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Understanding of lithium polysulfide (Li-PS) formation and the shuttle phenomenon is essential for practical application of the lithium/sulfur (Li/S) cell, which has superior theoretical specific energy (2600 Wh/kg). However, it suffers from the lack of direct observation on behaviors of soluble Li-PS in liquid electrolytes. Using in situ graphene liquid cell electron microscopy, we have visualized formation and diffusion of Li-PS simultaneous with morphological and phase evolutions of sulfur nanoparticles during lithiation. We found that the morphological changes and Li-PS diffusion are retarded by ionic liquid (IL) addition into electrolyte. Chronoamperometric shuttle current measurement confirms that IL addition lowers the experimental diffusion coefficient of Li-PS by 2 orders of magnitude relative to that in IL-free electrolyte and thus suppresses the Li-PS shuttle current, which accounts for better cyclability and Coulombic efficiency of the Li/S cell. This study provides significant insights into electrolyte design to inhibit the polysulfide shuttle phenomenon.

The micrometer-scale reticulated structure of highly sulfur-philic nitrogen-doped graphene oxide (NrGO) that is achieved by chemically controlling the nitrogen-doping degree improves the chemical and electrochemical stability of the active sulfur while providing sufficient sulfur/electrolyte interface for a facile electrochemical process so that a high specific energy of 325 W h kg−1can be achieved.

Rational design of sulfur electrodes is exceptionally important in enabling a high-performance lithium/sulfur cell. Constructing a continuous pore structure of the sulfur electrode that enables facile lithium ion transport into the electrode and mitigates the reconstruction of sulfur is a key factor for enhancing the electrochemical performance. Here, we report a three-dimensionally (3D) aligned sulfur electrode cast onto conventional aluminum foil by directional freeze tape casting. The 3D aligned sulfur–graphene oxide (S–GO) electrode consisting of few micron thick S–GO layers with 10–20 μm interlayer spacings demonstrates significant improvement in the performance of the Li/S cell. Moreover, the freeze tape cast graphene oxide electrode exhibits homogeneous reconfiguration behavior in the polysulfide catholyte cell tests and demonstrated extended cycling capability with only 4% decay of the specific capacity over 200 cycles. This work emphasizes the critical importance of proper structural design for sulfur–carbonaceous composite electrodes.

With the increasing interest in transition metal chalcogenides, sulfide minerals containing the disulfide unit (S22-) have gained intensive attention for potential applications in energy storage devices, such as lithium-ion batteries (LIBs). Vanadium tetrasulfide (VS4) possesses a unique linear-chain structure with a Peierls distortion and shows great promise for application in LIBs. However, its electrochemical reaction mechanism is still controversial, mainly due to the amorphous nature of the intermediates and final products. Here, by applying multiple X-ray spectroscopies, we reveal that VS4undergoes lithium intercalation and conversion reactions sequentially during the first discharge process, which are partially reversible in the subsequent charge process. However, an anomalous intercalation/conversion mixed reaction mechanism is dominant for the second cycle, mainly owing to the amorphization of the VS4electrode during the first cycle. In addition, the sulfur atoms are also involved in the redox reaction during cycling, with the anionic contribution of S22-↔2S2-transformation. Furthermore, we find that the formation process of the solid electrolyte interphase is highly dynamic during the discharge and charge processes. The present study provides deeper insights into the complex reaction mechanism of VS4. This knowledge can accelerate the development of high-performance VS4-based electrode materials for LIBs.

As the lightest and cheapest transition metal dichalcogenide, TiS2possesses great potential as an electrode material for lithium batteries due to the advantages of high energy density storage capability, fast ion diffusion rate, and low volume expansion. Despite the extensive investigation of its electrochemical properties, the fundamental discharge–charge reaction mechanism of the TiS2electrode is still elusive. Here, by a combination of ex situ and operando X-ray absorption spectroscopy with density functional theory calculations, we have clearly elucidated the evolution of the structural and chemical properties of TiS2during the discharge–charge processes. The lithium intercalation reaction is highly reversible and both Ti and sulfur are involved in the redox reaction during the discharge and charge processes. In contrast, the conversion reaction of TiS2is partially reversible in the first cycle. However, Ti—O related compounds are developed during electrochemical cycling over extended cycles, which results in the decrease of the conversion reaction reversibility and the rapid capacity fading. In addition, the solid electrolyte interphase formed on the electrode surface is found to be highly dynamic in the initial cycles and then gradually becomes more stable upon further cycling. Such understanding is important for the future design and optimization of TiS2based electrodes for lithium batteries.

Sulfur deposition is an effective method for creating composites of sulfur with various conductive materials. In this study we investigated the details of the deposition process of sulfur onto graphene oxide (GO). It was revealed that just mixing a polysulfide solution and a GO suspension resulted in the deposition of sulfur onto the GO under alkaline conditions. The combination of the alkaline deposition and subsequent acidic deposition at different temperatures yielded materials with various morphologies. The sulfur deposition rate influenced the morphology of the S deposit and the resulting Li/S cell performance. By controlling the process with a moderate time for the alkaline deposition and subsequent acidic deposition at a decreased temperature, a preferred morphology of the sulfur/GO composite with a high sulfur utilization was successfully synthesized. This preferred morphology of SGO provides for a high-performance Li/S cell.

High capacity and long cycle life are both desirable features for practical secondary cells. In this study, we compare two different synthesis processes for preparing active materials for lithium/sulfur cells using polysulfide and graphene oxide (GO) showing high sulfur utilization and cycling stability. The key factor determining cell performance is the oxygen-containing functional groups on GO and the fine structures. This study shows the possibility of application of GO for enhanced capacity and cycling stability.

Fully lithiated lithium sulfide (Li2S) has become a promising cathode material for Li/S cells due to its high theoretic capacity (1166mAhg−1) and specific energy (2600Whkg−1). However, low utilization of sulfur and poor rate capability still hinder the practical application of Li/S cells. In this paper, a carbon coated Li2S/graphene composite (Li2S/G@C) was developed by incorporating Li2S nano spheres with single-layered graphene and further forming a durable protective carbon layer on the surface of the Li2S particles using a facile CVD method. The high rate capability and remarkable cycle life of the Li2S/G@C cathode were demonstrated, which was mainly attributed to the unique structure of the Li2S/G@C that can significantly improve not only the electrical conductivity, but also the mechanical stability of the sulfur cathode.

We have investigated the chemical bonding interaction of S in a CTAB (cetyltrimethylammonium bromide, CH3(CH2)15N+(CH3)3Br–)-modified sulfur–graphene oxide (S–GO) nanocomposite used as the cathode material for Li/S cells by S K-edge X-ray absorption spectroscopy (XAS). The results show that the introduction of CTAB to the S–GO nanocomposite and changes in the synthesis recipe including alteration of the S precursor ratios and the sequence of mixing ingredients lead to the formation of different S species. CTAB modifies the cathode materials through bonding with Na2Sxin the precursor solution, which is subsequently converted to C–S bonds during the heat treatment at 155 °C. Moreover, GO bonds with CTAB and acts as the nucleation center for S precipitation. All these interactions among S, CTAB, and GO help to immobilize the sulfur in the cathode and may be responsible for the enhanced cell cycle life of CTAB–S–GO nanocomposite-based Li/S cells.

Lithium-ion batteries dominate the battery field, particularly for electric and hybrid vehicles. Monoclinic Li3V2(PO4)3has emerged as one of the most promising candidates for the cathode in lithium-ion batteries, offering better environmental safety and lower cost than competing materials. We have used in situX-ray absorption spectroscopy to characterize the evolution of the vanadium in a Li3V2(PO4)3cathode as it is cycled electrochemically. These data demonstrate the presence of significant kinetic effects such that the measured electrochemical behavior does not represent the bulk vanadium. When the cell is cycled between 3 and 4.5 V, there are two distinct vanadium species. When the potential is raised above 4.5 V, a third species is observed, consistent with formation of V5+. XANES data for the cathode after 3–4.8 V cycling are consistent with a severely distorted vanadium site, suggesting that lithium–vanadium antisite mixing may be responsible for the electrochemical irreversibility that is seen above 4.5 V.

Functionalized porous carbons are necessary for the reversible operation of lithium-sulfur batteries (LSBs), however, their appropriate utilization and physicochemical states in the sulfur cathode are still unclear. Although numerous studies regarding distribution of sulfur in the pores of the carbon framework in the cathode have been reported, sulfur distribution and oxygen coverage on the carbon surface after sulfur infiltration have not been clearly investigated. In this study, we scrutinized the role of the pores in the oxygen-functionalized mesoporous carbon nanoparticle (O-MCN). Furthermore, we elaborated sulfur distribution, oxygen coverage, and pore utilization of O-MCN under the three different sulfur infiltration process. The soft x-ray scanning transmission x-ray microscopy (STXM) was used for the first time in the LSB system. The STXM enabled probing of local distribution of sulfur and the chemical nature of sulfur and oxygen in O-MCNs. Our findings provide a comprehensive understanding about how the sulfur infiltration process impacts the sulfur utilization during the redox reaction of sulfur in the oxygen-functionalized mesoporous carbon.

Alkaline fuel cell technology has been reinvigorated since the recent rapid development and deployment of anion exchange membranes. Without the "acid-stability" requirement in low pH environments such as that of proton exchange membrane fuel cells, a much wider range of materials including noble metals, non-noble transition metals, and even metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media have been developed due to both thermodynamic and kinetic reasons. As compared to the rapidly increasing number of reports on the development of novel catalyst materials, the understanding of the reaction mechanisms of the various ORR electrocatalysts is quite insufficient, and the application and investigation in real alkaline anion exchange membrane fuel cells (AAEMFCs) is even scarcer. By reviewing the compositions, preparation methods, physiochemical properties and ORR performance of different categories of cathodic electrocatalysts that have emerged in the past few years, some common and intrinsic properties and factors that account for the superior activity of these materials may be extracted and summarized, which may further help to identify the reasons for the kinetic facility of the ORR in alkaline media. Some practical issues of utilization of the promising novel replacement materials for the state-of-the-art Pt-based cathodic electrocatalysts in AAEMFCs are pointed out. In addition to the progress on the development of novel materials with outstanding ORR activity, many and varied compositions and morphologies in one, two and three dimensions, scalable preparation technologies, low cost, and other unique properties, some feedback on the performance and especially the problems of their use as cathodes in AAEMFCs is urgently needed. Such feedback should provide guidelines for the design and manufacture of next-generation electrocatalysts and accelerate the application of AAEMFCs.

Lithium/sulfur (Li/S) cells have a theoretical specific energy five times higher than that of lithium-ion (Li-ion) cells (2600 vs. ~500Whkg−1). The conventional Li/S cells that use an organic liquid electrolyte are short-lived with low coulombic efficiency due to the polysulfide shuttle. We herein design carbon-coated NanoLi2S (NanoLi2S@carbon) composites, which consist of Li2S nanoparticles as the core and a carbon coating as the shell. The carbon shell prevents the NanoLi2S core from directly contacting the liquid electrolyte, which improves the performance of Li/S cells to provide longer cycle life and high sulfur utilization. The cyclability of Li/S cells is further enhanced by mixing the core–shell NanoLi2S@carbon composites with graphene oxide, which chemically immobilizes polysulfides in the cathode through their functional groups. The resulting Li/S cell shows an initial specific discharge capacity of 1263mAhg−1(normalized to sulfur) at the C/10 rate and a capacity retention of 65.4% after 200 cycles. The capacity decay mechanism during cycling is also characterized in detail using near edge X-ray absorption fine structure (NEXAFS) spectra.

was investigated to understand the effect of replacement of the cobalt by aluminum on the structural and electrochemical properties. In situ X-ray absorption spectroscopy (XAS) was performed, utilizing a novel in situ electrochemical cell, specifically designed for long-term X-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range. XAS measurements were performed at different states of charge (SOC) during cycling, at the Ni, Co, and the Mn edges, revealing details about the response of the cathode to Li insertion and extraction processes. The extended X-ray absorption fine structure (EXAFS) region of the spectra revealed the changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the SOC of the material. The oxidation states of the transition metals in the system are , , and in the as-made material (fully discharged), while during charging the is oxidized to through an intermediate stage of , is oxidized toward , and Mn was found to be electrochemically inactive and remained as . The EXAFS results during cycling show that the Ni-O changes the most, followed by Co-O, and Mn-O varies the least. These measurements on this cathode material confirmed that the material retains its symmetry and good structural short-range order leading to the superior cycling reported earlier.

and have been characterized using and magic angle spinning (MAS) nuclear magnetic resonance spectroscopy. was synthesized by a hydrothermal route and was synthesized at high temperature in an inert atmosphere. Both compositions give rise to single isotropic resonances. The MAS isotropic peak linewidth for is considerably larger than that for suggesting the presence of local disorder in the Li coordination sphere for In both samples, the isotropic peak is accompanied by a large, asymmetric spinning sideband manifold, arising from bulk magnetic susceptibility broadening and the paramagnetic interaction between the lithium nucleus and transition metal unpaired electrons. (c) 2002 The Electrochemical Society. All rights reserved.

magic angle spinning nuclear magnetic resonance was used to observe coexisting cubic and tetragonal phases in . Cubic phase peaks are observed at vs. ; tetragonal phase peaks are observed around . Cycling on the plateau does not result in significant changes in the cubic phase. A small amount of residual tetragonal phase accounting for [?]3% of the NMR intensity, however, is observed in spinel deep discharged to then returned to . (c)2000 The Electrochemical Society

We introduce a simple and easy way to functionalize the surface of various carbonaceous materials through the ultraviolet light/ozone (UV/O3) plasma where we utilize the zero-, one-, and two-dimensional carbon frameworks. In a general manner, the lamps of a UV/O3generator create two different wavelengths (λ = 185 and 254 nm); the shorter wavelength (λ = 185 nm) dissociates the oxygen (O2) in air and the longer wavelength (λ = 254 nm) dissociates the O3and creates the reactive and monoatomic oxygen radical, which tends to incorporate onto the defects of the carbons. By tailoring the association and dissociation of the oxygen with various forms, carbon black, carbon nanofibers, and graphite flakes, chosen as representative models for the zero-, one-, and two-dimensional carbon frameworks, their structure can be oxidized, respectively, which is known as photochemical oxidation. Various carbons have their own distinctive morphology and electron transport properties, which are applicable for the lithium–sulfur (Li–S) cell. We, here, report on the improvement of electrochemical performance of the lithium/sulfur cell through such an efficient functionalization approach.

To date, Li2S has drawn significant attention as a positive electrode active material for rechargeable lithium cells due to its high theoretical specific capacity and capability of pairing with a lithium-free anode which can obviate any safety concern of the lithium metal anode when using sulfur. In recent years, various approaches have been employed to develop Li/Li2S rechargeable cells for commercialization that meet the performance goals for high energy/power applications. It is expected that high lithium sulfide-loading cells with long cycle life, an excellent capacity delivery and low electrolyte:sulfur weight ratio (E/S ratio) can be achieved. Here, we report a Li2S electrode comprised of a novel Li2S/KB@Cf nanocomposite which delivers an areal capacity of 7.56 mAh cm-2and good cycling stability with a mass loading of 11.29  mg cm-2and a robust 3-dimensional (3D) aluminum foam current collector with a high open area. The high conductivity and scalability of the active material, the availability of 3D current collection for the active material and the control of the electrolyte/sulfur ratio offer the potential of realization of practical Li/S cells.

Alkaline fuel cell technology has been reinvigorated since the recent rapid development and deployment of anion exchange membranes. Without the “acid-stability” requirement in low pH environments such as that of proton exchange membrane fuel cells, a much wider range of materials including noble metals, non-noble transition metals, and even metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media have been developed due to both thermodynamic and kinetic reasons. As compared to the rapidly increasing number of reports on the development of novel catalyst materials, the understanding of the reaction mechanisms of the various ORR electrocatalysts is quite insufficient, and the application and investigation in real alkaline anion exchange membrane fuel cells (AAEMFCs) is even scarcer. By reviewing the compositions, preparation methods, physiochemical properties and ORR performance of different categories of cathodic electrocatalysts that have emerged in the past few years, some common and intrinsic properties and factors that account for the superior activity of these materials may be extracted and summarized, which may further help to identify the reasons for the kinetic facility of the ORR in alkaline media. Some practical issues of utilization of the promising novel replacement materials for the state-of-the-art Pt-based cathodic electrocatalysts in AAEMFCs are pointed out. In addition to the progress on the development of novel materials with outstanding ORR activity, many and varied compositions and morphologies in one, two and three dimensions, scalable preparation technologies, low cost, and other unique properties, some feedback on the performance and especially the problems of their use as cathodes in AAEMFCs is urgently needed. Such feedback should provide guidelines for the design and manufacture of next-generation electrocatalysts and accelerate the application of AAEMFCs.

Variation in the rate of anodic oxidation of normal saturated hydrocarbons (at current densities of half the maximum value or higher) with the carbon number parallels the variation in the rate of diffusion (in electrochemical equivalents) of the hydrocarbon through the electrolyte. This parallelism, not previously recognized, is consistent with the concept of diffusion-influenced anode reactions. The conditions under which this behavior is expected are presented.

Li(Ni0.4Co0.15Al0.05Mn0.4)O2was investigated to understand the effect of replacement of the cobalt by aluminum on the structural and electrochemical properties. In situ X-ray absorption spectroscopy (XAS) was performed, utilizing a novel in situelectrochemical cell, specifically designed for long-term X-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range. (1.0–4.7V)XAS measurements were performed at different states of charge (SOC) during cycling, at the Ni, Co, and the Mn edges, revealing details about the response of the cathode to Li insertion and extraction processes. The extended X-ray absorption fine structure (EXAFS) region of the spectra revealed the changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the SOC of the material. The oxidation states of the transition metals in the system are Ni2+, Co3+, and Mn4+in the as-made material (fully discharged), while during charging the Ni2+is oxidized to Ni4+through an intermediate stage of Ni3+, Co3+is oxidized toward Co4+, and Mn was found to be electrochemically inactive and remained as Mn4+. The EXAFS results during cycling show that the Ni–O changes the most, followed by Co–O, and Mn–O varies the least. These measurements on this cathode material confirmed that the material retains its symmetry and good structural short-range order leading to the superior cycling reported earlier.

We have employed tetra(ethylene glycol)dimethyl ether (TEGDME) as a polymer solvent in mixed electrolytes composed of N-methyl-n-butyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI), LiTFSI, and TEGDME and characterized their physical and electrochemical properties as well as the cyclability of Li∕Scells with PYR14TFSI+xLiTFSI (x=molesLiTFSI∕kgPYR14TFSI)+yTEGDME (y=kgTEGDME∕kgPYR14TFSI)electrolyte. The addition of the TEGDME polymer solvent to the PYR14TFSI+0.2mLiTFSI+yTEGDME mixtures resulted in a significant enhancement of ionic conductivity, particularly at lower temperatures. Interfacial impedance and galvanostatic Li cycling measurements show that the PYR14TFSI+0.2mLiTFSI+yTEGDME ternary mixture exhibits excellent compatibility with Li metal electrodes. The use of the ternary mixture as an electrolyte in a Li∕Scell provided good charge and discharge capability of the cell at room temperature with a discharge capacity of 887mAh∕gsulfur at 0.054mA∕cm2and at low temperature (∼0°C)with a discharge capacity of about 440mAh∕gsulfur at 0.033mA∕cm2for the first cycle, respectively (theoretical specific capacity 1672mAh∕gsulfur). In addition, the cell tested at 0°Cexhibited a stable cyclability after the 5thcycle, with a discharge capacity of 248mAh∕gsulfur for the 20thcycle.

After the recent upsurge of interest in the layered LiNi1∕3Co1∕3Mn1∕3O2system for use as a cathode material for rechargeable lithium batteries, we have studied the charge compensation mechanism and structural perturbations occurring during cycling of the novel layered system of Li1.05Ni0.35Co0.25Mn0.4O2coated with nano-crystallized LiCoO2, which effectively improved the rate capability. In addition, the LiCoO2evidently suppressed any structural change of the Li1.05Ni0.35Co0.25Mn0.4O2. In situ X-ray absorption spectroscopy (XAS) measurements were performed utilizing a novel in situ electrochemical cell, specifically designed for long-term X-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range (2.8–4.8V). The electrode contained 1.9mgof Li1.05Ni0.35Co0.25Mn0.4O2on a 25μmAl foil, and had an area of 0.79cm2. XAS measurements were performed at different states of charge (SOC) during cycling, at the Ni, Co, and the Mn edges, revealing details about the response of the cathode to Li insertion and extraction processes. Extended X-ray absorption fine structure region of the spectra revealed the changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the SOC of the material. We found that the oxidation states of the transition metals in the system are Ni2+, Co3+, and Mn4+in the fully discharged condition. During charging the Ni2+is oxidized to Ni4+through an intermediate stage of Ni3+, Co3+is oxidized almost to Co4+. Utilizing a combination of Faraday’s calculation and XAS results, the Co was found to be at Co3.89+at the end of the charge, whereas Mn was found to be electrochemically inactive and remains as Mn4+. These measurements on this cathode material confirmed that the material retains its symmetry and good structural short-range order leading to superior cycling.

The electrochemical stability and electrocatalytic performance in ethanol oxidation of a new class of anode electrocatalysts is presented. Nanopowders of the Laves-phase intermetallic compounds LnPt2(Ln=Ce,Pr)were utilized to exploit the strong oxidizing power of tetravalent lanthanides in an anode electrocatalyst. These nanopowders are stable in the environment of the anode of a polymer electrolyte membrane (PEM) fuel cell. Steady-state polarization curves in an operating PEM fuel cell demonstrate that the new electrocatalysts are active toward the electro-oxidation of ethanol. The new electrocatalysts exhibited ca. 225mVmore overpotential than PtRu at a given current density based on the total electrocatalyst surface area in the anode, but this may be due to issues with particle size and electrode structure. Analysis of the anode effluent with on-line gas chromatography showed that two-electron electro-oxidation to acetaldehyde was the main reaction pathway at potentials of interest and implied that ethanol adsorbs without C–C bond cleavage through the oxygen in the hydroxyl group.

An aqueous route for producing nanopowders of intermetallic compounds is presented. The method was developed to produce powders of PrPt2and CePt2for use as anode electrocatalysts in porous direct ethanol polymer electrolyte membrane (PEM) fuel cell anodes. Powders that are relatively pure with average particle diameters of ca. 25nmand specific surface areas of ca. 15m2∕gwere produced. X-ray powder diffraction patterns were utilized to verify the structure of the product and conduct rudimentary unit cell refinement. Nitrogen adsorption measurements confirmed the specific surface area that was determined from the X-ray diffraction results.