PEO based polymer in plastic crystal electrolytes for room temperature high-voltage lithium metal batteries

Lithium metal coupled with high voltage cathodes has been extensively investigated to meet the demand for higher energy density batteries. However, only a few electrolytes are compatible with both lithium anode and high voltage LiNi0.5Mn0.3Co0.2O2. Pure poly(ethylene oxide) electrolyte shows high-stability against lithium metal but has limited oxidation stability (typically < 3.8 V). Nitrile-based electrolyte with -C≡N groups exhibits excellent electrochemical stability against high voltage electrodes. Here, a novel type of poly(ethylene oxide) based polymer in plastic crystal (succinonitrile) electrolyte is designed to achieve stable cathode/electrolyte and anode/electrolyte interfaces simultaneously through strong intermolecular interactions. Li-Li symmetric cells with the polymer in plastic crystal electrolyte runs stably for 700 h at 1 mA cm−2. Even with a high cut-off voltage of 4.4 V, the Li// LiNi0.5Mn0.3Co0.2O2 cell delivers a high discharge capacity of 169 mA h g−1 and a capacity retention of 80% after 120 cycles. Our work highlights development of PEO-based electrolytes with higher energy density by inter-molecular design.