Atomic layer deposition (ALD) has emerged as a critical technique for synthesizing advanced battery materials, particularly for electrodes and solid-state electrolytes. Its unique self-limiting surface reactions enable precise thickness control at the atomic scale, conformal coatings on complex substrates, and improved interfacial stability—key requirements for next-generation energy storage systems. This discussion focuses on ALD's application in fabricating lithium cobalt oxide (LiCoO2) cathodes and solid-state electrolytes, emphasizing process parameters, material properties, and interfacial engineering.

The synthesis of LiCoO2 via ALD typically employs alternating pulses of lithium and cobalt precursors, often with ozone or water as oxidants. Common precursors include lithium tert-butoxide (LiOtBu) and cobaltocene (CoCp2), though alternative precursors are explored to optimize crystallinity and electrochemical activity. The self-limiting nature of ALD allows layer-by-layer growth with exceptional thickness precision, typically achieving 0.5–1.2 Å per cycle depending on process conditions. This precision enables the fabrication of ultrathin LiCoO2 films ranging from 10 nm to several hundred nanometers, with thickness uniformity maintained within ±2% across substrates. Post-deposition annealing between 400–700°C is often required to achieve the desired crystalline rhombohedral phase, with annealing atmosphere (oxygen or air) significantly influencing stoichiometry and electrochemical performance.

A critical advantage of ALD for LiCoO2 lies in its ability to coat high-aspect-ratio structures. Conventional slurry-cast electrodes suffer from limited active material utilization in thick electrodes, but ALD can conformally coat 3D architectures like nanowire arrays or porous scaffolds, increasing areal capacity without compromising ion transport. The technique also enables graded compositions by modulating precursor pulse sequences, allowing the creation of concentration-gradient electrodes that combine high capacity with improved stability.

For solid-state electrolytes, ALD excels in depositing thin-film lithium-containing ceramics such as LiPON (lithium phosphorous oxynitride), LLZO (garnet-type Li7La3Zr2O12), and perovskite-type Li3xLa2/3-xTiO3. LiPON deposition typically uses lithium hexamethyldisilazide (LiHMDS) as the lithium source with trimethyl phosphate (TMP) and nitrogen plasma, achieving ionic conductivities around 2×10−6 S/cm at room temperature. The amorphous nature of ALD-grown LiPON eliminates grain boundary resistance issues common in polycrystalline materials. For crystalline LLZO, ALD processes employ metalorganic precursors like lanthanum tris(N,N′-diisopropylacetamidinate) combined with lithium and zirconium precursors, followed by high-temperature crystallization. Challenges remain in achieving stoichiometric control due to the complex multicomponent system, with oxygen partial pressure during deposition critically affecting phase purity.

Interfacial engineering represents ALD's most significant contribution to battery materials. The technique can fabricate artificial solid-electrolyte interphase (SEI) layers with controlled composition and thickness, directly addressing degradation mechanisms at electrode-electrolyte interfaces. For LiCoO2 cathodes, ALD-grown Al2O3 or TiO2 coatings as thin as 2–5 nm have demonstrated improved cyclability by suppressing cobalt dissolution and electrolyte decomposition at high voltages. These coatings must balance ionic conductivity with electronic insulation—a parameter space where ALD's precision excels. Similarly, for solid-state batteries, ALD can deposit interfacial buffer layers that mitigate chemical incompatibility between electrodes and electrolytes. A notable example is the use of ultrathin LiNbO3 layers between LiCoO2 and LLZO, reducing interfacial resistance from >1000 Ω·cm² to <100 Ω·cm².

The temperature window for ALD in battery applications presents both opportunities and constraints. While many ALD processes operate between 150–350°C—compatible with polymer substrates for flexible batteries—some materials require higher temperatures for crystallization. This has led to the development of plasma-enhanced or radical-enhanced ALD processes that lower crystallization temperatures. For instance, plasma-assisted ALD of LiCoO2 can achieve crystalline phases at 250°C, compared to 450°C required for thermal ALD.

Scalability remains a consideration for industrial adoption. While ALD traditionally suffers from low deposition rates (typically 0.5–3 nm/min), spatial ALD architectures and roll-to-roll systems are being adapted for battery manufacturing. Recent demonstrations have shown ALD coating of electrode foils at web speeds exceeding 1 m/min, with the potential for integration into existing production lines. The technique's material efficiency—often exceeding 95% precursor utilization—also offers economic advantages despite higher initial capital costs compared to solution processes.

Future directions in ALD for battery materials include the development of novel precursor chemistries for multivalent systems (Mg2+, Ca2+), in situ characterization during deposition to optimize interfacial properties, and combinatorial approaches to rapidly screen composition-property relationships. The ability to deposit precisely controlled multilayers or nanocomposites opens possibilities for entirely new material designs, such as nanolaminate electrolytes combining ionically conductive and mechanically robust phases.

In summary, atomic layer deposition provides unparalleled control over the fabrication of battery electrodes and solid-state electrolytes, addressing critical challenges in thickness precision, 3D conformality, and interfacial stability. While process optimization and scale-up require further development, ALD's unique capabilities position it as an enabling technology for next-generation energy storage systems demanding higher energy density, longer cycle life, and improved safety characteristics. The technique's versatility in material selection and nanoscale engineering continues to expand the design space for advanced battery architectures.