(Na0.8-xK0.2Lix)0.5Bi0.5Ti0.985Ta0.015O3 lead-free ceramics with large strain and high recoverable energy density

•The doping of Li+ ion has an obvious influence on the strain and energy storage performance.•The TEM image and XPS spectra of O 1s for BNKTT-100xLi ceramics demonstrate the existence of PNRs and oxygen vacancies.•The maximum bipolar strain (S = 0.462%) and unipolar strain (Su = 0.443%) for x = 0.025 sample were obtained under 80 kV/cm, and its unipolar strain achieved 0.573% at 100 °C.•BNKTT-15Li ceramic exhibited outstanding energy storage performance with a recoverable energy density of 1.29 J/cm3 under applied 130 kV/cm field.