Interfacial pathways in Na2B12H12/SiO2 nanocomposites boost the ionic conductivity and enable solid-state sodium batteries at room temperature

Abstract

All-solid-state sodium metal batteries are an attractive alternative to Li-ion batteries due to their high energy density, improved safety, and the lower price of sodium. A major bottleneck is the development of suitable solid electrolytes with sufficient ionic conductivity and electrochemical stability. Here, we report new all-solid-state sodium metal batteries based on sodium closo-dodecahydridoborate (Na₂B₁₂H₁₂) electrolyte and both Prussian white (Na₂MnFe(CN)₆) and TiS₂ cathode active materials. Although the pristine Na₂B₁₂H₁₂ has a low ionic conductivity at room temperature, the conductivity increases by more than three orders of magnitude upon nanocomposite formation with mesoporous SiO₂ via high-energy ball milling. The high ionic conductivity (5 × 10⁻⁴ S cm⁻¹, 30 °C) and oxidative stability (3.9 V vs. Na⁺/Na) of Na₂B₁₂H₁₂/SiO₂ enable room-temperature battery operation with impressive capacity retention. Using a variety of techniques, including X-ray Raman scattering and electron energy loss spectroscopy, we show the presence of an interphase formed by an interface reaction between Na₂B₁₂H₁₂ and SiO₂. The observed interface effects are highly influenced by the morphology of the oxidic framework and the preparation conditions of the nanocomposite.