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Li and Mn-rich nickel cobalt manganese oxide (LMR-NCM) is one of the most promising cathode materials for realizing next-generation Li-ion batteries due to its high specific capacity of >250 mA h g-1 and operating potential > 4.5 V. Nevertheless, being plagued by severe capacity fading and voltage decay, the commercialization of LMR-NCM appears to be a distant goal. The anionic activity of oxygen and associated phase transformations are the reasons behind the unstable electrochemical performance. The tendency of LMR-NCM to react with CO2 and moisture further makes it prone to interfacial instability and degradation. Here, we report a neoteric method to mitigate the stability issues and improve the electrochemical performance of LMR-NCM by changing the electronic configuration of constituting O and transition metals via diethylzinc-assisted atomic surface reduction (Zn-ASR) using an extremely facile protocol. With the proposed Zn-ASR, a 2-3 nm thin layer of a reduced surface enriched with complex ZnOx or ZnOxRy was obtained on the LMR-NCM particles. X-ray photoelectron spectroscopy suggested the transfer of ethyl groups of diethylzinc to O atoms on the LMR-NCM surface, which ultimately led to the reduction of near-surface Mn and Ni atoms and impeded irreversible anionic activity. The presence of ZnOx/ZnOxRy also resulted in superior charge transfer and resistance against HF. As a result, in contrast to LMR-NCM, the Zn-ASR-treated sample exhibited substantially improved rate capabilities, facilitated charge transfer, enhanced capacity retention, reduced parasitic reactions, and long-term stability as reflected from in-depth electrochemical analysis, in operando gaseous evolution studies, and post-mortem microscopic analysis.

In a lithium–sulfur battery (LSB) discharge process, elemental sulfur is reduced to Li2S via a multi-step process. The soluble lithium-polysulfide (PS) (Li2Sn) intermediate species then diffuses th...

Exploring and identifying efficient materials with operative active sites for electrochemical oxygen evolution reaction (OER) is of paramount importance for the future of energy conversion technolo...

We demonstrate a novel surface modification of Li- and Mn-rich cathode materials 0.33Li2MnO3·0.67LiNi0.4Co0.2Mn0.4O2 for lithium-ion batteries (high-energy Ni-Co-Mn oxides, HE-NCM) via their heat treatment with trimesic acid (TA) or terephthalic acid at 600 °C under argon. We established the optimal regimes of the treatment-the amounts of HE-NCM, acid, temperature, and time-resulting in a significant improvement of the electrochemical behavior of cathodes in Li cells. It was shown that upon treatment, some lithium is leached out from the surface, leading to the formation of a surface layer comprising rock-salt-like phase Li0.4Ni1.6O2. The analysis of the structural and surface studies by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy confirmed the formation of the above surface layer. We discuss the possible reactions of HE-NCM with the acids and the mechanism of the formation of the new phases, Li0.4Ni1.6O2 and spinel. The electrochemical characterizations were performed by testing the materials versus Li anodes at 30 °C. Importantly, the electrochemical results disclose significantly improved cycling stability (much lower capacity fading) and high-rate performance for the treated materials compared to the untreated ones. We established a lower evolution of the voltage hysteresis with cycling for the treated cathodes compared to that for the untreated ones. Thermal studies by differential scanning calorimetry also demonstrated lower (by ∼32%) total heat released in the reactions of the materials treated with fluoroethylene carbonate (FEC)-dimethyl carbonate (DEC)/LiPF6 electrolyte solutions, thus implying their significant surface stabilization because of the surface treatment. It was established by a postmortem analysis after 400 cycles that a lower amount of transition-metal cations dissolved (especially Ni) and a reduced number of surface cracks were formed for the 2 wt % TA-treated HE-NCMs compared to the untreated ones. We consider the proposed method of surface modification as a simple, cheap, and scalable approach to achieve a steady and superior electrochemical performance of HE-NCM cathodes.

Catalyst poisoning is a prominent issue, reducing the lifetime of catalysts and increasing the costs of the processes that rely on them. The electrocatalysts that enable green energy conversion and storage, such as proton exchange membrane fuel cells and hydrogen bromine redox flow batteries, also suffer from this issue, hindering their utilization. Current solutions to protect electrocatalysts from harmful species fall short of effective selectivity without inhibiting the required reactions. This article describes the protection of a standard 50% Pt/C catalyst with a V2O5 coating through atomic layer deposition (ALD). The ALD selectively deposited V2O5 on the Pt, which enhanced hydrogen transport to the Pt surface and resulted in a higher mass activity in alkaline electrolytes. Cyclic voltammetry and X-ray photoelectron spectroscopy showed that the Pt was protected by the coating in the HBr/Br2 electrolyte which dissolved the uncoated 50% Pt/C in under 3 min.

Rechargeable metal–sulfur batteries (RMSBs) represent one of the most attractive electrochemical systems in terms of energy density and cost. In most of the proposed systems, the anode side is metallic and the cathode side is elemental sulfur impregnated in a porous matrix. Despite the relatively low voltage of these systems, they attract a lot of attention and are considered to be very promising as next-generation batteries for the following reasons: (1) utilization of active metal anodes enables a leap in specific energy due to the high capacity of metal anodes in comparison to intercalation compounds, (2) sulfur as a cathode exhibits high theoretical specific capacity (1675 mAh/g), and (3) system components make RMSBs low-cost, less toxic batteries. Nevertheless, the high reactivity of metallic anodes (e.g., Li, Na, Mg, and Al) and the solubility of sulfur species in the electrolyte render these batteries unstable and hinder their practical realization. In this Perspective, we focus on rechargeable sul...

Most of the recently discovered layered materials such as MoS2 or MoSe2 are n-type, while few materials, such as phosphorene, which suffers from rapid oxidation, are p-type. To form devices such as p–n junctions and heterojunctions, new p-type mono-/few-layers are needed. Here, we report a one-step synthesis of layered, crystalline, p-type copper sulfide by thermal annealing of a standard copper foil in an inert environment using chemical vapor deposition (CVD). Optical spectroscopies (photoluminescence and absorption) show definite correlating features around 2.5 eV. Surface photovoltage spectroscopy shows a photovoltage reduction around the same energy range, which would be expected from a bandgap of a p-type material, and p-type conductivity was also observed using a thermoelectric probe. TEM, XRD, and AFM showed that the synthesized material is layered and has a unique stoichiometry of Cu9S5. Using sonication and dropcasting, we succeeded to isolate few-layers and monolayers. We observed good bulk ele...

LiNi0.8Co0.1Mn0.1O2 (NCM811) is a promising cathode material for long range electric vehicles. However, the material suffers severe chemo-mechanical degradation that can cause gradual capacity loss upon prolonged cycling. Surface passivation of NMC811 was demonstrated to help in retaining the structural integrity of the material upon extended cycling. Herein, we report the surface passivation of the NCM811 using Li2S and Na2S precursors via direct and simple wet chemical treatment, for the mitigation of parasitic reactions at the electrode electrolyte interphase. This phenomenon is accompanied by increase in the oxidation state of sulfur (from sulfide to sulfate) and partial reduction in the oxidation state of nickel. Electrochemical performance measurements show that the M2SO4 (M: Li, Na) protection layer on NMC811 behaves as an artificial cathode electrolyte interphase (ACEI) that enhance the capacity retention by 25% during prolong cycling with respect to the untreated NMC811. Postmortem morphology studies reveal that the thin metal sulfates coatings remain on the cathode even after 100 cycles, while the untreated NCM811 shows severe morphological instabilities. Our study demonstrates that by simple chemical treatment of NMC811 can enhance its overall stability and cycling performance for the development of advanced high energy density Lithium-ion battery systems.

Li metal is among the most attractive anode materials for secondary batteries, with a theoretical specific capacity > 3800 mAh g–1. However, its extremely low electrochemical potential is associated with high chemical reactivity that results in undesirable reduction of electrolyte species on the lithium surface, leading to spontaneous formation of a solid electrolyte interphase (SEI) with uncontrolled composition, morphology, and physicochemical properties. Here, we demonstrate a new approach to stabilize Li metal anodes using a hybrid organic/inorganic artificial solid electrolyte interphase (ASEI) deposited directly on the Li metal surface by self-healing electrochemical polymerization (EP) and atomic layer deposition (ALD). This hybrid protection layer is thin, flexible, ionically conductive, and electrically insulating. We show that Li metal protected by the hybrid protection layer gives rise to very stable cycling performance for over 300 cycles at current density 1 mA/cm2 and over 110 cycles at curr...

Materials that undergo conversion reactions to form different materials upon lithiation typically offer high specific capacity for energy storage applications such as Li ion batteries. However, since the reaction products often involve complex mixtures of electrically insulating and conducting particles and significant changes in volume and phase, the reversibility of conversion reactions is poor, preventing their use in rechargeable (secondary) batteries. In this paper, we fabricate and protect 3D conversion electrodes by first coating multiwalled carbon nanotubes (MWCNT) with a model conversion material, RuO2, and subsequently protecting them with conformal thin-film lithium phosphous oxynitride (LiPON), a well-known solid-state electrolyte. Atomic layer deposition is used to deposit the RuO2 and the LiPON, thus forming core double-shell MWCNT@RuO2@LiPON electrodes as a model system. We find that the LiPON protection layer enhances cyclability of the conversion electrode, which we attribute to two factors. (1) The LiPON layer provides high Li ion conductivity at the interface between the electrolyte and the electrode. (2) By constraining the electrode materials mechanically, the LiPON protection layer ensures electronic connectivity and thus conductivity during lithiation/delithiation cycles. These two mechanisms are striking in their ability to preserve capacity despite the profound changes in structure and composition intrinsic to conversion electrode materials. This LiPON-protected structure exhibits superior cycling stability and reversibility as well as decreased overpotentials compared to the unprotected core-shell structure. Furthermore, even at very low lithiation potential (0.05 V), the LiPON-protected electrode largely reduces the formation of a solid electrolyte interphase.

This work continues our systematic study of Li- and Mn- rich cathodes for lithium-ion batteries. We chose Li2MnO3 as a model electrode material with the aim of correlating the improved electrochemical characteristics of these cathodes initially activated at 0 &deg, C with the sstructural evolution of Li2MnO3, oxygen loss, formation of per-oxo like species (O22&minus, ) and the surface chemistry. It was established that performing a few initial charge/discharge (activation) cycles of Li2MnO3 at 0 &deg, C resulted in increased discharge capacity and higher capacity retention, and decreased and substantially stabilized the voltage hysteresis upon subsequent cycling at 30 &deg, C or at 45 &deg, C. In contrast to the activation of Li2MnO3 at these higher temperatures, Li2MnO3 underwent step-by-step activation at 0 &deg, C, providing a stepwise traversing of the voltage plateau at &gt, 4.5 V during initial cycling. Importantly, these findings agree well with our previous studies on the activation at 0 &deg, C of 0.35Li2MnO3&middot, 0.65Li[Mn0.45Ni0.35Co0.20]O2 materials. The stability of the interface developed at 0 &deg, C can be ascribed to the reduced interactions of the per-oxo-like species formed and the oxygen released from Li2MnO3 with solvents in ethylene carbonate&ndash, methyl-ethyl carbonate/LiPF6 solutions. Our TEM studies revealed that typically, upon initial cycling both at 0 &deg, C and 30 &deg, C, Li2MnO3 underwent partial structural layered-to-spinel (Li2Mn2O4) transition.

Rechargeable magnesium batteries (RMBs) have attracted a lot of attention in recent decades due to the theoretical properties of these systems in terms of energy density, safety, and price. Nevertheless, to date, fully rechargeable magnesium battery prototypes with sufficient longevity and reversibility were realized only with low voltage and low capacity intercalation cathode materials based on Cheverel phases. The community is therefore actively looking for high-capacity cathodes that can work with metallic magnesium anodes in viable RMB systems. One of the most promising cathode materials, in terms of very high theoretical specific capacity, is, naturally, sulfur. A number of recent works studied the electrochemical performances of rechargeable sulfur cathodes in RMB, with success to some extent on the cathode side. Nevertheless, as known from the lithium-sulfur rechargeable battery systems, the formation of soluble polysulfides during discharge affects strongly the behavior of the anode side. In this article and the work it describes, we focus on soluble polysulfides impact on Mg-S electrochemichal systems. We carefully designed herein conditions that mimic the Mg-S battery prototypes containing balanced Mg and elemental sulfur electrodes. Under these conditions, we extensively studied the Mg anode behavior. The study shows that when elemental sulfur cathodes are discharged in the Mg-S cells containing electrolyte solutions in which Mg anodes behave reversibly, the polysulfide species thus formed migrate to the anode and eventually fully passivate it by the formation of very stable surface layers. The work involved electrochemical, spectroscopic, and microscopic studies. The present study clearly shows that to realize practical rechargeable Mg-S batteries, the transport of any sulfide moieties from the sulfur cathode to the magnesium anode has to be completely avoided. Such a condition is mandatory for the operation of secondary Mg-S batteries.

We demonstrate an atomic layer deposition (ALD) process for the solid electrolyte lithium phosphorousoxynitride (LiPON) using lithium tert-butoxide (LiOtBu), H2O, trimethylphosphate (TMP), and plasma N2 (PN2) as precursors. We use in-situ spectroscopic ellipsometry to determine growth rates for process optimization to design a rational, quaternary precursor ALD process where only certain substrate–precursor chemical reactions are favorable. We demonstrate via in-situ XPS tunable nitrogen incorporation into the films by variation of the PN2 dose and find that ALD films over approximately 4.5% nitrogen are amorphous, whereas LiPON ALD films with less than 4.5% nitrogen are polycrystalline. Finally, we characterize the ionic conductivity of the ALD films as a function of nitrogen content and demonstrate their functionality on a model battery electrode—a Si anode on a Cu current collector.

Enabled by a unique integrated fabrication and characterization platform, X-ray photoelectron spectroscopy (XPS) studies reveal the formation of a thin solid electrolyte interphase (SEI) layer on a Li–O2 cathode after the first cycle. Subsequent cycling indicates that this SEI layer is very stable in terms of both chemistry and morphology, even after extensive cycling, preserving reversibility at the cathode/electrolyte interface. Remarkably, even after cell failure, replacement of the lithium anode resulted in recovery of the cycling behavior with the same cathode. These results demonstrate that chemical stabilization of the cathode/electrolyte interface promotes long-term operation of DMSO-based Li–O2 Ru-catalyzed batteries. Characterization of the Li anode surface reveals electrolyte decomposition, and a partial mechanism is proposed for the observed chemical composition of the cathode SEI. These studies are enabled by conformal deposition of a heterogeneous OER catalyst on a freestanding, binder-free,...

Carbon/metal oxide composites are considered promising materials for high energy density supercapacitors. So far, impregnation of the oxide into ordered mesoporous carbon materials has been demonstrated either in hard-templated carbon synthesized by using ordered mesoporous silica or alumina scaffolds, or soft-templated carbon derived from surfactant micelles. The hard-template method can provide a high pore volume but the instability of these mesostructures hinders total electrode performances upon oxide impregnation. While the soft-template methods can provide a stable mesostructure, these methods produce scaffolds with a much smaller pore volume and surface area, leading to limited metal oxide loading and electrode capacitance. Herein, anodized aluminum oxide (AAO) and triblock copolymer F127 are used together as hard and soft-templates to fabricate ordered mesoporous carbon nanowires (OMCNWs) as a host material for Fe2O3 nanoparticles. This dual-template strategy provides a high pore volume and surface area OMCNW that retains its stable structure even for high metal oxide loading amounts. Additionally, the unique nanowire morphology and mesoporous structure of the OMCNW/Fe2O3 facilitate high ionic mobility in the composite, leading to >260 F g−1 specific capacitance with good rate capability and cycling stability. This work highlights the dual-template approach as a promising strategy for the fabrication of next generation heterogeneous composites for electrochemical energy storage and conversion.

We demonstrate the ultraclean atomic layer deposition (ALD) of Li2O and LiOH using lithium tert-butoxide (LiOtBu) precursor with H2O and plasma O2 as oxidants, along with conversion of Li2O and LiOH products to Li2CO3 upon CO2 dosing. Using LiOtBu and H2O results in LiOH below 240 °C and Li2O above 240 °C for otherwise identical process parameters. Substituting plasma O2 as the oxidation precursor results in a combination of Li2CO3 and Li2O products, indicating modification of the ALD reaction preventing volatilization of the C from the Li precursor. The chemistry of the films is definitively characterized for the first time with XPS utilizing an all-UHV transfer procedure from the ALD reactor. We use in situ UHV gas dosing to investigate the reaction mechanisms of ALD Li2O and LiOH with H2O and CO2 to simulate reactions upon air exposure. Lastly, we employ in situ spectroscopic ellipsometry to determine the reaction kinetics of thermal LiOH decomposition, and we report an activation energy of 112.7 ± 0.6...

We synthesized millimeter-tall, dense carpets of crystalline CNTs on nonpolished copper substrates with a thin Al2O3 (below 10 nm) underlayer and Fe (1.2 nm) layer as a catalyst using chemical vapor deposition (CVD). Preheating of the hydrocarbon precursor gases and in-situ formation of controlled amounts of water vapor were critical process parameters. High-resolution microscopy showed that the CNTs were crystalline with lengths up to a millimeter. Electrical conduction between the CNTs and the copper substrate was demonstrated using multiple methods (probe station, electrodeposition, and hydrolysis of water). Through TEM characterizations of cross sections, we demonstrated that copper diffusion into the alumina layer during the thermal process was the key to explain the observed electrical conductivity. Additionally, the high electrical conductivity of a thermally processed sample compared to the insulating behavior of a pristine sample confirmed the mechanistic hypothesis. Adsorption isotherm measureme...

Oxidative decomposition of organic-solvent-based liquid electrolytes at cathode material interfaces has been identified as a main reason for rapid capacity fade in high-voltage lithium ion batteries. The evolution of "cathode electrolyte interphase: (CEI) films, partly or completely consisting of electrolyte decomposition products, has also recently been demonstrated to be correlated with battery cycling behavior at high potentials. Using Density Functional Theory (DFT) calculations, the hybrid PBE0 functional, and the (001) surfaces of spinel oxides as models, we examine these two interrelated processes. Consistent with previous calculations, ethylene carbonate (EC) solvent molecules are predicted to be readily oxidized on the Li(x)Mn(2)O(4) (001) surface at modest operational voltages, forming adsorbed organic fragments. Further oxidative decompostion of such CEI fragments to release CO2 gas is however predicted to require higher voltages consistent with Li(x)Ni(0.5)Mn(1.5)O(4) (LNMO) at smaller x values. We argue that multi-step reactions, involving first formation of CEI films and then further oxidization of CEI at higher potentials, are most relevant to capacity fade. Mechanisms associated with dissolution or oxidation of native Li2CO3 films, which is removed before the electrolyte is in contact with oxide surfaces, are also explored., 8 figures

Oxygen reduction in nonaqueous electrolyte solutions containing Li salts is a complex field of research involving solution reactions with oxygen radicals and lithium oxides. The aprotic polar solve...

We present a new method for synthesis of thick, self-standing porous carbon electrodes with improved physicochemical properties and unique porous structure. The synthesis is based on the use of vertically aligned carbon nanotubes (VACNT) as templates for polymer-based activated carbon materials. The VACNT template enables the production of 1 mm thick, binder-free electrodes with high capacity values even at high rates (>160 Fg−1 at more than 1 Ag−1 for 1 mm thick electrode), and very good stability upon cycling. The electrochemical performance after more than 50,000 cycles, the pore characterization by adsorption isotherms, and the structural analysis of the composite electrode are also reported.

Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite-free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg(-1) ) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlSx . Herein, we demonstrate the first reversible Al/S battery in ionic-liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid-state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid-state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system.

In this Article, the consequence of continuous electrochemical oxidation at the positive electrode in an initially symmetrical capacitive deionization (CDI) cell, comprising two identical activated carbon electrodes, is examined and discussed. Extensive and intensive parameters of the CDI cell are defined, and the deviations occurring among them as a result of continuous electrochemical oxidation processes at the positive electrode during prolonged charge–discharge cycling are discussed. A special flow-through CDI cell containing activated carbon fiber (ACF) electrodes was developed for this purpose. Ex situ XPS measurements were conducted to prove the presence of oxidized surface groups on the positive electrode of these cells due to cycling. A surprising phenomenon that looks like an inversion functionality of the carbon electrodes occurring after numerous charge–discharge cycles is observed and explained.

We report on the possibility of removing boron (in the form of boric acid) from water by electrochemical means. We explore capacitive de-ionization (CDI) processes in which local changes in pH near the surface of high-surface-area activated carbon fiber (ACF) electrodes during charging are utilized, in order to dissociate boric acid into borate ions which can be electro-adsorbed onto the positive electrode in the CDI cells. For this purpose, a special flow-through CDI cell was constructed in which the feed solution flows through the electrodes. Local pH changes near the carbon electrode surface were investigated using a MgCl2 solution probe in three- (with reference) and two-electrode cells, and described qualitatively. We show that, to a certain extent, boron can indeed be removed from water by CDI.

Carbonaceous materials are widely used in electrochemistry. All allotropic forms of carbons—graphite, glassy carbon, amorphous carbon, fullerenes, nanotubes, and doped diamond—are used as important electrode materials in all fields of modern electrochemistry. Examples include graphite and amorphous carbons as anode materials in high-energy density rechargeable Li batteries, porous carbon electrodes in sensors and fuel cells, nano-amorphous carbon as a conducting agent in many kinds of composite electrodes (e.g., cathodes based on intercalation inorganic host materials for batteries), glassy carbon and doped diamond as stable robust and high stability electrode materials for all aspects of basic electrochemical studies, and more. Amorphous carbons can be activated to form very high specific surface area (yet stable) electrode materials which can be used for electrostatic energy storage and conversion [electrical double-layer capacitors (EDLC)] and separation techniques based on electro-adsorption, such as water desalination by capacitive de-ionization (CDI). Apart from the many practical aspects of activated carbon electrodes, there are many highly interesting and important basic aspects related to their study, including transport phenomena, molecular sieving behavior, correlation between electrochemical behavior and surface chemistry, and more. In this article, we review several important aspects related to these electrode materials, in a time perspective (past, present, and future), with the emphasis on their importance to EDLC devices and CDI processes.

Nickel nanotubes have been synthesized by the popular and versatile method of template-assisted electrodeposition, and a surface-directed growth mechanism based on the adsorption of the nickel-borate complex has been proposed.

We report herein on a study of the electrical double layer capacitance of microporous activated carbon fibers electrodes as a function of the concentration of the electrolyte in aqueous solutions. The accessibility of the subnanopores in the electrode-to-ion adsorption decreases as the ionic strength of the solutions decreases, due to the increase in the hydration shell of the ions. Evaluating the concentration effect on the effective size of the ions was possible by the use of highly selective carbon molecular sieve electrodes, produced by the chemical vapor deposition (CVD) of carbon on the ACF surface, which partially closes the entries to the pores. The CVD process was carried out by the pyrolysis of benzene. This study provides a basis for the rigorous evaluation of the size of solvated ions in solutions at different levels of solvation.

The electrochemical properties of nanoporous, activated carbon cloth electrodes in NaCl and NaNO 3 solutions were investigated before and after carbon chemical vapor deposition (CVD) on the high surface area of nanoporous carbon samples. Different CVD reagents, temperatures, and pressures were employed. We achieved a sharp ion sieving effect for CDV-treated carbon samples/electrodes by selecting a given CVD reagent (namely, benzene) and a temperature that was too low to affect chemical decomposition of benzene in the gaseous phase, but sufficiently high to enable its decomposition on the outer surface of the carbon substrate, to form surface carbon deposits. The electroadsorption stereo selectivity achieved by optimized CVD treatment was so sharp that clear discrimination could be obtained even between anions of very similar dimensions, such as Cl - and NO 3 - . Here, the nitrate behaves as the smaller entity since, being a planar ion, it fits better into the carbon micropores known to have slit-shaped pores. The CVD treatment affects mainly the mouths of the pores and not their interior/volume. This was proven by adsorption experiments. From the gas phase, the stereoselectivity obtained by these CVD treatments was also demonstrated by discrimination between the adsorption of CO 2 and N 2 into the CVD-treated activated carbon.

Mg metal is a promising anode material for next generation rechargeable battery due to its dendrite-free deposition and high capacity. However, the best cathode for rechargeable Mg battery was based on high molecular weight MgxMo3S4, thus rendering full cell energetically uncompetitive. To increase energy density, high capacity cathode material like sulfur is proposed. However, to date, only limited work has been reported on Mg/S system, all plagued by poor reversibility attributed to the formation of electrochemically inactive MgSx species. Here, we report a new strategy, based on the effect of Li(+) in activating MgSx species, to conjugate a dendrite-free Mg anode with a reversible polysulfide cathode and present a truly reversible Mg/S battery with capacity up to 1000 mAh/gs for more than 30 cycles. Mechanistic insights supported by spectroscopic and microscopic characterization strongly suggest that the reversibility arises from chemical reactivation of MgSx by Li(+).

Pushing lithium-ion battery (LIB) technology forward to its fundamental scaling limits requires the ability to create designer heterostructured materials and architectures. Atomic layer deposition (ALD) has recently been applied to advanced nanostructured energy storage devices due to the wide range of available materials, angstrom thickness control, and extreme conformality over high aspect ratio nanostructures. A class of materials referred to as conversion electrodes has recently been proposed as high capacity electrodes. RuO2 is considered an ideal conversion material due to its high combined electronic and ionic conductivity and high gravimetric capacity, and as such is an excellent material to explore the behavior of conversion electrodes at nanoscale thicknesses. We report here a fully characterized atomic layer deposition process for RuO2, electrochemical cycling data for ALD RuO2, and the application of the RuO2 to a composite carbon nanotube electrode scaffold with nucleation-controlled RuO2 growth. A growth rate of 0.4 A/cycle is found between ∼ 210-240 °C. In a planar configuration, the resulting RuO2 films show high first cycle electrochemical capacities of ∼ 1400 mAh/g, but the capacity rapidly degrades with charge/discharge cycling. We also fabricated core/shell MWCNT/RuO2 heterostructured 3D electrodes, which show a 50× increase in the areal capacity over their planar counterparts, with an areal lithium capacity of 1.6 mAh/cm(2).

The charge efficiency of electrochemical capacitive deionization (CDI) of salty-brackish water in symmetric cells comprising activated highly porous carbon electrodes was investigated as a function of the applied potential during charging (deionization) and discharging. The charge efficiency of water CDI in such cells is highly affected by the fact that the potential applied drives always simultaneously adsorption of counterions and desorption of co-ions. A previous stage of this work concentrated in the study of single activated carbon electrodes in processes. In this study, we demonstrated that it is possible to estimate the charge efficiency of symmetric CDI cells from measurements of single electrodes. Guidelines for improving the charge efficiency in water desalination by CDI processes are outlined herein. For instance, it was demonstrated based on experimental findings that it is possible to maximize the charge efficiency by applying discharge potentials (upon regeneration) higher than zero.