In this work, (1 − x)(0.92BaTiO3–0.08K0.5Bi0.5TiO3)–xNaNbO3 (0 ≤ x ≤ 0.08) [(1 − x)BTKBT–xNN] ceramics were prepared by using conventional solid state reaction method. Phase composition, microstructures, and energy storage properties were investigated. X-ray diffraction analysis for all samples showed that the tetragonal symmetry structure of the (1 − x)BTKBT–xNN ceramics. It was found that the tetragonal phase content decreases with increasing NN content. Variation of $${\text{V}^{\prime}_{\text{Na}}} - {\text{V}_{\text{O}}^{\cdot \cdot}} - {\text{V}^{\prime}_{\text{Na}}}$$ VNa′-VO··-VNa′ defect dipole concentration leads to the average grain size of the (1 − x)BTKBT–xNN ceramics reduces from 1.49 to 0.90 µm during sintering process. The 0.92BTKBT–0.08NN ceramic sample exhibits to processes the largest energy storage density of 1.96 J/cm3 with energy storage efficiency about 67.4% at breakdown strength 22 kV/mm.