Mechanism of the electrochemical insertion of lithium into LiMn2O4 spinels

LiMn2O4-based spinels have been extensively studied as positive electrode materials for Lithium-ion batteries. Our investigations have shown that, by using the Pechini process, the performance of these materials can be improved significantly through adjustments to the synthesis conditions and composition by means of selective doping. This paper reports the results of neutron and ex situ X-ray diffraction studies performed to examine the structural changes that occur during lithium ion insertion into various LixMn2O4 compositions. It appears that an ordering intercalation of lithium ions occurs in the lithium concentration range of 0.15-0.35, followed by a second-order phase transformation when the lithium population is close to 0.5, leading to a random lithium insertion into a single-spinel phase from x=0.5 to 1.0.