The phase structure and electrical properties of (K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics with nominal composition Li-0.03 (Na (x) K1-x )(0.97)Nb0.8Ta0.2O3 (LKNNT, x = 0.50-0.55) were investigated with an emphasis on the influence of Na/K ratio. By XRD and Raman measurements, it was revealed that the phase transition from the co-existence of O (1) and T (1) to the co-existence of O (2) and T (2) occurs when x = 0.52. At this Na/K ratio, a peak of dielectric constants was obtained, which also corresponds to a morphotropic phase boundary between T (1) and T (2) besides that between O (1) and O (2) in LKNNT ceramics. All the Li-0.03 (Na (x) K1-x )(0.97)Nb0.8Ta0.2O3 ceramics with x = 0.50 - 0.55 show excellent piezoelectric performance, and the piezoelectric coefficient d*(33) can reach as high as 335 pm/V. The room-temperature piezoelectric properties in the present LKNNT ceramics are not sensitive to the change of Na/K ratio, indicating that the orthorhombic to tetragonal phase co-existence dominates the enhancement of piezoelectric properties. However, the results on the piezoelectricity measurement at elevated temperature showed possible to further enhance piezoelectric properties by adjusting Na/K ratio in the tetragonal LKNNT ceramics.