Title of the invention: Electrode assembly and secondary battery including the same
Technical field
[One]
Cross-reference with related application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0152916 filed on November 30, 2018, and all contents disclosed in the documents of the Korean patent application are included as part of this specification.
[3]
The present invention relates to an electrode assembly and a secondary battery including the same, and more particularly, to an electrode assembly including an electrode tab and a secondary battery including the same.
Background
[4]
In recent years, as the demand for portable electronic products such as laptops, video cameras, portable telephones, etc. is rapidly increasing, and development of electric vehicles, energy storage batteries, robots, satellites, etc., There is a lot of research on it.
[5]
Examples of such secondary batteries include nickel cadmium batteries, nickel hydride batteries, nickel zinc batteries, and lithium secondary batteries. Among these, lithium secondary batteries are widely used in the field of advanced electronic devices because of the advantages of free charging and discharging, a very low self-discharge rate, a high operating voltage, and a high energy density per unit weight, as they have little memory effect than nickel-based secondary batteries have.
[6]
In general, a lithium secondary battery has a structure in which an electrode assembly composed of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is stacked or wound, and is embedded in a case of a metal can or laminate sheet, and an electrolyte is injected or impregnated therein. It is composed by being.
[7]
Electrode assemblies having a positive electrode/separator/cathode structure constituting a secondary battery are largely divided into a jelly-roll type (winding type) and a stack type (stack type) according to their structure. The jelly-roll type is a structure in which a separator is wound between a long sheet-shaped positive electrode and a negative electrode coated with an active material, and the stack type is a structure in which a plurality of positive and negative electrodes of a predetermined size are sequentially stacked with the separator interposed therebetween. Among them, the jelly-roll type electrode assembly is easy to manufacture and has the advantage of high energy density per weight.
[8]
In a secondary battery equipped with such an electrode assembly, if a large current flows within a short time due to high rate discharge, overcharging, external short circuit, etc., the electrode tab, especially the negative electrode tab, causes the separator to shrink due to heat generation, and the electrode active material and the separator are half As they become molten, damage such as pressing together may occur. In addition, an internal short circuit may occur due to damage to the separator, resulting in heat generation or explosion of the battery.
[9]
In particular, in order to implement a high-power and high-capacity model in recent years, components used are becoming thinner, and as a result, secondary batteries with low resistance and high capacity are increasing. However, as the resistance decreases and the capacity increases, a higher current is applied for a longer period of time, so that the problem of heat generation of the electrode tab due to an external short circuit has emerged as a more important task.
[10]
In order to overcome this problem, research on a secondary battery capable of effectively controlling heat generation of an electrode tab is required.
Detailed description of the invention
Technical challenge
[11]
The problem to be solved by the embodiments of the present invention is to solve the above problems, and to provide an electrode assembly for a secondary battery capable of effectively controlling heat generation of an electrode tab in situations such as an external short circuit or high rate discharge.
Means of solving the task
[12]
In a jelly-roll type electrode assembly in which a negative electrode sheet, a positive electrode sheet, and a separator interposed between the negative electrode sheet and the positive electrode sheet are wound together, the electrode assembly according to an embodiment of the present invention is attached to the negative electrode sheet or the positive electrode sheet. One or more electrode tabs having at least a portion extending outward; And a heat dissipation tape adhered to the electrode tab, wherein the electrode tab to which the heat dissipation tape is adhered is positioned between or on an outer circumferential surface of the wound electrode assembly, and the heat dissipation tape includes a heat diffusion layer And, the heat diffusion layer includes at least one of graphite and metal foil.
[13]
The graphite may include at least one of natural graphite and artificial graphite.
[14]
The metal foil may include at least one of Cu and Al.
[15]
The adhesion area of ​​the heat dissipation tape may be larger than the adhesion area of ​​the electrode tab.
[16]
The area corresponding to the adhesive area of ​​the heat dissipation tape may include an area corresponding to the attachment area of ​​the electrode tab.
[17]
The heat dissipation tape further includes an adhesive layer, and the adhesive layer may be positioned between the electrode tab and the heat diffusion layer, and between the negative electrode sheet or the positive electrode sheet and the heat diffusion layer.
[18]
The heat dissipation tape further includes an adhesive layer, the adhesive layer is positioned between the negative electrode sheet or the positive electrode sheet and the heat diffusion layer, and at least a portion of the electrode tab may contact the heat diffusion layer.
[19]
The thickness of the heat diffusion layer may be 17 μm to 1 mm.
[20]
The heat dissipation tape may further include an adhesive layer and a base layer, and the heat diffusion layer may be positioned between the adhesive layer and the base layer.
[21]
The base layer may include at least one of polyimide and polyethylene terephthalate.
[22]
The thickness of the adhesive layer may be 5 μm to 25 μm, and the thickness of the base layer may be 5 μm to 25 μm.
Effects of the Invention
[23]
According to embodiments of the present invention, heat generated in the electrode tab is rapidly diffused and discharged to the periphery through a heat dissipation tape attached to the electrode tab, such as an external short circuit, thereby preventing damage to the separator or an internal short circuit.
Brief description of the drawing
[24]
1 is a perspective view of an electrode assembly according to an embodiment of the present invention.
[25]
FIG. 2 is an exploded perspective view before the electrode assembly of FIG. 1 is wound.
[26]
3 and 4 are enlarged plan views of a negative electrode tab among electrode tabs according to an exemplary embodiment of the present invention.
[27]
5 is a front view as viewed from the direction C of FIG. 4.
[28]
6 is an enlarged plan view of a negative electrode tab among electrode tabs according to an embodiment of the present invention.
[29]
7 is a front view as viewed from the direction D of FIG. 6.
[30]
8 is an experiment result of comparing the temperature gradient between an electrode tab to which a heat dissipating tape including a heat diffusion layer is adhered and an electrode tab to which a tape not including a heat diffusion layer is adhered according to an embodiment of the present invention.
Mode for carrying out the invention
[31]
Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.
[32]
In order to clearly describe the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.
[33]
In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of description, and the present invention is not necessarily limited to the illustrated bar. In the drawings, the thicknesses are enlarged in order to clearly express various layers and regions. And in the drawings, for convenience of description, the thickness of some layers and regions is exaggerated.
[34]
In addition, when a part such as a layer, film, region, plate, etc. is said to be "on" or "on" another part, this includes not only "directly above" another part, but also a case where another part is in the middle. . Conversely, when one part is "right above" another part, it means that there is no other part in the middle. In addition, to be "above" or "on" the reference part means that it is located above or below the reference part, and means that it is located "above" or "on" in the direction opposite to gravity. no.
[35]
In addition, throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.
[36]
In addition, throughout the specification, the term "on a plane" means when the object portion is viewed from above, and when the object portion is viewed from above, it means when the object portion is viewed from the side.
[37]
1 is a perspective view of an electrode assembly according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view showing a state before the electrode assembly of FIG. 1 is wound for convenience of description.
[38]
1 and 2, the electrode assembly 100 according to an embodiment of the present invention is interposed between the negative electrode sheet 110, the positive electrode sheet 120, and the negative electrode sheet 110 and the positive electrode sheet 120. The separator 130 is wound together, and is attached to the negative electrode sheet 110 or the positive electrode sheet 120, and at least a portion of the electrode tabs 140 and 160 and the electrode tabs 140 and 160 extending outwardly Including a heat dissipation tape 170 to be adhered, the electrode tabs 140 and 160 to which the heat dissipation tape 170 is adhered are located between the center and the outer circumferential surface of the wound electrode assembly 100, and the heat dissipation tape 170 is It includes a diffusion layer. The heat diffusion layer includes at least one of graphite and metal foil. The heat diffusion layer will be described later. Meanwhile, although not shown, the electrode tab may be located on the outer peripheral surface of the wound electrode assembly.
[39]
The electrode assembly 100 is sealed and accommodated with an electrolyte in a case (not shown) to be manufactured as a secondary battery.
[40]
The electrode tabs 140 and 160 include a negative electrode tab 140 attached to the negative electrode sheet 110 and a positive electrode tab 160 attached to the positive electrode sheet 120. The negative electrode sheet 110 may have a negative electrode active material formed on its surface, and the negative electrode tab 140 may be attached to the negative electrode uncoated portion 115 on which the negative electrode active material is not formed on the surface of the negative electrode sheet 110. The positive electrode sheet 120 may have a positive electrode active material formed on its surface, and the positive electrode tab 160 may be attached to the positive electrode uncoated portion 125 on which the positive electrode active material is not formed on the surface of the positive electrode sheet 120.
[41]
Since the configuration of the positive electrode sheet 120 and the configuration of the negative electrode sheet 110 are the same or similar to each other, the following description will be made based on the negative electrode sheet 110 among the electrodes in FIGS. 3 to 7.
[42]
3 is an enlarged plan view of a negative electrode tab among electrode tabs according to an embodiment of the present invention. Among the electrode tabs, the negative electrode tab 140 is attached to the negative electrode sheet 110, and at least a portion thereof extends to the outside. The attachment method between the cathode tab 140 and the anode sheet 110 is not limited as long as electrical connection is possible with each other, but ultrasonic welding or resistance welding may be performed.
[43]
A heat radiation tape 170 is adhered to the negative electrode tab 140, and the heat radiation tape includes a heat diffusion layer.
[44]
In the secondary battery of the high-power and high-capacity model, when a large current flows within a short time due to high rate discharge, overcharge, external short-circuit, etc., a lot of heat is generated in the electrode tab, particularly the negative electrode tab 140 due to current concentration. In the secondary battery, charging or discharging occurs continuously and repeatedly due to an internal electrochemical reaction, and thus, when the secondary battery becomes high in capacity, heat generated by charging and discharging increases dramatically. Due to the heat generated by the negative electrode tab 140, the separator 130 may shrink, and the electrode active material of the negative electrode sheet 110 and the positive electrode sheet 120 and the separator 130 become semi-melted, causing damage to be pressed together. Can happen. In addition, due to damage to the separator 130, an internal short circuit may occur, resulting in heat generation of the secondary battery.
[45]
The heat dissipation tape 170 is to effectively eliminate heat generation at the electrode tab due to such current concentration, and includes a heat diffusion layer having excellent heat conduction properties, and is attached to the electrode tab to be locally within the electrode tab. The generated heat can be rapidly diffused and released around the environment. Through this, it is possible to prevent the separation membrane 130 from being damaged and causing an internal short circuit.
[46]
In the case of the negative electrode tab 140, which is a portion having a particularly high resistance among internal components of the secondary battery, the heat generation is greatest. Therefore, the heating problem of the electrode tab needs to be more importantly controlled in the negative electrode tab 140, but it is not necessarily limited to the negative electrode tab 140, and even in the case of the positive electrode tab 160, the heating phenomenon may still be a problem. I can. Accordingly, the heat dissipation tape may be adhered to at least one of the negative electrode tab 140 attached to the negative electrode sheet 110 and the positive electrode tab 160 attached to the positive electrode sheet 120.
[47]
Referring again to FIG. 3, the adhesion area A of the heat dissipation tape 170 is larger than the adhesion area B of the negative electrode tab 140. Specifically, since the adhesion area (A) to which the heat dissipation tape 170 is adhered is larger than the adhesion area (B) in which the negative electrode tab 140 is attached to the negative electrode sheet 110, the heat radiation tape 170 is a negative electrode tab ( 140), as well as the negative electrode sheet 110, in particular, the negative electrode uncoated portion 115 is also bonded. The adhesive area (A) of the heat dissipation tape 170 may vary depending on the size of the battery, but the length of the adhesive area (A) in the height direction is preferably 0.5 times or more of the length in the height direction of the negative electrode sheet parallel thereto. , It is preferable that the length of the adhesive area (A) in the width direction is 5mm to 50mm. If the length of the bonding area A in the width direction is less than 5 mm, heat generated locally in the negative electrode tab 140 cannot be effectively diffused and discharged. On the other hand, if the length of the adhesive area (A) in the width direction exceeds 50 mm, the outer diameter of the wound electrode assembly 100 increases due to the heat dissipation tape 170 more than necessary in a limited space in the secondary battery, thereby limiting the amount of active material. This may cause a decrease in capacity of the secondary battery, and may interfere with winding of the electrode assembly 100.
[48]
On the other hand, the length in the width direction of the adhesive area of ​​the heat dissipating tape 170 in the positive electrode tab 160 is preferably 5mm to 30mm. If it is less than 5 mm, heat generated locally in the positive electrode tab 160 cannot be effectively diffused and discharged. On the other hand, the heat dissipation tape 170 in the positive electrode tab 160 preferably covers all of the positive electrode uncoated part 125 for stable attachment of the positive electrode tab 160, but it is possible to reduce the capacity of the secondary battery. In consideration of the area of ​​the part 125, it is preferable that the length of the bonding area in the width direction is 30 mm or less.
[49]
In addition, the area corresponding to the adhesion area A of the heat dissipation tape 170 may include an area corresponding to the attachment area B of the negative electrode tab 140. That is, at least a portion of the negative electrode tab 140 extends to the outside, and the other part is attached to the negative electrode sheet 110 and covered by the heat radiation tape 170. Since the area corresponding to the adhesion area to which the negative electrode tab 140 is attached is included in the area corresponding to the adhesion area of ​​the heat dissipation tape 170, the heat generated from the negative electrode tab 140 can be effectively diffused to reduce the temperature of the heating area. In addition, damage such as tearing or penetrating the separator by the edge of the negative electrode tab 140 may be prevented.
[50]
It goes without saying that the characteristics of the adhesion area of ​​the heat dissipating tape can be applied to each other in the same or similar way even when the heat dissipating tape is adhered to the positive electrode tab.
[51]
4 is an enlarged plan view of a negative electrode tab among electrode tabs according to an exemplary embodiment of the present invention, and FIG. 5 is a front view viewed from a direction C of FIG. 4 and 5, the heat dissipation tape 170 further includes an adhesive layer 172, the adhesive layer 172 is between the negative electrode tab 140 and the heat diffusion layer 171 and the negative electrode sheet 110 It may be located between the heat diffusion layers 171. The heat diffusion layer 171 may be fixed and positioned on the negative electrode tab 140 and the negative electrode sheet 110 through the adhesive layer 172.
[52]
6 is an enlarged plan view of a negative electrode tab among electrode tabs according to another embodiment of the present invention, and FIG. 7 is a front view viewed from a direction D of FIG. 6. 6 and 7, the heat dissipation tape 270 further includes an adhesive layer 272, the adhesive layer 272 may be located between the negative electrode sheet 210 and the heat diffusion layer 271, the negative electrode At least a portion of the tab 240 may contact the heat diffusion layer 271. That is, the heat diffusion layer 271 can be fixed and positioned on the negative electrode tab 240 and the negative electrode sheet 210 through the adhesive layer 272 located between the negative electrode sheet 210 and the heat diffusion layer 271. In addition, since the heat diffusion layer 271 may directly contact at least a portion of the negative electrode tab 240, heat generated locally in the negative electrode tab 240 may be more rapidly diffused by high rate discharge.
[53]
It goes without saying that the characteristics of the heat dissipating tape including the adhesive layer may be applied to each other in the same or similar manner even when the heat dissipating tape is adhered to the positive electrode tab.
[54]
5 and 7 again, the heat dissipation tapes 170 and 270 according to embodiments of the present invention include not only the heat diffusion layers 171 and 271, but also the adhesive layers 172 and 272 and the base layers 173 and 273. ), and the heat diffusion layers 171 and 271 may be positioned between the adhesive layers 172 and 272 and the base layers 173 and 273.
[55]
As mentioned above, the heat diffusion layers 171 and 271 are for diffusing and dissipating heat generated from the electrode tab of the positive electrode tab or the negative electrode tab, and are not particularly limited as long as they have excellent thermal conductivity, It is preferable to include at least one of (Metal Foil), and graphite may include at least one of natural graphite and artificial graphite. Since the heat diffusion layers 171 and 271 are sheet-shaped, according to the heat diffusion principle, heat transfer is performed in a horizontal direction parallel to the heat diffusion layers 171 and 271.
[56]
The thickness of the heat diffusion layers 171 and 271 is preferably 17 μm to 1 mm. The specific thickness according to each material will be described below.
[57]
Natural graphite is a material having good productivity because it is easily formed in various thicknesses and widths, and is preferably formed in a thickness of 0.07 mm to 1 mm. If the thickness is less than 0.07mm, the heat diffusion layer may be too thin to limit heat transfer, and if the thickness is more than 1mm, the heat transfer effect may decrease due to the thickness more than necessary, and the capacity of the secondary battery may decrease. .
[58]
Artificial graphite is artificially produced graphite, and has excellent heat dissipation properties and can be manufactured into a thin film, and thus, it is preferably formed to a thickness of 17 μm to 40 μm. If the thickness is less than 17 μm, the heat diffusion layer may be too thin to limit heat transfer, and if the thickness is more than 40 μm, the heat transfer effect may be reduced due to the thickness more than necessary, and the capacity of the secondary battery may decrease. .
[59]
The metal foil is a material capable of forming a heat diffusion layer relatively inexpensively, and may include at least one of Cu and Al having high thermal conductivity, and is preferably formed to a thickness of 25 μm to 90 μm.
[60]
As mentioned above, the adhesive layers 172 and 272 are for fixing and positioning the heat dissipating tapes 170 and 270 including the heat diffusion layers 171 and 271 on the electrode tabs, and may include an acrylic adhesive.
[61]
The thickness of the adhesive layers 172 and 272 may be 5 μm to 25 μm. When the thickness is at least 5 μm or more, adhesion of the heat dissipation tapes 170 and 270 may be maintained, but if the thickness exceeds 25 μm, there may be a problem in that heat is not effectively diffused due to a thickness more than necessary.
[62]
The base layers 173 and 273 are layers that form the basis of the heat dissipation tapes 170 and 270, and are not particularly limited as long as they can perform insulation and heat resistance functions, but are among polyimide and polyethylene terephthalate. It is preferable to include at least one.
[63]
The thickness of the base layers 173 and 273 may be 5 μm to 25 μm. The thickness of 5 μm is the minimum thickness at which the base layers 173 and 273 can exhibit insulating performance, and if the thickness exceeds 25 μm, there may be a problem in that heat is not effectively diffused due to a thickness more than necessary.
[64]
Referring again to FIGS. 1 and 2, the electrode assembly 100 according to an embodiment of the present invention is a jelly-roll type wound with a separator 130 between the negative electrode sheet 110 and the positive electrode sheet 120. Of the electrode assembly 100. Since it is a jelly-roll type electrode assembly 100, there may be damage due to heat generated from the electrode tab at each bend of the negative electrode sheet 110, the positive electrode sheet 120, and the separator 130 in direct or indirect contact with the electrode tab. I can. However, the electrode assembly 100 according to an embodiment of the present invention can minimize the above damage due to the heat diffusion effect of the heat dissipation tape 170 adhered to the electrode tab. That is, when the heat dissipation tape of the present invention is applied to the jelly-roll type electrode assembly 100, damage due to heat can be further minimized.
[65]
The electrode assembly described above may be included in a secondary battery and applied to various devices. Such a device may be applied to a vehicle such as an electric bicycle, an electric vehicle, or a hybrid, but is not limited thereto and may be applied to various devices capable of using a secondary battery.
[66]
Experimental Example 1
[67]
Fig. 8 shows the results of an experiment comparing the temperature gradient between the electrode tab to which the heat dissipating tape including the heat diffusion layer of artificial graphite is adhered and the electrode tab to which the tape without the heat diffusion layer is attached. The thickness of the heat dissipating tape including the heat diffusion layer of artificial graphite is 40 μm, and the thickness of the heat diffusion layer of artificial graphite is 25 μm.
[68]
The heat dissipation tape including the heat diffusion layer exhibits a horizontal thermal conductivity of 74 W/mK, and the tape without the heat diffusion layer exhibits a horizontal thermal conductivity of 0.22 W/mK. Accordingly, it can be seen that the electrode tabs to which the heat dissipation tape including the heat diffusion layer is adhered have better heat diffusion than the electrode tabs to which the tape does not contain the heat diffusion layer, and thus the temperature of the electrode tabs is lower. The horizontal thermal conductivity means thermal conductivity in a direction parallel to the heat radiation tape.
[69]
Experimental Example 2
[70]
For a heat dissipation tape including a heat diffusion layer according to embodiments of the present invention, horizontal thermal conductivity of each case including artificial graphite, natural graphite, and metal foil and for the heat dissipation tape not including the heat diffusion layer is measured. It is shown in Table 1.
[71]
[Table 1]
[72]
Referring to Table 1, compared to the case where the heat diffusion layer is not included, the heat dissipation tape including the heat diffusion layer according to the embodiments of the present invention exhibits high horizontal thermal conductivity. Therefore, it is possible to more effectively dissipate heat generated inside the secondary battery, and in particular, as the heat dissipation tape including artificial graphite or natural graphite shows a horizontal thermal conductivity 3 to 8 times higher in the case of including a metal foil, graphite In particular, it is particularly preferable to include artificial graphite.
[73]
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 by those skilled in the art using the basic concept of the present invention defined in the following claims are also present. It belongs to the scope of rights of
[74]
[Explanation of code]
[75]
100: electrode assembly
[76]
140: cathode tab
[77]
160: anode tab
[78]
170, 270: heat dissipation tape
[79]
171, 271: heat diffusion layer
Claims
[Claim 1]
A jelly-roll type electrode assembly in which a negative electrode sheet, a positive electrode sheet, and a separator interposed between the negative electrode sheet and the positive electrode sheet are wound together, wherein at least one of at least one portion is attached to the negative electrode sheet or the positive electrode sheet and extends to the outside. Electrode tabs; And a heat dissipation tape adhered to the electrode tab, wherein the electrode tab to which the heat dissipation tape is adhered is positioned between or on an outer circumferential surface of the wound electrode assembly, and the heat dissipation tape includes a heat diffusion layer And the heat diffusion layer includes at least one of graphite and metal foil.
[Claim 2]
The electrode assembly of claim 1, wherein the graphite includes at least one of natural graphite and artificial graphite.
[Claim 3]
The electrode assembly of claim 1, wherein the metal foil includes at least one of Cu and Al.
[Claim 4]
The electrode assembly of claim 1, wherein an adhesion area of ​​the heat dissipation tape is greater than an adhesion area of ​​the electrode tab.
[Claim 5]
The electrode assembly of claim 4, wherein the area corresponding to the adhesive area of ​​the heat dissipating tape includes an area corresponding to the attachment area of ​​the electrode tab.
[Claim 6]
The electrode assembly of claim 5, wherein the heat dissipation tape further includes an adhesive layer, and the adhesive layer is positioned between the electrode tab and the heat diffusion layer and between the negative electrode sheet or the positive electrode sheet and the heat diffusion layer.
[Claim 7]
The electrode assembly of claim 5, wherein the heat dissipation tape further comprises an adhesive layer, the adhesive layer is positioned between the negative electrode sheet or the positive electrode sheet and the heat diffusion layer, and at least a portion of the electrode tabs contact the heat diffusion layer. .
[Claim 8]
The electrode assembly of claim 1, wherein the heat diffusion layer has a thickness of 17 μm to 1 mm.
[Claim 9]
The electrode assembly of claim 1, wherein the heat dissipation tape further includes an adhesive layer and a base layer, and the heat diffusion layer is positioned between the adhesive layer and the base layer.
[Claim 10]
The electrode assembly of claim 9, wherein the base layer includes at least one of polyimide and polyethylene terephthalate.
[Claim 11]
The electrode assembly of claim 9, wherein the adhesive layer has a thickness of 5 μm to 25 μm, and the base layer has a thickness of 5 μm to 25 μm.
[Claim 12]
A secondary battery comprising the electrode assembly according to any one of claims 1 to 11.