In Situ Carbon‐Coated Na ₂ CO ₃ @C as a High‐Capacity Sacrificial Additive: Enhancing Presodiation Efficiency via Defect‐Driven Electron Transfer

Introducing sacrificial additives to compensate for the irreversible loss of active sodium ions is essential for enhancing the energy density and cycling stability of sodium-ion batteries (SIBs). Herein, a simple spray-drying and pyrolysis process is employed, using glucose (Glu) as a carbon precursor to obtain uniformly carbon-coated Na₂CO₃@C (SC@C) as a sacrificial additive. The optimized SC@C-450 sample features a defect-rich carbon layer, which promotes decomposition via a surface-assisted electron transfer mechanism. During decomposition, CO₃ ² ^- species are activated by π-π interactions with carbon-centered radicals, which promote electron transfer into the π^* antibonding orbitals of C─O bonds, thereby facilitating Na⁺ release. This mechanism lowers the decomposition overpotential of SC@C-450 to 4.1 V (vs Na⁺/Na) and achieves a higher presodiation capacity of 502.8 mAh g^-1. When 6 wt.% SC@C-450 is incorporated into a Na₄Fe₃(PO₄)₂P₂O₇ (NFPP) cathode, the initial charge capacity is enhanced by 25.0% and the initial coulombic efficiency (ICE) is decreased from 96.0% to 80.1%, compared with the NFPP electrode without presodiation. Importantly, the addition of SC@C-450 does not compromise the rate performance or long-term cycling stability, maintaining 99.5% of its capacity after 3000 cycles. This study elucidates the critical role of interfacial electronic structure in sacrificial additive design and offers new insights for presodiation strategies in practical SIBs systems.