Interfacial pathways in Na2B12H12/SiO2nanocomposites 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 SiO2via 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.