In Operando X-ray diffraction and transmission X-ray microscopy of lithium sulfur batteries

Rechargeable lithium-sulfur (Li-S) batteries hold great potential for high-performance energy storage systems because they have a high theoretical specific energy, low cost, and are eco-friendly. However, the structural and morphological changes during electrochemical reactions are still not well understood. In this Article, these changes in Li-S batteries are studied in operando by X-ray diffraction and transmission X-ray microscopy. We show recrystallization of sulfur by the end of the charge cycle is dependent on the preparation technique of the sulfur cathode. On the other hand, it was found that crystalline Li(2)S does not form at the end of discharge for all sulfur cathodes studied. Furthermore, during cycling the bulk of soluble polysulfides remains trapped within the cathode matrix. Our results differ from previous ex situ results. This highlights the importance of in operando studies and suggests possible strategies to improve cycle life.     

Monitoring electrode/electrolyte interfaces of Li-ion batteries under working conditions: A surface-enhanced Raman spectroscopic study on LiCoO2 composite cathodes

Lithium-ion batteries are commonly used for electrical energy storage in portable devices and are promising systems for large-scale energy storage. However, their application is still limited due to electrode degradation and stability issues. To enhance the fundamental understanding of electrode degradation, we report on the Raman spectroscopic characterization of LiCoO₂ cathode materials of working Li-ion batteries. To facilitate the spectroscopic analysis of the solid electrolyte interface (SEI), we apply in situ surface-enhanced Raman spectroscopy under battery working conditions by using Au nanoparticles coated with a thin SiO₂ layer (Au@SiO₂). We observe a surface-enhanced Raman signal of Li₂CO₃ at 1090 cm⁻¹ during electrochemical cycling as an intermediate. Its formation/decomposition highlights the role of Li₂CO₃ as a component of the SEI on LiCoO₂ composite cathodes. Our results demonstrate the potential of Raman spectroscopy to monitor electrode/electrolyte interfaces of lithium-ion batteries under working conditions thus allowing relations between electrochemical performance and structural changes to be established.     

Mechanical degradation of electrode materials within single particle model in Li-ion batteries for electric vehicles

Mechanical degradation of electrode materials, in the form of particle cracking and fragmentation, disintegration, fracturing, and loss in contact between current collectors and the active electrode materials, can affect or deteriorate the performance of Li-ion batteries dramatically and even lead to the battery failure in electric vehicle. This paper firstly built a single particle model (SPM) based upon kinetics of electrochemical reactions. Then the Li-ion concentration, evolution of diffusion induced stresses within the SPM under potentiostatic or galvanostatic operating conditions were analyzed by utilizing a mathematical method. Next, evolution of stresses or strains in the SPM, at the core of relates with mechanical degradation of electrode materials, are elaborated in detail. Finally, surface and morphology of the electrodes dismantled from fresh and degraded cells after galvanostatic charge/discharge cycling have been analyzed to verify the hypothesis aforementioned by observing scanning electron microscopy and analyzing X-ray diffraction.     

锂电池电极过程的原位电化学原子力显微镜研究进展

随着人类对能源的使用与存储需求不断增加,高能量密度和高安全性能的二次锂电池体系正在被不断地开发与完善.深入理解充放电过程中锂电池内部电极/电解质界面的电化学过程以及微观反应机理,有利于指导电池材料的优化设计.原位电化学原子力显微镜将原子力显微镜的高分辨表界面分析优势与电化学反应装置相结合,能够在电池运行条件下实现对电极/电解质界面的原位可视化研究,并进一步从纳米尺度上揭示界面结构的演化规律与动力学过程.本文总结了原位电化学原子力显微镜在锂电池电极过程中的最新研究进展,主要包括基于转化型反应的正极过程、固体电解质中间相的动态演化以及固态电池界面演化与失效分析.     

Oxygenated interface on biomass burn tar balls determined by single particle scanning transmission X-ray microscopy

Carbonaceous particles originating from biomass burning can account for a large fraction of organic aerosols in a local environment. Presently, their composition, physical and chemical properties, as well as their environmental effects are largely unknown. Tar balls, a distinct type of highly spherical carbonaceous biomass burn particles, have been observed in a number of field campaigns. The Yosemite Aerosol Characterization Study that took place in summer 2002 occurred during an active fire season in the western United States; tar balls collected during this field campaign are described in this article. Scanning transmission X-ray microscopy and near-edge X-ray absorption fine structure spectroscopy are used to determine the shape, structure, and size-dependent chemical composition of approximately 150 individual spherical particles ranging in size from 0.15 to 1.2 mum. The elemental composition of tar balls is approximately 55% atomic carbon and approximately 45% atomic oxygen. Oxygen is present primarily as carboxylic carbonyls and oxygen-substituted alkyl (O-alkyl-C) functional groups, followed by moderate amounts of ketonic carbonyls. The observed chemical composition, density, and carbon functional groups are distinctly different from soot or black carbon and more closely resemble high molecular weight polymeric humic-like substances, which could account for their reported optical properties. A detailed examination of the carboxylic carbonyl and O-alkyl-C functional groups as a function of particle size reveals a thin oxygenated interface layer. The high oxygen content, as well as the presence of water-soluble carboxylic carbonyl groups, could account for the reported hygroscopic properties of tar balls. The presence of the oxygenated layer is attributed to atmospheric processing of biomass burn particles.     

A novel method for the in situ determination of concentration gradients in the electrolyte of Li-ion batteries

An electrochemical method has been developed for the in situ determination of concentration gradients in the electrolyte of sealed Li-ion batteries by measuring the potential difference between microreference electrodes. Formulas relating the concentration gradient and the potential difference between the microreference electrodes were derived from the Nernst-Planck equation. The concentration gradients in Li-ion batteries are theoretically and experimentally proven to be linear at steady state under galvanostatic charging and discharging conditions. Based on this finding, both the diffusion coefficient of the lithium ions in the electrolyte and the diffusion overpotential related to the concentration gradient have been calculated. It was found that the concentration gradient is proportional to the applied current over a wide current range and that the obtained diffusion coefficient of lithium ions is almost constant. For the batteries studied in this work, the diffusion overpotential is already noticeable at 0.30 A and the limiting current is estimated to be 1.1 A, corresponding to a C-rate of 3.7.     

In situ characterization of aluminum-containing mineral-microorganism aqueous suspensions using scanning transmission X-ray microscopy

In situ characterization of colloidal particles under hydrous conditions is one of the key requirements for understanding their state of aggregation and impact on the transport of pollutants in aqueous environments. Scanning transmission X-ray microscopy (STXM) is one of the few techniques that can satisfy this need by providing element- and chemical-state-specific 2-D maps at a spatial resolution better than 50 nm using soft X-rays from synchrotron radiation wiggler or undulator sources tuned to the absorption edges of different elements. X-ray absorption near-edge structure (XANES) spectra can also be collected simultaneously at a similar spatial resolution and can provide phase identification in many cases. In this study, we report STXM images and XANES spectroscopy measurements at or above the Al K-edge (E = 1559.6 eV) of various Al-containing minerals and synthetic oxides [alpha-Al2O3 (corundum), gamma-Al2O3, gamma-AlOOH (boehmite), alpha-Al(OH)3 (bayerite), KAl2(AlSi3O10)(OH)2 (muscovite), (Al,Mg)8(Si4O10)4(OH)8.nH2O (montmorillonite), and Mg6Al2(OH)16CO3.4H2O (hydrotalcite)] and demonstrate the capability of this spectromicroscopic tool to identify different Al-containing mineral colloids in multiphase mixtures in aqueous solution. We also demonstrate that STXM imaging at or above the C K-edge (E = 284.2 eV) and Al K-edge can provide unique information on the interactions between bacteria and Al-containing nanoparticles in aqueous suspensions. STXM images of a mixture of Caulobacter crescentus and montmorillonite and corundum particles just above the C and Al K-edges show that the mineral particles and bacteria are closely associated in aggregates, which is likely due to the binding of bacteria to clay and corundum particles by extracellular polysaccharides.     

LiCoO_2 electrode/electrolyte interface of Li-ion batteries investigated by electrochemical impedance spectroscopy

The storage behavior and the first delithiation of LiCoO2 electrode in 1 mol/L LiPF6-EC:DMC:DEC elec- trolyte were investigated by electrochemical impedance spectroscopy (EIS). It has found that, along with the increase of storage time, the thickness of SEI film increases, and some organic carbonate lithium compounds are formed due to spontaneous reactions occurring between the LiCoO2 electrode and the electrolyte. When electrode potential is changed from 3.8 to 3.95 V, the reversible breakdown of the resistive SEI film occurs, which is attributed to the reversible dissolution of the SEI film component. With the increase of electrode potential, the thickness of SEI film increases rapidly above 4.2 V, due to overcharge reactions. The inductive loop observed in impedance spectra of the LiCoO2 electrode in Li/LiCoO2 cells is attributed to the formation of a Li1-xCoO2/LiCoO2 concentration cell. Moreover, it has been demonstrated that the lithium-ion insertion-deinsertion in LiCoO2 hosts can be well described by both Langmuir and Frumkin insertion isotherms, and the symmetry factor of charge transfer has been evaluated at 0.5.     

In situ X-ray absorption spectroscopy of Sn species adsorbed on platinized platinum electrode in perchloric acid solution containing stannous ions

Journal of Solid State Electrochemistry - In situ X-ray absorption spectroscopy (XAS) was applied to investigate the Sn adlayer on platinized (pl-) Pt electrode in deaerated 0.2 M HClO4 solution...     

X-ray absorption spectroscopic study of LiCoO2 as the negative electrode of lithium-ion batteries.

Lithium cobalt oxide (LiCoO(2)) particles are modified using rotor blade grinding and re-annealing and used as the active electrode material versus lithium in the 3-0 V potential interval, in which a maximum capacity of 903 mA h g(-1) is achieved. X-ray absorption near edge structure spectra reveal the complete reduction of Co(3+) to Co metal at 0 V. Cell recharge leads to an incomplete reoxidation of cobalt. A maximum reversible capacity of 812 mA h g(-1) is obtained, although a poor capacity retention upon prolonged cycling may limit its application.     

XPS valence characterization of lithium salts as a tool to study electrode/electrolyte interfaces of Li-ion batteries

X-ray photoelectron valence spectra of lithium salts LiBF4, LiPF6, LiTFSI, and LiBETI have been recorded and analyzed by means of density functional theory (DFT) calculations, with good agreement between experimental and calculated spectra. The results of this study are used to characterize electrode/electrolyte interfaces of graphite negative electrodes in Li-ion batteries using organic carbonate electrolytes containing LiTFSI or LiBETI salts. By a combined X-ray photoelectron spectroscopy (XPS) core peaks/valence analysis, we identify the main constituents of the interface. Differences in the surface layers' composition can be evidenced, depending on whether LiTFSI or LiBETI is used as the lithium salt.     

Novel low temperature approaches for the eco-efficient synthesis of electrode materials for secondary Li-ion batteries

Hydrothermal/solvothermal reactions have been widely used over the years for the low temperature synthesis of inorganic compounds. New twists on such synthesis approaches were developed so as to prepare highly performing phosphate or silicate electrode materials at low cost. Herein we review the use of: (1) “Latent bases” to wisely monitor the reaction and (2) ionic liquids rather than water as reaction media to conduct the solvothermal process. The richness and versatility of such approaches towards the elaboration of a wide class of materials having controlled size and shape is highlighted. Ionothermal synthesis is shown to hold great promises for innovative inorganic synthesis.     

CoO nanorod arrays on carbon nanotube foams fabricated by reducing carbon dioxide as high-performance electrode materials for Li-ion batteries

Journal of Solid State Electrochemistry - We have successfully synthesized 3D carbon nanotube foams through a simple self-assembly method. Taking these carbon nanotube foams as substrates, we have...     

Recent progress in the application of in situ atomic force microscopy for rechargeable batteries

High energy density batteries are urgently required for sustainable life. The intrinsic understanding of the reaction mechanism at the interfaces is essential for the progress. In this short overview, recent advances in rechargeable batteries by in situ atomic force microscopy are summarized, providing nanoscale information on the solid product evolution and metal plating/stripping inside working batteries. Besides, the multifunctional imaging of the morphology along with mechanical and electrical properties can be achieved to assist further interfacial design. Extensive applications of in situ atomic force microscopy are encouraged to explore the electrochemical mechanism and advanced engineering.     

Time-resolved in situ small-angle X-ray scattering study of silica particle formation in nonionic water-in-oil microemulsions

The formation of silica particles by the ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) in the polyoxyethylene (5) nonylphenyl ether (NP-5)/cyclohexane/water microemulsion system was investigated by time-resolved small-angle X-ray scattering (SAXS). The SAXS data could be modeled as a combination of two species where one describes the silica-particle containing microemulsion droplets and the other the reverse droplets. The analysis allowed the determination of the evolution of the system of particles of silica and reverse droplets. A model of nucleation and growth of the silica particles is confirmed and the volume fraction versus time data for the silica particles is in agreement with first order kinetics with respect to TEOS concentration. Moreover to describe the long time evolution of the system, a correlation among the silica particles has been taken into account by introducing a structure factor with a local silica volume fraction eta = 0.1. This high local density is 2 orders of magnitude larger than the global silica fraction and can be explained in terms of depleting interaction.     

Revealing the conversion mechanism of CuO nanowires during lithiation-delithiation by in situ transmission electron microscopy

Being promising candidates for anodes in lithium-ion batteries (LIBs), transition metal oxide anodes utilizing the so-called conversion mechanism principle typically suffer from the severe capacity fading during the 1st cycle of lithiation-delithiation. Herein, we directly investigated these processes using an individual CuO nanowire anode and constructed a lithium ion battery (LIB) prototype within a transmission electron microscope.     

Recent progress on the recycling technology of Li-ion batteries

Lithium-ion batteries(LIBs)have been widely applied in portable electronic devices and electric vehicles.With the booming of the respective markets,a huge quantity of spent LIBs that typically use either LiFePO₄ or Li N_xCo_yMn_zO₂ cathode materials will be produced in the very near future,imposing significant pressure for the development of suitable disposal/recycling technologies,in terms of both environmental protection and resource reclaiming.In this review,we firstly do a comprehensive summary of the-state-of-art technologies to recycle Li N_xCo_yMn_zO₂ and LiFePO₄-based LIBs,in the aspects of pretreatment,hydrometallurgical recycling,and direct regeneration of the cathode materials.This closed-loop strategy for cycling cathode materials has been regarded as an ideal approach considering its economic benefit and environmental friendliness.Afterward,as for the exhausted anode materials,we focus on the utilization of exhausted anode materials to obtain other functional materials,such as graphene.Finally,the existing challenges in recycling the LiFePO₄ and Li N_xCo_yMn_zO₂ cathodes and graphite anodes for industrial-scale application are discussed in detail;and the possible strategies for these issues are proposed.We expect this review can provide a roadmap towards better technologies for recycling LIBs,shed light on the future development of novel battery recycling technologies to promote the environmental benignity and economic viability of the battery industry and pave way for the large-scale application of LIBs in industrial fields in the near future.     

Microdeformation behavior in nanotemplated epoxy thermosets: A study with in situ tensile deformation technique in transmission electron microscopy

Microdeformation behavior in nanostructured block copolymer‐toughened epoxy resins, or templated epoxy thermosets, was studied using an in situ tensile deformation technique performed directly in a transmission electron microscope. The observed microdeformation modes were found to correlate well with the macroscopic mechanical properties of the materials. In the order of decreasing macroscopic fracture toughness, the microdeformation modes were observed to change from large uniform plastic deformation over an extensive area, to localized plastic deformation bands, to little plastic deformation observed in the most brittle material. A similar trend was also observed when samples of the same material were tested at different temperatures, reflecting changes in the deformation mechanism as a function of temperature. Structural defects were observed in nanotoughening phases when plastic deformation was observed. The implication of the observed microdeformation modes to the macroscopic toughening mechanisms is discussed in the context of the micromorphology of the nanometer sized toughening phases and parameters of the epoxy matrix chemistry such as bromination, molecular weight, and interfacial miscibility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 393–406, 2009