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

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.