Impact of microwave synthesis conditions on the rechargeable capacity of LiCoPO4 for lithium ion batteries

Lithium transition metal phosphates have the capability of improving cathode energy densities up to 800 Wh kg^?1, a 27 % increase over conventional cathode active material energy densities. In this study, the effect of base-to-acid (NH₄OH:H₃PO₄) stoichiometric conditions on the intrinsic reversible capacity of lithium cobalt phosphate (LiCoPO₄) active material are investigated through microwave synthesis and electrochemical testing. Variation in solution pH results in an increase of 69 mAh g^?1 in achievable capacity. X-ray diffraction results show highly crystalline LiCoPO₄, with particle sizes ranging from 200 nm to greater than 1 μm based upon scanning electron microscopy. Electrochemical analysis with 1 M LiPF₆ EC:EMC (1:2 v/v) provides the highest capacity over multiple cycles. A discharge capacity of 128 mAh g^?1 (78 % of theoretical capacity) is achievable for intrinsic LiCoPO₄ without further treatment (e.g., carbon coating) at an effective 0.1 C rate with a proper constant current–constant voltage step. Analysis of reported synthesis techniques shows that microwave synthesis yields the highest capacity for the intrinsic LiCoPO₄ material to date.