Electrolyte for High Energy- and Power-density Zinc Batteries and Ion Capacitors.

Dendrites growth, limited coulombic efficiency (CE) and the lack of high-voltage electrolytes restrict the commercialization of zinc batteries and capacitors. These issues are resolved by a new electrolyte, based on the zinc(II)-betaine complex [Zn(bet) 2 ][NTf 2 ] 2 . Solutions in acetonitrile (AN) avoid dendrite formation. A Zn||Zn cell operates stably over 10110 hours (5055 cycles) at 0.2 mA·cm -2 or 110 hours at 50 mA·cm -2 , has an area capacity of 113 mAh·cm -2 at 80% depth of discharge. A zinc-graphite battery performs at 2.6 V with a midpoint discharge-voltage of 2.4 V. The capacity-retention at 3 A·g -1 (150C) is 97% after 1000 cycles and 68% after 10000 cycles. The charge/discharge time is about 24 seconds at 3.0 A·g -1 with an energy density of about 49 Wh·kg -1 at a power density of 6864 W·kg -1 based on the cathode. A zinc activated-carbon ion-capacitor (coin cell) exhibits a operating-voltage window of 2.5 V, an energy density of 96 Wh·kg -1 with a power density of 610 W·kg -1 at 0.5 A·g -1 . At 12 A·g -1 , 36 Wh·kg -1 and 13600 W·kg -1 are achieved with 90% capacity retention and an average CE of 96% over 10000 cycles. Quantum-chemical methods and vibrational spectroscopy revealed [Zn(bet) 2 (AN) 2 ] 2+ as the dominant complex in the electrolyte. This article is protected by copyright. All rights reserved.