High performance metal nitrides for super capacitors and Li-ion batteries – Advanced NiBaCa

The present project aims at a fundamental investigation of nitride based materials as electrodes for electrochemical storage devices, namely electrochemical supercapacitors and lithium ion batteries. For supercapacitor applications, the requirements are high energy and power densities together with long term cycling life. Both carbon based compounds and some metal oxides have been tested as potential electrode materials for supercapacitors and in some cases can fulfill the previous requirements. However, there is a need for higher energy density which can only be achieved by increasing the capacitance of the electrodes and/or enhancing the useful electrochemical window of the devices. Subsequently, the research efforts are directed toward the development of improved materials such as controlled porosity carbons or nanostructured metal oxides. However, the capacitance values still limited to 200-300 F/g for “bulk” electrodes. Recently, few reports claim improved capacitance alues for transition metal nitrides. Subsequently, the first axis of this project will be dedicated to the screening and selection of different nitrides, while trying to understand the charge storage mechanism taking place at the nitride electrode/electrolyte interface which rules the electrochemical properties and more specifically the cycling ability and the capacitance. Today's research on negative electrodes for the Li-ion technology is mainly split between(1) enhancing the electrochemical characteristics of the carbonaceous negative electrode by chemical or physical means and (2) finding alternative materials to substitute for the presently used carbonaceous negative electrode composites. The second approach has led to the discovery of new attractive materials (new ternary oxides, amorphous tin composite oxides, silicon/carbon nanocomposites etc...) which unfortunately exhibited in some cases poor capacity retention which limits their use in practical cells. Fundamental and applied research proposed as the second axis of this project is directed towards an intense effort for screening and evaluating a new group of materials, the transition metal nitrides and nitrides of elements of the groups III, IV and VA as negative electrode. In spite of a particular rich and unexpected valence behaviour, this new class of materials has been little investigated (except a few papers and those recently published by one of the partners on lithiated Co, Cu, Ni nitrides) after several decades of research dedicated to transition metal oxides. Therefore the wide screening of nitrides and oxynitrides compounds allowed by the use of the sputtering method (thin films materials), solid state reactions and soft chemistry synthesis (nitrides powder) will allow to get a lot of fundamental and applied data on the reactivity, structure, morphology, and electrochemical features of these compounds. A real alternative for the use of graphite as negative electrode is researched. Safety requirements for lithium-ion cells have become a critical issue. Safer negative electrode materials have been developed at the expense of cell voltage and subsequently power density which can be recovered if the electrode can sustain faster charge discharge rates compared to standard graphite electrode.The recent announcements on the performances of nitride based materials both in electrochemical capacitors and in lithium ion batteries open new challenges for scientific investigations of such compounds in electrochemical charge storage devices, with a perspective of fast technological transfer due to the availability of nitride based compounds for many other applications, such as hard coatings or conductive additives.The expertise of two partners in metallic nitrides chemistry and synthesis combined with that of two other partners deeply involved in the electrochemical investigation of electrode materials for supercapacitors and Li-ion batteries will enrich the field of materials chemistry and electrochemistry for energy storage and conversion.