Effect of Electrode/Electrolyte Coupling on Birnessite (δ-MnO₂) Mechanical Response and Degradation

Abstract

Understanding the deformation of energy storage electrodes at a local scale and its correlation to electrochemical performance is crucial for designing effective electrode architectures. In this work, the effect of electrolyte cation and electrode morphology on birnessite (δ-MnO2) deformation during charge storage in aqueous electrolytes was investigated using a mechanical cyclic voltammetry approach via operando atomic force microscopy (AFM) and molecular dynamics (MD) simulation. In both K2SO4 and Li2SO4 electrolytes, the δ-MnO2 host electrode underwent expansion during cation intercalation, but with different potential dependencies. When intercalating Li+, the δ-MnO2 electrode presents a nonlinear correlation between electrode deformation and electrode height, which is morphologically dependent. These results suggest that the stronger cation–birnessite interaction is the reason for higher local stress heterogeneity when cycling in Li2SO4 electrolyte, which might be the origin of the pronounced electrode degradation in this electrolyte.

Development of the ReaxFF Reactive Force Field for Li/Mn/O Battery Technology with Application to Design a Self-Healing Cathode Electrolyte Interphase

“…ReaxFF is calibrated against QM data, ensuring that MD simulations using ReaxFF approaches the accuracy of density functional theory (DFT) calculations, but with larger simulation system sizes and much lower computational costs. Our system of interest (ionic liquids) contains P, S, F, and N atom types; therefore, we started our force field training with recently developed Li/Mn/C/H/O force field by Tsai et al and added the P/S/N atom type in the force field. ,− Initially, we calibrated the ReaxFF parameters of the Li/Mn/O/N/S/P/F/C/H system using DFT calculations and QM training sets.…”

Incorporation of Fe3+ into MnO2 birnessite for enhanced energy storage: impact on the structure and the charge storage mechanisms

“…1,2 Among the most promising pseudocapacitive materials, the birnessite δ-MnO 2 stands out due to its abundance, low cost, high theoretical capacity and stable cycling performance in aqueous electrolyte. 3–10 Moreover, its reaction mechanisms upon cycling in aqueous electrolytes (1 M K 2 SO 4 ), subject of debate, was recently elucidated by Augustyn et al 11 They demonstrated that birnessite 2D structure, with a large interlayer spacing resulting from the presence of nanoconfined structural water molecules, enables extremely fast and efficient intercalation of partially hydrated alkaline ions, leading to capacitive like electrochemical signature.…”