Cation-Tuned Reaction Mechanisms in Metal Dicyanamide Anodes for Lithium-Ion Batteries with High Reversible Capacity.

In order to build rechargeable high-energy-density and long-term cycling stability batteries, significant efforts have been dedicated to the development of alternate anodes. Here, we designed two intercalation-type anodes based on the dicyanamide anion, N(CN), through strategic incorporation of metal cations─specifically by replacing Mn with Ni and Co─thereby enabling a transition from conversion-type for Mn[N(CN)] with compromised cycling performance to intercalation-type lithium storage mechanisms for Ni[N(CN)] and α-Co[N(CN)] including superior cycling performance. Ni[N(CN)] and α-Co[N(CN)] exhibit high specific capacities and cycling stability, maintaining reversible capacities of about 500 mAh·g over 200 cycles and 600 mAh·g over 400 cycles, respectively. These values notably surpass those of established negative electrode materials such as graphite (≈372 mAh·g), offering compelling performance comparisons. In addition, advanced characterization techniques reveal an intercalation mechanism facilitated by the N(CN) anion, which contributes to reversible capacity retention. Furthermore, we show, through density functional theory (DFT) calculations and quantum-chemical analysis, that the source of excellent electrical performance lies in the delocalized nature of the π-bonded N(CN) complex anion, electrostatically attached to Li. This mechanism, observed in transition-metal dicyanamides, is likely the key to their exceptional electrochemical performance and provides insight into the design of anode materials.