With the accelerated advancement in flexible electronic products, capacitors that possess extraordinary flexibility and superior energy storage capabilities are set to revolutionize the landscape of wearable electronics and pulsed power applications. Lead-free ferroelectric thin-film capacitors have garnered attention as promising candidates for energy storage solutions due to their excellent power density and rapid charge-discharge capabilities. This study focuses on the preparation of flexible xMn-Na0.5Bi0.5TiO3(NBT) thin films (where x = 0.01, 0.02, 0.03) on Mica substrates through the sol-gel method. The characterization of films with varying Mn concentrations reveals that all xMn-NBT films exhibit perovskite phase structures. The addition of Mn2+ ions facilitates the creation of polar nanoregions, leading to reduced ferroelectric hysteresis. Simultaneously, Mn2+ doping enhances polarization by modulating chemical pressure within the lattice, inhibiting changes in the oxidation state of Ti4+, thus further boosting energy storage performance. Notably, the 0.02Mn-NBT film stands out with the high breakdown strength and polarization, which can achieve a recoverable energy density of 9.4 J/cm3 and an efficiency of 55.6%. The work will significantly advance the application of NBT to flexible energy storage.