Bismuth-Loaded Carbon Nanotubes Supporter Inducing Persistent Mn2+ Deposition for Enhanced Stability of MnO2 Cathodes in Aqueous Zinc-Ion Batteries

Abstract

Manganese dioxide (MnO₂) cathodes are widely studied for aqueous zinc-ion batteries (AZIBs) because of their high theoretical capacity and energy density. However, the formation of “dead manganese” and Mn²⁺ dissolution during cycling lead to active materials loss and significant capacity decay, impeding their practical application. In this study, a novel oxygen-containing group-functionalized carbon nanotube supporter loaded with Bi₂O₃ (cCNTs−Bi) was constructed to improve the cyclic stability of MnO₂ cathodes. The results revealed that the oxygen-containing functional groups on cCNTs−Bi facilitate the deposition of Mn²⁺ ions from the electrolyte through electrostatic attraction. More importantly, the introduction of Bi³⁺ into MnO₂ to form Bi-O−Mn bonds weakens the interaction between the intercalated cations and oxygen atoms to ensure the diffusion of intercalated cations and reaction reversibility, thus reducing the accumulation of inactive phases such as ZnMn₂O₄ and zinc hydroxide sulfate. Consequently, cCNTs−Bi demonstrated outstanding stability over 2000 cycles. When combined with MnO₂, the composite retaining a discharge capacity of 295.5 mAh g⁻¹ after 120 cycles at 0.2 A g⁻¹, and of 104.5 mAh g⁻¹ after 1000 cycles at 1 A g⁻¹. This study clearly elucidate the dissolution deposition mechanism of MnO₂, providing theoretical support and guidance for enhancing the properties of MnO₂.