Lithium secondary battery

Abstract

The present application relates to the field of energy storage devices, in particular to a lithium secondary battery. The battery comprises a shell having a bottom, a cap assembly, a positive terminal, a negative terminal, an electrode assembly and electrolyte, wherein a side wall of the shell comprises a pair of main planes and a pair of side faces, and the opening is arranged opposite to the bottom; the electrode assembly is formed by winding a positive plate, a negative plate and a composite separation film comprising a polymer microporous film layer and a ceramic composite material layer; a first extension portion extends from one end of the positive plate facing the cap assembly and is electrically connected with the positive terminal; a second extension portion extends from one end of the positive plate facing the cap assembly and is electrically connected with the negative terminal; and the air permeability of the composite separation film and the thickness of the side faces satisfy the relationship of 0.05 s/(100 mL·μm)≤A/B≤1.0 s/(100 mL·μm). The present application provides a lithium secondary battery capable of improving the safety performance of the battery effectively.