Complex Impedance of Li-Ion-Battery Phase-Transformation Electrodes at History-Dependent States of Charge

Phase-transformation electrodes have desirable characteristics for lithium-ion batteries. These electrodes have been shown to be abuse resistant, have extended cycle life, and are suitable for fast-charging applications. These new materials have significantly different lithium incorporation behaviors than the more-conventional solid-solution reaction electrodes. This paper explores the implications of phase-transformation physics within a multiparticle electrode that contains a distribution of particle sizes. Phase-transformation physics is such that lithium distributions within the electrode particle ensemble is cycle-path dependent. For example, after charging, any maldistribution of lithium between particles does not naturally redistribute uniformly between all particles, as is the case for solid-solution reaction electrodes. Such maldistribution greatly influences the observed electrochemical impedance spectra. The implications of history-dependent inter-particle lithium distributions is characterized with a mesoscopic model. The model shows how the impedance spectra of a phase-transformation electrode, at a prescribed state of charge, depends on the path history to achieve the state of charge.