Stable Cycling of Na Metal Batteries at Ultrahigh Capacity.

The development of sodium metal batteries has long been impeded by dendrite formation issues. State-of-the-art strategies, exemplified by sodiophilic hosting/seeding layers, have demonstrated great success in suppressing dendrite formation. However, addressing high-capacity applications (>10 mAh cm) remains a significant challenge. Herein, the study revisits the interlayer strategy by simply covering a carbon nanotube (CNT) film onto the surface of a sodium metal anode, unlocking its overlooked potential for ultrahigh capacity applications. In situ Raman spectroscopy reveals the interlayer's fast-ion-storage feature, enabling deposition at the interface without capacity limitations. Consequently, in symmetric cells, one-year long-term reversible cycling and a record-high capacity of 50 mAh cm under 90% depth of discharge is achieved, representing a significant breakthrough for stabilizing Na anode. Furthermore, the full cell with a 50-µm thin metal anode and a high-loading NaV(PO) cathode (12 mg cm) delivers a stable capacity of 94 mAh g for 270 cycles (94% capacity retention).