Effect of MnO2 modification on electrochemical performance of LiNi0.2Li0.2Mn0.6O2 layered solid solution cathode

Pristine and MnO2-coated LiNi0.2Li0.2Mn0.6O2 powders have been synthesized in this paper. The effect of MnO2 coating on the physical and electrochemical properties is discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), discharge, cyclic and rate performance tests. The materials show layered structure before and after coating. The MnO2-coated LiNi0.2Li0.2Mn0.6O2 electrodes show better discharge capacity, first coulomb efficiency, cyclic performance and rate capacity compared with pristine LiNi0.2Li0.2Mn0.6O2. And the LiNi0.2Li0.2Mn0.6O2 coated with MnO2 decomposing from manganese carbonate has the best performance. The first coulomb efficiency is 82.7%. The discharge capacities at 0.1 and 10 C are 253 and 99 mAh g(-1), respectively, and it presents no obvious capacity loss after 50 cycles. The discharge and cyclic voltammetry (CV) curves show that the coated MnO2 reacts with Li+ during the charge and discharge cycle, which is responsible for higher discharge capacity after coating. Electrochemical impedance spectroscopy (EIS) results show that the R-ct of LiNi0.2Li0.2Mn0.6O2 electrode decreases after coating, which is due to the suppression of the solid electrolyte interfacial (SEI) layer development and is responsible for the better cyclic and rate performance. (C) 2012 Elsevier B.V. All rights reserved.