(103f) Lithium Air Rechargable Battery Challenges to Sustained Cycling

There is growing interest in with smaller and lighter weight batteries in combating global warming. Rechargeable Li batteries have been considered as serious contenders for hybrid electric vehicles and stationary power applications. Unfortunately, the energy density of current rechargeable lithium batteries is limited by the positive electrode, e.g. LiCoO₂ (130 mAhg^-1). A revolutionary advance from graphite-LiCoO₂ batteries to Li-air counterparts allows Li⁺ and e^- in the cell to react with O₂ from the air. This enables an increase in storage capacities up to 10 times while reducing cost significantly. The air cathode is the new challenge for the battery. In this work, novel nanostructured air cathode materials were fabricated, characterised by using XRD, TEM and SEM and tested as cathodes in rechargeable Li-air batteries. Such 3D nanomaterials displayed notable successes in terms of capacity (up to 3000 mAhg^-1), power and materials sustainability. The superior performance of the nanomaterials was attributed to their structures which acted as transport pores and ensured rapid insertion and removal of lithium via the following reversible reaction:

2 Li + O₂  Li₂O₂

The relationship between composition, especially ratios of catalyst to carbon, structure, properties and performance shall be discussed. Measures to tackle technical barriers in battery design and engineering will also be addressed.

We have investigated the use of graphene as an alternative carbon conducting material in the Li-air battery using bifunctional MnO₂/Au catalysts. This has provided significant improvement in its stability (stable cycling > 100) as well as a great  improvement in the lithium air cell capacity (10,000mAh/g).  

Battery performance is still affected by loss in capacity after repeated cycling due to instability of certain solvents and cathode carbon supports. A micro-macro homogeneous mathematical model was developed for the cycling operation of a porous Li-air cathode using a concentrated binary electrolyte theory. The model includes mechanism for solvent degradation and production of Li carbonates. The published physical and chemical property data is carefully applied in this model to predict the time dependance of electrolyte concentration, non-uniform porosity and reaction rate and loss of capacity after cycling.