Ultra-High-Rate Pseudocapacitive Energy Storage in Two-Dimensional Transition Metal Carbides

Typical commercial batteries require prolonged charging and therefore are limiting mobility of users. Systems that are capable of delivering high energy densities at relatively high charge/discharge rates are classified as pseudocapacitors and characterized by absence of phase transformations during operation. The use of fast surface redox storage mechanisms can enable devices that store much more energy than electrical double-layer capacitors (EDLCs) and, unlike batteries, can do so rapidly. Few pseudocapacitive transition metal oxides can provide a high power capability due to their low intrinsic electronic and ionic conductivity. Pseudocapacitors are a sub-class of supercapacitors that are differentiated from EDLCs on the basis of charge storage mechanism. Pseudocapacitive materials are usually tested at moderate charge–discharge rates, namely between those of batteries and EDLCs.