Optimized Phase and Crystallinity of Cr2(NCN)3 Dominating Electrochemical Lithium Storage Performance.

ABSTRACT

Cr2(NCN)3 is a potentially high-capacity and fast-charge Li-ion anode owing to its abundant and broad tunnels. However, high intrinsic chemical instability severely restricts its capacity output and electrochemical reversibility. Herein we report an effective crystalline engineering method for optimizing its phase and crystallinity. Systematic studies reveal the relevancy between electrochemical performance and crystalline structure; an optimal Cr2(NCN)3 with high phase purity and uniform crystallinity exhibits a high reversible capacity of 590 mAh g-1 and a stable cycling performance of 478 mAh g-1 after 500 cycles. In-operando heating XRD reveals its high thermodynamical stability over 600 °C, and in-operando electrochemical XRD proves its electrochemical Li storage mechanism, consisting of the primary Li-ion intercalation and subsequent conversion reactions. This study introduces a facile and low-cost method for fabricating high-purity Cr2(NCN)3, and it also confirms that the Li storage of Cr2(NCN)3 can be further improved by tuning its phase and crystallinity.