Toward high capacity and stable manganese-spinel electrode materials: A case study of Ti-substituted system
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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 degrees 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]O-4. Moreover, Ti substitution helps lower the concentration of Jahn-Teller Mn3+ ions in the spinet structure during discharging process and consequently improves the structural stability. The role of Ti substitution is also confirmed by the ab initio calculations. (C) 2013 Elsevier B.V. All rights reserved.