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The development of electrolytes capable of performing at a high voltage (>5 V) is essential for the advancement of lithium-ion batteries. In the present work, we have investigated a dinitrile–mononitrile-based electrolyte system that can offer electrochemical stability up to 5.5 V at room temperature. The electrolytes consist of 1.0 M lithium bis­(trifluoromethane)­sulfonamide in various volume proportions of glutaronitrile, a dinitrile, and butyronitrile, a mononitrile (10/0; 8/2; 6/4; 4/6; 2/8; 10/0). The ionic conductivity of the electrolytes was found to be 3.1 × 10–3–10.6 × 10–3 S cm–1 at 30 °C, comparable with commercially used carbonate-based electrolytes. However, butyronitrile reacts with Li metal to give 3-amino-2-ethylhex-2-ene-nitrile, 2,6-dipropyl-5-ethylpyrimidin-4-amine, and oligomers/polymers. These compounds have been characterized by nuclear magnetic resonance techniques, and based on these findings, a plausible mechanism of reactivity of mononitriles toward Li metal has been proposed. Finally, 5 wt % of vinylene carbonate is added to the glutaronitrile/butyronitrile (6/4 ratio) system to inhibit the reductive decomposition of butyronitrile. The resultant electrolyte system is used in the assembly of several coin cells consisting of a LiFePO4 composite cathode and a Li metal anode. The cells perform up to 3 C charge/discharge rate with reasonably good discharge capacity and also display a cycle life of more than 100 cycles at a 0.5 C rate with capacity retention above 95% at room temperature.

Exploring the benefits of a nanofibrous morphology in electrolyte materials for Li‐battery applications, an approach of fabricating single‐ion conducting electrolyte (SICE) membranes is reported. A nonwoven nanofabric SICE membrane, delivering an outstanding performance, surpassing the conventional liquid electrolyte system at ambient conditions, was fabricated by using an electrospinning technique. When soaked in a carbonate solvent system, the membrane shows high ionic conductivity, electrochemical stability above 5.2 V (vs. Li/Li+) and a lithium transference number (tnormalLnormali+ ) close to unity (0.93). Moreover, a LiFePO4|Li cell assembled with this membrane performs charge/discharge up to the 5 C rate under ambient conditions with a coulombic efficiency close to 100%. The discharge capacities of this battery are found to be higher than those of a battery assembled with a commercial separator/dual‐ion salt electrolyte system up to 2 C, which offers significant progress for SICEs. Unlike most of the earlier reported SICEs that performed like a bulk‐material entity, the innovative approach might be valuable for future developments.

Two thermoplastic triblock copolymers of poly(εcaprolactone)-based acidic (PCL-A) and basic (PCL-B) polymers are synthesized by atom transfer radical polymerization. PCL-A and PCL-B are sequentially electrospun on a sulfur electrode and then ionically cross-linked by an acid−base reaction via hot pressing at 70 °C, which is confirmed by infrared (IR) spectroscopy. The cross-linked PCL-A/PCL-B-electrospun sulfur electrode is assembled as a lithium−sulfur battery with an asymmetric gel polymer electrolyte. The cross-linked polymer is swollen by a liquid electrolyte to form an asymmetric gel polymer electrolyte. The cyclic voltammetry results indicate that the asymmetric gel polymer electrolyte can suppress the dissolution of lithium polysulfides (Li 2 S n ) into the electrolyte. Furthermore, the lithium−sulfur battery with the asymmetric gel polymer electrolyte exhibits enhanced cycle-life performance.