Suppressed High-Voltage Activation and Superior Electrochemical Performance of Co-Free Li-Rich Li2TiO3–LiNi0.5Mn0.5O2 Cathode Materials for Li-Ion Batteries

Although integrated Li- and Mn-rich layered oxides, composed of the active LiMO2 phase and the inactive Li2MnO3 phase, can provide a specific capacity of 250 mAh g–1, there are a few challenges such as an irreversible capacity loss in the first cycle, capacity decay, and discharge voltage decay upon cycling, which hinder their practical applications. The layered-to-spinel transition resulting from the cycling of Li2MnO3 to above 4.5 V leads to a decrease in the average discharge voltage and capacity decay upon cycling. As Li2TiO3 (LTO) is a monoclinic phase similar to Li2MnO3 and the Ti–O bond is relatively stronger than the Mn–O bond, it may suppress the loss of oxygen and also the layered-to-spinel transition during high-voltage cycling. In this regard, it is interesting to substitute the Li2MnO3 component in the Li- and Mn-rich oxides with Li2TiO3 and to test their cycling stability performance as the cathode material in Li-ion batteries. Herewith, the electrochemical performance of xLi2TiO3·(1 – x) LiNi0.5Mn0.5O2 (x = 0.33, 0.50, 0.66) and xLi2MnO3·(1 – x) LiNi0.5Mn0.5O2 (x = 0.5) binary systems has been evaluated. It is found that 0.5Li2TiO3·0.5LiNi0.5Mn0.5O2 (LTO-LNMO 5050) can deliver an initial specific capacity of about 197.8 mAh g–1 with 71% retention of capacity after 150 cycles upon cycling at a 0.1C rate. Alternately, the sample 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 (LMO-LNMO 5050) exhibits an initial specific capacity of 261 mAh g–1 with only 46.5% retention of capacity after 150 cycles. Thus, this study clearly depicts the better electrochemical performance of LTO-LNMO 5050 over LMO-LNMO 5050 in terms of cycling stability. The better performance of LTO-LNMO 5050 can be due to the structural stabilization provided by the LTO component, which has been evidenced by the ex situ Raman and transmission electron microscopy (TEM) study.