This paper reviews the literature on Lithium-ion battery characterization, control, and optimization. The paper examines the primary degradation processes in cycled cells, then proceeds to the challenges associated with controlling these processes. One key challenge is the multiplicity of complex phenomena contributing to battery aging, and the failure of most empirical battery health models to account for this multiplicity. This creates a need for identifying how batteries fail, and developing control-oriented fundamental models of their failure: a task that requires tight integration of experimental characterization techniques, system identification, and electrochemistry-based battery modeling and simulation. The paper provides an overview of battery degradation mechanisms and reactions, and the various methods used to characterize these reactions. We also highlight the battery control strategies currently in use, and the potential for long-term battery health improvements using model-based degradation control.