(Invited) A Tutorial on Atomic Layer Deposition and Its Application in Lithium-Ion Batteries

Abstract

Atomic layer deposition (ALD) is a deposition technique where thin films are deposited from sequential gas-surface reactions. Thanks to the self-limiting nature of these reactions, ALD provides interesting deposition characteristics such as atomic scale thickness control and deposition onto complex shaped substrates (including powders) with excellent uniformity and conformality. These features have enabled ALD to become a well-established tool in semiconductor manufacturing, and there is a growing consensus that other domains such as catalysis and energy storage can also strongly benefit from these unique coating characteristics. In this tutorial, two different types of potential applications of ALD in the field of lithium-ion batteries will be discussed: - ALD of the active components of a lithium-ion battery (positive and negative electrodes, solid electrolytes), either as functional layers in thin film batteries, or as thin film model systems. Novel battery concepts such as the 3D thin-film lithium-ion microbattery are promising for applications such as on-chip energy storage, and ALD could play an important role in the deposition of critical components of these battery stacks onto 3D nanostructured substrates, in particular for the interfaces and solid-electrolyte layers. Moreover, the excellent film quality, control over composition and crystallinity provided by ALD enable the synthesis of thin, planar model systems. Such thin film model systems with well-controlled properties provide simplified one-dimensional currents and are unbothered by the complex interplay of various components of the classical battery, such as binder, conductive additive, particle size, solvent composition etc, and can thus reveal potentially beneficial battery chemistries which would otherwise be obscured, or provide insights into otherwise very complex systems. - ALD modification of surfaces and interfaces. In particular, ALD of protective coatings onto electrode materials has been explored extensively to stabilise interfaces and thus enhance cell cycle life. As battery ageing for traditional lithium-ion batteries can already be problematic, novel architectures, battery concepts and material chemistries pose increasingly greater challenges in this direction, and surface/interface engineering have become important strategies to overcome ageing and improve battery performance. To obtain a high quality coating on the complex surface of battery electrodes, the low processing temperature in combination with the thickness control, uniformity and conformality provided by ALD can become key advantages.