Electrochemical Kinetics and Performance of Layered Composite Cathode Material Li[Li0.2Ni0.2Mn0.6]O2

Lithium-rich, manganese-rich (LMR) layered composite cathode material Li[Li0.2Ni0.2Mn0.6]O-2 synthesized by a co-precipitation method delivers a high discharge capacity of 281 mAh g(-1) at a low current density of C/25. However, significant increase of cell polarization and decrease of discharge capacity are observed at voltage below 3.5 V with increasing current densities. Galvanostatic intermittent titration technique (GITT) analysis and electrochemical impedance spectroscopy (EIS) measurements demonstrate that lithium ion intercalation/de-intercalation reactions into/out of this material are kinetically controlled by Li2MnO3 component and its activated MnO2 component. The relationship between the electrochemical kinetics and rate performance as well as cycling stability has been systematically investigated. High discharge capacity of 149 mAh g(-1) can be achieved at 10 C charge rate and C/10 discharge rate, indicating that the LMR cathode could withstand high charge rate (except initial activation process), which is very promising for practical applications. The results also reveal that the continuous formation of poorly conducting spinel phase is responsible for the capacity fading of LMR cathodes. (C) 2013 The Electrochemical Society. All rights reserved.