Structural and electrochemical properties of Li_0.44+xMn_1-yTi_yO₂ as a novel 4 V positive electrode material

The specific capacity of Li_0.44Mn_1-yTi_yO₂ (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 Li_0.44+xMn_1-yTi_yO₂ 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 Li_0.44+xMn_1-yTi_yO₂ 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 Li_0.44+xMn_1-yTi_yO₂ compounds. The maximum discharge capacity that has been achieved is 180 mAh g^-1 in the case of Li_0.72Mn_0.78Ti_0.22O₂ 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 Li_0.55MnO₂ has been improved to twice that in as-prepared Li_0.44MnO₂ (about 50 mAh g^-1). The structural differences between Li_0.44MnO₂ and Li_0.55MnO₂ are discussed based on XRD Rietveld analysis results.