Deciphering electrochemomechanical interplay in rechargeable aqueous Zn||MnO₂ batteries

Electrochemical reactions are generally accompanied by mechanical evolutions, which, in turn, play a critical role in the performance of the electrochemical system. In aqueous Zn||MnO₂ batteries, the intrinsically structural instability of MnO₂ and rampant side reactions create considerable strain/stress changes in operation. However, the electrochemistry-mechanics-performance relationship of the Zn||MnO₂ cell is still missing. Herein, we decode the electrochemomechanical interplay of Zn||β-MnO₂ pouch cells with different electrolytes via optical fiber sensors. The operando stress monitoring provides proof of the prevailing proton intercalation and Mn dissolution/deposition mechanisms in the system, where the basic zinc salts play a dominant role in stress evolution. Additionally, the non-monotonic stress variation during discharge implies Zn-compensated reaction. For cycling ageing, a negative correlation is found between early stress amplitudes and capacity retention in long cycles. For calendar ageing, greater stress variation during open-circuit ageing is linked with more severe self-discharge. Altogether, this work provides a deep understanding of the electrochemistry-mechanics-performance correlation in aqueous Zn||MnO₂ batteries, offering additional tools for electrolyte screening and battery design.