Suppressed High-Voltage Activation and Superior Electrochemical Performance of Co-Free Li-Rich Li₂TiO₃-LiNi_0.5Mn_0.5O₂ 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) LiNi_0.5Mn_0.5O₂ (x = 0.33, 0.50, 0.66) and xLi₂MnO₃·(1 - x) LiNi_0.5Mn_0.5O₂ (x = 0.5) binary systems has been evaluated. It is found that 0.5Li₂TiO₃·0.5LiNi_0.5Mn_0.5O₂ (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 0.5Li₂MnO₃·0.5LiNi_0.5Mn_0.5O₂ (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.