Electrode assembly and battery cell including the same

Abstract

The present invention includes an electrode assembly and a battery cell including the same, and the electrode assembly according to one embodiment of the present invention includes a plurality of unit cells, each including a negative electrode, a positive electrode, and a separator, stacked together and including a separator located between the plurality of unit cells, and includes a first unit cell in which one end of the negative electrode protrudes beyond one end of the positive electrode; and a second unit cell in which one end of the positive electrode protrudes beyond one end of the negative electrode.

Description

[Technical Field]

[0001] Cross-reference to related application(s) This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0050981 filed on April 25, 2022 and Korean Patent Application No. 10-2023-0022115 filed on February 20, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly and a battery cell including the same, and more particularly to an electrode assembly and a battery cell including the same that can ensure the stability of a battery cell by generating a short circuit under an overvoltage condition. [Background technology]

[0003] As technological development and demand for mobile devices increases, the demand for secondary batteries as an energy source is rapidly increasing. Therefore, much research is being conducted on secondary batteries that can meet various requirements.

[0004] Secondary batteries have attracted much attention as energy sources for power plants such as electric bicycles, electric vehicles, and hybrid electric vehicles, as well as for mobile devices such as mobile phones, digital cameras, and laptop computers.

[0005] Recently, as the need for large-capacity secondary battery structures has increased, including the use of secondary batteries as energy storage sources, there has been an increasing demand for battery packs with medium to large modular structures that assemble battery modules in which multiple secondary batteries are connected in series / parallel.

[0006] Currently, commercially available secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Among these, lithium secondary batteries are attracting the most attention due to their advantages of being freely chargeable and dischargeable, having a low self-discharge rate, and having a high energy density.

[0007] Secondary batteries are classified according to the shape of the battery case into cylindrical batteries and prismatic batteries, in which the electrode assembly is housed in a cylindrical or prismatic metal can, and pouch batteries, in which the electrode assembly is housed in a pouch-shaped case made of an aluminum laminate sheet.

[0008] Secondary batteries are also classified according to the structure of the electrode assembly, which is a stacked structure consisting of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. Representative examples include a jelly-roll (wound) electrode assembly, in which long sheet-shaped positive and negative electrodes are wound with a separator interposed between them, and a stack (layered) electrode assembly, in which multiple positive and negative electrodes cut to a predetermined size are stacked in sequence with a separator interposed between them. Recently, to address the issues associated with the jelly-roll and stacked electrode assemblies, a stack / folding electrode assembly, which is a hybrid of the jelly-roll and stacked types, has been developed.

[0009] FIG. 1 is a side view of a conventional electrode assembly.

[0010] Referring to FIG. 1, the electrode assembly is a stacked electrode assembly, and is mainly formed by stacking an anode 11, a first separator 13, and a cathode 12, or by stacking unit cells, each having a cathode 12, a first separator 13, and an anode 11 stacked in sequence, with a second separator 30 interposed therebetween.

[0011] Typically, the first separator 13 is formed to be longer than the positive electrode 12 or the negative electrode 11, so that the end of the first separator 13 in the electrode assembly is not bonded to the positive electrode 12 or the negative electrode 11. Here, the first separator 13 and the second separator 30 have substantially the same structure.

[0012] In addition, one end of the negative electrode 11 typically protrudes beyond one end of the positive electrode 12. In a unit cell having such a structure, in an overvoltage state where the battery's operating range is 4.5 V or higher, problems such as additional decomposition of the electrolyte and oxygen desorption from the positive electrode increase the possibility of the battery exploding. Therefore, a technology is needed to short-circuit the battery and prevent a sudden rise in voltage when the battery is overcharged. Summary of the Invention [Problem to be solved by the invention]

[0013] An object of the present invention is to provide an electrode assembly and a battery cell including the same, which have improved safety.

[0014] However, the problems to be solved by the embodiments of the present invention are not limited to the above problems, and can be variously expanded within the scope of the technical ideas included in the present invention. [Means for solving the problem]

[0015] According to one embodiment of the present invention, an electrode assembly including a plurality of stacked unit cells, each including a negative electrode, a positive electrode, and a separator, and a separator disposed between the unit cells, includes a first unit cell in which an end of the negative electrode protrudes beyond an end of the positive electrode; and a second unit cell in which an end of the positive electrode protrudes beyond an end of the negative electrode.

[0016] The second unit cell may include a second negative electrode, a second positive electrode, and a second separator located between the second negative electrode and the second positive electrode, wherein an end of the second positive electrode protrudes beyond an end of the second negative electrode, and the length of the second positive electrode is longer than the length of the second negative electrode.

[0017] The difference between the length of the second negative electrode and the length of the second positive electrode may be less than 1%.

[0018] The difference between the length of the second negative electrode and the length of the second positive electrode may be 0.4% or less.

[0019] The distance between the end of the second negative electrode and the end of the second separator may be longer than the distance between the second positive electrode and the end of the second separator.

[0020] The second unit cell may have lithium deposited at a lower potential than the first unit cell.

[0021] The second unit cell may deposit lithium when a voltage applied to the second unit cell is 4.5V or more and 5.5V or less.

[0022] The second unit cell may have a positive electrode whose capacity expression is greater than a negative electrode whose capacity expression is greater than a negative electrode whose capacity expression is greater.

[0023] The first unit cell may be at least one.

[0024] The second unit cell may be disposed adjacent to the outermost first unit cell.

[0025] The second unit cell may be the outermost unit cell.

[0026] The second unit cells may be located between the plurality of first unit cells.

[0027] As the number of the second unit cells increases, the maximum voltage during overcharging of the battery may decrease.

[0028] A battery cell according to another embodiment of the present invention includes the above-described electrode assembly. [Effects of the Invention]

[0029] According to the embodiment, the difference in length between one end of the negative electrode and one end of the positive electrode can be used to improve the safety of the electrode assembly and the battery cell including the electrode assembly.

[0030] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a side view of a conventional electrode assembly. [Figure 2] FIG. 2 is a side view of an electrode assembly according to an embodiment of the present invention. [Figure 3] 1A is a perspective view of a first unit cell constituting an electrode assembly according to an embodiment of the present invention, and FIG. 1B is a perspective view of a second unit cell constituting an electrode assembly according to an embodiment of the present invention. [Figure 4] FIG. 4 is a perspective view showing a second unit cell in an overcharged state according to an embodiment of the present invention. [Figure 5] 1 is a side view of a unit cell constituting an electrode assembly according to an embodiment of the present invention; [Figure 6] 1 is a graph showing the voltage applied to a battery when the battery is overcharged. [Figure 7] 1 is a photograph showing a conventional unit cell in an overcharged state. [Figure 8] 1 is a photograph of a unit cell according to an embodiment of the present invention in an overcharged state. DETAILED DESCRIPTION OF THE INVENTION

[0032] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may be embodied in various different forms and is not limited to the embodiments set forth herein.

[0033] In order to clearly explain the present invention, parts unnecessary for the explanation are omitted, and the same reference numerals are used throughout the specification to refer to the same or similar components.

[0034] Furthermore, the size and thickness of each component shown in the drawings are arbitrarily shown for the convenience of explanation, and the present invention is not necessarily limited to those shown in the drawings. In the drawings, thicknesses are exaggerated to clearly show multiple layers and regions. In the drawings, thicknesses of some layers and regions are exaggerated for the convenience of explanation.

[0035] Furthermore, when a layer, film, region, plate, or other part is said to be "on" another part, this does not only mean that it is "directly on" that other part, but also includes cases where there are other parts in between. Conversely, when a part is said to be "directly on" another part, it means that there are no other parts in between. Furthermore, being "on" a reference part means being located above or below the reference part, and does not necessarily mean being "on" in the opposite direction of gravity.

[0036] Furthermore, throughout the specification, when a part is said to "comprise" a certain element, this does not mean that it excludes other elements and may further include other elements, unless specifically stated to the contrary.

[0037] Also, throughout the specification, "on a plane" means when the subject part is viewed from above, and "on a cross section" means when the subject part is cut vertically and viewed from the side.

[0038] Fig. 2 is a side view of an electrode assembly according to an embodiment of the present invention. Fig. 3(a) is a perspective view of a first unit cell constituting an electrode assembly according to an embodiment of the present invention. Fig. 3(b) is a perspective view of a second unit cell constituting an electrode assembly according to an embodiment of the present invention.

[0039] 2, the electrode assembly 1000 is a stacked electrode assembly and includes a first unit cell 100, a second unit cell 200, and a third separator 300. The electrode assembly 1000 in FIG. 2 is a schematic view of a region when the center of the electrode assembly 1000 is cut in the z-axis direction.

[0040] 2 and 3(a), the first unit cell 100 has a structure in which a first positive electrode 120, a first separator 130, and a first negative electrode 110 are stacked. Specifically, the first unit cell 100 has a structure in which an end of the first negative electrode 110 protrudes beyond an end of the first positive electrode 120. That is, the length of the first negative electrode 110 of the first unit cell 100 may be longer than the length of the first positive electrode 120. However, the lengths of the first negative electrode 110 and the first positive electrode 120 may be shorter than the length of the first separator 130. Therefore, the end of the first separator 130 is not bonded to the first negative electrode 110 or the first positive electrode 120.

[0041] 2 and 3(b), the second unit cell 200 has a structure in which a second positive electrode 220, a second separator 230, and a second negative electrode 210 are stacked. More specifically, the second unit cell 200 has a structure in which an end of the second positive electrode 220 protrudes beyond an end of the second negative electrode 210. That is, the length of the second positive electrode 220 of the second unit cell 200 may be longer than the length of the second negative electrode 210. In this case, the difference between the lengths of the second negative electrode 210 and the second positive electrode 220 may be less than 1%.

[0042] However, the length of the second negative electrode 210 and the second positive electrode 220 may be shorter than the length of the second separation membrane 230. Therefore, the end of the second separation membrane 230 is not bonded to the second negative electrode 210 or the second positive electrode 220.

[0043] In this case, since the length of the second negative electrode 210 is shorter than the length of the second positive electrode 220, the distance between the end of the second negative electrode 210 and the end of the second separator 230 may be longer than the distance between the end of the second positive electrode 220 and the end of the second separator 230.

[0044] Referring to FIG. 2, the third separator 300 is stacked between the first unit cell 100 and the second unit cell 200, and is in contact with one side of the outermost first unit cell 100 and the outermost second unit cell 200.

[0045] That is, the third separator 300 is located between the first unit cell 100 and the second unit cell 200 and serves to insulate the first unit cell 100 from the second unit cell 200. The third separator 300 may perform the same function as the first separator 130 of the first unit cell 100 and the second separator 230 of the second unit cell 200 and may be made of the same material.

[0046] 2, the electrode assembly 1000 according to an embodiment of the present invention may include one or more first unit cells 100 and one or more second unit cells 200. That is, the total number of the first unit cells 100 and the second unit cells 200 may be two or more.

[0047] For example, the total number of first unit cells 100 and second unit cells 200 constituting the electrode assembly 1000 may be 20, specifically, 19 first unit cells 100 and 1 second unit cell 200. In this case, when a plurality of first unit cells 100 are stacked to form a stack, the second unit cell 200 may be provided adjacent to the first unit cell 100 located outermost in the stacking direction of the stack. In other words, the second unit cell 200 may be the outermost unit cell of the stack.

[0048] However, the electrode assembly 1000 is not limited to the above structure. Furthermore, the number of first unit cells 100 and second unit cells 200 is not limited to the above and can be freely changed by the user. For example, second unit cells 200 may be positioned on both outermost sides of a stack of a plurality of first unit cells 100, or at least one second unit cell 200 may be positioned between the first unit cells 100 to form the electrode assembly 1000. In other words, the number of second unit cells 200 may be at least one. In this case, as the number of second unit cells 200 increases, the maximum voltage of the battery during overcharge may decrease.

[0049] FIG. 4 is a perspective view showing a second unit cell in an overcharged state according to an embodiment of the present invention.

[0050] Referring to FIG. 4, when an overvoltage is applied to the battery and the battery is overcharged, the second unit cell 200 according to an embodiment of the present invention deposits lithium (Li), causing a short circuit in the battery.

[0051] Normally, the operating range of a lithium secondary battery does not exceed 4.5V. However, issues can arise where the battery is overcharged to a voltage above 4.5V due to malfunction of the charger or BMS (Battery Management System).

[0052] When the battery is overcharged, the end of the second positive electrode 220 of the second unit cell 200 protrudes further than the end of the second negative electrode 210, and therefore the second negative electrode 210 is more overcharged than the second positive electrode 220, making it more likely that lithium deposition will occur.

[0053] More specifically, the reason why lithium deposition occurs in the second anode 210 of the second unit cell 200 is as follows: If the end of the second cathode 220 protrudes beyond the end of the second anode 210, the capacity of the locally protruding second cathode 220 will be greater than the capacity of the second anode 210. In this case, excess lithium ions that are not inserted into the second anode 210 during charge will be generated in the form of lithium deposition.

[0054] That is, when the same voltage is applied to the first unit cell 100 and the second unit cell 200, lithium is not deposited in the first unit cell 100, but lithium 211 may be deposited in the second unit cell 200. In this case, lithium 211 deposited in the second unit cell 200 may cause a short circuit in the battery, preventing a voltage increase and improving the stability of the battery.

[0055] That is, in the electrode assembly according to an embodiment of the present invention including the second unit cell 200, deposition of lithium 211 occurs at a lower potential than in a conventional electrode assembly including only the first unit cell 100. Such deposition of lithium 211 causes a short circuit in the negative electrode, which prevents the voltage of the battery from increasing, thereby improving the stability of the battery.

[0056] FIG. 5 is a side view of a unit cell constituting an electrode assembly according to an embodiment of the present invention.

[0057] 5, the second negative electrode 210, the second positive electrode 220, and the second separator 230 constituting the second unit cell 200 described in FIGS. 2 to 4 will be described in detail. The first unit cell 100 is identical to the second unit cell 200 except for the length of the positive and negative electrodes. Therefore, the second unit cell 200 will be mainly described here.

[0058] 5, the second anode 210 is formed by coating an anode current collector 211 with an anode coating layer 212. The anode current collector 211 is generally made of copper (Cu), and the anode coating layer 212 is located on one side and the other side of the anode current collector 211. The anode coating layer 212 is formed by mixing an anode active material, a conductive agent, and a binder and coating the anode current collector 211 with the anode coating layer 212.

[0059] The second positive electrode 220 is formed by coating a positive electrode coating layer 222 on a positive electrode current collector 221. The positive electrode current collector 221 is generally made of aluminum (Al), and the positive electrode coating layer 222 is located on one side and the other side of the positive electrode current collector 221. The positive electrode coating layer 222 is formed by mixing a positive electrode active material, a conductive agent, and a binder and coating the positive electrode current collector 221 with the positive electrode coating layer 222.

[0060] The second separator 230 is positioned between the second anode 210 and the second cathode 220. Specifically, the second separator is positioned between the anode coating layer 212 of the second anode 210 and the cathode coating layer 222 of the second cathode 220. If the anode coating layer 212 and the cathode coating layer 222 of the second anode 210 come into contact with each other, a short circuit of the battery will occur, and to prevent this, the second separator 230 is positioned therebetween.

[0061] [Table 1]

[0062] Figure 6 is a graph showing the voltage applied to the battery when it is overcharged. Table 1 shows the maximum voltages applied to the comparative example and experimental example when it is overcharged.

[0063] The comparative example is a battery including the conventional electrode assembly of Figure 1, and the experimental example is a battery including an electrode assembly 1000 including a first unit cell 100 and a second unit cell 200 of Figures 2 and 3. In particular, the experimental example may be an electrode assembly 1000 including a second unit cell 200 located at the outermost position of a stack of first unit cells 100, in which the difference in length between the second anode 210 and the second cathode 220 constituting the second unit cell 200 is 0.4%.

[0064] Referring to FIG. 6 and Table 1, it can be seen that when the battery is overcharged, the maximum voltage applied to the battery is lower in the experimental example, which is the battery according to one embodiment of the present invention.

[0065] Specifically, the experiment measured the maximum voltage at which a short circuit occurs when the current is applied to the battery up to 8V at a charging rate of 1C.

[0066] In the comparative example, the voltage rose to 6.243V during overcharging, after which a short circuit occurred and the voltage dropped again. In contrast, in the experimental example, the voltage rose to 5.369V during overcharging, after which a short circuit occurred and the voltage dropped again. Specifically, a short circuit may occur when the voltage applied to the experimental example is between 4.5V and 5.5V. Referring to the experimental results, it can be seen that the maximum voltage of the experimental example is about 1V lower than the maximum voltage of the comparative example.

[0067] Therefore, under the same experimental conditions, the experimental example according to one embodiment of the present invention exhibited a smaller voltage increase and a smaller maximum voltage than the comparative example, and therefore was superior in terms of battery stability.

[0068] Figure 7 is a photograph showing a conventional unit cell in an overcharged state, and Figure 8 is a photograph showing a unit cell according to an embodiment of the present invention in an overcharged state.

[0069] The conventional unit cell may be the first unit cell in FIGS. 2 and 3, and the unit cell according to one embodiment of the present invention may be the second unit cell in FIGS.

[0070] 7 and 8, under the same overcharge condition, lithium is not deposited in the first unit cell, but lithium is deposited in the second unit cell. That is, lithium is deposited in the battery cell including the second unit cell at the same potential as in the battery cell including only the first unit cell. Also, lithium is more easily deposited in the battery cell including the second unit cell at a lower potential than in the battery cell including only the first unit cell. Specifically, lithium may be deposited in the second unit cell when the voltage applied to the second unit cell is between 4.5V and 5.5V.

[0071] A battery cell including a unit cell according to an embodiment of the present invention has improved stability compared to conventional battery cells because lithium is deposited above a certain voltage, thereby suppressing a voltage rise.

[0072] The electrode assembly and the battery cell including the electrode assembly may be applied to a battery module, a battery pack, and various devices. Such devices may be applied to transportation means such as electric bicycles, electric vehicles, and hybrid vehicles, but the present invention is not limited thereto. The present invention may be applied to various devices that can use a battery module and a battery pack including the same, and these are also within the scope of the present invention.

[0073] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0074] 1000: Electrode assembly 100: First unit cell 110: First negative electrode 120: First positive electrode 130:First separation membrane 200: Second unit cell 210: Second negative electrode 220: Second positive electrode 230:Second separation membrane 300:Third separation membrane

Claims

1. An electrode assembly including a plurality of stacked unit cells, each including a negative electrode, a positive electrode, and a separator, and a separator positioned between the unit cells, a first unit cell in which an end of the negative electrode protrudes beyond an end of the positive electrode; and a second unit cell in which an end of the positive electrode protrudes beyond an end of the negative electrode; Including, The electrode assembly, wherein lithium is deposited in the second unit cell at a lower potential than in the first unit cell.

2. the second unit cell includes a second negative electrode, a second positive electrode, and a second separator disposed between the second negative electrode and the second positive electrode; an end of the second positive electrode protrudes beyond an end of the second negative electrode; The electrode assembly according to claim 1 , wherein the second positive electrode has a length greater than the length of the second negative electrode.

3. The electrode assembly according to claim 2 , wherein the difference between the length of the second negative electrode and the length of the second positive electrode is less than 1%.

4. The electrode assembly of claim 2 , wherein a difference between the length of the second negative electrode and the length of the second positive electrode is 0.4% or less.

5. The electrode assembly of claim 2 , wherein a distance between an end of the second negative electrode and an end of the second separator is longer than a distance between the second positive electrode and an end of the second separator.

6. The electrode assembly of claim 1 , wherein lithium is deposited in the second unit cell when a voltage applied to the second unit cell is 4.5V or more and 5.5V or less.

7. The electrode assembly according to claim 1 , wherein the second unit cell has a positive electrode whose capacity is greater than a negative electrode whose capacity is greater than a negative electrode whose capacity is greater than a positive electrode whose capacity is greater than a negative electrode whose capacity is greater than a negative electrode whose capacity is greater than a negative electrode.

8. The electrode assembly of claim 1 , wherein the number of the first unit cells is at least one.

9. 9. The electrode assembly of claim 8, wherein when a plurality of the first unit cells are stacked to form a stack, the second unit cell is adjacent to the first unit cell located at an outermost position in a stacking direction of the stack.

10. The electrode assembly of claim 9 , wherein the second unit cell is an outermost unit cell.

11. The electrode assembly of claim 8 , wherein the second unit cell is located between a plurality of the first unit cells.

12. The electrode assembly of claim 1 , wherein the maximum voltage of the battery during overcharge decreases as the number of the second unit cells increases.

13. A battery cell comprising the electrode assembly according to any one of claims 1 to 12.

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