1]Mutual citations and related applications
[2]This application claims the benefit of priority based on the date of Korea Patent Application No. 10-2017-0086050 06 years 07 January 2017, and all information disclosed in the literature of the Korea patent application are included as part of the specification.
[3]
Art
[4]
The present invention relates to relates to a secondary battery, particularly a secondary battery that can ensure the safety by dispersing the short circuit current generated during needle penetration.
BACKGROUND
[5]
In general, a secondary battery (secondary battery), unlike primary batteries that can not be charged refers to a cell capable of charging and discharging, such secondary batteries are widely used in high-tech electronic apparatus fields such as phones, notebook computers, and camcorders.
[6]
Wherein the secondary battery includes an electrode assembly of a can type secondary battery with the electrode assembly is classified as a pouch-shaped secondary battery incorporated in the pouch, the pouch type secondary battery includes an electrode assembly, electrolyte, and the electrolyte the electrode assembly incorporated in the metal can and a pouch for receiving the. And the electrode assembly has a structure in which a plurality of electrodes and a plurality of separation membrane are alternately stacked, the plurality of electrodes is provided with an anode and a cathode.
[7]
However, the above-described secondary battery has a problem that a fire or explosion occurs, the positive electrode and the negative electrode of the electrode assembly upon needle penetration, and the excessive short circuit current to flow as short circuit, while the high heat caused by the short circuit current.
Detailed Description of the Invention
SUMMARY
[8]
The present invention has been invented to solve the above problems, an object of the present invention substantially reduce the amount of heat dispersing the excessive short circuit current occurring in needle penetration, and thus a secondary battery that can prevent ignition or explosion to provide.
Problem solving means
[9]
A secondary battery according to the first embodiment of the present invention for achieving the above object, the plurality of basic units in a state of interposing the separators which is laminated to the first and second electrodes alternately, a plurality of base units wraps to repeatedly stacked, and an electrode assembly is provided with a splitting film, the electrode assembly, the separation of containing the protection unit are respectively laminated on the outermost separation film which is located at the top or bottom film, the protection unit is the has a structure to be laminated with the second protective electrode in order from the outermost separation film, the separation membrane and the first protective electrode, and the second protective electrode which is located at the top or the bottom of the electrode assembly is a second collector, and the second house the coating has a cross-sectional structure including a second electrode active material is coated with the second electrode active material on the inside surface of the whole, the inner surface is the It may flush facing the center of the electrode assembly.
[10]
The protection unit is in the second protective electrode is connected through a short occurs, the needle of the electrode assembly caused by the needle penetrating Short (Short Circuit) current reduces the amount of heat by the bypass (bypass).
[11]
The first protective electrode may comprise a first collector and the second parts of the first electrode active material provided on one of both sides of the house.
[12]
On the other hand, the secondary battery according to the second embodiment of the present invention separate wraps so that the plurality of basic units and the plurality of basic units repeatedly stacked in a state of interposing the separators which is laminated to the first and second electrodes are alternately includes an electrode assembly in which the film is provided, the electrode assembly, comprising a protective unit to be laminated respectively on the outermost separation film which is located at the top or the bottom of the separating film, wherein the protective unit is the uppermost or lowermost end of the electrode assembly It has a structure to be laminated to the outermost second protection electrode in order from the separation film, the separation membrane and the first protective electrode, and the second protective electrode which is located in the second to the inner surface of the entire second current collector, and the second house 2 being a cross-section of the coating structure including a second electrode active material of the electrode active material is coated, the inner surface of the entirety of the second house of the electrode assembly A face looking plant at the first protective electrode being of a cross-section coating structure including a first current collector with the first first electrode active material is the first active material applied to the inner surface of the collector portion, wherein the first the inner surface of the collector may be flush facing the center of the electrode assembly.
[13]
The protection unit is thereby caused by the needle penetrating the short occurs, the second protective electrode and the first protective electrode to short (Short Circuit) a bypass (bypass) current having a cross-section the coating structure which is connected through the needle of the electrode assembly It can reduce the calories.
[14]
The plurality of basic units are doedoe the electrodes of the same polarity and having a bi-cell (bicell) located at both ends, both ends of the bi-cell is located at the top and bottom of the electrode assembly may have a first electrode position.
[15]
The second current collector may be provided with any of the metals of Cu, Al, Ni, Fe, and Pb.
[16]
The second current collector may be provided with a metal of Al, the total of the first house may be provided with a metal of Cu.
[17]
Wherein the first electrode and the first protective electrode is a cathode, the second electrode and the second protective electrode may be a cathode.
[18]
It may include a protective film surrounding the laminated protection unit at the top or the bottom of the electrode assembly.
[19]
Wherein the second thickness of the second house including the protective electrode may be larger than the whole of the second house including a second electrode of the base unit thickness.
[20]
The protective unit can be coupled to the first electrode and the separator or the second electrode and bond the outermost separation film with a small bonding strength than that of the separation membrane within, or not bonded to the outermost separation film of the electrode assembly or the base unit have.
[21]
Further comprising a casing for receiving the protection units stacked electrode assembly, the electrode assembly may be accommodated in the case to a state in which the protection unit toward the inner surface of the case.
[22]
The protective film may be left connected integrally to the end of the separation film to wrap the stack protection unit at the top or the bottom of the electrode assembly.
Effects of the Invention
[23]
The present invention has an effect as described below.
[24]
First: The secondary battery according to the present invention has a first protective electrode, a separator and a characterized by 2 comprising a protection unit including a protective electrode, and the second protective electrode has a cross section coated structure of the electrode active material coating only one surface , such a characteristic as to the second protective electrode is connected through the bed in case of short circuit of the electrode assembly caused by the needle penetrating short (short Circuit) because of the current it is possible to bypass (bypass). That is, the short circuit current can be dispersed in the second protective electrode, whereby it is possible to greatly reduce the amount of heat generated by the short circuit current, as a result, it is possible to prevent the ignition or explosion greatly ensuring the safety.
[25]
Second: the first protective electrode in the protection units of the secondary battery of the present invention has a feature that has the electrode active material coated on both sides of the structure, on the other because of the same features, and to increase the strength of the protection unit, in particular including the rechargeable battery it is possible to use the first electrode to the first protective electrode can increase the ease and efficiency of use.
[26]
Third: it has the characteristic that the first protective electrode has a cross section coated structure of the electrode active material is coated only on one side in the protection units of the secondary battery of the present invention, on the other, due to features such as short circuit that occurs when the electrode assembly, a short caused by the needle through can at the same time as the first and the second protective electrode bypass (bypass) through the needle-like current. That is, the short circuit current can be dispersed by the first and second protective electrode, whereby it is possible to greatly reduce the amount of heat generated by the short circuit current, as a result, ignite or to significantly prevent explosion greatly ensuring the safety have.
[27]
Fourth: the primary unit in the secondary battery of the present invention has a feature that the electrodes of the same polarity is provided to the bi-cell is located at both ends, on the other due to the same characteristics by stacking a plurality of basic unit in the first direction largely securing battery capacity can do.
[28]
Fifth: and a second collector of the first current collector of the first protective electrode is formed of Al, and the second protective electrode in the protection units of the secondary battery of the present invention is characterized by the formation of Cu, due to these features a short circuit current to a more stable it is possible to lower the amount of heat by the bypass.
[29]
Sixth: protection units of the secondary battery of the present invention has a feature that is protected by a protective film attached to the distal end of the separation film, it is possible to protect the protection unit from an external impact due to these features, it is possible to obtain a stable fixing force .
[30]
Seventh: The second current collector thickness of the second protective electrode in the protection units of the secondary battery of the present invention has a feature that a larger than the entire second collector of the second electrode included in the base unit, due to this characteristic the short it is possible to by-pass the electric current more stably, so that it is possible to significantly prevent the ignition or explosion.
[31]
Eighth: protection units of the secondary battery of the present invention has a feature that the not bonded to the outermost separation film or or small bonding force coupled to the outermost separation film, In the protection unit due to the same characteristics from the outermost separation film It can be easily separated.
[32]
Ninth: A secondary battery according to the present invention, but accommodating an electrode assembly with a protection unit stacked on the case, having a characterized in that the protection unit accommodated in a state facing the inner surface of the case, due to this feature through the case needle has to penetrate the protective unit, so that it is possible to reliably bypass the short circuit current.
Brief Description of the Drawings
[33]
1 is a cross-sectional view illustrating a secondary battery according to the first embodiment of the present invention.
[34]
Figure 2 is a view showing a laminated state around the electrode assembly according to a first embodiment of the present invention.
[35]
3 is a view showing a state after lamination of an electrode assembly according to a first embodiment of the present invention.
[36]
Figure 4 is an enlarged cross-sectional view showing a protection unit of the electrode assembly according to a first embodiment of the present invention.
[37]
Figure 5 is a cross-sectional view showing a state where the needle penetrates the electrode assembly according to a first embodiment of the present invention.
[38]
Figure 6 is a cross-sectional view showing the electrode assembly according to a second embodiment of the present invention.
[39]
Figure 7 is a cross-sectional view showing the electrode assembly according to a third embodiment of the present invention.
Best Mode for Carrying Out the Invention
[40]
With reference to the accompanying drawings the invention will now be described an embodiment of the invention in detail, so can be easily implemented by those of ordinary skill in the art belong. However, the invention is not to be implemented in many different forms and limited to the embodiments set forth herein. And the part not related to the description in order to clearly describe the present invention in the figures was in nature and not restrictive. Like reference numerals designate like elements throughout the specification.
[41]
[Rechargeable battery according to a first embodiment of the present invention;
[42]
As shown in secondary battery 1 in accordance with a first embodiment of the present invention, the electrode assembly 100 and electrolyte (not shown), and a case 130 accommodating the electrode assembly 100 and electrolyte It includes.
[43]
The electrode assembly
[44]
The electrode assembly 100 includes a plurality of basic units and the plurality of basic units are stacked in Fig. 2 and as shown in Figure 3, in a state of interposing the separator the first electrode and the second electrode are alternately repeated wraps such as laminated includes a separation film (130).
[45]
The plurality of basic units are doedoe the electrodes of the same polarity and having a bi-cell (bicell) located at both ends, both ends of the bi-cell is located at the top and bottom of the electrode assembly 100 has a first electrode position. For example, the plurality of basic units has a first bi-cell 110, the second includes a second bi-cell 120, the first bi-cell 110 includes a first electrode 10, a separator 20, a second electrode 30, a separator 20 and the first electrode 10 has a five-layer structure laminated in sequence, wherein the second bi-cell 120, the second electrode 30, a separator 20, a first electrode 10, a separator 20 and the second electrode 30 has a five-layer structure is stacked in sequence.
[46]
This electrode assembly 100 is the first bi-cell 110, and the second bi-cell, being formed as laminated in 120 shifts the outermost layer (top and bottom) of the electrode assembly 100 is provided with a first the bi-cell 110 are laminated.
[47]
The separation film 130 to be interposed between the first bi-cell 110, and the second bi-cell 120, has a long sheet shape, and the first bi-cell 110, the upper surface of the second the bi-cell 120 are arranged so as to be alternately stacked. For example, the separation film 130 Referring to FIG. 2, from left to right the first bi-cell 110, a first bi-cell 110, the second bi-cell 120, a second bi-cell 120 and the first bi-cell 110 are arranged in order. And the separation film 130 has a first bi-cell 110, such as in closed right-to-left direction is illustrated in Figure 3, in a state of being interposed between the separation film 130, a second bi-cell ( 120), a first bi-cell 110, the second bi-cell 120, and a first bi-cell 110, it is possible to manufacture the electrode assembly 100 while sequentially stacked. The distal end of the separation film (130) As the outside of the stacked electrode assembly 100 is wound at least once it is possible to protect the electrode assembly 100.
[48]
Wherein the first electrode 10 is a cathode and the second electrode 30 may be a positive electrode.
[49]
case
[50]
The case 200 is designed to receive sealingly the electrode assembly and an electrolyte, the electrode assembly 100 and a receiving portion 210 for receiving an electrolyte, a sealing part (220 to seal sealingly to the receptacle (210) ) a.
[51]
On the other hand, the secondary battery according to the first embodiment of the present invention, the short circuit current occurring in the bed through the electrode assembly by-pass, that is, by reducing the amount of heat dissipation, resulting in fire or protection unit for preventing an explosion to secure safety It comprises 140.
[52]
Protection units
[53]
The protection unit 140 is as shown in Figure 3, are respectively laminated on the outermost separation film 130 which is located at the top or the bottom of the electrode assembly 100, the top of the electrode assembly 100 or the from the outermost separation film 130 is located at the lowermost end has a structure which is in turn laminated with the second protective electrode 141, a separator 142 and the first protective electrode 143.
[54]
The second protective electrode 141 has a cross-sectional structure of the coating. For example, the second a protective electrode 141, a second current collector (141a), and the second collector (141a) of the inner surface of the second electrode that is coated with the second electrode active material, the active material in part (141b) and including, an inner surface of the second collector (141a) is a surface facing the center of the electrode assembly 100. On the other hand, the outer surface of the second collector (141a) is formed of solid portion with no second electrode active material.
[55]
The second protective electrode 141, a first bi-cell contact in FIG. 4 and as shown in Figure 5, the coating on the inner surface the second electrode coating portion (141b) and the outermost separation film 130 ( the second passivation 110) for increasing the battery capacity through the mutual reaction between the first electrode 10. on the other hand, due to the needle (1) through which is connected via a short occurs, the needle (1) of the electrode assembly 100, the electrode 141, more specifically to reduce the amount of heat by the second current collector (141a), the outer surface in the entire coated portion short (short Circuit), a current bypass (bypass) formed on the second protective electrode 141 and it can, as a result, it is possible to prevent the ignition or explosion due to the temperature reduction of the electrode assembly 100, can be increased as a result to secure the stability of the secondary battery.
[56]
On the other hand, the first protective electrode 143 is a second protective as to protect the electrode 141, the first collector (143a), and the first current collector a first electrode which is provided on both sides of (143a) the active material portion It includes (143b).
[57]
Wherein the first and the protective electrode 143 is a cathode, the second protective electrode 141 may be a positive electrode.
[58]
On the other hand, the second current collector (141a) is to more stably disperse the short circuit current may be provided by any of the metals of Cu, Al, Ni, Fe, and Pb, in particular, which can greatly improve the dispersibility of the short circuit current It may be provided with a metal Al.
[59]
On the other hand, the first collector (143a) may be provided with a metal of Cu to reliably protected than the second protective electrode 141.
[60]
On the other hand, may include a protective film 131 to protect the protective unit (140) laminated to the top or the bottom of the electrode assembly 100, the protective film 131 is the top of the electrode assembly 100 or the a state including the protection unit 140 is stacked at the bottom surround the electrode assembly 100 more than once. Here, the protective film 131 and the separation film 130 is formed of the same material.
[61]
On the other hand, the protection unit 140 has the first electrode 10 and the membrane 20 in, or not bonded to the outermost separation film 130 of the electrode assembly 100 or the base unit or the second electrode a small bonding strength than the bonding strength between the 30 and the membrane 20 is joined to the outermost separation film 130.
[62]
That is, due to the adhesion difference between the basic units and the protection unit 140 can easily separate the protection unit (140) from the outermost separation film 130. At this time, due to the adhesion difference between the basic units and the protection unit 140, it is possible to prevent exfoliation of the electrode and the separator of the base unit.
[63]
On the other hand, the electrode assembly 100 that includes a protection unit (140) when the inner upper surface or when the protection unit 140, when accommodated in the case 200 is viewed from the inside surface (Fig. 1 of the case 200, ) it is in a state facing the accommodated in the case 200. That is, toward the higher the potential for needle penetration portion arranged a protective unit (140).
[64]
Therefore, the secondary battery according to the first embodiment of the present invention can be dispersed in the short circuit current occurring during needle penetration by providing an electrode assembly 100 that includes a protection unit 140 more effectively, and therefore heat of the electrode assembly and the zoom can be reduced, it is possible to secure the safety as a result to prevent the ignition or explosion.
[65]
Or less, in the following description of an embodiment of the present invention using the same reference numerals in the configuration having the same form and function as those of the above-described embodiment, the configuration, and duplicate description is omitted.
[66]
[Rechargeable battery according to a second embodiment of the present invention;
[67]
As illustrated in the second exemplary secondary battery 6 according to the embodiment of the present invention, "contain, the electrode assembly (100 electrode assembly 100 ') is in a state of interposing the separator the first electrode and the and a plurality of basic units are two electrodes that are alternately stacked, wrapping the plurality of basic units to be repeatedly stacked comprises a separation film (130).
[68]
The plurality of basic units are doedoe the electrodes of the same polarity and having a bi-cell (bicell) located at both ends, both ends of the bi-cell is located at the top and bottom of the electrode assembly 100 'has a first electrode position. That is, the plurality of basic unit comprises a first bi-cell 110, the first (as not shown in Figure 6) two-by-cell 120.
[69]
Wherein the plurality of basic units has the same configuration and functions as those of the first embodiment a plurality of basic units described previously, overlapping description will be omitted accordingly.
[70]
On the other hand, the secondary battery safety by reducing the amount of heat by the short circuit current occurring in the bed through the electrode assembly (100 ') by-pass, i.e. dispersion and prevent the resulting fire or explosion in accordance with a second embodiment of the present invention 'includes the protection unit (140 protection unit 140' to secure) are respectively laminated on the outermost separation film 130 which is located at the top or the bottom of the electrode assembly (100 '), the electrode assembly ( "from the outermost separation film 130 which is located at the top or the bottom of) in this order to the second protective electrode 141, a separator 142 and the first protective electrode (143, 100 has a structure to be laminated to).
[71]
The second protective electrode 141, a second current collector (141a), and the cross section coating comprising the inner surface of the second electrode that is coated with the second electrode active material, the active material in the portion (141b) of the second current collector (141a) has a structure, the inner surface of the entire (141a) and the second house is the surface facing the center of the electrode assembly 100.
[72]
The first protective electrode (143 ') includes a first collector (143a) and said first collector (143a), the inner surface the end surface coating comprising a first electrode coating portion (143b) which is one electrode active material is coated on the being in the structure, the inner surface of the first collector (143a) may be flush facing the center of the electrode assembly 100 '.
[73]
The protection unit 140 'have the same configuration, the first and second protective electrode (143' and formed from a) 141, the only electrode end surface coating structure of the active material is coated on one side, so that due to the needle through the electrode assembly to "the first and second protective electrode (143 short occurs, which is connected through the needle of a) 141, the correctly the first and second current collectors (143a) (141a) than 100, short ( Short Circuit) can greatly reduce the amount of heat by each bypass (bypass) for the current, so that as the electrode assembly 100 'has a temperature significantly reduced it is possible to prevent the ignition or explosion.
[74]
Therefore, the secondary battery according to a second embodiment of the invention comprises an "electrode assembly (100 comprises a) protecting unit 140," "the first and second protective electrode (143 of the protection unit 140 ' and 141) can be increased to secure the safety of the secondary battery by forming an electrode active material only in the cross-sectional structure of the coating is coated on one side.
[75]
[Rechargeable battery according to a third embodiment of the present invention;
[76]
As it is shown in Figure secondary battery according to a third embodiment of the present invention 7, the second comprising a second current collector (141a) of the protective electrode 141, the second home thickness of the (141a) is the area of ​​the entire (141a) of the second house included in the second electrode 30, the second protective electrode 141, the second can be formed larger than the thickness of the second home, and thus included in the base unit it is possible to greatly secure to significantly enhance the dispersibility of the short circuit current, so that it is possible to secure larger than the safety of the secondary battery.
[77]
[Rechargeable battery according to a fourth embodiment of the present invention;
[78]
A secondary battery according to a fourth embodiment of the present invention may be laminated to the continuous protection unit 140 to be laminated respectively on the outermost separation film 130 which is located at the top or bottom of the electrode assembly 100, two or more . That is, the laminate by at least two protection units (140) in the outermost separation film 130 is continuous, so that it is possible to greatly secure the safety due to the needle penetration.
[79]
[Rechargeable battery according to a fifth embodiment of the present invention;
[80]
Fifth Embodiment In the secondary battery, a protective film 131 according to an embodiment of the present invention the outermost separation protected unit (140) laminated to the top or bottom of the film 130, the electrode assembly 100 as it is connected integrally with the distal end of the to be wrapped.
[81]
That is, the secondary battery has two protection units 140 and the plurality of basic units on the upper surface of the separation film 130, the protective film attached integrally, as shown in Figure 2 according to a fifth embodiment of the present invention disposed one may take the following, the volume of the separation film 130, producing a protective unit 140, the electrode assembly 100 disposed at the top or the bottom.
[82]
The scope of the invention is represented by the claims below rather than the description above, it is possible to various embodiments derived from the meaning and scope of the appended claims and their equivalents concept.

Claims

[Claim 1]And a plurality of basic units in a state of interposing the separators which is laminated to the first and second electrodes alternately, wrapping the plurality of basic units to be repeatedly stacked, and an electrode assembly is provided with a splitting film, the electrode assembly is the separation comprises a protection unit in which each laminated on the outermost separation film, and the protective unit which is located at the top or bottom of the film, the second protective electrode in order from the outermost separation film which is located at the top or the bottom of the electrode assembly , has a structure stacked in the separator and the first protective electrode, the second protective electrode section including a second collector and the second collector to the entire inner surface of the parts of the second electrode active material is coated with the second electrode active material have a coating structure, the inner surface of the secondary battery - surface facing the center of the electrode assembly.
[Claim 2]
The method according to claim 1, wherein the protection unit is in the second protective electrode is connected through a short occurs, the needle of the electrode assembly caused by the needle penetrating Short (Short Circuit) current bypass (bypass) by the secondary battery which reduces the amount of heat .
[Claim 3]
The method according to claim 1, wherein the first protective electrode is a secondary cell comprising a first current collector, and wherein a first electrode active material provided on one of both sides of the house.
[Claim 4]
And a plurality of basic units in a state of interposing the separators which is laminated to the first and second electrodes alternately, wrapping the plurality of basic units to be repeatedly stacked, and an electrode assembly is provided with a splitting film, the electrode assembly is the separation film of the uppermost or comprises a protective unit respectively laminated on the outermost separation film, and the protective unit which is located at the bottom of the first protective electrode in order from the outermost separation film which is located at the top or the bottom of the electrode assembly , the separation membrane and has a structure that is stacked in the second protective electrode, the second protective electrode section including a second collector and the second collector to the entire inner surface of the parts of the second electrode active material is coated with the second electrode active material being of the coating structure, and the surface facing the center of the second inner side surface of the collector is the electrode assembly, wherein the first electrode is the protection 1, collector and, being of a cross-section coating structure including a first current collector to the entire inner surface of the parts of the first electrode active material 1, the active material is coated, the inner surface of the entirety of the first current collector is at the center of the electrode assembly rechargeable batteries - surface viewing.
[Claim 5]
The method according to claim 4, wherein the protection unit has the second protective electrode and the first short (Short Circuit) current to a first protective electrode with the end face coating structure Short occurrence of the electrode assembly are connected through the needle due to the needle penetration by path (bypass) by the secondary battery which reduces the amount of heat.
[Claim 6]
The method according to claim 1 or claim 4, doedoe the plurality of basic units are provided with a bi-cell (bicell) located on the electrode of the same polarity at both ends, both ends of the bi-cell is located at the top and bottom of the electrode assembly has a first electrode location secondary battery.
[Claim 7]
The method according to claim 1 or claim 4, wherein the second collector is Cu, Al, Ni, Fe, and any of the secondary battery is provided with a metal of Pb.
[Claim 8]
The method according to claim 1 or claim 4, wherein the second collector is a secondary battery that is provided with a metal Al.
[Claim 9]
The method according to claim 4, wherein the first collector is a secondary battery that is provided with a metal of Cu.
[Claim 10]
The method according to claim 1 or claim 4, wherein the first electrode and the first protective electrode is a cathode and the second electrode and the second protective electrode is the positive electrode for a secondary battery.
[Claim 11]
The method according to claim 1 or claim 4, the secondary battery including a protection film surrounding the stack protection unit at the top or the bottom of the electrode assembly.
[Claim 12]
The method according to claim 1 or claim 4, wherein the second thickness of the second house including the protective electrode is a secondary cell that is larger than the thickness of the entire second house included in the second electrode of the base unit.
[Claim 13]
The method according to claim 1 or claim 4, wherein the protection unit has the in or not bonded to the outermost separation film of the electrode assembly or the base unit as the first electrode and the membrane or small binding force than the bonding strength between the second electrode and the membrane a secondary battery that is coupled to the outermost separation film.
[Claim 14]
The method according to claim 1 or claim 4, further comprising a case for receiving the protection units stacked electrode assembly, the electrode assembly is a secondary battery that is accommodated in the case to a state in which the protection unit toward the inner surface of the case.
[Claim 15]
The method according to claim 11, wherein the protective film is connected to a secondary battery integrally with a distal end of the separation film wraps the protection unit stacked at the top or the bottom of the electrode assembly.