Anode-Free Sodium Metal Pouch Cell Using Cu₃P Nanowires In Situ Grown on Current Collector

Anode-free sodium metal battery (AFSMB) promises high energy density but suffers from the difficulty of maintaining high cycling stability. Nonuniform sodium (Na) deposition on the current collector is largely responsible for capacity decay in the cycling process of AFSMB. Here, a unique copper phosphide (Cu₃P) nanowire is constructed on copper (Cu₃P@Cu) as a sodium deposition substrate by an in situ growth method. Superior electrochemical performance of Cu₃P@Cu anode is delivered in asymmetric cells with an average Coulombic efficiency of 99.8% for over 800 cycles at 1 mA cm^-2 with 1 mA h cm^-2. The symmetric cell of Cu₃P@Cu displayed a cycling lifespan of over 2000 h at 2 mA cm^-2 with 1 mA h cm^-2. Cryo-transmission electron microscope characterization and first principles calculation revealed that the low Na⁺ absorption energy and low Na⁺ diffusion energy barrier on Na₃P promoted uniform Na nucleation and deposition, thus enhancing the Na surface stability. Moreover, anode-free Na₃V₂(PO₄)₃//Cu₃P@Cu full pouch cell delivered a considerable cycling capacity of ≈15 mA h in 170 cycles, demonstrating its practical feasibility.