High-performance zinc-ion battery cathode enabled by deficient manganese monoxide/graphene heterostructures

Understanding the Adsorption Behavior of Different Crystal Surfaces of Manganese Monoxide to Strontium Nitrate Solutions: A Molecular Dynamics Simulation

Manganese monoxide (MnO), a versatile manganese oxide, is highly regarded for its potential to address heavy metal and radioactive contamination effectively. In this study, we investigated the adsorption mechanism of strontium nitrate solution on MnO crystal surfaces using molecular dynamics simulations. We examined the effects of adsorption and diffusion of ions and water molecules on three distinct MnO crystal surfaces. The results revealed significant differences in the adsorption capacities of Sr2+, NO3-, and H2O on the MnO crystal surfaces. The radial distribution function (RDF), the non-bond interaction energy (Eint), and mean square displacement (MSD) data indicate that Sr2+ exhibits the strongest interaction with the MnO (111) crystal surface. This results in a shift of Sr2+ from outer-sphere adsorption to inner-sphere adsorption. This strong interaction is primarily due to the increase in the number and prominence of non-bridging oxygen atoms on the MnO crystal surfaces.

High valence MnO2 as an aqueous zinc ion battery cathode prepared using a secondary hydrothermal method

Aqueous zinc-ion batteries (AZIBs) have emerged as promising energy storage systems due to their inherent safety and high capacity, with manganese oxides attracting attention for their cost-effectiveness and environmental compatibility. However, the poor cycling stability of manganese-based oxides, primarily due to Jahn-Teller distortions caused by Mn3+, limits their practical applications. Herein, a high valence MnO2 (H-MnO2) material was prepared via a simple secondary hydrothermal method, yielding an increased average manganese valence from 3.31 to 3.89. A Zn/H-MnO2 aqueous battery that utilized H-MnO2 as a cathode achieves an exceptional capacity of 420 mA h g-1 at 0.1 A g-1 and retains a capacity of 92.6% after 900 cycles at 2.0 A g-1. The structural transformation of the electrode material and changes in the elemental content during charging and discharging reveal that the H-MnO2 electrode undergoes a chemical transformation mechanism during these processes. This work demonstrates that increasing the average manganese valence state is a critical strategy for improving both capacity and cycling stability in manganese-based AZIBs.

Inside-out regulation of MnO toward fast reaction kinetics in aqueous zinc ion batteries

An "inside-out regulation" strategy is proposed to improve the Zn2+ storage of MnO by Ni doping into the lattice and graphene wrapping outside the nanoparticles. The as-prepared Ni-MnO@rGO exhibits 112 mA h g-1 at 2.0 A g-1 over 800 cycles, due to the improved transport of electrons and ions from the synergistical function of intrinsic doping and external graphene encapsulation.

Challenges and Strategies in the Development of Zinc-Ion Batteries

Although promising, the practical use of zinc-ion batteries (ZIBs) remains plagued with uncontrollable dendrite growth, parasitic side reactions, and the high intercalation energy of divalent Zn²⁺ ions. Hence, much work has been conducted to alleviate these issues to maximize the energy density and cyclic life of the cell. In this holistic review, the mechanisms and rationale for the stated challenges shall be summarized, followed by the corresponding strategies employed to mitigate them. Thereafter, a perspective on present research and the outlook of ZIBs would be put forth in hopes to enhance their electrochemical properties in a multipronged approach.