Stable Cycling of Na Metal Batteries at Ultrahigh Capacity

Abstract 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 ⁻² ) 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 ⁻² 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 Na ₃ V ₂ (PO ₄ ) ₃ cathode (12 mg cm ⁻² ) delivers a stable capacity of 94 mAh g ⁻¹ for 270 cycles (94% capacity retention).