Enhanced electrochemical lithium storage performance of Mg2FeH6 anode with TiO2 coating

Light-weight metal hydrides are potential high-capacity conversion anode materials for lithium-ion batteries, but the poor reaction reversibility and cyclic stability of hydride anodes need to be improved. In this work, the ternary hydride Mg2FeH6 was composited with the graphite (G) by ball-milling, and the Mg2FeH6-G composite electrode was further coated with amorphous TiO2 film by magnetron sputtering. The resultant Mg2FeH6-G/TiO2 electrode exhibited a stable charge capacity of 412 mAh g−1 over 100 cycles, which is much higher than 46 mAh g−1 at 20th cycle for the pure Mg2FeH6 electrode, or 185 mAh g−1 at 100th cycle for the Mg2FeH6-G electrode. There is only little capacity degradation after 20 cycles for the Mg2FeH6-G/TiO2 electrode and the charge capacity retention is 84.7% after 100 cycles. The remarkable improvement in the cyclic stability of Mg2FeH6-G/TiO2 electrode is mainly attributed to the dense TiO2 coating that maintains the structural integrity of electrode during cycling. The TiO2 coating also prevents the direct contact of high active LiH/MgH2 with the liquid electrolyte, and thus ensures the high reversibility of conversion reaction of MgH2 during cycling.