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 (V₂ C) MXene with engineered interlayer spacing for desirable storage capacity is demonstrated. The interlayer distance of pristine V₂ 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 V₂ C MXene to form a new interlayer-expanded structure via strong V-O-Co bonding. The intercalated V₂ 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.

Keywords: Li-ion storage; XANES; atomic cobalt covalence; interlayer spacing engineer; layered materials.