Atomic Cobalt Covalently Engineered Interlayers for Superior Lithium‐Ion Storage

Abstract With the unique‐layered structure, MXenes show potential as electrodes in energy‐storage devices including lithium‐ion (Li + ) capacitors and batteries. However, the low Li + ‐storage capacity hinders the application of MXenes in place of commercial carbon materials. Here, the vanadium carbide (V 2 C) MXene with engineered interlayer spacing for desirable storage capacity is demonstrated. The interlayer distance of pristine V 2 C MXene is controllably tuned to 0.735 nm resulting in improved Li‐ion capacity of 686.7 mA h g −1 at 0.1 A g −1 , the best MXene‐based Li + ‐storage capacity reported so far. Further, cobalt ions are stably intercalated into the interlayer of V 2 C MXene to form a new interlayer‐expanded structure via strong V–O–Co bonding. The intercalated V 2 C MXene electrodes not only exhibit superior capacity up to 1117.3 mA h g −1 at 0.1 A g −1 , but also deliver a significantly ultralong cycling stability over 15 000 cycles. These results clearly suggest that MXene materials with an engineered interlayer distance will be a rational route for realizing them as superstable and high‐performance Li + capacitor electrodes.