Revealing the solid electrolyte interface on calcium metal anodes

Owing to its low potential, crustal abundances and environmental friendliness, calcium metal anode(CMA) is emerging as a powerful contender in post-lithium era. However, the passivation of CMA fatally hinders its development. Recently, several feasible electrolytes have been developed. Nevertheless, as a pivotal part, the solid electrolyte interface(SEI) formed on CMA has not been paid enough attention to. In this review, based on the passivation mechanism of CMA, the favorable composition of SE...     

The understanding of solid electrolyte interface (SEI) formation and mechanism as the effect of flouro-o-phenylenedimaleimaide (F-MI) additive on lithium-ion battery

Solid electrolyte interface (SEI) is a critical factor that influences battery performance. SEI layer is formed by the decomposition of organic and inorganic compounds after the first cycle. This study investigates SEI formation as a product of electrolyte decomposition by the presence of flouro-o-phenylenedimaleimaide (F-MI) additive. The presence of fluorine on the maleimide-based additive can increase storage capacity and reversible discharge capacity due to high electronegativity and high electron-withdrawing group. The electrolyte containing 0.1 wt% of F-MI-based additive can trigger the formation of SEI, which could suppress the decomposition of remaining electrolyte. The reduction potential was 2.35 to 2.21 V vs Li/Li⁺ as examined by cyclic voltammetry (CV). The mesocarbon microbeads (MCMB) cell with F-MI additive showed the lowest SEI resistance (Rsei) at 5898 Ω as evaluated by the electrochemical impedance spectroscopy (EIS). The morphology and element analysis on the negative electrode after the first charge-discharge cycle were examined by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). XPS result showed that MCMB cell with F-MI additive provides a higher intensity of organic compounds (RCH₂OCO₂Li) and thinner SEI than MCMB cell without an additive that provides a higher intensity of inorganic compound (Li₂CO₃ and Li₂O), which leads to the performance decay. It is concluded that attaching the fluorine functional group on the maleimide-based additive forms the ideal SEI formation for lithium-ion battery.     

Kinetics of electric double layer formation at the blocked spherical or cylindrical electrode/solid electrolyte interface under galvanodynamic and potentiodynamic conditions

The kinetics of charging of the blocked (inert) electrode/solid electrolyte interface is studied for spherical or cylindrical electrodes by the impedance method in two modes (galvanodynamic and potentiodynamic). The case of slow diffusion and adsorption-desorption is analyzed for species of one type, namely, defects of the solid-electrolyte rigid sublattice (minor carriers). The roles that both the slow lattice defects and the fast conduction ions play in the electric double layer formation are taken into account. Calculations involve the use of both the diffusion model of a spherical or cylindrical electrode in electrolyte (proposed by Jacobsen and West) and the ac circuit of an ideally polarizable planar electrode in a solid electrolyte (developed by Grafov, Ukshe, and Bukun).     

Molecular dynamics simulations of the Li-ion diffusion in the amorphous solid electrolyte interphase

The solid electrolyte interphase (SEI), a passivation film covering the electrode surface, is crucial to the lifetime and efficiency of the lithium-ion (Li-ion) battery. Understanding the Li-ion diffusion mechanism within possible components in the mosaic-structured SEI is an essential step to improve the Li-ion conductivity and thus the battery performance. Here, we investigate the Li-ion diffusion mechanism within three amorphous SEI components (i.e., the inorganic inner layer, organic outer layer, and their mixture with 1:1 molar ratio) via ab initio molecular dynamic (AIMD) simulations. Our simulations show that the Li-ion diffusion coefficient in the inorganic layer is two orders of magnitude faster than that in the organic layer. Therefore, the inorganic layer makes a major contribution to the Li-ion diffusion. Furthermore, we find that the Li-ion diffusivity in the organic layer decreases slightly with the increase of the carbon chain from the methyl to ethyl owing to the steric hindrance induced by large groups. Overall, our current work unravels the Li-ion diffusion mechanism, and provides an atomic-scale insight for the understanding of the Li-ion transport in the SEI components.     

Reducing oxy-contaminations for enhanced Li-ion conductivity of halide-based solid electrolyte in water-mediated synthesis

Journal of Solid State Electrochemistry - Liquid-mediated synthesis offers a new approach to producing or applying solid electrolytes (SEs) in all-solid-state Li-ion batteries (ASSLIB). Li-ion...     

On the history of solid electrolyte fuel cells

The path to the discovery of galvanic solid electrolyte gas cells (J.-M. Gaugain 1853) and to the first industrially produced solid electrolyte gas cells (Nernst lamps 1897) is described. The development of the fundamentals of solid electrolyte fuel cells started with the work of Haber 1905, Schottky 1935, Baur 1937 and Wagner 1943. Extensive work in the field of solid oxide fuel cells (SOFCs) was done in the fifties by Peters and Möbius. After 1960, a rapidly growing number of scientists worked on the different problems of SOFCs, and by 1970 the basis was established on which the broad technologically orientated development of SOFCs proceeds today.     

Studies on film formation on cathodes using pyrazole derivatives as electrolyte additives in the Li-ion battery

Pyrazole derivatives are flame retardants and provide thermal protection on cathodes, as they help to form a thick protective film. A thicker film provides more protection and delays the thermal decomposition of the cathode. Among the tested pyrazoles, bis(trifluoromethyl)pyrazole (BFTMP) serves as the best flame retardant additive. Additionally, a cell with BFTMP shows better capacity retention than a cell with no additive in full-cell cycle life tests.     

Interphase-exchange processes at the interface of fluorine-conducting solid electrolyte with alkaline solutions

Kinetics of fluorideion exchange at the interface between a LaF₃:Eu²⁺ single crystal and solution with different pF and pH is studied by the galvanostatic and potentiometric methods and also by impedance spectroscopy. Anodic galvanostatic transients are linearized in the coordinates ln (η–η_max) vs. t, which suggests that the exchange rate in alkaline solutions is limited by surface diffusion of fluorine adions. The surface concentration of fluorine adions с ₀ and the surface diffusion flow ν ₀ are assessed. Impedance spectroscopy studies of the exchange processes indicate that the charge-transfer resistance R _F and the heterogeneous reaction resistance R _P increase with the increase in the рН of the fluoride-containing solution and also with the increase in the time of exposure of the fluoride-selective electrode membrane in a neutral solution with pH 6.4 and the high (pF 2) content of fluorides.     

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.     

Modification of electrolyte transport within the cathode for high-rate cycle performance of Li-ion battery

During high-rate cycling of Li-ion batteries (LIBs) at elevated temperatures, the detachment of the cathode materials from their Al substrate is a major cause of the deterioration in the performance of LIBs. This detachment is suppressed by the addition of an electrolyte additive, poly(ethylene glycol) methyl ether methacrylate, which can act as a buffer zone to prevent the abrupt mass transport of electrolyte within the cathode and as a swing to transport Li⁺ ions dissociating from the active materials of the cathode. Owing to the dual effects of this type of monomer, an acrylate monomer with one side ether chain, the cathode materials are maintained without detachment from the Al substrate, even under severe cycling conditions. This idea can be applied to LIBs for a series of electric vehicles, which require superior high-rate performance at elevated temperatures.     

Ionic solvation at the solid/electrolyte interface: A statistical-mechanical approach

We have studied studied the influence of the size of ions on their adsorbability at a solid surface in the presence of a molecular solvent. Ions and molecules are represented respectively by charged hard spheres and dipolar hard spheres and the surface is just a neutral hard wall. We have found that the electrostatic interaction between ions and molecules can induce the exclusion of small ions from the surface. A pure MSA (mean spherical approximation) calculation would not give any effect of the solvation on the ionic density profile. The present calculation is limited to the case of infinite ionic dilution.     

Low-temperature performance of Li-ion cells with a LiBF<Subscript>4</Subscript>-based electrolyte

The effect of LiBF₄ on the low-temperature performance of a Li-ion cell was studied by using a 1:1:1 (wt) EC/DMC/DEC mixed solvent. The results show that the LiBF₄-based electrolyte has a 2- to 3-fold lower ionic conductivity and shows rather higher freezing temperature compared with a LiPF₆-based electrolyte. Owing to electrolyte freezing, cycling performance of the Li-ion cell using LiBF₄ was significantly decreased when the temperature fell below –20 °C. However, impedance data show that at –20 °C the LiBF₄ cell has lower charge-transfer resistance than the LiPF₆ cell. In spite of the relatively lower conductivity of the LiBF₄-based electrolyte, the cell based on it shows slightly lower polarization and higher capacity in the liquid temperature range (above –20 °C) of the electrolyte. This fact reveals that ionic conductivity of the electrolytes is not a limitation to the low-temperature performance of the Li-ion cell. Therefore, LiBF₄ may be a good salt for the low-temperature electrolyte of a Li-ion cell if a solvent system that is of low freezing temperature, high solubility to LiBF₄, and good compatibility with a graphite anode can be formulated. Electronic Publication     

The adsorption and condensed film formation of cetyltrimethylammonium bromide at the mercury/electrolyte interface

The adsorption of cetyltrimethyammonium bromide (CTAB) on a hanging mercury electrode is studied in various electrolyte systems and temperatures. A condensed film is formed at negative potentials and at room temperature only in the presence of KBr. The decrease of the temperature favors the formation of the condensed film. Hysterisis phenomena are observed during the potential scans at both directions. Capacity time curves at the potentials where the film is formed show a nucleation and growth mechanism, with induction time depending on potential, which has been investigated using Avrami formulation and has been explained as a progressive one-dimensional nucleation with constant growth rate. The nucleation rate increases while moving toward more negative potentials. A linear decrease of the capacitance with time was observed in some cases independent of the measuring potential in a relative large potential range. The different types of micelles can affect the adsorption of CTAB on mercury. An unusual capacitance transient observed at a very narrow negative potential range is attributed to the formation of hemicylinders. The condensed film in the presence of the other electrolytes is observed only at high concentrations (1 M) and very low temperatures (5 degrees C).     

Potentiometric cells with oxygen-conducting solid electrolyte based on ceria

The present work presents studies of potentiometric cells with electrolyte of 0.98Ce_0.8(Sm_0.75Sr_0.2Ba_0.05)_0.2O_1.875 + 0.02TiO₂ and electrodes of silver or various materials with a perovskite structure. The oxygen activity limit is determined, above which electrolyte features preferred oxygen conductivity. Electrode materials are suggested that feature an equilibrium potential in the gas mixtures with the oxygen content from 1 to 21% and their lower temperature applicability limit is determined. The rate of potential response of the electrodes to a fast change in the oxygen partial pressure over the electrodes is determined. The results of studies are of interest for development of electrochemical devices with electrolyte based on ceria operating at 500–750°C.     

Fabrication and performance test of solid oxide fuel cells with screen-printed yttria-stabilized zirconia electrolyte membranes

Yttria-stabilized zirconia (YSZ) membranes were deposited onto porous NiO?CYSZ anode supports by screen printing. Combined with La_0.7Sr_0.3MnO₃?CYSZ composite cathode, the prepared anode-supported solid oxide fuel cells (SOFCs) were electrochemically tested. A typical SOFC with a 30-??m-thick YSZ electrolyte membrane gave the maximum power densities (MPDs) of 0.26, 0.53, 0.78, and 1.03?W/cm² at 650, 700, 800, and 850?°C, respectively, using hydrogen as fuel and stationary air as oxidant. Replacement of stationary air with pure oxygen flow exerted a significant positive effect on the MPDs of the cell. Using 100- and 200-ml/min oxygen as oxidants, the MPDs of the cell were enhanced 35.3% and 68.6%, respectively. Polarization analysis indicated that, at the MPD points, the electrode polarization resistances accounted for 80% of the cell total resistances.     

Fabrication and performance test of solid oxide fuel cells with screen-printed yttria-stabilized zirconia electrolyte membranes

Yttria-stabilized zirconia (YSZ) membranes were deposited onto porous NiO–YSZ anode supports by screen printing. Combined with La_0.7Sr_0.3MnO₃–YSZ composite cathode, the prepared anode-supported solid oxide fuel cells (SOFCs) were electrochemically tested. A typical SOFC with a 30-μm-thick YSZ electrolyte membrane gave the maximum power densities (MPDs) of 0.26, 0.53, 0.78, and 1.03 W/cm² at 650, 700, 800, and 850 °C, respectively, using hydrogen as fuel and stationary air as oxidant. Replacement of stationary air with pure oxygen flow exerted a significant positive effect on the MPDs of the cell. Using 100- and 200-ml/min oxygen as oxidants, the MPDs of the cell were enhanced 35.3% and 68.6%, respectively. Polarization analysis indicated that, at the MPD points, the electrode polarization resistances accounted for 80% of the cell total resistances.

     

Unraveling the stabilization mechanism of solid electrolyte interface on ZnSe by rGO in sodium ion battery

Transition metal selenides have been widely studied as anode materials of sodium ion batteries(SIBs),however,the investigation of solid-electrolyte-interface(SEI)on these materials,which is critical to the electrochemical performance of SIBs,remains at its infancy.Here in this paper,ZnSe@C nanoparticles were prepared from ZIF-8 and the SEI layers on these electrodes with and without reduced graphene oxide(rGO)layers were examined in details by X-ray photoelectron spectroscopies at varied charged/discharged states.It is observed that fast and complicated electrolyte decomposition reactions on ZnSe@C leads to quite thick SEI film and intercalation of solvated sodium ions through such thick SEI film results in slow ion diffusion kinetics and unstable electrode structure.However,the presence of rGO could efficiently suppress the decomposition of electrolyte,thus thin and stable SEI film was formed.ZnSe@C electrodes wrapped by rGO demonstrates enhanced interfacial charge transfer kinetics and high electrochemical performance,a capacity retention of 96.4%,after 1000 cycles at 5 A/g.This study might offer a simple avenue for the designing high performance anode materials through manipulation of SEI film.     

Kinetics of the formation of solid phase in electrolyte for electroless nickel deposition

The effect of 1-(3-methyl-4-phenylpyrazolyl)-3-phenylthiourea (PPTU) on the kinetics of formation of particles of the solid phase in the bulk of electrolyte for nickel plating is investigated by photocolorimetry and photon correlation spectroscopy. It is established that PPTU favors the formation of larger particles as compared to the solution containing no additive and, depending on the concentration, can accelerate or slow down the formation and growth of metal particles and affect the location of the process.     

Investigations on the determination of NO2 with galvanic nitrate solid electrolyte cells

Solid electrolyte cells for detecting NO₂ with Ba(NO₃)₂ or Sr(NO₃)₂ partially replaced by γ-Al₂O₃ as solid electrolytes have been studied. The cell tension depends on the NO₂- as well as on the NO-concentration. Investigations of the establishment of the NO₂-NO-O₂-equilibrium by the catalytic effects of the used electrode materials Pt and Au have shown that a decomposition of NO₂ below 400°C cannot be expected.