An anodeless, mechanically flexible and energy/power dense sodium battery prototype

Sodium metal batteries (SMBs) have aroused considerable attention as a viable technology for gigawatt-scale energy storage applications due to the lower cost of resources and theoretical energy density that surpasses that of lithium ion batteries (LIBs). Nevertheless, the practical deployment of SMBs is burdened by the cation utilization inefficiency, dendritic deposit propagation, and unexploited energy potential due to the excessive use of inactive species (the pre-stored Na reservoir, massive deposition substrates and flooded electrolyte). Herein, we propose an enabling anode-less SMB design through carbothermal encapsulation of various zinc-containing multialloys (from ternary to medium/high entropy alloys, MEAs/HEAs) within the interweaved carbon nanotube (CNT) as the light weight, mechanically flexible Na deposition substrates. Upon Na-Zn alloying prior to the Na deposition process, the heterogeneous NaZn₁₃ species could uniformly diffuse within the CNT, which effectively tailored the Na affinity of the deposition scaffold with the zero-nucleation overpotential. Both the theoretical modeling and experimental evaluations validate the preferential Na nucleation within the composite scaffold and the oriented deposit propagation along the nanotubes up to 10 mA h cm⁻². As the presodiated Cu₂NiZn@CNT substrate coupled with the NaVPO₄F cathode (∼11.7 mg cm⁻²) in a proof-of-concept anode-less (N/P = 0.2), lean-electrolyte (20 μL mA h⁻¹) model (20 mA h), a gravimetric energy density of 351.6 W h kg⁻¹ at the maximized power output of 1335.5 W kg⁻¹ (calculations based on the electroactive materials), and robust cycling (93.7% for 200 cycles) upon various geometric flexing states are simultaneously achieved. This work opens an uncharted territory of the MEA/HEAs derived mechanically flexible, light weight, sodiophilic scaffold, which thus leads to a quantum leap forward in feasible prototyping of energy-dense metallic batteries.