Structural evolution in LiFePO4-based battery materials: In-situ and ex-situ time-of-flight neutron diffraction study

Neutron diffraction has been used for in-situ studying of the charge discharge processes in commercial lithium batteries with LiFePO4 (LFP) and graphite electrodes. The diffraction data were obtained with time-of-flight diffractometer in the process of three complete charge discharge cycles performed at a low rate (0.1 C) at room temperature. The experimental data allowed detailed tracing of the multistage process of Li insertion into graphite followed by the formation of several LiCn phases, as well as the reversible transition of LiFePO4 <-> FePO4. A comparison of the charge discharge processes in a battery with a pure LFP cathode and LFP containing similar to 1% of vanadium (LFPV) is made. In the second case, an evidently larger part of the anode material passes into the final LiC6 state. Analysis of the diffraction patterns of LFP and LFPV powders revealed a marked shrinkage of crystallite size in the LFPV case, which correlates with better electrochemical properties of LFPV compared to LFP. (C) 2014 Elsevier B.V. All rights reserved.