Initiating Jahn–Teller Effect in Vanadium Diselenide for High Performance Magnesium‐Based Batteries Operated at −40 °C

Abstract Poor electronic and ionic conductivity of electrode materials at low temperatures of −20 °C and below has significantly impeded development of batteries for cold conditions. However, for the first time, layer‐structured metallic vanadium diselenide (1T‐VSe 2 ) is reported as a cathode material for low‐temperature Mg 2+ /Li + hybrid batteries. A high electronic conductivity and fast ion diffusion kinetics for 1T‐VSe 2 are demonstrated at selected temperatures, and a very safe 1T‐VSe 2 /Mg battery for operation at temperatures to −40 °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‐VSe 2 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.