Position-Dependent Storage in Mixed Conductors: Generalized Storage Model, Improved Mott-Schottky Analysis and Correct CV-Response

Abstract

In this work, TiO2 and Nb2O5 thin films have been used as model systems to study the fundamental issues related to charge storage and transport in solids. Firstly, the storage capacity of lithium in TiO2 as a function of thickness for various electron-accepting substrates is measured precisely. Contributions from bulk and boundary storage were deconvoluted based on the electrochemistry and electron microscopy results. The results allow for working at three basic points. (1) Such experimental and theoretical investigation of the bulk and interfacial defect chemistry enables deriving the entire profile and embedding bulk and boundary contributions into a common generalized thermodynamic model, and hence a unification of battery intercalation electrode and supercapacitive storage1. (2) Bias-dependent resistance and capacitance measurements across the LixTiO2/electronic conductor interface allow us to improve the Mott-Schottky model by implementing a charge density that has been determined by the preparation conditions2. (3) Cyclic voltammetry (CV) performed at these systems leads to a description that is adjusted to the solid state and deviates significantly from the description in liquids. All these fundamental studies are highly relevant to energy-related application3.1. C. Xiao, H. Wang, R. Usiskin, P. A. van Aken, J. Maier, submitted.2. C. Xiao, J. Maier, in preparation.3. C. Xiao, R. Usiskin, J. Maier, in preparation.