Zinc Dicyanamide:\nA Potential High-Capacity Negative\nElectrode for Li-Ion Batteries

We demonstrate that the β-polymorph of zinc dicyanamide,\nZn[N(CN)<sub>2</sub>]<sub>2</sub>, can be efficiently used as a negative\nelectrode material for lithium-ion batteries. Zn[N(CN)<sub>2</sub>]<sub>2</sub> exhibits an unconventional increased capacity upon\ncycling with a maximum capacity of about 650 mAh·g<sup>–1</sup> after 250 cycles at 0.5C, an increase of almost 250%, and then maintaining\na large reversible capacity of more than 600 mAh·g<sup>–1</sup> for 150 cycles. Such an increased capacity is primarily attributed\nto the increased level of activity in the conversion reaction. A combination\nof conversion-type and alloy-type mechanisms is revealed in this anode\nmaterial via advanced characterization studies and theoretical calculations.\nThis mechanism, observed here for the first time in transition-metal\ndicyanamides, is probably responsible for the outstanding electrochemical\nperformance. We believe that this study guides the development of\nnew high-capacity anode materials.