Photogenerated Holes Induced Deep Sodium Storage of TiO ₂ /CdSe/NFPP Cathode for High‐Efficiency Photorechargeable Sodium Batteries

Resource-friendly photorechargeable sodium batteries (PRSBs) integrate energy storage devices with solar cells, offering a promising path for sustainable energy. Herein, a novel TiO₂/CdSe/Na₃Fe₂(PO₄)P₂O₇ (NFPP) cathode was prepared layer-by-layer utilizing resource-abundant commercialized NFPP and photoactive CdSe. The aligned energy levels with type II band structure ensure effective transfer of photogenerated holes from CdSe (-5.71 eV) to higher valence band of NFPP (-5.10 eV). Experimental results reveal that, during charging, the induced holes in NFPP accelerate the transition of Fe²⁺ to Fe³⁺ with a change of O-Fe hybrid orbitals. The calculations of bond valence sum and energy distribution reveal that NFPP-holes possesses broad Na⁺ transport path with reduced transport barrier (from 0.512 to 0.428 eV), improving Na⁺ extraction efficiency. Additionally, photogenerated holes could regulate surface charge distribution on NFPP and thus form a film-forming agent fluoroethylene carbonate (FEC)-dominated electric double layer. Finally, it converts to a thinner (9.75 nm illumination) NaF-rich cathode interphase layer, avoiding subsequent excessive electrolyte decomposition. As a result, the NFPP under illumination delivers high capacity of 119.1 mAh g^-1 at 1 C, showing 41.11% improvement compared to dark conditions.