A lignin-derived flexible porous carbon material for highly efficient polyselenide and sodium regulation

Low-cost and sustainable sodium-selenium (Na-Se) batteries are promising energy storage media for the advancement of electromobility and large-scale energy storage. However, the sluggish kinetics of Se cathodes and the unpredictable metal electrodeposition of Na at the anode remain critical challenges. In this work, we reveal the catalytic effect of atomic Fe on the conversion of polyselenides (SPSs) to Na₂Se by density functional theory (DFT) calculations. Then, we prepare a lignin-derived flexible porous carbon matrix loaded with atomic Fe (Fe-BC/rGO, BC: lignin-derived porous carbon material; rGO: reduced graphene oxide) as a Se host to further verify the DFT calculation results. Due to the encapsulation of Se into the porous carbon matrix, the catalytic effect of atomic Fe on the conversion of SPSs to Na₂Se and the continuous electron/ion transportation path, the prepared Se@Fe-BC/rGO cathode can deliver a high reversible capacity of 213 mA h g^-1 at 2 A g^-1, which is much better than the electrochemical performance of a Se cathode without atomic Fe loading (Se@BC/rGO). In addition, we further reveal the advantageous effect of the presence of the Fe-BC/rGO film in regulating the interfacial Na electrodeposition at the anode. Due to the porous structure and the catalytic effect of atomic Fe, a very low nucleation overpotential of 15.3 mV is achieved at a current density of 1 mA cm^-2, which is much lower than that of the BC/rGO film. Therefore, this work provides a low-cost and sustainable strategy for simultaneously solving the challenges of the Se cathode and the Na metal anode for future Na-Se batteries.