Novel high entropy oxide as anode for high performance lithium-ion capacitors

A fresh type of lithium-ion battery anode called high entropy oxide (HEO) has a remarkable specific capacity and outstanding cycle performance. The advantage of HEO consists in the distinct adjustable contents along with governable chemical constitution, which makes it possible to develop novel electrode materials using infinite combinations of elements. We successfully synthesized (FeCoNiCuZn)3O4 material via a straightforward hydrothermal way in this work. At a lofty current density of 1 A g−1, obtaining an invertible capacity of 540 mAh g−1 behind 500 cycles, the unique structure of (FeCoNiCuZn)3O4 exhibits remarkable stability. We analyzed the valence states of the metal elements and further investigated their relationship with electrochemical and kinetic properties after using X-ray photoelectron spectroscopy (XPS). Subsequently, by incorporating the (FeCoNiCuZn)3O4 anode with activated carbon (AC) in a lithium-ion hybrid capacitor (LIHC), which could deliver an outstanding power density of 4000 W kg−1 and energy density of 158 Wh kg−1 while maintaining excellent capacity retention property even after 5000 cycles, the anode showed considerable performance. This is the first time HEO has been used in LIHC, as far as we are aware.