Preparation and characterization of o-LiMnO2 cathode materials

Small particle-sized orthorhombic LiMnO2 powders were prepared via Pechiniʹs route with Li/Mn molar ratio ranging between 1.00 and 1.20, followed by calcinations at 300 °C in air and heat-treatment at temperatures between 700 and 900 °C for various durations under flowing nitrogen. The effects of heat-treatment conditions and starting Li/Mn molar ratio on the crystalline structure and the electrochemical properties were investigated with XRD, SEM, and capacity retention study. Orthorhombic phase were found exclusively in the samples prepared with starting Li/Mn molar ratios between 1.00 and 1.05 followed by heat-treatment at 800 °C for 15 h, whereas monoclinic Li2MnO3 and tetragonal Li2Mn2O4 were also observed in the samples prepared with Li/Mn ratios higher than 1.10. The charge/discharge curves of capacity retention studies and the cyclic voltammograms showed that the transformation of o-LiMnO2 into cycle-induced spinel phase proceeds more progressively and the capacity loss upon cycling are more significant for the samples containing the impurity phases than the well-ordered o-LiMnO2 sample. The sample synthesized with starting Li/Mn ratio of 1.05 followed by heat treatment at 800 °C for 15 h showed the most promising cycling performance among the prepared powders with the maximum discharge capacity of 158 mAh g−1 at 20th cycle and capacity loss of 3% between 20th and 80th cycles at 30 °C.