LaMnO3 perovskite oxide has got tremendous attraction in electrochemical field owing to their favourable physical and chemical properties. However, aggregated and distorted morphology of regular perovskites that are prepared at higher temperatures (> 500 degrees C) led to lesser active sites provided to enable the electrochemical reaction. Here we propose a green synthetic approach to overcome these deficiencies and to obtain better electrochemical performance. 3D polyhedron structured LaMnO3 nanoparticles are synthesized using natural lemon juice (LJ) as a green surfactant. The aggregation of these particles is removed and a well separated individual particle has been formed. This well defined polyhedron structured LMO nanoparticle possessed a 3 fold enhancement in its specific capacitance. A symmetric two electrode cell system has also been fabricated to investigate the real life application of LMO as a supercapacitor. The electrode in this symmetric cell configuration could deliver a maximum energy density of 52.5 Wh kg(-1) at a power density of 1000 W kg(-1). This is an outstanding result among aqueous electrolyte symmetric supercapacitors. Moreover, the room temperature fluctuation effect on the specific capacitance of LMO cell has also been investigated. This LJ assisted synthesize of LMO perovskite presented here enlighten a simple paradigm for fabricating high energy electrochemical storage devices.