Platelike LiMPO₄ (M = Fe, Mn, Co, Ni) for Possible Application in Rechargeable Li Ion Batteries: Beyond Nanosize

The peculiarities of LiMPO4 (M = Fe, Mn, Co, Ni) formation with controlled platelike crystal shape using layered M(OH)2 hydroxides as templates were studied. Thin, platelike crystals of NH4MPO4·H2O with Mn, Fe, and Co were formed in aqueous solutions as intermediate products, whereas for NH4NiPO4·6H2O, particles in the form of spherulites were observed. For replacement of ammonium groups by lithium cations, a solid-state reaction between NH4MPO4·xH2O and Li2CO3 at elevated temperatures was used. The obtained LiMPO4 particles repeat completely the shape of the intermediated NH4MPO4·xH2O crystals. The surface of platelike particles represents a cellular structure and consists of agglomerated, slightly randomized crystallites of several hundred nanometers, which are oriented along the c-axis perpendicular to the plate surface. It was shown in the LiFePO4 example that the cathode materials, consisting of platelike particles and reduced graphene oxide (RGO), have the discharge capacity of 145 mAh/g in Li ion batteries after 10 cycles with 0.1C. This value can successfully compete with the best literature results reported for nanosized LiFePO4/RGO cathode materials. A possible explanation of that is discussed