Sodiophilic Au-diamane polypropylene separator enabled dendrite-free sodium metal batteries†

Sodium metal is considered a promising anode material for sodium metal batteries (SMBs) owing to its high theoretical specific capacity and low electrochemical potential. Nevertheless, its practical application is hindered by the challenge of dendrite formation. To address this issue, a separator modification strategy was adapted to enhance the performance of sodium metal anodes (SMAs) using Au nanoparticle-decorated two-dimensional diamane on a commercial polypropylene substrate (Au-diamane/PP) separator. The sodiophilic Au-diamane/PP separator facilitates improved Na⁺ ion diffusion kinetics and induces a dendrite-free deposition morphology, effectively suppressing dendrite growth. The dendrite-free deposition behavior was systematically characterized using in situ optical microscopy and ex situ scanning electron microscopy. The symmetric Na||Na cell incorporating the Au-diamane/PP separator exhibits exceptional cycling stability, maintaining operation for more than 2100 h at 2 mA cm⁻² with 1 mA h cm⁻². The sodiophilicity originates from the in situ formed AuNa₂ alloy formed on the surface of diamane during the discharging process. Additionally, a full cell with a Na₃V₂(PO₄)₃@C cathode, Au-diamane/PP separator, and Na metal anode delivers a high reversible capacity of 88.4 mA h g⁻¹ even after more than 300 cycles. Our work underscores the potential of the Au-diamane/PP separator in advancing the development of SMBs with extended cycle life and enhanced performance.