A Chemical Approach to Raise Cell Voltage and Suppress Phase Transition in O3 Sodium Layered Oxide Electrodes

Sodium ion batteries (NIBs) are one of the versatile technologies for low-cost rechargeable batteries. O3-type layered sodium transition metal oxides (NaMO2, M = transition metal ions) are one of the most promising positive electrode materials considering their capacity. However, the use of O3 phases is limited due to their low redox voltage and associated multiple phase transitions which are detrimental for long cycling. Herein, a simple strategy is proposed to successfully combat these issues. It consists of the introduction of a larger, nontransition metal ion Sn4+ in NaMO2 to prepare a series of NaNi0.5Mn0.5-ySnyO2 (y = 0-0.5) compositions with attractive electrochemical performances, namely for y = 0.5, which shows a single-phase transition from O3 double left right arrow P3 at the very end of the oxidation process. Na-ion NaNi0.5Sn0.5O2/C coin cells are shown to deliver an average cell voltage of 3.1 V with an excellent capacity retention as compared to an average stepwise voltage of approximate to 2.8 V and limited capacity retention for the pure NaNi0.5Mn0.5O2 phase(.) This study potentially shows the way to manipulate the O3 NaMO2 for facilitating their practical use in NIBs.