Exploring the working mechanism of Li+ in O3-type NaLi0.1Ni0.35Mn0.55O2 cathode materials for rechargeable Na-ion batteries

Na-ion batteries (NIBs) have recently attracted much attention, due to their low cost and the abundance of sodium resources. In this work, NaLi0.1Ni0.35Mn0.55O2 as a promising new kind of cathode material for Na-ion batteries was synthesized by a co-precipitation method. Powder XRD patterns show that the sample has a primary O3-type structure after Li+ substitution. The material delivers excellent electrochemical performance, with an initial discharge specific capacity of 128 mA h g(-1) and a capacity retention of 85% after 100 cycles at a rate of 12 mA g(-1) in the voltage range of 2.0-4.2 V. In a widened voltage range of 1.5-4.3 V, the specific capacity can reach up to 160 mA h g(-1). The structural stability of the material is substantially improved compared with lithium-free NaNi0.5Mn0.5O2, which can be attributed to the formation of an O'3 phase caused by Li-substitution, as proven by in situ XRD and solid state NMR (ss-NMR) measurements.