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.