Charge Storage Mechanisms in Batteries and Capacitors: A Perspective of the Electrochemical Interface

Abstract Researchers developing the next generation of energy storage systems are challenged to understand and analyze the different charge storage mechanisms, and subsequently use this understanding to design and control materials and devices that bridge the gap between high specific energy and power at a target cycle life. Correctly identifying and quantifying the prominent charge storage mechanism is of the utmost importance for understanding how the system functions and tuning material properties for specific applications. The different charge storage mechanisms are defined by a characteristic current‐time scaling that has been defined for electrochemical interfaces with faradaic diffusion‐limited charge storage. However, the characteristic current‐time scaling for faradaic non‐diffusion‐limited (or pseudocapacitive) charge storage remains unelucidated despite to date many battery types, particularly those having 2D electrode materials and electrolytes with ionic liquids, deep eutectic solvents, or highly concentrated electrolytes, exhibit electrochemical interfaces with pseudocapacitive charge storage. This perspective discusses the necessary mathematical expressions and theoretical frameworks for all charge storage mechanisms which are corroborated with experimental data. This perspective can be used as a guide to quantitatively disentangle and correctly identify charge storage mechanisms and to design electrochemical interfaces and materials with targeted performance metrics for a multitude of electrochemical devices.