Search

With ever more increasing use of electrochemical-energy storage devices, in particular, lithium power sources, there is a call for the development of special-purpose approaches to studying the processes that take place in these devices (including those at buried charge interfaces) during their operation. The use of neutron reflectometry in studies of electrochemical interfaces enables us to determine, at a new level, the effects that the initial parameters of the electrode surface, external conditions, electrolyte composition, overvoltage, current density, and other parameters have on their evolution. The high penetrating power of neutrons enables the study of complex systems that closely model actual storage devices in terms of operating conditions. This work addresses current issues concerning the development of methods of neutron reflectometry in the specular-reflection mode for investigating model planar interfaces between solid electrodes and liquid electrolytes. These include ensuring the possibilities of contrast-variation experiments involving isotopic substitution in the electrolyte and enhancing the sensitivity of the method to probing the structure of thin layers formed on the electrode surface. The adaptation of neutron-reflectometry experiments to study the structures of electrochemical interfaces is presented by the example of the GRAINS reflectometer at the IBR-2 reactor, Joint Institute for Nuclear Research, Dubna, Russia.

Oxygen reduction reaction (ORR) is a crucial process that drives the operation of several energy storage devices. ORR can proceed on the neat carbon surface in the absence of a catalyst, and its electrochemical activity is determined by its microstructure and chemical composition. Oxygen functional groups unavoidably existing on the carbon surface can serve as adsorption sites for ORR intermediates; the presence of some oxygen functionalities gives rise to an increase in the density of electronic states (DOS) at the Fermi level (FL). Both factors should have a positive impact on the electron transfer rate that was demonstrated for ORR in aqueous media. To study the O-groups effect on the aprotic ORR, which is now of interest due to the extensive development of aprotic metal-air batteries, we use model oxidized carbon electrodes (HOPG and single-layer graphene). We demonstrate that oxygen functionalities (epoxy, carbonyl, and lactone) do not affect the rate of one-electron oxygen reduction in aprotic media in the absence of metal cations since their introduction practically does not increase DOS at FL. However, in Li+-containing electrolytes, oxygen groups enhance both the rate of second electron transfer and carbon degradation due to its oxidation by LiO2 yielding carbonate species.

Based on the quantum-mechanical theory of electron transfer (ET), the parameter was proposed to describe the electrochemical activity of doped graphenes. The parameter is calculated using the density of states (DOS), local density of state (LDOS) values, which are in turn obtained from the density functional theory (DFT) calculations and reorganization energies of redox system. DOS describes the contribution of the electronic structure of the electrode to the ET process, while the LDOS describes the electron density contribution of the atoms at some distance from the surface electrode. Reorganization energy corresponds to the restriction of solvation shell and bonds in redox system due to ET process. The overall contribution of these parameters enables a comprehensive assessment of the activity that is acceptable for semi-quantitative analysis. Calculations have shown that the proposed activity parameter correlates well with the calculated ET rate constants. Theoretical study of the oxygen reduction reaction (ORR) on graphene doped with p-elements in the framework of quantum-mechanical theory showed that ET activity decreases in series P-Gr > S-Gr > N-Gr > B-Gr > O-Gr > Gr. According to our estimates, the mixed or adiabatic regime of ET is probably observed on doped graphenes for all steps of ORR. Using N- and B-graphenes as an example and activity parameter, the influence of the applied potential and the atomic fraction of the doped element on the ET activity are studied.

Gibbs free energies for Li+ solvation in water, methanol, acetonitrile, DMSO, dimethylacetamide, dimethoxyethane, dimethylformamide, gamma-butyrolactone, pyridine, and sulfolane have been calculated using the cluster-continuum quasichemical theory. With n independent solvent molecules S initial state forming the "monomer" thermodynamic cycle, Li+ solvation free energies are found to be on average 14 kcal mol-1 more positive compared to those from the "cluster" thermodynamic cycle where the initial state is the cluster Sn. We ascribe the inconsistency between the "monomer" and "cluster" cycles mainly to the incorrectly predicted solvation free energies of solvent clusters Sn from the SMD and CPCM continuum solvation models, which is in line with the earlier study of Bryantsev et al., J. Phys. Chem. B, 2008, 112, 9709-9719. When experimental-based solvation free energies of individual solvent molecules and solvent clusters are employed, the "monomer" and "cluster" cycles result in identical numbers. The best overall agreement with experimental-based "bulk" scale lithium cation solvation free energies was obtained for the "monomer" scale, and we recommend this set of values. We expect that further progress in the field is possible if (i) consensus on the accuracy of experimental reference values is achieved; (ii) the most recent continuum solvation models are properly parameterized for all solute-solvent combinations and become widely accessible for testing.

Potassium-ion batteries (PIBs) have attracted great interest due to their high-energy-density and low-cost. The lack of stable anode material greatly limits the quick development of PIBs. Phosphorus-metal compounds are regarded as a class of materials with promising prospects as anode material for PIBs with a low operating voltage and high conductivity. Among them, due to the challenging synthesis method, the application of SnP is limited. Herein, a facile approach to synthesize trigonal SnP@C through alloying red phosphorus with tin on carbon material is reported. It is found that carbon substrate can largely reduce vibrational and configurational entropies, playing a critical role on the formation of metastable SnP. When applied as anode in PIBs, the SnP@C composite delivers a high reversible capacity of 478.1 mAh·g−1 at 50 mA g−1 and a stable cycling performance at 1000 mA g−1. The good electrochemical performance is associated with the SnP@C as well as the carbon, which could suppress the phase separation during charge/discharge process to maintain structural stability. This work may open a new avenue for low-cost synthesis of metastable phases for advanced energy storage systems.

The development of high specific energy Li–O2 batteries faces a problem of poor cycling as a result of passivation of the positive electrode by both the discharge product (Li2O2) and side products ...

The metallic lithium electrode has major concerns such as extremely high reactivity and nonuniform needle-like electrodeposition, limiting its wide application as a negative electrode in secondary batteries. Its reactions with the electrolyte leading to solid electrolyte interphase (SEI) formation play an important role, and controlling its composition and properties can help to overcome both difficulties. Even though solid electrolyte interphase chemistry and properties seem to be well known, many surface chemistry experiments reported are not perfect with respect to the purity needed for Li studies and can be interpreted alternatively. Here, we studied reactions between lithium and propylene carbonate and ethylene carbonate in model reactions realized in an ultra-high vacuum. In addition to the already reported reaction pathway yielding lithium carbonate and semicarbonate, our theoretical (DFT) modeling confirms the preference of alternative routes. Along with the most beneficial final lithium carbonates, dilithium 1,2-dialkoxide (DD) can form barrierlessly as a final product by two-electron transfer. Experimental XPS/NEXAFS studies of gas phase and solid-gas model reactions revealed that in both cases DD is the main reaction product. Understanding of the discovered reaction pathway can also be essential for reactions in liquid electrolytes, although the low electric conductivity of the SEI makes it less probable.

The development of high-energy lithium-oxygen batteries has significantly slowed by numerous challenges including capacity limitations due to electrode surface passivation by the discharge product Li2O2. Since the passivation rate and intensity are dependent on the deposit morphology, herein, we focus on the mechanisms governing Li2O2 formation within the porous cathode. We report evidence of homogeneous nucleation of Li2O2 crystallites and their further assembly in bulk of the electrolyte solution in DMSO, which possesses a high donor number. After careful estimation of the superoxide ion concentration distribution within a phenomenological model, it was found that the high stability of superoxide ions formed during the ORR towards disproportionation and sufficient diffusivity of (0.5-1.2) × 10-6 cm2 s-1 enabled Li2O2 nucleation and crystallization not only at the surface but also in the electrolyte, and the reaction zone spread throughout the internal space of the porous electrode. High initial supersaturation promoted the homogeneous nucleation of Li2O2 nanoplates, which instantly assembled into mesocrystals also in the solution bulk. These results were supported by operando SAXS/WAXS and morphology observations. Thus, although homogeneous nucleation is not dominant, it is important for achieving a high capacity in Li-O2 batteries.

Solid electrolytes are of high interest for the development of advanced electrochemical energy storage devices with all-solid-state architectures. Here, we report the fabrication of the electrolyte membranes based on LiTFSI (LiN(CF3SO2)2) and PEO–PVDF blends with improved properties. We show that addition of PVDF enables preparation of free-standing films of the compositions within the so called “crystallinity gap” of the LiTFSI–PEO system known to provide high ion conductivity. We show that optimal PVDF content enables preparation of the films with reasonable elastic modulus and high ionic conductivity of about 0.3 mS cm−1 at 60 °C and about 0.1 mS cm−1 at room-temperature. Combining FTIR spectroscopy, XRD and DSC measurements we show that a noticeable fraction of PVDF remains crystalline and enhances the mechanical properties of the material, and at the same time it additionally promotes LiTFSI dissociation and disordering. Density functional theory calculations showed that the Li+–PEO–PVDF complexation energy magnitude is almost as high as that of Li–PEO complexes, thus the salt dissociation ability can be retained in spite of the introduction of the substantial amounts of PVDF required for mechanical stability.

The sensitivity of the method of specular neutron reflectometry was studied with respect to the nanoscale structure of planar electrochemical interfaces in which a metal anode (copper) was in contact with an aprotic liquid lithium ion electrolyte (lithium perchlorate in propylene carbonate). The structure of the lithium enriched layers formed on the working electrode including solid electrolyte interphase and next depositions was analyzed in terms of the scattering length density depth profiles obtained from the modelling of the reflectivity curves. The preferable choice of fully deuterated electrolyte for better analysis of the structural features of such layers was experimentally proven. From the comparison of the profiles obtained for interfaces with fully deuterated and fully protonated electrolytes the porosity of the deposited layer was estimated. A principal change in the interface profile evolution was observed when non-electroactive additive (TBA+) is present in the electrolyte.

The ring electrode of an RRDE setup is commonly used to detect redox active species produced at the disk electrode. It is especially useful when some side processes occur at the disk (e.g. passivation film growth) along with a main electrochemical reaction of interest, which produces a soluble redox-active specie. Unfortunately, the detected ring current signal is a delayed and smeared-out representation of the disk faradaic process so that fast changes of its magnitude cannot be studied. The deconvolution approach is a mathematical data processing procedure that enables reconstruction of the disk signal with a hypothetically infinite accuracy. There are, however, practical limitations arising mainly from inevitable presence of noise in the measured ring current used for the reconstruction. In this paper the deconvolution approach is discussed in details and its applicability is investigated basing on a series of experiments with a model system. A procedure to filter out spurious artifacts from the reconstructed disk signal is proposed and tested.

Advanced lithium batteries, including Li–air, Li–sulfur and high-voltage Li-ion systems, attract constantly increasing attention worldwide. Each of these systems have unique problems, yet development of solid electrolyte membrane capable of separating anode and cathode, while being penetrable only for Li+, is crucial for all of them. In this paper, we suggest a new recipe combining glass crystallization and tape-casting techniques for thin lithium-conductive membranes preparation. We show that the powders prepared by grinding glass–ceramics and containing residual traces of glassy phase are beneficial ceramic fillers for tape casting. Such fillers enhance sintering and support the preparation of denser membranes. Taking DTA, dilatometry and SEM data into account, we have optimized the sintering procedure enabling fabrication of liquid-tight 10–100-µm-thin membranes with ionic conductivity reaching 0.22 mS cm−1 at 25 °C. Therefore, we consider such permeable membranes as a viable option for Li+ ions separator between anode and cathode of advanced lithium batteries.

In this study, for the first time, chemically modified carbon nanotubes (CNTs) were used as a conductive additive in the cathode composite for lithium—sulfur batteries. Oxidation of pure CNTs has been carried out using modified Hummers’ method, and to partially remove oxygen groups from the CNT surface and increase their electronic conductivity, oxidized CNTs have been hydrothermally treated. The cathode slurry was mixed in water with a water-soluble LA133 binder. Despite the decrease in electronic conductivity of CNTs after chemical treatment, the presence of structural defects and oxygen groups provides uniform distribution of modified CNTs in the sulfur-based composite, which results in more than twice higher electrode specific capacity compared with the electrodes comprising pure CNTs. Using chemically modified CNTs as a conductive additive is proposed as an effective way for the preparation of nontoxic and cost-effective water-based cathode slurries in lithium—sulfur batteries.

Electrical conductivity in solid ionic conductors can be enhanced by faster ionic mobility resulting from optimizing the conducting pathways, increase of charge carrier concentration or improvement of crystallite interconnectivity. Here, we investigated the lithium ion mobility in two NASICON-type glass-ceramics of Li1.5Al0.5Ge1.5(PO4)3 (LAGP) composition, prepared with and without adding Y2O3 (5 vol%) to the glass melt before crystallization. We applied variable-temperature 7Li nuclear magnetic resonance (NMR) spectroscopy, T1 relaxation time and self-diffusion measurements as well as impedance spectroscopy to study ionic dynamics. For both materials an Arrhenius behavior of ionic mobility is obtained from various experimental approaches, thus showing a single thermally activated process in a wide temperature range with very similar activation energies of about 0.3 eV for yttrium-free and yttrium-modified LAGP ceramics. A near five-fold conductivity enhancement in the yttrium-modified sample cannot be explained by faster ionic dynamics because only minor changes of ionic mobility are registered by NMR. In conjunction with the theoretical calculations of NMR parameters and bond valence site energies, this observation suggests that the most influencing factors on ionic conductivity are an intergrain connectivity and an Li concentration enhancement, offering thus an efficient strategy for improved ionic conductors.

One of the approaches to tackle the problem of limited electrolyte electrochemical stability, which controls the development of novel electrochemical storage devices, is the use of solid electrolytes. Here, we focus on one of the most promising among oxide-based glass-ceramic materials, Li1+xAlxGe2−xP3O12, to investigate the physical and chemical mechanisms that govern the enhancement of Li-conductivity upon variation of its composition and glass crystallization conditions during a two-step heat treatment. Using X-ray and neutron diffraction, small-angle neutron scattering and Raman spectroscopy we found that the addition of 6–18 mol% yttria makes the polyphosphate chains in glass more thermally stable. This leads to sudden and uniform glass crystallization over the whole volume. This peculiar glass structure governs the further crystallization behavior and ensures the optimal organization of intergrain boundaries. The highest Li-conductivity is achieved for a sample with 12 mol% yttria annealed for 2 hours at 750 °C. In addition, nuclear magnetic resonance together with bond valence sum analysis provides further insight into atomistic mechanisms of ionic conductivity in NASICON-based lithium-conductive ceramics.

In this paper for the first time, a comparison was made of the electrochemical activity of graphene oxides synthesized by modified Hummer's, Brodie and electrochemical methods in aprotic media. Electrodes based on these GOs exhibit electrochemical activity in an aprotic solvent of propylene carbonate with 0.1 M (C4H9)4NClO4 electrolytes in the potential range from -3 to 1 V rel. Ag+/Ag in 0.01M AgNO3 0.1M (C4H9)4NClO4 in acetonitrile. These redox processes are irreversible. Despite the fact that the types of oxygen groups in GO synthesized by different methods are the same, the ratio of these groups is different. The specific capacity of electrodes based on GO during redox processes in aprotic media correlates with the C:O ratio determined from elemental analysis. The use of new active electrode materials based on graphene in electrochemical processes will allow the creation of electrochemical energy storage devices with a higher energy density and capacity.

The search for new environmental-friendly materials for energy storage is ongoing. In the presented paper, we propose polymer microgels as a new class of redox-active colloids (RACs). The microgel stable colloids are perspective low-viscosity fluids for advanced flow batteries with high volumetric energy density. In this research, we describe the procedure for the anchoring of 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) redox-active sites to the polymeric chains of water-soluble microgels based on poly(

Lithium plating-one of the critical processes in the desired high-energy lithium metal batteries-is accompanied by lithium whisker growth, which causes several problems that prevent the employment of metallic lithium anodes in rechargeable systems. They include low coulombic efficiency, electrolyte consumption, and the risk of short circuits, which can lead to thermal runaway of the battery. In recent years several strategies were suggested to mitigate whisker growth. The mechanism of this process, however, still lacks understanding. Here, we reveal the importance of surface diffusion along grain boundaries in solid lithium. We show that, at first, the plating of lithium onto a lithium substrate is possible as bulk crystal growth with a planar crystallization front for the Li grains with oblique (nonperpendicular to the surface) grain boundaries. Further, the developed compressive stress makes lithium diffusion to the grain base unfavorable, and new grains nucleate at the surface. The latter are the cause of the whisker growth from their roots. These findings indicate that the control of grain-boundary diffusion and grain size and structure paves the way to overcome the nonuniform morphology of plated lithium.

The development of high specific energy Li-O

The development of high-energy lithium-oxygen batteries has significantly slowed by numerous challenges including capacity limitations due to electrode surface passivation by the discharge product Li

The development of high-capacity rechargeable and safe metallic lithium negative electrodes for next-generation batteries requires an in-depth understanding of reasons for nonuniform lithium plating during lithium-metal battery charge. It drives the interest for the tools enabling efficient monitoring of electrochemical interfaces where lithium electrodeposition occurs. We report on a three-electrode electrochemical cell designed to track lithium electrodeposition from aprotic electrolytes by neutron reflectometry (NR) in the specular reflectivity mode. We performed a case study of Li plating from LiClO 4 solution in propylene carbonate. The sensitivity was optimized by tuning the neutron scattering contrast for a given electrode material (Cu film) and the electrolyte, which was done employing a deuterated solvent. The analysis of the scattering length density (SLD) profiles derived from the modeling of the reflectivity data clearly demonstrated that the deposition of nm-thin Li layers above initially formed solid-electrolyte interphase (SEI) layer can be detected and their roughness, which is a characterizing parameter of electrodeposition nonuniformity, can be estimated. It makes NR a proper tool for further studies of “dendritic” lithium growth.

In this paper, for the first time, we report the results of molecular dynamics simulation of the electrode/electrolyte interface of a Li–O2 cathode under potentials close to experimental values in 1 M dimethyl sulfoxide (DMSO) solution of LiPF6 salt. Electric potential profiles, solvent structuring near the electrode surface, and salt ion distributions are presented and discussed here as well as potentials of mean force (PMFs) of oxygen and its reduction products. The latter would be of a great use for future theoretical studies of reaction kinetics as PMF is essentially the work term required for reaction rate constant estimations. At the electrode/electrolyte interface under realistic potentials, oxygen anions are effectively pushed out of the reaction layer, making the second reduction of superoxide anion hardly probable. This indicates that the main cause of the electrode surface passivation should be lithium superoxide presence near the electrode surface. The way to suppress the passivation is to shi...

Electrochemical oxygen reduction in aprotic media is a key process that determines the operation of advanced metal–oxygen power sources, e.g., Li–O2 batteries. In such systems oxygen reduction on carbon-based positive electrodes proceeds through a complicated mechanism that comprises several chemical and electrochemical steps involving either dissolved or adsorbed species, and as well side reactions with carbon itself. Here, cyclic voltammetry was used to reveal the effects of imperfections in the planar sp2 surface structure of carbon on the Li oxygen reduction reaction (Li-ORR) mechanism by means of different model carbon electrodes (highly oriented pyrolytic graphite (HOPG), glassy carbon, basal, and edge planes of pyrolytic graphite), in dimethyl sulfoxide (DMSO)-based electrolyte. We show that the first electron transfer step O2 + e– ⇆ O2– (followed by ion-coupling Li+ + O2– ⇆ LiO2) does not involve oxygen chemisorption on carbon as evidenced by the independence of its rate on the carbon electrode su...

We report an approach to stabilize the electrochemical performance of silicon- and germanium-based thin film anodes by using carbon nanowall matrices. Silicon and germanium layers were deposited onto vertically oriented carbon nanowall scaffolds and this procedure has been repeated multiple times producing multilayered structures with increased silicon and germanium areal mass loading. It was demonstrated that the areal specific capacity of multilayered anodes achieves up to 2 mA h cm−2 without sacrificing cycling stability. Based on post-mortem SEM analysis of the electrodes we speculate that the reason for the improved cycling stability of multilayered highly loaded silicon/graphene composites is the ability to relax the mechanical stresses in the films.

One of the difficulties limiting the development of high capacity Li-O2 batteries is the positive electrode passivation by the discharge product Li2O2 which is deposited mostly due to the second electron transfer of oxygen reductionwhich requires the presence of Li+ in the Stern layer. To suppress the passivation and shift the reaction zone of Li2O2 formation towards the electrolyte bulk, we propose to use additional cations in the electrolyte. Using molecular dynamics simulations, we investigate the ability of various cations to replace Li+ ions in the first cation layers near the electrode, with EMI+ (1-ethyl-3-methylimidazolium) and PP13+ (N-methyl-N-propylpiperidinium) showing pronounced effects. However, our experimental studies including cycling voltammetry and discharge capacity measurements in high and low donor number solvents reveal practically no effect of such addition. Therefore, Li+ should be fully eliminated from electron transfer zone, and this is possible by anchoring of additional cations according to the simulations. We optimized the surface density for these cations, although the experimental support of this approach looks challenging.

Achieving theoretical promises of 1000 W h/kg specific energy for lithium-air batteries is quite challenging due to limited transport in the cathode along with electrode passivation. Transport can be enhanced in the electrodes with complex hierarchical pore architecture. Here, using computer simulations we analyze the effects of cathode pore size distribution (PSD) on capacity and discharge curve shape. Calculations considering a broad PSD revealed that even small discharge product resistivity prevents larger pores from accumulating the discharge product and thus turning them into non-clogging oxygen supply channels. Thus optimization of cathode architecture by adding of large-scale cavities enables cell capacity enhancement.

Fundamental understanding of growth mechanisms of Li2O2 in Li-O2 cells is critical for implementing batteries with high gravimetric energies. Li2O2 growth can occur first by 1e(-) transfer to O2, forming Li(+)-O2(-) and then either chemical disproportionation of Li(+)-O2(-), or a second electron transfer to Li(+)-O2(-). We demonstrate that Li2O2 growth is governed primarily by disproportionation of Li(+)-O2(-) at low overpotential, and surface-mediated electron transfer at high overpotential. We obtain evidence supporting this trend using the rotating ring disk electrode (RRDE) technique, which shows that the fraction of oxygen reduction reaction charge attributable to soluble Li(+)-O2(-)-based intermediates increases as the discharge overpotential reduces. Electrochemical quartz crystal microbalance (EQCM) measurements of oxygen reduction support this picture, and show that the dependence of the reaction mechanism on the applied potential explains the difference in Li2O2 morphologies observed at different discharge overpotentials: formation of large (∼250 nm-1 μm) toroids, and conformal coatings (

Understanding and controlling the kinetics of O2 reduction in the presence of Li(+)-containing aprotic solvents, to either Li(+)-O2(-) by one-electron reduction or Li2 O2 by two-electron reduction, is instrumental to enhance the discharge voltage and capacity of aprotic Li-O2 batteries. Standard potentials of O2 /Li(+)-O2(-) and O2/O2(-) were experimentally measured and computed using a mixed cluster-continuum model of ion solvation. Increasing combined solvation of Li(+) and O2(-) was found to lower the coupling of Li(+)-O2(-) and the difference between O2/Li(+)-O2(-) and O2/O2(-) potentials. The solvation energy of Li(+) trended with donor number (DN), and varied greater than that of O2 (-) ions, which correlated with acceptor number (AN), explaining a previously reported correlation between Li(+)-O2(-) solubility and DN. These results highlight the importance of the interplay between ion-solvent and ion-ion interactions for manipulating the energetics of intermediate species produced in aprotic metal-oxygen batteries.

Heterostructures have great potential in developing high-rate sodium-ion batteries because of their boosted charge transfer capability. However, the rational design of heterostructures with ideal electrochemical performance under high current density is still a challenge. Herein, we successfully developed a facile approach to address the aforementioned problem by synthesizing vertically aligned MoS2/CoS2 heteronanosheets with high content 1T MoS2 as the anode for sodium-ion batteries. The MoS2/CoS2 heterostructure exhibits superior rate performance (274 mAh g−1 at 10 A g−1), high discharge capacity (548 mAh g−1 at 0.2 A g−1), and excellent long-cycle stability (capacity retention of 90.6% after 150 cycles under 1 A g−1). The improved rate performance could be attributed to novel design of heterostructures with accelerated charge transfer capability and enhanced electronic conductivity by 1T phase of MoS2. Density functional theory (DFT) calculations further verify that abundant built-in electric fields are induced by the constructed MoS2/CoS2 heterostructure, which can greatly facilitate charge transport. This work presents a highly conductive and stable heterostructure with advanced sodium storage performance and beyond.

Lithium metal anode is strongly considered as the ‘Holy Grail’ anode for the next generation energy storage system. However, the major obstacle towards lithium metal batteries (LMBs) is the unstable solid electrolyte interface (SEI) because of its high reactivity, which can result in dendrite growth, dead lithium accumulation and even short circuit. Herein, the highly ion-conductive, stretchable and stable artificial SEI layer derived from Polymethyl methacrylate (PMMA)/Poly(vinylidene fluoride) (PVDF) hybrid polymer is fabricated through an in-situ reaction during the preparation and electrochemical process. In this way, LiF and Li-O bond would be generated in the interface of the PMMA/PVDF layer and lithium metal, which can provide fast ion transport channels during lithium stripping and plating process. Furthermore, the robust and flexible polymer coating can simultaneously adapt the volume change and suppress dendrite growth. Therefore, based on the synergistic effect between PMMA and PVDF, the PMMA/PVDF-Li delivers ultrahigh cycling stability at 2 mA cm−2 with an areal capacity of 1 mAh cm−2 for more than 2000 h. The corresponding PMMA/PVDF-Li||NCA full cell also exhibits superior stability with a high capacity retention of 82.3% at 2 C rate after 300 cycles.

In this review paper, we provide a short overview of the application of magnetic resonance techniques in electrochemical studies. Brief theoretical descriptions, sensitivity aspects, challenges and new opportunities of nuclear magnetic resonance and electron paramagnetic resonance have been presented here. Particular attention will be paid to the studies using ex situ and in situ methodologies and their combination to address the questions concerning the intrinsic structures and the structural transformations, ionic mobility and interfacial interactions in the energy storage and energy conversion systems. In addition, theoretical approaches to support the experimental NMR observables as well as magnetic resonance imaging have been discussed in the context of improving electrochemical performance, cycling stability and safety of batteries.

One of the key factors responsible for the poor cycleability of Li–O2 batteries is a formation of byproducts from irreversible reactions between electrolyte and discharge product Li2O2 and/or intermediate LiO2. Among many solvents that are used as electrolyte component for Li–O2 batteries, acetonitrile (MeCN) is believed to be relatively stable towards oxidation. Using near ambient pressure X-ray photoemission spectroscopy (NAP XPS), we characterized the reactivity of MeCN in the Li–O2 battery. For this purpose, we designed the model electrochemical cell assembled with solid electrolyte. We discharged it first in O2 and then exposed to MeCN vapor. Further, the discharge was carried out in O2 + MeCN mixture. We have demonstrated that being in contact with Li–O2 discharge products, MeCN oxidizes. This yields species that are weakly bonded to the surface and can be easily desorbed. That’s why they cannot be detected by the conventional XPS. Our results suggest that the respective chemical process most probably does not give rise to electrode passivation but can decrease considerably the Coulombic efficiency of the battery., This work of A.K-G., J.J.V-V. and D.M.I. was supported by the Russian Ministry of Science and Education (RFMEFI61614×0007) and Bundesministerium für Bildung and Forschung (Project No. 05K2014) in the framework of the joint Russian-German research project “SYnchrotron and NEutron STudies for Energy Storage (SYNESTESia)”. T.K.Z acknowledges Center for Electrochemical Energy of Skolkovo Institute of Science and Technology for financial support. The work of O.O.K., A.I.B and L.V.Y. is performed within the joint project of the Russian Science Foundation (16-42-01093) and DFG (LA655-17/1). We are grateful to HZB for beamtime granted at ISISS and RGBL beamlines. T.K.Z. and A.S.F. thank to the Russian German laboratory at HZB for support provided. Authors are appreciated to Victor Vizgalov for solid electrolyte membrane preparation. Travelling of T.K.Z. was supported by German-Russian Interdisciplinary Science Center (G-RISC).

Li/O 2 batteries draw much attention due to its outstanding theoretical specific energy, but the value of practically achievable specific energy is still under the question. In this paper we employ a numerical model of Li/O 2 cell, which takes into account mass transport processes, to simulate non-uniform product precipitation at different discharge current densities in acetonitrile, dimethyl sulfoxide and 1,2-dimethoxyethane-based electrolytes. Even for 1,2-dimethoxyethane, which has the highest oxygen mobility and solubility, oxygen transport restrictions at 1 mA/cm 2 lead to cell-level specific energy of about 650 Wh/kg if a pure oxygen is supplied to the cell. Finally, in order to assist the ongoing search for new cathode materials, which can be alternative to carbon, we also investigate the effect of electrode material density on cell-level specific energy and show that materials with densities up to 10 g/cm 3 can be used without serious penalty to the specific energy.

Using X-ray photoemission microscopy, we discovered that oxidation of commercial large-scale graphene on Cu foil, which typically has bilayer islands, by atomic oxygen proceeds with the formation of the specific structures: though relatively mobile epoxy groups are generated uniformly across the surface of single-layer graphene, their concentration is significantly lower for bilayer islands. More oxidized species like carbonyl and lactones are preferably located at the centers of these bilayer islands. Such structures are randomly distributed over the surface with a mean density of about 3× 106 cm–2 in our case. Using a set of advanced spectromicroscopy instruments including Raman microscopy, X-ray photoelectron spectroscopy (μ-XPS), Auger electron spectroscopy (nano-AES), and angle-resolved photoelectron spectroscopy (μ-ARPES), we found that the centers of the bilayer islands where the second layer nucleates have a high defect concentration and serve as the active sites for deep oxidation. This information can be potentially useful in developing lateral heterostructures for electronics and optoelectronics based on graphene/graphene oxide heterojunctions., The work is performed within the joint project of the Russian Science Foundation (16-42-01093) and DFG (LA655-17/1). The work of O.O.K. was supported by the Russian Foundation of Basic Researches (individual project 16-33-60229).

In this paper we propose a new and simple method to tune the carbon nanowall microstructure by sharp variation of CH4/H2 plasma conditions. Using theoretical calculations we demonstrated that the sharp variation of gas pressure and discharge current leads to significant variation of plasma radical composition. In some cases such perturbation creates the necessary conditions for the nucleation of smaller secondary nanowalls on the surface of primary ones.

Unfortunately, the practical applications of Li-O2 batteries are impeded by poor rechargeability. Here, for the first time we show that superoxide radicals generated at the cathode during discharge react with carbon that contains activated double bonds or aromatics to form epoxy groups and carbonates, which limits the rechargeability of Li-O2 cells. Carbon materials with a low amount of functional groups and defects demonstrate better stability thus keeping the carbon will-o'-the-wisp lit for lithium-air batteries.

One of the key problems hindering practical implementation of lithium–air batteries is caused by carbon cathode chemical instability leading to low energy efficiency and short cycle life. Titanium carbide (TiC) nanopowders are considered as an alternative cathode material; however, they are intrinsically reactive toward oxygen, and its stability is controlled totally by a surface overlayers. Using photoemission spectroscopy, we show that lithium–air battery discharge product, lithium peroxide (Li2O2), easily oxidizes clean TiC surface. At the same time, TiC surface, which was treated by molecular oxygen under ambient conditions, shows much better stability in contact with Li2O2 that can be explained by the presence of a surface layer containing a significant amount of elemental carbon in addition to oxides and oxycarbides. Nevertheless, such protective coatings produced by room temperature oxidation are not practically useful as one of its components, elemental carbon, is oxidized in the presence of lithium–air battery discharge intermediates. These results are of critical importance in understanding of TiC surface chemistry and in design of stable lithium–air battery electrodes. We postulate that dense, uniform, carbon-free titanium dioxide surface layers of 2–3 nm thickness on TiC will be a promising solution, and thus further efforts should be taken for developing synthetic protocols enabling preparation of TiO2/TiC core–shell structures., This work was financially supported by the Russian Ministry of Science and Education (RFMEFI61614X0007) and Bundesministerium für Bildung and Forschung (project no. 05K2014) in the framework of the joint Russian-German research project “SYnchrotron and NEutron STudies for Energy Storage (SYNESTESia)”.

The (0001) surface of layered InSe semiconductor crystals is studied experimentally using X-ray photoelectron spectroscopy and theoretically within the context of the method of the electron density functional with periodic boundary conditions. It was found that the structure of the surface layer of atoms and their state has much in common with the corresponding structure and state in the volume. The InSe(0001) surface is resistant to long exposure to air, which makes this material promising for applications as a standard for composition analysis when using electron spectroscopy.