Synthesis, Structure, and Properties of the New Intercalation Cathode Material MoO_2.8F_0.2

Abstract

The widespread adoption of multivalent batteries is hampered by the lack of stable, reliable, high voltage cathodes that can reversibly intercalate divalent cations. In lithium-based systems, molybdenum trioxide has been studied for several years as a high capacity cathode material. Although its voltage is lower than other systems, e.g. V2O5, it has advantages including crystallographic stability on cycling. A key issue that is believed to limit its performance is that, as a d0 metal oxide, it has limited electronic conductivity at top of charge.1 In this poster we will be discussing the role of fluoride incorporation into the layered charged cathode MoO3 and its effect on the materials physical properties. Utilizing synthetic methodologies developed in our lab we have studied the fluoride solubility in the host material as a way to induce electronic conductivity across the whole range of use. We have shown that the maximum fluoride incorporation in the material yields a stoichiometry of MoO2.8F0.2. Incorporation above this value results in isolation of the perovskite phase MoO2.6F0.4. We have evaluated the material using multiple intercalating cations and compared it to the undoped parent material. While the electrochemical activity of the material using a lithium-based electrolyte is similar, remarkable differences have been observed when Mg is used as the cation. While the undoped material has little or no activity, the fluorinated materials shows excellent cycleability and structural reversibility.2 References: (1) Spahr, M. E.; Novák, P.; Haas, O.; Nesper, R., Electrochemical insertion of lithium, sodium, and magnesium in molybdenum(VI) oxide. J. Power Sources 1995, 54, 346-351. (2) Incorvati, J. T.; Wan, L. F.; Key, B.; Zhou, D.; Liao, C.; Fuoco, L.; Holland, M.; Wang, H.; Prendergast, D.; Poeppelmeier, K. R.; Vaughey, J. T., Reversible Magnesium Intercalation into a Layered Oxyfluoride Cathode. Chemistry of Materials 2016, 28, 17-20. Figure 1