(Invited) Potentiometric Entropy Measurements and Isothermal Operando Calorimetry to Identify the Charging Mechanisms of Battery Materials

Abstract

This talk presents recent development in potentiometric entropy measurements and isothermal operando calorimetry to gain insight into the charging mechanisms of lithium ion batteries. First, the concept, design, and operation of two unique experimental apparatuses will be presented. Then, the effects of material composition, crystallographic structure, and particle size on the cell’s thermodynamic behavior, polarization, and lithium ion transport will be discussed for different Wadsley-Roth materials (e.g., TiNb2O7, PNb9O25, (W0.2V0.8)3O7) under quasi-equilibrium conditions. Particular attention will be paid to phase transition, lithium ion intercalation and ion ordering in solid solution, and/or two-phase coexistence occurring during charging/discharging. Finally, instantaneous heat generation rates measured by isothermal operando calorimetry at each electrode will be used to identify the causes of energy dissipation and to provide insight into the transport and interfacial phenomena taking place in the electrodes at different states of charge and charging rates. Here, special emphasis will be placed on the contributions of Joule heating associated with resistive losses, heat of mixing due to ion concentration gradient, and reversible entropic changes.