Electrochemical Oscillation in Li-Ion Batteries

Two-phase reactions are prevalent in Li-ion batteries, whereas the underlying dynamics of phase separation in a real electrode still remain elusive, since numerous electrode particles constitute a formidably complex system for existing experimental techniques. Here we present an intriguing oscillatory phenomenon in the typical phase-separating electrode material Li₄Ti₅O₁₂. During galvanostatic processes, the voltage oscillates due to the discrete nature of multi-particle phase-separating reactions, and the subtle oscillatory signals allow us to evaluate the fraction of actively phase-separating particles in real time. Through the analysis of oscillatory phenomena, we unveil the dependence of the active fraction on the depth of charge/discharge, cycling current, and working temperature, considerably deepening our understanding of the multi-particle phase-separation reaction. Moreover, it is the first time that electrochemical oscillations have been identified in rechargeable battery systems, opening up a new frontier for both theoretical and experimental researchers. Despite remarkable achievements in developing Li-ion batteries over recent decades, many fundamental scientific issues underpinning Li-ion batteries are far from being adequately understood. Among them is the phase-separating reaction, which is prevalent in battery electrode materials, whereas collective phase behavior remains elusive due to the numerous nanoparticles in a real electrode. Here we report an electrochemical oscillation phenomenon originating from the discretely phase-separating behavior in a multi-particle electrode. The oscillation signals enable us to directly monitor the fraction of actively phase-separating electrode particles in real time, making a major advance in the fundamental understanding of phase-separating battery materials. This finding builds a bridge between the macroscopic electrochemistry and microscopic dynamics of the phase-separating reaction, filling a critical gap in our understanding of multi-particle storage systems with phase-separating materials. Electrochemical oscillation phenomenon is observed in a rechargeable battery for the first time, suggesting a self-reorganization of the multi-particle phase-separation dynamics. The subtle oscillatory signals can serve as an indicator for the fraction of actively phase-separating particles in real time. Consequently, the dependence of active fraction on the depth of charge/discharge, applied current rate, and working temperature are unambiguously revealed. This finding builds a bridge between the macroscopic electrochemistry and the microscopic phase-separating reaction in multi-particle systems.