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

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%H-2/N-2 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 approximate to 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.