Phosphorus-induced Na_xPO_y-rich solid electrolyte interphase for durable and low-temperature sodium-ion batteries

Sodium-ion batteries (SIBs) are promising alternatives to lithium-ion batteries, yet carbon-based anodes suffer from capacity fading and severe performance degradation at low temperatures due to increased interfacial impedance and sluggish ion transport. Herein, a phosphorus‑nitrogen co-doping strategy is proposed to reconstruct the solid electrolyte interphase (SEI). While nitrogen and phosphorus synergistically enhance the bulk electronic conductivity and defect density, phosphorus uniquely converts intrinsic P-C/P-N bonds into a thermodynamically stable, amorphous Na_xPO_y-rich SEI layer. This inorganic SEI endows the electrode with excellent mechanical strength and isotropic low-energy-barrier pathways for rapid Na⁺ migration. Consequently, the optimized electrode maintains high cycling stability at temperatures as low as -15 °C. Furthermore, a Long Short-Term Memory (LSTM)-based model is explored as a supplementary tool for rapid capacity forecasting across temperatures. This work provides a rational design paradigm for high-performance, wide-temperature-range SIB anodes, with preliminary full-cell tests demonstrating practical applicability.