Revealing the Thermodynamic Mechanism of Phase Transition Induced by Activation Polarization in Lithium-Ion Batteries.

Enhancing the phase transition reversibility of electrode materials is an effective strategy to alleviate capacity degradation in the cycling of lithium-ion batteries (LIBs). However, a comprehensive understanding of phase transitions under microscopic electrode dynamics is still lacking. In this paper, the activation polarization is quantified as the potential difference between the applied potential (U) and the zero-charge potential (ZCP) of electrode materials. The polarization potential difference facilitates the phase transition by driving Li-ion adsorption and supplying an electron-rich environment. A novel thermodynamic phase diagram is constructed to characterize the phase transition of the example MoS under various Li-ion concentrations and operating voltages using the grand canonic fixed-potential method (FPM). At thermodynamic quasi-equilibrium, the ZCP is close to the U, and thus is used to form the discharge curve in the phase diagram. The voltage plateau is observed within the phase transition region in the simulation, which will disappear as the phase transition reversibility is impaired. The obtained discharge curve and phase transition concentration both closely match the experimental results. Overall, the study provides a theoretical understanding of how polarization affects phase evolution in electrode dynamics, which may provide a guideline to improve battery safety and cycle life.