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.