Superstructure in the Metastable Intermediate-Phase Li2/3FePO4 Accelerating the Lithium Battery Cathode Reaction

• Published in: Angewandte Chemie International Edition 2015-07, Vol.54 (31), p.8939-8942
• Main Authors: Nishimura, Shin-ichi, Natsui, Ryuichi, Yamada, Atsuo
• Format: Article
• Language: English
• Subjects: cathode materials; LiFePO4; Lithium; lithium-ion batteries; olivine; solid-state structures
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201501165

LiFePO4 is an important cathode material for lithium‐ion batteries. Regardless of the biphasic reaction between the insulating end members, LixFePO4, x≈0 and x≈1, optimization of the nanostructured architecture has substantially improved the power density of positive LiFePO4 electrode. The charge transport that occurs in the interphase region across the biphasic boundary is the primary stage of solid‐state electrochemical reactions in which the Li concentrations and the valence state of Fe deviate significantly from the equilibrium end members. Complex interactions among Li ions and charges at the Fe sites have made understanding stability and transport properties of the intermediate domains difficult. Long‐range ordering at metastable intermediate eutectic composition of Li2/3FePO4 has now been discovered and its superstructure determined, which reflected predominant polaron crystallization at the Fe sites followed by Li+ redistribution to optimize the LiFe interactions. Understanding of intermediate phases in the battery electrode reaction is critical to maximize cell performance. Using a combined analysis of electron, neutron, and X‐ray diffraction, a superstructure in the metastable intermediate Li2/3FePO4 was determined. The superstructure is stabilized by charge‐ordering stripes at Fe sites followed by Li redistribution to optimize the local interactions.