Rechargeable sodium batteries—VI. Cycling behavior of VS 2, ‘VCl 3 + nS’ and NbS 2Cl 2 cathodes in molten NaAlCl 4

Abstract

The electrochemistry of VS 2 in molten NaAlCl 4 has been investigated in relation to its usefulness as a reversible positive electrode for sodium batteries operating in the moderate temperature range of 160–200°C. VS 2 reacted with NaAlCl 4 during early stages of cell cycling, and became VS 2Cl showing a reversible capacity of ∼ 2.8 electrons/vanadium. The electrochemistry of mixtures of VCl 3 and S in molten NaAlCl 4 showed similarities to that of VS 2Cl. The VS x Cl y cathodes obtained via the two different routes exhibited excellent rechargeability as evidenced by the long-term cycling behavior of cells of the configuration, Na (l)/β″-Al 2O 3/NaAlCl 4(l), cathode material. When NbS 2Cl 2 was used as the cathode material it underwent a structural change in the first cycle to form what appeared to be NbS 2Cl 2, the Nb analog of VS x Cl y . The structurally modified niobium sulfur chloride cathode exhibited excellent rechargeability.