Atomic layer deposition-enabled ultrastable freestanding carbon-selenium cathodes with high mass loading for sodium-selenium battery

Melt diffusion followed by vapor deposition is judiciously combined with atomic layer deposition (ALD) to construct Al₂O₃–coated (Se/porous N-doped carbon nanofibers)@Se composite (denoted SC@Se-Al₂O₃) materials for sodium-selenium (Na-Se) batteries. High mass loading, ultrastable and free-standing carbon-selenium cathode is conveniently achieved by tailoring both the Se content and the thickness of deposited Al₂O₃ layer. Importantly, in contrast to only 176 mAh g⁻¹ of the electrode without Al₂O₃ deposition after 660 cycles, the composite with a Se content of 67 wt% and a 3-nm Al₂O₃ thickness retains a reversible capacity of 503 mAh g⁻¹ after 1000 cycles with no capacity fading at 0.5 A g⁻¹. These findings clearly suggest that ALD strategy provides a viable, controllable and effective means of tuning the electrode performance towards high mass loading of active materials and long cycle life of the resulting battery for energy storage applications.