Toward understanding the lithiation/delithiation process in Fe_0.5TiOPO₄/C electrode material for lithium-ion batteries

Fe_0.5TiOPO₄/C composite was used as anode material for LIB and exhibits excellent cycling performance when the electrode is cycled in two different voltage ranges [3.0-1.3 V] and [3.0-0.02 V] where different insertion mechanisms were involved. A detailed in situ XANES spectroscopy study coupled to the electrochemical analyses, clearly established that the structure of Fe_0.5TiOPO₄/C electrode materials is preserved when cycled between 3.0 and 1.3 V. Furthermore, a formation of new phase at the end of first discharge was evidenced, with a reversible capacity of 100 mA h g^-1 after 50 cycles at C/5 rate. At highly lithiated states, [3.0-0.02 V] voltage range, a reduction-decomposition reaction highlights the Li-insertion/extraction behaviors, and low phase crystallinity is observed during cycling, in addition an excellent rate behavior and a reversible capacity of 250 mA h g^-1 can still be maintained after 50 cycles at high cycling rate 5C.