Understanding and illustrating the irreversible self-discharge in rechargeable batteries by the Evans Diagram

As an intermediary between chemical and electric energy, rechargeable batteries with high conversion efficiency are indispensable to empower electric vehicles and stationary energy storage systems. Self-discharge with adverse effects on energy output and lifespan is a long-existing challenge and intensive endeavors have been devoted to alleviating it. Previous reports mainly focused on examining key factors influencing the rate of self-discharge, however, its origination has rarely been revealed from the viewpoint of fundamental electrochemistry. The Evans Diagram, which is a corrosion polarization diagram based on kinetics (corrosion current density) and thermodynamics (potential), is an informative method for analyzing the corrosion process of metals. In this perspective, after an introduction to electrochemical fundamentals, as well as the identical origination of battery self-discharging and metal corrosion, we first transferred the concept of the Evans Diagram to illustrate the origination and evolution of self-discharge in rechargeable batteries. The corresponding Evans Diagram has been proposed for different key factors, which were eventually used as guidance to exploit thermodynamical and kinetical solutions to alleviate the parasitic reactions induced by self-discharge. This contribution is believed to provide new insights towards understanding and regulating self-discharge problems, and promote the establishment of feasible protocols for battery storage in practice.