Probing In Operando Manganese Dissolution and Associated Mechanical Deformation in LiMn₂O₄ Cathodes

Mn dissolution has been an Achilles heel of cost-effective Mn-based transition metal oxide cathodes, such as spinel LiMn₂O₄ (LMO). The Mn dissolution leads to rapid capacity fade due to degradation in the cathode structure and formation of a solid-electrolyte interface on anodes. Extensive ex situ and chronical studies have unveiled that unfavorable cycling conditions lead to manganese dissolution into the electrolyte; however, the mechanism behind the manganese dissolution remains under debate. Here, we report the operando Mn dissolution profile and its correlation with the electro-chemomechanical instabilities in the LMO cathode. We carried out operando characterization of Mn ion concentration in the electrolyte via UV-vis spectroscopy and in operando strain measurement in the cathode using digital image correlation. Mn dissolution is accompanied by strain evolution in the LMO induced by phase transition. Overdischarging further exacerbates the dissolution in successive cycles. Image analysis further tracks the distribution and transport of the Mn species in the electrolyte during cycling. We foresee that in operando electro-chemo-mechanical techniques developed in this study can be applied to investigate transition metal dissolution in other battery cathodes.