Lithium insertion/deinsertion mechanisms in the transition metal pnictides LixMPn4

This paper presents a combined experimental and computational study of the electrochemical reactivity of the ternary transition metal pnictides Li(x)MPn(4) (M = Ti, V; Pn = P, As) towards Li. These materials show high specific capacities (500 < C < 1000 mAhg(-1)) in their first charge/discharge cycles which are holded on to 80% after 20 cycles and are very promising as negative electrode material in Li-ion battery. The high reversible charge/discharge process is associated with a destruction/recovering of the long-range cubic order. On the basis of electronic structure calculations we rationalize this mechanism by means of the contraction/elongation of the M-Pn bonds of the strongly bonded MPn(4) tetrahedra.