Yi Cui

Discovering Underpotentially Deposited Crystalline Sodium Metal Nanoparticles on the Surface of Hard Carbon Anodes

Sodium-ion batteries are attractive candidates for low-cost and scalable energy storage in which hard carbon (HC) anodes are used. However, sodium (Na) metal plating in HC anodes at voltages above the plating potential remains a critical problem. The location and spatial distribution of crystalline sodium (c-Na) metal nanoparticles, the clusters associated with Na storage in HCs, are important for understanding this underpotential plating behavior but remain unclear. Here, we implement a cryogenic electron microscopy (cryo-EM) and electron tomography (cryo-ET) workflow that directly localizes c-Na metal clusters in sodiated HC samples: cryo-ET maps nanoscale three-dimensional (3D) distributions, while cryo-EM resolves local structure and chemistry. Our workflow reveals that c-Na metal clusters reside predominantly on the surfaces or near surfaces of individual HC particles. This finding challenges existing interpretations in the literature that locate the c-Na metal clusters within closed nanopores in the bulk of the HC, presumably because prior characterization using nonimaging techniques and two-dimensional (2D) projection images associated with traditional transmission electron microscopy (TEM) lacks the spatial 3D information necessary to resolve the full spatial distribution. Our discovery is an important step toward explaining the underpotential plating phenomenon of Na metal in HC anodes, suggesting that particle-level surface and near-surface interfaces are relevant targets to mitigate plating alongside bulk-pore, electrode, and electrolyte/interphase design.

Quantifying Sodium Metal SEI Dissolution and Relation to Corrosion Using Quartz Crystal Microbalance

Sodium-metal batteries present a more abundant alternative to lithium-based batteries, with high theoretical capacity and comparable reduction potential. Ether electrolytes perform well in sodium-metal batteries under continuous cycling and are presumed to have a stable solid-electrolyte interphase (SEI). However, the solubility of sodium SEI components is a cause for concern, and SEI evolution during calendar aging is not commonly studied for the ether sodium-metal system. In this work, SEI mass formation and dissolution are quantitatively measured for NaPF6 in diglyme. For varying potential hold levels, significant SEI dissolution is observed, from 55 to 76% of the originally formed SEI. Characterization shows that in addition to organic component dissolution, inorganic salts such as NaF and NaxPOyFz are unstable in SEI during open circuit rest. This instability results in continuous corrosion of sodium metal during calendar aging, highlighting an important understanding and concern of SEI stability in sodium-metal batteries.

Determining depth-resolved spatial distribution of solid–electrolyte interphase using non-destructive angle-resolved X-ray photoelectron spectroscopy for lithium-metal batteries

The solid electrolyte interphase is a key performance regulator in Li-metal batteries, which are regarded as an important technology for future energy storage. Understanding this crucial interphase through non-destructive analysis is essential to advance the performance and lifespan of Li-metal batteries. We introduce angle-resolved X-ray photoelectron spectroscopy as a non-destructive technique for the depth-profile analysis of the solid electrolyte interphase in Li-metal batteries. Importantly, we show that this characterization technique displays a distinct advantage in preserving the solid electrolyte interphase's integrity compared to traditional sputtering-based depth-profiling. Our findings add to the understanding of compositional differences in the solid electrolyte interphase before the onset of Li electrodeposition and after Li plating. Moreover, we find significant variations in the thickness and distribution of solid electrolyte interphase species across different classes of electrolytes, which strongly influence the solid electrolyte interphase's protective properties and, by extension, Li-metal battery performance. This study benchmarks the application of angle-resolved X-ray photoelectron spectroscopy in revealing detailed, depth-resolved chemical composition of the solid electrolyte interphase in a non-destructive approach. Understanding the solid–electrolyte interphase formed on lithium is vital for improving the lifetime of lithium metal batteries. Here, authors show that angle-resolved X-ray photoelectron spectroscopy can reveal the depth-dependent composition of the interfacial layer without damaging it by ion sputtering.

p‐Block Aluminum Tailoring Termination‐Acidity of Two‐Dimensional MoS 2 Nanosheets for Alkaline Hydrogen Evolution Reaction

Molybdenum disulfide (MoS 2 ) has shown promising electrocatalytic hydrogen evolution reaction (HER) activity in acidic electrolyte, while its high‐pH alkaline HER performance is critically poor due to the sluggish water dissociation kinetics. Herein, utilizing local oxygen coordination brought by p‐block aluminum (Al 3+ ) cations, we report a termination‐acidity tailoring strategy to optimize the surface chemistry of MoS 2 catalyst to construct an acid‐like interface. Accordingly, the well‐designed AlO x ‐MoS 2 catalyst exhibits a considerable HER activity in 1.0 m KOH, achieving a low overpotential of 98 mV at 10 mA/cm 2 (η 10 ) with a small Tafel slope value (75 mV/dec). In contrast, an inferior HER activity (η 10 = 545 mV, Tafel slope = 130 mV/dec) is observed in bare oxygen modified MoS 2 (O‐MoS 2 ) counterpart. Moreover, the AlO x ‐MoS 2 catalyst displays an exceptional electrochemical stability, continuous hydrogen generation over 150 h without significant activity loss. Multiple spectroscopy characterizations and theory simulation demonstrate that the introduction of AlO x groups into in‐plane MoS 2 surface enriches protons at solid‐liquid interface, accelerating proton recombination. Additionally, the strong coordination ability of Al 3+ stabilizes the local acid‐like environment via ‐Al‐OH‐Mo‐ motifs. Our work may provide a simple but feasible surface‐chemistry modification strategy to fully trigger the intrinsic alkaline HER activity of MoS 2 itself.

Inhibition of Calendar Aging Induced Li Metal Corrosion Using Selected Area Insulating Layer Current Collectors

Li metal is a promising anode for next-generation batteries, but its high per-cycle capacity loss hinders its commercial adoption. A major contributor is the corrosion of Li during calendar aging, which accelerates the generation of degradation byproducts, such as the solid electrolyte interphase (SEI) and isolated Li (i-Li). Here, we reveal that Li corrosion is spatially heterogeneous: five times more capacity is lost at the edge overhang area of the current collector than at the center in the coin cell form factor. To address this, we developed a selected-area insulating layer (SAIL) that prevents Li plating in the overhang, yielding a 94% reduction in corrosion-induced capacity loss. Electron microscopy and titration gas chromatography were employed to visualize the morphological heterogeneity and quantify the disconnected Li loss at the center versus the overhang. Preventing dendritic Li plating in the overhang of the current collector can therefore substantially mitigate calendar aging-induced capacity loss.

Targeting 100% LithiumUtilization in Lithium MetalBatteries

Anode-free lithium metal batteries (AFLMBs) represent the ultimate solution to mankind’s quest for the Holy Grail of batteries, where the cell-level energy density is maximized on the assumption that lithium (Li0) must be fully utilized with near 100% Coulombic efficiency. Although substantial progress has been made since the anode-free concept was first proposed, the challenges presented by the most powerful anode material that can be found on the periodic table still remain unresolved due to its extreme reactive nature, which not only makes it impossible to retain 100% reversibility but also induces inhomogeneity during repeated plating/stripping cycles and persistent capacity loss over a long period of time. The isolated study approaches, emphasizing either individual electrolyte components or interphasial chemistry engineering, but mostly focused on the negative-electrode current collector, hinder insight into issues arising when these components are assembled into cells and forced to interface with each other. In this review, we attempt to examine this high-dimensional topic from a panoramic perspective, with the focus placed on the liquid electrolytes. We first outline the fundamental operating principles of key individual battery components, together with practical perspectives for evaluating lithium utilization and reversibility in AFLMBs. We then discuss how these components interact when assembled into full cells, how such interactions give rise to heterogeneous electrochemical and mechanical behaviors, and how these phenomena can be characterized and regulated. It is also outlined that a hierarchical perspective on lithium behavior, spanning from the nano- to cell-scale, is essential to enable plating, stripping, and recovery in AFLMBs. Finally, we present perspectives from leading researchers actively working on the various elements that constitute AFLMBs and integrate these viewpoints to clarify the future research directions of this field. By providing a system-level framework for understanding AFLMBs, this review aims to guide future research efforts and contribute to addressing the broader challenges of sustainable energy storage.

Defect-Engineered Hexagonal Boron Nitride Enables Ionic Conduction for Lithium Metal Batteries

Engineering the Current Collector Interface by Atomic Layer Deposition for Fast Charging of Lithium Metal Batteries

Enabling fast charging conditions in high energy density batteries is crucial for supporting the electrification of the transportation sector. Here, we introduce a strategy to support fast charging in lithium metal batteries by using atomic layer deposition to coat the copper current collector with a resistive Al2O3 thin film. The film constrains electron transfer to low-resistance defect sites, leading to the regulation of Li+ ion transfer and concentration profiles. Results show that limiting nucleation sites promotes the lateral growth of beneficial low-surface-area lithium deposits at current densities of up to 20 mA cm–2, an effect attributed to the radial diffusion of Li+ ions. We also show that the Al2O3 thin film incorporates a greater degree of beneficial inorganic species and LiF into the solid electrolyte interface at high current densities. For charging rates of 5 mA cm–2, the cumulative benefits allow cells with the resistive Al2O3 coating to achieve Coulombic efficiencies nearly 8% greater than bare copper over the first 100 cycles and support an additional 100 cycles at Coulombic efficiencies above 80% in carbonate electrolytes.

Redox Staining of Metallic Lithium inside Batteries for Multimodal Visualization and Identification with Multiscale Spatial Resolution

SEI Characterization Using XPS: Resolving Rinsing Effects through Cryogenic Implementation

Freestanding Ordered Intermetallic Nanomembranes Released from Etchable Oxide Templates

Universality Class of Ion-Intercalation Models

Gas–Solid van der Waals Interaction Driving the Dynamic Evolution of Surface Nanostructures

Microphysical variability in stratiform clouds: Aircraft observations

A facile ambient post modification method towards red fluorescent flame-formed carbon dots

In this work, a room-temperature HNO 3 wash is found to be effective in red-shifting the fluorescence of flame-formed carbon dots, especially for the green fluorescent carbon dots from premixed flames. Characterization techniques together with quantum chemistry calculations are carried out to investigate the mechanisms behind the red-shifted fluorescence. It was found that a room-temperature HNO 3 wash can significantly red-shift the fluorescence of flame-formed carbon dots from ∼535 nm to ∼620 nm and cause a shorter fluorescence lifetime. The particle diameter and in-plane correlation length of the aromatic lands were not significantly changed, but the N-containing species were detected after the HNO 3 wash. Further spectroscopic analysis showed that the responsible nitrogen species for the red-shifted fluorescence was –NO 2 , which possibly stemmed from the C=C reactive sites on the flame-formed carbon dots, as the C=C content decreased while the –NO 2 content increased after the HNO 3 wash. The excited state analysis shows that –NO 2 functional groups can lower the HOMO-LUMO gap of the flame-formed carbon dots and red-shift the 1π→π* transition. The hole-electron analysis shows that the excitation of the unmodified model is the local excitation within the π-conjugated domain, while that of the N-modified model is the charge transfer excitation from the π-conjugated domain to the peripheral –NO 2 functional groups, which can lead to the non-radiative decay and low quantum yield. This work also provides direct evidence for the presence of special reactive sites relevant to C=C on the flame-formed carbon dots that can readily react with HNO 3 at room temperature and load –NO 2 functional groups on them.

Hydrotrope-enabled high concentration aqueous electrolytes for reversible and sustainable iron metal anodes

CuiMaterials Letters

GelMA/PEDOT:PSS hydrogel beads combined with electrical stimulation as a potential method for bone organoid construction

This study developed a simple strategy for bone organoid construction using GelMA/PEDOT:PSS hydrogel beads (fabricated via pipette extrusion-UV crosslinking) combined with electrical stimulation (ES). The hydrogel beads exhibited uniform size of 2.29 ± 0.13 mm and porous structure of 100–200 μm pores. ES (75 mV/mm, 75 Hz, 80 % duty cycle) triggered Ca 2+ influx in HEK293T cells with 6–8 min and upregulated Opg expression in BMSCs. The combination of BMSCs-laden hydrogel beads and ES (20 min every other day) enhanced Osx/Runx2 expression post-osteogenic induction. This low-cost, facile system shows potential for bone organoid engineering.

Revealing Solvent-Assisted Li ⁺ Transport in the Solid Electrolyte Interphase operando

The performance of energy-dense lithium metal batteries is critically influenced by the properties of the solid electrolyte interphase (SEI). Yet, progress in understanding this layer has been limited by the lack of accurate operando characterization because the SEI evolves dynamically during cycling. Here, we apply dynamic electrochemical impedance spectroscopy (dEIS) to resolve the real-time evolution of the SEI on lithium metal in ether-based electrolytes with varying degrees of fluorination. We find that faster stabilization of the compact SEI resistance correlates with improved passivation and higher Coulombic efficiency. Unexpectedly, compact SEI resistance correlates directly with Li+ solvation energy, revealing that weaker Li+ solvation increases not only bulk but also interphase resistance. These findings challenge the conventional view of the SEI as a purely solid-phase conductor and instead support a solvent-assisted Li+ transport mechanism within the compact SEI. This framework emphasizes the need to balance SEI ionic conductivity with the Li+ solvation environment to maximize lithium metal battery performance.

Methanol steam reforming with samarium-stabilized copper sites for efficient hydrogen production

The rational design of Cu-based catalysts with tailored interfacial structures and electronic states remains challenging yet essential for advancing hydrogen production via methanol steam reforming (MSR). Here, we developed a samarium-mediated strategy to construct a 30Sm-CuAl catalyst. The introduction of Sm promotes Cu dispersion and induces strong metal-support interactions, resulting in the formation of Sm 2 O 3 -encapsulated Cu nanoparticles enriched with Cu + -O-Sm interfaces. The optimized 30Sm-CuAl demonstrates exceptional MSR performance, achieving a hydrogen production rate of 1,126 mmol g cat −1 h −1 at 250°C. Mechanistic studies revealed that the reaction follows the formate pathway in x Sm-CuAl, with formate accumulation identified as the primary reason for the deactivation of 30Sm-CuAl. Dynamic regeneration of 30Sm-CuAl through redox treatment restores its activity, thereby enabling cyclic operation. These findings provide insights into rare-earth oxide regulation of Cu-based catalysts and lay the foundation for targeted resolution of formate intermediate accumulation to enhance MSR stability.

Geochemical constraints on the origin of Li-rich claystones in a carbonate weathering environment: Insights from the Jiujialu Formation, central Guizhou

• Lithium originated from nearby Loushanguan Group argillaceous dolomite. • Lithium is mainly structural in smectite; exchangeable lithium is minimal. • Alkaline, reducing karst settings favored smectite and lithium enrichment. • A selective lithium enrichment mechanism is inferred but remains unclear. Lithium is recognized as a critical element with widespread applications in emerging industries. In recent years, the unusual enrichment of lithium in claystones from southwestern China has attracted significant attention. However, the sources, host minerals, and enrichment mechanisms of lithium remain poorly understood. This study investigates the major and trace element compositions and mineral assemblages of co-deposited detrital materials in argillaceous dolomite, and claystones from four sections of the Lower Carboniferous Jiujialu Formation (C 1 jj) in central Guizhou Province, South China. The results show that detrital materials in the argillaceous dolomite with an average lithium content of approximately 46.17 ppm are primarily composed of quartz, muscovite, and microcline. A positive correlation between the δ 7 Li values of Li-rich claystones and their host dolomites suggests that lithium released during the weathering of argillaceous carbonate rocks became enriched in the overlying weathering crust, forming the Li-rich claystones. The lithium content and δ 7 Li values in the claystones correlate with the Chemical Index of Alteration (CIA), showing enrichment at the intermediate weathering stage (CIA = 75–90) and depletion during intense weathering (CIA > 90). Moreover, when the MgO content of the bulk claystone is below 0.25 wt%, lithium content increases sharply with MgO, accompanied by high δ 7 Li values, indicating Mg-poor smectite phase as the Li host. High-lithium claystones exhibit broader smectite peaks in X-ray diffraction (XRD) compared to their low-lithium counterparts, indicating that smectite plays a key role in lithium enrichment. Given the sensitivity of lithium isotopes to clay mineral formation—which is closely influenced to environmental conditions—this study proposes that intermediate weathering (CIA = 75–90) and an alkaline, poorly drained, reducing, and low-salinity depositional environment are favorable for the formation of Li-rich smectite during the weathering of argillaceous carbonate rocks. Notably, although carbonate rocks are typically poor in lithium, the widespread occurrence of Li-rich claystones in carbonate weathering–sedimentary systems suggest a possible mechanism of selective lithium enrichment during clay mineral formation under such conditions. This mechanism warrants further investigation.