I. Introduction
Rechargeable batteries have become ubiquitous energy storage devices in recent years for use in both mobile applications, including electric vehicles (EVs) and consumer devices, as well as stationary applications such as to mitigate the impact of fluctuating renewable generation to grid systems in the form of large-scale battery energy storage systems [1], [2]. These modern applications require safe, reliable, and efficient operation under a wide range of operating conditions, currently being dominated by lithium-ion (Li-ion) batteries. Li-ion batteries are experiencing rapid development as one of the most important energy storage technologies due to their relatively high cell voltage, low self-discharge, and an excellent tradeoff between power and energy densities [3]. However, conventional Li-ion batteries use organic electrolytes and porous electrodes, which poses several challenges in battery safety and cycling performance. First, the organic electrolytes, most of which are in liquid form, are highly flammable and can cause fire hazards/explosions during faulty conditions due to thermal runaway. Second, the organic liquid electrolyte usually has low conductivity, which places intrinsic technical limits on modern high-power applications such as fast charging for EVs. Furthermore, the porous electrodes have almost reached their theoretical power density limits, which makes the further increase of the power/energy density in EVs difficult [4].