Electron transmission matrix and anion regulation strategy-derived oxygen-deficient δ-MnO2 for a high-rate and long-life aqueous zinc-ion battery

Abstract

Ion migration and electron transmission are vital for manganese dioxides in zinc ion batteries. δ-MnO₂ is believed to be more suitable for zinc ion storage due to its layered structure. However, the performance of δ-MnO₂ is still hampered by the frustrating conductivity and sluggish reaction kinetics. Herein, atomic engineering is adopted to modify δ-MnO₂ at the atomic level to obtain oxygen-deficient δ-MnO₂ (N–MnO₂). Meanwhile, hollow carbon microtubes (HCMTs) obtained from green and renewable energy grass are proposed as cross-connected electron transmission matrices (CETMs) for MnO₂. The biomass-derived CETMs not only optimize reaction kinetics but also facilitate the ion storage performance of MnO₂. The as-prepared N–MnO₂@HCMTs exhibit high rate capability and enhanced pseudocapacitve behavior contributed by the oxygen-deficient N–MnO₂ and CETMs. Ex situ analysis reveals the reversible insertion/extraction of H⁺ and Zn²⁺ in N–MnO₂@HCMTs during charge/discharge processes. Moreover, the quasi-solid-state N–MnO₂@HCMTs//Zn cells are assembled and they deliver extraordinary discharge capacity and a long cyclic lifespan. This study may provide insights for further exploration of cathode materials in AZIBs and promote the large-scale production of aqueous Zn–MnO₂ batteries.