Electrostatically Assembling 2D Nanosheets of MXene and MOF-Derivatives into 3D Hollow Frameworks for Enhanced...

As an essential member of 2D materials, MXene (e.g., Ti₃ C₂ T_x ) is highly preferred for energy storage owing to a high surface-to-volume ratio, shortened ion diffusion pathway, superior electronic conductivity, and neglectable volume change, which are beneficial for electrochemical kinetics. However, the low theoretical capacitance and restacking issues of MXene severely limit its practical application in lithium-ion batteries (LIBs). Herein, a facile and controllable method is developed to engineer 2D nanosheets of negatively charged MXene and positively charged layered double hydroxides derived from ZIF-67 polyhedrons into 3D hollow frameworks via electrostatic self-assembling. After thermal annealing, transition metal oxides (TMOs)@MXene (CoO/Co₂ Mo₃ O₈ @MXene) hollow frameworks are obtained and used as anode materials for LIBs. CoO/Co₂ Mo₃ O₈ nanosheets prevent MXene from aggregation and contribute remarkable lithium storage capacity, while MXene nanosheets provide a 3D conductive network and mechanical robustness to facilitate rapid charge transfer at the interface, and accommodate the volume expansion of the internal CoO/Co₂ Mo₃ O₈ . Such hollow frameworks present a high reversible capacity of 947.4 mAh g^-1 at 0.1 A g^-1 , an impressive rate behavior with 435.8 mAh g^-1 retained at 5 A g^-1 , and good stability over 1200 cycles (545 mAh g^-1 at 2 A g^-1 ).