Optimized evolution of a secondary structure of LiFePO4: balancing between shape and impurities

Abstract

The kinetically helpful hollow secondary structure of LiFePO₄ olivine (LFP) was optimized by a balance between its impurities and shape. In a thermodynamic process using hydrothermal treatment (+HyT), a relatively small amount of hollow structure was developed without any impurities by a sequential precipitation method using the difference of the solubility products (K_sp) between two precipitates (Li₃PO₄ and Fe₃(PO₄)₂). On the other hand, a kinetically controlled process without hydrothermal treatment (−HyT) produced the opposite result of a greater amount of hollow structure with impurities (Li₃PO₄). By removing the LFP impurities from the latter process (−HyT*), therefore, optimized hollow LFP was obtained without impurities. The resultant cathode material showed enhanced capacities, especially at high rate discharges, due to the improved accessibility of ions into the primary particles of the hollow secondary structure of LFP.