Patent Description:
The present disclosure relates to a secondary battery and a device including same, and more particularly, to a secondary battery that prevents disconnection of an electrode tab, and a device including same.

Recently, as energy source price is increasing due to the depletion of fossil fuels and increasing interest is being paid to environmental pollution, the demand for environmentally-friendly alternative energy sources is bound to play an important role in the future life. Thus, research into techniques for generating various kinds of power, such as nuclear energy, solar energy, wind energy, and tidal power, is underway, and power storage apparatuses for more efficient use of the generated energy are also drawing much attention.

In particular, along with the technology development and increased demand for mobile devices, demand for batteries as energy sources has been increasing rapidly, and accordingly, much research on batteries which can meet the various needs has been carried out.

Typically, the demand for the lithium secondary battery, such as a lithium ion battery or a lithium ion polymer battery, which have advantages such as a high energy density, a discharge voltage, an output stability, and the like is high.

Further, the secondary battery may be classified based on the structure of an electrode assembly having a structure in which a cathode and an anode are stacked with a separator being interposed therebetween. Typically, there may mentioned, for example, a jelly-roll type electrode assembly having a structure in which long sheets of cathodes and anodes are wound in the state in which a separator is interposed therebetween, a stacked-type electrode assembly having a structure in which pluralities of cathodes and anodes, cut by a certain size unit, are sequentially stacked in the state in which separators are interposed therebetween, or the like. In recent years, in order to solve problems caused by the jelly-roll type electrode assembly and the stacked-type electrode assembly, there has been developed a stacked/folded type electrode assembly, which is a combination of the jelly-roll type electrode assembly and the stacked-type electrode assembly, having a structure in which unit cells stacked with predetermined units of the cathodes and the anodes are sequentially wound with a separator being interposed therebetween in the state of having been placed on a separation film.

Further, based on the shape of a battery case, the secondary battery may be classified into a cylindrical battery where an electrode assembly is mounted in a cylindrical case, a prismatic battery where an electrode assembly is mounted in a prismatic can, and a pouch type battery where an electrode assembly is mounted in a pouch type case of an aluminum laminate sheet.

<FIG> is a perspective view of a conventional pouch type secondary battery, and <FIG> is a cross-sectional view taken along the cutting line A-A' of <FIG>.

Referring to <FIG> and <FIG>, a conventional pouch type battery cell <NUM> can be manufactured by housing an electrode assembly <NUM> inside a pouch case <NUM> and then sealing the case. The electrode assembly <NUM> may include electrodes, and a separator disposed between the electrodes. The electrodes include an electrode tab 21t, and the electrode tab 21t may be joined to the electrode lead <NUM> by a method such as welding. As the electrode lead <NUM> is exposed to the outside of the pouch type battery case <NUM>, an electrical connection of the electrode assembly <NUM> may be made.

In this case, the electrode assembly <NUM> may be a stacked-type electrode assembly in which a plurality of electrodes cut in units of a predetermined size are sequentially stacked with a separator being interposed therebetween. All the electrode tabs 21t extending from the respective electrodes may be joined to the electrode lead <NUM>.

The electrode assembly <NUM> repeats contraction and expansion as charge and discharge are repeated. As shown in <FIG>, the electrode assembly <NUM> causes expansion in its thickness direction (direction parallel to the z-axis). Since the electrode lead <NUM> included in the conventional secondary battery <NUM> is not flexible and is interposed between the sealed battery cases <NUM>, there is no choice but to fix the position in a state in which the electrode tabs 21t are joined. At this time, when the electrode assembly <NUM> expands in its thickness direction (direction parallel to the z-axis), the electrode lead <NUM> is fixed and thus, a large tension is generated on the electrode tab 21t. In particular, in the stacked-type electrode assembly, the electrode tab 21t located on the outermost side exerts the largest tension at expansion of the electrode assembly <NUM>, and thus, in the worst case, it may lead to disconnection.

Therefore, there is a need to develop a technique that can prevent disconnection of the electrode tab when expansion of the electrode assembly occurs.

<CIT> discloses a flat battery. <CIT> discloses a power storage unit and electronic device.

It is an object of the present disclosure to provide a secondary battery that can reduce tension applied to the electrode tab even if expansion of the electrode assembly occurs, and prevent disconnection of the electrode tab located on the outermost side.

However, the technical problem to be solved by embodiments of the present disclosure is not limited to the above-described problems, and can be variously expanded within the scope of the technical idea included in the present disclosure.

According to one embodiment of the present disclosure, there is provided a secondary battery comprising: an electrode assembly including electrode sheets on which electrode tabs are formed and a separator located between the electrode sheets; a battery case in which the electrode assembly is housed; and an electrode lead connected to the electrode tab and protruding to the outside of the battery case, wherein the electrode lead includes a flexible part having stretchability in a direction parallel to the protruding direction of the electrode lead, and wherein the flexible part is located inside the battery case.

The flexible part may have a bent shape.

The flexible part can stretch in a direction parallel to the protruding direction of the electrode lead.

The flexible part may include at least one of gold (Au) and silver (Ag).

The battery case may include an upper case and a lower case, the sealing part of the upper case and the sealing part of the lower case may be heat-sealed to each other, and the flexible part may be located between a portion of the electrode lead where the sealing parts are located and the electrode assembly.

The electrode lead includes a first part connected to the flexible part and the electrode tab; a second part connected to the flexible part and protruding to the outside of the battery case; and a fixing part connected to each of the first part and the second part.

The flexible part may include a first flexible part and a second flexible part, and the fixing part may be located between the first flexible part and the second flexible part.

The fixing part may include at least one of a glass material, a ceramic material, carbon graphite, and an alloy material having low flexibility.

The fixing part may have a straight line shape.

The electrode assembly may be a stacked-type electrode assembly in which the electrode sheets are stacked, and when the electrode sheets expand in the thickness direction, the flexible part can stretch in a direction perpendicular to the thickness direction.

According to the embodiments of the present disclosure, the flexible part is formed on the electrode lead, whereby it is possible to reduce the tension applied to the electrode tab even if expansion of the electrode assembly occurs. Thereby, it is possible to prevent disconnection of the electrode tab located on the outermost side.

Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out them. The present disclosure may be modified in various different ways, and is not limited to the embodiments set forth herein.

Portions that are irrelevant to the description will be omitted to clearly describe the present disclosure, and like reference numerals designate like elements throughout the description.

In addition, it will be understood that when an element such as a layer, film, region, or plate is referred to as being "on" or "above" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, it means that other intervening elements are not present. Further, the word "on" or "above" means disposed on or below a reference portion, and does not necessarily mean being disposed on the upper end of the reference portion toward the opposite direction of gravity.

Further, throughout the description, when a portion is referred to as "including" or "comprising" a certain component, it means that the portion can further include other components, without excluding the other components, unless otherwise stated.

Further, throughout the description, when referred to as "planar", it means when a target portion is viewed from the upper side, and when referred to as "cross-sectional", it means when a target portion is viewed from the side of a cross section cut vertically.

<FIG> is an exploded perspective view of a secondary battery according to an embodiment of the present disclosure. <FIG> is a perspective view which shows a state in which the secondary battery of <FIG> is assembled. <FIG> is a cross-sectional view taken along the cutting line B-B' of <FIG>.

Referring to <FIG>, the secondary battery <NUM> according to an embodiment of the present disclosure includes an electrode assembly <NUM>, a battery case <NUM> in which the electrode assembly <NUM> is housed, and electrode leads <NUM> and <NUM> protruding to the outside of the battery case <NUM>.

The electrode assembly <NUM> includes electrode sheets <NUM> and <NUM> on which electrode tabs 210t are formed and a separator <NUM> located between the electrode sheets <NUM> and <NUM>. In particular, the electrode assembly <NUM> according to the present embodiment may be a stacked-type electrode assembly, a jelly-roll type electrode assembly, or a stacked/folded type electrode assembly, but is preferably a stacked-type electrode assembly. Specifically, the stacked-type electrode assembly may have a structure in which a plurality of electrode sheets <NUM> and <NUM> are stacked with a separator <NUM> being interposed therebetween.

Each of the electrode sheets <NUM> and <NUM> may be formed by applying an electrode active material onto an electrode current collector, and a part of the electrode current collector may protrude to provide an electrode tab 210t. The electrode sheets <NUM> and <NUM> may be divided into a cathode sheet and an anode sheet, and a separator <NUM> may be interposed between the cathode sheet and the anode sheet. As an example, the electrode sheet <NUM> may be a cathode sheet, and the electrode tab 210t protruding therefrom may be a cathode tab. The other electrode sheet <NUM> may be an anode sheet, and an electrode tab (not shown) protruding therefrom may be an anode tab.

Further, the electrode tab according to the present embodiment may be connected to the electrode lead. As an example, electrode tabs 210t having any one polarity may be joined to any one electrode lead <NUM>, and electrode tabs (not shown) having the other polarity may be joined to the other electrode leads <NUM>. These electrode leads <NUM> and <NUM> may protrude from both end parts of the battery case <NUM>. <FIG> and <FIG> show that two electrode leads <NUM> and <NUM> protrude in mutually opposite directions, but the protruding direction is not particularly limited. That is, a structure in which the two electrode leads <NUM> and <NUM> protrude in the same direction from one side of the secondary battery <NUM> is also possible. One of the two electrode leads <NUM> and <NUM> may be a cathode lead, and the other may be an anode lead.

Meanwhile, the battery case <NUM> according to the present embodiment may be a pouch type case. The battery case <NUM> may include an upper case <NUM> and a lower case <NUM> that are heat-sealed to each other. Although not specifically shown in the figure, the battery case <NUM> including the upper case <NUM> and the lower case <NUM> may be a laminated sheet including a resin layer and a metal layer. Specifically, each of the upper case <NUM> and the lower case <NUM> may include an inner resin layer for sealing, a metal layer for preventing penetration of material and an outer resin layer on the outermost side.

The outer resin layer has excellent tensile strength and weather resistance compared to its thickness, and may have electrical insulation, in order to protect the pouch type secondary battery <NUM> from the outside. The outer resin layer may include a polyethylene terephthalate (PET) resin or a nylon resin. The metal layer can prevent air, moisture, and the like from flowing into the pouch type secondary battery <NUM>. The metal layer may include aluminum (Al). The inner resin layer may be heat-sealed to each other by heat and pressure applied in a state in which the electrode assembly <NUM> is mounted. The inner resin layer may include casted polypropylene (CPP) or polypropylene (PP).

Recessed storage parts 310R and 320R in which the electrode assembly <NUM> can be seated may be formed in each of the upper case <NUM> and the lower case <NUM>, and the electrode assembly <NUM> may be stored in the storage parts 310R and 320R. The method of forming the storage parts 310R and 320R are not particularly limited, and a deep drawing process using a pressing punch can be applied.

Sealing parts <NUM> and <NUM> may be provided along the outer periphery of each of the storage parts 310R and 320R of the upper case <NUM> and the lower case <NUM>. The sealing part <NUM> of the upper case <NUM> and the sealing part <NUM> of the lower case <NUM> may be heat-sealed to each other to seal a battery case <NUM>. More specifically, the inner resin layer of the sealing part <NUM> of the upper case <NUM> and the inner resin layer of the sealing part <NUM> of the lower case <NUM> may be heat-sealed in a state of facing each other. Meanwhile, <FIG> illustrates an upper case <NUM> and a lower case <NUM> in which a storage part is formed and which are separated from each other, but it may be a laminated sheet in which one side of the upper case and one side of the lower case are integrally formed, and may be a plate-shaped structure in which the storage part is formed in only one of the upper case and the lower case, and the storage part is not formed in the other.

Next, a flexible part formed on an electrode lead according to an embodiment of the present disclosure will be described in detail with reference to <FIG> and <FIG> and the like. In order to avoid repetition of the description, any one of the two electrode leads <NUM> and <NUM> will be mainly described, but it goes without saying that the structure of the flexible part according to the present embodiment can be formed in other electrode leads <NUM> as well.

<FIG> is a plan view of the electrode lead included in the secondary battery of <FIG> as viewed in the -z-axis direction on the xy plane.

Referring to <FIG>, <FIG> and <FIG>, the electrode lead <NUM> according to the present embodiment has a flexible part 400f having stretchability in a direction parallel to the protruding direction (direction parallel to the y-axis) of the electrode lead <NUM>, and the flexible part 400f is located inside the battery case <NUM>.

Specifically, the flexible part 400f according to the present embodiment has a bent shape and may stretch in a direction parallel to the protruding direction (direction parallel to the y-axis) of the electrode lead <NUM>. In other words, the flexible part 400f according to the present embodiment may be in a form compressed in a direction parallel to the protruding direction (parallel to the y-axis) of the electrode lead <NUM>.

The flexible part 400f is preferably made of a material having excellent ductility, malleability, elasticity, and toughness, and may include, for example, at least one of gold (Au) and silver (Ag). Such a flexible part 400f may be formed in the middle of the electrode lead <NUM>. Specifically, as shown in <FIG> and <FIG>, the existing plate-shaped metal material constituting the electrode lead <NUM> can be joined to both ends of the metal material constituting the flexible part 400f by a method such as welding. That is, for example, the electrode lead <NUM> including the flexible part 400f can be manufactured by welding a metal member containing aluminum (Al) or copper (Cu) to both ends of the metal member containing silver (Ag).

<FIG> is a cross-sectional view which shows a state in which the electrode assembly is expanded with respect to the electrode assembly and the electrode lead included in the secondary battery of <FIG>.

In the conventional electrode assembly <NUM> (see <FIG>), since the electrode lead <NUM> is not flexible and its position is fixed, a large tension is generated in the electrode tab 21t along with expansion of the electrode assembly <NUM>, and the electrode tab 21t located on the outermost side has a risk of disconnection. On the other hand, referring to <FIG> together with <FIG> and <FIG>, since the flexible part 400f of the electrode lead <NUM> according to the present embodiment has stretchability, it may stretch in a direction perpendicular to the thickness direction when the electrode assembly <NUM> expands in the thickness direction (direction parallel to the z-axis). In other words, along with the expansion of the electrode assembly <NUM>, the flexible part 400f according to the present embodiment can be stretched in a direction parallel to the protruding direction (parallel to the y-axis) of the electrode lead <NUM>, in particular, in the direction in which the electrode assembly <NUM> is located (-y-axis direction).

By stretching the flexible portion 400f, it is possible to prevent excessive tension from being generated in the electrode tab 210t, and it is possible to prevent disconnection of the electrode tab 210t located at the outermost side.

At this time, as described above, the flexible part 400f included in the electrode lead <NUM> is located inside the battery case <NUM>. Specifically, referring back to <FIG>, the sealing part <NUM> of the upper case <NUM> and the sealing part <NUM> of the lower case <NUM> are heat-sealed to each other, and the flexible part 400f may be located between a portion where the sealing parts <NUM> and <NUM> in the electrode lead <NUM> are located and the electrode assembly <NUM>. If the flexible part 400f is formed in the outer part which is the outside of the portion where the sealing parts <NUM> and <NUM> in the electrode lead <NUM> are located, the tension applied to the electrode tab 210t cannot be reduced at expansion of the electrode assembly <NUM> because of being the outside of the portion fixed by the sealing parts <NUM> and <NUM>. Therefore, it is preferable that the flexible part 400f according to the present embodiment is formed inside the battery case <NUM>.

Next, a fixing part according to an embodiment of the present invention will be described in detail with reference to <FIG> and <FIG>.

<FIG> is a cross-sectional view which shows an electrode assembly and an electrode lead according to an embodiment of the present invention. <FIG> is a plan view of the electrode assembly and the electrode lead of <FIG> as viewed in the -z-axis direction on the xy plane. In particular, <FIG> corresponds to a cross section taken along the yz plane, similar to the cross section of <FIG> or <FIG>.

Referring to <FIG> and <FIG>, the formation of the flexible part 400f' on the electrode lead <NUM>' according to the embodiment of the present invention is similar to the contents described above, but the fixing part <NUM> can be further formed.

Specifically, the electrode lead <NUM>' according to the present embodiment includes a first part <NUM> connected to the flexible part 400f' and the electrode tab 210t, a second part <NUM> connected to the flexible part 400f' and protruding to the outside of the battery case, and a fixing part <NUM> connected to each of the first part <NUM> and the second part <NUM>.

More specifically, the flexible part 400f ' according to the present embodiment may include a first flexible part 400f1 and a second flexible part 400f2. A first part <NUM> may be joined to one end of each of the first flexible part 400f1 and the second flexible part 400f2, and a second part <NUM> may be joined to the other end of each of the first flexible part 400f1 and the second flexible part 400f2. As the joining method, weld-joining can be used as described above.

In this case, the fixing part <NUM> may be connected to each of the first part <NUM> and the second part <NUM> while being located between the first flexible part 400f1 and the second flexible part 400f2. Wherein, the fixing part <NUM> may also be connected to each of the first part <NUM> and the second part <NUM> by a method such as welding.

Any material that can be easily cut or broken can be applied to the fixing part <NUM> without particular limitation. In one example, the fixing part <NUM> may include at least one of a glass material, a ceramic material, carbon graphite, and an alloy material having low flexibility. Further, unlike the flexible part 400f' having a serpentine shape, the fixed part <NUM> may have a straight line shape.

Since the flexible part 400f contains a material having excellent ductility, malleability, elasticity, and toughness, the flexible part 400f' is not fixed in the process of welding the electrode tab 210t to the electrode lead <NUM>', so that welding cannot proceed smoothly. Therefore, in the present embodiment, the fixed part <NUM> of a straight line shape is provided to fix the compressed form of the flexible part 400f'. Further, since the fixing part <NUM> can keep the distance between the first part <NUM> and the second part <NUM> constant, it is possible to prevent the flexible part 400f ' from being stretched even before the electrode assembly <NUM> is expanded. Instead, since the fixing part <NUM> according to the present embodiment includes a metal material with slightly weak strength, it does not hinder the stretching of the flexible part 400f' while being cut along with the expansion of the electrode assembly <NUM>.

Meanwhile, <FIG> is a plan view which shows an electrode lead according to another modified embodiment of the present disclosure, which specifically shows the position of the deformed fixing part <NUM>. The electrode lead <NUM>" according to the present embodiment includes a first part <NUM>, a second part <NUM>, and a fixing part <NUM>. The fixing unit <NUM> according to the present embodiment is not particularly limited to its position and number as long as it connects the first part <NUM> and the second part <NUM>. As an example, referring to <FIG>, one flexible part 400f" that is connected to the first part <NUM> and the second part <NUM> is formed, and the two fixing parts <NUM> may be connected to each of the first part <NUM> and the second part <NUM> with one flexible part 400f" being interposed therebetween. That is, the two fixing parts <NUM> may be arranged on both sides of the flexible part 400f" in the x-axis direction. The fixing part <NUM> shown in <FIG> can also fix the compressed form of the flexible part 400f", and the spacing between the first part <NUM> and the second part <NUM> can be kept constant prior to expansion of the electrode assembly.

Meanwhile, referring back to <FIG> and <FIG>, a lead film <NUM> may be located on each of the electrode leads <NUM> and <NUM>. The lead film <NUM> may be located between the upper case <NUM> and the lower case <NUM> in the form of wrapping the electrode leads <NUM> and <NUM>, respectively.

The lead film <NUM> may not only prevent a short circuit from occurring between the electrode leads <NUM> and <NUM> and the metal layer of the battery case <NUM>, but also improve the sealing properties of the pouch type battery case <NUM>. The electrode leads <NUM> and <NUM> made of a metal material have a slightly large contact resistance when heat-sealing to the inner resin layer of the pouch type battery case <NUM>, which may cause a reduction in the surface adhesion. However, if the lead film <NUM> is provided as in the present embodiment, such an adhesion reduction phenomenon can be prevented. Further, the lead film <NUM> includes an insulating material and thus can block the application of current from the electrode leads <NUM> and <NUM> to the pouch type battery case <NUM>.

The lead film <NUM> may be formed of a film having insulating properties and heat sealing properties. The lead film <NUM> may include, for example, at least one of polyimide (PI), polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET).

Although the terms representing directions such as front, rear, left, right, upper and lower directions are used herein, these merely represent for convenience of explanation, and may differ depending on a position of an observer, a position of an object, or the like.

The above-mentioned secondary batteries according to the present embodiments can gathered in plural numbers to form a battery module. Such battery modules may be mounted together with various control and protection systems such as BMS(battery management system), and a cooling system to form a battery pack.

The secondary battery, the batter module and the battery pack can be applied to various devices. Such a device can be applied to a vehicle means such as an electric bicycle, an electric vehicle, or a hybrid vehicle, but the present disclosure is not limited thereto, and is applicable to various devices that can use a secondary battery.

Claim 1:
A secondary battery (<NUM>) comprising:
an electrode assembly (<NUM>) including electrode sheets (<NUM>, <NUM>) on which electrode tabs (210t) are formed and a separator (<NUM>) located between the electrode sheets;
a battery case (<NUM>) in which the electrode assembly is housed; and
an electrode lead (<NUM>, <NUM>', <NUM>", <NUM>) connected to the electrode tab and protruding to the outside of the battery case,
wherein the electrode lead includes a flexible part (400f, 400f', 400f") having stretchability in a direction parallel to the protruding direction of the electrode lead, and
wherein the flexible part is located inside the battery case,
characterized in that the electrode lead comprises a first part (<NUM>) connected to the flexible part and the electrode tab; a second part (<NUM>) connected to the flexible part and protruding to the outside of the battery case; and a fixing part (<NUM>) connected to each of the first part and the second part.