Vanadium-Substituted LiCoPO4 Core with a Monolithic LiFePO4 Shell for High-Voltage Lithium-Ion Batteries

Abstract

High-voltage lithium-ion cathodes are a promising solution for achieving higher energy density batteries. However, the use of high-voltage cathodes is presently limited by the irreversible chemical reactions occurring between the cathode and the electrolyte at the high operating voltages. Metal-oxide coatings on micrometer-sized high-voltage cathode materials have been employed to improve the electrochemical performance, but it is often difficult to achieve a robust, durable, monolithic coating on nanoparticles. This study presents a low-temperature microwave-assisted solvothermal process for realizing a robust, monolithic coating of LiFePO4 on the high-voltage (∼4.8 V) LiCo1-3x/2Vx□x/2PO4 (x = 0, 0.02, and 0.04) nanoparticles, offering a stable cathode-electrolyte interface. The core-shell cathode obtained exhibits enhanced electrochemical performance compared to the uncoated sample with an initial discharge capacity of 145 mAh/g. A lower operating voltage of LiFePO4 (∼3.4 V) raises the Fermi energy of the cathode surface above the energy of the highest occupied molecular orbital of the electrolyte, offering a chemically stable cathode-electrolyte interface analogous to the stable solid electrolyte interphase layer formed on carbon anodes.