Superstructure in the Metastable Intermediate-Phase Li2/3FePO4 Accelerating the Lithium Battery Cathode Reaction†
This work was supported by JSPS KAKENHI grant Numbers 23245042 and 19205027. The neutron diffraction data were collected under the assistance of Prof. Toru Ishigaki at Ibaraki University. The synchrotron experiments were performed under approval of the Photon Factory Program Advisory Committee (Proposal No. 2011G683, 2013G670). Preliminary experiments were performed at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2011B1872 and 2013A1665).
Abstract
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 LiFe interactions.
