Properties, functions, and challenges: current collectors

Current collectors always play a vital role in battery and supercapacitor cells which bridges the electrons from active materials toward external devices. However, the second function of a current collector – as a substrate to cultivate the growth of active material – has always been overlooked and ignored. Likewise, the growing interest in preparing active materials directly with current collectors has molded integrated electrodes, eliminating the use of additional binders and additives. In this review, we discuss the importance of current collectors, their functions and capabilities, and their role in integrated electrodes. Likewise, methods of preparing binder-free integrated electrodes and controlling the mass to an optimized and desirable structure that can unlock superior electrochemical properties are also elaborated. We also suggest accurate analysis techniques to determine the precise mass of active electrode materials from integrated electrodes. Last, considerations and outlooks are discussed to provide insight into the future direction of research for inexpensive, sustainable, and functional current collectors. • Number of current collectors are discussed. • Integrated electrode vs. bulk and pasted powder are compared. • The types, properties, limitations, and challenges are discussed. • Unique functions and capabilities of current collectors are critically investigated. • Last, outlook and future directions towards inexpensive, functional, and sustainable conductive current collectors are discussed.