This book presents a comprehensive investigation of charge storage in a mixed conductor (general materials case). As it includes bulk and boundary zones, it leads to a unification of battery insertion electrode and supercapacitor storage concepts, which are unnecessarily considered as two separate phenomena. Following and extending the quantitative concept of job-sharing storage, a generalized picture that encompasses bulk and space charge storage (insertion electrode and supercapacitor storage) is developed. The system under consideration is titanium dioxide (TiO2) thin films, in which lithium is inserted, and the results are evaluated as a function of distance from the current collector. Measuring the capacity as a function of size enables distinguishing between bulk storage (lithium ions and electrons stored in TiO2) and space charge storage at the interface (lithium ions stored on the TiO2 side of the interface to the current collector, and electrons on the current collector's side). Variation of size and nature of the current collector allows optimizing the ratio of energy to power density, which was not possible before. In the same context, this thesis investigates the space charge behavior in a discretized manner rather than by using the analytical Poisson-Boltzmann function. In this way, a more precise definition and demarcation of electrode and double layer capacity is achieved. This thesis opens new avenues for tailoring power versus energy density in examples of practical interest, addressing one of the central challenges in energy research. This book benefits students and researchers interested in defect chemistry, electrochemistry, and energy storage research.