A special issue of ChemSusChem has just been published online. Dedicated to the chemistry of energy conversion and storage, it is guest-edited by Prof. Dang Sheng Su of the National Laboratory of Materials Science at the Chinese Academy of Sciences. The issue contains papers highlighting the important developments in the chemistry of energy and storage during the last two years.
Chemical bond forming and breaking is at the heart of energy research. As Prof. Su writes in the editorial, energy obtained from physical sources (photovoltaic, geo, hydro, wind energy) is only sustainable if it can be stored in chemical bonds.
The article featured on the cover of this special issue is a great example of the rational design of energy materials through understanding at the molecular level. Prof De Chen and co-workers in Trondheim, Norway designed a high performance binder-free anode for lithium-ion batteries. They began by growing aligned carbon nanotubes (ACNTs) on stainless-steel foil. The conductive 3D nanotube structures provide a large surface area and reduce electron and lithium diffusion distances, while the metal foil acts as a current collector.
The researchers then coated the nanotubes with a metal oxide (MnO2) as the active material for lithium storage. The thin metal oxide film renders the entire material electrochemically active and enables a high energy storage capacity. However, the cycling performance of such metal-oxide-coated carbon materials can be poor. The process of lithium ion storage in these materials involves the reversible formation and decomposition of Li2O, accompanied by the reduction and oxidation of the metal oxide. The reduction of MnO2 by metallic lithium is thermodynamically favorable.
However, the reverse reaction is only favorable for nanosized materials. During the cycling, the process of lithium uptake causes an increase in the size of the metal oxide particles and in aggregation, resulting in a drop in capacity. The authors found that coating the active film with a stable material like carbon could suppress aggregation and improve anode performance. Mechanistic investigations showed that the carbon layer not only prevents the aggregation of manganese oxide but also provides a more stable solid-electrolyte interphase film, improving cyclic stability.
This work and the other articles featured in this special issue show that chemistry remains a core discipline in energy research.