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We report on stabilization of Li–S cells with different types of composite sulfur cathodes using ethereal LiTFSI/LiNO3/DOL/DME electrolyte solutions containing a-priori 0.1 M Li2S8. These electrolyte solutions enable an improved cycling behavior for Li–S cells compared to Li2S8-free electrolyte solutions, thanks to the presence of LiSxspecies from the beginning of operation. We show that Li anodes cycled in Li∣S cells with solutions containing Li2S8possess flatter and more uniform surface, higher dimensions of the surface structures in average and, as a result, a lower surface area. This surface morphology ensures a low rate of parasitic surface reactions of the electrolyte components on the Li anodes’ surface, slower depletion of the electrolyte solution in the cells and stabilization of the cells cycling. Besides, the presence of Li2S8maintains a better integrity of composite sulfur/carbon/PVdF cathodes, ensuring a better electronic contact between the particles in the composite cathodes. We believe that we outline herein a logical approach for practical Li–S batteries, emphasizing high energy density, cost effectiveness and relatively simple production procedures.

We previously showed that, for neutral electrolytes of small cations and relatively larger anions, it is possible to design certain pore sizes in active carbons that are large enough to electroadsorb cations but too small to allow anion electroadsorption. This situation leads to an electrical double-layer (EDL) capacitance that is significant only at potentials that are negative to the potential of zero charge (PZC); hence, much smaller capacitance is measured at potentials positive to the PZC. It was found that when the electrolyte is a strong acid (e.g., H2SO4, HCl), a considerable capacitance is observed at positive potentials, even when the average pore size is too small to allow the insertion of large anions in neutral electrolyte solutions. This effect disappears when the pore size becomes considerably larger than the size of the ions. In this case, the EDL capacitance at positive potentials for both neutral and acidic solutions is comparable. The following four-step mechanism was found to comply best with the experimental data:  (1) By acid catalysis, the protons form carbonium species within the conjugated carbon network. (2) The anions react with the carbonium ions, providing uncharged species in an activated state, which are chemibound as surface groups to the walls of the pores. (3) Because these surface groups are effectively much smaller in size than are the charged ions, they can migrate by chemical bond exchange within the carbon skeleton via constrictions (known to exist in microporous and molecular sieving carbons), which are too narrow to accommodate hydrated charged species. (4) Upon reaching wider spaces, the uncharged species are reionized and solvated by water molecules, which can fill small pores. The justification for the above mechanism is thoroughly discussed and demonstrated by the experimental results.

A new low-modulus β Ti−Nb alloy with low elastic modulus and excellent corrosion resistance is currently under consideration as a surgical implant material. The usefulness of such materials can be dramatically enhanced if their surface structure and surface chemistry can be controlled. This control is achieved in two stages. Electropolishing and anodic oxidation of the Ti45Nb alloy provide a surface with a uniform oxide layer that is a mixture of TiO2 and Nb2O5. The impact of each of these two steps on the morphology of the surface and on the thickness and chemistry of the oxide layer has been assessed. In addition, as a first step toward controlling the surface chemistry of this material, a self-assembled monolayer (SAM) based on hexadecylphosphonic acid (HDPA) is attached to the anodized surface. The SAM is characterized based on its wetting properties and by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. Using variable angle XPS analysis, detailed information is obtained about the orientation and structure of the SAM, its thickness, and the chemistry of its interaction with the metal oxide surface of the alloy. Further support for the creation of a true monolayer film is obtained from FTIR measurements on a model oxide surface analogous to that of the alloy. This is the first report of SAM attachment to this alloy and opens the possibility of monolayer control of its biocompatibility.

We explored routes for the synthesis of LiMn 2O 4 spinel from five different polymorphs of MnO 2 as the manganese source. These included α and β-MnO 2 and three types of γ MnO 2 (electrochemically produced EMD, and two types of chemically produced CMD). The synthesis included a lithiation step by mild reduction of the MnO 2 with glucose in a LiOH solution, followed by calcination of the lithiated product. This route was shown in a previous study to produce highly pure, nanocrystalline LiMn 2O 4. The effect of the application of ultrasound radiation in the lithiation step on the quality of the products was also explored. It was found that the degree of lithiation, the purity of the Li xMn 2O 4 spinel phase obtained and its electrochemical behavior as a Li insertion electrode material depend strongly on the nature of the MnO 2 material in terms of crystal structure and morphology. The effect of ultrasound radiation was found to be detrimental. A very good electrochemical performance (capacity, stability) in repeated Li intercalation–deintercalation cycling was obtained with LiMn 2O 4 originating from nanometric CMD. The tools for this study included XRD, TEM, surface area measurements (BET method), atomic absorption and standard electrochemical techniques (voltammetry, chronopotentiometry).

The influence of leaching chemistry on the performance of Mo6S8 cathodes for rechargeable Mg batteries was studied by XRD, XPS, and electrochemical methods. It is shown that Cu2Mo6S8, chemically leached in I2/AN (acetonitrile) or in HCl/H2O, is able to accommodate the theoretical amount of Mg²⁺ ions upon the first discharge of the electrode (two Mg atoms per formula unit). In contrast, the process of Mg extraction upon charging the electrode cannot be completed at room temperature, resulting in capacity loss between the first and subsequent cycles. Electrochemical experiments at elevated temperatures reveal that the capacity loss is not related to the leaching process, but results from an intrinsic kinetic problem of the Mg extraction from the MgMo6S8 phase. Despite the initial capacity loss, the materials leached in I2/AN or in HCl/H2O show excellent stability upon long-term cycling, with a specific capacity of 90−100 mA·h/g.

In an attempt to form a proton-selective environment in porous carbons that is similar to that of proton-conducting polymers, we used highly oxidized molecular sieving carbons that are covered by oxygen-containing surface groups. Naturally, it would be assumed that the free electron pairs of the surface oxygen atoms are those that provide specific adsorption sites for protons. However, we discovered that selective adsorption of protons takes place within the pores of the molecular sieving carbon electrode, even in the absence of surface oxides.

Certain microporous carbons have pores of molecular dimensions, the size of which can be adjusted over a wide range to fit the dimensions of a large variety of molecules. With knowing the dimensions of these molecules, size-calibrated porous carbons can be produced. In this work, we took advantage of the electronic conductivity of carbon in using it as an electrode in electrolytic solutions. By changing the electrode potential, we could induce electroadsorption and electrodesorption of ions of different dimensions into pore-calibrated carbons, thus enabling us to estimate effective ion sizes. A few fundamental questions such as whether ions accommodated in the electrodes' pores are in a solvated state, which is important for novel electrochemical energy storage devices and for microbiological systems, could be addressed. Analysis of the results indicates that all the cations that are employed are electroadsorbed in the electrode pores in hydrated states. Compared with the monovalent cations, the bivalent cations exhibit dimensions that make them almost twice as big. Monovalent anions are basically adsorbed in a nonhydrated state. The doubly charged sulfate anion is adsorbed in the hydrated state. The nitrate, a multiatom planar anion, has a smaller effective dimension than the monoatomic halogen anions, in accordance with the observation that the pores in many activated carbons are slit-shaped. The analysis of the results enabled us to establish a scale of ionic effective dimensions in aqueous media, as presented below (MTBE stands for methyl tert-butyl ether):  cations, [3.62 Å, N2] < Cs⁺ < K⁺ < Na⁺ < Li⁺ < [4.21 Å, CF4] < [5.05 Å, SF6] < [5.8 Å, MTBE] < Ba²⁺, Ca²⁺, and Mg²⁺; anions, [3.62 Å, N2] < NO3^- < Cl^- < F^- < Br^- < [4.21 Å, CF4] < ClO4^- < [5.05 Å, SF6] < [5.8 Å, MTBE] < SO^2-. We discovered that as long as the pore size is considerably greater than the ion size, the electric double-layer capacity at moderate concentrations is independent of both the size and charge of the ions in solutions.

In this work we analyzed the phenomenon of quasi solid state (QSS) lithiation of sulfur-carbon (S/C) composite electrodes with sulfur confined in the micropores of carbon matrices based on our recent studies and data published in literature. We demonstrated that the existence of sulfur in the form of small molecules is not a necessary condition for the realization of QSS mechanism. QSS operation behavior was demonstrated both for carbons with small up to 1nm micropores and for carbons with larger pore size up to 2–3 nm. A key role in the operation of S/C electrodes via a QSS mechanism plays surface electrolyte interphase (SEI) which is formed on the surface of S/C composite during the initial discharge. The formation of SEI was supported by X-ray photoelectron spectroscopy and by scanning electron microscopy. Small pore size (up to 1 nm) of the carbon matrices has a positive effect on the cycling of S/C electrodes. A superior cycling performance for more than 3500 charge-discharge cycles was demonstrated for S/C composite electrodes based on carbons synthesized by carbonization of polyvinylidene dichloride (PVDC) resin.

Low temperature electrochemical performance of amorphous monolithic columnar silicon anodes was studied in comparison to graphite composite anodes in identical cycling conditions in terms of areal capacity and current density in 1M LiPF6in fluoroethylene carbonate (FEC): dimetylcarbonate (DMC) 1:4 electrolyte solution. Marked advantage of amorphous columnar silicon anodes over composite graphite was demonstrated in 0–−30°C, especially −20–−30°C temperature range. Much higher gravimetric and volumetric capacities of Si binder free anodes compared to composite graphite electrodes provide great promise for their application in Li ion batteries at low temperature conditions.

Activated microporous carbon with narrow pores up to 1 nm, high surface area of about 1000 m2/g and pore volume of 0.43 cc/g was synthesized by facile one-step carbonization of polyvinylidene dichloride (PVDC) resin at high temperature without any additional activation process and was used for the preparation of sulfur-carbon (S/C) composite electrodes with sulfur content of 40 wt% in the composite S/C powder and 32 wt% in the composite electrode. The electrodes thus obtained, demonstrate a very stable cycling performance with more than 2000 charge-discharge cycles delivering about 600 mAh/g at a current rate of 1.04 A/g with Coulombic efficiency close to 100% at 30°C. Stable and highly reversible behavior was also obtained at 45°C for hundreds of cycles. Quasi-solid state type of behavior with single reduction plateau was observed for these Li-S cells using organic carbonates based electrolyte solutions. The formation of solid electrolyte interphase (SEI) on the surface of the cycled S/C electrodes was demonstrated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). For the composite sulfur electrodes prepared with PVDC-derived carbon the shuttle phenomena are fully avoided due to appropriate encapsulation, surface protection and quasi-solid state operation mechanism.

The effect of the electrolyte solution composition and the cycling protocol on the long-term cycling performance and surface chemistry of monolithic amorphous columnar silicon film electrodes was investigated using electrochemical tools, XPS, SEM and EDS. An excellent cycling stability of Si electrodes in fluoroethylene carbonate (FEC)-based electrolyte solutions was demonstrated. It relates to the ability of FEC to form polyenes, as well as to a high rate of HF formation in its water contaminated LiPF6solutions, measured by 19F NMR spectroscopy. We found that excellent passivation in FEC solutions related to a low content of oxygen containing moieties in surface films. Galvanostatic tests and spectroscopic analyzes revealed also a strong dependence of the composition and properties of the surface films on amorphous Si electrodes on the cycling procedure. Repeated deep discharge of Si electrodes down to 10 mV vs. Li/Li+from the very beginning of the electrodes life ensures the formation of thin effective surface films on their surface and good cycling performance. Cycling stability of Si electrodes in LiPF6solutions decreases in the following order FEC/DMC > 3,4-trans-difluoroethylene carbonate (DFEC)/DMC > ethylene carbonate (EC)/DMC > propylene carbonate (PC).

We developed a methodology of in situ Fourier transform infrared (FTIR) measurements of gaseous products formed in an electrochemical cell upon polarization. LiNi0.8Co0.15Al0.05O2(NCA) cathodes were explored at potentials of up to 5.5 V vs Li in the ionic liquid (IL)-based electrolyte solution, LiTFSI/N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide. The polarization of the NCA electrodes formed CO2and CO due to the liberation of oxygen and the parallel dissolution of nickel ions, which oxidizes the carbon black in the composite electrode. The oxygen was mostly liberated from the NCA and also due to minor contribution from the surface groups on the carbon black additive.

We report on the electrochemical characterization of activated, highly porous carbons in TEABF4(TEA=tetraethylammonium)/propylene carbonate solutions. One of two selected carbons had a large number of micropores, whereas the other contained mesopores. The behavior of charged carbon electrodes upon prolonged storage at elevated temperatures was explored. A combined application of various electroanalytical techniques enabled the determination of the electrodes' capacitance retention and serial resistance as functions of storage time. The loss of capacitance of the charged electrodes during storage of electric double-layer capacitor (EDLC) pouch cells, determined by their postmortem electrochemical characterization, was more pronounced for the carbon electrode of higher porosity. The capacitance loss concerned the negative carbon electrode only and was attributed to the partial trapping of cations in the porous structure. The trapped cations could be completely released at moderate anodic polarizations of the carbon electrode. The mechanism of the trapping phenomenon seems to be complex, comprising a number of potential and time-dependent steps, such as penetration of the cations into the smallest pores of the carbon electrode (less than 1nm) and adsorption of the cations within the walls of the smallest pores containing energetically different types of carbon sites.

In this paper, the study of three types of graphite electrodes in two types of ionic liquid solutions (ILs) using in situ Raman spectroscopy and X-ray diffraction in conjunction with electrochemical techniques such as voltammetry is described. The graphite materials included two types of synthetic flakes, differing from each other in their average particle size, and natural graphite flakes. The ILs included 1-methyl-1-propylpiperidinium bis(trifluoromethyl sulfonyl)imide (MPPp-TFSI) and 1-methyl-1-butyl pyrrolidinium bis(trifluoromethyl sulfonyl)imide (BMP-TFSI). The Li salt was Li TFSI. The graphite electrodes can intercalate with both Li ions and IL cations simultaneously. The latter intercalate with graphite at higher potentials (the onset potential is 0.7V). The graphite electrodes develop passivation in the above Li TFSI/Li solutions upon their cathodic polarization, which blocks the intercalation of the IL cations but allows highly reversible intercalation with lithium. In situ Raman spectroscopy proved to be a very useful tool for studying both Li and IL cation intercalation processes with graphite electrodes and for determining their onset and reversibility. The effectiveness of the passivation of graphite electrodes in these solutions depends on both the type of graphite used and the structure of the IL cations. The most effective passivation, developed during a first cathodic polarization of the electrodes, was found for natural graphite electrodes and for MPPp+-based solutions. The important factors that may determine the performance of graphite electrodes in these systems are discussed.

In this work, the behavior of composite graphite electrodes comprising synthetic graphite flakes in solutions based on a 1-methyl-1-propylpiperidinium [bis(trifluoromethylsulfonyl)] imide (MPPpTFSI)ionic liquid (IL) was investigated, using in situ Raman spectroscopy with microscopic lateral resolution, in conjunction with cyclic voltammetry. Both pure IL and IL solutions containing a LiN(SO2CF3)2(LiTFSI) salt were studied. Upon cathodic polarization, the IL cations (MPPp+)are intercalated. This process is irreversible in a pure IL solution. When the solution comprises both IL and a Li salt (LiTFSI), the graphite electrodes can intercalate simultaneously the IL cations MPPp+and the Li cations at potentials ∼0.5Vand below 0.3Vvs Li∕Li+, respectively. The graphite electrodes become passivated due to the presence of the Li salt by the formation of surface films, which are Li–ion conducting, but electronically insulating. Hence, upon consecutive voltammetric cycling, the IL cation–intercalation is suppressed, while reversible Li intercalation becomes the dominant process. Raman spectroscopy enables one to distinguish among the various processes in these systems.

We report on the study of the electrochemical behavior of copper and brass electrodes in concentrated aqueous KOHsolutions. Passive films are formed on the surface of anodically polarized, pure polycrystalline copper and a Cu-30Znalloy (α-brass), in aqueous 30% (7 M) and 45% (11.7 M) KOHelectrolyte solutions, at two characteristic potentials (corresponding to the two major anodic peaks in the voltammograms of these systems). The structure and composition of the films were determined by ex situ X-ray diffraction (XRD), in situ and ex situ micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The formation of crystalline cubic Cu2O, on the surface of Cu and Cu-30Znelectrodes in highly concentrated KOHsolutions, occurs at potentials above −400mVvs a standard hydrogen electrode (SHE). A porous passive layer is formed at potentials above −150mVvs SHE on pure Cu surfaces. In a 30%KOHsolution, this surface layer consists of Cu(OH)2, while in a 45%KOHsolution, the surface films comprise a Cu2O∕Cu(OH)2structure with the Cu2Oas the inner layer. The anodic polarization of Cu-30Zn(α-brass) leads to a complete dezincification of the surface, at potentials −350mVvs SHE, in both electrolyte solutions. Porous surface layers are formed on brass at these anodic potentials and have duplex structure, Cu2O∕Cu(OH)2, where the Cu(OH)2content increases with an increase in the KOHconcentration. At potentials −150mVvs SHE, the Cu(OH)2layer shows a preferential orientation of (020).

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