Structurally stabilized olivine lithium phosphate cathodes with enhanced electrochemical properties through Fe doping

Abstract

Controlling the crystallographic structure in olivine lithium phosphates is crucial for obtaining superior electronic (J. Electrochem. Soc., 2002, 149, A1184-A1189) and ionic conductivities (Electrochem. Solid-State Lett., 2006, 9, A352-A355; Electrochem. Solid-State Lett., 2006, 9, A439-A442; Nat. Mater., 2002, 1, 123-128), and stability, for use as cathodes in lithium batteries. Here, we report a completely new approach to enhance Li⁺ extraction and transport in LiCoPO₄ through Fe doping. We show that preferential Fe occupation of the 4c sites suppresses 4a–4c antisite mixing of Li and Co, thereby stabilizing the olivine structure by compensating for the Co-encapsulating oxygen octahedron shrinkage due to Co²⁺ oxidation during Li⁺ extraction. The structural stabilization gives rise to ∼10% higher charge capacity at a two-fold lower resistance than the undoped counterparts besides accelerating the intercalation/extraction kinetics. Our findings provide key atomistic-level insights that pave the way for the rational design and realization of new types of metal-doped cathode materials for lithium batteries and related applications.