Contriving gel polymer electrolyte to drive quasi-solid-state high-voltage Li metal batteries at ultra-low temperatures

Abstract

Gel polymer electrolytes (GPEs) synergizing the benefits of solid and liquid electrolytes are promising electrolyte candidates for future Li metal batteries (LMBs). However, the poor performance of current GPEs in subzero temperatures, particularly in extremely cold conditions, limits their practical applications. Here, we contrive a new and simple GPE recipe for low-temperature operation only using common electrolyte components, viz. single-solute LiBF4 (Li salt and initiator), polymeric monomer 1,3-Dioxolane (DOL), and high-dielectric-constant solvent fluoroethylene carbonate (FEC), demonstrating unique multiple-function of each component and achieving fast kinetics and interfacial stability at -60 ~-20 °C. New insights into how the solvation structures evolve during in-situ polymerization are proposed. Distinctive Li+ solvation structures involve Poly-DOL, BF4- and FEC, regulating stable solid electrolyte interphases, which contain robust LiF and Li+-conducting LixBOyFz. Consequently, Li|GPE|LiNi0.8Co0.1Mn0.1O2 and Li|GPE|LiCoO2 cells release impressive capacities of ~142 and ~155 mAh g-1 at -20 °C, with excellent capacity retention of 94% (200 cycles) and 96% (350 cycles), respectively. Notably, the GPE enables Li//LiCoO2 pouch cells to operate as low as -60 °C, delivering a high capacity of ~112 mAh g-1, which represents the lowest operating temperature and the competitive performance (capacity and cycling life) for high-voltage LMBs reported to date in the GPE field.