In this study, a series of Li0.058(Na0.535K0.480)0.966(Nb0.90Ta0.10)O3 (LNKNT) + (x)ZnO + (y)LiF (x = 0, 0.4, and 0.6 wt%; y = 0 and 0.2 wt%) lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method. The codoping of ZnO and LiF could significantly improve the sintering ability of LNKNT ceramics by reducing the optimal sintering temperature from 1090 to 990 °C. The crystal phases and microstructures were analyzed by X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. The dielectric characteristics, electromechanical coupling factors, piezoelectric constants, and P–E curves were also measured and investigated. From the results, as 0.6 wt% ZnO and 0.2 wt% LiF were added into pure LNKNT ceramics, uniform and condensed grains can be obtained easily, and thus the sintering temperature can be decreased from 1090 °C (pure LNKNT) to 990 °C. Compared with pure LNKNT, ZnO/LiF codoped LNKNT has better orthorhombic and tetragonal coexistence phases. In this study, the optimal d33 values were improved from 279 pC/N (pure LNKNT) to 304 pC/N (LNKNT-6Z2LF), and kp were improved from 0.46 (LNKNT) to 0.48 (LNKNT-6Z2LF). Hence, the codoping of ZnO and LiF can improve the sintering ability of the LNKNT ceramics effectively.