Breaking the High-Voltage Limit of Na2CO3 Presodiation: An Interfacial Engineering Approach to Ampere-Hour Sodium-Ion Devices

Na2CO3 is a promising sacrificial presodiation agent owing to its high capacity, excellent air stability, and low cost. However, its practical application is severely hampered by a high decomposition overpotential (>4.3 V vs Na/Na+), inducing detrimental electrolyte oxidation and cell degradation. To break this high-voltage limit, we propose an in situ interfacial dual-modification strategy, synergistically introducing interfacial oxygen vacancies and triggering electronic reconstruction, which thermodynamically lowers the reaction Gibbs free energy and kinetically diminishes the activation barriers, resulting in a dramatically reduced decomposition potential by 350 mV. Operando three-electrode diagnostics within a full sodium-ion capacitor reveal that this interface engineering not only facilitates efficient Na+ release (496.9 mAh g–1) at lower potential but also reduces the actual working potential of cathode, thereby fundamentally avoiding high-voltage parasitic reactions, according well with the DEMS and TOF-SIMS results. Consequently, the full cell achieves a considerable 117.4% enhancement in energy density. Most importantly, this strategy demonstrates compelling practicality in ampere-hour-level devices, delivering a substantial 22.4% boost in energy density with only 3 wt % additive in 1.5 Ah pouch cells. This work bridges microscopic interfacial chemistry and macroscopic device performance, providing a scalable and efficient blueprint for low-potential presodiation toward high-energy-density sodium-ion devices.