In situ transmission electron microscopy observation of microstructure and phase evolution in a SnO₂ nanowire during lithium intercalation

New Suggestion of Highly Durable Electrode Design for Ordered Mesoporous Ni-Mn Binary Transition Metal Oxide Anode Material in Lithium-Ion Batteries

Anode materials storing large-scale lithium ions gradually decrease electrochemical performance due to severe volume changes during cycling. Therefore, there is an urgent need to develop anode materials with high electrochemical capacity and durability, without deterioration arising due to the volume changes during the electrochemical processes. To date, mesoporous materials have received attention as anode materials due to their ability to mitigate volume expansion, offer a short pathway for Li+ transport, and exhibit anomalous high capacity. However, the nano-frameworks of transition metal oxide collapse during conversion reactions, demanding an improvement in nano-framework structure stability. In this study, ordered mesoporous nickel manganese oxide (m-NMO) is designed as an anode material with a highly durable nanostructure. Interestingly, m-NMO showed better cycle performance and higher electrochemical capacity than those of nickel oxide and manganese oxide. Operando small-angle X-ray scattering and ex situ transmission electron microscopic results confirmed that the binary m-NMO sustained a highly durable nanostructure upon cycling, unlike the single metal oxide electrodes where the mesostructures collapsed. Ex situ X-ray absorption spectroscopy proved that nickel and manganese showed different electrochemical reaction voltages, and thus undergoes sequential conversion reactions. As a result, both elements can act as complementary nano-propping buffers to maintain stable mesostructure.

In situ synthesis of hierarchically-assembled three-dimensional ZnS nanostructures and 3D printed visualization

Nanomaterials have gained enormous interest in improving the performance of energy harvest systems, biomedical devices, and high-strength composites. Many studies were performed fabricating more elaborate and heterogeneous nanostructures then the structures were characterized using TEM tomographic images, upgrading the fabrication technique. Despite the effort, intricate fabrication process, agglomeration characteristic, and non-uniform output were still limited to presenting the 3D panoramic views straightforwardly. Here we suggested in situ synthesis method to prepare complex and hierarchically-assembled nanostructures that consisted of ZnS nanowire core and nanoparticles under Ag₂S catalyst. We demonstrated that the vaporized Zn and S were solidified in different shapes of nanostructures with the temperatures solely. To our knowledge, this is the first demonstration of synthesizing heterogeneous nanostructures, consisting of a nanowire from the vapor-liquid-solid and then nanoparticles from the vapor-solid grown mechanism by in situ temperature control. The obtained hierarchically-assembled ZnS nanostructures were characterized by various TEM technologies, verifying the crystal growth mechanism. Lastly, electron tomography and 3D printing enabled the nanoscale structures to visualize with centimeter scales. The 3D printing from randomly fabricated nanomaterials is rarely performed to date. The collaborating work could offer a better opportunity to fabricate advanced and sophisticated nanostructures.

Recent advances in dendrite-free lithium metal anodes for high-performance batteries

With the merits of high energy density, light weight, and low electrode potential, lithium metal anodes (LMAs) have lately sparked worldwide attention in the field of batteries. However, their low Coulombic efficiency, tremendous volume expansion, and serious dendrite growth make lithium metal batteries (LMBs) unsuitable for a wide variety of applications. Moreover, when lithium dendrite crosses the electrolyte and reaches the cathode material, it may cause short circuit and safety issues for batteries. Herein, to accelerate the development of LMBs, we give a brief summary of the dendrite growth mechanisms in both liquid and solid systems of electrolytes. In particular, various modification approaches to dendrite-free lithium metal batteries are discussed. Furthermore, advanced in situ characterization techniques for the real-time observation of lithium dendrite growth are presented. To address the application issues, various potential research routes for improving the performance of LMBs are provided as well.

Insight into Reversible Conversion Reactions in SnO2 -Based Anodes for Lithium Storage: A Review

Various anode materials have been widely studied to pursue higher performance for next generation lithium ion batteries (LIBs). Metal oxides hold the promise for high energy density of LIBs through conversion reactions. Among these, tin dioxide (SnO₂ ) has been typically investigated after the reversible lithium storage of tin-based oxides is reported by Idota and co-workers in 1997. Numerous in/ex situ studies suggest that SnO₂ stores Li⁺ through a conversion reaction and an alloying reaction. The difficulty of reversible conversion between Li₂ O and SnO₂ is a great obstacle limiting the utilization of SnO₂ with high theoretical capacity of 1494 mA h g^-1 . Thus, enhancing the reversibility of the conversion reaction has become the research emphasis in recent years. Here, taking SnO₂ as a typical representative, the recent progress is summarized and insight into the reverse conversion reaction is elaborated. Promoting Li₂ O decomposition and maintaining high Sn/Li₂ O interface density are two effective approaches, which also provide implications for designing other metal oxide anodes. In addition, some in/ex situ characterizations focusing on the conversion reaction are emphatically introduced. This review, from the viewpoint of material design and advanced characterizations, aims to provide a comprehensive understanding and shed light on the development of reversible metal oxide electrodes.

Metaphosphate-Bridged Interface Boosts High-Performance Lithium Storage

Carbon materials with well-dispersed SnO_x particles exhibit excellent lithium-storage performance. However, the volume change of SnO_x and the weak interaction between SnO_x and carbon induce an unsteady SnO_x-C interface during the lithiation/delithiation process. This phenomenon results in enhanced charge transfer resistance and reduced electrical contact of active materials, which leads to low reversibility of tin oxidation, restricted capacity, sluggish kinetics, structural deterioration, and rapid capacity decay. Herein, tin oxide/carbon composites with a metaphosphate-bridged interface are synthesized to construct a robust interfacial contact between tin oxides and carbon. The metaphosphate group functions as a bridge between SnO_x and carbon and results in excellent electrochemical stability during the charge/discharge process, which is favorable for electrode structural integrity. The formation of the metaphosphate-bridged interface provides a steady transport channel for e^-/Li⁺ and thus improves the reversibility of the conversion reaction. The enhanced charge transfer and interaction can also boost the charge transfer between SnO_x and carbon, which leads to higher SnO_x utilization. Thus, the prepared P-SnO_x/C anode exhibits enhanced lithium-storage performance in terms of specific capacity, cycling stability, and rate performance.

Ionic liquids on oxide surfaces

Ionic liquids (ILs) supported on oxide surfaces are being investigated for numerous applications including catalysis, batteries, capacitors, transistors, lubricants, solar cells, corrosion inhibitors, nanoparticle synthesis and biomedical applications. The study of ILs with oxide surfaces presents challenges both experimentally and computationally. The interaction between ILs and oxide surfaces can be rather complex, with defects in the oxide surface playing a key role in the adsorption behaviour and resulting electronic properties. The choice of the cation/anion pair is also important and can influence molecular ordering and electronic properties at the interface. These controllable interfacial behaviours make ionic liquid/oxide systems desirable for a number of different technological applications as well as being utilised for nanoparticle synthesis. This topical review aims to bring together recent experimental and theoretical work on the interaction of ILs with oxide surfaces, including TiO₂, ZnO, Al₂O₃, SnO₂and transition metal oxides. It focusses on the behaviour of ILs at model single crystal surfaces, the interaction between ILs and nanoparticulate oxides, and their performance in prototype devices.

Microstructural evolution in self-catalyzed GaAs nanowires during in-situ TEM study

The microstructural evolutions in self-catalyzed GaAs nanowires (NWs) were investigated by using in situ heating transmission electron microscopy (TEM). The morphological changes of the self-catalyst metal gallium (Ga) droplet, the GaAs NWs, and the atomic behavior at the interface between the self-catalyst metal gallium and GaAs NWs were carefully studied by analysis of high-resolution TEM images. The microstructural change of the Ga-droplet/GaAs-NWs started at a low temperature of ∼200 °C. Formation and destruction of atomic layers were observed at the Ga/GaAs interface and slow depletion of the Ga droplet was detected in the temperature range investigated. Above 300 °C, the evolution process dramatically changed with time: The Ga droplet depleted rapidly and fast growth of zinc-blende (ZB) GaAs structures were observed in the droplet. The Ga droplet was completely removed with time and temperature. When the temperature reached ∼600 °C, the decomposition of GaAs was detected. This process began in the wurtzite (WZ) structure and propagated to the ZB structure. The morphological and atomistic behaviors in self-catalyzed GaAs NWs were demonstrated based on thermodynamic considerations, in addition to the effect of the incident electron beam in TEM. Finally, GaAs decomposition was demonstrated in terms of congruent vaporization.

In Situ TEM Study on Conversion-Type Electrodes for Rechargeable Ion Batteries

Conversion-type materials have been considered as potentially high-energy-density alternatives to commercially dominant intercalation-based electrodes for rechargeable ion batteries and have attracted tremendous research effort to meet the performance for viable energy-storage technologies. In situ transmission electron microscopy (TEM) has been extensively employed to provide mechanistic insights into understanding the behavior of battery materials. Noticeably, a great portion of previous in situ TEM studies has been focused on conversion-type materials, but a dedicated review for this group of materials is missing in the literature. Herein, recent developments of in situ TEM techniques for investigation of dynamic phase transformation and associated structural, morphological, and chemical evolutions during conversion reactions with alkali ions in secondary batteries are comprehensively summarized. The materials of interest broadly cover metal oxides, chalcogenides, fluorides, phosphides, nitrides, and silicates with specific emphasis on spinel metal oxides and recently emerged 2D metal chalcogenides. Special focus is placed on the scientific findings that are uniquely obtained by in situ TEM to address fundamental questions and practical issues regarding phase transformation, structural evolution, electrochemical redox, reaction mechanism, kinetics, and degradation. Critical challenges and perspectives are discussed for advancing new knowledge that can bridge the gap between prototype materials and real-world applications.

Unveiling the Complex Redox Reactions of SnO2 in Li-Ion Batteries Using Operando X-ray Photoelectron Spectroscopy and In Situ X-ray Absorption Spectroscopy

We experimentally determine the redox reactions during (de-)lithiation of the SnO₂ working electrode cycled in (Li₂S)₃-P₂S₅ solid electrolyte by combining operando X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy. Specifically, we have accurately determined the composition changes in the SnO₂ working electrode upon cycling and identified the onset voltage formation of the various phases. Starting from the open-circuit potential, we find that, on lithiation, the Sn M-edge absorption spectra reveal unequivocally the formation of SnO_x (x ≤ 1) and Li₂SnO₃ already at a potential of 1.6 V vs Li⁺/Li, while Sn 3d/Sn 4d, O 1s, and Li 1s core-level spectra show the formation of Sn⁰ and Li₂O along the first potential plateau at 0.8 V vs Li⁺/Li and of Li₈SnO₆ at lower potentials. Below 0.6 V vs Li⁺/Li, an alloying reaction takes place until the end of the lithiation process at 0.05 V vs Li⁺/Li, as shown by the formation of Li_xSn. During delithiation, both the conversion and alloying reactions are found to be partially reversible, starting by the re-formation of Sn⁰ at 0.3 V vs Li⁺/Li and followed by the re-formation of Li₈SnO₆ and SnO_x above 0.5 V vs Li⁺/Li. The conversion and alloying reactions are found to overlap during both lithiation and delithiation. Finally, we validate the theoretical prediction for the SnO₂ conversion and alloy (de-)lithiation reactions and clarify the open questions about their reaction mechanism.

Translation Initiation Factor eIF4E Positively Modulates Conidiogenesis, Appressorium Formation, Host Invasion and Stress Homeostasis in the Filamentous Fungi Magnaporthe oryzae

Translation initiation factor eIF4E generally mediates the recognition of the 5'cap structure of mRNA during the recruitment of the ribosomes to capped mRNA. Although the eIF4E has been shown to regulate stress response in Schizosaccharomyces pombe positively, there is no direct experimental evidence for the contributions of eIF4E to both physiological and pathogenic development of filamentous fungi. We generated Magnaporthe oryzae eIF4E (MoeIF4E3) gene deletion strains using homologous recombination strategies. Phenotypic and biochemical analyses of MoeIF4E3 defective strains showed that the deletion of MoeIF4E3 triggered a significant reduction in growth and conidiogenesis. We also showed that disruption of MoeIF4E3 partially impaired conidia germination, appressorium integrity and attenuated the pathogenicity of ΔMoeif4e3 strains. In summary, this study provides experimental insights into the contributions of the eIF4E3 to the development of filamentous fungi. Additionally, these observations underscored the need for a comprehensive evaluation of the translational regulatory machinery in phytopathogenic fungi during pathogen-host interaction progression.

In Situ Electrochemical Study of Na-O2/CO2 Batteries in an Environmental Transmission Electron Microscope

Metal-air batteries are potential candidates for post-lithium energy storage devices due to their high theoretical energy densities. However, our understanding of the electrochemistry of metal-air batteries is still in its infancy. Herein we report in situ studies of Na-O₂/CO₂ (O₂ and CO₂ mixture) and Na-O₂ batteries with either carbon nanotubes (CNTs) or Ag nanowires as the air cathode medium in an advanced aberration corrected environmental transmission electron microscope. In the Na-O₂/CO₂-CNT nanobattery, the discharge reactions occurred in two steps: (1) 2Na⁺ + 2e^- + O₂ → Na₂O₂; (2) Na₂O₂+ CO₂ → Na₂CO₃ + O₂; concurrently a parasitic Na plating reaction took place. The charge reaction proceeded via (3) 2Na₂CO₃ + C → 4Na⁺ + 3CO₂ + 4e^-. In the Na-O₂/CO₂-Ag nanobattery, the discharge reactions were essentially the same as those for the Na-O₂/CO₂-CNT nanobattery; however, the charge reaction in the former was very sluggish, suggesting that direct decomposition of Na₂CO₃ is difficult. In the Na-O₂ battery, the discharge reaction occurred via reaction 1, but the reverse reaction was very difficult, indicating the sluggish decomposition of Na₂O₂. Overall the Na-O₂/CO₂-CNT nanobattery exhibited much better cyclability and performance than the Na-O₂/CO₂-Ag and the Na-O₂-CNT nanobatteries, underscoring the importance of carbon and CO₂ in facilitating the Na-O₂ nanobatteries. Our study provides important understanding of the electrochemistry of the Na-O₂/CO₂ and Na-O₂ nanobatteries, which may aid the development of high performance Na-O₂/CO₂ and Na-O₂ batteries for energy storage applications.

Stress-resilient electrode materials for lithium-ion batteries: strategies and mechanisms

Next-generation high-performance lithium-ion batteries (LIBs) with high energy and power density, long cycle life and uncompromising safety standards require new electrode materials beyond conventional intercalation compounds. However, these materials face a tradeoff between the high capacity and stable cycling because more Li stored in the materials also brings instability to the electrode. Stress-resilient electrode materials are the solution to balance this issue, where the decoupling of strong chemomechanical effects on battery cycling is a prerequisite. This review covers the (de)lithiation behaviors of the alloy and conversion-type anodes and their stress mitigation strategies. We highlight the reaction and degradation mechanisms down to the atomic scale revealed by in situ methods. We also discuss the implications of these mechanistic studies and comment on the effectiveness of the electrode structural and chemical designs that could potentially enable the commercialization of the next generation LIBs based on high-capacity anodes.

A Nano-Rattle SnO2@carbon Composite Anode Material for High-Energy Li-ion Batteries by Melt Diffusion Impregnation

The huge volume expansion in Sn-based alloy anode materials (up to 360%) leads to a dramatic mechanical stress and breaking of particles, resulting in the loss of conductivity and thereby capacity fading. To overcome this issue, SnO₂@C nano-rattle composites based on <10 nm SnO₂ nanoparticles in and on porous amorphous carbon spheres were synthesized using a silica template and tin melting diffusion method. Such SnO₂@C nano-rattle composite electrodes provided two electrochemical processes: a partially reversible process of the SnO₂ reduction to metallic Sn at 0.8 V vs. Li⁺/Li and a reversible process of alloying/dealloying of Li_xSn_y at 0.5 V vs. Li⁺/Li. Good performance could be achieved by controlling the particle sizes of SnO₂ and carbon, the pore size of carbon, and the distribution of SnO₂ nanoparticles on the carbon shells. Finally, the areal capacity of SnO₂@C prepared by the melt diffusion process was increased due to the higher loading of SnO₂ nanoparticles into the hollow carbon spheres, as compared with Sn impregnation by a reducing agent.

Intercalating Sn/Fe Nanoparticles in Compact Carbon Monolith for Enhanced Lithium Ion Storage

Given its high-capacity of multielectron (de-)lithiation, SnO2 is deemed as a competitive anode substance to tackle energy density restrictions of low-theoretical-capacity traditional graphite. However, its pragmatic adhibition seriously encounters poor initial coulombic efficiency from irreversible Li2O formation and drastic volume change during repeated charge/discharge. Here, an applicable gel pyrolysis methodology establishes a SnO2/Fe2O3 intercalated carbon monolith as superior anode materials for Li ion batteries to effectively surmount problems of SnO2. Its bulk-like, micron-sized, compact, and non-porous structures with low area surfaces (14.2 m2 g−1) obviously increase the tap density without compromising the transport kinetics, distinct from myriad hierarchically holey metal/carbon materials recorded till date. During the long-term Li+ insertion/extraction, the carbon matrix not only functions as a stress management framework to alleviate the stress intensification on surface layers, enabling the electrode to retain its morphological/mechanic integrity and yielding a steady solid electrolyte interphase film, but also imparts very robust connection to stop SnO2 from coarsening/losing electric contact, facilitating fast electrolyte infiltration and ion/electron transfer. Besides, the closely contacted and evenly distributed Fe2O3/SnO2 nanoparticles supply additional charge-transfer driving force, thanks to a built-in electric field. Benefiting from such virtues, the embedment of binary metal oxides in the dense carbons enhances initial Coulombic efficiency up to 67.3%, with an elevated reversible capacity of 726 mAh/g at 0.2 A/g, a high capacity retention of 84% after 100 cycles, a boosted rate capability between 0.2 and 3.2 A g−1, and a stable cycle life of 466 mAh/g over 200 cycles at 1 A g−1. Our scenario based upon this unique binary metal-in-carbon sandwich compact construction to achieve the stress regulation and the so-called synergistic effect between metals or metal oxides and carbons is economically effective and tractable enough to scale up the preparation and can be rifely employed to other oxide anodes for ameliorating their electrochemical properties.

Facile synthesis of SnO2@carbon nanocomposites for lithium-ion batteries

SnO₂@C nanocomposite nanostructure approach is demonstrated, which confers shielding for volume expansion because of carbon. The SnO₂@C nanocomposite anode exhibits superior cycling stability and rate capability due to the stable electrode structure.

Tin Oxide Based Nanomaterials and Their Application as Anodes in Lithium-Ion Batteries and Beyond

Herein, recent progress in the field of tin oxide (SnO2 )-based nanosized and nanostructured materials as conversion and alloying/dealloying-type anodes in lithium-ion batteries and beyond (sodium- and potassium-ion batteries) is briefly discussed. The first section addresses the importance of the initial SnO2 micro- and nanostructure on the conversion and alloying/dealloying reaction upon lithiation and its impact on the microstructure and cyclability of the anodes. A further section is dedicated to recent advances in the fabrication of diverse 0D to 3D nanostructures to overcome stability issues induced by large volume changes during cycling. Additionally, the role of doping on conductivity and synergistic effects of redox-active and -inactive dopants on the reversible lithium-storage capacity and rate capability are discussed. Furthermore, the synthesis and electrochemical properties of nanostructured SnO2 /C composites are reviewed. The broad research spectrum of SnO2 anode materials is finally reflected in a brief overview of recent work published on Na- and K-ion batteries.

Review of Recent Development of In Situ/Operando Characterization Techniques for Lithium Battery Research

The increasing demands of energy storage require the significant improvement of current Li-ion battery electrode materials and the development of advanced electrode materials. Thus, it is necessary to gain an in-depth understanding of the reaction processes, degradation mechanism, and thermal decomposition mechanisms under realistic operation conditions. This understanding can be obtained by in situ/operando characterization techniques, which provide information on the structure evolution, redox mechanism, solid-electrolyte interphase (SEI) formation, side reactions, and Li-ion transport properties under operating conditions. Here, the recent developments in the in situ/operando techniques employed for the investigation of the structural stability, dynamic properties, chemical environment changes, and morphological evolution are described and summarized. The experimental approaches reviewed here include X-ray, electron, neutron, optical, and scanning probes. The experimental methods and operating principles, especially the in situ cell designs, are described in detail. Representative studies of the in situ/operando techniques are summarized, and finally the major current challenges and future opportunities are discussed. Several important battery challenges are likely to benefit from these in situ/operando techniques, including the inhomogeneous reactions of high-energy-density cathodes, the development of safe and reversible Li metal plating, and the development of stable SEI.

Disruption of putative short-chain acyl-CoA dehydrogenases compromised free radical scavenging, conidiogenesis, and pathogenesis of Magnaporthe oryzae

Short-chain acyl-CoA dehydrogenase (Scad) mediated β-oxidation serves as the fastest route for generating essential energies required to support the survival of organisms under stress or starvation. In this study, we identified three putative SCAD genes in the genome of the globally destructive rice blast pathogen Magnaporthe oryzae, named as MoSCAD1, MoSCAD2, and MoSCAD3. To elucidate their function, we deployed targeted gene deletion strategy to investigate individual and the combined influence of MoSCAD genes on growth, stress tolerance, conidiation and pathogenicity of the rice blast fungus. First, localization and co-localization results obtained from this study showed that MoScad1 localizes to the endoplasmic reticulum (ER), MoScad2 localizes exclusively to the mitochondria while MoScad3 partially localizes to the mitochondria and peroxisome at all developmental stages of M. oryzae. Results obtained from this investigation showed that the deletion of MoSCAD1 and MoSCAD2 caused a minimal but significant reduction in the growth of ΔMoscad1 and ΔMoscad2 strains, while, growth characteristics exhibited by the ΔMoscad3 strain was similar to the wild-type strain. Furthermore, we observed that deletion of MoSCAD2 resulted in drastic reduction in conidiation, delayed conidia germination, triggered the development of abnormal appressorium and suppressed host penetration and colonization efficiencies of the ΔMoscad1 strain. This study provides first material evidence confirming the possible existence of ER β-oxidation pathway in M. oryzae. We also infer that mitochondria β-oxidation rather than peroxisomal and ER β-oxidation play an essential role in the vegetative growth, conidiation, appressorial morphogenesis and progression of pathogenesis in M. oryzae.

Monodisperse tin nanoparticles and hollow tin oxide nanospheres as anode materials for high performance lithium ion batteries

Monodisperse Sn nanoparticles and hollow/amorphous SnO_x nanospheres are prepared via a facile colloidal method, and they exhibit good electrochemical performances as anode materials in lithium ion batteries.

Yolk–shell structured SnSe as a high-performance anode for Na-ion batteries

Yolk–shell structured SnSe nanoparticles have been investigated as anode materials in Na-ion batteries for the first time, and exhibit excellent Na⁺ storage performance.

Atomic-Scale Observation of Electrochemically Reversible Phase Transformations in SnSe2 Single Crystals

2D materials have shown great promise to advance next-generation lithium-ion battery technology. Specifically, tin-based chalcogenides have attracted widespread attention because lithium insertion can introduce phase transformations via three types of reactions-intercalation, conversion, and alloying-but the corresponding structural changes throughout these processes, and whether they are reversible, are not fully understood. Here, the first real-time and atomic-scale observation of reversible phase transformations is reported during the lithiation and delithiation of SnSe₂ single crystals, using in situ high-resolution transmission electron microscopy complemented by first-principles calculations. Lithiation proceeds sequentially through intercalation, conversion, and alloying reactions (SnSe₂ → Li_x SnSe₂ → Li₂ Se + Sn → Li₂ Se + Li₁₇ Sn₄ ) in a manner that maintains structural and crystallographic integrity, whereas delithiation forms numerous well-aligned SnSe₂ nanodomains via a homogeneous deconversion process, but gradually loses the coherent orientation in subsequent cycling. Furthermore, alloying and dealloying reactions cause dramatic structural reorganization and thereby consequently reduce structural stability and electrochemical cyclability, which implies that deep discharge for Sn chalcogenide electrodes should be avoided. Overall, the findings elucidate atomistic lithiation and delithiation mechanisms in SnSe₂ with potential implications for the broader class of 2D metal chalcogenides.

Single-Nanostructured Electrochemical Detection for Intrinsic Mechanism of Energy Storage: Progress and Prospect

Energy storage appliances are active by means of accompanying components for renewable energy resources that play a significant role in the advanced world. To further improve the electrochemical properties of the lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and lithium-sulfur (Li-S) batteries, the electrochemical detection of the intrinsic mechanisms and dynamics of electrodes in batteries is required to guide the rational design of electrodes. Thus, several researches have conducted in situ investigations and real-time observations of electrode evolution, ion diffusion pathways, and side reactions during battery operation at the nanoscale, which are proven to be extremely insightful. However, the in situ cells are required to be compatible for electrochemical tests and are therefore often challenging to operate. In the past few years, tremendous progresses have been made with novel and more advanced in situ electrochemical detection methods for mechanism studies, especially single-nanostructured electrodes. Herein, a comprehensive review of in situ techniques based on single-nanostructured electrodes for studying electrodes changes in LIBs, SIBs, and Li-S batteries, including structure evolution, phase transition, interface formation, and the ion diffusion pathway is provided, which is instructive and meaningful for the optimization of battery systems.

A core-shell structure of polydopamine-coated phosphorus-carbon nanotube composite for high-performance sodium-ion batteries

The electrochemical performance of red phosphorus is severely limited by its low electrical conductivity and large-volume-expansion-induced material pulverization and continuous solid electrolyte interphase (SEI) growth. Conductive coating has been regarded as an ideal approach to address these issues. In this paper, we design a rational strategy to improve the sodium storage performance of red phosphorus by in situ coating of a polydopamine layer on phosphorus-carbon nanotube hybrid (P-CNT@PD) via a self-polymerization of dopamine under weak base conditions. The in situ generated PD coating can provide an elastic buffer for accommodating the volume change of active materials and prevent their direct contact with the electrolyte. Due to the conductive and elastic PD coating, the P-CNT@PD composite presents a high rate capacity (1060 mA h g-1 at the second discharge and 730 mA h g-1 after 2000 cycles at 2.6 A g-1) and excellent cycling stability (470 mA h g-1 after 5000 cycles at 5.2 A g-1) as an anode for sodium ion batteries. This facile and scalable synthesis route provides a favorable approach for the mass production of high performance electrodes for sodium ion batteries.

Atomic-Scale Probing of Reversible Li Migration in 1T-V1+ xSe2 and the Interactions between Interstitial V and Li

Ionic doping and migration in solids underpins a wide range of applications including lithium ion batteries, fuel cells, resistive memories, and catalysis. Here, by in situ transmission electron microscopy technique we directly track the structural evolution during Li ions insertion and extraction in transition metal dichalcogenide 1T-V_{1+ x}Se₂ nanostructures which feature spontaneous localized superstructures due to the periodical interstitial V atoms within the van der Waals interlayers. We find that lithium ion migration destroys the cationic orderings and leads to a phase transition from superstructure to nonsuperstructure. This phase transition is reversible, that is, the superstructure returns back after extraction of lithium ion from Li _yV_{1+ x}Se₂. These findings provide valuable insights into understanding and controlling the structure and properties of 2D materials by general ionic and electric doping.

Emerging tools for studying single entity electrochemistry

Electrochemistry studies charge transfer and related processes at various microscopic structures (atomic steps, islands, pits and kinks on electrodes), and mesoscopic materials (nanoparticles, nanowires, viruses, vesicles and cells) made by nature and humans, involving ions and molecules. The traditional approach measures averaged electrochemical quantities of a large ensemble of these individual entities, including the microstructures, mesoscopic materials, ions and molecules. There is a need to develop tools to study single entities because a real system is usually heterogeneous, e.g., containing nanoparticles with different sizes and shapes. Even in the case of "homogeneous" molecules, they bind to different microscopic structures of an electrode, assume different conformations and fluctuate over time, leading to heterogeneous reactions. Here we highlight some emerging tools for studying single entity electrochemistry, discuss their strengths and weaknesses, and provide personal views on the need for tools with new capabilities for further advancing single entity electrochemistry.

Facile synthesis of hierarchical CNF/SnO2/Ni nanostructures via self-assembly process as anode materials for lithium ion batteries

Hierarchical carbon nanofibre (CNF)/SnO₂/Ni nanostructures of graphitized carbon nanofibres and SnO₂ nanocrystallines and Ni nanocrystallines have been prepared via divalent tin-alginate assembly on polyacrylonitrile (PAN) fibres, controlled pyrolysis and ball milling. Fabrication is implemented in three steps: (1) formation of a tin-alginate layer on PAN fibres by coating sodium alginate on PAN in a water medium followed by polycondensation in SnCl₂ solution; (2) heat treatment at 450°C in a nitrogen atmosphere; (3) ball milling the mixture of CNF/SnO₂ fibres and Ni powder. The CNF/SnO₂/Ni nanocomposite exhibits good lithium ion storage capacity and cyclability, providing a facile and low-cost approach for the large-scale preparation of anode materials for lithium ion batteries.

In situ analytical techniques for battery interface analysis

Interface is a key to high performance and safe lithium-ion batteries or lithium batteries.

In Situ High-Resolution Transmission Electron Microscopy (TEM) Observation of Sn Nanoparticles on SnO2 Nanotubes Under Lithiation

We trace Sn nanoparticles (NPs) produced from SnO2 nanotubes (NTs) during lithiation initialized by high energy e-beam irradiation. The growth dynamics of Sn NPs is visualized in liquid electrolytes by graphene liquid cell transmission electron microscopy. The observation reveals that Sn NPs grow on the surface of SnO2 NTs via coalescence and the final shape of agglomerated NPs is governed by surface energy of the Sn NPs and the interfacial energy between Sn NPs and SnO2 NTs. Our result will likely benefit more rational material design of the ideal interface for facile ion insertion.

Direct Realization of Complete Conversion and Agglomeration Dynamics of SnO2 Nanoparticles in Liquid Electrolyte

The conversion reaction is important in lithium-ion batteries because it governs the overall battery performance, such as initial Coulombic efficiency, capacity retention, and rate capability. Here, we have demonstrated in situ observation of the complete conversion reaction and agglomeration of nanoparticles (NPs) upon lithiation by using graphene liquid cell transmission electron microscopy. The observation reveals that the Sn NPs are nucleated from the surface of SnO₂, followed by merging with each other. We demonstrate that the agglomeration has a stepwise process, including rotation of a NP, formation of necks, and subsequent merging of individual NPs.

Direct Studies on the Lithium-Storage Mechanism of Molybdenum Disulfide

Transition metal sulfides are regarded as a type of high-performance anode materials for lithium ion batteries (LIBs). However, their electrochemical process and lithium-storage mechanism are complicated and remain controversial. This work is intended to give the direct observation on the electrochemical behavior and find out the lithium-storage mechanism of molybdenum disulfide (MoS₂) using in situ transmission electron microscopy (TEM). We find that single-crystalline MoS₂ nanosheets convert to Mo nanograins (~2 nm) embedded in Li₂S matrix after the first full lithiation. After the delithiation, the Mo nanograins and Li₂S transform to a large number of lamellar MoS₂ nanocrystals. The discharge-charge cycling of MoS₂ in LIBs is found to be a fully reversible conversion between MoS₂ and Mo/Li₂S rather than the electrochemical conversion between S and Li₂S proposed by many researchers. The in situ real-time characterization results give direct evidence and profound insights into the lithium-storage mechanism of MoS₂ as anode in LIBs.

Stabilizing the Nanostructure of SnO2 Anodes by Transition Metals: A Route to Achieve High Initial Coulombic Efficiency and Stable Capacities for Lithium Storage

To dramatically stabilize the nanostructure of Sn and achieve ultrahigh reversibility of conversion reactions in lithiated SnO₂ , a series of SnO₂ -transition metal-graphite ternary nanocomposites are produced by ball milling, demonstrating high initial Coulombic efficiencies up to 88.6%, high reversible capacity (>700 mAh g^-1 at 2 A g^-1 ), and ultralong cycling life (90.3% of capacity retention after 1300 cycles).

Polymer-Templated Formation of Polydopamine-Coated SnO2 Nanocrystals: Anodes for Cyclable Lithium-Ion Batteries

Well-controlled nanostructures and a high fraction of Sn/Li₂ O interface are critical to enhance the coulombic efficiency and cyclic performance of SnO₂ -based electrodes for lithium-ion batteries (LIBs). Polydopamine (PDA)-coated SnO₂ nanocrystals, composed of hundreds of PDA-coated "corn-like" SnO₂ nanoparticles (diameter ca. 5 nm) decorated along a "cob", addressed the irreversibility issue of SnO₂ -based electrodes. The PDA-coated SnO₂ were crafted by capitalizing on rationally designed bottlebrush-like hydroxypropyl cellulose-graft-poly (acrylic acid) (HPC-g-PAA) as a template and was coated with PDA to construct a passivating solid-electrolyte interphase (SEI) layer. In combination, the corn-like nanostructure and the protective PDA coating contributed to a PDA-coated SnO₂ electrode with excellent rate capability, superior long-term stability over 300 cycles, and high Sn→SnO₂ reversibility.

Unlocking the potential of SnS2: Transition metal catalyzed utilization of reversible conversion and alloying reactions

The alloying-dealloying reactions of SnS₂ proceeds with the initial conversion reaction of SnS₂ with lithium that produces Li₂S. Unfortunately, due to the electrochemical inactivity of Li₂S, the conversion reaction of SnS₂ is irreversible, which significantly limit its potential applications in lithium-ion batteries. Herein, a systematic understanding of transition metal molybdenum (Mo) as a catalyst in SnS₂ anode is presented. It is found that Mo catalyst is able to efficiently promote the reversible conversion of Sn to SnS₂. This leads to the utilization of both conversion and alloying reactions in SnS₂ that greatly increases lithium storage capability of SnS₂. Mo catalyst is introduced in the form of MoS₂ grown directly onto self-assembled vertical SnS₂ nanosheets that anchors on three-dimensional graphene (3DG) creating a hierarchal nanostructured named as SnS₂/MoS₂/3DG. The catalytic effect results in a significantly enhanced electrochemical properties of SnS₂/MoS₂/3DG; a high initial Coulombic efficiency (81.5%) and high discharge capacities of 960.5 and 495.6 mA h g⁻¹ at current densities of 50 and 1000 mA g⁻¹, respectively. Post cycling investigations using ex situ TEM and XPS analysis verifies the successful conversion reaction of SnS₂ mediated by Mo. The successful integration of catalyst on alloying type metal sulfide anode creates a new avenue towards high energy density lithium anodes.

A HOPS Protein, MoVps41, Is Crucially Important for Vacuolar Morphogenesis, Vegetative Growth, Reproduction and Virulence in Magnaporthe oryzae

The homotypic fusion and protein sorting protein complex (HOPS) is the first known tether complex identified in the endocytic system that plays a key role in promoting homotypic vacuolar fusion, vacuolar biogenesis and trafficking in a wide range of organisms, including plant and fungi. However, the exact influence of the HOPS complex on growth, reproduction and pathogenicity of the economically destructive rice blast fungus has not been investigated. In this study, we identified M. oryzae vacuolar protein sorting 41 (MoVps41) an accessory subunit of HOPS complex and used targeted gene deletion approach to evaluate its contribution to growth, reproduction and infectious life cycle of the rice blast fungus. Corresponding results obtained from this study showed that MoVps41 is required for optimum vegetative development of M. oryzae and observed that MoVps41 deletion mutant displayed defective vegetative growth. Our investigation further showed that MoVps41 deletion triggered vacuolar fragmentation, compromised membrane integrity and pathogenesis of the ΔMovps41 mutant. Our studies also showed for the first time that MoVps41 plays an essential role in the regulation of sexual and asexual reproduction of M. oryzae. In summary, our study provides insight into how MoVps41 mediated vacuolar fusion and biogenesis influences reproduction, pathogenesis, and vacuolar integrity in M. oryzae and also underscores the need to holistically investigate the HOPS complex in rice blast pathogen.

Multi-yolk-shell SnO2/Co3Sn2@C Nanocubes with High Initial Coulombic Efficiency and Oxygen Reutilization for Lithium Storage

The challenging problems of SnO₂ anode material for lithium ion batteries are the poor electronic conductivity and the low oxygen reutilization due to the irreversibility of Li₂O generated in the initial discharge leading to a theoretical initial Coulombic efficiency (ICE) of only 52.4%. Different from these strategies, this work proposes a novel strategy to level up the oxygen reutilization in SnO₂ by introducing Co₃Sn₂ nanoalloys which can release Co atoms to reversibly react with Li₂O instead. According to this protocol, multi-yolk-shell SnO₂/Co₃Sn₂@C nanocubes are designed and successfully prepared using hollow CoSn(OH)₆ nanocubes as precursors followed a hydrothermal carbon coating and calcination treatment. The unique multi-yolk-shell nanostructure offers adequate breathing space for the volumetric deformation during long-term cycling. Moreover, the removal of Li₂O allows a high electronic conductivity and resultant rate performance. As a result, the efficient reutilization of oxygen enables a high ICE of 71.7% and a reversible capacity of 1003 mA h g^-1 after 200 cycles at 100 mA g^-1. Cyclic voltammetry, cycling performance at different voltage windows, and X-ray photoelectron spectroscopy confirm the proposed mechanism. This strategy employing oxygen-poor metals or alloys provides a novel approach to enhance the oxygen reutilization in SnO₂ for higher reversibility.

Interfacial Stability of Li Metal-Solid Electrolyte Elucidated via in Situ Electron Microscopy

Despite their different chemistries, novel energy-storage systems, e.g., Li-air, Li-S, all-solid-state Li batteries, etc., face one critical challenge of forming a conductive and stable interface between Li metal and a solid electrolyte. An accurate understanding of the formation mechanism and the exact structure and chemistry of the rarely existing benign interfaces, such as the Li-cubic-Li_7-3xAl_xLa₃Zr₂O₁₂ (c-LLZO) interface, is crucial for enabling the use of Li metal anodes. Due to spatial confinement and structural and chemical complications, current investigations are largely limited to theoretical calculations. Here, through an in situ formation of Li-c-LLZO interfaces inside an aberration-corrected scanning transmission electron microscope, we successfully reveal the interfacial chemical and structural progression. Upon contact with Li metal, the LLZO surface is reduced, which is accompanied by the simultaneous implantation of Li⁺, resulting in a tetragonal-like LLZO interphase that stabilizes at an extremely small thickness of around five unit cells. This interphase effectively prevented further interfacial reactions without compromising the ionic conductivity. Although the cubic-to-tetragonal transition is typically undesired during LLZO synthesis, the similar structural change was found to be the likely key to the observed benign interface. These insights provide a new perspective for designing Li-solid electrolyte interfaces that can enable the use of Li metal anodes in next-generation batteries.

Kinetic Phase Evolution of Spinel Cobalt Oxide during Lithiation

Spinel cobalt oxide has been proposed to undergo a multiple-step reaction during the electrochemical lithiation process. Understanding the kinetics of the lithiation process in this compound is crucial to optimize its performance and cyclability. In this work, we have utilized a low-angle annular dark-field scanning transmission electron microscopy method to visualize the dynamic reaction process in real time and study the reaction kinetics at different rates. We show that the particles undergo a two-step reaction at the single-particle level, which includes an initial intercalation reaction followed by a conversion reaction. At low rates, the conversion reaction starts after the intercalation reaction has fully finished, consistent with the prediction of density functional theoretical calculations. At high rates, the intercalation reaction is overwhelmed by the subsequently nucleated conversion reaction, and the reaction speeds of both the intercalation and conversion reactions are increased. Phase-field simulations show the crucial role of surface diffusion rates of lithium ions in controlling this process. This work provides microscopic insights into the reaction dynamics in non-equilibrium conditions and highlights the effect of lithium diffusion rates on the overall reaction homogeneity as well as the performance.