(Invited) Atomic Layer Deposition: Eye on the Future of Batteries
Authors: Kozen Alexander C , Noked Malachi , Lin Chuan-Fu , Pearse Alexander J , Gregorczyk Keith , Lee Sang Bok , Rubloff Gary W 
Published: February 2020

Over the past few years, as atomic layer deposition (ALD) has emerged as a promising technique to improve the performance of electrochemical energy storage devices. In conventional battery architectures and chemistries, ALD layers have been used to protect the surface of anodes1 and cathodes,2 resulting in improved electrode stability and enhanced cycling performance. Beyond conventional Li-ion batteries, ALD has allowed fabrication of ultra-high performance 3D nanoheterostructures that combine intimate contact between high electrical conductivity current collectors and thin layers of active material for incredible charge/discharge rate capabilities proportional to the active material surface area. Both anode3 and cathode4 nanoheterostructures exhibit significantly higher charge/discharge rate capabilities over their bulk electrode counterparts in ½ cell geometries. The culmination of this architecture uses the high degree of control inherent in the ALD process to fabricate arrays of opposing cylindrical heterostructures inside a nanoporous template, and can achieve nearly 50% theoretical capacity while charging/discharging at a rate of 150 C.5

However, use of liquid electrolytes present a number of challenges with high power electrodes. High charge/discharge rates, desirable for fast charging of plug-in hybrid vehicles and personal electronic devices exacerbate already present safety issues, particularly that of Li dendrite formation and subsequent cell failure. Increased electrode surface area may mitigate dendrite formation by lowering the local current density, but deleterious electrolyte degradation reactions can consume electrolyte and result in eventual cell failure.
Use of solid state electrolytes, previously only suitable for niche applications due to their low inherent ionic conductivity and limitations in fabrication process, can now be expanded to new applications such as the previously described 3D batteries by utilizing ALD processes. A number of suitable ALD process for well-known solid electrolytes have been developed,6,7 allowing deposition of thin, conformal solid electrolyte layers at temperatures as low as 150˚C. The current status of 3D solid state batteries will be discussed, as will remaining challenges.
ALD’s capability for very thin solid electrolyte layers opens the door to advanced electrode protection, and and recent results showcasing the utility of ALD solid electrolyte coatings for protection layers on 3D nanoheterostructured electrodes and next-generation Li metal anodes will be discussed. In the case of conversion electrode materials, ALD coatings can prevent electrolyte decomposition and solid electrolyte interphase formation, lowering overpotential required for charge and discharge. Additionally, ALD coatings mechanically constrain conversion electrode particles, preventing volume expansion and fracturing of the coatings upon cycling.8 ALD layers applied to Li metal anodes can prevent electrolyte decomposition and Li dendrite formation by chemical stabilization of the electrode surface, resulting in both higher capacities and longer cycling lifetimes in the case of the Li-S and Li-Air systems.9,10

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