Author:
S Wang，J Yang，X Wu，Y Li，Z Gong，...
Abstract：
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.
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