  This chapter illustrates the use of defect physics as a conceptual and
theoretical framework for understanding and designing battery materials. It
starts with a methodology for first-principles studies of defects in complex
transition-metal oxides. The chapter then considers defects that are activated
in a cathode material during synthesis, during measurements, and during battery
use. Through these cases, it discusses possible defect landscapes in the
material and their implications, guidelines for materials design via
defect-controlled synthesis, mechanisms for electronic and ionic conduction and
for electrochemical extraction and (re-)insertion, and effects of doping.
Although specific examples are taken from studies of battery cathode materials,
the computational approach and discussions are general and applicable to any
ionic, electronic, or mixed ionic-electronic conducting materials.
