Thin Films of Organic Electrode Materials for All-Solid-State 3D-Microbattery Applications

Abstract

The miniaturization of electronic devices demands for energy storage systems of equal size. As the conventional liquid electrolyte cells do not scale well enough, the current focus is on all-solid-state thin film batteries. In order to increase the energy density while preserving the power density of the cells, nanostructuring of the substrate to increase the effective surface area is seen as a viable option. Such an approach places an apparent need for a thin-film deposition method capable of manufacturing the electrode and electrolyte materials on high aspect ratio substrates. A strong candidate for the task is the atomic layer deposition (ALD) technique which is based on sequential surface reactions of gaseous precursors. The surface saturation limited growth results in excellent conformality over complex surface features. However, the availability of ALD processes for Li-ion battery materials is severely lacking. By utilizing combined atomic/molecular layer deposition (ALD/MLD) technique, we broaden the range of available electrode materials to those based on conjugated carbonyl systems. These organic electrode materials combine the high gravimetric energy density with abundant and environmentally benign constituents. We present demonstrative ALD/MLD processes for both anode and cathode materials and verify the electrochemical activity of the as-deposited thin films. Also shown is that the nanoscaling of the materials can be utilized to overcome the inherently poor kinetics of organic electrode materials without relying on any conductive additives. As the ALD/MLD method allows for making the cathode material directly in the fully-lithiated reduced state, the as-deposited pair can be combined into a full cell without an additional lithiation step.