM>/(g<NUM> × s<NUM>) ≥ <NUM>. In this way, the temperature increment difference between the conductive sheets and the welding region welded between the first tab and the first electrode plate is relatively small.

In some embodiments, the second tab is welded to the collection portion, a conductivity of the second tab is g<NUM> S/mm, a welding area between the second tab and the collection portion is a<NUM> mm<NUM>, and the electrochemical device satisfies min(g<NUM>, g<NUM>) × a<NUM>/(g<NUM> × s<NUM>) ≥ <NUM>. In this way, the temperature increment difference between the conductive sheets and the welding region welded between the first tab and the first electrode plate is relatively small.

In some embodiments, in a <NUM> environment temperature, a current intensity for discharging the electrochemical device at a constant current from a <NUM> % state of charge to a <NUM>% state of charge within <NUM> hour is I mA, and the electrochemical device satisfies <NUM> ≤ (g<NUM> × s<NUM>)/I ≤ <NUM>. In this way, the flow capacity of the first tab is sufficient. Therefore, the temperature increment difference between a main region and the first tab is relatively small, the cycle capacity retention rate of the electrochemical device is still high, and the manufacturing cost of the first tab is reduced.

In some embodiments, the first tab includes a first portion, a second portion, and a third portion connected in sequence. The first portion is connected to the first current collector, the second portion is located outside the first current collector and disposed in a bent shape, and the third portion protrudes from the housing. The first tab includes a bent second portion. Therefore, when the first tab is impacted, the first tab can relieve a part of the impact force through deformation of the second portion, thereby reducing the impact force that finally reaches a junction between the first tab and the first electrode plate. Therefore, the electrochemical device according to this embodiment of this application alleviates the problem that the junction between the first tab and the first electrode plate is prone to be damaged by an external impact when the first tab is directly connected to the first electrode plate.

In some embodiments, the electrode assembly includes a first surface and a second surface that are opposite to each other in the thickness direction. The second portion includes: a first connecting section and a second connecting section. One end of the first connecting section is connected to the first portion and the other end extends toward the first surface. The second connecting section is located on a side of the first connecting section, the side of the first connecting section is away from the electrode assembly. One end of the second connecting section is connected to an end of the first connecting section, the end of the first connecting section is away from the first portion. The other end of the second connecting section is connected to the third portion. In this way, when the first tab is impacted, the second connecting section elastically bends toward the first connecting section, thereby removing a part of the impact force.

In some embodiments, the second portion further includes a bend section. The first connecting section and the second connecting section are disposed opposite to each other along the first direction. The bend section respectively connects an end of the first connecting section and an end of the second connecting section, the end of the first connecting section is close to the first surface, and the end of the second connecting section is close to the first surface. In this way, the second portion is of a U-shaped structure on the whole.

In some embodiments, in the thickness direction, a distance between the first surface and an end of the third portion is L<NUM> mm, the end of the third portion is close to the second portion, and a distance between the first surface and a part of the first portion is L<NUM> mm, the part of the first portion overlaps the first current collector in the thickness direction. An L<NUM>/L<NUM> ratio is less than or equal to <NUM>. A second direction is perpendicular to the first direction and the thickness direction. When the first tab is subjected to an external force along the first direction or bears a component force along the first direction, the second connecting section bends toward the electrode assembly. If, in the thickness direction, the end that is of the second connecting section and that is away from the first surface goes clearly beyond the end of the first connecting section, the end of the first connecting section is away from the first surface; then the end of the second connecting section, which is away from the first surface, may be inserted upside down until touching the second electrode plate in the electrode assembly, thereby causing a short circuit in the electrochemical device. Setting the L<NUM>/L<NUM> ratio to a value less than or equal to <NUM> is intended to make the end of the second connecting section which is away from the first surface, not go beyond, or just slightly go beyond the end of the first connecting section, the end of the first connecting section is away from the first surface, thereby reducing the risk of the short circuit.

In some embodiments, the first electrode plate is a negative electrode plate, and the second electrode plate is a positive electrode plate. The first tab is made of a material that includes copper, a copper alloy, nickel, or a nickel alloy. The second tab is made of a material that includes aluminum or an aluminum alloy.

In some embodiments, a cross-sectional area of the second tab is s<NUM> mm<NUM>, and s<NUM> is greater than s<NUM>. Because the first electrode plate accepts or donates electrons through the first tab while the second electrode plate accepts and donates electrons through plenty of conductive sheets and the second tab, it is more difficult for the first tab to dissipate heat compared with a whole formed by the conductive sheets and the second tab. Setting s<NUM> to be greater than s<NUM> increases the surface area of the first tab, thereby increasing the heat dissipation speed of the first tab, and in turn, making the heat dissipation more uniform between the first tab and the second tab.

In some embodiments, the first electrode plate further includes a first active material layer disposed on the first current collector. A first recess is disposed in the first active material layer. The first recess exposes the first current collector. The first tab is disposed at the first recess and connected to the first current collector.

According to a second aspect, this application further provides an electronic device. The electronic device includes the electrochemical device described above. Because the electronic device includes the electrochemical device, the electronic device also alleviates the problem of poor consistency between the active material layer of the first electrode plate and the active material layer of the second electrode plate.

To describe the technical solutions in some embodiments of this application more clearly, the following outlines the drawings to be used in the description of the embodiments. Evidently, the drawings outlined below merely illustrate some embodiments of this application, and a person of ordinary skill in the art may obtain other drawings according to the structure shown in the drawings.

For ease of understanding this application, the following describes this application in more detail with reference to drawings and specific embodiments. It is hereby noted that an element referred to herein as being "fixed to" or "fastened to" another element may be directly disposed on the other element, or may be fixed or fastened to the other element with one or more elements in between. An element referred to herein as "connected to" another element may be connected to the other element directly or with one or more elements in between. The terms "vertical", "horizontal", "left", "right", "in", "out" and other similar expressions used herein are merely for ease of description.

Unless otherwise defined, all technical and scientific terms used herein bear the same meanings as what is normally understood by a person skilled in the technical field of this application. The terms used in the specification of this application are merely intended to describe specific embodiments but not to limit this application. The term "and/or" used herein is intended to include any and all combinations of one or more relevant items enumerated.

In addition, to the extent that no mutual conflict occurs, the technical features described below in different embodiments of this application may be combined with each other.

In this specification, the meanings of "mounting" or "installation" include fixing or confining an element or unit to a specific position or place by welding/soldering, screwing, snap-fit connection, bonding, or other means, where the element or unit may be held stationary in the specific position or place or may move within a limited range, and the element or unit may be detachable or undetachable after being fixed or confined to the specific position or place, without being limited in embodiments of this application.

Referring to <FIG>, <FIG> is a schematic diagram of an electrochemical device <NUM> according to an embodiment of this application; <FIG> is a schematic sectional view of the electrochemical device <NUM> sectioned along a line A-A; <FIG> is a schematic sectional view of the electrochemical device sectioned along a line B-B; and <FIG> is a schematic sectional view of the electrochemical device sectioned along a line C-C. The electrochemical device <NUM> includes a housing <NUM>, an electrode assembly <NUM>, a first tab <NUM>, and a second tab <NUM>. The housing <NUM> is configured to mount and support the foregoing structures, and also constitutes a protection structure of the electrochemical device <NUM>. The electrode assembly <NUM> is accommodated in the housing <NUM>, and includes a first electrode plate <NUM>, a second electrode plate <NUM>, and a separator <NUM> disposed between the first electrode plate <NUM> and the second electrode plate <NUM>. The first electrode plate <NUM>, the second electrode plate <NUM>, and the separator <NUM> are stacked and then wound. The first electrode plate <NUM> includes a first current collector <NUM>. The second electrode plate <NUM> includes a second current collector <NUM> and a plurality of conductive sheets <NUM> disposed together with the second current collector <NUM> in one piece. The conductive sheets <NUM> protrude from the second current collector <NUM> along a first direction X shown in the drawing. The conductive sheets <NUM> are stacked in a shown thickness direction Z of the electrode assembly <NUM> to form a collection portion <NUM>. The first direction X is perpendicular to the thickness direction Z. The first tab <NUM> is connected to the first current collector <NUM> and protrudes out of the housing <NUM>. The second tab <NUM> is connected to the collection portion <NUM> and protrudes out of the housing <NUM>. The "plurality" mentioned herein means two or more. The following describes the housing <NUM>, the electrode assembly <NUM>, the first tab <NUM>, and the second tab <NUM>.

For the housing <NUM>, referring to <FIG>, the housing <NUM> is in a box shape that is relatively flat as a whole. The thickness direction of the housing is consistent with the thickness direction Z of the electrode assembly <NUM>. The housing <NUM> includes a third surface <NUM> and a fourth surface <NUM> that are opposite to each other along the thickness direction Z. The housing <NUM> also includes a first end <NUM> and a second end <NUM> disposed opposite to each other. The first end <NUM> is an end of the housing <NUM>, and the first tab <NUM> and the second tab <NUM> protrude from the end of the housing <NUM>. The second end <NUM> is an end of the housing <NUM>, the end being away from the first tab <NUM>. A direction formed by connecting the first end <NUM> and the second end <NUM> is consistent with the first direction X. In addition, an accommodation cavity <NUM> is disposed inside the housing <NUM>, and is configured to accommodate the electrode assembly <NUM>. A part of the first tab <NUM>, the conductive sheets <NUM>, and a part of the second tab <NUM>.

In this embodiment, the electrochemical device <NUM> is a pouch-type battery. The housing <NUM> is made of a flexible sheet, such as an aluminum plastic film. Specifically, referring to <FIG> and <FIG> together with other drawings, the housing <NUM> includes a body portion <NUM> and a sealing portion <NUM> connected to the body portion <NUM>. An accommodation cavity <NUM> is disposed in the body portion <NUM>, and the electrode assembly <NUM> is accommodated in the accommodation cavity <NUM>. The sealing portion <NUM> is formed by extending the surface of the body portion <NUM> outward, and is a region for sealing the housing <NUM> during the shaping of the housing. The first tab <NUM> and the second tab <NUM> pass through the sealing portion <NUM> to protrude out of the housing <NUM>. Understandably, in other embodiments of this application, the electrochemical device <NUM> may be a hard-shell battery instead. Accordingly, the housing <NUM> may be made of a hard material, such as a polymer material or a metal material.

For the electrode assembly <NUM>, referring to <FIG> together with other drawings, the electrode assembly <NUM> includes a first electrode plate <NUM>, a second electrode plate <NUM>, and a separator <NUM> that are stacked. The first electrode plate <NUM> and the second electrode plate <NUM> are of opposite polarities, and are separated by the separator <NUM> in between. The first electrode plate <NUM>, the second electrode plate <NUM>, and the separator <NUM> wound together, and are wound as a whole to form a columnar structure with oblate end faces. The electrode assembly <NUM> includes a first surface <NUM> and a second surface <NUM> that are disposed opposite to each other along the thickness direction Z. The first surface <NUM> is disposed close to the third surface <NUM>, and the second surface <NUM> is disposed close to the fourth surface <NUM>.

In this embodiment, the first electrode plate <NUM> is a negative electrode plate, and the second electrode plate <NUM> is a positive electrode plate. Referring to <FIG>, which is a schematic connection diagram of the first electrode plate <NUM> and the first tab <NUM> both in a flattened state, the first electrode plate <NUM> includes a first current collector <NUM> and a first active material layer <NUM>. The first current collector <NUM> is a base material layer configured to bear the first active material layer <NUM>, and is also a carrier of transferred electrons in the first electrode plate <NUM>. The first active material layer <NUM> is disposed on the surface of the first current collector <NUM>, and is a carrier of lithium ions intercalated or deintercalated. The first active material layer <NUM> includes a first recess <NUM> to expose the first current collector <NUM>. At the first recess <NUM>, the first tab <NUM> is connected to the first current collector <NUM>. Definitely, in other embodiments of this application, the first active material layer <NUM> may include no first recess <NUM>. Accordingly, a blank foil region uncoated with the first active material layer <NUM> is disposed at an end of the first current collector <NUM>. The first current collector <NUM> is connected to the first tab <NUM> by the blank foil region.

With respect to the material of the first current collector <NUM>, in some embodiments, the material of the first current collector <NUM> includes copper, and specifically a copper foil. Understandably, in other embodiments, the first current collector <NUM> may be made of another appropriate conductive material. For example, in some embodiments, the first current collector <NUM> includes a copper alloy, nickel, or a nickel alloy. The first active material layer <NUM> includes a negative active material. For example, in some embodiments, the first active material layer <NUM> includes graphite, a conductive agent, and a binder. The foregoing materials are mixed and stirred well and applied onto the surface of the first current collector <NUM> to generate a first active material layer <NUM>.

Referring to <FIG>, which is a schematic diagram of the second electrode plate <NUM> in a flattened state, the second electrode plate <NUM> includes a second current collector <NUM>, a second active material layer <NUM>, and a plurality of conductive sheets <NUM> that protrude from the second current collector <NUM> along the first direction X. The second current collector <NUM> is a base material layer configured to bear the second active material layer <NUM>, and is also a carrier of transferred electrons in the second electrode plate <NUM>. The second active material layer <NUM> is disposed on the surface of the second current collector <NUM>, and is a carrier of lithium ions intercalated or deintercalated.

With respect to the material of the second current collector <NUM>, in some embodiments, the material of the second current collector <NUM> includes aluminum, and specifically an aluminum foil. Understandably, in other embodiments, the second current collector <NUM> may be made of another appropriate conductive material. For example, in some embodiments, the second current collector <NUM> includes an aluminum alloy, nickel, or a nickel alloy. The second active material layer <NUM> includes a positive active material. For example, in some embodiments, the second active material layer <NUM> includes lithium iron phosphate particles, a dispersant, a binder, and a conductive agent. The foregoing materials are mixed and stirred well and applied onto the surface of the second current collector <NUM> to generate a second active material layer <NUM>.

The conductive sheets <NUM> are a sheet structure, and is connected to the second current collector <NUM>. The conductive sheets <NUM> are spaced out along a winding direction of the second electrode plate <NUM>, so as to divide the second electrode plate <NUM> into a plurality of regions staggered along the winding direction. Still referring to <FIG>, one end of each conductive sheet <NUM> is connected to the second current collector <NUM>, and such ends are disposed sequentially along the thickness direction Z. The other end of each conductive sheet <NUM> is located away from the second electrode plate <NUM>, and such other ends are stacked. The stacked part of the conductive sheets <NUM> constitutes a first collection portion <NUM>. In this way, the conductive sheets <NUM> connect the foregoing regions in parallel, thereby reducing the overall internal resistance of the second electrode plate <NUM> and reducing the heat emission of the second electrode plate <NUM>.

In some embodiments, the conductive sheets <NUM> are formed together with the second current collector <NUM> in one piece. In other words, the conductive sheets <NUM> are formed by extending the edge of the second current collector <NUM> outward. In the process of making the electrochemical device <NUM>, the surface of the second current collector <NUM> is coated with the second active material layer <NUM>. Subsequently, a shape shown in <FIG> is cut out by die-cutting a part uncoated with the second active material layer <NUM> on the second current collector <NUM> by using a cutting device. Afterward, the first electrode plate <NUM>, the separator <NUM> and the second electrode plate <NUM> are sequentially stacked and wound, and the conductive sheets <NUM> are roughly aligned along the thickness direction. Afterward, the ends that are of the conductive sheets <NUM> and that are located away from the second electrode plate <NUM> are stacked and welded fixedly to form the electrode assembly <NUM> shown in <FIG>. Understandably, in other embodiments of this application, the conductive sheets <NUM> and the second current collector may be formed separately instead, and connected by welding or other means, without being limited in this application.

In some embodiments, the collection portion <NUM> is U-shaped on the whole, and includes a first extension section <NUM>, a second extension section <NUM>, and a third extension section <NUM> that are connected in sequence. Along an extension path of the collection portion <NUM>, the first extension section <NUM> is a part of the collection portion <NUM>, the part of the collection portion <NUM> is close to the second electrode plate <NUM>. The third extension section <NUM> is a part of the collection portion <NUM>, the part of the collection portion <NUM> is away from the second electrode plate <NUM>. Along the first direction X, the first extension section <NUM> is opposite to the third extension section <NUM>, and the first extension section <NUM> is located between the electrode assembly <NUM> and the third extension section <NUM>. The second extension section <NUM> is connected to the first extension section <NUM> and the third extension section <NUM> separately. In this way, the first extension section <NUM>, the second extension section <NUM>, and the third extension section <NUM> close in together to form a U-shaped structure. Understandably, notwithstanding that the collection portion <NUM> in this embodiment extends in a U-shape, the collection portion <NUM> in other embodiments of this application may extend in any other shape such as a rectilinear or arc shape, without being particularly limited in this application.

For the first tab <NUM>, still referring to <FIG> together with <FIG>, one end of the first tab <NUM> is connected to the electrode assembly <NUM>, and the other end extends out of the housing <NUM> along the first direction X, thereby constituting a conductive terminal of the electrochemical device <NUM>. The conductive terminal is configured to be connected to an external electrical load. The first tab <NUM> is a sheet structure extending in a bent shape as a whole, and includes a first portion <NUM>, a second portion <NUM>, and a third portion <NUM> that are connected in sequence. The following describes the first portion <NUM>, the second portion <NUM>, and the third portion <NUM> with reference to <FIG>.

The first portion <NUM> is connected to the first electrode plate <NUM>, and is in a flat shape as a whole, and extends along the first direction X. The first portion <NUM> is located at the first recess <NUM>, and is fixed to the first current collector <NUM> by welding.

The second portion <NUM> is located outside the first electrode plate <NUM>, and is disposed in a bent shape. One end of the second portion <NUM> is connected to the first portion <NUM>, and the other end is connected to the third portion <NUM>. In this embodiment, the second portion <NUM> is U-shaped on the whole, and includes a first connecting section <NUM>, a second connecting section <NUM>, and a bend section <NUM>. One end of the first connecting section <NUM> is connected to the first portion <NUM>, and the other end extends toward the first surface <NUM>. One end of the bend section <NUM> is connected to an end of the first connecting section <NUM>, the end of the first connecting section <NUM> is oriented toward the first surface <NUM>. The bend section is bent away from the electrode assembly <NUM> against the first connecting section <NUM>. Along the first direction X, the second connecting section <NUM> is located on a side of the first connecting section <NUM>, the side of the first connecting section <NUM> is away from the electrode assembly <NUM>, and the second connecting section <NUM> is disposed opposite to the first connecting section <NUM> along the first direction X. One end of the second connecting section <NUM> is connected to the end of the bend section <NUM>, the end of the bend section <NUM> is away from the first connecting section <NUM>. The other end of the second connecting section <NUM> extends away from the first surface <NUM>. In other words, an end of the second connecting section <NUM>, which is away from the third portion <NUM>, is indirectly connected to the first connecting section <NUM> by the bend section <NUM>. In this way, the first connecting section <NUM>, the bend section <NUM>, and the second connecting section <NUM> together form a U-shaped structure.

Understandably, although in this embodiment, the second portion <NUM> includes the first connecting section <NUM>, the bend section <NUM>, and the second connecting section <NUM> simultaneously and the three sections form a U-shaped structure, this application is not limited to such a structure, and any structure that ensures the second portion <NUM> to be in a bent shape is appropriate. For example, in some other embodiments of this application, the second connecting section <NUM> of the second portion <NUM> is directly connected to the first connecting section <NUM>. In this case, the second portion <NUM> is of a V-shaped structure. Put differently, in some circumstances, the bend section <NUM> is omissible. As another example, in some other embodiments of this application, the second portion <NUM> includes two V-shaped structures mentioned above. The two V-shaped structures are connected in sequence, so that the second portion <NUM> is continuously bent.

The third portion <NUM> is flat as a whole. One end of the third portion <NUM> is connected to an end of the second portion <NUM>, the end of the second portion <NUM> is away from the first portion <NUM>. The other end of the third portion <NUM> extends out of the housing <NUM>. When the first tab <NUM> is impacted, the first tab <NUM> can remove at least a part of the impact force on the first tab <NUM> by virtue of elastic deformation of the second portion <NUM>, so as to reduce the impact force finally transmitted to the first portion <NUM> and effective on a connection region between the first portion <NUM> and the first electrode plate <NUM>.

In some embodiments, a sharp-corner transition between the first portion <NUM>, the second portion <NUM>, and the third portion <NUM> needs to be avoided because the sharp-corner transition leads to stress concentration in the connection region between the foregoing three portions of the first tab <NUM>, and affects mechanical properties of the first tab <NUM>. To avoid the sharp-corner transition, the second portion <NUM> includes a rounded corner at an end close to the first portion <NUM>, and is connected to the first portion <NUM> by the rounded corner. The second portion <NUM> includes a rounded corner at an end close to the third portion <NUM>, and is connected to the third portion <NUM> by the rounded corner.

In some embodiments, the electrochemical device <NUM> satisfies: L<NUM>/L<NUM> ≤ <NUM>. Viewed along the second direction Y, an end of the third portion <NUM> which is close to the second portion <NUM> on a side away from the first surface <NUM> is at a distance of L<NUM> mm from the first surface <NUM> along the thickness direction Z. The side of the first portion <NUM> which is away from the first surface <NUM> is at a distance of L<NUM> mm from the first surface <NUM> along the thickness direction Z. A person skilled in the art is able to obtain a distance between a left side of a lower end of the third portion <NUM> and the first surface <NUM> in <FIG> by taking a CT image of the electrochemical device <NUM> along the second direction Y and then measuring the distance with a CT device or instrument, and the distance is L<NUM>. A person skilled in the art is able to obtain a distance between a left side of the first portion <NUM> and the first surface <NUM> in <FIG> by taking a CT image of the electrochemical device <NUM> along the second direction Y and then measuring the distance with a CT device or instrument, and the distance is L<NUM>.

When the first tab <NUM> is subjected to an external force along the shown first direction X or bears a component force along the first direction X, the second connecting section <NUM> bends toward the electrode assembly <NUM>. If, in the thickness direction Z, the end of the second connecting section <NUM>, which is away from the first surface <NUM>, goes clearly beyond the end of the first connecting section <NUM> which is away from the first surface <NUM>, then the end of the second connecting section <NUM> which is away from the first surface <NUM> may be inserted upside down until touching the second electrode plate <NUM> in the electrode assembly <NUM>, thereby causing a short circuit in the electrochemical device <NUM>. Setting the L<NUM>/L<NUM> ratio to a value less than or equal to <NUM> is intended to make the end of the second connecting section <NUM> which is away from the first surface <NUM>, not go beyond the end of the first connecting section <NUM> which is away from the first surface <NUM>, or just slightly go beyond the end of the first connecting section <NUM> which is away from the first surface <NUM>, thereby reducing the risk of the short circuit.

It is hereby noted that the shape of the first tab <NUM> is not particularly limited in this application, and may be a continuously bent shape as in the above embodiment, or a rectilinear extension shape.

For the second tab <NUM>, referring to <FIG> together with other drawings, one end of the second tab <NUM> is connected to the collection portion <NUM>, and the other end extends out of the housing <NUM> through the first end <NUM>, thereby constituting another conductive terminal of the electrochemical device <NUM>. The conductive terminal is configured to be connected to an external electrical load. In this embodiment, the second tab <NUM> includes a fourth portion <NUM> and a fifth portion <NUM>. The fourth portion <NUM> overlaps the third extension section <NUM>. The fifth portion <NUM> is at a bent angle to the fourth portion <NUM>, and extends in a straight line. One end of the fifth portion <NUM> is connected to the fourth portion <NUM>, and the other end extends out of the housing <NUM> along the first direction X.

In some embodiments, the cross-sectional area of a cross section of the first tab <NUM> perpendicular to an extension path of the first tab is s<NUM> mm<NUM>, the cross-sectional area of a cross section of the second tab <NUM> perpendicular to an extension path of the second tab is s<NUM> mm<NUM>, and the first tab <NUM> and the second tab <NUM> satisfy s<NUM> > s<NUM>. Because the first electrode plate <NUM> accepts or donates electrons through the first tab <NUM> while the second electrode plate <NUM> accepts and donates electrons through plenty of conductive sheets <NUM> and the second tab <NUM>, it is more difficult for the first tab <NUM> to dissipate heat compared with a whole formed by the conductive sheets <NUM> and the second tab <NUM>. Setting s<NUM> to be greater than s<NUM> increases the surface area of the first tab <NUM>, thereby increasing the heat dissipation speed of the first tab, and in turn, making the heat dissipation more uniform between the first tab <NUM> and the second tab <NUM>.

The first electrode plate <NUM> accepts or donates electrons through the first tab <NUM> while the second electrode plate <NUM> accepts or donates electrons through a plurality of conductive sheets <NUM> connected in parallel. The difference in the flow capacity between the first tab <NUM> and the plurality of conductive sheets <NUM> leads to a difference in the heat emission between the first tab and the conductive sheets. Therefore, the temperature increment differs between the first tab <NUM> and the conductive sheets <NUM> during use of the electrochemical device <NUM>. The inconsistency between the temperature increment of the first tab and the temperature increment of the conductive sheets reduces the consistency between the first active material layer <NUM> and the second active material layer <NUM>, and in turn, deteriorates the performance of the electrochemical device <NUM>, for example, reduces the cycle capacity retention rate of the electrochemical device.

For ease of understanding the subsequent experimental data, the following describes the relevant terms or parameters:.

The term "cycle capacity retention rate" mentioned herein means a ratio (%) of the capacity of a fresh electrochemical device <NUM> at the end of several charge-and-discharge cycles to a discharge capacity of the electrochemical device <NUM> in a first-cycle test. The term "<NUM>th-cycle capacity retention rate" mentioned herein means a ratio of the capacity of a fresh electrochemical device <NUM> at the end of <NUM> charge-and-discharge cycles to a discharge capacity of the electrochemical device in a first-cycle charge-and-discharge test.

The conductivity of the first tab <NUM> is g<NUM> S/mm. The values of the conductivity may be looked up in technical data according to the type of the material, or the conductivity of a given material may be measured according to the national/industrial standard. In this embodiment, the first tab <NUM> is made of copper, and therefore, g<NUM> = <NUM>. Definitely, in other embodiments of this application, the first tab <NUM> may be made of other materials, and g<NUM> changes accordingly.

The cross-sectional area of a cross section of the first tab <NUM> perpendicular to an extension direction of the first tab is s<NUM> mm<NUM>. In this embodiment, the first tab <NUM> is a sheet structure that is uniform in both width and thickness, b<NUM> mm in width, and c<NUM> mm in thickness. Therefore, by measuring the width b<NUM> and thickness c<NUM> of the first tab <NUM>, the cross-sectional area of the first tab <NUM> can be calculated with reference to an area calculation formula.

The conductivity of the conductive sheets <NUM> is g<NUM> S/mm. In this embodiment, the conductive sheets <NUM> are formed together with the second current collector <NUM> in one piece, both being made of aluminum. Therefore, g<NUM> = <NUM>. Definitely, in other embodiments of this application, the conductive sheets <NUM> may be made of other materials, and g<NUM> changes accordingly.

The sum of cross-sectional areas of cross sections of the conductive sheets <NUM> perpendicular to an extension direction of the conductive sheets is s<NUM> mm<NUM>. In this embodiment, the conductive sheets <NUM> are uniform in both width and thickness, b<NUM> mm in width, and c<NUM> mm in thickness. Therefore, by measuring the width b<NUM>, thickness c<NUM>, and the number N of the conductive sheets <NUM>, the sum of the cross-sectional areas of the conductive sheets <NUM> can be calculated according to an area calculation formula. If the conductive sheets <NUM> are not uniform in width or thickness, the cross-sectional area of each conductive sheet <NUM> is calculated separately, and the cross-sectional areas of all the conductive sheets <NUM> are summed.

The conductivity of the first current collector <NUM> is g<NUM> S/mm. In this embodiment, the first current collector is made of copper, and therefore, g<NUM> = <NUM>. Definitely, in other embodiments of this application, the first current collector may be made of other materials, and g<NUM> changes accordingly.

The welding area between the first tab <NUM> and the first electrode plate <NUM> is a<NUM> mm<NUM>. In fact, the welding area may be measured in various ways. For example, in some embodiments, the first tab <NUM> is spot-welded to the first current collector, and therefore, the first tab <NUM> may be separated from the first current collector <NUM> first, and then the welding face is placed under a microscope. The microscope is adjusted until the spot-welding region is clearly distinguishable from the non-spot-welding region, and then the welding region is photographed. The frame of the welding region is delineated by graphics software, and the area of each spot-welding region is calculated. The areas of all spot-welding regions add up to the welding area. For example, in some other embodiments, the first tab <NUM> is welded to the first current collector <NUM> by pull-welding such as tin-soldering, in which only one welding region exists. Therefore, the first tab <NUM> may be separated from the first current collector first, and then the welding face is placed under a microscope. The microscope is adjusted until the welding region is clearly distinguishable from the non-welding region, and then the welding region is photographed. The frame of the welding region is delineated by graphics software, and the area of the welding region is calculated.

The conductivity of the second tab <NUM> is g<NUM> S/mm. In this embodiment, the second tab <NUM> is made of aluminum, and therefore, g<NUM> = <NUM>. Definitely, in other embodiments of this application, the second tab <NUM> may be made of other materials, and g<NUM> changes accordingly.

The welding area between the second tab <NUM> and the collection portion <NUM> is a<NUM> mm<NUM>. The method for measuring the welding area may be obtained by reference to the method for measuring the welding area between the first tab <NUM> and the first current collector as described above, and is omitted herein.

Under a <NUM> environment, a current intensity for discharging the electrochemical device <NUM> at a constant current from a <NUM> % state of charge (SOC) to a <NUM>% SOC within <NUM> hour is I mA. In other words, if the capacity of the electrochemical device <NUM> is <NUM> mAh, I is <NUM>. In addition, the corresponding I value of the electrochemical device <NUM> may be obtained by discharging the electrochemical device <NUM> under the above conditions.

In this application, the electrochemical device <NUM> satisfies <NUM> ≤ (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) ≤ <NUM>. The flow capacity of the first tab <NUM> is positively correlated with the conductivity g<NUM> and the cross-sectional area s<NUM> of the first tab. Therefore, (g<NUM>×s<NUM>) represents the flow capacity of the first tab <NUM>. Similarly, (g<NUM>×s<NUM>) represents the overall flow capacity of all conductive sheets <NUM>. The following describes, with reference to experimental data, how the difference in the flow capacity between the first tab <NUM> and the whole conductive sheets <NUM> affects the cycle capacity retention rate of the electrochemical device <NUM>.

Referring to Table <NUM>, which shows the test results of the temperature increment and the cycle capacity of the electrochemical device <NUM> compared between different embodiments.

A method for measuring the temperature increment in Table <NUM> includes the following steps:.

S501: Charge an electrochemical device <NUM> to <NUM>% SOC in a <NUM>±<NUM> environment.

S502: Leave the electrochemical device <NUM> to stand for <NUM> minutes to make the temperature of the electrochemical device be equal to the ambient temperature.

S503: Stick a temperature sensor onto a first tab <NUM>, and stick another temperature sensor onto a second tab <NUM>. Considering that the temperature of the conductive sheets <NUM> is not conveniently measurable and the second tab <NUM> is connected to the conductive sheets <NUM>, this method indirectly measures the temperature of the conductive sheets <NUM> by measuring the temperature of the second tab <NUM>.

S504: Discharge the electrochemical device <NUM> to a <NUM>% SOC at a current of <NUM> I.

S505: Record a maximum value of the temperature differences measured by the two temperature sensors at the same time, and input the data into Table <NUM>.

A method for measuring the <NUM>th-cycle capacity retention rate includes the following steps:.

Referring to Embodiments <NUM> to <NUM> first. The main difference in the electrochemical device <NUM> between the four embodiments lies in the cross-sectional area s<NUM> of the first tab <NUM>, and other parameters such as the conductivity g<NUM> of the first tab, the sum s<NUM> of the cross-sectional areas of the conductive sheets <NUM>, and the conductivity g<NUM> of the conductive sheets <NUM> are the same. Therefore, the flow capacity ratio of the electrochemical device <NUM> differs between the embodiments accordingly.

As can be seen with reference to Embodiments <NUM> to <NUM>, when the flow capacity ratio satisfies (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) < <NUM>, the temperature increment difference between the first tab <NUM> and the second tab <NUM> is greater than <NUM>, and the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is less than <NUM>%.

Referring to Embodiment <NUM> and Embodiments <NUM> to <NUM>. The main difference in the electrochemical device <NUM> between the four embodiments lies in the width of the conductive sheets <NUM>, that is, the sum s<NUM> of the cross-sectional areas of the conductive sheets <NUM>. Other parameters such as cross-sectional area s<NUM> of the first tab <NUM>, the conductivity g<NUM> of the first tab, and the conductivity g<NUM> of the conductive sheets <NUM> are the same. Therefore, the flow capacity ratio of the electrochemical device <NUM> differs between the embodiments accordingly.

As can be seen with reference to Embodiment <NUM> and Embodiments <NUM> to <NUM>, when the flow capacity ratio satisfies (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) > <NUM>, the temperature increment difference between the first tab <NUM> and the second tab <NUM> is greater than <NUM>, and the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is less than <NUM>%.

As can be seen with reference to Embodiments <NUM> to <NUM>, when the flow capacity ratio satisfies <NUM> ≤ (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) ≤ <NUM>, the temperature increment difference between the first tab <NUM> and the second tab <NUM> is less than <NUM>. Therefore, the consistency of the active material layer between the first electrode plate <NUM> and the second electrode plate <NUM> is still relatively high after <NUM> charge-and-discharge cycles, and the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is still higher than <NUM>%.

As can be seen with reference to Embodiments <NUM>, <NUM>, and <NUM>, although both (g<NUM>×s<NUM>) and (g<NUM>×s<NUM>) have changed, as long as the ratio between them remains unchanged, the temperature increment between the first tab <NUM> and the second tab <NUM> as well as the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> are not significantly different between such embodiments.

In addition, the temperature difference between the first tab <NUM> and the conductive sheets <NUM> is not only affected by the conductivity g<NUM> of the first tab <NUM>, the conductivity g<NUM> of the second tab <NUM>, the cross-sectional area s<NUM> of the first tab <NUM>, and the sum s<NUM> of cross-sectional areas of conductive sheets <NUM>, but also limited by the area of the welding region of the first tab <NUM>. For example, if the welding area of the first tab <NUM> is unduly small, the temperature rise of the welding region will be faster than that of the first tab <NUM>. Consequently, the temperature increment of the first tab <NUM> increases accordingly, that is, the temperature rise of the first tab <NUM> is faster than that of the conductive sheets <NUM>. Similarly, the temperature difference between the first tab <NUM> and the conductive sheets <NUM> is also limited by the area of the welding region of the second tab <NUM>. For example, if the welding area of the second tab <NUM> is unduly small, the temperature rise of the welding region will be faster than that of the conductive sheets <NUM>. Consequently, the temperature increment of the conductive sheets <NUM> increases accordingly, that is, the temperature rise of the conductive sheets <NUM> is faster than that of the first tab <NUM>.

In this application, in order to ensure a relatively small temperature increment difference between the conductive sheets <NUM> and the welding region that is welded between the first tab <NUM> and the first electrode plate <NUM>, the electrochemical device <NUM> satisfies: min(g<NUM>, g<NUM>) × a<NUM>/(g<NUM> × s<NUM>) ≥ <NUM>. By analogy, in order to further ensure a relatively small temperature increment difference between the conductive sheets <NUM> and the welding region that is welded between the first tab <NUM> and the first electrode plate <NUM>, the electrochemical device <NUM> further satisfies: min(g<NUM>, g<NUM>) × a<NUM>/(g<NUM> × s<NUM>) ≥ <NUM>.

Specifically, referring to Table <NUM>, which shows the test results of the temperature increment of the electrochemical device <NUM> compared between different embodiments, the main difference of the electrochemical device <NUM> between the embodiments lies in the welding area between the first tab <NUM> and the first electrode plate <NUM>. This test aims to indirectly control the change of the flow capacity ratio by controlling the change of the welding area, and, according to the test results of the temperature increment, examine how the flow capacity ratio is related to the temperature increment difference between the welding region and the conductive sheets <NUM>. In this experiment, both the first tab <NUM> and the first current collector <NUM> are made of copper, and therefore, min(g<NUM>, g<NUM>) = <NUM>. Both the conductive sheets <NUM> and the second tab <NUM> are made of aluminum, and therefore, min(g<NUM>, g<NUM>) = <NUM>. In this application, min(gm, gn) means gm or gn, whichever is the minimum.

As can be seen with reference to Embodiments <NUM> to <NUM>, when min(g<NUM>, g<NUM>) × a<NUM>/(g<NUM> × s<NUM>) is less than <NUM>, the temperature increment difference between the first tab <NUM> and the second tab <NUM> is greater than <NUM>, and the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is less than <NUM>%. When min(g<NUM>, g<NUM>) × a<NUM>/(g<NUM> × s<NUM>) is greater than or equal to <NUM>, the temperature increment difference between the welding region of the first tab <NUM> and the second tab <NUM> is less than <NUM>, and the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is higher than <NUM>%.

As can be seen with reference to Embodiments <NUM> to <NUM>, when min(g<NUM>, g<NUM>) × a<NUM>/(g<NUM> × s<NUM>) is less than <NUM>, the temperature increment difference between the first tab <NUM> and the second tab <NUM> in the electrochemical device <NUM> is greater than <NUM>, and the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is less than <NUM>%. When min(g<NUM>, g<NUM>) × a<NUM>/(g<NUM> × s<NUM>) is greater than or equal to <NUM>, the temperature increment difference between the first tab <NUM> and the second tab <NUM> is less than <NUM>, and the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is higher than <NUM>%.

In addition, considering that heat dissipation is more difficult in the middle part of the electrochemical device <NUM>, the temperature increment also differs between the main part of the electrochemical device <NUM>, the first tab <NUM>, and the conductive sheets <NUM> during the use of the electrochemical device <NUM>. The temperature increment difference also affects the <NUM>th-cycle capacity retention rate of the electrochemical device to some extent.

Referring to Table <NUM>, which shows the test results of the temperature increment of the electrochemical device <NUM> compared between different embodiments, among the electrochemical devices <NUM> prepared in different embodiments, the flow capacity of an aggregate of the conductive sheets <NUM> is roughly identical to the flow capacity of the first tab <NUM>. Specifically, the electrochemical device satisfies <NUM> ≤ (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) ≤ <NUM>. The main difference of the electrochemical device <NUM> between different embodiments lies in the flow capacity of the first tab <NUM> and the flow capacity of the overall structure formed by the conductive sheets <NUM>. This test aims to examine, by controlling the change of the flow capacity of the first tab <NUM> and by reference to the test results of the temperature increment, how the temperature difference between the main part of the electrochemical device <NUM> and the first tab <NUM> (second tab <NUM>) is related to the flow capacity of the first tab <NUM> (second tab <NUM>).

In this application, the electrochemical device satisfies <NUM> ≤ (g<NUM> × s<NUM>)/I ≤ <NUM>. Specifically, as can be seen with reference to Embodiments <NUM> to <NUM>, when (g<NUM>×s<NUM>)/I is less than <NUM>, the temperature increment difference between the body portion <NUM> of the electrochemical device <NUM> and the first tab <NUM> is greater than <NUM>. When (g<NUM>×s<NUM>)/I is greater than or equal to <NUM>, the temperature increment difference between the body portion <NUM> of the electrochemical device <NUM> and the first tab <NUM> is less than <NUM>. However, when (g<NUM>×s<NUM>)/I is greater than <NUM>, the temperature increment difference between the body portion <NUM> of the electrochemical device <NUM> and the first tab <NUM> is less than <NUM>, indicating that under this condition, the temperature increment difference is extremely small and further increase of the flow capacity of the first tab <NUM> is not much significant but increases the manufacturing cost of the first tab <NUM>. The setting of <NUM> ≤ (g<NUM>×s<NUM>)/I ≤ <NUM> ensures a sufficient flow capacity of the first tab <NUM>, and therefore, ensures that the temperature increment difference between the main region and the first tab <NUM> is relatively small, ensures that the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is still high, and also ensures that the manufacturing cost of the first tab <NUM> remains relatively low.

To sum up, the electrochemical device <NUM> according to an embodiment of this application includes a housing <NUM>, an electrode assembly <NUM>, a first tab <NUM>, and a second tab <NUM>. The electrode assembly <NUM> is accommodated in the housing <NUM> and includes a first electrode plate <NUM>, a second electrode plate <NUM>, and a separator <NUM>. The first electrode plate <NUM> includes a first current collector <NUM>. The second electrode plate <NUM> includes a second current collector <NUM> and a plurality of conductive sheets <NUM> disposed together with the second current collector <NUM> in one piece. The plurality of conductive sheets <NUM> protrude from the second current collector <NUM> along the first direction X. The plurality of conductive sheets <NUM> are stacked in the thickness direction of the electrode assembly <NUM> to form a collection portion <NUM>. The first tab <NUM> is connected to the first current collector <NUM>, and the second tab <NUM> is connected to the collection portion <NUM>.

The electrochemical device <NUM> according to this embodiment of this application satisfies: <NUM> ≤ (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) ≤ <NUM>. This setting ensures that the temperature increment difference between the first tab <NUM> and the conductive sheets <NUM> is relatively small, and therefore, the consistency between the active material layer of the first electrode plate <NUM> and the active material layer of the second electrode plate <NUM> is still relatively high after <NUM> charge-and-discharge cycles, and the <NUM>th-cycle capacity retention rate of the electrochemical device <NUM> is still relatively high.

Based on the same inventive concept, this application further provides an electronic device. Referring to <FIG>, which is a schematic diagram of an electronic device <NUM> according to an embodiment of this application, the electronic device includes the electrochemical device <NUM> according to the foregoing embodiment and a load structure powered by the electrochemical device <NUM>. In this embodiment, the electronic device <NUM> includes a mobile phone. Understandably, in other embodiments of this application, the electronic device may be a tablet computer, a computer, an unmanned aerial vehicle, or any other electrically powered devices.

Because the electronic device includes the electrochemical device, the electronic device also alleviates the problem of poor consistency between the active material layer of the first electrode plate and the active material layer of the second electrode plate.

Claim 1:
An electrochemical device (<NUM>), comprising:
a housing (<NUM>);
an electrode assembly (<NUM>) accommodated in the housing (<NUM>); the electrode assembly (<NUM>) comprising a first electrode plate (<NUM>), a second electrode plate (<NUM>) and a separator (<NUM>) disposed between the first electrode plate (<NUM>) and the second electrode plate (<NUM>); wherein the first electrode plate (<NUM>), the second electrode plate (<NUM>), and the separator (<NUM>) are stacked and then wound; the first electrode plate (<NUM>) comprises a first current collector (<NUM>); the second electrode plate (<NUM>) comprises a second current collector (<NUM>) and a plurality of conductive sheets (<NUM>) disposed together with the second current collector (<NUM>) in one piece; and the plurality of conductive sheets (<NUM>) protrude from the second current collector (<NUM>) along a first direction (X), the plurality of conductive sheets (<NUM>) are stacked in a thickness direction (Z) of the electrode assembly (<NUM>) to form a collection portion (<NUM>), and the first direction (X) is perpendicular to the thickness direction (Z);
a first tab (<NUM>), connected to the first current collector (<NUM>) and protruding out of the housing (<NUM>); and
a second tab (<NUM>), connected to the collection portion (<NUM>) and protruding out of the housing (<NUM>), wherein
a conductivity of the first tab (<NUM>) is g<NUM> S/mm,
a cross-sectional area of the first tab (<NUM>) perpendicular to an extension path of the first tab (<NUM>) is s<NUM> mm<NUM>,
a conductivity of the plurality of conductive sheets (<NUM>) is g<NUM> S/mm,
a sum of cross-sectional areas of the plurality of conductive sheets (<NUM>) perpendicular to an extension direction of the conductive sheets (<NUM>) is s<NUM> mm<NUM>, and <NUM> ≤ (g<NUM> × s<NUM>)/(g<NUM> × s<NUM>) ≤ <NUM>.