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

Weak binding and affinity between the conductive support and iodine species leads to inadequate electron transfer and the shuttle effect. Herein, redox kinetics and duration are significantly boosted by introducing a Nb2 CTX host that is classified as a layered 2D Nb-based MXene. With a facile electrodeposition strategy, initial I- ions are electrically driven to insert in the nanosized interlayers and are electro-oxidized in situ. Linear I2 is firmly confined inside and benefits from the rapid charge supply from the MXene. Consequently, an aqueous Zn battery based on a Zn metal anode and ZnSO4 electrolyte delivers an ultraflat plateau at 1.3 V, which contributes to 84.5% of the capacity and 89.1% of the energy density. Record rate capability (143 mAh g-1 at 18 A g-1 ) and lifespan (23 000) cycles are achieved, which are far superior to those of all reported aqueous MXenes and I2 -metal batteries. Moreover, the low voltage decay rate of 5.6 mV h-1 indicates its superior anti-self-discharge properties. Physicochemical analyses and density functional theory calculations elucidate that the localized electron transfer and trapping effect of the Nb2 CTX MXene host are responsible for enhanced kinetics and suppressed shuttle behavior. This work can be extended to the fabrication of other I2 -metal batteries with long-life-time expectations.