FeNCN as new molecular negative electrode materials for Li- and Na-ion

We report evidence for the electrochemical activity of transition metal carbodiimides versus
lithium and sodium1. In particular, the iron carbodiimide FeNCN can be efficiently used as a
negative electrode material for alkali-metal-ion batteries (Li and Na), similarly to its oxide
analogue FeO. Based on 57Fe Mössbauer and infrared spectroscopy (IR) data, the
electrochemical reaction mechanism can be explained by the reversible transformation of the
Fe–NCN into Li/Na–NCN bonds during discharge and charge processes. These new electrode
materials exhibit higher capacity compared to well-established negative electrode references
such as graphite or hard carbon. Contrary to its oxide analogue, iron carbodiimide does not
require heavy treatments (nanoscale tailoring, sophisticated textures, coating etc.) to obtain
long cycle life with density current as high as 9 A/g for hundreds of charge/discharge cycles.
Similar to the iron compound, several other transition metal carbodiimides (MxNCNy with M
= Mn, Cr, Zn) can cycle successfully versus lithium and sodium. Their electrochemical
activity and performances open the way to the design of a novel family of anode materials for
both Li- and Na-ion batteries.