A large number of intercalation compounds used as battery electrodes undergo first-order phase transitions upon ion insertion/extraction. While having considerable impact on battery performance and cycle life, the fundamental aspects of phase transition kinetics at the mesoscale level in these systems are not well explored. In this talk, we present recent theoretical and modeling studies that help reveal several unique aspects of phase boundary migration in battery compounds. We discover that phase boundary movement in intercalation compounds can proceed in three distinct kinetic modes, including a novel hybrid mode in which phase growth is surface-reaction-limited (SRL) or diffusion-limited along different directions. The existence of hybrid phase boundary movement is confirmed in LiFePO4 by in-situ characterization. In the SRL transformation regime, a counter-intuitive phenomenon is predicted that antisite defects can enhance phase boundary speed by orders of magnitude in electrodes that exhibit strong diffusion anisotropy. We demonstrate such effect in LiFePO4 and suggest it as a general defect-engineering strategy to improve the rate capability of electrodes. Finally, we show that ion-intercalation-induced stress could trigger the morphology instability of phase boundary through a mechanism analogous to the classical Asaro-Tiller-Grinfeld instability for epitaxial thin film growth. As this phenomenon increases the kinetic resistance and promotes stress concentration in electrodes, its implications for battery performance and long-term stability and related mitigation methods require further investigation.

Mesoscopic behavior of phase boundary migration in intercalation compounds for energy storage applications

2019 Spring National Meeting

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