Jake T. Herb

Tuning Sodium Ion Conductivity in the Layered Honeycomb Oxide Na(3-x)Sn(2-x)Sb(x)NaO6.

A series of compounds with the composition Na(3-x)Sn(2-x)Sb(x)NaO6 (x = 0.0, 0.2, 0.4, 0.6, 0.7, 0.8, 0.9, and 1.0) has been prepared by solid-state reaction and characterized by powder X-ray diffraction, neutron diffraction (for x = 0.0), and impedance spectroscopy. The compounds have a layered structure derived from that of α-NaFeO2, with alternating Na3 planes and NaSn2O6 slabs with honeycomb in-plane ordering. The structure of the parent compound, Na2SnO3, has been determined as a two-layer honeycomb in monoclinic space group C2/c. Due to charge neutrality requirements, the substitution of Sb(5+) for Sn(4+) creates sodium site vacancies that facilitate high sodium ion mobility. A decrease in layer stacking disorder is also observed. The conductivity increases linearly with x and has a maximum at x = 0.8 (1.43 × 10(-3) S/cm at 500 °C with suboptimal sample densities). This material may be of interest as a solid Na ion electrolyte.

A fluorinated dialkoxide-based magnesium-ion electrolyte

Efficient large scale electrochemical energy storage systems, such as those based on multivalent ions, are a prerequisite for the realization of intermittent renewable energy sources. From the perspectives of both cost and environmental concerns, it is of critical importance that components of these systems are synthesized using sustainable chemical processes starting from their initial conception. Herein, we report on a fluorinated dialkoxide-based magnesium-ion electrolyte that is synthesized through an atom-efficient and scalable process without the use of any metal alkyls. The electrolyte composition results in high solution conductivity (4.77 mS cm−1 at 26.3 °C), low overpotentials, ca. 100% coulombic efficiency for electrodeposition/dissolution, and good performance in full battery cells using Chevrel phase Mo6S8.