Effect of copper substitution on the electrochemical properties of high entropy layered oxides cathode materials for sodium-ion batteries

摘要

Layered oxide cathode materials in batteries usually experience complex phase transition during intercalating-deintercalating reaction, leading to poor cycle stability. However, high entropy oxides (HEOs) which can sup-press the intermediate phase change have been reported with stable crystal structure and improved cycle stability as cathode materials for sodium-ion batteries (SIBs). Here we synthesize a non-toxic Cu substituted HEOs NaNi0.4-xCuxFe0.2Mn0.2Ti0.2O2 (x = 0, 0.1, 0.2, 0.3, 0.4) via high temperature solid-state reaction, and the effect of Cu substitution is analyzed in detail. NaNi0.3Cu0.1Fe0.2Mn0.2Ti0.2O2 delivers an initial specific capacity of 123.6 mA h g-1 at 0.1C rate corresponding to a capacity retention of 90.05 after 50 cycles, while NaNi0.4-Fe0.2Mn0.2Ti0.2O2 delivers a reversible an initial specific capacity of 129.1 mA h g-1corresponding to a capacity retention of 74.83 . Cu substitution inhibits the phase transition and improve cycle stability of the material during cycling without sacrificing much capacity. This result constitutes a step forward in increasing the prac-ticality of SIBs.