Photogenerated Holes Induced Deep Sodium Storage of TiO/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 TiO/CdSe/NaFe(PO)PO (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 Fe to Fe 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 at 1 C, showing 41.11% improvement compared to dark conditions.