(Invited) Atomic/Molecular Layer Deposition for Thin-Film Lithium-Ion Batteries

Abstract

All-solid-state thin-film batteries are seen as viable technologies for powering a wide variety of miniature electronic devices, for instance microelectronics, medical implants, and radio-frequency identification tags, due to their safety, and flexibility in size and design. In order to increase the energy density while preserving the power density of the cells, increasing the effective surface area through microstructuring of the substrate is seen as a promising option. This concept of all-solid-state 3D-microbattery places an apparent need for a thin-film deposition method capable of manufacturing the electrode and electrolyte materials on high aspect ratio substrates; a formidable challenge given the limitations of the currently used thin-film deposition methods. 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. As the basic research on new ALD processes for Li-containing thin films is only in early stage, the true impact of the ALD technique in the Li-ion battery field is yet to be demonstrated. This talk focuses on the use of ALD on depositing lithium-containing materials and on the aspects of manufacturing an all-ALD thin-film battery. As the all-solid-state thin-film layout enables unconventional approaches, a special emphasis is placed on fully organic electrode materials. Conjugated carbonyls are a promising group of redox active materials that in conventional bulk-format batteries suffer from solubility issues as well as from their inherently poor electronic conductivity. Here, the all-solid-state thin-film setup should mitigate both issues allowing for the full utilization of their perceived high redox reaction kinetics. The deposition of both positive and negative electrode materials is demonstrated by utilizing the combined atomic/molecular layer deposition (ALD/MLD) technique. In comparison to the conventional inorganic materials, this approach allows for simple, binary deposition processes, low deposition temperatures, and environmentally benign constituents. As well as enabling ultrafast redox kinetics, the thin-film approach might provide new information on the conduction mechanisms of the conjugated carbonyl based materials.