Structural and electrochemical characterization of NH4F-pretreated lithium-rich layered Li[Li0.2Ni0.13Co0.13Mn0.54]O2 cathodes for lithium-ion batteries

Abstract

Even though Li-rich layered oxide is considered to be a promising cathode material for Li-ion batteries because of the high discharge capacity, it still suffers from many fundamental challenges such as low initial coulombic efficiency, the voltage fading upon cycling and poor rate performance. In this work, lithium-rich layered Li[Li0.2Ni0.13Co0.13Mn0.54]O2 cathode materials are pretreated by NH4F through a facile solid state method to overcome these problems. After pretreating, the spinel phase LiM2O4 coating layer is formed accompanying with the formation of oxygen vacancies caused by NH3 decomposed from NH4F. Compared with the pristine material, materials pretreated by appropriate amount of NH4F present significantly improved electrochemical performances such as high initial coulombic efficiency and improved stability in successive electrochemical cycling, excellent rate capability and suppressed voltage decay. The pretreated material delivers the highest initial coulombic efficiency of 102.2% (NF10) compared to 74.5% of NF0 and the highest voltage retention of 90.6% compared to 86.2% of NF0. The NF0 delivers the best comprehensive performance, with higher initial coulombic efficiency and voltage retention, improved rate performance and capacity stability.