Toward a Drift-Diffusion Device Conceptualization of Alkali-Ion Rocking-Chair Batteries

Though rocking-chair batteries are ubiquitously associated with driving electronic devices, descriptions of their dynamical operation have generally been decoupled from the conventional drift-diffusion framework applied to solid-state electronic devices—the latter having enjoyed enormous success in the design of ubiquitous technologies including transistors, solid-state lasers, and light-emitting diodes. Building on long-standing Newman-type descriptions of battery operation, herein we discuss and present a theoretical framework for also conceptualizing the operation of alkali-ion rocking-chair batteries in terms of a competition between ion drift and diffusion via forces and concentration gradients, respectively. It is argued that the key link needed to facilitate a stronger physical bridge between coupled ionic and electronic degrees of freedom lies in the concept of a quasielectric field acting on ions between heterojunctions of ionic materials; a concept borrowed from the solid-state-device literature, where it has been extensively applied in heterojunction devices for decades, and extended in this work via the internal-energy contribution per ion particle. Within a model polymer redox battery system, for which a zero-vacuum reference energy for ions is also proposed, this approach is shown to capture standard battery concepts, including charging, discharging, capacity loss, internal resistances, nonequilibrium charge densities, and operating voltages. In this manner, the findings presented seek to provide a fundamental lasting bridge between electrochemical and electronic device descriptions.