Voltage plateau variation in a bismuth-potassium battery

Voltage plateau is an eigenvalue associated with the electrochemical reaction and hence a feasible tool for real-time detection of the state of charge in batteries. The variation of voltage plateau generally relates to the degradation of batteries, indicating the changes in the structure and/or the composition of electrode materials. In this work, we focus on a voltage plateau variation in a bismuth-potassium cell, investigating the electrode evolutions by two in situ methodologies. The phase transition reveals an intermediate phase in the reaction process, featuring a very limited but constant mass fraction. An irreversible structural collapse that follows leads to the exponential magnifying of the intermediate phase, taking responsibility for the distinct diffraction peaks and new voltage plateaus in the following cycles. This reaction mechanism builds the bridge between voltage plateau variation and electrode evolution, highlighting a combined effect of intermediate phase and structural collapse.