Novel Electro-Analytical Tools for Phase-Transformation Electrode Materials

Abstract

Abstract : We measured and compared phase transformation accommodation energy (AE) for Li(4)Ti(5)O(12) and LiFePO(4) with different particle size by using of galvanostatic intermittent titration (GITT). The results showed that charge AE was larger than that for discharge; The AE for the 1st cycle was larger than next cycles due to inducing of defects; Because of smaller volume difference, AE of Li(4)Ti(5)O(12) was lower than that of LiFePO(4); AE of LiFePO(4) with small particle size was lower than that of LiFePO(4) with large particle size. By plugging the AE measured by GITT into mixed control model, we simulated the discharge curves in GITT and obtained lithium ion diffusivity in alpha (D(alpha)Li(+)) and Beta (D(Beta) Li(+)) phase and interface mobility (M) during phase transformation for Li(4)Ti(5)O(12) and LiFePO(4) respectively. For LiFePO(4): D(alpha)Li(+) tilde 10(-14)-10(-13) cm/(2)/s, D(Beta)Li(+) tilde 10(-15) - 10(-14) cm (2)/s and M tilde 10(-15) mmol/Js; for Li(4)Ti(5)O(12):D(alpha)Li(+) tilde 10(-11)-10(-10)cm(2)/s, D(Beta)Li(+) tilde 10(-12)-10(-11)cm(2)/s and M tilde 10(-13) mmol/Js. The values of D(alpha)Li(+) and D(beta)Li(+) calculated by mixed control theory were consistent with those gained in one phase region according to traditional GITT and potentiostatic intermittent titration (PITT) method. We also discovered the effects of phase transformation on cyclic voltammetry (CV), and electromechanical impedance spectroscopy (EIS) tests.