Investigation of the effects of mechanochemical treatment on NaAlH4 based anode materials for Li-ion batteries

Sodium alanate has proven to be a feasible candidate for electrochemical applications. Within a lithium cell, NaAlH4 closely approaches its theoretical capacity of 1985 mAhg−1 upon the first discharge. Despite its high specific capacity, NaAlH4 suffers from poor cycle efficiency, mostly due to the severe volume expansion following the conversion reaction and resulting in damage to electrode mechanical integrity with loss of electrical contact. Synthesis of an appropriate composite alanate/carbon by high energy ball milling demonstrates an ability to mitigate these deleterious effects, whereby large improvements in terms of electrochemical reversibility can be achieved. In order to highlight the effects of mechanochemical treatment on the electrochemical properties of NaAlH4, new insights on such NaAlH4/C composites are reported. Solid state NMR has been used to study the impact of ball milling on the NaAlH4 crystal structure, while, the hydrogen content and associated desorption properties have been evaluated by thermal programmed desorption measurements. Also, electrochemical features have been analyzed via the combined application of potentiodynamic cycling with galvanostatic acceleration and electrochemical impedance spectroscopy measurements. Finally, new evidence concerning the reversibility of the conversion processes has been obtained by ex-situ NMR measurements on cycled electrodes.