Nonlinear Potentiodynamic Battery Charging Protocols for Fun, Education, and Application

Abstract

Most secondary batteries in academia are (dis)­charged by applying a constant current (CC) followed by a constant voltage (CV), i.e., a CCCV procedure. The usual concept is then to condense data for interpretation into representations such as differential capacity, or dQ/dV, graphs. This is done to extract information related to phenomena such as the growth of the solid electrolyte interphase or, more broadly, degradation. Typically, these measurements take several months because measurements for differential capacity analysis need to be performed at relatively low C-rates. An alternate charging schedule to CCCV is pulsed charging, where CC sections are interrupted by an open-circuit measurement on a second time scale. These and similar partially constant current strategies primarily target diffusive effects during charging and broadly fall into a linear charging category, where the time derivative for the actuated property is mostly zero. Herein, the author explores nonlinear charging, i.e., the process of actively applying a potential with a nontrivial time derivate and a resulting nontrivial current time derivative, to engineer (dis)­charge cycles with enhanced information density. This method of nonlinear charging is then used to charge a cell such that some potential ranges in the differential capacity diagram are omitted. This study is purely a simulative endeavor and not backed by experimentation owing mainly to the lack of facile implementation of arbitrary function inputs for battery cyclers and might point to limitations of the underlying theory. If found to be confirmed through an experiment, then this technique would, however, motivate a new roadmap to better understand secondary battery degradation inspired by electrocatalyst degradation.