Deciphering the operating principle of aqueous zinc-ion batteries with MnO2-based cathodes

Abstract

In the race for next-generation low-cost batteries, aqueous zinc-ion batteries (ZIB) based on MnO2 cathodes bring both high sustainability and well-established cell chemistry of the individual electrodes. In recent years, cycling stability and usable capacity have increased significantly compared to first-generation ZIBs, which were successors of the non-rechargeable alkaline MnO2 battery. Experimental observations revealed that cycling behaviour is subject to two distinct phases with significantly different kinetics, and precipitation from the electrolyte was observed in cells with a ZnSO4 electrolyte. Improvements have been found experimentally through changes in electrolyte composition and optimization of the cathode structure. The role of precipitation in understanding the working principle has also been highlighted in recent research.

We present a consistent full-cell model to describe the cycling behaviour of ZIBs. The complex formation in the near-neutral aqueous electrolyte is described in a quasi-particle framework which couples local speciation with transport properties of the electrolyte. This approach was originally developed and successfully used to model near-neutral zinc-air batteries. Our model reproduces the unique features observed empirically. This takes into account the inherent pH instability of the near-neutral aqueous electrolyte, and in this way, we can accurately describe the precip-itation and dissolution characteristics at the MnO2 cathodes and identify critical as-pects and possible improvements for future experiments.

This work is supported by the Federal Ministry of Education and Research (BMBF) via the project ZIB (03XP0204D).