Microwave-Assisted Solvothermal Synthesis of Three Polymorphs of LiCoPO₄ and Their Electrochemical Properties

Abstract

Many investigations have been conducted on polyanion cathodes for lithium-ion batteries, specifically LiMPO 4 (M = Fe, Mn, Co, Ni), but a majority were restricted to the olivine polymorph with the Pnma space group. This study presents the synthesis and characterization of three orthorhombic polymorphs of LiCoPO 4 belonging to the space groups Pnma, Pn 2 1 a, and Cmcm . The three polymorphs were synthesized with a microwave-assisted solvothermal (MW-ST) synthesis method at a relatively low temperature of 260 °C. The properties and morphology of the materials were characterized with X-ray diffraction, inductively coupled plasma–optical omissions spectroscopy, Raman and infrared spectroscopy, scanning electron microscopy, thermogravometric analysis, galvanostatic charge/discharge, and cyclic voltammetry. The electrochemical properties of the Cmcm polymorph and nanosized Pn 2 1 a polymorph are reported for the first time.