Lead-free relaxor ferroelectric ceramic capacitors, owing to ultrafast discharge rates and ultrahigh power density, find widespread application in pulsed power devices. However, conventional Bi0.5Na0.5TiO3-based ceramics are limited in their commercial applications due to the severe lack of energy storage density caused by high remnant polarization and low breakdown electric field strength. In this study, the solid solution properties of (1-x)Bi0.5Na0.5TiO3-xSrZrO3 (x=0, 0.025, 0.05, 0.075, abbreviated as BNT-xSZ) lead-free ferroelectric ceramics were systematically investigated, and the effect of lattice distortion on their structure and energy storage performance was explored. The study revealed that the lattice distortion introduced by SrZrO3 doping caused the c/a ratio of the ceramic to gradually approach unity. This enhanced local structural disorder suppressed long-range polar ordering, resulting in an increase in the ceramic's relaxation coefficient γ from 1.62 to 1.86. However, excessive doping can readily induce structural instability. Furthermore, SrZrO3 doping hindered elemental diffusion and inhibited grain boundary migration, which reduced the grain size from 5.79 μm (pure) to 1.83 μm (x = 0.025). Impedance analysis revealed that the resistance and activation energy Ea of BNT-0.025SZ were significantly higher than those of BNT. The excellent insulating properties and high Ea of BNT-0.025SZ contributed to increased oxygen vacancy migration resistance, thus improving the breakdown electric field. Therefore, BNT-0.025SZ achieved a high energy storage density of 2.08 J/cm3 and an outstanding efficiency of 83.14% under an electric field of 300 kV/cm. These findings clearly elucidate the effect of lattice distortion on the structural stability of BNT-xSZ binary solid solutions and provide theoretical guidance for designing lead-free ferroelectric ceramics with high energy storage performance.