The ionic electrolyte and compatible cathode are major challenges to develop advanced low temperature solid oxide fuel cells (LT-SOFCs). Perovskite La0.6Sr0.4Co0.2Fe0.8O3-delta(LSCF) has considered as desired SOFC cathodes due to its unique advantages including high mixed electronic and ionic conductivity and excellent catalytic activity for oxygen reduction reaction. Our present work demonstrates the first application of LSCF tuned as functional electrolyte through composing with sodium carbonate. The mixed ionic and electronic conductor (MIEC)/carbonate LSCF/Na2CO3 nanocomposites can make use of the intrinsic high ionic conductivity of LSCF, and extend the three phase electrocatalytic reaction region into the electrolyte region along with suppress its electronic contribution, ultimately tuned as functional electrolyte material. Through optimizing Na2CO3 content, the novel LSCF/Na2CO3 nanocomposite gives rise to an superior fuel cell performance of 700 mW/cm(2) at 550 degrees C. This work has demonstrated a new approach to develop electrolyte materials tuned from MIEC for advanced LT-SOFCs for next-generation.