Novel lead-free diphasic (1-x)Ba0.9Sr0.1Ti0.9Hf0.1O3-xNa(0.5)Bi(0.5)TiO(3)(BSTH-NBT) ceramic nanocomposites were synthesized via an economically viable modified mechano-chemical activation technique. In the present investigation, we have developed an energy storage composite material by systematically optimizing the charge transport behavior and charge storage characteristics between the ferroelectric BSTH and piezoelectric NBT phase. The composite withx = 0.09 NBT concentration has shown the best energy storage properties with 1.61 J/cm(3)discharge energy density along with 80.1% energy efficiency. The BSTH and NBT had a synergetic effect on the ferroelectric properties of the composites. The improvement in ferroelectric and piezoelectric properties along with excellent aging characteristics in composite materials is mainly attributed to enhancement in microstructural density, grain boundary interface, and stress effects. The improved dispersibility and excellent compatibility between BSTH and NBT phase have resulted in approximately 20% enhancement in breakdown strength of composite compared to pure BSTH ceramic.