Atomic layer deposition (ALD) has emerged as a critical technique for enhancing the performance and longevity of batteries and supercapacitors. Its ability to deposit ultra-thin, conformal, and pinhole-free films makes it particularly valuable for modifying electrode surfaces, stabilizing interfaces, and fabricating solid-state electrolytes. The precision of ALD allows for atomic-level control over film thickness and composition, enabling tailored material properties that address key challenges in energy storage systems.

One of the most significant advantages of ALD is its conformal coating capability, which ensures uniform coverage even on high-aspect-ratio or nanostructured surfaces. This is particularly beneficial for battery electrodes, where non-uniform coatings can lead to uneven electrochemical reactions, accelerated degradation, and reduced cycle life. For example, ALD-deposited alumina (Al₂O₃) or titania (TiO₂) coatings on lithium-ion battery cathodes have been shown to suppress transition metal dissolution and reduce electrolyte decomposition at high voltages. Similarly, coatings on silicon or lithium metal anodes can mitigate volume expansion and dendrite formation, improving mechanical stability and safety.

In solid-state batteries, ALD plays a crucial role in fabricating thin-film solid electrolytes with minimal defects. Materials such as lithium phosphate (Li₃PO₄), lithium lanthanum titanate (LLTO), and lithium aluminum oxide (LiAlO₂) have been deposited via ALD to achieve high ionic conductivity and excellent interfacial stability. The ability to precisely control stoichiometry and crystallinity is essential for optimizing ion transport and preventing short circuits caused by lithium dendrites. Furthermore, ALD enables the deposition of interfacial buffer layers between solid electrolytes and electrodes, reducing interfacial resistance and enhancing charge transfer kinetics.

Supercapacitors also benefit from ALD coatings, particularly in the modification of carbon-based electrodes. Thin films of metal oxides like ruthenium oxide (RuO₂) or manganese oxide (MnO₂) can be conformally deposited onto porous carbon structures, significantly increasing pseudocapacitive contributions without sacrificing power density. The conformality of ALD ensures that even the internal surfaces of highly porous electrodes are uniformly coated, maximizing active material utilization. Additionally, ALD can be used to deposit ultrathin dielectric layers in electrostatic double-layer capacitors, improving breakdown voltage and energy density.

Despite its advantages, ALD faces scalability challenges that limit its widespread adoption in industrial battery and supercapacitor production. The process is inherently slow due to its sequential, self-limiting reaction mechanism, making high-throughput manufacturing difficult. Batch processing of large electrode quantities is also constrained by reactor size and precursor distribution uniformity. Moreover, the cost of high-purity precursors and the need for precise temperature and pressure control increase operational expenses.

Efforts to improve ALD scalability include spatial ALD designs, which separate precursor exposure zones to enable continuous deposition, and roll-to-roll ALD systems for flexible substrates. Another approach involves combining ALD with other deposition techniques, such as chemical vapor deposition or magnetron sputtering, to reduce processing time while maintaining coating quality. For instance, a hybrid process might use ALD for the initial nucleation layer followed by a faster technique for bulk deposition.

Material selection is another critical factor in ALD for energy storage applications. While oxides like Al₂O₃ and TiO₂ are commonly used due to their chemical stability and ease of deposition, emerging materials such as lithium garnets (e.g., Li₇La₃Zr₂O₁₂) and sulfide-based solid electrolytes require further process optimization. Achieving the desired crystallinity and ionic conductivity often necessitates post-deposition annealing, which can complicate integration with temperature-sensitive components.

In summary, ALD offers unparalleled precision in depositing functional layers for batteries and supercapacitors, addressing key challenges in interfacial stability, electrolyte performance, and electrode durability. However, its slow deposition rate and high costs remain barriers to large-scale implementation. Continued advancements in reactor design, precursor chemistry, and hybrid deposition methods will be essential to fully realize the potential of ALD in next-generation energy storage technologies.