Solvothermal Synthesis, Development, and Performance of LiFePO₄ Nanostructures

We report the synthesis and nanostructural development of polycrystalline and single crystalline LiFePO 4 (LFP) nanostructures using a solvothermal media (i.e., water–tri(ethylene glycol) mixture). Crystal phase and growth behavior were monitored by powder and synchrotron X-ray diffraction, as well as transmission electron microscopy (TEM), while particle morphologies were examined using scanning electron microscopy (SEM). Initially, thin (100 nm) platelets of Fe 3 (PO 4 ) 2 ·8H 2 O (vivianite, VTE) formed at short reaction times followed by the nucleation of LFP (20 nm particles) on the metastable VTE surfaces. Upon decrease in pH, primary LFP nanocrystals subsequently aggregated into polycrystalline diamond-like particles via an oriented attachment (OA). With increasing reaction time, the solution pH further decreased, leading to a dissolution–recrystallization process (i.e., Ostwald ripening, OR) of the oriented polycrystalline LFP particles to yield evenly sized, single crystalline LiFePO 4 . Samples prepared at short reaction durations demonstrated a larger discharge capacity at higher rates compared with the single crystalline particles. This is due to the small size of the primary crystallites within larger secondary LiFePO 4 particles, which reduced the lithium ion diffusion path while subsequently maintaining a high tap density. Understanding the relationship between solution conditions and nanostructural development as well as performance revealed by this study will help to develop synthetic guidelines to enable efficient lithium ion battery performance.