JP4562693B2 - Secondary battery with improved stability by fixing a separator to the battery case - Google Patents

Description

  The present invention relates to a secondary battery in which a separator is fixed to a battery case to improve stability, and more specifically, an electrode assembly in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween is provided in the battery case. The battery case is a secondary battery manufactured by sealing the battery case, and at least a part of the outer peripheral surface of the separator is fixed together with the sealing part of the battery case, so that the battery is heated when the battery is abnormally heated. The present invention relates to a secondary battery characterized in that a short circuit is prevented from being caused by contraction of the battery, and a battery module comprising such a secondary battery.

  As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources has increased rapidly. Among these secondary batteries, lithium secondary batteries with high energy density and discharge voltage A lot of research has been conducted, and it has been commercialized and widely used.

  Generally, a secondary battery is built in a battery case of a metal can or a laminated sheet in a state where an electrode assembly composed of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is laminated or wound. Then, an electrolyte solution is injected or impregnated.

  One of the main research subjects in such a secondary battery is to improve safety. For example, a secondary battery has a high internal temperature caused by an abnormal operating condition of the battery, such as an internal short circuit, an overcharged condition that exceeds the allowed current and voltage, exposure to high temperature, deformation due to dropping or external impact. And high pressure can cause battery explosion.

  As one of the safety problems, the internal short circuit due to the shrinkage or breakage of the separator that occurs when the battery is exposed to high temperature is a very serious situation, and many studies have been conducted on the cause investigation and alternatives for this. .

  Generally, porous polymer membranes such as polyethylene and polypropylene are used for the separator, and these have the advantages of being inexpensive, excellent in chemical resistance, and suitable for battery operation. Easy to shrink in high temperature environment.

  In order to solve such problems, generally, a method of applying an adhesive layer between a separator and an electrode and attaching it is frequently used. As such an adhesive layer, PVDF which is also used as an electrode active material fixing agent is mainly used. However, such an adhesive layer has the disadvantages that ion mobility is lowered and low rate characteristics are exhibited as compared with the case where it is not applied. In addition, since the adhesive layer coating operation itself must be added in a separate process, it may cause many problems due to an increase in the number of work steps.

  On the other hand, in the pouch-shaped secondary battery, the problem that the sealing force of the battery case is reduced and the electrolyte solution leaks frequently occurs. FIG. 1 is an exploded perspective view schematically showing a general structure of a conventional typical pouch-shaped secondary battery.

  Referring to FIG. 1, the pouch-shaped secondary battery 10 includes an electrode assembly 30, electrode tabs 40 and 50 extending from the electrode assembly 30, and electrode leads 60 and 70 welded to the electrode tabs 40 and 50. , And a battery case 20 that houses the electrode assembly 30.

  The electrode assembly 30 is a power generation element in which a positive electrode and a negative electrode are sequentially stacked with a separator interposed therebetween, and has a stacked type or stacked / folded type structure. The electrode tabs 40, 50 are extended from each electrode plate of the electrode assembly 30, and the electrode leads 60, 70 are electrically connected to the plurality of electrode tabs 40, 50 extended from each electrode plate, for example, by welding. And a part of the battery case 20 is exposed to the outside. In addition, an insulating film 80 is attached to a part of the upper and lower surfaces of the electrode leads 60 and 70 in order to improve the sealing property with the battery case 20 and to ensure an electrical insulation state.

  The battery case 20 is made of an aluminum laminate sheet, forms a space in which the electrode assembly 30 can be accommodated, and has a pouch shape as a whole.

  The secondary battery 10 is manufactured by mutually heat-sealing the contact portion of the outer peripheral surface of the battery case 20 with the electrode assembly 30 attached to the storage part of the battery case 20. The part has a weak sealing force due to repeated contraction / expansion due to continuous use of the battery, external impact, etc., and the performance and safety of the battery are reduced due to the inflow of external substances, leakage of electrolyte, etc. It is a part to be.

  Therefore, many techniques for solving this problem have been proposed, but there are problems that increase the manufacturing cost of the battery or complicate the assembly process.

  For this reason, during the battery assembly process, there is an increasing need for a technique capable of suppressing the shrinkage of the separator on the structural side and preventing the decrease in the sealing force of the battery case.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a secondary battery that can improve safety only by structural changes without additional additives and additional steps in the assembly process. Is to provide. Specifically, an object of the present invention is to provide a secondary battery that can prevent the internal short circuit by suppressing the shrinkage phenomenon of the separator at a high temperature, and can reduce the sealing part of the battery case to improve the sealing power. There is to do.

  Another object of the present invention is to provide a battery module including such a secondary battery as a unit battery.

  In order to achieve the above object, according to the secondary battery of the present invention, after the electrode assembly in which the positive electrode and the negative electrode are laminated with the separator interposed therebetween is built in the battery case, the battery case is sealed. A secondary battery manufactured in a stopped state, wherein the battery case includes a lower case having a concave storage portion that can store an electrode assembly, and an upper case that seals the storage portion as a lid of the lower case And the electrode assembly is attached to the storage portion so that the electrode direction protrudes in one side surface direction a adjacent to the connection portion of the case, and is attached to the storage portion. Among the outer peripheral surfaces, the outer peripheral surface of the separator corresponding to the other side surface direction b and the facing surface direction c of the connecting portion is fixed together as a surplus portion to the sealing portion of the battery case.

  Thereby, this invention suppresses shrinkage | contraction of a separator by fixing the said separator surplus part to the sealing part of a battery case, and the positive electrode and negative electrode which are facing centering on a separator contact and short-circuit. Can be prevented. That is, during the battery assembly process, the safety of the battery can be improved by only a partial change in the structural aspect without additional additives and additional processes.

  Preferably, by making the length of the battery case in the direction a shorter than the length of the battery case in the direction c, the sealing performance of the entire battery can be further improved. That is, there is an effect that the sealing part of the battery case can be reduced and the sealing performance can be improved.

  The electrode assembly according to the present invention is not particularly limited as long as it has a structure in which a plurality of electrode tabs are connected to form a positive electrode and a negative electrode. For example, a product in which a plurality of electrodes having a predetermined size are sequentially stacked. It can be suitably applied to a heavy electrode assembly.

  The stacked electrode assembly is divided into a full cell or a bicell according to a structure in which electrodes are stacked. Here, the full cell is a positive electrode / separator / negative electrode or a positive electrode / separator / negative electrode / separator / positive electrode / separator / negative electrode in which electrodes at both ends are laminated so as to form a positive electrode and a negative electrode, respectively. The bicell is an electrode assembly in which electrodes at both ends are formed to form the same electrode, and is a positive type bicell comprising positive electrode / separator / negative electrode / separator / positive electrode, and negative electrode / Negative electrode type bicelle consisting of / separator / positive electrode / separator / negative electrode.

  The full cell itself can constitute one electrode assembly, and in some cases, a part or the whole separation membrane of the electrode assembly can be fixed together to the sealing part of the battery case described above, You may produce in a larger size.

  In the case of a bicelle, a positive electrode type bicelle and a negative electrode type bicelle can be arranged alternately to form one electrode assembly. Here, as described above, the separator interposed between the bicells and / or the separator constituting the bicell itself may be made larger to constitute electricity according to the present invention.

  In particular, the battery according to the present invention can be suitably applied to a pouch-shaped battery in which an electrode assembly is built in a pouch-shaped case made of a laminate sheet including a metal layer and a resin layer, specifically, an aluminum laminate sheet.

  The pouch-like case is sealed by, for example, heat welding with the electrode assembly built therein, and the separator surplus portion can be heat-sealed together and fixed to the heat-sealed sealing portion. . Specifically, when the pouch-shaped case is composed of an upper case and a lower case as described above, the separator surplus portion is sealed between the upper case and the lower case in a state of being interposed between the contact portions. It is heat-sealed together with the stop.

  At this time, the portion where the separator surplus portion is heat-sealed preferably has a size of 30 to 70% with respect to the width of the sealing portion of the case. This is to prevent the sealing force of the battery case from being reduced by the separator surplus portion. That is, since the mutual coupling force is relatively lower in the sealing portion where the separator surplus portion is located than in the sealing portion in contact with the battery case, the sealing performance of the battery case is only reduced. Therefore, by making the width of the sealing portion of the battery case larger than the width of the sealing portion of the currently used battery case, or by limiting the portion where the separator surplus portion is located in the sealing portion, Compensation for deterioration of case sealing performance.

  In some cases, the surplus portions of all separators or the surplus portions of some separators constituting the electrode assembly may be fixed to the sealing portion of the battery case. For example, in the case of a stacked electrode assembly, since all the separators constituting the electrode assembly are separated, a heat shrink phenomenon may occur in each separator. Therefore, in this case, it is preferable that the surplus portions of all the separators are fixed to the sealing portion of the battery case.

  In a preferred example, the separator surplus part may be fixed together at the time of sealing the battery case after being fixed in advance to the part to be sealed of the battery case by an adhesive. This is for enhancing the bonding strength of the separator surplus portion with respect to the battery case and improving the sealing performance of the battery case.

  In another preferable example, the separator surplus portion may be fixed together at the time of sealing the battery case after being fixed to the sealing portion of the battery case in a state where they are pre-bonded by heat fusion. Good.

  In the two structures described above, the separator surplus portion can be fixed or fixed to the sealing portion of the battery case by pre-bonding or fixing, preventing the separator surplus portion from separating and moving separately. can do. In some cases, both the structures can easily fix the separator surplus portion and seal the battery case, and may be applied together in one secondary battery.

  The present invention also relates to a medium-to-large battery module including the secondary battery as a unit battery.

  According to the present invention, by using a secondary battery having high safety and excellent sealing properties as a unit battery, excellent safety which is particularly problematic in a medium-to-large battery module composed of a large number of secondary batteries. And long-life requirements can be solved at the same time.

  According to the present invention, there is an effect that the shrinkage phenomenon of the separator can be suppressed at a high temperature to prevent an internal short circuit, and the sealing portion of the battery case can be reduced to improve the sealing force.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 2 is an exploded perspective view showing a secondary battery according to an embodiment of the present invention. The one side surface direction a, the other side surface direction b, and the opposing surface direction c in the present invention can be easily confirmed from FIG.

  Referring to FIG. 2, the secondary battery 100 can accommodate the electrode assembly 200 in which a positive electrode 210, a negative electrode 220, and a separator 230 having a larger size are sequentially stacked, and the electrode assembly 200 can be accommodated. A battery case 300 having a structure in which a lower case 310 in which a concave storage portion 340 is formed and an upper case 320 that seals the storage portion 340 as a lid are interconnected on one side is configured. . Therefore, after the electrode assembly 200 is attached to the housing part 340 of the lower case 310 and the upper case 320 is covered, the sealing parts 360, 361, and 362 where the lower case 310 and the upper case 320 are in contact are heat-sealed and sealed. By doing so, a secondary battery can be manufactured.

  The electrode assembly 200 includes a positive electrode 210 and a negative electrode 220 from which a positive electrode tab 211 and a negative electrode tab 221 protrude from one side surface, and a separator 230 interposed therebetween. Therefore, the electrode assembly 200 has a separator surplus portion 231 in which the separator 230 protrudes from the four side surfaces by a predetermined length on the entire shape surface.

  In such an electrode assembly 200, the positive electrode tab 211 and the negative electrode tab 221 are one of both side surfaces 350, 351 adjacent to the connecting portion 330 of the upper case 320 and the lower case 310, and in the direction a of one side surface 350. It attaches to the accommodating part 340 of the lower case 310 so that it may protrude. At this time, the separator surplus portion 231 of the electrode assembly 200 protrudes in the direction b of the other side surface 351 facing the one side surface 350 and in the direction c of the side surface 352 facing the connecting portion 330 of the cases 310 and 320, respectively. The sealing part 361 and the opposed surface sealing part 362 are fixed together by heat fusion together with the battery case 300.

  In producing the secondary battery 100, the sealing property of the battery case 300 is inversely proportional to the lengths of the sealing portions 360, 361, and 362. Therefore, the sealing portions 360, 361, and 362 occupy the entire battery. As the size increases, the sealing performance of the battery case 300 decreases. That is, the connecting portion 330 of the upper case 320 and the lower case 310 integrated with each other has a sealing power superior to that of the sealing portions 360, 361, and 362 by heat fusion. When the connecting portion 330 is formed in a bent shape, a further excellent sealing property can be obtained.

  In this connection, in the conventional secondary battery 10 as shown in FIG. 1, the length of the sealing portion from which the electrode tabs 40 and 50 protrude is shorter than the length of both side surfaces adjacent to the sealing portion. Therefore, the length of the connecting portion where the battery case 20 is bent is also short.

  In contrast, in the secondary battery according to the present invention, as shown in FIG. 2, the electrode tabs 211 and 221 are formed on the sealing portion 360 on one side surface adjacent to the connecting portion 330, so that the conventional secondary battery Compared to the battery, the connecting portion 330 is obtained in a relatively large size, and an increase in the size can be expected to improve the sealing performance.

  Hereinafter, the present invention will be described in more detail through examples. However, the following examples are for illustrating the present invention, and the scope of the present invention is not limited to these examples.

[Example 1]
The positive electrode has a generally known composition and is prepared by coating a slurry of lithium cobalt oxide, PVDF and a conductive material on an aluminum current collector. The negative electrode has a generally known composition and has graphite, PVDF and a conductive material. The slurry was coated on a copper current collector.

  An electrode assembly is assembled by interposing a separator cut to a larger size between the positive electrode and the negative electrode, and the electrode assembly is placed inside a battery case having a length longer than the width as shown in FIG. After attaching the solid, the sealing part of the battery case was heat-sealed together with the separator surplus part of the electrode assembly to complete the secondary battery.

[Comparative Example 1]
A secondary battery was completed in the same manner as in Example 1 except that the separator surplus part of the electrode assembly was not thermally fused together with the sealing part of the battery case.

[Comparative Example 2]
As shown in FIG. 1, the length of the sealing part in the protruding direction of the electrode tab is the same as that of Example 1 except that a battery case having a size smaller than the length of the side sealing part was used. Thus, a secondary battery was completed.

[Experimental Example 1]
The 20 batteries prepared in Example 1 and Comparative Examples 1 and 2 were subjected to overcharge and high-temperature exposure experiments, and after 300 cycles of charge and discharge, the electrolyte solution was sealed in the battery case sealing part. The presence or absence of leakage was confirmed.

  As a result, in all the batteries of Example 1, no short circuit was caused, and no electrolyte leakage was observed. On the other hand, among the batteries of Comparative Example 1 in which the separator was not fixed to the sealing portion, a short circuit occurred in six batteries. Moreover, although the separator was fixed to the sealing part, the battery of the comparative example 2 using the battery case having a long length with respect to the width did not cause a short circuit in all of the batteries. Liquid leakage was confirmed.

  A person having ordinary knowledge in the field to which the present invention belongs will be able to make various applications and modifications within the scope of the present invention based on the above contents.

It is a disassembled perspective view which shows the general structure of the conventional pouch-shaped secondary battery. It is a disassembled perspective view which shows the secondary battery which concerns on one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Secondary battery 200 Electrode assembly 210 Positive electrode 220 Negative electrode 230 Separator 231 Separator surplus part 211 Positive electrode tab 221 Negative electrode tab 300 Battery case 310 Lower case 320 Upper case 330 Connection part 340 Storage part 350, 351 Both sides 352 Side surface 360, 361, 362 sealing part a one side direction,
b Other side direction c Opposite side direction

Claims (11)

A secondary battery,
A positive electrode, a negative electrode, and an electrode assembly that is laminated with a separator interposed therebetween are built in the battery case, and then the battery case is sealed and formed.
The battery case includes a lower case having a concave storage portion that can store the electrode assembly, and an upper case that seals the storage portion as a lid of the lower case, and is connected to each other and integrated. With a structure that becomes
The electrode assembly is attached to the storage portion with its electrode direction protruding in one side surface direction a adjacent to the connecting portion of the case,
Among the outer peripheral surfaces of the separator, the outer peripheral surface of the separator corresponding to the other side surface direction b and the facing surface direction c of the connecting portion is fixed together as a surplus portion together with the sealing portion of the battery case,
Said length of said battery case in the direction a is is shorter than the length of the battery case of the direction c, the secondary battery.   The secondary battery according to claim 1, wherein the electrode assembly has a structure (stacked structure) in which a plurality of electrodes having a predetermined size are sequentially stacked.   The secondary battery according to claim 2, wherein the electrode comprises the electrode assembly having a plurality of bicell or full cell structures.   The secondary battery according to claim 1, wherein the battery case is made of a laminate sheet including a metal layer and a resin layer.   The secondary battery according to claim 4, wherein the battery case is a pouch-shaped case made of an aluminum laminate sheet.   The secondary battery according to claim 5, wherein the pouch-like case is sealed by thermal fusion, and the separator surplus portion is thermally fused together to the thermal fusion sealing portion.   The secondary battery according to claim 6, wherein the portion where the separator surplus portion is heat-sealed has a size of 30 to 70% with respect to the width of the sealing portion.   The secondary battery according to claim 1, wherein the separator whose surplus portion is fixed to the sealing portion of the battery case is all or a part of separators constituting the electrode assembly.   2. The secondary battery according to claim 1, wherein the separator surplus portion is fixed together at the time of sealing the battery case after being fixed to the sealing portion of the battery case by an adhesive.   2. The separator surplus part according to claim 1, wherein the separator surplus part is fixed to the sealing part of the battery case in a state of being mutually coupled by heat fusion, and then fixed together when the battery case is sealed. Secondary battery.   A medium- or large-sized battery module comprising the secondary battery according to any one of claims 1 to 10 as a unit battery.

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