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)₂^-, through strategic incorporation of metal cations─specifically by replacing Mn²⁺ with Ni²⁺ and Co²⁺─thereby enabling a transition from conversion-type for Mn[N(CN)₂]₂ with compromised cycling performance to intercalation-type lithium storage mechanisms for Ni[N(CN)₂]₂ and α-Co[N(CN)₂]₂ including superior cycling performance. Ni[N(CN)₂]₂ and α-Co[N(CN)₂]₂ exhibit high specific capacities and cycling stability, maintaining reversible capacities of about 500 mAh·g^-1 over 200 cycles and 600 mAh·g^-1 over 400 cycles, respectively. These values notably surpass those of established negative electrode materials such as graphite (≈372 mAh·g^-1), offering compelling performance comparisons. In addition, advanced characterization techniques reveal an intercalation mechanism facilitated by the N(CN)₂^- 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)₂^- 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.