Lithium secondary battery having improved safety by using bimetal tab
The present disclosure relates to a lithium secondary battery having improved safety. In the lithium secondary battery, the property of a bimetal bent in one direction at high temperature under an abnormal operating condition is used to cause a disconnection between an electrode tab and an electrode lead and to increase the internal resistance of a unit cell, thereby improving the safety of a lithium secondary battery.
1. A lithium secondary battery comprising: a cathode plate, a separator, and an anode plate stacked successively; electrode tabs extended from one side of each of the cathode plate and the anode plate by a predetermined length; electrode leads electrically connected to the electrode tabs; and at least one bimetal tab defined by two metal plates laminated and joined together, the two metal plates having different heat expansion coefficients from one another,
wherein the at least one bimetal tab is attached to a first one of the electrode tabs or the first one of the electrode tabs comprises the bimetal tab,
wherein the at least one bimetal tab overlaps at least one of the electrode leads to define an overlap region,
wherein a surface of the at least one bimetal tab is welded to a surface of at least one of the electrode leads by a weld zone comprising at least a portion of the overlap region, and wherein, at a predetermined high temperature indicating an abnormal operating condition, the at least one bimetal tab is configured to deflect due to differential heat expansion of the two metal plates such that the bimetal tab disconnects from the at least one of the electrode leads by separating from one another at the weld zone.
2. The lithium secondary battery according to claim 1 , wherein the first electrode tab is a cathode tab.
3. The lithium secondary battery according to claim 1 , wherein the one of the two metal plates having a larger heat expansion coefficient faces the at least one of the electrode leads.
4. The lithium secondary battery according to claim 3 , wherein the one of the two metal plates having a larger heat expansion coefficient includes a copper/zinc alloy, a nickel/molybdenum/iron alloy or a nickel/manganese/iron alloy.
5. The lithium secondary battery according to claim 4 , wherein the one of the two metal plates having a smaller heat expansion coefficient includes a nickel/iron alloy.
6. The lithium secondary battery according to claim 1 , wherein the weld zone comprises 50-80% of the total area of the overlap region.
7. The lithium secondary battery according to claim 1 , wherein the weld zone is formed in a continuous pattern.
8. The lithium secondary battery according to claim 1 , wherein the predetermined high temperature is a temperature of 80-130° C.
9. A battery pack comprising the lithium secondary battery as defined in claim 1 as a unit cell.
10. The lithium secondary battery according to claim 1 , wherein the first electrode tab is an anode tab.
11. The lithium secondary battery according to claim 1 , wherein the weld zone is formed in a discontinuous pattern.