Search

Interfaces have crucial, but still poorly understood, roles in the performance of secondary solid-state batteries. Here, using crystallographically oriented and highly faceted thick cathodes, we directly assess the impact of cathode crystallography and morphology on the long-term performance of solid-state batteries. The controlled interface crystallography, area and microstructure of these cathodes enables an understanding of interface instabilities unknown (hidden) in conventional thin-film and composite solid-state electrodes. A generic and direct correlation between cell performance and interface stability is revealed for a variety of both lithium- and sodium-based cathodes and solid electrolytes. Our findings highlight that minimizing interfacial area, rather than its expansion as is the case in conventional composite cathodes, is key to both understanding the nature of interface instabilities and improving cell performance. Our findings also point to the use of dense and thick cathodes as a way of increasing the energy density and stability of solid-state batteries. Interfaces play crucial, but still poorly understood, roles in the performance of secondary solid-state batteries. Using crystallographically oriented and highly faceted thick cathodes, the impact of cathode crystallography and morphology on long-term performance is investigated.

Interface between halide based solid electrolytes and layered transition metal oxide cathodes has been found to be electro-chemically stable due to stability of chloride compounds, in particular, at >4V range. The extent of interfacial stability is correlated with the type of cationic and anionic species in the solid electrolyte compound, a fact supported by theoretical prediction and yet, not accurately measured in composite cathode mixtures. By altering the architecture of cathode into a dense additive-free structure, we have identified differences in interfacial stability of chloride compounds which are hidden in composite cathode formats. In this work, we report the use of dense cathode to track the electrochemical evolution of interface between a hybrid halide solid electrolyte composed of chloride and fluoride species. Introducing fluoride compounds is known to be a promising method to expand the oxidation stability while the nature of such expansion is found to be related to kinetics rather than thermodynamics, we report. Furthermore, fluorination of solid electrolyte is generally accompanied with loss of ionic conductivity due to strong electronegative fluoride ions. We demonstrate a fundamental change of solid-state battery assembly from conventional electrolyte pelletizing followed by electrode placement, to a bottom-up assembly route starting with dense cathode, thin (2/hybrid halide solid electrolyte up to 4.4V vs. Li. Our findings pave the way for expanding the voltage stability of solid electrolytes without compromising the cell performance due to ionic conductivity overpotential issues.

Creating thick electrodes with low porosity can dramatically increase the available energy in a single cell and decrease the number of electrode stacks needed in a full battery, which results in higher energy, lower cost, and easier to manufacture batteries. However, existing electrode architectures cannot simultaneously achieve thick electrodes with high active material volume fractions and good power. These particle-based architectures rely on electrolyte transport within the pores of the cathode to fully lithiate active material particles during discharge. As cathode solid volume fractions approach 100%, batteries experience electrolyte depletion which leads to inaccessible cathode reaction sites (see Fig. 1A). The additional theoretical capacity that comes from increased cathode density, therefore, is impractical if that energy cannot be fully extracted. We combine experiments and simulations of high density and high thickness cathodes to understand the transport and performance trade-offs of LIBs as the cathode solid volume fraction approaches 100%, which we use to reveal the cathode properties needed to achieve high performance at high relative density and thickness. We use one- and two-dimensional simulations to compare the discharge performance of two cathode architectures, a traditional particle-based architecture and a continuous cathode architecture created via electrodeposition. In addition, a model with spaced diffusion-barriers explores the design space between these two architectures and elucidates the influence of increasing solid-diffusion length on discharge performance. We show that there is a large opportunity space for improved energy density at high relative densities by using new electrode manufacturing techniques to create continuous diffusion pathways and high diffusivities. Increasing the solid diffusion length from 4.78 µm to 55 µm in cathodes with high diffusivity leads to an increase in areal capacity (from 1.6 mAh/cm2 to 4.8 mAh/cm2) for a 110 µm thick, 95% dense LCO cathode discharged at a 1C rate. We also apply concepts and designs from these models to simulate the discharge performance of thick, high-density lithium-ion batteries with solid electrolytes to motivate even higher energy battery architectures. When discharged at a 1C rate, solid-state batteries with traditional particle-based composite cathodes (110 µm thick) cannot extract any energy at volume fractions above 94%, while batteries with high-diffusivity continuous cathodes and no solid electrolyte in the cathode region can achieve 3.8 mAh/cm2 at 95% solid volume fraction. These new cathode architectures which contain no electrolyte in the cathode region can significantly improve the gravimetric energy density of solid-state lithium-ion batteries. This work uses a comparative analysis of cathode architectures to explore the interdependent impact of solid volume fraction, solid-diffusivity, cathode thickness, and discharge rate on lithium-ion battery areal capacity. We should how a combination of high diffusivity and continuous solid-state diffusion pathways provides an exciting path for realizing ultra-dense and thick cathodes with high energy density. Figure 1

Interfaces have crucial, but still poorly understood, roles in the performance of secondary solid-state batteries. Here, using crystallographically oriented and highly faceted thick cathodes, we directly assess the impact of cathode crystallography and morphology on the long-term performance of solid-state batteries. The controlled interface crystallography, area and microstructure of these cathodes enables an understanding of interface instabilities unknown (hidden) in conventional thin-film and composite solid-state electrodes. A generic and direct correlation between cell performance and interface stability is revealed for a variety of both lithium- and sodium-based cathodes and solid electrolytes. Our findings highlight that minimizing interfacial area, rather than its expansion as is the case in conventional composite cathodes, is key to both understanding the nature of interface instabilities and improving cell performance. Our findings also point to the use of dense and thick cathodes as a way of increasing the energy density and stability of solid-state batteries.

3D structured porous electrodes have been considered as a possible solution for accommodating the volume change of alloying lithium ion battery anode materials during cycling. However, lab-scale porous electrodes tend to be thin, and the loading of the activity materials is also small, the combination of which results in electrodes with impractically low areal and volumetric capacities. Here, we develop a high areal and volumetric capacity 3D-structured Sn/C anode by using a two steps electroplating process. An electrode with a 20%v/v Sn loading exhibits a high volumetric/areal capacity of ∼879 mA h/cm3/6.59 mA h/cm2 after 100 cycles at 0.5 C and a good rate performance of about 750 mA h/cm3 and 5.5 mA h/cm2 (delithiation) at 10 C in a half-cell configuration. The 3D Sn/C anode also shows good compatibility with a commercial LCO cathode in a full cell configuration.

Silicon-based anodes are one of the promising candidates for the next generation high-power/energy density lithium ion batteries (LIBs). However, a major drawback limiting the practical application of the Si anode is that Si experiences a significant volume change during lithiation/delithiation, which induces high stresses causing degradation and pulverization of the anode. This study focuses on crack initiation within a Si anode during the delithiation process. A multi-physics-based finite element (FE) model is built to simulate the electrochemical process and crack generation during delithiation. On top of that, a Gaussian process (GP)-based surrogate model is developed to assist the exploration of the crack patterns within the anode design space. It is found that the thickness of the Si coating layer, TSi, the yield strength of the Si material, σFc, the cohesive strength between Si and the substrate, σFs, and the curvature of the substrate, ρ, have large impacts on the cracking behavior of Si. This coupled FE simulation-GP surrogate model framework is also applicable to other types of LIB electrodes and provides fundamental insights as building blocks to investigate more complex internal geometries.

Artificial neural network (ANN) models were developed from a six-year process database to quantify causes of membrane fouling in the first stage of a full-scale, three-stage reverse osmosis (RO) system. The data comprised 59 hydraulic and water quality parameters, representing 190 runs between membrane cleanings. The runs were segmented into a Phase 1 period of initial particle deposition followed by a Phase 2 period of gradual biofilm and scale growth. The phases were modeled separately. Rather than specific flux, a fouling indicator Pfoul′ was calculated from RO system pressures which are normally modulated in part to compensate for fouling. The ANN modeling found that the best predictors of Phase 1 fouling were total chlorine, electrical conductance, TDS, ammonia, and the cartridge filter pressure drop. The best predictors of Phase 2 fouling were turbidity, nitrate, organic nitrogen, nitrite, and total chlorine. These results are consistent with known Phase 1 and 2 fouling mechanisms. The predictive electrical conductance, TDS, and turbidity are “bulk” water quality parameters which were found significantly correlated to sparsely measured cations, sulfates, chlorides, and alkalinity. Simulations with different chlorine concentrations demonstrate how the model could be used to reduce fouling rates.

All battery electrodes have complex internal three-dimensional architectures that have traditionally been formed through the random packing of the electrode components. What is now emerging is a new concept in battery electrode design, where the important electronic and ionic pathways, as well as the chemical interactions between the components of the electrode, are deterministically designed. Deterministic design enables far better properties than are possible through random packing, including dramatic improvements in both power and energy. Such a design approach is particularly attractive for emerging high-energy-density materials, which require available free volume as they swell during cycling. In addition to controlled structure, another important facet of the design of such systems is the stable chemical linkages between the active material and the conductive network that survive the lithiation and delithiation processes. In this Perspective, we discuss and provide our views on deterministically designed battery electrodes.

Interfaces have crucial, but still poorly understood, roles in the performance of secondary solid-state batteries. Here, using crystallographically oriented and highly faceted thick cathodes, we directly assess the impact of cathode crystallography and morphology on the long-term performance of solid-state batteries. The controlled interface crystallography, area and microstructure of these cathodes enables an understanding of interface instabilities unknown (hidden) in conventional thin-film and composite solid-state electrodes. A generic and direct correlation between cell performance and interface stability is revealed for a variety of both lithium- and sodium-based cathodes and solid electrolytes. Our findings highlight that minimizing interfacial area, rather than its expansion as is the case in conventional composite cathodes, is key to both understanding the nature of interface instabilities and improving cell performance. Our findings also point to the use of dense and thick cathodes as a way of increasing the energy density and stability of solid-state batteries. Interfaces play crucial, but still poorly understood, roles in the performance of secondary solid-state batteries. Using crystallographically oriented and highly faceted thick cathodes, the impact of cathode crystallography and morphology on long-term performance is investigated.

Pseudocapacitive materials can produce charge storage devices that have both high energy and power density. Although many pseudocapacitive anode materials have been identified, there is a lack of equivalently fast charging cathode materials necessary to create full-cell devices. Recently, thin-film studies from our group have identified nanoporous LiMn2O4 with ∼15 nm domains as a pseudocapacitive cathode material. In this work, we use this insight to create nanoporous LiMn2O4 powders that can be used in practical, slurry-type thick electrode systems. Using these materials, we specifically examine the role of crystalline domain size in controlling charge storage kinetics. Four nanoporous LiMn2O4 powders were synthesized with crystallite sizes of 10, 20, 40, and 70 nm, and their charge/discharge kinetics were studied. Smaller crystallite sizes showed lower capacity but faster charge/discharge speeds, longer cycle life, and higher capacitive contribution based on kinetic analysis, whereas larger crystallite ...

This work aims to improve the poor cycle lifetime of silicon-based anodes for Li-ion batteries by tuning microstructural parameters such as pore size, pore volume, and specific surface area in chemically synthesized mesoporous silicon. Here we have specifically produced two different mesoporous silicon samples from the magnesiothermic reduction of ordered mesoporous silica in either argon or forming gas. In situ X-ray diffraction studies indicate that samples made in Ar proceed through a Mg2Si intermediate, and this results in samples with larger pores (diameter ≈ 90 nm), modest total porosity (34%), and modest specific surface area (50 m2 g–1). Reduction in forming gas, by contrast, results in direct conversion of silica to silicon, and this produces samples with smaller pores (diameter ≈ 40 nm), higher porosity (41%), and a larger specific surface area (70 m2 g–1). The material with smaller pores outperforms the one with larger pores, delivering a capacity of 1121 mAh g–1 at 10 A g–1 and retains 1292 mA...

This work reports the design and simulated performance of high energy density lithium metal primary microbatteries whose 2016 Wh/L and 605 Wh/kg energy densities are 3X greater than the best microbatteries. The simulations match experimental data and give insight into the excellent energy and power density performance. The high energy density is the result of the ultra-thick and dense cathode which has high lithium-ion diffusivity and electronic conductivity. These results show great promise towards realizing the next generation of high performance microbatteries.

A major challenge in the field of water electrolysis is the scarcity of oxygen-evolving catalysts that are inexpensive, highly corrosion-resistant, suitable for large-scale applications and able to oxidize water at high current densities and low overpotentials. Most unsupported, non-precious metals oxygen-evolution catalysts require at least ~350 mV overpotential to oxidize water with a current density of 10 mA/cm(2) in 1 M alkaline solution. Here we report on a robust nanostructured porous NiFe-based oxygen evolution catalyst made by selective alloy corrosion. In 1 M KOH, our material exhibits a catalytic activity towards water oxidation of 500 mA/cm(2) at 360 mV overpotential and is stable for over eleven days. This exceptional performance is attributed to three factors. First, the small size of the ligaments and pores in our mesoporous catalyst (~10 nm) results in a high BET surface area (43 m(2)/g) and therefore a high density of oxygen-evolution catalytic sites per unit mass. Second, the open porosity facilitates effective mass transfer at the catalyst/electrolyte interface. Third and finally, the high bulk electrical conductivity of the mesoporous catalyst allows for effective current flow through the electrocatalyst, making it possible to use thick films with a high density of active sites and ~3×10(4) cm(2) of catalytic area per cm(2) of electrode area. Our mesoporous catalyst is thus attractive for alkaline electrolyzers where water-based solutions are decomposed into hydrogen and oxygen as the only products, driven either conventionally or by photovoltaics.

Silicon-based lithium ion battery anodes are attracting considerable attention due to their high theoretical capacity. However, the significant volume change of silicon during lithiation/de-lithiation cycles restricts its application. A novel bi-continuous Si anode, designed to mitigate the effect of cycling-induced volume changes, is investigated in this study. The effects of the design parameters and the operating conditions of the anode are explored via multi-physics simulation model. It is found that, with the novel anode structure, battery charging C rate has little impact on the mechanical properties. However, the anode structural design parameters would largely influence the stress distribution on the anode. Thus, a Gaussian Processes (GP) based surrogate model is developed to assist the design optimization of the Si anode, while using the simulated results from a multiphysics simulation model as training data. An optimized Si anode design can then be extracted efficiently based upon the developed surrogate model.

Billions of internet connected devices used for medicine, wearables, and robotics require microbattery power sources, but the conflicting scaling laws between electronics and energy storage have led to inadequate power sources that severely limit the performance of these physically small devices. Reported here is a new design paradigm for primary microbatteries that drastically improves energy and power density by eliminating the vast majority of the packaging and through the use of high-energy-density anode and cathode materials. These light (50-80 mg) and small (20-40 µL) microbatteries are enabled though the electroplating of 130 µm-thick 94% dense additive-free and crystallographically oriented LiCoO2 onto thin metal foils, which also act as the encapsulation layer. These devices have 430 Wh kg-1 and 1050 Wh L-1 energy densities, 4 times the energy density of previous similarly sized microbatteries, opening up the potential to power otherwise unpowerable microdevices.

Tin metal is an attractive negative electrode material to replace graphite in Li-ion batteries due to its high energy density. However, tin undergoes a large volume change upon alloying with Li, which pulverizes the particles, and ultimately leads to short cycling lifetimes. Nevertheless, nanoporous materials have been shown to extend battery life well past what is observed in nonporous material. Despite the exciting potential of porous alloying anodes to significantly increase the energy density in Li-ion batteries, the fundamental physics of how nanoscale architectures accommodate the electrochemically induced volume changes are poorly understood. Here, operando transmission X-ray microscopy has been used to develop an understanding of the mechanisms that govern the enhanced cycling stability in nanoporous tin. We found that in comparison to dense tin, nanoporous tin undergoes a 6-fold smaller areal expansion after lithiation, as a result of the internal porosity and unique nanoscale architecture. The e...

Next generation Li-ion batteries will require negative electrode materials with energy densities many-fold higher than that found in the graphitic carbon currently used in commercial Li-ion batteries. While various nanostructured alloying-type anode materials may satisfy that requirement, such materials do not always exhibit long cycle lifetimes and/or their processing routes are not always suitable for large-scale synthesis. Here, we report on a high-performance anode material for next generation Li-ion batteries made of nanoporous Sn powders with hierarchical ligament morphology. This material system combines both long cycle lifetimes (more than 72% capacity retention after 350 cycles), high capacity (693 mAh/g, nearly twice that of commercial graphitic carbon), good charging/discharging capabilities (545 mAh/g at 1 A/g, 1.5C), and a scalable processing route that involves selective alloy corrosion. The good cycling performance of this system is attributed to its nanoporous architecture and its unique hierarchical ligament morphology, which accommodates the large volume changes taking place during lithiation, as confirmed by synchrotron-based ex-situ X-ray 3D tomography analysis. Our findings are an important step for the development of high-performance Li-ion batteries.

The short charging times and high power capabilities associated with capacitive energy storage make this approach an attractive alternative to batteries. One limitation of electrochemical capacitors is their low energy density and for this reason, there is widespread interest in pseudocapacitive materials that use Faradaic reactions to store charge. One candidate pseudocapacitive material is orthorhombic MoO3 (α-MoO3), a layered compound with a high theoretical capacity for lithium (279 mA h g-1 or 1,005 C g-1). Here, we report on the properties of reduced α-MoO3-x(R-MoO3-x) and compare it with fully oxidized α-MoO3 (F-MoO3). The introduction of oxygen vacancies leads to a larger interlayer spacing that promotes faster charge storage kinetics and enables the α-MoO3 structure to be retained during the insertion and removal of Li ions. The higher specific capacity of the R-MoO3-x is attributed to the reversible formation of a significant amount of Mo4+ following lithiation. This study underscores the potential importance of incorporating oxygen vacancies into transition metal oxides as a strategy for increasing the charge storage kinetics of redox-active materials.

Interface stability plays a crucial role in realization of solid state batteries (SSBs) as safer, higher energy density alternatives to conventional Li ion batteries. Recent developments in inorganic halide solid electrolytes appear to be providing a path to stable interfaces between the solid electrolyte and higher voltage cathodes, although understandings of this interface, and how this interface controls cell performance have been quite limited. Here, using Li3YCl6 and Li3InCl6 as example halide solid electrolytes and thick dense conductive additive and binder-free LiCoO2 cathodes we show that the interface dominates cell performance. Using this halide solid electrolyte-solid cathode system, we demonstrate for the first time the role of cathode crystallography on interfacial phenomena. Our findings highlight that minimizing the interfacial area, rather than its expansion as with a conventional composite cathode-solid electrolyte mixture is key to both understanding the nature of interface instabilities and optimizing cell performance.

Xerion Advanced Battery Corp, founded in 2010, is in the process of commercializing two battery technologies: a) a nanoscale metal foam, produced through electrodeposition, that enables high performance alloy-type active material based electrodes, and b) a single-step electroplating process to manufacture lithiated transition metal oxide (LTMO) cathodes. Xerion’s process benefits from the combined synthesis and electrode formation in just one step – revolutionizing the current commercial slurry-electrode manufacturing process (>20 steps). Certain LTMO’s can be grown as a monolithic structure up to 500 m thick (~ 5 times thicker than state of the art), while simultaneously controlling the crystalline orientation, porosity, surface area and morphology. Ultra-thick textured electrodes significantly decrease the volume, thickness and weight of the resulting battery without compromising run time or power-density. In addition, the deposition process can be applied onto arbitrary shapes giving way to storage solutions that could be integrated as structural and load bearing components leading to low form-factors, ultra-light weight solutions, and new designs. Safety is also improved because conductive agents are not added to the electrode eliminating secondary conductive pathways, which can prevent hard shorts that lead to disastrous thermal run-away events. The transformative electroplating process can utilize low purity feedstocks instead of highly purified lithium hydroxides and lithium carbonates to produce highly pure Li-ion battery cathodes at a fraction of the cost. This feedstock flexibility arises from selective solubility and differences in redox potential of the desired material and the undesired impurity phases. While commercial active material manufacturing requires feedstock purity >99.5%, purities as low as 50% have been demonstrated with Xerion’s molten salt process. As a result, cost modeling has shown that cost to manufacture cells using this process is reduced by up to 50% even when using an expensive cathode chemistry like LiCoO2. The single-step manufacturing method that produces safe batteries with high energy, fast charging, and high-power characteristics, while simultaneously reducing the cost, is possible through the innovative technology being brought to the market by Xerion Advanced Battery Corporation.

Silicon-based anodes are considered to be one of the most competitive candidates for next generation high power/energy density lithium ion batteries. A main drawback limiting their practical application is significant volume changes in Si during lithiation-delithiation, which induce high stresses and cause degradation and pulverization of the anode. A novel structured silicon anode, consisting of a metal scaffold coated with a layer of Si, has been introduced to address this issue and to improve the cycle life performance of Si anodes. In this paper, the impact of non-uniform metal scaffold structures on the mechanical performances of the Si anode is investigated. A multi-physics based finite element (FE) model is developed, where the geometric of the non-uniform structured anode is built based on experimental measurements. The stress distribution and deformation of the anode after full lithiation are predicted and compared with experimental results. It is found that large tensile stress concentrations are shown on the surfaces of Si layers; the volume-expansion induced stress is sensitive to the degree of non-uniformity of the scaffold. Sharp edges on the scaffold could result in high compressive stress. Rounding these edges is found to be a promising approach to reduce stress concentrations and improve the structural integrity of the anode.

Pseudocapacitors with nondiffusion-limited charge storage mechanisms allow for fast kinetics that exceed conventional battery materials. It has been demonstrated that nanostructuring conventional battery materials can induce pseudocapacitive behavior. In our previous study, we found that assemblies of metallic 1T MoS2 nanocrystals show faster charge storage compared to the bulk material. Quantitative electrochemistry demonstrated that the current response is capacitive. In this work, we perform a series of operando X-ray diffraction studies upon electrochemical cycling to show that the high capacitive response of metallic 1T MoS2 nanocrystals is due to suppression of the standard first-order phase transition. In bulk MoS2, a phase transition between 1T and triclinic phases (LixMoS2) is observed during lithiation and delithiation in both the galvanostatic traces (as distinctive plateaus) and the X-ray diffraction patterns with the appearance of the additional peaks. MoS2 nanocrystal assemblies, on the othe...

Pseudocapacitors with nondiffusion-limited charge storage mechanisms allow for fast kinetics that exceed conventional battery materials. It has been demonstrated that nanostructuring conventional battery materials can induce pseudocapacitive behavior. In our previous study, we found that assemblies of metallic 1T MoS

Control over the morphology of nanostructured materials is of primary importance in structure-property relationship studies. Although the size of ligaments and pores in dealloyed nanoporous metals can be controlled by thermal and/or (electro)chemical treatments, tuning the shape of those ligaments is much harder. In the present work, we use corroding media with different reactivity to effectively tailor the ligament shape in nanoporous tin (NP-Sn) during dealloying by free corrosion. NP-Sn architectures with nanowire and granular ligament shapes were made by controlling the pH of the corroding solution, and thus the rate of Sn oxidation relative to the etching rate of the sacrificial component. The standard nanowire structure was formed under acidic conditions where oxidation was slow, but a hierarchical granular structure was formed when fusion of the Sn nanocrystals was inhibited by surface oxidation. To demonstrate the advantages of this architectural control, these two materials systems were investigated as electrodes for Na-ion battery anodes. Similar initial Na storage capacities of $\ensuremath{\sim}500$ and 550 mAh/g were achieved in the nanowire and granular materials, respectively, but the cycle life of the two materials was quite different. NP-Sn with a granular ligament shape showed enhanced stability with a capacity retention of $\ensuremath{\sim}55%$ over 95 cycles at a specific current of 40 mA/g. By contrast, NP-Sn with a nanowire ligament shape showed very fast capacity fading within the first 10 cycles. This work thus demonstrates the dramatic impact of the nanoscale morphology on the electrochemical performance of nanoporous materials and highlights the need for both shape and size control in dealloyed nanoporous metals.

A major challenge in the field of water electrolysis is the scarcity of oxygen-evolving catalysts that are inexpensive, highly corrosion-resistant, suitable for large-scale applications and able to oxidize water at high current densities and low overpotentials. Most unsupported, non-precious metals oxygen-evolution catalysts require at least ∼350 mV overpotential to oxidize water with a current density of 10 mA cm−2 in 1 M alkaline solution. Here we report on a robust nanostructured porous NiFe-based oxygen evolution catalyst made by selective alloy corrosion. In 1 M KOH, our material exhibits a catalytic activity towards water oxidation of 500 mA cm−2 at 360 mV overpotential and is stable for over eleven days. This exceptional performance is attributed to three factors. First, the small size of the ligaments and pores in our mesoporous catalyst (∼10 nm) results in a high BET surface area (43 m2 g−1) and therefore a high density of oxygen-evolution catalytic sites per unit mass. Second, the open porosity facilitates effective mass transfer at the catalyst/electrolyte interface. Third and finally, the high bulk electrical conductivity of the mesoporous catalyst allows for effective current flow through the electrocatalyst, making it possible to use thick films with a high density of active sites and ∼3 × 104 cm2 of catalytic area per cm2 of electrode area. Our mesoporous catalyst is thus attractive for alkaline electrolyzers where water-based solutions are decomposed into hydrogen and oxygen as the only products, driven either conventionally or by photovoltaics.

Single-layer and few-layer transition metal dichalcogenides have been extensively studied for their electronic properties, but their energy-storage potential has not been well explored. This paper describes the structural and electrochemical properties of few-layer TiS2 nanocrystals. The two-dimensional morphology leads to very different behavior, compared to corresponding bulk materials. Only small structural changes occur during lithiation/delithiation and charge storage characteristics are consistent with intercalation pseudocapacitance, leading to materials that exhibit both high energy and power density.

Pseudocapacitive charge storage materials offer the opportunity to bridge the gap between high energy density battery materials and high power density electrical double layer capacitor materials through the rational design of transition metal oxide nanoscale architectures. The research reported in this paper describes the origins and development of pseudocapacitance in MoO2. Micron-size particles of MoO2 exhibit a reversible monoclinic to orthorhombic phase transition upon lithium insertion/deinsertion, however, this phase transformation is suppressed when using 15 nm nanocrystals of MoO2. The nanoscale MoO2 exhibits pseudocapacitive behavior and achieves substantially better energy storage kinetics than the corresponding bulk material. Such size-dependent electrochemical behavior is an essential feature of an extrinsic pseudocapacitor material. The high power capability of nanoscale MoO2 is improved further by synthesizing hybrid materials in which MoO2 nanoparticles are grown on reduced graphene oxide (RGO) scaffolds. Electrode architectures containing MoO2-RGO hybrid materials preserve the pseudocapacitance of MoO2 as lithium capacities of nearly 150 mAh g−1 are obtained at a rate of 50 C. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0141505jes] All rights reserved.

LiNi0.5Mn1.5O4 epitomizes the challenges imposed by high electrochemical potential reactivity on the durability of high energy density Li-ion batteries. Postsynthesis coatings have been explored as a solution to these challenges, but the fundamentals of their function have not been ascertained. To contribute to this understanding, the surface of LiNi0.5Mn1.5O4 microparticles was modified with Mg2+, a coating component of literature relevance, using two different heat treatment temperatures, 500 and 800 °C. A combination of characterization tools revealed that Mg2+ was introduced mainly as an inhomogeneous MgO coating in the sample treated at 500 °C, and into the spinel lattice at the subsurface of the particles at 800 °C. Comparing the properties of these two different materials with an unmodified baseline afforded the opportunity to evaluate the effect of varying surface chemistries. Coulometry in Li metal half cells was used as a macroscopic measure of side reactions at the electrode–electrolyte interfa...

The short charging times and high power capabilities associated with capacitive energy storage make this approach an attractive alternative to batteries. One limitation of electrochemical capacitors is their low energy density and for this reason, there is widespread interest in pseudocapacitive materials that use Faradaic reactions to store charge. One candidate pseudocapacitive material is orthorhombic MoO

A synthesis methodology is demonstrated to produce MoS2 nanoparticles with an expanded atomic lamellar structure that are ideal for Faradaic-based capacitive charge storage. While much of the work on MoS2 focuses on the high capacity conversion reaction, that process is prone to poor reversibility. The pseudocapacitive intercalation-based charge storage reaction of MoS2 is investigated, which is extremely fast and highly reversible. A major challenge in the field of pseudocapacitive-based energy storage is the development of thick electrodes from nanostructured materials that can sustain the fast inherent kinetics of the active nanocrystalline material. Here a composite electrode comprised of a poly(acrylic acid) binder, carbon fibers, and carbon black additives is utilized. These electrodes deliver a specific capacity of 90 mAh g−1 in less than 20 s and can be cycled 3000 times while retaining over 80% of the original capacity. Quantitative kinetic analysis indicates that over 80% of the charge storage in these MoS2 nanocrystals is pseudocapacitive. Asymmetric full cell devices utilizing a MoS2 nanocrystal-based electrode and an activated carbon electrode achieve a maximum power density of 5.3 kW kg−1 (with 6 Wh kg−1 energy density) and a maximum energy density of 37 Wh kg−1 (with 74 W kg−1power density).

This paper describes a new divide and conquer approach that leverages big environmental data, utilizing all available categorical and time-series data without subjectivity, to empirically model hydrologic and water-quality behaviors across expansive regions. The approach decomposes large, intractable problems into smaller ones that are optimally solved; decomposes complex signals into behavioral components that are easier to model with sub-models; and employs a sequence of numerically optimizing algorithms that include time-series clustering, nonlinear, multivariate sensitivity analysis and predictive modeling using multi-layer perceptron artificial neural networks, and classification for selecting the best sub-models to make predictions at new sites. This approach has many advantages over traditional modeling approaches, including being faster and less expensive, more comprehensive in its use of available data, and more accurate in representing a system's physical processes. This paper describes the application of the approach to model groundwater levels in Florida, stream temperatures across Western Oregon and Wisconsin, and water depths in the Florida Everglades.

Charleston Water System (Charleston Water) in Charleston, South Carolina and the American Water Works Association Research Foundation (AwwaRF) have been engaged in a tailored collaboration research project to address concerns related to inadvertent or deliberate attacks on water distribution systems involving chemical contaminants. Colorado State University (CSU) and Advanced Data Mining International are also involved in this research effort. The thesis of the research is that a combination of "field-grade" water quality monitoring sensors and intelligent software can provide reliable, relatively low cost security monitoring for water distribution systems. The types of sensors being evaluated are already widely used to measure water chemistry properties - conductivity, pH, chlorine residual, turbidity, total organic carbon, and UV-254 absorption. The intelligent software is called a Decision Support System (DSS), which employs an artificial intelligence technology called Case-Based Reasoning. The DSS will automatically learn and retain "normal" patterns of water quality behavior; identify unprecedented patterns (outliers) that indicate a potential problem; generate alarms; and make recommendations to operators about what to do. Different sensor arrays composed of multi-parameter devices and individual sensors have been installed at three sites in Charleston Water's distribution system with varying degrees of operational success. A problem that has affected the reliability of the sensors is pressure surges caused by pumping. Similarly, additional sensors such as those deployed by Charleston Water were installed in an experimental pilot loop operated by CSU in which the dynamic behaviors of water chemistry variables could be measured. Seven organic and inorganic chemical contaminants were tested in the pilot loop, each at increasing concentrations up to their LD50s. The contaminants were sodium arsenate, sodium cyanide, sodium fluoroacetate, nicotine, cycloheximide, dicrotophos, and aldicarb. This paper will present intermediate findings that describe practical knowledge acquired in the deployment of the various field-grade sensors in Charleston Water's distribution system, results from the experimental studies conducted in the pilot loop at CSU, and details of the DSS presently under development.