Hydrothermal synthesis, silver decoration and electrochemistry of LiMPO4 (M=Fe, Mn, and Co) single crystals
Résumé
Ionothermal synthesis was recently reported as a very attractive method to design new electrode materials for lithium ion batteries. Here, we report the use of hydrothermal synthesis, using water or a water-ionic liquid (IL) mixture as reacting medium, to prepare hexagonal shaped micrometric LiMPO4 (M=Fe, Mn and Co) single crystals oriented along the b direction at 260 °C. The influence of the reacting medium and the reaction time on the size of single crystals has been ascertained with the feasibility of growing after one month reacting time 700 μm LiFePO4 single crystals in water-IL media and smaller ones (80-120 μm) in water. The latter exhibit electrochemical capacities of 145 mAh/g at C/2 rate with excellent capacity retention when cycled at 100 °C. Last, we show a novel way to decorate the surface of "LiFePO4" crystals through the reduction of silver nitrate into metallic silver. This enables an easy determination of the crystal growth directions while providing insights in the lithium diffusion processes.