Key points are not available for this paper at this time.
Abstract α‐MnN(CN) 2 2 ( Pnnm ) with divalent Mn 2+ being octahedrally coordinated by six N(CN) 2 − dicyanamide (dca ‒ ) complex anions is known since 1999. A novel β polymorph is now prepared and its structure characterized via powder X‐ray diffraction. β‐MnN(CN) 2 2 also crystallizes orthorhombically ( Cmcm ) but with Mn 2+ tetrahedrally coordinated to four N(CN) 2 − anions. Property‐wise, α‐MnN(CN) 2 2 can be efficiently used as a negative electrode material for lithium‐ion batteries, maintaining a large reversible capacity of more than 600 mAh g −1 for 250 cycles tested at 0.5 C, comparing favorably to well‐established negative electrode references such as graphite (≈372 mAh g −1 ). The electrochemical lithiation/delithiation mechanism of α‐MnN(CN) 2 2 is investigated using advanced characterization techniques and theoretical calculations. Upon lithiation, α‐MnN(CN) 2 2 undergoes a reversible conversion reaction, forming LiN(CN) 2 and metallic manganese, which are transformed back into α‐MnN(CN) 2 2 upon delithiation. Further, there is evidence for reversible and additional charge/discharge processes on the dca ‒ anion throughout the entire discharge/charge process in α‐MnN(CN) 2 2 , reflecting an anionic charge compensation. Moreover, density‐functional (DFT) and chemical‐bonding theory are employed to investigate the detailed anodic behavior of α‐MnN(CN) 2 2 via conversion reaction during (de‐)lithiation processes. This mechanism, evidenced for the first time in transition metal dicyanamides, is likely behind its outstanding electrochemical properties.
Qiao et al. (Fri,) studied this question.