In the relentless quest to unravel the complexities of electrochemical interfaces, researchers have achieved a groundbreaking triumph in understanding one of the most enigmatic phenomena in battery science—the solid electrolyte interphase (SEI) that forms on lithium anodes. This elusive interface plays a pivotal role in determining battery longevity and efficiency yet has remained largely inscrutable due to its sensitivity and dynamic nature under conventional analysis conditions. Traditional methods, primarily X-ray photoelectron spectroscopy (XPS) conducted at room temperature under ultrahigh vacuum (UHV), have unintentionally altered the SEI’s chemistry and structure, obscuring the true nature of this critical layer.
Recognizing this fundamental challenge, an international team of scientists has pioneered the use of cryogenic X-ray photoelectron spectroscopy (cryo-XPS), an innovative technique that freezes the SEI in its pristine state instantly by plunge freezing before exposure to vacuum conditions. This radical advancement preserves the SEI’s authentic chemical environment, fundamentally transforming our ability to characterize and understand the interface with unprecedented accuracy. The implications ripple across the domains of electrochemistry, materials science, and beyond, promising to unlock new pathways for energy storage technologies.
Conventional XPS analyses performed at room temperature encounter significant obstacles. The exposure to UHV conditions leads to volatile species within the SEI evolving or being lost, which distorts the actual interphase composition. Moreover, reactions triggered by the vacuum and X-ray exposure can modify the SEI chemistry, thinning this already delicate layer and skewing data interpretation. Consequently, the prevailing understanding of SEI constituents and thickness derived from these measurements has been questioned, impeding progress in the rational design of more robust battery systems.
The introduction of cryo-XPS changes this narrative profoundly. By plunge freezing lithium electrodes immediately following cycling, the SEI’s molecular and structural integrity is locked in place. Cooling the sample to cryogenic temperatures (typically liquid nitrogen temperatures) minimizes molecular motion and curtails volatility, preventing the loss or transformation of labile SEI components during subsequent UHV analysis. This cryogenic approach yields a far more representative snapshot of the SEI’s real-time chemistry, delivering new insights that challenge previously held assumptions.
One of the most striking revelations from this work is the discovery of a significantly thicker SEI layer than what room temperature XPS had suggested. This preserved thickness corresponds to a diversity and richness in interphase species that were previously underestimated or entirely missed. Key electrolyte decomposition products such as lithium fluoride (LiF) and lithium oxide (Li2O), which contribute significantly to the SEI’s chemical stability and ionic conductivity, are retained in the cryo-preserved state. These findings illuminate critical pathways of interphase formation and degradation, offering clues for engineering safer and longer-lasting lithium metal anodes.
Furthermore, the cryo-XPS data provides a nuanced perspective on the chemical speciation within the SEI. Variations in the dominant compounds across different electrolyte chemistries become more discernible, allowing a direct linkage between electrolyte formulation and resultant interphase structure. This capability to correlate interface chemistry with electrochemical performance metrics heralds a new era of targeted electrolyte design, where formulations can be optimized to produce ideal SEIs tailored for specific battery applications.
The implications extend well beyond lithium metal batteries. Many interfacial phenomena in energy storage, catalysis, and corrosion science hinge on understanding delicate surface layers under realistic conditions. Cryo-XPS offers a versatile toolkit for stabilizing and probing a broad spectrum of sensitive interfaces, facilitating more accurate mechanistic studies. This methodological leap could catalyze advances in fields as diverse as solid-state batteries, fuel cells, and electronic devices, where interfacial chemistry governs overall functionality.
Underlying the success of cryo-XPS is a delicate balance of experimental finesse and technological innovation. The meticulous plunge freezing process must be rapid enough to circumvent any significant chemical rearrangement post-electrode cycling but compatible with the stringent vacuum and analytical requirements of XPS instrumentation. The checkpoint of maintaining cryogenic temperatures throughout transportation and handling ensures the sample remains in its frozen pristine state until analysis, a factor crucial for generating reproducible and accurate data.
The researchers thoroughly validated their approach by comparing results from traditional room temperature analysis and cryo-XPS, highlighting the transformative impact of the latter. The shifts in spectral signatures and elemental ratios provide compelling evidence that previous characterizations underestimated critical SEI constituents due to volatilization and alteration at ambient conditions. This validation underscores cryo-XPS not merely as a complementary method but as a vital new standard for studying battery interfaces and other sensitive materials.
Looking ahead, this breakthrough sets the stage for multifaceted investigations into dynamic SEI evolution during battery operation, including cycling-dependent transformations and the response to extreme electrochemical conditions. Integrated with in situ or operando electrochemical techniques, cryo-XPS could resolve temporal chemical trajectories with spatial fidelity, advancing mechanistic understanding to unprecedented levels. Such insights will be instrumental in breaking performance barriers in next-generation energy storage technologies.
This pioneering effort also serves as a clarion call to the scientific community regarding the necessity of cryogenic preservation when studying sensitive surfaces. The reliance on room temperature and UHV environments, though historically essential, must give way to practices that safeguard the authenticity of complex and reactive interphases. Cryo-XPS emerges as a cornerstone technique, potentially revolutionizing surface science by offering a method that authentically captures the ephemeral and intricate realities of functional interfaces.
In summary, the advent of cryogenic X-ray photoelectron spectroscopy marks a paradigm shift in the interrogation of solid electrolyte interphases on lithium anodes. Through immediate plunge freezing and low-temperature analysis, researchers have unveiled a thicker, compositionally richer pristine SEI, untouched by the distortions of conventional room temperature vacuum studies. This leap not only enhances comprehension of battery interface chemistry but propels the field towards more deliberate and strategic manipulations of electrolyte and electrode materials, promising longer-lasting, safer batteries for the energy future.
The discovery stands as a testament to the profound impact that innovative analytical methodologies can have on established scientific challenges. As the energy storage landscape evolves rapidly towards higher performance and sustainability, tools like cryo-XPS will be indispensable in translating molecular-level insights into practical technological breakthroughs. The interface between fundamental science and applied battery engineering just became dramatically clearer, heralding a new chapter in the quest for transformative energy solutions.
Subject of Research:
Understanding the chemical environment and composition of the pristine solid electrolyte interphase (SEI) on lithium anodes using advanced cryogenic X-ray photoelectron spectroscopy (cryo-XPS).
Article Title:
Cryogenic X-ray photoelectron spectroscopy for battery interfaces
Article References:
Shuchi, S.B., D’Acunto, G., Sayavong, P. et al. Cryogenic X-ray photoelectron spectroscopy for battery interfaces. Nature 646, 850–855 (2025). https://doi.org/10.1038/s41586-025-09618-3
DOI:
https://doi.org/10.1038/s41586-025-09618-3
Tags: advancements in battery technologycryogenic techniques in electrochemistrycryogenic X-ray photoelectron spectroscopydynamic behavior of battery interfaceselectrochemical interface analysisEnergy Storage Solutionsenhancing battery longevity and efficiencylithium anodes battery researchmaterials science innovationsovercoming XPS limitationspreserving SEI chemical environmentsolid-electrolyte interphase characterization
