Lithium battery with excellent safety

Disclosed herein is a lithium battery which exhibits minimal dimensional deformation of a case thereof and easily discharges gas therefrom. The lithium battery includes an electrode assembly in which cathode and anode plates face each other with a separator therebetween; a case body receiving the electrode assembly and an electrolyte, the case body including a barrel-shaped sidewall open at a top thereof and a bottom bulging in a direction away from the electrode assembly; and a top cap disposed on the top of the case body and provided with a safety exhaust outlet through which gas is discharged upon increase in internal pressure.