Novel Electroanalytical Techniques for Phase Transformation Electrodes
All the existing electroanalytical techniques including cyclic voltammetry (CV), potentiostatic intermittent titration (PITT), galvanostatic intermittent titration (GITT), and electrochemical impedance spectroscopy (EIS) rely on classical Fickian diffusion in a solid solution phase, and thus are not valid for phase transformation electrodes. Phase transformation materials (such as LiFePO4, Li4Ti5O12) have been recognized as next generation electrode materials for electric vehicle and renewable energy storage applications. The “apparent” diffusion coefficients of LiFePO4 in two-phase regions obtained using existing electroanalytical techniques are four orders of magnitude lower than those in the single phase region (black square in Figure 1). We developed phase transformation electroanalytical techniques by integrating mixed-control phase transformation theory with GITT, PITT, EIS and CV techniques. For the first time, the true Li-ion diffusion coefficients and interface mobilities of LiFePO4 electrode materials were obtained by my group using phase transformation PITT, GITT and CV. The similar Li+ diffusion coefficients in single and phase transformation regions (Figure 1) validated our phase transformation electroanalytical techniques. Three papers have been published in the Journal of Physical Chemistry C and the Journal of Power Sources. The developed phase transformation electroanalytical techniques can be applied to any ion-insertion electrodes including hydride, magnesium, and sodium batteries.