Structural and electrochemical properties of Li0.44+xMn1−yTiyO2 as a novel 4 V positive electrode material

The specific capacity of Li0.44Mn1−yTiyO2 (0 < y < 0.22) positive electrode materials has been improved by an additional lithium-insertion treatment in molten LiNO3–LiOH salt at a low temperature. High-purity specimens of the lithium-inserted Li0.44+xMn1−yTiyO2 have been successfully prepared. We have conducted a systematic experimental study of the structural and electrochemical properties of these compounds. The inserted lithium content, x, in Li0.44+xMn1−yTiyO2 increases together with the substituted Ti content, y. The initial charge capacity increases from 130 mAh g−1 (y = 0) to 145 mAh g−1 (y = 0.22) for the Li0.44+xMn1−yTiyO2 compounds. The maximum discharge capacity that has been achieved is 180 mAh g−1 in the case of Li0.72Mn0.78Ti0.22O2 between 2.5 and 4.8 V with a fixed current density of 30 mA g−1 (C/6) at 30 °C. The discharge capacity at the 4 V plateau region (about 100 mAh g−1) in the lithium-inserted Li0.55MnO2 has been improved to twice that in as-prepared Li0.44MnO2 (about 50 mAh g−1). The structural differences between Li0.44MnO2 and Li0.55MnO2 are discussed based on XRD Rietveld analysis results.