Mesoporous ZnCo2O4-CNT microflowers as bifunctional material for supercapacitive and lithium energy storage

Abstract

As one kind of binary transition metal oxide, ZnCo2O4 (ZCO) displays excellent specific capacitance/capacity and high energy density as electrodes of supercapacitors (SCs) and lithium ion battery (LIBs). Introducing carbon materials has become a common method to obtain higher performance. In this work, the electronic property of ZnCo2O4 was firstly studied by Density Functional Theory to provide a theoretical support for the ZnCo2O4-CNT (ZCO-CNT) composite as electrode materials. Then, the composite was synthesized in a facile one-step hydrothermal way. The homogenous combination of the ZnCo2O4 microflower with CNTs provided continuous electron transmission channels and fast electron transfer inside the composite, which also absorbed the stress in electrochemical reactions, and therefore helped maintaining a stable composite structure during cycling. Besides, the microscale dimension of ZCO-CNT flowers can also alleviate self-aggregation and stable structure during electrochemical reactions. As the positive electrode of asymmetric supercapacitor, the ZCO-CNT//activated carbon device demonstrated an energy density of 24.46 Wh·kg−1 at a power density of 750 W·kg−1, as well as a high capacitance retention of 84.6% after 3000 cycles. Furthermore, as for LIBs, ZCO-CNT was regarded as a kind of potential anode electrode material. An excellent reversible capacity of 1200 mAh·g−1 could be obtained after 120 cycles at 200 mA·g−1.