Application of Sodium‐Rich Multifunctional Hard Carbon Synthesized via Multi‐Alloy Grafting Strategy for Presodiation in High‐Performance Sodium‐Ion Batteries

In sodium-ion pouch batteries based on hard carbon, an additional source of active sodium significantly enhances the battery's initial coulombic efficiency and compensates for the loss of active sodium ions during cycling. This study investigates the interaction between metallic sodium with carbon materials and develops a composite powder material of sodium-rich lithium-aluminum using a multi-alloy grafting strategy, to replenish the initial loss of active sodium in the hard carbon materials. To enhance the stability and utilization of this highly active sodium source, a novel slurry system based on polyethylene oxide (PEO) as a binder and dimethyl carbonate (DMC) as a solvent is introduced. Furthermore, this study designs a hard carbon composite electrode structure with a stable layer and sacrificial layer (NPH), which not only accommodates current battery processing environments but also demonstrates excellent potential in practical applications. Ultimately, the soft-packed sodium-ion battery consists of NPH electrodes with composite sodium ferric pyrophosphate (NFPP) and demonstrates excellent initial coulombic efficiency (91%) and ultra-high energy density (205 Wh kg^-1). These results indicate significant technological and application implications for future energy storage.