Li-Rich Cathode Materials for Rechargeable Na Batteries: Ion-Exchange Method

Abstract

The relatively low capacity and limited cycling retention of many known Na-ion battery prototypes are presumably due to the fact that most of the cathode materials undergo multiple phase transformations which lead to instability during cycling (due to stresses that challenge their crystal structure). Such structural transformations and the consequent instability of Na ions insertion cathodes could be one of the major problems that limit the practical development of Na-ion batteries. To overcome this issue, we investigated new cathode compounds that are synthesized through Li–Na ion exchange. We start from O3-Li rich cathode materials and produced by electrochemical ion exchange the new cathode material Na1Li0.05Mn0.54Ni0.13Co0.2O2-x. Also, the stability of electrochemically prepared Na insertion cathode materials in cycling experiments was insufficient for practical consideration. In turn, cathodes prepared from the same Li precursors coated by a thin layer of alumina via atomic layer deposition, followed by electrochemical Na/Li ion exchange, demonstrated stable capacity (>170 mAh/g) during prolonged cycling. Their average discharge voltage was 300 mV higher compared to the counterpart uncoated Na intercalation cathodes. The structure and behavior of these electrodes were thoroughly explored by a variety of analytical and surface tools, in conjunction with electrochemical techniques