Getting the Most out of ALD
Authors: Trevey James E , Lichty Paul R , King David M 
Published: February 2020

The benefits of producing tailored interfaces using the atomic layer deposition (ALD) technique have been widely demonstrated in the field of energy storage. As mobility and portability requirements grow, so does the need for higher energy density materials, higher power density systems, and enhanced lifecycles of devices, all of which create additional stresses at interfaces within energy storage modules such as lithium-ion batteries, fuel cells, and supercapacitors.  It is now widely accepted that the interfaces of lithium-ion battery electrode materials can be highly dynamic in nature, and are the source of detrimental effects such as electrolyte decomposition, particle fracturing, crystal phase transformations and other causes of performance fade.  The next generation of energy storage devices will be designed and engineered with tailored interfaces, and the cost of ALD has fallen to a price point that is compelling enough to be adopted into product development cycles for mobile and stationary power applications.

As it pertains to secondary battery technologies, there exist two distinct approaches for how to apply ALD onto cathodes and anodes, namely particle coating and electrode coating.  From an electrode-electrolyte interface perspective, the features and benefits of ALD on particles (ALDP) and ALD on Electrodes (ALDE) may appear to be similar, however the implications on when and how these coatings can be industrialized within the value chain are drastically different, resulting in different cost metrics and scaling requirements and accompany different manufacturing risks. 

Here, we will discuss ALD methodologies and best-suited applications in an effort to clarify the most appropriate steps towards the industrialization of an ALD-enabled energy storage future.  There are many metrics with which to evaluate the adoption of ALD into any technology, however all can be distilled down to a cost per relevant unit basis. Typically a significant amount of technological input is required from the value chain to formulate the ALD value proposition in an unbiased manner.  In the case of energy storage applications, the final product must have a justifiably lower cost per energy unit per charge/discharge cycle, or $/Wh/cycle. For batteries, in order to arrive at the cost savings attributable to tailored interfaces, consideration must be given to the following three stages of ALD development:

Discovery and Demonstration - Determining the optimal ALD method and/or chemistry in coin and/or small pouch cells, and validating performance in cells of appropriate size and format for the market segment.

Pack/Module Performance – Comparing ALD-enabled battery performance to its base competitor battery

Manufacturing Considerations – Quantifying materials, labor and capital costs required to implement the optimized ALD process into a battery manufacturing line and manufacturing risks associated with how the ALD process is implemented

There has been increasing attention placed on whether ALDP or ALDE is ‘better’ from a performance perspective without fully quantifying all facets of performance, what performance benefits are of value to particular applications, and costs and risks to deliver these benefits to the marketplace.  It is hypothesized that a majority of this attention stems from the different goals being sought by academic institutions as compared to industrial entities. For example, ALDE experimentation may be better aligned with the objectives of an academic institution or research-based facility whose focus may be discovery/exploration relying on small quantities of material. In such a research based scenario, ALDE facilitates rapid and comparable data collection as one electrode can be sectioned and used for a panel of chemistry/coating conditions which coincides well with early stage “Discovery and Demonstration” above.  Conversely, a company seeking to produce and sell batteries will be more focused on “Pack/Module Performance” and “Manufacturing Considerations” as these will determine if a particular technology has a value proposition that can be brought to market. In this particular scenario ALDP would be the best avenue as it lends more readily to the production of commercial scale quantities of material.

Ultimately the scientific and industrial community alike have still only scratched the surface of the ALD-enabled energy storage story.  Conventional ALD coatings such as Al2O3, TiO2 and ZnO have shown tremendous promise using both ALDP and ALDE approaches, but next generation coatings that have atomically-precise tailored compositions or morphologies are under development that remove the tradeoff between barrier coatings and performance, providing for higher conductivities suitable for advanced batteries.  ALD is a means to engineer an energy storage future on an atomic level, with the potential for revolutionizing the battery as we know it, and having the potential to significantly impact other energy storage and generation systems.