Electrochemical Na-Migration into Delithiated Phase LizNi1/3Mn1/3Co1/3O2: Structure and Electrochemical Properties

Abstract

This work aims to investigate Na-migration into the delithiated phase LizNi1/3Mn1/3Co1/3O2 (LizNMC), which is prepared via galvanostatic oxidation from initial phase LiNi1/3Mn1/3Co1/3O2 (LiNMC). XRD patterns showed the structural conservation of the delithiated phase comparing to the origin state. In electrochemical study, a reversible 0.48 Na-migration ions per mole was observed (120 mAh/g) at rate C/10, corresponding to a partial oxidation state of Ni4+/Ni2+. The smooth charge-discharge curves indicated an essential role of inner remaining Li+ ions in the delithiated phase to prevent the drastic gliding octahedra layers during Na insertion/extraction. The cycling tests remarked the stable performances in long-term test at C/10 as well as rate capability (from C/10 to 1C). The discharge capacities were found out 100 mAh/g at C/5, 80 mAh/g at C/2 and 40 mAh/g at 1C; a capacity retention of 100% was observed after staircase. The diffusion coefficients DNa of 10−9-10−10 cm2/s obtained from GITT data suggest a high mobility of sodium ion in the delithiated phase LizNMC.