Engineering Synergistic Cathodes for Li–O2 Batteries: Catalysis, Carbon-Free Hosts, and Multiscale Architectures

Lithium–oxygen (Li–O2) batteries offer exceptionally high theoretical energy density, but their practical development remains limited by sluggish oxygen redox kinetics, insulating discharge products, parasitic reactions, transport losses, and poor electrode durability. This review develops an engineering framework linking four coupled cathode-design strategies: conventional electrocatalysis, single-atom catalysis, carbon-free or carbon-minimized hosts, and multiscale structural and morphological engineering. A structured narrative assessment of the literature through 2026 is used to compare how these strategies influence ORR/OER kinetics, electronic and oxygen transport, Li2O2 nucleation and decomposition, interfacial stability, and electrode-level manufacturability. Particular emphasis is placed on the trade-offs that arise when catalytic activity, conductivity, porosity, chemical stability, mass loading, and fabrication complexity are optimized simultaneously. The review identifies engineering design principles for integrated cathodes and evaluates remaining barriers associated with thick-electrode transport, lean-electrolyte operation, air contaminants, scalable fabrication, standardized testing, and long-term cycling. The resulting framework provides an engineering-oriented roadmap for translating high-performing Li–O2 cathode concepts from laboratory demonstrations toward more realistic energy-storage devices.