Zn2SiO4@C submicro-ellipsoids assembled from oriented nanorods with outstanding rate performance for Li-ion capacitors

Abstract

Lithium-ion capacitors (LICs), as a highly potential energy converter, integrate the advantages of supercapacitors and batteries and can provide a balanced output of energy and power density. However, the tardy dynamics of the battery-type anode usually results in the sacrifice of power or energy density. Herein, a highly conductive Zn₂SiO₄@C network assembled from uniform submicro-ellipsoids is designed and prepared, in which the short nanorods are oriented and closely arranged and the nitrogen-doped carbon permeated into the whole submicro-ellipsoid. This rectilinear, ordered and multipath charge transfer mode in the Zn₂SiO₄@C hybrid ensures a rapid electrochemical kinetics, leading to a remarkable specific capacity of 1746 mA h g⁻¹ at 0.2 A g⁻¹ over 500 cycles, and a superior capacity ratio of 71% even at 5 A g⁻¹ (compared with the reversible capacity at 0.2 A g⁻¹). The LIC assembled using the Zn₂SiO₄@C anode and graphene hydrogel cathode shows an outstanding energy density of 215 W h kg⁻¹ at 196 W kg⁻¹. Even at an ultra-high power density of 9999 W kg⁻¹, the energy density remains at 79 W h kg⁻¹. The rational and optimal construction of micro-/nano-structured ellipsoid materials provides a new path for the design and synthesis of high-energy and high-power LICs.