Optimized integration of intercalation and conversion behaviors for Cu2O/MnO2 hybrid cathodes of zinc ion batteries

Abstract

δ-MnO₂ has received constantly growing attention due to its stable tunnel-type crystalline structures for Zn²⁺ or Zn²⁺/H⁺ intercalation, however, only partial Mn active sites exhibit electrochemical reactions, and most Mn atoms would stay the same to maintain the structure frame, indicative of low capacity and long cycling life theoretically. By comparison, for Cu-based conversion-typed materials, all Cu sites can perform electrochemical reactions if fully utilized, resulting in high rate capacity, however, short cycling life due to fracture, and even pulverization induced by volume changes during cycling. In this work, a hybrid cathode with intercalation and conversion behaviors is devised, in which intertwined δ-MnO₂ nanosheets shell wrap conversion-typed Cu₂O core firmly for stable conversion reaction during cycling. As a result, the optimized Cu₂O/MnO₂ (denoted as MCO) cathode demonstrates the hybrid properties of long cycling life and high rate capacity, inheriting from δ-MnO₂ and Cu₂O, respectively. MCO cathodes with carbon cloth current collectors in full batteries deliver reversible capacities of 291.9 mA h g⁻¹ at 1 A g⁻¹, and retain 95% capacity at 20.0 A g⁻¹ after 4300 cycles. Additionally, the energy density of 513.94 Wh kg⁻¹ and power density of 7.2 kW kg⁻¹ based on the MCO mass are exhibited, verifying its practical application. This work demonstrates the combination of intercalation and conversion in one electrochemical system and may provide new perspectives for the optimizing application of hybrid mechanisms.