The electrochemical activity of the nitrosyl ligand in copper nitroprusside: a new possible redox mechanism for lithium battery electrode materials?

The unconventional redox mechanism of copper nitroprusside in the electrochemical reaction with lithium is studied by a wide range of techniques. After a simple and reproducible synthesis, pristine copper nitroprusside is characterized using a wide range of techniques. The material is formulated and electrochemically tested in coin cells to explore its electrochemical signature and cyclability. Multiple redox processes involving both Fe and Cu centres are identified at an early stage and further investigated by operando XAFS. Moreover, operando FTIR unveils the unexpected participation of the nitrosyl ligand in the electrochemical reaction. A gradual and irreversible transformation of the material, also reported by operando Mössbauer spectroscopy, occurs in the first cycles. Then, the material is able to withstand several electrochemical cycles without efficiency loss, even though no optimization on formulation has been carried out. Altogether, the nitrosyl group is electrochemically active beyond metals’ centres, giving as result a remarkable increase in capacity compared to other analogue compounds. We thus believe this study may open the way to further research on other electroactive nitrosyl-containing materials.