Rechargeable Batteries from the Perspective of the Electron Spin

Rechargeable batteries generate current through the transfer of electrons between paramagnetic and/or metallic electrode materials. Electron spin probes, such as electron paramagnetic resonance (EPR) and magnetometry, can therefore provide detailed insight into the underlying energy storage mechanisms. These techniques have been applied ex situ, and more recently operando, to both intercalation- and conversion-type batteries. After briefly presenting the principles of EPR and magnetometry, this Focus Review provides a critical discussion of recent studies that leverage these tools to understand the local structure, defect chemistry, and charge-discharge and failure mechanisms of rechargeable batteries. Challenges in data collection and interpretation are addressed, and strategies to facilitate EPR spectral assignment and expand the scope of EPR and magnetometry studies of battery systems are suggested.