Solvothermal water-diethylene glycol synthesis of LiCoPO4 and effects of surface treatments on lithium battery performance

Abstract

Olivine-structured LiCoPO₄ is prepared via a facile solvothermal synthesis, using various ratios of water/diethylene glycol co-solvent, followed by thermal treatment under Ar, air, 5%H₂/N₂ or NH₃. The diethylene glycol plays an important role in tailoring the particle size of LiCoPO₄. It is found that using a ratio of water/diethylene glycol of 1 : 6 (v/v), LiCoPO₄ is obtained with a homogenous particle size of ∼150 nm. The bare LiCoPO₄ prepared after heating in Ar exhibits high initial discharge capacity of 147 mA h g⁻¹ at 0.1C with capacity retention of 70% after 40 cycles. This is attributed to the enhanced electronic conductivity of LiCoPO₄ due to the presence of Co₂P after firing under Ar. The effects of carbon, TiN and RuO₂ coating are also examined. Contrary to other studies, it is found that the solvothermally synthesised LiCoPO₄ samples produced here do not require conductive coatings to achieve good performance.