Enhanced Redox Kinetics and Duration of Aqueous I₂/I⁻ Conversion Chemistry by MXene Confinement

Weak binding and affinity between the conductive support andiodine species leads to inadequate electron transfer and the shuttle effect.Herein, redox kinetics and duration are significantly boosted by introducing aNb₂CT_X host that is classified as a layered 2DNb-based MXene. With a facile electrodeposition strategy, initial I⁻ ionsare electrically driven to insert in the nanosized interlayers and areelectro-oxidized in situ. Linear I₂ is firmly confined insideand benefits from the rapid charge supply from the MXene. Consequently, anaqueous Zn battery based on a Zn metal anode and ZnSO₄ electrolytedelivers an ultraflat plateau at 1.3 V, which contributes to 84.5% of thecapacity and 89.1% of the energy density. Record rate capability (143 mAh g⁻¹ at18 A g⁻¹) and lifespan (23 000) cycles are achieved, which arefar superior to those of all reported aqueous MXenes and I₂–metalbatteries. Moreover, the low voltage decay rate of 5.6 mV h⁻¹ indicatesits superior anti-self-discharge properties. Physicochemical analyses anddensity functional theory calculations elucidate that the localized electrontransfer and trapping effect of the Nb₂CT_X MXenehost are responsible for enhanced kinetics and suppressed shuttle behavior.This work can be extended to the fabrication of other I₂–metalbatteries with long-life-time expectations.