冷冻电镜（Cryo-EM/eCryo-EM）解析 SEI/电极界面

The electrified interface between a liquid and a solid underpins diverse phenomena, from ion-transfer during battery operation to action potentials enabling biological communication. However, conventional tools are blind to the nanoscale dynamics of this metastable interface. Here, we leverage electrified cryo–electron microscopy (eCryo-EM), a technique that rapidly freezes and kinetically traps these dynamic, nonequilibrium states during battery operation for nanoscale characterization. Collective snapshots of the electrified interface at controlled time intervals quantifies early-stage growth kinetics of the solid electrolyte interphase (SEI), a passivation film that governs electron and ion transport. Unexpectedly, the diffusivity of charged species of the two SEI films with differing chemistry and performance are estimated to be within 10% of the other, indicated by the slope of their diffusion-limited SEI growth regimes. Instead, the slope of the reaction-limited SEI growth regimes differs by a factor of 3, suggesting that lowered reactivity of the high-performance electrolyte is largely responsible for its high coulombic efficiency.

ConspectusThe development of clean energy generation, transmission, and distribution technology, for example, high energy density batteries and high efficiency solar cells, is critical to the progress toward a sustainable future. Such advancement in both scientific understanding and technological innovations entail an atomic- and molecular-resolution understanding of the key materials and fundamental processes governing the operation and failure of the systems. These dynamic processes span multiple length and time scales bridging materials and interfaces involved across the entire device architecture. However, these key components are often highly sensitive to air, moisture, and electron-beam radiation and therefore remain resistant to conventional nanoscale interrogation by electron-optical methods, such as high-resolution (scanning) transmission electron microscopy and spectroscopy.Fortunately, the rapid progress in cryogenic electron microscopy (cryo-EM) for physical sciences starts to offer researchers new tools and methods to probe these otherwise inaccessible length scales of components and phenomena in energy science. Specifically, weakly bonded and reactive materials, interfaces and phases that typically degrade under high energy electron-beam irradiation and environmental exposure can potentially be protected and stabilized by cryogenic methods, bringing up thrilling opportunities to address many crucial yet unanswered questions in energy science, which can eventually lead to new scientific discoveries and technological breakthroughs.Thus, in this Account, we aim to highlight the significance of cryo-EM to energy related research and the impactful results that can be potentially spawned from there. Due to the limited space, we will mainly review representative examples of cryo-EM methodology for lithium (Li)-based batteries, hybrid perovskite solar cells, and metal-organic-frameworks, which have shown great promise in revealing atomic resolution of both structural and chemical information on the sensitive yet critical components in these systems. We will first emphasize the application of cryo-EM to resolve the nanostructure and chemistry of solid-electrolyte interphases, cathode-electrolyte interphase, and electrode materials in batteries to reflect how cryo-EM could inspire rational materials design and guide battery research toward practical applications. We then discuss how cryo-EM helped to reveal guest intercalation chemistry in weakly bonded metal-organic-frameworks to develop a complete picture of host-guest interaction. Next, we summarize efforts in hybrid perovskite materials for solar cells where cryo-EM preserved the volatile organic molecules and protected perovskites from any air or moisture contamination. Finally, we conclude with perspectives and brief discussion on future directions for cryo-EM in energy and materials science.

Deep chemical and structural investigation of battery components is increasingly imperative for exploring new electrode materials and their performance iterations for the next‐generation of energy storage devices with high energy density. This is particularly true in the research realm of lithium (Li) metal and its derivatives for the robust anode. Conventionally, both Li metal and its solid electrolyte interphase (SEI) layer are chemically reactive and sensitive to electron‐beam irradiation, making the high‐resolution observation difficult to perform at native environment. Recently, the emergence of cryo‐electron microscopy (EM) has brought great opportunities to reveal the physicochemical properties of these energy materials. By means of cryo‐EM, the high‐resolution imaging of the samples at the nanometer or even atomic scale while maintaining their native state can be realized. Herein, the contributions of cryo‐EM to the characterization of sensitive battery materials are focused on, which are tentatively classified as the following: the visualization of Li dendrites, inactive Li, and the discussion regarding electrode interface chemistry. The review concludes by providing several proposals for the development of cryo‐EM in the future. It is hoped that this work will shed light on the in‐depth understanding of battery materials for high‐performance rechargeable batteries.

… lithium metal atoms and their interface with the solid electrolyte interphase (SEI). We observe that … Although we use Li metal as an example to demonstrate the utility of cryo-EM, the …

Cryo-electron microscopy study finds that EC-based electrolyte can exfoliate the graphite surface and destabilize the SEI. Useful additives including FEC, DTD, TPP, and VC can form a stable SEI to protect the graphite anode.

Safe and high‐energy‐density rechargeable batteries are increasingly indispensable in the pursuit of a wireless and fossil‐free society. Advancements in present battery technologies and the investigation of next‐generation batteries highly depend on the ever‐deepening fundamental understanding and the rational designs of working electrodes, electrolytes, and interfaces. However, accurately analyzing energy materials and interfaces is severely hindered by their intrinsic limitations of air and electron‐beam sensitivity, which restrains the research of energy materials in a low‐efficiency trial‐and‐error paradigm. The emergence of cryogenic electron microscopy (cryo‐EM) has enabled the nondestructive characterization of air‐ and electron‐beam sensitive energy materials in the microscale and nanoscale, and even at atomic resolutions, affording closer insights into the primary chemistry and physics of working batteries. Herein, the development of cryo‐EM and the applications in detecting energy materials are reviewed and analyzed from its overwhelming advantages in disclosing the underlying mystery of energy materials. Critical sample preparation methods as the precondition for cryo‐EM are compared, which strongly affect the characterization accuracy. Furthermore, new developments in the analysis of energy materials, especially bulk electrodes and interfaces in lithium metal batteries, are presented according to different functions of cryo‐EM. Finally, future directions of cryo‐EM for analyzing energy materials are prospected.

Progress and potential The initial invention of electron microscopy (EM) for highresolution imaging of inorganic solids has been upgraded with the development of cryogenic functionalities in the recent decades, along with the continuous advances in imaging technologies (detectors, software), enabling the unequivocal identification of materials with high beam sensitivity. The adoption of cryogenic EM in the battery field has boosted the understanding of electrochemically driven phenomena in batteries, particularly on metal anodes, metastable phases, and associated interfaces. In this perspective, we give a brief overview of the development of cryogenic electron microscopy (cryo-EM) and review its success in different branches within the battery field, demonstrating how the knowledge gained by cryogenic EM has advanced the understanding of battery systems. We emphasize that optimized workflows are required for different types of materials to minimize the discrepancies in this field. We further put forward our best practices for sample preparation during cryo-EM measurements with an outlook on artificial intelligence assisted data collection and analysis workflow that will benefit the entire material science community. SUMMARY The recent adoption of cryogenic electron microscopy (cryo-EM) in the battery field has boosted the understanding of electrochemically driven phenomena in batteries, particularly on metal anodes, metastable phases, and associated interfaces. With the advances in battery research by cryo-EM since 2017, concerns have arisen due to the differences in sample preparation and transfer procedures that could yield an inconsistent dataset and contradicting interpretations. Herein, we review the development of cryo-EM and its successful landings in different branches within the battery field, demonstrating how the knowledge gained by cryo-EM has advanced the understanding of battery systems. We emphasize that the discrepancies in this area will be eventually minimized when the optimized workflows are established for different materials. We further put forward our best practices for sample preparation during cryo-EM measurements with an outlook on artificial intelligence assisted data collection and analysis workflow that will benefit the entire material science community at large.

The 3D nanocomposite structure of plated lithium (LiMetal) and solid electrolyte interphases (SEI), including a polymer‐rich surficial passivation layer (SEI exoskeleton) and inorganic SEI “fossils” buried inside amorphous Li matrix, is resolved using cryogenic transmission electron microscopy. With ether‐based DOLDME‐LiTFSI electrolyte, LiF and Li2O nanocrystals are formed and embedded in a thin but tough amorphous polymer in the SEI exoskeleton. The fast Li‐stripping directions are along [1¯10] or [121¯] , which produces eight exposed {111} planes at halfway charging. Full Li stripping produces completely sagging, empty SEI husks that can sustain large bending and buckling, with the smallest bending radius of curvature observed approaching tens of nanometers without apparent damage. In the 2nd round of Li plating, a thin LiBCC sheet first nucleates at the current collector, extends to the top end of the deflated SEI husk, and then expands its thickness. The apparent zero wetting angle between LiBCC and the SEI interior means that the heterogeneous nucleation energy barrier is zero. Due to its complete‐wetting property and chemo‐mechanical stability, the SEI largely prevents further reactions between the Li metal and the electrolyte, which explains the superior performance of Li‐metal batteries with ether‐based electrolytes. However, uneven refilling of the SEI husks results in dendrite protrusions and some new SEI formation during the 2nd plating. A strategy to form bigger SEI capsules during the initial cycle with higher energy density than the following cycles enables further enhanced Coulombic efficiency to above 99%.

… the lower vapour pressure of different frozen SEI species at cryoT. This is … (cryo-EM), in which cryogenic conditions have led to important discoveries on preserved interfaces in batteries …

… To overcome the difficulties in characterizing such interfaces … (cryo-EM) have recently been introduced to battery research … and also prompted cryo-EM-based examination of the SEI in …

Since its introduction to battery research in 2017, cryogenic electron microscopy (cryo-EM) has emerged as a powerful tool for probing the delicate structures of Li metal electrodes and their interphases....

Summary Most battery materials are beam sensitive, especially after cycling, which can be hardly characterized by electron microscopy (EM) with a high-energy beam. Inspired by structural biology, cryogenic EM (cryo-EM) offers a way to preserve the native state and image the battery materials at the nano/atomic scale. In this perspective, we highlight strategies on how to preserve the pristine intrinsic information of battery materials in terms of sample preparation, transformation, and imaging. Some key technical breakthroughs for the development of the cryo-EM are briefly illustrated to demonstrate its working principles. Recent achievements on cryo-EM characterization of battery materials are reviewed, especially Li metal. These profound observations demonstrate the increasing essential role of cryo-EM on diagnosing and characterizing the chemical, morphological, and atomic structure of battery materials. The new insights and knowledge obtained through this emerging new toolset will benefit the battery research field tremendously.

Summary Cathode electrolyte interphase (CEI), the intimate coating layer formed on the positive electrode, has been thought to be critical. However, many aspects of CEI remain unclear. This originates from the lack of effective tools to characterize structural and chemical properties of these sensitive interphases at nanoscale. Here, we develop a protocol to preserve the native state and directly visualize the interface on the positive electrode using cryogenic electron microscopy. We find that under normal operation conditions, there does not exist an intimate coating layer at the single-particle level in carbonate-based electrolyte. However, upon brief external electrical shorting, a solid-electrolyte interphase, which usually forms on anodes, could form on cathodes and be electrochemically converted into a stable, conformal CEI in situ. The conformal CEI helps improve Coulombic efficiency and overall capacity retention of the battery. This generates a different perspective of CEI in commercial carbonate-based electrolytes than previously understood.

… Here we adapt a technique that has enabled cryo-transmission electron microscopy (cryo-TEM) of hydrated specimens in biology—immobilization of liquids by rapid freezing, that is, …

Metallic lithium anodes are highly promising for revolutionizing current rechargeable batteries because of their ultrahigh energy density. However, the application of lithium metal batteries is considerably impeded by lithium dendrite growth. Here, a biomacromolecule matrix obtained from the natural membrane of eggshell is introduced to control lithium growth and the mechanism is motivated by how living organisms regulate the orientation of inorganic crystals in biomineralization. Specifically, cryo-electron microscopy is utilized to probe the structure of lithium at the atomic level. The dendrites growing along the preferred < 111 > crystallographic orientation are greatly suppressed in the presence of the biomacromolecule. Furthermore, the naturally soluble chemical species in the biomacromolecules can participate in the formation of solid electrolyte interphase upon cycling, thus effectively homogenizing the lithium deposition. The lithium anodes employing bioinspired design exhibit enhanced cycling capability. This work sheds light on identifying substantial challenges in lithium anodes for developing advanced batteries. Inspired by the role of proteins in regulating eggshell mineralization, here Tao, Liu and colleagues apply trifluoroethanol modified eggshell membrane to combat lithium dendrite. Cryo-electron microscopy reveals that the growth along the most favored crystallographic direction is suppressed.

ConspectusLithium (Li)-metal batteries are one of the most promising candidates for the next-generation energy storage devices due to their ultrahigh theoretical capacity. The realistic development of a Li metal battery is greatly impeded by the uncontrollable dendrite proliferation upon the chemically active metallic Li. To visualize the micromorphology or even the atomic structure of Li deposits is undoubtedly crucial, while imaging the sensitive Li still faces a huge challenge technically.Cryogenic electron microscopy (cryo-EM), an emerging imagery technology renowned for structural elucidation of biomaterials, is offering increased possibilities for analyzing sensitive battery materials reaching subangstrom resolution. Particularly for revealing metallic Li, cryo-EM exhibits remarkable superiority compared with the conventional electron imaging technique. On the one hand, cryo-EM could prevent the low melting-point Li metal from being damaged by the high electron dose induced thermal effect. On the other hand, the extremely low temperature immensely retards the rate of the side reaction where the Li reacts with the atmosphere or water vapor before the vacuum state. Consequently, the cryo-EM could acquire a high-resolution image of electron-beam sensitive Li in its native state at the nano- or even atomic scale, thus benefiting the fundamental perception and rational design of Li metal anodes.Thus, in this Account, we aim to highlight the significance of cryo-EM in analyzing metallic Li and developing a high-performance Li metal battery. We focus on how highly resolved cryo-EM realizes the breakthrough in detecting the crucial evolution during battery cycling, e.g., lattice ordering of Li, nanostructures of the solid electrolyte interphase (SEI), nucleation sites, and interface between the solid electrolyte and the Li anode. First, we briefly summarize the progress of Li metal imaging by cryo-EM in a timed sequence. In particular, the recent studies from our group are classified in order to systematically delineate the advantages that cryo-transmission electron microscopy (cryo-TEM) addressed on understanding and developing the Li metal battery. Second, the efforts of exhibiting the long-range ordering Li lattice are described to cognize the crystal orientation of both Li dendrites and uniform spheres. Subsequently, the nanostructures of SEI detected by cryo-TEM, maybe the most key information during Li plating/stripping, are systematically summarized. Benefitting from the subangstrom visualization on the newly formed and the particular inactive SEI after long-term cycling, we emphasize cryo-TEM's guidance in designing a robust, highly Li+ conductive, and Li-restoration facilitated SEI. We then propose the strategy of introducing a nucleation-site to enable uniform Li deposition by showing the evidence of Li nucleation atomically monitored through cryo-TEM. Moreover, the series of the work of atomic imagery and corresponding optimization of the interfaces between the polymer-based solid electrolyte and the Li anode are concluded. Finally, critical perspectives about the further step of cryo-TEM in the realistic development of high-energy density battery systems are also succinctly reviewed.

… of Li metal dendrites … cryo-TEM can potentially be a powerful technique to image beam-sensitive battery electrode materials (Figure 1). Herein, we extend the use of cryo-TEM to Li metal …

The solid electrolyte interphase (SEI) dictates the cycling stability of lithium‐metal batteries. Here, direct atomic imaging of the SEI's phase components and their spatial arrangement is achieved, using ultralow‐dosage cryogenic transmission electron microscopy. The results show that, surprisingly, a lot of the deposited Li metal has amorphous atomic structure, likely due to carbon and oxygen impurities, and that crystalline lithium carbonate is not stable and readily decomposes when contacting the lithium metal. Lithium carbonate distributed in the outer SEI also continuously reacts with the electrolyte to produce gas, resulting in a dynamically evolving and porous SEI. Sulfur‐containing additives cause the SEI to preferentially generate Li2SO4 and overlithiated lithium sulfate and lithium oxide, which encapsulate lithium carbonate in the middle, limiting SEI thickening and enhancing battery life by a factor of ten. The spatial mapping of the SEI gradient amorphous (polymeric → inorganic → metallic) and crystalline phase components provides guidance for designing electrolyte additives.

High-concentrated non-flammable electrolytes (HCNFE) in lithium metal batteries prevent thermal runaway accidents, but the microstructure of their solid electrolyte interphase (SEI) remains largely unexplored, due to the lack of direct imaging tools. Herein, cryo-HRTEM is applied to directly visualize the native state of SEI at the atomic scale. In HCNFE, SEI has a uniform laminated crystalline-amorphous structure that can prevent further reaction between the electrolyte and lithium. The inorganic SEI component, Li2 S2 O7 , is precisely identified by cryo-HRTEM. Density functional theory (DFT) calculations demonstrate that the final Li2 S2 O7 phase has suitable natural transmission channels for Li-ion diffusion and excellent ionic conductivity of 1.2 × 10-5 S cm-1 .

Current density has been perceived to play a critical rule for controlling Li deposition morphology and solid electrolyte interphase (SEI). However, the atomic level mechanism of current density on Li deposition and the SEI remains unclear. Here based on cryogenic transmission electron microscopy (TEM) imaging combined with energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) electronic structure analyses, we reveal the atomic level correlation of Li deposition morphology and SEI with current density. We discover that increasing current density leads to increased overpotential for Li nucleation and growth, leading to the transition from growth-limited to nucleation-limited mode for Li dendrite. Independence of current density, the electrochemically deposited Li metal (EDLi) exhibits crystalline whisker-like morphology. The SEI formed at low current density (0.1 mA cm-2) is monolithic amorphous; while, a current density of above 2 mA cm-2 leads to a mosaic structured SEI, featuring an amorphous matrix with Li2O and LiF dispersoids, and the thickness of the SEI increases with the increase of current density. Specifically, the Li2O particles is spatially located at the top surface of the SEI, while LiF is spatially adjacent to the Li-SEI interface. These results offer possible ways of regulating crucial microstructural and chemical features of EDLi and SEI through altering deposit conditions and consequently direct correlation with battery performance.

… lithium dendritic growth and dead lithium formation. In this work, we use state-of-the-art cryo-EM imaging and spectroscopic techniques to characterize the structure and chemistry of the …

… We observed fast Fourier transform (FFT) reflection spots in cryo-TEM images corresponding … and extended SEI growth on Li metal portion in a Li metal dendrite calendar aged for 7 days…

Potassium‐based solid electrolyte interphases (SEIs) have a much smaller damage threshold than their lithium counterpart; thus, they are significantly more beam sensitive. Here, an ultralow‐dose cryogenic transmission electron microscopy (cryo‐TEM) technique (≈8 e Å−2 s−1 × 10 s), which enables the atomic‐scale chemical imaging of the electron‐beam‐sensitive potassium metal and SEI in its native state, is adapted. The potassium‐based SEI consists of large brackets of diverse inorganic phases (≈hundreds of nanometers) interspersed with amorphous phases, which are different from the tiny nanocrystalline inorganic phases (≈a few nanometers) formed in a lithium‐based SEI. Organic phosphate‐based electrolyte solvents induce the formation of a thin and stable SEI layer for enhanced cycling performance, while the carbonate ester‐based electrolytes result in large quantities of metastable KHCO3, and K4CO4 products in the SEI, depleting the potassium reserves in the battery. The findings provide deep insights and guidance in the selection of optimum electrolytes that should be used for potassium batteries.

The growth and penetration of lithium dendrites through electrolytes and separators remain key challenges to realizing high-energy density lithium-metal batteries. Using mechanically strong electrolytes and separators has been considered a promising strategy based on the commonly believed softness of lithium. However, dendrite formation persists in stiff solid electrolytes, suggesting distinct mechanical behaviors. We measured the mechanical properties of individual lithium dendrites using an air-free protocol. We found that lithium dendrites are unexpectedly strong and brittle, with fracture stress greater than ~150 megapascals, unlike the ductile bulk metal. Cryo-transmission electron microscopy and mechanical modeling showed that this behavior arises from solid electrolyte interface constraints and nanoscale strengthening. These findings provide alternative mechanisms for dendrite penetration and dead lithium formation as well as guidance for design strategies for lithium-metal batteries.

Summary The commercialization of the silicon (Si) anode has been hindered by the instability of its solid-electrolyte interphase (SEI), yet a comprehensive understanding of SEI properties remains underdeveloped owing to the challenge of characterizing this nanoscale passivation layer. In this work, we visualize the structure and chemistry of the SEI on silicon anodes using atomic-resolution cryogenic (scanning) transmission electron microscopy (cryo-(S)TEM) and electron energy loss spectroscopy (EELS), revealing its evolution over the first cycle. We discover the origin of the Si SEI instability in ethylene carbonate (EC) electrolytes, owing to the high reversibility of the SEI. The role of the critical electrolyte additive fluoroethylene carbonate is revealed, which extends the cyclability of the Si anode through deposition of an electrochemically irreversible polycarbonate layer on the anode surface. These findings provide a nuanced view into the Si anode instability in commercial EC-based electrolytes and the role of additives for SEI stabilization.

Cryogenic transmission electron microscopy (cryo-TEM) is a valuable tool recently proposed to investigate battery electrodes. Despite being employed for Li-based battery materials, cryo-TEM measurements for Na-based electrochemical energy storage systems are not commonly reported. In particular, elucidating the chemical and morphological behavior of the Na-metal electrode in contact with a non-aqueous liquid electrolyte solution could provide useful insights that may lead to a better understanding of metal cells during operation. Here, using cryo-TEM, we investigate the effect of fluoroethylene carbonate (FEC) additive on the solid electrolyte interphase (SEI) structure of a Na-metal electrode. Without FEC, the NaPF6-containing carbonate-based electrolyte reacts with the metal electrode to produce an unstable SEI, rich in Na2CO3 and Na3PO4, which constantly consumes the sodium reservoir of the cell during cycling. When FEC is used, the Na-metal electrode forms a multilayer SEI structure comprising an outer NaF-rich amorphous phase and an inner Na3PO4 phase. This layered structure stabilizes the SEI and prevents further reactions between the electrolyte and the Na metal. The solid electrolyte interphase (SEI) strongly affects the cycling behaviour of rechargeable alkali metal cells. Here, the authors investigate via cryo-electron microscopy the SEI formed on a Na metal electrode using fluoroethylene carbonate-containing electrolyte.

: It is crucial to comprehend the effect of the solid electrolyte interphase (SEI) on battery performance to develop stable Li metal batteries. Nonetheless, the exact nanostructure and working mechanisms of the SEI remain obscure. Here, we have investigated the relationship between electrolyte components and the structural configuration of interfacial layers using an optimized cryogenic transmission electron microscopy (Cryo-TEM) analysis and theoretical calculation. We revealed a unique dual-layered inorganic-rich nanostructure, in contrast to the widely known simple specific component-rich SEI layers. The origin of stable Li cycling is closely related to the Li-ion diffusion mechanism via diverse crystalline grains and numerous grain boundaries in the fine crystalline-rich SEI layer. The results can elucidate a particular issue pertaining to the chemical structure of SEI layers that can induce uniform Li diffusion and rapid Li-ion conduction on Li metal anodes, developing stable Li metal batteries.

The stability of lithium batteries is tied to the physicochemical properties of the solid-electrolyte interphase (SEI). Owing to the difficulty in characterizing this sensitive interphase, the nano...

Understanding the interfacial reaction mechanism between sulfide solid‐state electrolytes (SSEs) and metallic lithium (Li) under thermal runaway is of great significance in improving the safety of all‐solid‐state Li metal batteries (ASLMBs). Herein, multiscale methods including in situ optical microscopy‐thermal infrared imaging combination technique, cryogenic electron microscopy, thermodynamic simulation, and ab initio molecular dynamics methods are utilized to investigate the thermal chemical stability of sulfide SSEs Li10GeP2S12 (LGPS) and Li6PS5Cl (LPSCl) against metallic Li under high temperatures. The results indicate that drastic thermal runaway happened between LGPS and metallic Li at 300 °C due to the continuous Li‐Germanium alloying reaction. In contrast, LPSCl maintains stability against metallic Li up to 400 °C, which is attributed to the formation of Li2S‐LiP‐Li3P‐LiCl stable interphases in the interfacial reaction between LPSCl and metallic Li. The electrical insulation interphase prevents the further reaction between LPSCl and metallic Li via kinetically decreasing the chemical potential of metallic Li to be within the electrochemical window of LPSCl. This work demonstrates the critical role of stable electrically insulated interphases between metallic Li anode and SSEs in improving the safety of ASLMBs.

Many modern energy devices rely on solid-liquid interfaces, highly reactive materials, or both, for their operation and performance. The difficulty of characterizing such materials means these devices often lack high-resolution characterization in an unaltered state.&#13;\nHere, we demonstrate how cryogenic sample preparation and transfer can extend the capabilities of FIB/SEM techniques to the solid-liquid interfaces and reactive materials common to energy devices by preserving their integrity through all stages of preparation and characterization. We additionally show how cryo-FIB/SEM paired with energy dispersive X-ray spectroscopy enables nanoscale elemental mapping of cross-sections produced in these materials and discuss strategies to achieve optimal results. Finally, we consider current limitations of the technique and propose future developments that could enhance its capabilities. Our results illustrate that cryo-FIB/SEM will be a useful technique for fields where solid-liquid interfaces or reactive materials play an important role and could, thus far, not be characterized at high resolution.

Abstract A fundamental understanding of solid-electrolyte interphase (SEI) is paramount importance for controlling the cycling performance of rechargeable lithium metal batteries. The structural and chemical evolution of SEI with respect to electrochemical operating condition remains barely established. Here we develop a unique method for imaging the evolution of SEI formed on the Cu foil under sweeping electrochemical potential. By using cryogenic TEM imaging combined with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy electronic structure analyses, we reveal that, for the vinylene carbonate (VC)-free electrolyte, the SEI formed at 1.0 V is a monolithic amorphous structure, which evolves to amorphous matrix embedded with Li2O particles as the voltage decreases to 0 V. In the case of VC-containing electrolyte, the SEI is featured by an amorphous matrix with Li2O particles from 1.0 V to 0 V. The thickness of SEI formed on Cu foil increases with decreasing voltage. Associated with the localized charge modulation by the surface topographic feature and defects in the Cu foil, the SEI layer shows direct spatial correlation with these structural defects in the Cu. In addition, upon Li deposition, the SEI formed on the Li metal has similar thickness with, but different composition from the SEI formed on the Cu foil at 0 V. Those results provide insight toward SEI engineering for enhanced cycling stability of Li metal.

With the rapid development of technologies such as portable electronics and electrical vehicles and scalable energy storage, the batteries that provide the power need to be further improved to gain a better user experience and a larger market share. The progress of battery technology heavily depends on the in-depth characterization of electrodes, electrolytes, and interfaces. However, the precise analysis of the sensitive components is hindered due to their inherent instability nature. Cryogenic electron microscopy (Cryo- EM ), which enables the nondestructive characterization of sensitive materials at atomic resolution, has been applied in the energy research field recently, leading to a deeper understanding of reaction mechanisms and fundamental properties of energy storage materials. This chapter focuses on the application of Cryo-EM in analyzing the morphology, composition, and evolution of key materials and interfaces, as well as its history and workflow. It aims to demonstrate the importance of Cryo-EM in the energy-storage revolutions.

… based on the actual porous electrode structure, and the … In this study, Cryo-FIB-SEM with the function of frozen-cutting … is constant and that the formation of SEI is ignored. Figure 2 …

… Many materials, such as battery electrodes, are heterogeneous in … finer details in both structural and chemical variations 45 . … in adapting cryo-ET techniques for 3D imaging of materials. …

All‐solid‐state Li batteries (ASSLBs) are attracting increasing attentions due to their improved safety and high energy density compared with conventional liquid electrolyte‐based Li‐ion batteries (LIBs). ASSLBs based on sulfide solid‐state electrolytes (SEs) is one of the most popular categories, because sulfide SEs have a very competitive ionic conductivity (up to over 10−2 S cm−1 at room temperature), medium mechanical stiffness, decent contact with electrode materials, and negligible grain boundary resistance. However, interface problems between electrode materials and sulfide SEs seriously plague the development of high‐performance sulfide‐based ASSLBs. In‐depth understandings on the electrode interface problems are pivotal to propose and explore effective strategies to alleviate those issues. In recent years, diverse advanced characterization techniques have been developed, which deepen insights into the problematic interface from physical, chemical, electrochemical, and mechanochemical perspectives. Herein, electrode interfaces and their fundamental knowledge in sulfide‐based ASSLBs are first clarified. Second, various emerging characterizations are overviewed to illustrate the interfacial issues on both oxide cathode/sulfide SE and Li anode/sulfide SE interfaces. Meanwhile, advantages and disadvantages of each characterization techniques are explicated. Finally, an outlook of advanced characterizations that are specifically adapted for interface analysis in sulfide‐based ASSLBs is proposed.

… 3D structures of electrodes, electrolytes, and their interfaces. In lithium metal batteries, cryogenic ET (Cryo-ET… Han et al. revealed a polymer-rich SEI structure embedding nanocrystalline …

… -dose cryo-TEM and EELS under conditions that suppress detectable bulk Li–Si alloying (0.1 V vs Li/Li + cutoff, 10 cycles), we resolve the atomic-scale nanostructures of the intrinsic SEI …

Summary Battery decay and failure depend strongly on the solid electrolyte interphase (SEI), a surface corrosion layer that forms on the surface of all battery electrodes. Recently, we revealed the atomic structure of these reactive and sensitive battery materials and their SEIs using cryoelectron microscopy (cryo-EM). However, the SEI nanostructure's fundamental role and effect on battery performance remain unclear. Here, we use cryo-EM to discover the function of two distinct SEI nanostructures (i.e., mosaic and multilayer) and correlate their stark effects with Li metal battery performance. We identify fluctuations in crystalline grain distribution within the SEI as the critical feature differentiating the mosaic SEI from the multilayer SEI, resulting in their distinct electrochemical stripping mechanisms. Whereas localized Li dissolution occurs quickly through regions of high crystallinity in the mosaic SEI, uniform Li stripping is observed for the more ordered multilayer SEIs, which reduces Li loss during battery cycling by a factor of three. This dramatic performance enhancement from a subtle change in SEI nanostructure highlights the importance of cryo-EM studies in revealing crucial failure modes of high-energy batteries at the nanoscale.

In Li metal batteries (LMBs), which boast the highest theoretical capacity, the chemical structure of the solid electrolyte interphase (SEI) serves as the key component that governs the growth of reactive Li. Various types of additives have been developed for electrolyte optimization, representing one of the most effective strategies to enhance the SEI properties for stable Li plating. However, as advanced electrolyte systems become more chemically complicated, the use of additives is empirically optimized. Indeed, their role in SEI formation and the resulting cycle life of LMBs are not well-understood. In this study, we employed cryogenic transmission electron microscopy combined with Raman spectroscopy, theoretical studies including molecular dynamics (MD) simulations and density functional theory (DFT) calculations, and electrochemical measurements to explore the nanoscale architecture of SEI modified by the most representative additives, lithium nitrate (LiNO3) and vinylene carbonate (VC), applied in a localized high-concentration electrolyte. We found that LiNO3 and VC play distinct roles in forming the SEI, governing the solvation structure, and influencing the kinetics of electrochemical reduction. Their collaboration leads to the desired SEI, ensuring prolonged cycle performance for LMBs. Moreover, we propose mechanisms for different Li growth and cycling behaviors that are determined by the physicochemical properties of SEI, such as uniformity, elasticity, and ionic conductivity. Our findings provide critical insights into the appropriate use of additives, particularly regarding their chemical compatibility.

… eCryo-EM is simple: rather than disassembling a battery … at key interfaces between battery materials,” explains Li. … to exploring the capabilities of eCryo-EM and to broadening its reach: “…

… the catalyst/membrane interface towards the … (eCryo-EM) technique that enables electrical biasing to a TEM grid, which is rapidly frozen to explore non-equilibrium states during battery …

Interfaces play a fundamental role in many areas of chemistry. However, their localized nature requires characterization techniques with high spatial resolution in order to fully understand their structure and properties. State-of-the-art atomic resolution or in situ scanning transmission electron microscopy and electron energy-loss spectroscopy are indispensable tools for characterizing the local structure and chemistry of materials with single-atom resolution, but they are not able to measure many properties that dictate function, such as vibrational modes or charge transfer, and are limited to room temperature samples containing no liquids. Here, we outline emerging electron microscopy techniques that are allowing these limitations to be overcome and highlight several recent studies that were enabled by these techniques. We then provide a vision for how these techniques can be paired with each other and with in situ methods to deliver new insights into the static and dynamic behavior of functional interfaces.

The uncontrolled deposition/dissolution process of lithium dendrites during electrochemical cycling in batteries limits the large-scale application of Li metal anodes. Investigating the microstructure of Li dendrites is a focal point. Currently, the only way to protect and observe sensitive Li dendrites is through low-temperature transmission electron microscopy (LT-TEM), whereas room-temperature characterization is still lacking. In this work, the room-temperature microstructure of Li dendrites was obtained by TEM using both vacuum- and inert-gas-transfer methods. Detailed comparison between LT- and room-temperature (RT-)TEM characterizations was provided to show the pros and cons of each method. Especially, RT-TEM shows the advantage of flexible incorporation with multifunctional characterizations, such as 3D tomography. By using RT-TEM, microstructural evolution of Li dendrites during the electrodeposition/dissolution process, including increase of the quantity of inorganic Li2O compounds in the solid electrolyte interphase, lateral growth behavior, and two types of inactive Li, has been revealed, enriching the understanding of the structure-property relationship of Li dendrites.

Cryogenic electron microscopy (cryo-EM) was the basis for the 2017 Nobel Prize in Chemistry for its profound impact on the field of structural biology by freezing and stabilizing fragile biomolecules for near atomic-resolution imaging in their native states. Beyond life science, the development of cryo-EM for the physical sciences may offer access to previously inaccessible length scales for materials characterization in systems that would otherwise be too sensitive for high-resolution electron microscopy and spectroscopy. Weakly bonded and reactive materials that typically degrade under electron irradiation and environmental exposure can potentially be stabilized by cryo-EM, opening up exciting opportunities to address many central questions in materials science. New discoveries and fundamental breakthroughs in understanding are likely to follow. In this Perspective, we identify six major areas in materials science that may benefit from the interdisciplinary application of cryo-EM: (1) batteries, (2) soft polymers, (3) metal-organic frameworks, (4) perovskite solar cells, (5) electrocatalysts, and (6) quantum materials. We highlight long-standing questions in each of these areas that cryo-EM can potentially address, which would firmly establish the powerful tool's broad scope and utility beyond biology.

The advancement of battery technology necessitates a profound understanding of the physical, chemical, and electrochemical processes at various scales. Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) has emerged as an indispensable tool for battery research, enabling high-resolution imaging and multiscale analysis from macroscopic structures to nanoscale features at multiple dimensions. This review starts with introducing the fundamentals of focused beam and matter interaction under the framework of FIB-SEM instrumentation and then explores the application of FIB-SEM characterization on rechargeable batteries (lithium-ion batteries and beyond), with a focus on cathode and anode materials, as well as solid-state batteries. Analytical techniques such as Energy Dispersive X-ray Spectroscopy, Electron Backscatter Diffraction, and Secondary Ion Mass Spectrometry are discussed in the context of their ability to provide detailed morphological, crystallographic, and chemical insights. The review also highlights several emerging applications in FIB-SEM including workflow to maintain sample integrity, in-operando characterization, and correlative microscopy. The integration of Artificial Intelligence for enhanced data analysis and predictive modeling, which significantly improves the accuracy and efficiency of material characterization, is also discussed. Through comprehensive multimodal and multiscale analysis, FIB-SEM is poised to significantly advance the understanding and development of high-performance battery materials, paving the way for future innovations in battery technology.

Neurons exhibit varying electrophysiological properties due to dynamic changes in spatiotemporal molecular networks. In situ cryo-electron tomography (cryo-ET) provides advantages for high-resolution visualization of macromolecular complexes within their cellular context. Although correlation with fluorescent labeling allows cryo-ET to target specific cellular regions, it does not adequately reflect the electrophysiological properties of heterogeneous neurons. To bridge high-resolution molecular imaging with electrophysiological properties of individual neurons, we develop a Correlative Voltage Imaging and cryo-ET (CoVET) technique. The nondestructive nature of voltage imaging is compatible with cryo-ET, enabling a direct correlation between neuronal electrophysiology and molecular structures. Neurons are clustered based on their electrophysiological properties, allowing for single-cell-guided structural analysis using cryo-ET. We analyze the translational landscapes of individual neurons and find distinct structural characteristics and spatial networks among ribosomes from different electrophysiological clusters. Our results highlight the importance of the correlation between the electrophysiological properties and molecular structures. The functional–structural link in neurons remains unclear despite its importance. Here, authors developed CoVET, a method combining voltage imaging with cryo-electron tomography to directly correlate neuronal function with molecular architecture.

Recent advances in the water-energy landscape hinge upon our improved understanding of the complex morphology of materials involved in water treatment and energy production. Due to their versatility and tunability for applications ranging from drug delivery to fuel cells, polymeric systems will play a crucial role in shaping the future of water-energy nexus applications. Electron tomography (ET) stands as a transformative approach for elucidating the intricate structures inherent to polymers, offering unparalleled insights into their nanoscale architectures and functional properties in three dimensions. In particular, the various morphological and chemical characteristics of polymer membranes provide opportunities for perturbations to standard ET for the study of these systems. We discuss the applications of transmission electron microscopy in establishing structure-function relationships in polymeric membranes with an emphasis on traditional ET and cryogenic ET (cryo-ET). The synergy between ET and cryo-ET to unravel structural complexities and dynamic behaviors of polymer membranes holds immense potential in driving progress and innovation across frontiers related to water-energy nexus applications. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering , Volume 15 is June 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Transmission electron microscopy (TEM) is a crucial analysis method in materials science and structural biology, as it offers a high spatiotemporal resolution for structural characterization and reveals structure-property relationships and structural dynamics at atomic and molecular levels. Despite technical advancements in EM, the nature of the electron beam makes the EM imaging inherently detrimental to materials even in low-dose applications. We introduce SHINE, the Self-supervised High-throughput Image denoising Neural network for Electron microscopy, accelerating minimally invasive low-dose EM of diverse material systems. SHINE uses only a single raw image dataset with intrinsic noise, which makes it suitable for limited-size datasets and eliminates the need for expensive ground-truth training datasets. We quantitatively demonstrate that SHINE overcomes the information limit in the current high-resolution TEM, in situ liquid phase TEM, time-series scanning TEM, and cryo-TEM, facilitating unambiguous high-throughput structure analysis across a broad spectrum of materials.

Innovations in nanofabrication have expedited advances in hollow‐structured nanomaterials with increasing complexity, which, at the same time, set challenges for the precise determination of their intriguing and complicated 3D configurations. Conventional transmission electron microscopy (TEM) analysis typically yields 2D projections of 3D objects, which in some cases is insufficient to reflect the genuine architectures of these 3D nano‐objects, providing misleading information. Advanced analytical approaches such as focused ion beam (FIB) and ultramicrotomy enable the real slicing of nanomaterials, realizing the direct observation of inner structures but with limited spatial discrimination. Electron tomography (ET) is a technique that retrieves spatial information from a series of 2D electron projections at different tilt angles. As a unique and powerful tool kit, this technique has experienced great advances in its application in materials science, resolving the intricate 3D nanostructures. Here, the exceptional capability of the ET technique in the structural, chemical, and quantitative analysis of hollow‐structured nanomaterials is discussed in detail. The distinct information derived from ET analysis is highlighted and compared with conventional analysis methods. Along with the advances in microscopy technologies, the state‐of‐the‐art ET technique offers great opportunities and promise in the development of hollow nanomaterials.

Lithium, zinc, sodium, potassium, and magnesium metal batteries have emerged as the core direction of next‐generation energy storage technologies due to their ultrahigh theoretical capacities. However, the uncontrollable dendrite growth and unstable solid electrolyte interface of metal anodes during cycling lead to battery short‐circuiting, capacity fading, and safety hazards, severely hindering their commercialization process. Further design of excellent electrode‐electrolyte interfaces requires precisely identifying and addressing related scientific challenges from multiple dimensions. Specifically, this review focuses on the evolution of the solid electrolyte interphase with philic‐phobic properties on the surface of metal electrodes and discusses key influencing factors governing its evolution, including electrolyte additives and artificial solid electerolyte interphase. The research progress in solid electrolyte interface with philic‐phobic properties regulation using electrolyte additives and other methods in recent years is systematically summarized. Additionally, the influence mechanisms of electrode–electrolyte interface design on battery performance under extreme environments for lithium metal batteries and novel metal batteries are emphatically discussed. Future research needs to deeply explore the micro‐mechanisms and develop more efficient materials and technologies to further improve battery performance and meet the growing demands of the energy storage field.