Lithium-ion and 'beyond lithium' batteries face degradation challenges, particularly under prolonged use or adverse conditions. Traditional methods often fall short in understanding phenomena like metallic lithium morphology changes and transition metal ion behaviour. This thesis presents pulse Electron Paramagnetic Resonance (pEPR) as a complementary method for exploring these issues.

Initially, pEPR is used to study metallic lithium deposits at battery anodes, analyzing skin effect and electron mobility to assess lithium morphology. The method reveals ongoing morphology changes after lithium deposition due to surface diffusion. It also monitors lithium plating at graphite anodes, detailing onset, rate, and dead lithium presence.

The second part leverages pEPR and Density Functional Theory to explore solvation preferences of transition metal ions. Mn²⁺ and Cu²⁺ ions were observed to form a solvation shell of cyclic carbonates, whereas Mn2+ forms fluorophosphate complexes upon heating. To investigate dissolved transition metal ions in operating batteries, V₂O₅ cathodes were analysed. Significant vanadyl ion dissolution was observed, with selective coordination by glycol dianion ligands and formation of fluorophosphate ligands upon extended storage.

This research demonstrates pEPR's potential in enhancing the understanding of battery degradation, aiding in the development of more efficient energy storage systems.