Ion-Gated Transistors as In Operando Diagnosis Tools for Battery Electrode Materials

Lithium ion batteries (LIBs) are one of the major components in the portable electronics revolution as well as in the transition to a more sustainable society based on electric mobility. Despite enormous progress, scientists are still facing tremendous challenges to improve the energy density, cycle-life, reliability and safety of LIBs.<br/>Electrochemical Impedance Spectroscopy (EIS) has been widely exploited to study physicochemical phenomena taking place during battery operation, e.g. the evolution of the stability of the Solid Electrolyte Interphase (SEI, a passivation layer formed on electrode surfaces from decomposition products of electrolytes) as well as the response of the electrodes, for different states of the electrode charge.<br/>Nanostructured transition metal oxides are extremely attracting candidates as LIB electrode materials for their abundance and chemical versatility, among others. EIS has indicated that, with metal oxides, the electronic properties of the electrodes change with the degree of lithiation, during charge-discharge. Unfortunately, EIS still does not enable a clear discrimination between the effect of the charge transfer at the SEI versus the effect of the electronic conductivity of the electrodes on the electronic properties of the electrodes. This knowledge gap prevents the optimal exploitation of the batteries.<br/>We will discuss the use of ion-gated transistors (IGTs), making use of ionic compounds as the gating media, to study in operando the electronic properties of electrode materials for LIBs at different states of charge. In other words, we will bridge the worlds of electronics and electrochemistry to study electronic aspects of battery electrode materials.The LIB electrode material will be used as the transistor channel material of a corresponding IGT. Specifically, our contribution will revolve around the (i) preparation of the battery electrode materials and their electrochemical (cyclic voltammetry) characterization, the patterning of the battery electrode materials and transistor assembly, and (iii) transistor characterization and extraction of relevant parameters for LIBs (density of charge carriers, charge carrier mobility).