Size Effects on Carbon-Free LiFePO₄ Powders: The Key to Superior Energy Density

C-free ${\mathrm{LiFePO}}_4$ crystalline powders were prepared by a synthesis method based on direct precipitation under atmospheric pressure. The particle size distribution is extremely narrow, centered on ca. $140\mathrm{nm}$. A soft thermal treatment, typically at $500°C$ for $3h$ under slight reducing conditions was shown to be necessary to obtain satisfactory electrochemical ${\mathrm{Li}}^{+}$ deinsertion/insertion properties. This thermal treatment does not lead to grain growth or sintering of the particles, and does not alter the surface of the particles. The electrochemical performances of the powders obtained by this synthesis method are excellent, in terms of specific capacity ($147\mathrm{mAh}{g}^{-1}$ at 5C-rate) as well as in terms of cyclability (no significant capacity fade after more than 400 cycles), without the need of carbon coating.