Creation of an extrinsic pseudocapacitive material presenting extraordinary cycling-life with the battery-type material Co(OH)2 by S2− doping for application in supercapacitors

Some battery-type materials show the potential for storing high density energy in supercapacitors because of their high theoretical capacity. So far, the very unsatisfied electrochemical performance is still the label of these battery-type materials, which is attributed to their diffusion-controlled kinetics of energy storage. Some efforts try to transform their electrochemical behavior to extrinsic pseudocapacitive behavior through nanostructuring. However, the extrinsic pseudocapacitive materials are rare due to the restriction of no phase transformation. In this work, we propose an alternative strategy to create an extrinsic pseudocapacitive material from the typical battery-type material Co(OH)2 by S2− doping. The doped S2− ions further increase energy barrier for the intercalation of OH− ions into the interlayer space of Co(OH)2, thus suppressing its bulk phase transformation. Also, the decreased OH− ions-Co(OH)2 interaction plus the surface reaction feature induced by S2− doping results in the pseudocapacitive behavior. Thus, the S2− doped Co(OH)2 presents the comprehensive electrochemical signatures of pseudocapacitive materials and an extraordinary cycling life of 200,000 charge-discharge cycles. This work initiates a new way for acquiring electrode materials with high electrochemical performance for application in supercapacitors.