Presodiated Hard Carbon Anode with an Inorganic-Rich Interphase for Solid-State Sodium Batteries

Hard carbon (HC) anode based solid-state sodium-ion batteries (SSIBs) possess highly intrinsic safety and cost effectiveness in the application of large-scale energy storage. However, it is hindered by large interfacial impedance and sluggish Na + transport kinetics from the solid–solid electrode contact. Here, we propose an electrochemical presodiation strategy to in situ form a thin, uniform, and inorganic-rich (NaF/Na 2 O) solid-electrolyte interphase (SEI) on the HC anode. Such an SEI layer provides stable and good contact, leading to markedly reduced charge-transfer resistance and robust Na + transport in a polymer-based solid electrolyte. The evidence for reversible Na + insertion/extraction in the HC anode for SSIBs was first revealed by in situ X-ray diffraction. Consequently, the presodiated HC-based half-cell exhibits a reversible capacity of 275.2 mAh·g –1 and good cycling stability with 90.9% retention after 100 cycles at 0.1 C. Finally, the presodiated HC-based SSIBs were constructed with the Na 3 V 2 (PO 4 ) 3 cathode, delivering a high capacity of 106.9 mAh·g –1 at 0.1 C and good cycling stability without external pressure. These findings highlight inorganic engineering of the SEI as a powerful strategy for boosting interfacial kinetics toward regular pressure HC anode-based SSIBs.