Formation of a heterostructure of semiconductor materials is a promising method to develop an electrolyte with high ionic conductivity at low operational temperature of solid oxide fuel cells (LT-SOFCs). Herein, we develop various heterostructure composites by introducing a pure ionic conductor Sm0.2Ce0.8O2-δ (SDC) into a semiconductor LiNi0.8Co0.15Al0.05O2 (LNCA) for LT-SOFCs electrolyte. The morphology, crystal structure, elemental distribution, micro-structure, and oxidation states of the composite of LNCA-SDC are analyzed and studied via X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high resolution-transmission electron microscopy (HR-TEM), high energy dispersive spectrometry, and X-ray photoelectron spectroscopy (XPS). Electrochemical studies found that the optimal weight ratio of 0.5 LNCA-1.5 SDC heterostructure composite exhibits relatively high ionic conductivity (0.12 S cm-1 at 520 °C), which is much higher than that of SDC. The designed composite of LNCA-SDC heterostructures with optimal weight ratio (0.5:1.5) delivers a remarkable fuel cell power output of 0.735 W cm-2 at 520 °C. The formation of the heterostructure and reconstruction of energy bands at the interface play the crucial roles in enhancing ionic conduction to improve electrochemical performance. The prepared composite heterostructure delivers a unique and insightful strategy of electrolyte in advanced LT-SOFCs.