Neutron diffraction and Raman analysis of LiMn1.5Ni0.5O4 spinel type oxides for use as lithium ion battery cathode and their capacity enhancements

• PND is a highly suitable tool for discriminating between ordered and disordered phases.
• Heat treatment at 600 °C for 20 h results in disordered phase (Fd-3m).
• Treatment at 600 and 700 °C produces nanoparticles (~ 10 & 50 nm respectively).
• Propylene carbonate is successfully used to optimize the cathode performance.
• Hitherto highest capacity for submicron particles of ordered phase (P4332) ~ 137 mAh/g.

LiMn1.5Ni0.5O4 cathode materials for lithium ion batteries (LIBs) were synthesized by the low cost wet-chemical Pechini technique. Phase analysis by X-ray diffraction shows that extended heat treatment at 900 °C causes precipitation of LixNi1 − xO with consequent reduction in specific energy capacity. Raman spectroscopy and powder neutron diffraction have been extensively integrated into characterization of variously annealed samples and provided key information on Ni–Mn order–disorder for samples studied electrochemically. A fully disordered, nano-crystalline product (space group Fd-3m) is obtained at 600 °C, while ordered materials (space group P4332) are obtained for samples with a final treatment at 700 °C. Crystallographic data are obtained from Rietveld refinements. Samples treated at 600 and 700 °C are received as nano-sized particles, ~ 10 and ~ 50 nm, respectively, while well faceted particles are obtained at higher temperatures. The addition of propylene carbonate significantly improves cathode performance when followed by a leaching step that yields a porous cathode tape. The ordered material calcinated at 900 °C and thereafter at 700 °C for 10 h shows a specific capacity of ~ 137 mAh/g at 0.04 C and ~ 130 mAh/g at 2 C discharge rates; the highest capacities so far reported for sub-micron particles of the ordered phase. This study provides a route to performance enhanced pure LiMn1.5Ni0.5O4 spinel materials for LIB cathodes.