Toward high capacity and stable manganese-spinel electrode materials: A case study of Ti-substituted system

LiMn2−xTixO4 (x = 0, 0.5, 1) cathode materials have been synthesized by a conventional solid state method. The capacity of the as-prepared LiMn2O4, LiMn1.5Ti0.5O4 and LiMnTiO4 are 252, 198 and 157 mAh g−1, respectively, when charging/discharging over the voltage range of 2.0-4.8 V at a current density of 40 mA g−1, all of which are consistent with more than 1 Li+ ion insertion into the spinel structure. Compared with the pristine LiMn2O4, Ti-substituted samples exhibit much better cycling stability both at room temperature and 60 °C between 2.0 V and 4.8 V. The underlying mechanism has been investigated by an in situ X-ray diffraction technique. The results demonstrate that Ti4+ ions can suppress the Jahn-Teller distortion associated with Mn3+, and stabilize the spinel structure during the charging/discharging process. Ti-O bond is stronger than Mn-O bond which yields a more stable spinel framework, i.e., [Mn2−xTix]O4. Moreover, Ti substitution helps lower the concentration of Jahn-Teller Mn3+ ions in the spinel structure during discharging process and consequently improves the structural stability. The role of Ti substitution is also confirmed by the ab initio calculations.