In Situ Carbon-Coated Na₂CO₃@C as a High-Capacity Sacrificial Additive: Enhancing Presodiation Efficiency via...

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.