Nanodiamonds in energy storage: Emerging roles, mechanisms, and prospects for next-generation batteries and supercapacitors

Nanodiamonds (NDs) and diamond-derived nanostructures are increasingly investigated for electrochemical energy storage because of their mechanical robustness, tunable surface chemistry, chemical stability, and nanoscale interfacial activity. However, their reported functions remain fragmented across electrode, electrolyte, separator, and supercapacitor studies, and performance improvements are frequently attributed to NDs without adequately distinguishing their contributions from those of conductive carbons, dopants, binders, secondary phases, and electrode architecture. This review addresses this gap by critically correlating ND synthesis routes, including detonation, high-pressure-high-temperature processing, chemical vapor deposition, and laser ablation, with crystallinity, defect density, surface chemistry, dispersion, conductivity, and electrochemical performance. Recent applications in lithium, sodium, dual-ion, lithium‑sulfur, and zinc-based batteries are examined with emphasis on NDs as structural reinforcements, nanoscale spacers, nucleation regulators, electrolyte additives, and separator modifiers. The available evidence indicates that pristine NDs generally function as structural and interfacial regulators rather than intrinsically conductive or dominant charge-storage phases. Their incorporation can stabilize electrode architectures, regulate ion flux and metal deposition, modify solid-electrolyte interphases, improve separator wettability and mechanical resistance, and suppress dendrite growth and polysulfide migration. For supercapacitors, improved performance is primarily achieved through doping, nanostructuring, porous architectures, surface graphitization, and hybridization with conductive or redox-active materials, which balance charge transport with the stability of the sp 3 -diamond framework. Key limitations include aggregation, purification requirements, inactive mass, resistive interfaces, irreversible capacity loss, complex fabrication, and limited validation under practical cell conditions. Future progress requires synthesis-matched controls, quantitative assessment of ND-specific contributions, operando characterization, scalable processing, and testing in high-loading, lean-electrolyte, and pouch-cell configurations.