Electrode assembly and secondary battery including the same

Abstract

An electrode assembly according to an embodiment of the present application includes a plurality of unit cells for forming a radial structure with respect to a center, wherein a thickness of the unit cells decreases as it travels from an outer side of the radial structure toward the center based on a horizontal cross section, and an electrode tab is formed on at least one of an upper edge, a lower edge, an outer edge, or a center edge of a current collector included in the unit cell.

Description

TECHNICAL FIELD

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0068992, filed on June 8, 2020, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0003] The present application relates to an electrode assembly and a secondary battery including the same, and particularly to an electrode assembly having a radial structure and a secondary battery including the same. BACKGROUND

[0004] Recently, the demand for portable electronic products such as laptop computers, camcorders, mobile phones, etc. is rapidly increasing, and the development of electric vehicles, energy storage batteries, robots, and satellites is active, and thus, much research has been conducted on secondary batteries used as driving power sources for these products.

[0005] An electrode assembly installed in a battery case is a power generating element constructed in a stacked structure including a positive electrode, a diaphragm, and a negative electrode, and the power generating element can be repeatedly charged and discharged and is classified into jelly-roll type, stacked type, and stacked / folded type. The jelly-roll type is a structure obtained by inserting a diaphragm between long sheet type positive and negative electrodes coated with an active material and then winding it, the stacked type is a structure in which a plurality of positive and negative electrodes having a predetermined size are sequentially stacked with a diaphragm inserted therebetween, and the stacked / folded type is a hybrid structure of the jelly-roll type and the stacked type. Among the electrode assemblies of these types, the jelly-roll type electrode assembly has the advantage of being easy to manufacture and having a high energy density per unit weight.

[0006] Secondary batteries are classified into cylindrical batteries in which an electrode assembly is installed in a cylindrical metal can, prismatic batteries in which an electrode assembly is installed in a prismatic metal can, and pouch-type batteries in which an electrode assembly is installed in a pouch-type case made of an aluminum laminate sheet, according to the shape of the battery case. Among the batteries of these types, the cylindrical battery has the advantage of having a relatively large capacity and having a stable structure.

[0007] Secondary batteries include, for example, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, and lithium secondary batteries. Among these batteries, the lithium secondary battery has almost no memory effect compared to nickel-based secondary batteries, has the advantages of having freedom of charge and discharge, having a very low self-discharge rate, having a high operating voltage, and having a high energy density per unit weight, and thus, the lithium secondary battery is widely used in the field of advanced electronic devices.

[0008] Figure 1 An exploded perspective view of a conventional jelly-roll electrode assembly that is not wound is shown.

[0009] Referring to Figure 1 A conventional jelly-roll electrode assembly 10 inserted into a secondary battery includes a positive electrode sheet 20, a negative electrode sheet 30, and a separator 40 disposed between the positive electrode sheet 20 and the negative electrode sheet 30. When wound in a jelly-roll shape, the separator 40 is preferably additionally arranged under the negative electrode sheet 30 in order to prevent the positive electrode sheet 20 and the negative electrode sheet 30 from being folded on each other.

[0010] The positive electrode sheet 20 can include a positive electrode mixture layer 22 formed by applying a positive active material to a positive current collector, and a positive electrode uncoated region 23 to which the positive active material is not applied and exposes the positive current collector. The positive tab 21 can be bonded to the positive electrode uncoated region 23 by a method such as welding.

[0011] In a similar manner, the negative electrode sheet 30 can include a negative electrode mixture layer 32 formed by applying a negative active material to a negative current collector, and a negative electrode uncoated region 33 to which the negative active material is not applied and exposes the negative current collector. The negative tab 31 can be bonded to the negative electrode uncoated region 33 by a method such as welding.

[0012] Here, the positive electrode sheet 20 and the negative electrode sheet 30 generally have a rectangular sheet form to be wound in a jelly-roll shape, and thus the distance through which electrons move from the positive tab 21 or the negative tab 31 through the positive current collector or the negative current collector increases. When the distance through which electrons move increases as described above, the electron transport resistance significantly increases, which is a disadvantage, and this disadvantage can be exacerbated particularly under high current operating conditions.

[0013] In other words, in the case of a lithium secondary battery, in general, lithium ions in an electrolyte solution exhibit high ionic conductivity within a certain concentration range, and when the lithium ion concentration is less than or greater than the certain concentration, the ionic conductivity decreases. The electrolyte solution concentration or the lithium ion concentration of the lithium secondary battery is not constant, and the lithium ion concentration around the positive electrode and the negative electrode travels in opposite directions depending on the battery operating conditions.

[0014] Therefore, there is a need for a new method for a secondary battery to address this problem. SUMMARY

[0015] TECHNICAL PROBLEM

[0016] The present application is directed to providing an electrode assembly for reducing transport resistance and providing structural stability, and a device including the same.

[0017] The object of the present application is not limited to the above-mentioned object, and can be extended in various ways within the scope and range of the concept of the present application.

[0018] Technical Solution

[0019] Embodiments of the present application provide an electrode assembly including a plurality of unit cells for forming a structure in a radial shape with respect to a center, in which a thickness of the unit cells decreases as proceeding from an outer side of the radial structure toward the center based on a horizontal cross section, and an electrode tab formed on at least one of an upper edge, a lower edge, an outer edge, and a center edge of a current collector included in the unit cells.

[0020] The unit cell can include, in order, a positive electrode, a first diaphragm, a negative electrode, and a second diaphragm.

[0021] The positive electrode can include a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector, and the negative electrode can include a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector.

[0022] The positive electrode tab can be formed on at least one of an upper edge, an outer edge, and a center edge of the positive electrode current collector.

[0023] The negative electrode tab can be formed on at least one of a lower edge, an outer edge, and a center edge of the negative electrode current collector.

[0024] A thickness of at least one of the positive electrode mixture layer and the negative electrode mixture layer can decrease as proceeding from the outer side of the radial structure toward the center.

[0025] A density of at least one of the positive electrode mixture layer and the negative electrode mixture layer can increase as proceeding from the outer side of the radial structure toward the center.

[0026] The positive electrode current collector, the positive electrode mixture layer, the first diaphragm, the negative electrode mixture layer, the negative electrode current collector, and the second diaphragm can be stacked in order.

[0027] A through hole can be formed in the current collector.

[0028] The electrode assembly can further include an electrode lead bonded to the electrode tab.

[0029] Another embodiment of the present application provides a secondary battery including an electrode assembly, a battery case for receiving the electrode assembly, and a cap assembly disposed on the electrode assembly, in which the electrode tab is bonded to the electrode lead and connected to the cap assembly or the battery case.

[0030] Advantageous Effects

[0031] Embodiments of the present application propose a plurality of cell configurations for forming a radial structure to reduce a transmission resistance, and can improve the performance of a secondary battery by applying a current collector formed with a through hole to reduce the variation range of the concentration of an electrolyte solution in the secondary battery.

[0032] In addition, the structural stability of the assembly can be increased according to the tab structure formed at one edge of the current collector, and the increase in weight can be minimized.

[0033] Effects of the present application are not limited to the above-mentioned effects, and other unmentioned effects can be clearly understood by those skilled in the art from the description of the claims. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 An exploded perspective view of a conventional jelly-roll electrode assembly that is not wound is shown.

[0035] Figure 2 A perspective view of an electrode assembly according to an embodiment of the present application is shown.

[0036] Figure 3 A partial cross-sectional view of a portion of a cross-section with respect to A-A' of Figure 2 is shown.

[0037] Figure 4 A partial cross-sectional view of a portion of a cross-section with respect to B-B' of Figure 2 is shown.

[0038] Figure 5 (a) to Figure 5 (c) show a positive current collector and a positive tab according to various embodiments of the present application.

[0039] Figure 6 (a) to Figure 6 (c) show a negative current collector and a negative tab according to various embodiments of the present application.

[0040] Figure 7 (a) to Figure 7 (c) show a combination structure of a positive tab and a positive lead according to a modified embodiment of the present application.

[0041] Figure 8 (a) to Figure 8 (c) show a combination structure of a negative tab and a negative lead according to a modified embodiment of the present application.

[0042] Figure 9 An exploded perspective view of a secondary battery according to an embodiment of the present application is shown.

[0043] Figure 10 and Figure 11A graph showing comparative results and evaluation results of voltage variation and temperature variation at the time of charge and discharge of a secondary battery according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0044] The present application will be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of the present application are shown. As those skilled in the art will appreciate, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application.

[0045] Portions unrelated to the description will be omitted for clarity of the description of the present application, and the same elements will be denoted by the same reference numerals throughout the specification.

[0046] For better understanding and ease of description, the size and thickness of each configuration shown in the drawings are arbitrarily shown, but the present application is not limited thereto. In the drawings, the thickness of layers, films, panels, regions, etc. is exaggerated for clarity. The thickness of some layers and regions is exaggerated for ease of explanation.

[0047] It should be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. The phrase "on" or "above" means positioned above or below the target portion, and does not necessarily mean positioned on the upper side of the target portion based on the direction of gravity.

[0048] Unless explicitly described to the contrary, the word "comprise" and variations such as "comprises" or "comprising" will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

[0049] The phrase "in plan view" means to observe the target portion from the top, and the phrase "in cross-sectional view" means to observe a cross-section of the target portion cut vertically from the side.

[0050] Figure 2 A perspective view of an electrode assembly according to an embodiment of the present application is shown. Figure 3 A partial cross-sectional view of a portion of a cross-section with respect to A-A' of Figure 2 is shown. Figure 4 A partial cross-sectional view of a portion of a cross-section with respect to B-B' of Figure 2 is shown. In detail, Figure 3 A cross-sectional view with respect to line A-A' of Figure 2 corresponds to a cross-section of an electrode assembly of Figure 4 A cross-sectional view with respect to line B-B' of Figure 2a cross section of the electrode assembly 100 cut along a vertical direction.

[0051] Referring to Figures 2 to 4 , the electrode assembly 100 according to the embodiment of the present application includes a plurality of unit cells 100U for forming a radial structure with respect to a center. Based on a horizontal cross section, a thickness of the unit cell 100U decreases as a direction proceeding from an outer side of the radial structure toward the center, and an electrode tab 211a and 311a is formed on at least one of an upper edge, a lower edge, an outer edge, and a center edge of a current collector 210 and 310 included in the unit cell 100U. Here, the horizontal cross section indicates a cross section taken by an x-y plane shown in FIG. 1, and the horizontal cross section corresponds to a cross section with respect to a line A-A'. Figure 2

[0052] The electrode assembly 100 according to the present embodiment can have a cylindrical shape, the center indicates an inner central region of the electrode assembly 100 in terms of the horizontal cross section, and the outer side indicates an outer region of the peripheral surface of the electrode assembly 100 in terms of the horizontal cross section. A hollow space passing through in a vertical direction (or z-axis direction) can be formed in the center of the electrode assembly 100.

[0053] As described above, the unit cell 100U according to the present embodiment forms a radial structure, and based on a horizontal cross section, a thickness of the unit cell 100U decreases as a direction proceeding from an outer side of the radial structure toward the center. A plurality of unit cells 100U can be configured into a cylindrical electrode assembly 100. Specifically, n (n is an integer equal to or greater than 5) unit cells 100U can be gathered together to form the electrode assembly 100, and a peripheral surface of the electrode assembly 100 can have a circular shape, a shape close to a circle in terms of the horizontal cross section, an n-polygonal shape, or a sector shape. In other words, a shape of the horizontal cross section of the electrode assembly 100 can be determined by the number of unit cells 100U, and the shape of the horizontal cross section can be an n-polygonal shape when the number is small, and the shape of the horizontal cross section can form a circular shape when the number is large. For example, when the cross-sectional shape of the electrode assembly 100 is an n-polygonal shape, and the number n is equal to or greater than 5, or the number n is equal to or greater than 10, the cross-sectional shape can be considered to belong to the circular category.

[0054] The current collectors 210 and 310 according to the present embodiment can include a positive electrode current collector 210 and a negative electrode current collector 310, and the electrode tabs 211a and 311a can include a positive electrode tab 211a and a negative electrode tab 311a. In detail, the unit cell 100U according to the present embodiment can include a positive electrode 200, a first diaphragm 400, a negative electrode 300, and a second diaphragm 500, which are sequentially stacked.

[0055] ​The positive electrode 200 can include a positive electrode current collector 210 and a positive electrode mixture layer 220 formed on the positive electrode current collector 210. The positive electrode mixture layer 220 can be formed by applying a positive electrode active material to the positive electrode current collector 210.

[0056] The negative electrode 300 can include a negative electrode current collector 310 and a negative electrode mixture layer 320 formed on the negative electrode current collector 310. The negative electrode mixture layer 320 can be formed by applying a negative electrode active material to the negative electrode current collector 310.

[0057] Referring to Figure 3 , the thickness of at least one of the positive electrode mixture layer 220 and the negative electrode mixture layer 320 can decrease as a direction in which the center of the radial structure is approached from the outside of the radial structure. In particular, it is preferable that the thickness of the positive electrode mixture layer 220 and the negative electrode mixture layer 320 decrease as the direction in which the center of the radial structure is approached from the outside of the radial structure.

[0058] That is, according to the present embodiment, by designing the thickness of the mixture layers 220 and 320 loaded on the current collectors 210 and 310 to decrease as the direction in which the center of the radial structure is approached from the outside of the radial structure, the thickness alignment of the unit cells 100U can be provided and the radial structure can be formed.

[0059] The density of at least one of the positive electrode mixture layer 220 and the negative electrode mixture layer 320 can increase as the direction in which the center of the radial structure is approached from the outside of the radial structure. In particular, it is desirable that the density of the positive electrode mixture layer 220 and the negative electrode mixture layer 320 increase as the direction in which the center of the radial structure is approached from the outside of the radial structure.

[0060] As described above, according to the present embodiment, when the thickness of the mixture layers 220 and 320 loaded on the current collectors 210 and 310 is designed to decrease as the direction in which the center of the radial structure is approached from the outside of the radial structure, capacity unevenness can occur depending on the positioning and direction of the unit cells 100U. In the present embodiment, the capacity unevenness caused by the thickness alignment of the unit cells 100U can be compensated for by designing the density of the mixture layers 220 and 320 loaded on the current collectors 210 and 310 to increase as the direction in which the center of the radial structure is approached from the outside of the radial structure. For example, a region in which the thickness of the mixture layers 220 and 320 loaded on the current collectors 210 and 310 is small can be provided with a high density of the mixture layers 220 and 320. The density alignment of the mixture layers 220 and 320 can be achieved by applying pressure in one direction or reducing pressure when pressure is applied using a roller while the mixture layers 220 and 320 are uniformly loaded on the current collectors 210 and 310.

[0061] With regard to the unit cell 100U, the positive electrode current collector 210, the positive electrode mixture layer 220, the first diaphragm 400, the negative electrode mixture layer 320, the negative electrode current collector 310, and the second diaphragm 500 can be sequentially stacked. Thus, when a plurality of unit cells 100U are gathered together to construct the electrode assembly 100, the second diaphragm 500 of one unit cell 100U can face the positive electrode current collector 210 of another adjacent unit cell 100U. That is, with regard to the electrode assembly 100 according to the present embodiment, the first diaphragm 400 can be positioned between the positive electrode mixture layer 220 and the negative electrode mixture layer 320, and the second diaphragm 500 can be positioned between the positive electrode current collector 210 and the negative electrode current collector 310.

[0062] As described above, the electrode tabs are formed on at least one of the upper edge, the lower edge, the outer edge, and the center edge of the current collectors 210 and 310 included in the unit cell 100U, and now will be described with reference to Figure 5 (a) to Figure 5 (c), respectively. Figure 6 (a) to Figure 6 (c), respectively.

[0063] Figure 5 (a) to Figure 5 (c) illustrate the positive electrode current collector and the positive electrode tab according to various embodiments of the present application, and Figure 6 (a) to Figure 6 (c) illustrate the negative electrode current collector and the negative electrode tab according to various embodiments of the present application.

[0064] Referring to Figure 5 (a) to Figure 5 (c), the positive electrode tabs 211a, 211b, and 211c can be formed on at least one of the upper edge, the outer edge, and the center edge of the positive electrode current collector 210. In detail, Figure 5 (a) illustrates the positive electrode tab 211a formed at the upper edge of the positive electrode current collector 210, Figure 5 (b) illustrates the positive electrode tab 211b formed at the outer edge of the positive electrode current collector 210, and Figure 5 (c) illustrates the positive electrode tab 211c formed at the center edge of the positive electrode current collector 210. Here, the upper edge denotes an edge positioned in the z-axis direction in Figure 2 , the outer edge denotes an edge positioned on the outer side of the electrode assembly 100 in Figure 2 , and the center edge is an edge positioned at the center of the electrode assembly 100 in Figure 2 .

[0065] Each of the positive tabs 211a, 211b, and 211c can extend upward. The positive tab 211a formed at the upper edge can extend upward in a straight line, and the positive tabs 211b and 211c formed at the outer edge or the central edge can be bent and can extend upward.

[0066] Referring to Figure 6 (a) to Figure 6 (c), the negative tabs 311a, 311b, and 311c can be formed on at least one of a lower edge, an outer edge, and a central edge of the negative current collector 310. In detail, Figure 6 (a) illustrates the negative tab 311a formed at the lower edge of the negative current collector 310, Figure 6 (b) illustrates the negative tab 311b formed at the outer edge of the negative current collector 310, and Figure 6 (c) illustrates the negative tab 311c formed at the central edge of the negative current collector 310. The lower edge is an edge positioned in the z-axis direction in Figure 2 the outer edge indicates an edge positioned on the outer side of the electrode assembly 100 in Figure 2 the central edge indicates an edge positioned at the center of the electrode assembly 100 in Figure 2 .

[0067] Each of the negative tabs 311a, 311b, and 311c can extend downward. The negative tab 311a formed at the lower edge can extend downward in a straight line, and the negative tabs 311b and 311c formed at the outer edge or the central edge can be bent and can extend downward.

[0068] The positive tabs 211a, 211b, and 211c can be configured as a single body with the positive current collector 210. That is, a portion of the positive current collector 210 in a plate shape can protrude to form the positive tabs 211a, 211b, and 211c. In a similar manner, the negative tabs 311a, 311b, and 311c can be configured as a single body with the negative current collector 310. That is, a portion of the negative current collector 310 in a plate shape can protrude to form the negative tabs 311a, 311b, and 311c.

[0069] The electrode assembly 100 according to the present embodiment can be configured by combining one of the positive tabs 211a, 211b, and 211c with one of the negative tabs 311a, 311b, and 311c. In detail, for example, the positive tab 211a formed at the upper edge can be combined with the negative tab 311a formed at the lower edge, the positive tab 211b formed at the outer edge can be combined with the negative tab 311b formed at the outer edge, and the positive tab 211c formed at the center edge can be combined with the negative tab 311c formed at the center edge. The positive tab 211b formed at the outer edge can be combined with the negative tab 311c formed at the center edge. There is no particular limitation on the respective combinations, and various types of combinations are possible.

[0070] For example, with reference to Figure 2 The electrode assembly 100 described can exhibit a shape in which the positive tab 211a is formed at the upper edge of the positive current collector and the negative tab 311a is formed at the lower edge of the negative current collector.

[0071] Differently from what is illustrated, as one embodiment in the present embodiment, the positive tab can be formed at the lower edge and can extend downward, and the negative tab can be formed at the upper edge and can extend upward.

[0072] With regard to Figure 1 In the case of the conventional jelly-roll electrode assembly 10, the positive tab 20 and the negative tab 30 are configured as rectangular tabs for winding, and thus the distance through which electrons travel through the positive current collector or the negative current collector increases, and the electron transport resistance increases. For example, in the case of the conventional jelly-roll electrode assembly 10, the positive current collector or the negative current collector can have a thickness of several micrometers to several tens of micrometers, and can have a length of several hundred millimeters to 1 meter. When the electrode tab is positioned at the center of the current collector, the electron must move half the length of the current collector, i.e., several hundred millimeters.

[0073] On the other hand, the electrode assembly 100 according to the present embodiment has an outer shape similar to the cylindrical shape of the conventional jelly-roll electrode assembly 10, and includes a plurality of unit cells 100U forming a radial structure, and the positive tabs 211a, 211b, and 211c and the negative tabs 311a, 311b, and 311c can be formed for each of the unit cells 100U. That is, the electrode assembly 100 forms a new configuration, thereby reducing the distance through which electrons travel through the positive current collector 210 or the negative current collector 310. For example, in the case of the electrode assembly according to the present embodiment, the positive current collector or the negative current collector can have a thickness of several micrometers and a length of about 60 millimeters. Compared to the conventional jelly-roll electrode assembly 10, the path through which electrons travel can be further reduced when forming an electrode assembly having a similar size and shape. Accordingly, the electrode assembly 100 can solve the problem of increased resistance to electron transport of the conventional jelly-roll electrode assembly 10.

[0074] Referring to Figure 3 and Figure 4 The through holes 212 and 312 can be formed in the current collectors 210 and 310 according to the embodiment of the present application, and can be formed in the thickness direction of the current collectors 210 and 310. In detail, ions generally travel between the positive mixture layer 220 and the negative mixture layer 320 with the first diaphragm 400 positioned between the positive mixture layer 220 and the negative mixture layer 320. As described above, the second diaphragm 500 is positioned between the positive current collector 210 and the negative current collector 310, and the through holes 212 and 312 are formed in the positive current collector 210 and the negative current collector 310, respectively, and thus the positive mixture layer 220 and the negative mixture layer 320 can contact the second diaphragm 500 through the through holes 212 and 312. Accordingly, ions can travel between the positive mixture layer 220 and the negative mixture layer 320 with the second diaphragm 500 positioned between the positive mixture layer 220 and the negative mixture layer 320. That is, when the secondary battery is charged and discharged, the transport of ions can be performed in a bidirectional manner due to the second diaphragm 500 and the porous current collectors 210 and 310 in which the through holes 212 and 312 are formed, and thus the performance of the secondary battery can be improved.

[0075] By applying the current collectors 210 and 310 in which the through-holes 212 and 312 are formed to the unit cells 100U, the degree of change in the electrolyte solution concentration or lithium ion concentration in the secondary battery can be reduced, and the performance of the battery can be improved. By applying the current collectors 210 and 310 in which the through-holes 212 and 312 are formed in the thickness direction to the unit cells 100U, the lithium ion concentration in the electrolyte solution can be maintained within a predetermined range. Thus, the overvoltage factor related to the electrolyte solution among the overvoltage factors from the secondary battery can be reduced, and the performance of the battery can be improved.

[0076] According to the embodiment of the present application, the area fraction for forming the through-holes 212 and 312 can be in the range of 10% to 80%. In detail, the area fraction of the formed through-holes 212 and 312 can be in the range of 10% to 80%, 10% to 70%, 10% to 50%, 20% to 90%, 30% to 90%, or 30% to 60%. The area fraction of the formed through-holes 212 and 312 can represent the ratio of the area of the through-holes 212 and 312 to the area of the current collectors 210 and 310.

[0077] According to the embodiment of the present application, 10 to 500 through-holes 212 and 312 can be formed per unit area of 10 cm x 10 cm. In detail, 10 to 300, 10 to 200, 10 to 100, 10 to 70, 30 to 50, 50 to 500, 100 to 200, 50 to 300, 100 to 500, 30 to 200, or 10 to 200 through-holes 212 and 312 can be formed per unit area. For example, the current collectors 210 and 310 can have a mesh form.

[0078] By controlling the number of the through-holes 212 and 312 per unit area or the area fraction thereof within the range, the degree of change in the current collector can be reduced without causing excessive deterioration in mechanical strength, and the degree of change in the electrolyte solution concentration or lithium ion concentration in the secondary battery can be reduced.

[0079] A modified embodiment of the electrode lead combined to the electrode tab according to the present application will now be described with reference to Figure 7 and Figure 8 A modified embodiment of the electrode lead combined to the electrode tab according to the present application will now be described with reference to

[0080] Figure 7 (a) to Figure 7 (c) shows a combined structure of a positive electrode tab and a positive electrode lead according to a modified embodiment of the present application, and Figure 8 (a) to Figure 8 (c) shows a combined structure of a negative electrode tab and a negative electrode lead according to a modified embodiment of the present application.

[0081] A modified embodiment of the electrode lead combined to the electrode tab according to the present application will now be described with reference to Figure 7 (a) toFigure 7 (c), the positive tab 211a, 211b, and 211c can be formed on at least one of the upper edge, the outer edge, and the center edge of the positive current collector 210. In detail, Figure 7 (a) illustrates the positive tab 211a formed at the upper edge of the positive current collector 210, Figure 7 (b) illustrates the positive tab 211b formed at the outer edge of the positive current collector 210, and Figure 7 (c) illustrates the positive tab 211c formed at the center edge of the positive current collector 210. The positive lead 213 can be coupled to the corresponding positive tab 211a, 211b, and 211c. Each of the positive leads 213 can extend upward.

[0082] Referring to Figure 8 (a) to Figure 8 (c), the negative tab 311a, 311b, and 311c can be formed on at least one of the lower edge, the outer edge, and the center edge of the negative current collector 310. In detail, Figure 8 (a) illustrates the negative tab 311a formed at the lower edge of the negative current collector 310, Figure 8 (b) illustrates the negative tab 311b formed at the outer edge of the negative current collector 310, and Figure 8 (c) illustrates the negative tab 311c formed at the center edge of the negative current collector 310. The negative lead 313 can be coupled to the corresponding negative tab 311a, 311b, and 311c. Each of the negative leads 313 can extend downward.

[0083] The electrode assembly according to the present embodiment can be configured with a combination of one of the coupling structures of the positive tabs 211a, 211b, and 211c and the positive lead 213 and one of the coupling structures of the negative tabs 311a, 311b, and 311c and the negative lead 313.

[0084] As one embodiment, the positive lead 213 coupled to the positive tab 211a formed at the upper edge can be combined with the negative lead 313 coupled to the negative tab 311a formed at the lower edge. The electrode assembly of the above configuration is advantageous in that the manufacturing process of the electrode assembly is relatively simple because the positive lead 213 and the negative lead 313 are each positioned on the upper side and the lower side of the electrode assembly 100.

[0085] As another embodiment, the positive electrode lead 213 combined with the positive electrode tab 211b formed at the outer edge can be combined with the negative electrode lead 313 combined with the negative electrode tab 311b formed at the outer edge. The electrode assembly of the above configuration has an advantage in that structural stability against deformation of the electrode is obtained because the electrode leads 213 and 313 hold the electrode assembly at the outer side.

[0086] As another embodiment, the positive electrode lead 213 combined with the positive electrode tab 211b formed at the outer edge can be combined with the negative electrode lead 313 combined with the negative electrode tab 311b formed at the outer edge. The electrode assembly of the above configuration has an advantage in that structural stability against deformation of the electrode, particularly swelling in the outer direction, is obtained because the electrode leads 213 and 313 hold the electrode assembly at the outer side.

[0087] As another example, the positive electrode lead 213 combined with the positive electrode tab 211c formed at the center edge can be combined with the negative electrode lead 313 combined with the negative electrode tab 311c formed at the center edge. The electrode assembly of the above configuration has an advantage in that additional increase in weight is minimized.

[0088] The combination of the positive electrode tabs 211a, 211b, 211c with the positive electrode lead 213 or the combination of the negative electrode tabs 311a, 311b, 311c with the negative electrode lead 313 is not particularly limited, and, for example, welding combination can be performed.

[0089] Figure 9 A disassembled perspective view of a secondary battery according to an embodiment of the present application is shown.

[0090] Referring to Figure 9 , the secondary battery includes an electrode assembly 100 including unit cells forming a radial structure with respect to a center, a battery case 600 for receiving the electrode assembly 100, and a cap assembly 700 positioned on the electrode assembly 100.

[0091] The battery case 600 receives the electrode assembly 100 impregnated with an electrolyte solution, and can have a cylindrical shape.

[0092] The cap assembly 700 can include an upper cap 710 and a safety vent 720. The upper cap 710 is positioned on the safety vent 720 and can be electrically connected to the safety vent 720 since the upper cap 710 is closely attached to the safety vent 720. The center of the upper cap 710 is protruded upward and the upper cap 710 is indirectly connected to the positive electrode 200 of the electrode assembly 100 through the positive electrode tab 211a, and thus the upper cap 710 can serve as a positive electrode terminal through connection with an external circuit.

[0093] A gasket 800 for sealing can be positioned between the battery case 600 and the cap assembly 700. In detail, the gasket 800 can be positioned between the battery case 600 and the cap assembly 700, and the end portion of the battery case 600 is bent, thereby forming a crimping portion. Thereby, the cap assembly 700 can be mounted and the secondary battery can be sealed.

[0094] The electrode tabs 211a and 311a can be directly connected to the cap assembly 700 or the battery case 600. In detail, the positive electrode tab 211a extending upward can be connected to the cap assembly 700 so that the upper cap 710 of the cap assembly 700 can serve as a positive electrode terminal. The negative electrode tab 311a extending downward can be connected to the bottom portion of the battery case 600 so that the bottom portion of the battery case 600 can serve as a negative electrode terminal. The respective electrode tabs 211a and 311a can be connected to the cap assembly 700 or the battery case 600, and in another way, the electrode tabs 211a and 311a can be combined to each other and can be connected to the cap assembly 700 or the battery case 600.

[0095] Although not shown, as a modified embodiment of the present application, the electrode tabs can be combined to the electrode leads and can be connected to the cap assembly 700 or the battery case 600. In detail, the positive electrode lead combined with the positive electrode tab and extending upward can be connected to the cap assembly 700, and the upper cap 710 of the cap assembly 700 can serve as a positive electrode terminal. The negative electrode lead combined with the negative electrode tab and extending downward can be connected to the bottom portion of the battery case 600, and the bottom portion of the battery case 600 can serve as a negative electrode terminal. The respective electrode leads can be connected to the cap assembly 700 or the battery case 600, and in another way, the electrode leads can be combined to each other and can be connected to the cap assembly 700 or the battery case 600.

[0096] Referring to Figure 2Based on the horizontal cross-section, a hollow space penetrating in the vertical direction (or z-axis direction) can be formed at the center of the electrode assembly 100, and the diameter ratio of the inner diameter to the outer diameter can be in the range of 1:1.1 to 1:100. The diameter ratio of the inner diameter to the outer diameter of the electrode assembly 100 is calculated based on the average of the inner diameter and the outer diameter. In a detailed embodiment, the diameter ratio of the inner diameter to the outer diameter of the electrode assembly 100 can be in the range of 1:1.1 to 1:100, 1:1.5 to 1:80, 1:2 to 1:50, 1:10 to 1:100, or 1:30 to 1:100.

[0097] For the unit cell 100U, based on the horizontal cross-section, the ratio (Dout:Din) of the thickness (Din) of the inner end portion forming the inner circumference in the center direction to the thickness (Dout) of the outer end portion forming the outer circumferential surface can be in the range of 1:1.5 to 1:10. In a detailed embodiment, the ratio (Dout:Din) can be in the range of 1:1.1 to 1:100, 1:1.5 to 1:80, 1:2 to 1:50, 1:10 to 1:100, or 1:30 to 1:100.

[0098] As described above, the unit cell 100U has a radial structure whose thickness decreases as it progresses in one direction. This shape is different from a square cell, a pouch cell, or a cylindrical cell. Existing secondary batteries have different external shapes, and unit cells configured to a battery are manufactured to have a uniform total thickness, while having a stacked form or a wound form. In contrast, for the unit cell 100U, based on the horizontal cross-section, the gap between the electrodes 200 and 300 decreases as it progresses from the outside of the radial structure to the center.

[0099] The positive active material can include a lithium-containing oxide. A lithium-containing transition metal oxide can be used as the lithium-containing oxide. In one example, the positive mixture layer 220 can include a conductive material and a binder polymer in addition to the positive active material, and if necessary, the positive mixture layer 220 can also include a positive additive commonly used by those skilled in the art.

[0100] The positive current collector 210 is a metal having high conductivity, and is not particularly limited in terms of material, as long as it is a metal to which the positive active material slurry is easily attached and which is not reactive in the voltage range of the secondary battery. In detail, the positive current collector 210 can be a foil made of aluminum, nickel, or a combination thereof.

[0101] When the carbon material is used as the negative active material, low-crystalline carbon and high-crystalline carbon can be used. Soft carbon and hard carbon are representative of the low-crystalline carbon. The high-crystalline carbon includes high-temperature calcined carbon, such as natural graphite, condensed graphite, pyrolytic carbon, carbon fiber based on mesophase pitch, mesocarbon microbead, mesophase pitch, or coke derived from petroleum or coal tar pitch.

[0102] The negative current collector 310 can be a foil manufactured by using copper, gold, nickel, a copper alloy, or a combination thereof. The negative current collector 310 can stack substances made of these materials and can use these materials.

[0103] The first diaphragm 400 and the second diaphragm 500 can use a porous substance used for a lithium secondary battery, and for example, can use a polyolefin-based porous membrane or use a nonwoven fabric, but are not particularly limited thereto. Examples of the polyolefin-based porous membrane include a membrane made of each of a polyethylene-based and a polyolefin-based polymer, the polyethylene-based being, for example, high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, and the polyolefin-based polymer being, for example, polypropylene, polybutene, or polyamylene, or a mixed polymer thereof.

[0104] The electrode assembly according to another embodiment of the present application can be applied to a solid-state battery. Although not shown in detail, a solid electrolyte layer can be positioned between the positive electrode and the negative electrode instead of the diaphragm. That is, instead of the first diaphragm and the second diaphragm, a solid electrolyte layer filled with a solid electrolyte is disposed at the corresponding positions, and thus an electrode assembly for a solid-state battery can be formed.

[0105] According to the embodiment of the present application, the electrolyte solution can use a non-aqueous electrolyte including a non-aqueous electrolyte. As the non-aqueous electrolyte, for example, a non-protic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, polypropylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used. Without being particularly limited thereto, various electrolyte solution components used in the field of lithium secondary batteries can be increased or decreased within an appropriate range.

[0106] The electrode assembly according to the embodiment will now be described in detail.

[0107] Embodiment 1

[0108] 100 parts by weight of NCM (LiNi 0.8 Co 0.1 Mn 0.1 O2) as a positive active material, 1.5 parts by weight of carbon black (FX35, Denka) as a conductive material, and 2.3 parts by weight of polyvinylidene fluoride (KF9700, Kureha) as a binder polymer were added to a solvent of NMP (N-methyl-2-pyrrolidone) to manufacture a positive mixture layer slurry. The slurry of the positive mixture layer was coated on one side of an aluminum current collector formed with through-holes having a loading amount of 640 mg / 25 cm 2 As for the aluminum current collector, the through-holes were formed with an area fraction of about 40%, and about 50 through-holes were formed per unit area of 10 cm x 10 cm. The positive mixture layer was pressed to sequentially decrease to a thickness level of about 40% in one direction.

[0109] 100 parts by weight of synthetic graphite (GT, Zichen (China)) as a negative active material, 1.1 parts by weight of carbon black (Super-P) as a conductive material, 2.2 parts by weight of butadiene styrene rubber, and 0.7 parts by weight of carboxymethyl cellulose were added to water as a solvent to manufacture a negative active material slurry, and the slurry was coated on one side of a copper current collector formed with through-holes, and the slurry was dried and compressed to thereby manufacture a negative electrode. As for the copper current collector, the through-holes were formed with an area fraction of about 40%, and about 50 through-holes were formed per unit area of 10 cm x 10 cm. The negative mixture layer was pressed so as to sequentially decrease to a thickness level of about 40% in one direction.

[0110] A diaphragm having a melting point of 165°C and a one-side width of 200 mm was used, the diaphragm having a microporous structure formed by uniaxially stretching polypropylene using a dry method. An electrode assembly was manufactured by repeatedly setting a unit cell in which a first diaphragm was disposed between a positive electrode and a negative electrode and a second diaphragm was positioned outside the positive electrode and the negative electrode. The electrode assembly had a structure in which, on the basis of a horizontal cross section, fifty unit cells were set in a radial form with respect to the center.

[0111] The electrode assembly was installed in a cylindrical battery case, and an electrolyte solution of a 1M LiPF6 carbonate-based solution was injected to complete a secondary battery.

[0112] Embodiment 2

[0113] The method of manufacturing a secondary battery was the same as in Embodiment 1, except that the aluminum current collector and the copper current collector used a current collector having a mesh structure.

[0114] Comparative Example 1

[0115] The manufacturing method of the positive electrode and the negative electrode is the same as that of Embodiment 1 except that no thickness through hole is formed in the positive electrode current collector and the negative electrode current collector, respectively, and no thickness gradient is formed in the positive electrode mixture layer and the negative electrode mixture layer.

[0116] Experimental Example 1: Evaluation of Physical Properties of Secondary Battery

[0117] The physical properties of the secondary batteries manufactured according to Embodiment 1 and Comparative Example 1 were evaluated. In detail, each of the secondary batteries was charged and discharged, and the change in voltage and temperature was measured during the charging and discharging, respectively. The secondary batteries were charged and discharged at 20℃ and 1C.

[0118] Figure 10 The evaluation results of the change in voltage when the secondary batteries were charged and discharged were shown, and Figure 11 The evaluation results of the change in temperature when the secondary batteries were charged and discharged were shown.

[0119] Referring to Figure 10 It was found that the discharge voltage of the secondary battery according to Embodiment 1 was higher and the charge voltage was lower than that of Comparative Example 1. It was thus found that the secondary battery according to Embodiment 1 provides higher power when applied to a product and requires less charging power when charged.

[0120] Referring to Figure 11 It was found that the temperature of the secondary battery according to Embodiment 1 was lower and the change in temperature was very small when compared with Comparative Example 1. Thus, the secondary battery according to Embodiment 1 can require lower cooling performance and can be designed in a more compact manner.

[0121] The secondary battery according to Embodiment 1 can be applied to various mobile devices and wearable devices, and is particularly suitable for small devices such as hearable devices or smartwatches, and is particularly suitable for devices that are limited in weight and volume of the secondary battery and require long-time use.

[0122] The secondary battery according to Embodiment 1 can also be used for power tools having excellent output and capable of operating by receiving power from a battery-based motor, and is suitable for: electric vehicles including drones, electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheelers including electric bicycles and electric scooters; transportation means using high-power electric power such as electric golf carts; and electric power storage systems.

[0123] In the present embodiment, terms indicating directions such as front, rear, right, left, top, and bottom are used, but these terms are for convenience of explanation and are variable depending on the position of the target material or the position of the observer.

[0124] While the present application has been described in connection with the embodiments currently considered to be the most practical and preferred, it is to be understood that this application is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0125] Reference Signs

[0126] 100: electrode assembly

[0127] 100U: unit cell

[0128] 200: positive electrode

[0129] 210: positive electrode current collector

[0130] 211a, 211b, 211c: positive electrode tab

[0131] 300: negative electrode

[0132] 310: negative electrode current collector

[0133] 311a, 311b, 311c: negative electrode tab

Claims

1. An electrode assembly, comprising: Multiple cell units, wherein the multiple cell units are configured to form a radial structure about a center, Specifically, based on the horizontal cross-section, the thickness of the cell decreases as it travels from the outer side of the radial structure towards the center. Electrode contacts are formed on at least one of the upper edge, lower edge, outer edge, and center edge of the current collector included in the cell. The unit cell includes a positive electrode, a first separator, a negative electrode, and a second separator stacked sequentially. The positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The thickness of at least one of the positive electrode mixture layer and the negative electrode mixture layer decreases as it travels from the outer side of the radial structure toward the center, and The density of at least one of the positive electrode mixture layer and the negative electrode mixture layer increases as it travels from the outer side of the radial structure toward the center, thereby compensating for capacity non-uniformity caused by the thickness alignment of the cell.

2. The electrode assembly according to claim 1, wherein, A positive electrode contact is formed on at least one of the upper edge, outer edge, and central edge of the positive current collector.

3. The electrode assembly according to claim 1, wherein, A negative electrode contact is formed on at least one of the lower edge, outer edge, and center edge of the negative electrode current collector.

4. The electrode assembly according to claim 1, wherein, The positive current collector, the positive electrode mixture layer, the first separator, the negative electrode mixture layer, the negative current collector, and the second separator are stacked sequentially.

5. The electrode assembly according to claim 1, wherein, A through hole is formed in the current collector.

6. The electrode assembly according to claim 1, further comprising: Electrode leads, which are connected to the electrode contacts.

7. A secondary battery, comprising: The electrode assembly according to any one of claims 1 to 6; A battery case for receiving the electrode assembly; as well as A cover assembly, the cover assembly being disposed on the electrode assembly, The electrode tabs are coupled to the electrode leads and connected to the cover assembly or the battery box.

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