Michael Gratzel and colleagues at the Swiss Federal Institute of Technology in Lausanne note in current lithium-ion batteries, large quantities of carbon black, graphite or other conductive materials must be added to improve cathode conductivity.

"Sometimes, the conductive additives occupy practically half the volume of the active materials to form a continuous conduction network, greatly decreasing the energy density of the cell," the researchers said.

Gratzel's group reports the first use of a "molecular charge transport layer," consisting of a self-assembled monolayer of triarylamine phosphonate adsorbed at the surface of the cathode material lithium iron phosphate to improve its conductivity.

They said the total electrode size, the space occupied by the molecular charge transport layer, is negligibly small, greatly reducing the volume of conductive additive. That offers the possibility of substantially increasing the energy storage density and rate capacity at equal amounts of loading of conductive additives.

The research is to appear in the April 4 issue of the Journal of the American Chemical Society.