Improved reversibility of NaAlH4 in lithium cells

NaAlH4 has recently emerged as a potential anodic material in lithium ion cell. Through a conversion reaction1, it is able to develop more than 1700 mAh/g upon first discharge2,3. Despite its high specific capacity, NaAlH4 suffers of poor cycle efficiency, mostly due to the severe volume expansion following the conversion reaction and resulting in damages to electrode mechanical integrity with loss of electric contact. Large improvements in terms of electrochemical reversibility have been achieved mixing NaAlH4 with carbon by High Energy Ball Milling2. Mechanochemical treatments promote the creation of an intimately mixed carbon-hydride composite material in which carbon act as coating agent and limits large volumetric changes preventing grain growth and sintering. Furthermore, the improved thermal hydrogen desorption kinetics suggest an increased hydride mobility in the complex respect the bare alanate. In order to better understand the role of mechanochemical treatments on the electrochemical properties of NaAlH4, we report a comprehensive study of our NaAlH4/C composite by the use of advanced technique like solid state NMR, Temperature Programmed Desorption and Electrochemical Impedance Spectroscopy. 1. Y. Oumellal et al., Nat. Mater., 2008,11(7), 2. L. Silvestri et al., J. Phys. Chem. C, 2015, 119(52), 3. J. A. Teprovich, J. Phys. Chem. C, 2015, 119(9).