Defect Engineering Build Organic-Inorganic Composite Electrolytes with stable electrochemical window and interface for all-solid-state lithium-ion batteries

Abstract

In this study, Na1+xAlxTi2-x(PO4)3 (NATP) with oxygen vacancies was synthesized using a high-temperature solid-phase method. Then, NATP and polyacrylonitrile (PAN) were combined to form NATP-PAN composite solid-state electrolytes. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses demonstrated the presence of oxygen defects in NATP. Al3+ doping created oxygen vacancies in NATP, which decreased the activation energy for Li+ ions transport; this increased the mobility of Li+ ions in the material, broadening the electrochemical window of the electrolyte. The Na1.3Al0.3Ti1.7(PO4)3-PAN solid-state electrolytes achieved an excellent ionic conductivity of 4.51 × 10−4 S cm−1 at 20°C and a wide electrochemical stability window of 5.2 V (vs. Li+/Li). Na1.3Al0.3Ti1.7(PO4)3-PAN composite electrolyte was used to assemble a Li||Li symmetric half-cell, which exhibited good interface stability and an overpotential of approximately ±60 mV at a current density of 0.25 mA cm−2. Furthermore, Li׀Na1.3Al0.3Ti1.7(PO4)3-PAN׀LiFePO4 was assembled into an all-solid-state lithium metal battery, which exhibited excellent electrochemical performance, with the initial discharge capacity of 255.0 mA h g−1 at 0.1 C. After 100 cycles, the discharge capacity was maintained at 229.6 mA h g−1, and the capacity retention rate was 90.0%. Increasing dopant concentration, the oxygen defect concentration is increasing, which plays a crucial role in the ionic conductivity as well as the interface stability.