In situ formed self-embedded ion/electron conductive skeletons enabling highly stable sodium metal anodes

Abstract

Sodium (Na) metal has been considered as one of the most promising anodes for achieving next-generation battery systems with high energy density and low cost. Nevertheless, the uncontrolled dendrite growth, infinite volume expansion, and unstable solid/electrolyte interphase severely hinder the practical application of Na metal batteries. Herein, a self-embedded 3D ion/electron-conductive framework consisting of Na₁₅Sn₄ (3D IECF) throughout the Na metal (referred to as NSN-3D IECF) is successfully prepared through the spontaneous alloy reaction between Na and Sn (4Sn + 15Na → Na₁₅Sn₄). The self-embedded 3D IECF, featuring an interconnection network, not only facilitates rapid Na⁺ transfer under high current density, but also offers abundant space for Na⁺ deposition, which alleviates the volume expansion of the electrode during repeated cycling and maintains the interfacial stability of the anode/electrolyte. Meanwhile, the strong affinity between metallic Na and Na₁₅Sn₄ lowers the nucleation energy barrier, achieving uniform and compact Na metal deposition with a dendrite-free morphology. Benefiting from these merits, the NSN-3D IECF-based symmetrical cell exhibits excellent stability at 1 mA cm⁻² and 1 mA h cm⁻² for more than 4000 h and a low polarization voltage (10 mV). More importantly, the full battery paired with the Na₃V₂(PO₄)₂F₃ cathode maintains a reversible capacity of 106.2 mA h g⁻¹ after 650 cycles at 5 C.