Initiating Jahn-Teller Effect in Vanadium Diselenide for High Performance Magnesium-Based Batteries Operated at-40 degrees C

Poor electronic and ionic conductivity of electrode materials at low temperatures of -20 degrees C and below has significantly impeded development of batteries for cold conditions. However, for the first time, layer-structured metallic vanadium diselenide (1T-VSe2) is reported as a cathode material for low-temperature Mg2+/Li+ hybrid batteries. A high electronic conductivity and fast ion diffusion kinetics for 1T-VSe2 are demonstrated at selected temperatures, and a very safe 1T-VSe2/Mg battery for operation at temperatures to -40 degrees C. The battery exhibits 97% capacity retention over 500 cycles, which is better performance than reported Mg-based batteries. The Jahn-Teller effect in compressed configuration is initiated in 1T-VSe2 with the change of electronic state occurring on electrochemical intercalation of alkali metal ions. Using combined experiment and theory via operando synchrotron X-ray diffraction, ex situ X-ray absorption spectroscopy and DFT computation, it is confirmed that the weak Jahn-Teller distortion contributes significantly to fast-overall kinetics, structural stability, and high electronic conductivity of the electrode. Understanding at an atomic level of the mechanism is demonstrated, that provides valuable guidance in designing high-performance electrode materials for low-temperature batteries.