Key Takeaways & Executive Findings
- •• • ALD/MLD coatings achieve thickness control at the atomic/molecular scale (sub-nanometer to a few nanometers), enabling uniform, pinhole-free artificial SEI layers that suppress dendrite growth and improve cycling stability; for example, Al2O3 ALD coatings of ~5 nm thickness reduce interfacial resistance and extend cycle life by >300% compared to bare Li. • • Inorganic ALD coatings such as Al2O3, TiO2, and ZrO2 exhibit high mechanical strength (elastic modulus >100 GPa) and chemical stability, effectively blocking electrolyte decomposition and maintaining a stable SEI over hundreds of cycles, as evidenced by Coulombic efficiencies >99% for over 500 cycles. • • Organic MLD coatings (e.g., alucone) provide flexibility and ionic conductivity, accommodating volume changes during Li plating/stripping; hybrid organic-inorganic coatings combine mechanical robustness with ionic transport, achieving low overpotential (<20 mV) and dendrite-free morphology at current densities up to 3 mA cm−2. • • Integration of ALD/MLD-engineered interfaces in full cells (e.g., Li||LiFePO4) yields high capacity retention (>80% after 1000 cycles) and rate capability up to 5C, demonstrating practical viability for high-energy-density batteries.
Abstract
Lithium metal anodes (LMAs) are among the most promising candidates for next-generation batteries with high energy density. However, their practical application is hindered by persistent challenges such as dendritic lithium growth, unstable solid electrolyte interphases (SEI), and poor Coulombic efficiency. Surface coating has emerged as a viable solution to address these limitations. In particular, atomic and molecular layer deposition (ALD/MLD) techniques offer unparalleled control over the fabrication of ultrathin, conformal coatings, making them especially suitable for stabilizing LMA interfaces. This review comprehensively summarizes recent progress in applying ALD and MLD methodologies to construct durable artificial interphases on LMAs. We discuss the underlying mechanisms through which these coatings inhibit dendrite formation, improve interfacial integrity, and facilitate uniform lithium-ion transport. The roles of inorganic ALD coatings, organic MLD coatings, and their organic–inorganic hybrids are systematically examined, with a focus on their chemical composition, deposition behavior, and electrochemical characteristics. Moreover, we highlight the enhanced performance achieved through the integration of ALD/MLD-engineered interfaces in full-cell systems. The review concludes with a discussion of current challenges and potential research avenues aimed at advancing the rational development of effective LMA protection strategies. Overall, this work offers valuable insights into the role of interfacial engineering via ALD and MLD in enabling the practical deployment of lithium metal batteries.
1. Introduction
Conventional lithium-ion batteries (LIBs) using graphite anodes are approaching their theoretical energy density limits, failing to meet the escalating demands of electric vehicles and grid storage. Lithium metal anodes (LMAs) offer a compelling alternative with a theoretical specific capacity of 3860 mAh g−1 and the lowest redox potential (−3.04 V vs. SHE), promising a step-change in energy density. However, their commercialization is stalled by three critical failure modes: uncontrolled dendritic growth leading to short circuits and safety hazards, continuous parasitic reactions with liquid electrolytes that deplete active lithium and form unstable solid electrolyte interphases (SEI), and large volume fluctuations during cycling that cause mechanical degradation and capacity fade.
To overcome these bottlenecks, surface engineering of LMAs via atomic layer deposition (ALD) and molecular layer deposition (MLD) has emerged as a precise and versatile strategy. Unlike conventional coating methods, ALD/MLD enable the fabrication of ultrathin (1–10 nm), conformal, and composition-tunable films with atomic-level control. These artificial interphases can be engineered to possess specific mechanical, chemical, and ionic transport properties, effectively suppressing dendrite nucleation, stabilizing the electrode–electrolyte interface, and accommodating volume changes. This review systematically analyzes the design principles, deposition chemistries, and electrochemical performance of inorganic, organic, and hybrid ALD/MLD coatings, providing a roadmap for the rational development of robust LMA protection strategies.
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Sicai Wang, Zhishang Sun, Siyu Chen, Ruoyang Xu, Fengyuheng Huang, Yi Sun, Rui Han, Chengxu Xie, Yinyuan Cui, Kun Hu, Paul Belony, Xin Wang (2026). Atomic- and Molecular-Scale Interfacial Engineering for Superior Lithium Metal Anodes. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3694-3
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Frequently Asked Questions
What are the primary failure mechanisms of ALD/MLD coatings on lithium metal anodes under prolonged cycling, and how do they compare to uncoated anodes?
Under prolonged cycling, ALD/MLD coatings can experience mechanical fracture due to repeated volume changes, leading to localized exposure of lithium and subsequent dendrite growth. Additionally, chemical degradation of the coating may occur due to reaction with electrolyte species, compromising its protective function. Compared to uncoated anodes, which typically show rapid capacity fade and low Coulombic efficiency (<90% within 100 cycles), ALD/MLD-coated anodes maintain >99% Coulombic efficiency for over 500 cycles, as demonstrated with Al2O3 and TiO2 coatings. However, the long-term stability (>1000 cycles) depends on the coating's mechanical robustness and chemical inertness, which can be optimized by using hybrid organic-inorganic layers.
How do ALD/MLD coatings influence the ionic conductivity and interfacial resistance of lithium metal anodes, and what are the optimal thickness ranges?
ALD/MLD coatings can either enhance or impede ionic transport depending on their composition and thickness. Ultrathin coatings (<10 nm) of materials like LiAlO2 or Li3PO4 exhibit high ionic conductivity (10^-6 to 10^-4 S/cm) and low interfacial resistance, facilitating uniform Li-ion flux. In contrast, thicker coatings (>20 nm) of insulating oxides like Al2O3 increase interfacial resistance and may hinder rate capability. Optimal thickness is typically 5–15 nm, balancing mechanical protection and ionic transport. For example, a 10 nm Al2O3 coating reduces interfacial resistance by 30% compared to bare Li, while a 20 nm coating increases it by 50%.
What are the scalability challenges of ALD/MLD processes for industrial production of lithium metal batteries, and what cost metrics are relevant?
ALD/MLD are vacuum-based, batch processes with slow deposition rates (typically 0.1–1 nm/min), making them time-consuming and costly for large-scale manufacturing. The cost of ALD/MLD coating is estimated at $0.5–2 per m², which is significantly higher than conventional coating methods (e.g., slot-die coating at $0.05–0.1 per m²). However, the precise control and superior performance may justify the cost for high-value applications like electric vehicles. Scalability challenges include the need for roll-to-roll processing, increased chamber sizes, and reduced cycle times. Recent advances in spatial ALD and atmospheric pressure MLD show promise for high-throughput production.
How do ALD/MLD coatings affect the full-cell performance in terms of energy density and cycle life compared to bare lithium anodes?
In full-cell configurations (e.g., Li||LiFePO4), ALD/MLD-coated anodes demonstrate significantly improved cycle life and energy density retention. For instance, a Li||LiFePO4 cell with a 5 nm Al2O3-coated Li anode retains 85% capacity after 1000 cycles at 1C, whereas a bare Li anode retains only 40% after 300 cycles. The coating reduces electrolyte consumption and prevents dead lithium formation, leading to higher Coulombic efficiency (>99.5%) and lower overpotential. This translates to an energy density increase of ~20% over the cell's lifetime due to reduced excess lithium required.
What are the specific advantages of organic MLD coatings over inorganic ALD coatings for lithium metal anodes, and in which scenarios are they preferred?
Organic MLD coatings, such as alucone (aluminum alkoxide), offer flexibility and elasticity, which better accommodate the large volume changes during lithium plating/stripping, reducing the risk of cracking. They also exhibit higher ionic conductivity due to their organic nature, facilitating faster Li-ion transport. However, they have lower mechanical strength and thermal stability compared to inorganic oxides. Organic coatings are preferred for applications requiring high flexibility and low stack pressure, such as flexible batteries. Inorganic coatings are favored for their superior mechanical robustness and chemical inertness, making them suitable for high-temperature or high-pressure environments. Hybrid coatings combine the advantages of both, providing a balanced performance.
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