Study of lithium intercalation into different nanostructured cathode based on oxides of transition metal using ionic liquid (ILs) with low viscosity synthesized from phosphonium and tetracyanoborate like electrolytes.

Abstract

At present, the challenge of lithium ion batteries is to develop systems with higher ciclability, and high power and energy densities. While the carbon negative electrode possess good performance (high cyclability and high reversible charge density above 370 mAhg-1) cobalt oxide, LiCoO2, the electroactive material that is typically used as positive electrodes, have many disadvantages, such as low practice specific charge (140 mAhg-1), and thermal instability in charged(oxidized) state. Among the various active materials which can be used as positive electrodes, the composite transition metal NMC (LiNi1/3Mn1/3Co1/3O2) and NCA (LiNi0.8Co0.15 Al0.05O2) are promising ones due to their low cost, good charge storage capacity and low toxicity. On the other hand the need for lithium-ion batteries with high power and high energy density carries a safety related issue due to problems associated to the organic solvents typically used as electrolytes. It is known that ionic liquids (ILs) can be used as electrolytes once they are non-flammable and have high thermal and electrochemical stability. However, ILs with good transport properties which allow easy diffusion of lithium are necessary. For this reason ILs derived from tetracyanoborate anion and phosphonium cation will be prepared. These structures have low coordination capacity that causes a decrease of coulombic interactions. In this project cathodes derived from transition metals and ionic liquids with excellent transport properties will be prepared.