From theoretical energy to practical utilization: interfacial stability, transport kinetics, and cell-level design in high-energy lithium-metal batteries

Lithium-metal batteries are widely regarded as one of the most promising routes toward cell-level energy densities beyond the limit of conventional graphite-based lithium-ion batteries. However, the practical energy delivered by a lithium-metal cell is not determined only by the theoretical capacity of the cathode or the low potential of lithium metal. In many cases, the accessible energy is gradually consumed by voltage decay, interfacial impedance growth, parasitic reactions, inactive component weight and incomplete utilization of thick electrodes. This review therefore focuses on the conversion of theoretical energy into practically deliverable full-cell energy rather than providing a broad survey of all high-energy lithium-metal battery chemistries. High-voltage layered oxides are discussed as representative systems for voltage preservation and cathode interfacial stabilization, while selected conversion cathodes are used to illustrate how sluggish reaction kinetics, mass transport limitations, and lean-electrolyte constraints reduce the utilization of high theoretical capacity. Lithium-metal anodes and pouch-cell design are further analyzed from the viewpoint of lithium inventory management and full-cell mass efficiency. By linking interfacial stability, transport kinetics, lithium reversibility, and cell-level design, this review emphasizes that practical energy density should be evaluated by retained capacity, average discharge voltage, electrolyte-to-capacity ratio, negative-to-positive electrode capacity ratio, areal capacity, and full-cell specific energy under realistic testing conditions.