Iodine-redox-chemistry-modulated ion transport channels in MXene enables high energy storage capacity

Ti3C2Tx MXene anode often faces the great challenge of a low capacity due to its sluggish ion transport kinetics. Herein we report iodine-redox-chemistry-modulated intelligent ion transport channels in Ti3C2Tx MXene, enabling its Li-ion storage beyond theoretical capacity. The −I terminations modified on the Ti3C2Tx surface (I−Ti3C2Tx) are oxidized into linear −I3 in the late stage of the charging process, which dramatically expand the interlayer spacing of Ti3C2Tx to accelerate the Li-ion extraction. Meanwhile such self-expanded ion transport channels are more conducive to the Li-ion insertion in the following discharging process, during which the −I terminations are regenerated. This voltage-responsive and reversible conversion between the −I and −I3 terminations in Ti3C2Tx MXene achieves an intelligent bidirectional adjustment of ion transport channels. As a consequence, the I−Ti3C2Tx delivers high capacity (1.8-fold capacity of the pristine Ti3C2Tx at 0.1 A g−1), outstanding rate capability (4.5 times the capacity of the pristine Ti3C2Tx at 2.0 A g−1), and long-term cycling stability (268.5 mAh g−1 at 1.0 A g−1 over 800 cycles), even in a full cell (300.7 mAh g−1 at 0.1 A g−1) and with a wide temperature environment. This work provides an effective approach for maximizing the actual capacity of Ti3C2Tx MXene.