O3-type NaNi0·33Li0·11Ti0·56O2-based electrode for symmetric sodium ion cell

Abstract

Abstract Layered materials Na 0.67+3x Ni 0.33 Li x Ti 0.67-x O 2 with Li-substitution as x = 0, 0.05 and 0.11 have been synthesized and investigated as “bi-functional” electrodes for symmetric sodium ion cells. The samples with lithium substitution up to 0.11 are confirmed to be a single phase without impurities and introducing lithium into the transition metal layer increases the interlayer space of the layered materials. It is found that O3-type NaNi 0·33 Li 0·11 Ti 0·56 O 2 exhibits two electrochemical working windows, 0.4–0.8 V and 3.1–3.75 V, for sodium ion storage. The as-proposed material thus can be employed as both positive and negative electrodes. As positive electrode, it shows a high working voltage of ca. 3.75 V versus Na + /Na and an initial capacity of 91 mAh g −1 with 19% capacity loss after 100 cycles. When utilized as negative electrode, it delivers a low average voltage of ca. 0.65 V versus Na + /Na, along with a reversible capacity of 125 mAh g −1 and 76% capacity retention after 200 cycles. A symmetric full cell based on the O3-type NaNi 0·33 Li 0·11 Ti 0·56 O 2 “bi-functional” electrode has been developed. The cell exhibits a high voltage of 3.1 V and an energy density of 100 W h kg −1 based on the total mass of active electrode materials.