K-Mn3o4-Ncs@Pani Nanochains for High-Rate and Stable Aqueous Zinc-Ion Batteries: A Doping and Morphology-Tailored Synthesis Strategy

Abstract

Aqueous zinc ion batteries (AZIBs) are promising energy storage solutions due to their high energy density and safety. However, developing cathode materials that offer both high energy density and durability for Zn2+ storage remains challenging. Manganese oxide-based cathodes have been developed for AZIBs due to their high discharge voltage and desirable capacity, but face challenges like poor conductivity, slow reaction kinetics, and dissolution during cycling. Doping, morphology/structure design, and protective layers are effective for enhancing the structure, conductivity, and electronic properties of Mn-based oxides. A synthetic strategy combining these methods for Mn3O4 cathodes is proposed for AZIBs, showing that K+ regulates local electronic structure, induces oxygen vacancies, improves conductivity, and provides more active sites for Zn2+ diffusion. Additionally, K-Mn3O4-NCs, with a unique chain-like nanostructure and high aspect ratio, synthesized via Mn2+ chelation with NTA and calcination, show reduced interparticle contact resistance, shorter Zn2+ diffusion length, and faster reaction kinetics. Meanwhile, the in-situ polymerized PANI layer on K-Mn3O4-NCs shields against corrosion, connects 1D K-Mn3O4-NCs into a continuous conductive network, suppresses volume expansion, and improves stability. Electrochemical analysis shows that K-Mn3O4-NCs@PANI exhibits higher stability and faster reaction kinetics due to a reduced bandgap, increased oxygen defects, and less Coulombic repulsion between zinc ions and manganese oxide hosts. The K-Mn3O4-NCs@PANI cathode achieved a high capacity of 510 mAh g-1 at 0.1 A g-1 and excellent rate performance of 203.2 mAh g-1 at 5 A g-1. After 20,000 cycles, it maintained a capacity of 90.3 mAh g-1 at 5 A g-1, showing exceptional long-term stability with a minimal decay rate of 0.026‰ per cycle.

Keywords: Aqueous zinc ion batteries, Mn3O4 nanochain, K+ ion doping, Fast reaction kinetics, Long-term Stability