Abstract
Li(Mn1.5Ni0.5)O4 (MNO) is promising spinel cathode material for lithium ion batteries (LIB) due to its increased intercalation potential and improved capacity retention compared to LiMn2O4. Still, improvements to this materials performance must be achieved before MNO is a viable option for commercial LIB cells. In situ X-ray diffraction of Li(Mn1.5Ni0.5)O4 was performed using a novel electrochemical cell based on coin cell hardware. A diffractogram of the pristine material showed a spinel structure with a Ni2+ oxidation state. As the cell was charged through its 4.75V plateau, a transition between spinels with Ni2+, Ni3+, and Ni4+ oxidation was observed. As the oxidation stage on the nickel increased the lattice parameter of the corresponding spinel was reduced. As discharged ensued the spinel reversed its phases change until only the Ni2+ spinel was present. When discharge reached the 2.75V plateau a tetragonal spinel phase was formed, which upon subsequent cell charging was completely converted back to a cubic spinel phase. Lattice parameter changes of each phase were calculated and showed a characteristic strain release during phase changes. After 15 full cycles the transition between these phases was no longer complete and the formation of the tetragonal spinel phase was no longer detected. A discussion of how these cycle-induced changes to phase transition behavior relate to capacity fade and overall cell performance is presented.
