Search

The Al3+ ion electrochemistry of MoTe2 in aqueous batteries is illustrated.

The ability to freeze and stabilize reaction intermediates in their metastable states and obtain their structural and chemical information with high spatial resolution would be very powerful to unravel the fundamentals in many important materials technologies such as catalysis and batteries. Here, we develop an electrified operando-freezing methodology for the first time to preserve these metastable states under electrochemical reaction conditions for cryogenic electron microscopy (cryo-EM) imaging and spectroscopy. Using Cu catalysts for CO2 reduction as a model system, we observe restructuring of the Cu catalyst in a CO2 atmosphere while the same catalyst remains intact in an air atmosphere at the nanometer scale. Furthermore, we discover the existence of single valance Cu (1+) state and C-O bonding at the electrified liquid-solid interface of the operando-frozen samples, which are key reaction intermediates that traditional ex situ measurements fail to detect. This work highlights our novel technique to study the local structure and chemistry of electrified liquid-solid interfaces, which has broad impact for many electrochemical reactions.

Electrodeposition of lithium metal is critical for high energy batteries. However, the simultaneous formation of a surface corrosion film termed the solid electrolyte interphase (SEI) complicates the deposition process. Here, we decouple these two intertwined processes by outpacing corrosion at ultrafast deposition current densities while also avoiding mass transport limitations. Using cryogenic-electron microscopy, we discover the intrinsic deposition morphology of metallic lithium to be that of a rhombic dodecahedron, which is surprisingly independent of electrolyte chemistry or current collector substrate. In a coin cell architecture, these rhombic dodecahedra reveal a key failure mode at high current densities: rather than promoting dendritic morphologies, the near point-contact electrical connectivity of the polyhedra to the current collector accelerates inactive Li formation that can explain poor cycling efficiency at high current densities. While Li deposition and SEI formation have always been tightly linked in past studies, our experimental approach enables new opportunities to fundamentally understand these processes decoupled from each other and bring about new insights to engineer better batteries.

Poor fast-charge capabilities limit the usage of rechargeable Li metal anodes. Understanding the connection between charging rate, electroplating mechanism, and Li morphology could enable fast-charging solutions. Here, we develop a combined electroanalytical and nanoscale characterization approach to resolve the current-dependent regimes of Li plating mechanisms and morphology. Measurement of Li

Cryo-electron microscopy (cryo-EM) has emerged as a vital tool to reveal the native structure of beam-sensitive biomolecules and materials. Yet high-resolution cryo-EM analysis is still limited by the poorly controlled specimen preparation and urgently demands a robust supporting film material to prepare desirable samples. Here, we developed a bilayer Janus graphene membrane with the top-layer graphene being functionalized to interact with target molecules on the surface, while the bottom layer being kept intact to reinforce its mechanical steadiness. The ultraclean and atomically thin bilayer Janus membrane prepared by our protocol on one hand generates almost no extra noise and on the other hand reduces the specimen motion during cryo-EM imaging, thus allowing the atomic-resolution characterization of surface functional groups. Using such Janus membranes in cryo-EM specimen preparation, we were able to directly image the lithium dendrite and reconstruct macromolecules at near-atomic resolution. Our results demonstrate the bilayer Janus design as a promising supporting material for high-resolution cryo-EM and EM imaging.

Silicon (Si) is a promising anode candidate for next-generation lithium-ion batteries (LIBs) due to its high theoretical capacity. Solar Si photovoltaic waste possesses good purity and high output. Using it as the raw material for battery anodes can synchronously solve the problem of solid waste pollution and enable high energy density LIBs. A critical issue impeding the practical application of Si is the undesirable side reactions at the electrolyte-particle interface and the resulting increase in impedance during cycling. Herein, a Si-P core shell structure with chemical bonding at the Si-P interface is fabricated through a simple mechanical alloying reaction between red P and solar Si photovoltaic waste. The P nanoshell with thickness within 15 nm converts to Li3P during the initial lithiation process and maintains its phase on cycling. The as-formed Li3P nanolayer functions as a stable, ionically conductive protective layer that reduces the direct contact between Si and electrolytes, and thus suppresses undesired side reactions. The Si-P nanocomposite exhibits stable electrochemical cycling with a high reversible capacity of 1,178 mAhg−1 after 500 cycles at 1,200 mA g−1, as well as excellent rate capability (912 mAh g−1 at 2 C). With 15 wt% addition to graphite, a graphite/Si-P hybrid electrode shows a high overall reversible specific capacity of 447 mAh g−1 and 88.3% capacity retention after 100 cycles at high areal capacity of 2.64 mAh cm−2 at 100 mA g−1, indicating its promise as a drop-in anode in practical LIBs.

Mesenchymal stem cell–derived exosomes (MSC-Exos) have been shown to promote angiogenesis. Treating MSCs with ischemic rat brain extracts was sufficient to augment their benefits in stroke. However, no similar analyses of ischemic heart extracts have been performed to date. We aim to determine whether MSC-Exos derived from MSCs pretreated with ischemic rat heart extract were able to promote angiogenesis and to clarify underlying mechanisms. ELISA (enzyme-linked immunosorbent assay) of heart extracts revealed a significant increase of vascular endothelial growth factor (VEGF) at 24 h post-MI (myocardial infarction) modeling, and time-dependent decreases in hypoxia inducible factor–1α (HIF-1α). MTT and wound healing assays revealed human umbilical vein endothelial cells (HUVECs) migration and proliferation increased following MSCE-Exo treatment (exosomes derived from MSC pretreated with ischemic heart extracts of 24 h post-MI) relative to MSCN-Exo treatment (exosomes derived from MSC pretreated with normal heart extracts). Proteomic analyses of MSCE-Exo and MSCN-Exo were conducted to screen for cargo proteins promoting angiogenesis. Result revealed several angiogenesis-related proteins were upregulated in MSCE-Exo, including DMBT1 (deleted in malignant brain tumors 1). When DMBT1 was silenced in MSCs, HUVECs with MSCDMBT1 RNAi-Exo treatment exhibited impaired proliferative and migratory activity and reductions of DMBT1, p-Akt, β-catenin, and VEGF. To explore how ischemic heart extracts took effects, ELISA was conducted showing a significant increase of IL-22 at 24 h post-MI modeling. P-STAT3, IL22RA1, DMBT1, and VEGF proteins were increased in MSCE relative to MSCN, and VEGF and DMBT1 were increased in MSCE-Exos. Together, these suggest that IL-22 upregulation in ischemic heart extracts can increase DMBT1 in MSCs. Exosomes derived from those MSCs deliver DMBT1 to HUVECs, thereby enhancing their migratory and proliferative activity.

Electrifying ammonia synthesis will be vital to the decarbonization of the chemical industry, as the Haber-Bosch process contributes significantly to global carbon emissions. A lithium-mediated pathway is among the most promising ambient-condition electrochemical ammonia synthesis methods. However, the role of metallic lithium and its passivation layer, the solid electrolyte interphase (SEI), remains unresolved. Here, we apply a multiscale approach that leverages the powerful cryogenic transmission electron microscopy (cryo-TEM) technique to reveal new insights that were previously inaccessible with conventional methods. We discover that the proton donor (e.g. ethanol) governs lithium reactivity toward nitrogen fixation. Without ethanol, the SEI passivates lithium metal, rendering it inactive for ammonia production. Ethanol disrupts this passivation layer, enabling continuous reactivity at the lithium surface. As a result, metallic lithium is consumed via reactions with nitrogen, proton donor, and other electrolyte components. This reactivity across the SEI is vital to device-level performance of lithium-mediated ammonia synthesis.

Rechargeable lithium (Li) metal batteries must have long cycle life and calendar life (retention of capacity during storage at open circuit). Particular emphasis has been placed on prolonging the cycle life of Li metal anodes, but calendar ageing is less understood. Here, we show that Li metal loses at least 2–3% of its capacity after only 24 hours of ageing, regardless of the electrolyte chemistry. These losses of capacity during calendar ageing also shorten the cycle life of Li metal batteries. Cryogenic transmission electron microscopy shows that chemical corrosion of Li and the continuous growth of the solid electrolyte interphase—a passivation film on Li—cause the loss of capacity. Electrolytes with long cycle life do not necessarily form a solid electrolyte interphase with more resistance to chemical corrosion, so functional electrolytes must simultaneously minimize the rate of solid electrolyte interphase growth and the surface area of electrodeposited Li metal. Batteries keep degrading even when they are not in operation, but their calendar life is rarely studied in advanced batteries that are still in the development stage. Here the authors quantify the calendar ageing of Li metal anodes and report its underlying mechanisms.

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.

Gas-phase heterogeneous catalysis is a process spatially constrained on the two-dimensional surface of a solid catalyst. Here, we introduce a new toolkit to open up the third dimension. We discovered that the activity of a solid catalyst can be dramatically promoted by covering its surface with a nanoscale-thin layer of liquid electrolyte while maintaining efficient delivery of gas reactants, a strategy we call three-phase catalysis. Introducing the liquid electrolyte converts the original surface catalytic reaction into an electrochemical pathway with mass transfer facilitated by free ions in a three-dimensional space. We chose the oxidation of formaldehyde as a model reaction and observed a 25000-times enhancement in the turnover frequency of Pt in three-phase catalysis as compared to conventional heterogeneous catalysis. We envision three-phase catalysis as a new dimension for catalyst design and anticipate its applications in more chemical reactions from pollution control to the petrochemical industry.

Novel anode materials for lithium-ion batteries were synthesized by

Statins are first-line drugs used to control patient lipid levels, but there is recent evidence that statin treatment can lower colorectal cancer (CRC) incidence by 50% and prolong CRC patient survival through mechanisms that are poorly understood. In this study, we found that the treatment of APCmin mice by the mevalonate pathway inhibitor lovastatin significantly reduced the number of colonic masses and improved hypersplenism and peripheral anemia. Furthermore, reverse transcription polymerase chain reaction (RT-PCR) analysis of colonic mass tissues showed a potent inhibitory effect in both Wnt/β-catenin signaling and YAP/TAZ signaling in the lovastatin treatment group. The results of our transcriptomic analyses in RKO indicated that lovastatin regulated several proliferation-related signaling pathways. Moreover, lovastatin suppressed important genes and proteins related to the canonical Wnt/β-catenin and alternative Wnt-YAP/TAZ signaling pathways in RKO and SW480 cells, and these effects were rescued by mevalonic acid (MVA), as confirmed through a series of Western blotting, RT-PCR, and reporter assays. Given that statins suppress oncogenic processes primarily through the inhibition of Rho GTPase in the mevalonate pathway, we speculate that lovastatin can inhibit certain Rho GTPases to suppress both canonical Wnt/β-catenin signaling and alternative Wnt-YAP/TAZ signaling. In RKO cells, lovastatin showed similar inhibitory properties as the RhoA inhibitor CCG1423, being able to inhibit β-catenin, TAZ, and p-LATS1 protein activity. Our results revealed that lovastatin inhibited RhoA activity, thereby suppressing the downstream canonical Wnt/β-catenin and alternative Wnt-YAP/TAZ pathways in colon cancer cells. These inhibitory properties suggest the promise of statins as a treatment for CRC. Altogether, the present findings support the potential clinical use of statins in non-cardiovascular contexts and highlight novel targets for anticancer treatments.

Preservation of cycling behavior Understanding the changes in interfaces between electrode and electrolyte during battery cycling, including the formation of the solid-electrolyte interphase (SEI), is key to the development of longer lasting batteries. Z. Zhang et al . adapt a thin-film vitrification method to ensure the preservation of liquid electrolyte so that the samples taken for analysis using microscopy and spectroscopy better reflect the state of the battery during operation. A key finding is that the SEI is in a swollen state, in contrast to current belief that it only contained solid inorganic species and polymers. The extent of swelling can affect transport through the SEI, which thickens with time, and thus might also decrease the amount of free electrolyte available for battery cycling. —MSL

Summary Lithium (Li) metal is the ultimate anode material for Li batteries because of its highest capacity among all candidates. Recent research has focused on stable interphase and host materials to address its low stability and reversibility. Here, we discover that tortuosity is a critical parameter affecting the morphology and electrochemical performances of hosted Li anodes. In three types of hosts—vertically aligned, horizontally aligned, and random reduced graphene oxide (rGO) electrodes with tortuosities of 1.25, 4.46, and 1.76, respectively—we show that high electrode tortuosity causes locally higher current density on the top surface of electrodes, resulting in thick Li deposition on the surface and degraded cycling performance. Low electrode tortuosity in the vertically aligned rGO host enables homogeneous Li transport and uniform Li deposition across the host, realizing greatly improved cycling stability. Using this principle of low tortuosity, the designed electrode shows through-electrode uniform morphology with anodic Coulombic efficiency of ∼99.1% under high current and capacity cycling conditions.

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...

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.

Summary Despite rapid progress of hybrid organic-inorganic halide perovskite solar cells, using transmission electron microscopy to study their atomic structures has not been possible because of their extreme sensitivity to electron beam irradiation and environmental exposure. Here, we develop cryoelectron microscopy (cryo-EM) protocols to preserve an extremely sensitive perovskite, methylammonium lead iodide (MAPbI3) under various operating conditions for atomic-resolution imaging. We discover the precipitation of lead iodide nanoparticles on MAPbI3 nanowire’s surface after short UV illumination and surface roughening after only 10 s exposure to air, while these effects remain undetected in conventional X-ray diffraction. We establish a definition for critical electron dose and find this value for MAPbI3 at cryogenic condition to be 12 e−/A2 at 1.49 A spatial resolution. Our results highlight the importance of cryo-EM since traditional techniques cannot capture important nanoscale changes in morphology and structure that have important implications for perovskite solar cell stability and performance.

Abstract Li metal is the ultimate anode choice due to its highest theoretical capacity and lowest electrode potential, but it is far from practical applications with its poor cycle lifetime. Recent research progresses show that materials designs of interphase and host structures for Li metal are two effective ways addressing the key issues of Li metal anodes. Despite the exciting improvement on Li metal cycling capability, problems still exist with these methodologies, such as the deficient long-time cycling stability of interphase materials and the accelerated Li corrosion for high surface area three-dimensional composite Li anodes. As a result, Coulombic efficiency of Li metal is still not sufficient for full-cell cycling. In the near future, an interphase protected three-dimensional composite Li metal anode, combined with high performance novel electrolytes might be the ultimate solution. Besides, nanoscale characterization technologies are also vital for guiding future Li metal anode designs. Graphic Abstract

Operations of lithium-ion batteries have long been limited to a narrow temperature range close to room temperature. At elevated temperatures, cycling degradation speeds up due to enhanced side reactions, especially when high-reactivity lithium metal is used as the anode. Here, we demonstrate enhanced performance in lithium metal batteries operated at elevated temperatures. In an ether-based electrolyte at 60 °C, an average Coulombic efficiency of 99.3% is obtained and more than 300 stable cycles are realized, but, at 20 °C, the Coulombic efficiency drops dramatically within 75 cycles, corresponding to an average Coulombic efficiency of 90.2%. Cryo-electron microscopy reveals a drastically different solid electrolyte interface nanostructure emerging at 60 °C, which maintains mechanical stability, inhibits continuous side reactions and guarantees good cycling stability and low electrochemical impedance. Furthermore, larger lithium particles grown at the elevated temperature reduce the electrolyte/electrode interfacial area, which decreases the per-cycle lithium loss and enables higher Coulombic efficiencies. The performance of Li-ion batteries deteriorates at elevated temperatures due to increased activity of electrode materials and parasitic reactions. Here Yi Cui and colleagues report much-improved battery cyclability at 60 °C and use cryo-electron microscopy to shed light on the origin of the phenomenon.

Low-cycle fatigue (LCF) test was performed at 296 K and 80 K to investigate the effects of cryogenic environment on the LCF performance of 9%Ni steel joints welded by flux cored arc welding (FCAW). The test results indicated that the LCF performance in cryogenic environment was higher than that at room temperature. The gap of fatigue lifetime decreased with the increment of strain amplitude. The LCF performance at room temperature and in cryogenic environment was very close when total strain amplitude was 0.8%. The LCF specimens underwent cyclic hardening and cyclic softening before fracture at room temperature. No obvious cyclic softening was observed during LCF test at cryogenic temperature. The fracture location was at PMZ at room temperature, but at weld center in cryogenic environment. The transformation of brass texture mainly occurred in PMZ at cryogenic temperature after LCF test. The strengthening effects of brass texture in PMZ increased the stress concentration in weld center. The microvoids appeared near precipitates at grain boundaries led to the intergranular propagation of fatigue cracks in weld center. Research results contributed to safe service and fatigue lifetime estimation of LNG containers made by 9% Ni steel in cryogenic environment.

Developing a viable metallic lithium anode is a prerequisite for next-generation batteries. However, the low redox potential of lithium metal renders it prone to corrosion, which must be thoroughly understood for it to be used in practical energy-storage devices. Here we report a previously overlooked mechanism by which lithium deposits can corrode on a copper surface. Voids are observed in the corroded deposits and a Kirkendall-type mechanism is validated through electrochemical analysis. Although it is a long-held view that lithium corrosion in electrolytes involves direct charge-transfer through the lithium-electrolyte interphase, the corrosion observed here is found to be governed by a galvanic process between lithium and the copper substrate-a pathway largely neglected by previous battery corrosion studies. The observations are further rationalized by detailed analyses of the solid-electrolyte interphase formed on copper and lithium, where the disparities in electrolyte reduction kinetics on the two surfaces can account for the fast galvanic process.

Electrochemical CO2 reduction to formate provides an avenue to reduce globally accelerating CO2 emissions and produce value-added products. Unfortunately, high selectivity in formate electrosynthesis has thus far only been achieved at highly cathodic potentials. Here we use density functional theory to investigate the effect of alloying Cu and Sn on the activity and selectivity towards formate. A theoretical thermodynamic analysis of the reaction energetics suggests that the incorporation of copper into tin could suppress hydrogen evolution and CO production, thus favouring formate generation. Consistent with theoretical trends, the designed CuSn3 catalysts by co-electrodeposition exhibit a Faradaic efficiency of 95% towards formate generation at −0.5 V versus RHE. Furthermore, the catalysts show no degradation over 50 h of operation. In situ Sn L3-edge and Cu K-edge X-ray absorption spectroscopy indicate electron donation from Sn to Cu, which indicates positive oxidation states of Sn in CuSn3 under operating conditions. The electroreduction of carbon dioxide to formate represents a desirable strategy for the production of fuels and commodity chemicals. Now, guided by density functional theory, Cui and colleagues report CuSn3 alloys that exhibit high activity and selectivity for formate production from CO2 electroreduction at potentials as low as −0.5 V versus RHE.

The nanostructure design of a prereserved hollow space to accommodate 300% volume change of silicon anodes has created exciting promises for high-energy batteries. However, challenges with weak mechanical stability during the calendering process of electrode fabrication and poor volumetric energy density remain to be solved. Here we fabricated a pressure-resistant silicon structure by designing a dense silicon shell coating on secondary micrometer particles, each consisting of many silicon nanoparticles. The silicon skin layer significantly improves mechanical stability, while the inner porous structure efficiently accommodates the volume expansion. Such a structure can resist a high pressure of over 100 MPa and is well-maintained after the calendering process, demonstrating a high volumetric capacity of 2041 mAh cm–3. In addition, the dense silicon shell decreases the surface area and thus increases the initial Coulombic efficiency. With further encapsulation with a graphene cage, which allows the silico...

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.

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.