Tunable pseudocapacitive contribution by dimension control in nanocrystalline-constructed (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O solid solutions to achieve superior lithium-storage properties.

Ultrafine crystalline materials have been extensively investigated as high-rate lithium-storage materials due to their shortened charge-transport length and high surface area. The pseudocapacitive effect plays a considerable role in electrochemical lithium storage when the electrochemically active materials approach nanoscale dimensions, but this has received limited attention. Herein, a series of (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O electrodes with different particle sizes were prepared and tested. The ultrafine (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O nanofilm (3-5 nm) anodes show a remarkable rate capability, delivering high specific charge and discharge capacities of 829, 698, 602, 498 and 408 mA h g-1 at 100, 200, 500, 1000 and 2000 mA g-1, respectively, and a dominant pseudocapacitive contribution as high as 90.2% toward lithium storage was revealed by electrochemical analysis at a high scanning rate of 1.0 mV s-1. This work offers an approach to tune the lithium-storage properties of (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O by size control and gives insights into the enhancement of pseudocapacitance-assisted lithium-storage capacity.