Porous VC@VSe heterostructure with built-in electric field as catalytic host materials for high-performance aqueous Cu-Se batteries.

Conversion-type aqueous copper-selenium (Cu-Se) batteries have gained considerable attention due to their high theoretical capacity, safety and environmental friendliness. However, the multi-electron intermediate conversion reaction of selenium cathode generally possesses sluggish kinetics, which seriously impedes the further development of Cu-Se batteries. Herein, the porous VC@VSe heterostructure (P-VC@VSe) with built-in electric field (BIEF) were successfully synthesized by the sacrificial template method and in situ selenization strategy, which were used as the selenium host materials for aqueous Cu-Se batteries to effectively enhance the selenium conversion reaction kinetics. The porous structure of P-VC@VSe not only provides faster access for the transport of polyselenide intermediates during electrochemical reactions, but also exposes more catalytic active sites, which in turn improves the catalytic activity of the material. In addition, the built-in electric field generates at the interface of the P-VC@VSe heterostructure facilitates the acceleration of charge transfer and thus improves the kinetics of the redox reaction of selenium. Benefiting from the synergistic effect of the porous structure and the built-in electric field, the Se/P-VC@VSe cathode possessed a discharge specific capacity of 1182.2 mAh g at a current density of 1 A g, which was much higher than those of Se/P-VC (796.6 mAh g) and Se (597.0 mAh g) cathodes. In addition, it also maintained a specific capacity of 1054.6 mAh g after 6000 cycles at 10 A g, demonstrating excellent cycling stability. Meanwhile, a series of characterizations and density functional theory calculations were performed to systematically explore the conversion mechanism of aqueous Cu-Se batteries. This work provides promising insights into the construction of high-performance MXene-based catalytic host materials for aqueous Cu-Se batteries.