Dual metal (Fe and Mg) substituted layered titanium-based P2 and O3-type negative electrodes for rechargeable sodium batteries

A first attempt was made to enhance the electrochemical performances, using the binary metal (Fe and Mg) substitution on the layered Titanium-based P2-type Na0.5Ni0.2Ti0.6O2 (P2-NNTFMO) and O3-type NaNi0.2Ti0.6O2 (O3-NNTFMO) anode materials, via traditional solid state reaction for sodium ion batteries (SIBs). The XPS analysis of the O3-NNTFMO negative material exhibit the presence of Ti, Ni, Fe and Mg ions happens in +4, +2, +3 and +1 valance states respectively. The discharge and charge curves reveal the P2-NNTFMO and O3-NNTFMO anode materials have the charge capacities of 117.60 and 128.48 mAh/g respectively. The limited amount of co-substitution (Fe and Mg) in transition metal oxide layers would enlarge the sodium ion diffusion layers during cycling for O3 and P2-type anodes, due to the shrinkage of TMO6 octahedrons and decrease of TM-O bond lengths.