Heterointerface synergy between a 3 × 3 tunnel τ-MnO2 cathode and Mg2(OH)3Cl·4H2O for achieving long cycle-life aqueous zinc-ion batteries†

Abstract

Manganese dioxide is considered an ideal cathode candidate material for aqueous zinc-ion batteries. However, its poor conductivity and nanostructural degeneration impede its further application. Herein, a 3 × 3 tunnel-structured τ-MnO₂ cathode material was synthesized through the addition of excessive Mg²⁺. During its preparation, a portion of Mg²⁺ was embedded into the 3 × 3 tunnel of τ-MnO₂ to stabilize the microstructure, while another portion of Mg²⁺ formed a new phase, i.e., Mg₂(OH)₃Cl·4H₂O, adjoining τ-MnO₂, resulting in a cathode material with heterointerface synergy between τ-MnO₂ and Mg₂(OH)₃Cl·4H₂O. The charge arrangement of the heterointerface between τ-MnO₂ and Mg₂(OH)₃Cl·4H₂O enabled more active sites and accelerated ion-diffusion kinetics. The introduction of Mg₂(OH)₃Cl·4H₂O increased the proportion of Mn(IV) and suppressed the structural instability caused by Jahn–Teller distortion, thereby improving the electrochemical performance of the τ-MnO₂ cathode (capacity retention of 86.7% after 1800 cycles at 1 A g⁻¹).