High-performance lead-free piezoelectric ceramics 0.94(K0.45Na0.55)(1-x)Li-x(Nb0.85Ta0.15)O-3-0.06AgNbO(3) (KNNLTAg-x) were successfully prepared by spark plasma sintering technique. The doping effect of Li on the structural and electrical properties of KNNLTAg-x (x=0, 0.02, 0.04, 0.06, 0.08 and 0.10) ceramics was studied. The lattice structure, ferroelectric and piezoelectric properties of the KNLNTAg-x ceramics are highly dependent on the Li doping level. In particular, the Li dopant has a great impact on both Curie temperature T-c and orthorhombic-tetragonal transition temperature TO-T. The 4% Li-doped sample exhibited relatively high TO-T of 95 degrees C, leading to a stable dynamic piezoelectric coefficient (d(33)*) of 220-240pm/V in a broad temperature range from 25 degrees C to 105 degrees C. Additionally, the 2% Li-doped sample shows a high d(33)* of 320pm/V at 135 degrees C, suggesting its great potential for high-temperature applications.