The period unified intercalation chemistry with material-level strategies to maximize energy density, safety, and cycle life. Layered oxide cathodes such as LiCoO2 demonstrated high voltage operation with reversible Li intercalation around 4 V, spurring rapid adoption in early cells, while phosphate-olivine cathodes like LiFePO4 offered safer, inexpensive, scalable alternatives with practical capacities around 100–110 mAh/g. Foundational concepts such as the solid electrolyte interphase explained interfacial stability and guided electrolyte design, and zero-strain insertion materials like Li[Li1/3Ti5/3]O4 showed how to decouple lattice expansion from capacity to enable durable, fast-charging operation; together they seeded early aging analyses that would inform long-term reliability modelling. Historical Significance: These innovations established the core architecture of modern lithium-ion batteries—layered oxide cathodes forming the high-energy backbone, phosphate-olivine cathodes delivering scalable safety, and interfacial chemistry concepts that shaped electrolyte engineering and longevity. Zero-strain anode strategies and early degradation studies provided the first systematic framework for aging, guiding subsequent industrial development and research toward durable, reliable cells.