Interfacial Stabilizing Effect of Lithium Borates and Pyrrolidinium Ionic Liquid in Gel Polymer Electrolytes for Lithium-Metal Batteries

Abstract

The next generation of reversible batteries will be high-energy-density systems such as lithium-metal batteries. However, metallic lithium as the anode requires an electrolyte that prevents the formation of Li dendrites. The keynote of this work is a gel polymer electrolyte with a copolymer matrix made of PVdF(HFP), which is compatible with Li metal electrodes. The obtained gel polymer electrolytes contain lithium borate (LiBOB or LiDFOB), ionic liquid (EtMeImNTf2 or MePrPyrNTf2), and sulfolane (TMS). In this study, lithium borates are a central aspect affecting the performance of the electrolyte and electrodes. In turn, the ionic liquid in a mixture with sulfolane plays the double role of a lithium salt solvent and gel polymer membrane plasticizer, ensuring thermal stability and a higher proportion of amorphous areas in the polymer electrolyte. Furthermore, MePrPyrNTf2 in the presence of lithium borates reduces the resistance (RSEI) of the layer formed at the electrolyte|Li electrode interface. Most gel electrolytes exhibit long-term stability at the GPE|Li interface. Membranes containing LiBOB or LiDFOB and pyrrolidinium ionic liquid also ensure compatibility with the olivine cathode in the cell, which delivers a capacity of 120 mAh g-1 (C/10) after 80 cycles and retains this value after an additional 105 cycles at C/2 and C/10.