AMADEus Seminar - Pr. Bruce Dunn - Wednesday 13 July 2016 - 4:00 pm ICMCB (Amphi)

Abstract: The advantages in using nanostructured materials are especially well documented for lithium ion batteries as high energy density, and fast charge/discharge rates have been reported for both anode and cathode material systems. What is not necessarily appreciated is that as electrochemically active materials approach nanoscale dimensions, the charge storage mechanism from faradaic processes occurring at the surface of the material, referred to as the pseudocapacitive effect, becomes increasingly important. Currently, there is considerable interest in exploring materials which exhibit pseudocapacitive charge storage because of the prospect of achieving the energy density of battery materials from the redox reactions, in combination with the power density of traditional double layer capacitors.

This paper will review our work on determining the conditions under which nanoscale materials lead to pseudocapacitive energy storage. One key feature associated with pseudocapacitance is that the rate of charge storage is determined by surface-like kinetics rather than semi-infinite diffusion as occurs with battery materials. Another important consideration with this mechanism is that the structure does not undergo a first-order phase transition upon Li⁺ insertion. However, even with materials that exhibit such phase transitions, nanostructuring the material can effectively suppress the structural change and lead to promising properties. Morphology is another parameter that can be used to develop pseudocapacitive properties in oxides.  Both mesoporous materials, which possess an interconnected pore network, and two-dimensional nanosheets of transition metal oxides, exhibit surface-controlled kinetics indicative of pseudocapacitive behavior.

The ensemble of these results suggests that we can expect an increasing number of materials to be developed that retain high energy density at charge/discharge rates which are well above those of battery materials.