Publications

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Custom-form factor batteries fabricated in non-conventional shapes can maximize the overall energy density of the systems they power, particularly when used in conjunction with energy dense materials (e.g., Li metal anodes and conversion cathodes). Additive manufacturing (AM), and specifically material extrusion (ME), have been shown as effective methods for producing custom-form cell components, particularly electrodes. However, the AM of several promising energy dense materials (conversion electrodes such as iron trifluoride) have yet to be demonstrated or optimized. Furthermore, the integration of multiple AM produced cell components, such as electrodes and separators, along with a custom package remains largely unexplored. In this work, iron trifluoride (FeF3) and ionogel (IG) separators are conformally printed using ME onto non-planar surfaces to enable the fabrication of custom-form Li-FeF3 batteries. To demonstrate printing on non-planar surfaces, cathodes and separators were deposited onto cylindrical rods using a 5-axis ME printer. ME printed FeF3 was shown to have performance commensurate with FeF3 cast using conventional means, both in coin cell and cylindrical rod formats, with capacities exceeding 700 mAh/g on the first cycle and ranging between 600 and 400 mAh/g over the next 50 cycles. Additionally, a ME process for printing polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) based IGs directly onto FeF3 is developed and enabled using an electrolyte exchange process. In coin cells, this process is shown to produce cells with similar capacity to cells built with Celgard separators out to 50 cycles, with the exception that cycling instabilities are observed during cycles 8–20. When using printed and exchanged IGs in a custom cylindrical cell package, 6 stable high-capacity cycles are achieved. Overall, this work demonstrates approaches for producing high-energy-density Li-FeF3 cells in coin and cylindrical rod formats, which are translatable to customized, arbitrary geometries compatible with ME printing and electrolyte exchange.

Manganese dioxide is a promising cathode material for energy storage applications because of its high redox potential, large theoretical energy density, abundance, and low cost. It has been shown that the performance of MnO₂ electrodes in rechargeable alkaline Zn/MnO₂ batteries could be improved by nanostructuring and by increasing the concentration of defects in MnO₂. However, the underlying mechanism of this improvement is not completely clear. We used an ab initio density functional computational approach to investigate the influence of nanostructuring and crystal defects on the electrochemical properties of the MnO₂ cathode material. The mechanism of electrochemical discharge of MnO₂ in Zn/MnO₂ batteries was studied by modeling the process of H ion insertion into the structures of pyrolusite, ramsdellite, and nsutite polymorphs containing oxygen vacancies, cation vacancies, and open surfaces. Our calculations showed that the binding energies of H ions inserted into the structures of MnO₂ polymorphs were strongly affected by the presence of surfaces and bulk defects. In particular, we found that the energies of H ions inserted under the surfaces and attached to the surfaces of MnO₂ crystals were significantly lower than those for bulk MnO₂. Furthermore, the results of our study provide an explanation for the influence of crystal defects and nanostructuring on the electrochemical reactivity of MnO₂ cathodes in rechargeable alkaline Zn/MnO₂ batteries.

Achieving commercially acceptable Zn-MnO2 rechargeable batteries depends on the reversibility of active zinc and manganese materials, and avoiding side reactions during the second electron reaction of MnO2. Typically, liquid electrolytes such as potassium hydroxide (KOH) are used for Zn-MnO2 rechargeable batteries. However, it is known that using liquid electrolytes causes the formation of electrochemically inactive materials, such as precipitation Mn3O4 or ZnMn2O4 resulting from the uncontrollable reaction of Mn3+ dissolved species with zincate ions. In this paper, hydrogel electrolytes are tested for MnO2 electrodes undergoing two-electron cycling. Improved cell safety is achieved because the hydrogel electrolyte is non-spillable, according to standards from the US Department of Transportation (DOT). The cycling of “half cells” with advanced-formulation MnO2 cathodes paired with commercial NiOOH electrodes is tested with hydrogel and a normal electrolyte, to detect changes to the zincate crossover and reaction from anode to cathode. These half cells achieved ≥700 cycles with 99% coulombic efficiency and 63% energy efficiency at C/3 rates based on the second electron capacity of MnO2. Other cycling tests with “full cells” of Zn anodes with the same MnO2 cathodes achieved ~300 cycles until reaching 50% capacity fade, a comparable performance to cells using liquid electrolyte. Electrodes dissected after cycling showed that the liquid electrolyte allowed Cu ions to migrate more than the hydrogel electrolyte. However, measurements of the Cu diffusion coefficient showed no difference between liquid and gel electrolytes; thus, it was hypothesized that the gel electrolytes reduced the occurrence of Cu short circuits by either (a) reducing electrode physical contact to the separator or (b) reducing electro-convective electrolyte transport that may be as important as diffusive transport.

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Li-metal batteries (LMBs) employing conversion cathode materials (e.g., FeF₃) are a promising way to prepare inexpensive, environmentally friendly batteries with high energy density. Pseudo-solid-state ionogel separators harness the energy density and safety advantages of solid-state LMBs, while alleviating key drawbacks (e.g., poor ionic conductivity and high interfacial resistance). In this work, a pseudo-solid-state conversion battery (Li-FeF₃) is presented that achieves stable, high rate (1.0 mA cm^–2) cycling at room temperature. The batteries described herein contain gel-infiltrated FeF₃ cathodes prepared by exchanging the ionic liquid in a polymer ionogel with a localized high-concentration electrolyte (LHCE). The LHCE gel merges the benefits of a flexible separator (e.g., adaptation to conversion-related volume changes) with the excellent chemical stability and high ionic conductivity (~2 mS cm^–1 at 25 °C) of an LHCE. The latter property is in contrast to previous solid-state iron fluoride batteries, where poor ionic conductivities necessitated elevated temperatures to realize practical power levels. Importantly, the stable, room-temperature Li-FeF₃ cycling performance obtained with the LHCE gel at high current densities paves the way for exploring a range of architectures including flexible, three-dimensional, and custom shape batteries.

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Conversion cathode materials are gaining interest for secondary batteries due to their high theoretical energy and power density. However, practical application as a secondary battery material is currently limited by practical issues such as poor cyclability. To better understand these materials, we have developed a pseudo-two-dimensional model for conversion cathodes. We apply this model to FeS2 – a material that undergoes intercalation followed by conversion during discharge. The model is derived from the half-cell Doyle–Fuller–Newman model with additional loss terms added to reflect the converted shell resistance as the reaction progresses. We also account for polydisperse active material particles by incorporating a variable active surface area and effective particle radius. Using the model, we show that the leading loss mechanisms for FeS2 are associated with solid-state diffusion and electrical transport limitations through the converted shell material. The polydisperse simulations are also compared to a monodisperse system, and we show that polydispersity has very little effect on the intercalation behavior yet leads to capacity loss during the conversion reaction. We provide the code as an open-source Python Battery Mathematical Modeling (PyBaMM) model that can be used to identify performance limitations for other conversion cathode materials.

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Grid scale batteries need to be inexpensive to manufacture, safe to operate, and non-toxic in composition. Zinc aqueous (alkaline) batteries hold much promise, but good cycle life and utilization of the zinc has proven difficult partly because zinc is susceptible to H₂ gas evolution in KOH. Water-insalt electrolyte (WiSE) can address this shortcoming by lowering the activity of free water molecules in solution, thus reducing H₂ gas evolution. In this work, we show the relevant fundamental physicochemical properties of an acetate-based WiSE to establish the practicality and performance of this class of WiSE for battery application. Research and understanding of acetate WiSE is in a nascent state, presently.

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The present study has used a variety of characterization techniques to determine the products and reaction pathways involved in the rechargeable Li-FeS2 system. We revisit both the initial lithiation and subsequent cycling of FeS2 employing an ionic liquid electrolyte to investigate the intermediate and final charge products formed under varying thermal conditions (room temperature to 100 °C). The detection of Li2S and hexagonal FeS as the intermediate phases in the initial lithiation and the electrochemical formation of greigite, Fe3S4, as a charge product in the rechargeable reaction differ significantly from previous reports. The conditions for Fe3S4 formation are shown to be dependent on both the temperature (∼60 °C) and the availability of sulfur to drive a FeS to Fe3S4 transformation. Upon further cycling, Fe3S4 transforms to a lower sulfur content iron sulfide phase, a process which coincides with the loss of sulfur based on the new reaction pathways established in this work. The connection between sulfur loss, capacity fade, and charge product composition highlights the critical need to retain sulfur in the active material upon cycling.

Conversion cathodes represent a viable route to improve rechargeable Li+battery energy densities, but their poor electrochemical stability and power density have impeded their practical implementation. Here, we explore the impact cell fabrication, electrolyte interaction, and current density have on the electrochemical performance of FeS2/Li cells by deconvoluting the contributions of the various conversion and intercalation reactions to the overall capacity. By varying the slurry composition and applied pressure, we determine that the capacity loss is primarily due to the large volume changes during (de)lithiation, leading to a degradation of the conductive matrix. Through the application of an external pressure, the loss is minimized by maintaining the conductive matrix. We further determine that polysulfide loss can be minimized by increasing the current density (>C/10), thus reducing the sulfur formation period. Analysis of the kinetics determines that the conversion reactions are rate-limiting, specifically the formation of metallic iron at rates above C/8. While focused on FeS2, our findings on the influence of pressure, electrolyte interaction, and kinetics are broadly applicable to other conversion cathode systems.

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Zinc oxide is of great interest for advanced energy devices because of its low cost, wide direct bandgap, non-toxicity, and facile electrochemistry. In zinc alkaline batteries, ZnO plays a critical role in electrode passivation, a process that hinders commercialization and remains poorly understood. Here, novel observations of an electroactive type of ZnO formed in Zn-metal alkaline electrodes are disclosed. The electrical conductivity of battery-formed ZnO is measured and found to vary by factors of up to 104, which provides a first-principles-based understanding of Zn passivation in industrial alkaline batteries. Simultaneous with this conductivity change, protons are inserted into the crystal structure and electrons are inserted into the conduction band in quantities up to ≈1020 cm−3 and ≈1 mAh gZnO−1. Electron insertion causes blue electrochromic coloration with efficiencies and rates competitive with leading electrochromic materials. The electroactivity of ZnO is evidently enabled by rapid crystal growth, which forms defects that complex with inserted cations, charge-balanced by the increase of conduction band electrons. This property distinguishes electroactive ZnO from inactive classical ZnO. Knowledge of this phenomenon is applied to improve cycling performance of industrial-design electrodes at 50% zinc utilization and the authors propose other uses for ZnO such as electrochromic devices.

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In alkaline zinc–manganese dioxide batteries, there is a need for selective polymeric separators that have good hydroxide ion conductivity but that prevent the transport of zincate (Zn(OH)₄)^2-. Here we investigate the nanoscale structure and hydroxide transport in two cationic polysulfones that are promising for these separators. We present the synthesis and characterization for a tetraethylammonium-functionalized polysulfone (TEA-PSU) and compare it to our previous work on an N-butylimidazolium-functionalized polysulfone (NBI-PSU). We perform atomistic molecular dynamics (MD) simulations of both polymers at experimentally relevant water contents. The MD simulations show that both polymers develop well phase separated nanoscale water domains that percolate through the polymer. Calculation of the total scattering intensity from the MD simulations reveal weak or nonexistent ionomer peaks at low wave vectors. The lack of an ionomer peak is due to a loss of contrast in the scattering. The small water domains in both polymers, with median diameters on the order of 0.5–0.7 nm, lead to hydroxide and water diffusion constants that are 1–2 orders of magnitude smaller than their values in bulk water. This confinement lowers the conductivity but also may explain the strong exclusion of zincate from the PSU membranes seen experimentally.

Lithium/fluorinated graphite (Li/CFx) primary batteries show great promise for applications in a wide range of energy storage systems due to their high energy density (>2100 Wh kg^–1) and low self-discharge rate (<0.5% per year at 25 °C). While the electrochemical performance of the CF_x cathode is indeed promising, the discharge reaction mechanism is not thoroughly understood to date. In this article, a multiscale investigation of the CF_x discharge mechanism is performed using a novel cathode structure to minimize the carbon and fluorine additives for precise cathode characterizations. Titration gas chromatography, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, cross-sectional focused ion beam, high-resolution transmission electron microscopy, and scanning transmission electron microscopy with electron energy loss spectroscopy are utilized to investigate this system. Results show no metallic lithium deposition or intercalation during the discharge reaction. Crystalline lithium fluoride particles uniformly distributed with <10 nm sizes into the CF_x layers, and carbon with lower sp2 content similar to the hard-carbon structure are the products during discharge. This article deepens the understanding of CF_x as a high energy density cathode material and highlights the need for future investigations on primary battery materials to advance performance.

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The galvanostatic intermittent titration technique (GITT) is widely used to evaluate solid-state diffusion coefficients in electrochemical systems. However, the existing analysis methods for GITT data require numerous assumptions, and the derived diffusion coefficients typically are not independently validated. To investigate the validity of the assumptions and derived diffusion coefficients, we employ a direct-pulse fitting method for interpreting the GITT data that involves numerically fitting an electrochemical pulse and subsequent relaxation to a one-dimensional, single-particle, electrochemical model coupled with non-ideal transport to directly evaluate diffusion coefficients. Our non-ideal diffusion coefficients, which are extracted from GITT measurements of the intercalation regime of FeS2 and independently verified through discharge predictions, prove to be 2 orders of magnitude more accurate than ideal diffusion coefficients extracted using conventional methods. We further extend our model to a polydisperse set of particles to show the validity of a single-particle approach when the modeled radius is proportional to the total volume-to-surface-area ratio of the system.

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Resurrecting a battery chemistry thought to be only primary, we demonstrate the first example of a rechargeable alkaline zinc/copper oxide battery. With the incorporation of a Bi2O3additive to stabilize the copper oxide-based conversion cathode, Zn/(CuO-Bi2O3) cells are capable of cycling over 100 times at >124 W h/L, with capacities from 674 mA h/g (cycle 1) to 362 mA h/g (cycle 150). The crucial role of Bi2O3in facilitating the electrochemical reversibility of Cu2O, Cu(OH)2, and Cuowas supported by scanning and transmission electrochemical microscopy, cyclic voltammetry, and rotating ring-disc electrode voltammetry and monitoredvia operandoenergy-dispersive X-ray diffraction measurements. Bismuth was identified as serving two roles, decreasing the cell resistance and promoting Cu(I) and Cu(II) reduction. To mitigate the capacity losses of long-term cycling CuO cells, we demonstrate two limited depth of discharge (DOD) strategies. First, a 30% DOD (202 mA h/g) retains 99.9% capacity over 250 cycles. Second, the modification of the CuO cathode by the inclusion of additional Cu metal enables performance at very high areal capacities of ∼40 mA h/cm2and unprecedented energy densities of ∼260 W h/L, with near 100% Coulombic efficiency. This work revitalizes a historically primary battery chemistry and opens opportunity to future works in developing copper-based conversion cathode chemistries for the realization of low-cost, safe, and energy-dense secondary batteries.

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Anodic stripping voltammetry (ASV) has been widely used for the detection of several heavy metal ions in neutral and acidic solution, in many cases employing electrodes and/or solutions incorporating Bi. In this work we demonstrate that Bi(OH)4− ion concentration can be measured in highly alkaline 8.5 M KOH solution using ASV. The addition of Pb in similar concentrations to the Bi(OH)4− being measured is shown to improve both the sensitivity and precision of the method. When the Pb additive is employed, a formal limit of detection of 8.5 ppb is achieved, compared to 17.3 ppb when the Pb additive is not used. Due to the use of Bi additives in alkaline battery chemistries, it follows that separators which limit Bi(OH)4− diffusion into the bulk electrolyte and away from the electrodes are of interest. For this purpose, we utilize ASV to determine Bi(OH)4− diffusion rates through Celgard 3501, cellophane 350P00, and Nafion 211. Bi(OH)4− crossover rates, as determined by ASV, are shown to be repeatable and consistent with expectations from the known separator structure.

Rechargeable alkaline Zn–MnO2 (RAM) batteries are a promising candidate for grid-scale energy storage owing to their high theoretical energy density rivaling lithium-ion systems (∼400 Wh/L), relatively safe aqueous electrolyte, established supply chain, and projected costs below $100/kWh at scale. In practice, however, many fundamental chemical and physical processes at both electrodes make it difficult to achieve commercially competitive energy density and cycle life. This review presents a detailed and timely analysis of the constituent materials, current commercial status, electrode processes, and performance-limiting factors of RAM batteries. We also examine recently reported strategies in RAM and related systems to address these issues through additives and modifications to the electrode materials and electrolyte, special ion-selective separators and/or coatings, and unconventional cycling protocols. We conclude with a critical summary of these developments and discussion of how future studies should be focused toward the goal of energy-dense, scalable, and cost-effective RAM systems.

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Grid-level energy storage systems are needed to enable intermittent renewables. Li-ion, Pb-acid battery systems have been implemented but pose safety and environmental risks. Successful grid storage must be safe, reliable, and low-cost.

Grid-level energy storage systems are needed to enable intermittent renewables. Li-ion, Pb-acid battery systems have been implemented but pose safety and environmental risks. Successful grid storage must be safe, reliable, and low-cost.

Alkaline zinc-manganese dioxide (Zn-MnO2) batteries are well suited for grid storage applications because of their inherently safe, aqueous electrolyte and established materials supply chain, resulting in low production costs. With recent advances in the development of Cu/Bi-stabilized birnessite cathodes capable of the full 2-electron capacity equivalent of MnO2 (617 mA h/g), there is a need for selective separators that prevent zincate (Zn(OH)4)2- transport from the anode to the cathode during cycling, as this electrode system fails in the presence of dissolved zinc. Herein, we present the synthesis of N-butylimidazolium-functionalized polysulfone (NBI-PSU)-based separators and evaluate their ability to selectively transport hydroxide over zincate. We then examine their impact on the cycling of high depth of discharge Zn/(Cu/Bi-MnO2) batteries when inserted in between the cathode and anode. Initially, we establish our membranes' selectivity by performing zincate and hydroxide diffusion tests, showing a marked improvement in zincate-blocking (DZn (cm2/min): 0.17 ± 0.04 × 10-6 for 50-PSU, our most selective separator vs 2.0 ± 0.8 × 10-6 for Cellophane 350P00 and 5.7 ± 0.8 × 10-6 for Celgard 3501), while maintaining similar crossover rates for hydroxide (DOH (cm2/min): 9.4 ± 0.1 × 10-6 for 50-PSU vs 17 ± 0.5 × 10-6 for Cellophane 350P00 and 6.7 ± 0.6 × 10-6 for Celgard 3501). We then implement our membranes into cells and observe an improvement in cycle life over control cells containing only the commercial separators (cell lifetime extended from 21 to 79 cycles).

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Large-scale integration of energy storage on the electric grid will be essential to enabling greater penetration of intermittent renewable energy sources, modernizing the grid for increased flexibility security, reliability, and resilience, and enabling cleaner forms of transportation. The purpose of this report is to summarize Sandia's research and capabilities in energy storage and to provide a preliminary roadmap for future efforts in this area that can address the ongoing program needs of DOE and the nation. Mission and vision statements are first presented followed by an overview of the organizational structure at Sandia that provides support and activities in energy storage. Then, a summary of Sandia's energy storage capabilities is presented by technology, including battery storage and materials, power conversion and electronics, subsurface-based energy storage, thermal/thermochemical energy storage, hydrogen storage, data analytics/systems optimization/controls, safety of energy storage systems, and testing/demonstrations/model validation. A summary of identified gaps and needs is also presented for each technology and capability.

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Li-ion batteries currently dominate electrochemical energy storage for grid-scale applications, but there are promising aqueous battery technologies on the path to commercial adoption. Though aqueous batteries are considered lower risk, they can still undergo problematic degradation processes. This perspective details the degradation that aqueous batteries can experience during normal and abusive operation, and how these processes can even lead to cascading failure. We outline methods for studying these phenomena at the material and single-cell level. Considering reliability and safety studies early in technology development will facilitate translation of emerging aqueous batteries from the lab to the field.

Rechargeable alkaline Zn/MnO2 batteries are an attractive solution for large-scale energy storage applications. Recently, Bi and Cu additives have been used to increase the cycle life and capacity of rechargeable Zn/MnO2 batteries, with an equivalent of the full two-electron capacity realized for many cycles, in the absence of zinc. However, the mechanism of the effect of Bi and Cu on the performance of rechargeable Zn/MnO2 batteries has not been investigated in detail. We apply first-principles density functional computational methods to study the discharge mechanisms of the unmodified and Bi/Cu-modified γ-MnO2 electrodes in rechargeable alkaline Zn/MnO2 batteries. Using the results of our calculations, we analyze the possible redox reaction pathways in the γ-MnO2 electrode and identify the electrochemical processes leading to the formation of irreversible discharge reaction products, such as hausmannite and hetaerolite. Our study demonstrates the possibility of formation of intermediate Bi-Mn and Cu-Mn oxides in deep-cycled Bi/Cu-modified MnO2 electrodes. The formation of intermediate Bi-Mn and Cu-Mn oxides could reduce the rate of accumulation of irreversible reaction products in the MnO2 electrode and improve the rechargeability and cyclability of Zn/MnO2 batteries.

Rechargeable alkaline batteries containing zinc anodes suffer from redistribution of active material due to the high solubility of ZnO in the electrolyte, limiting achievable capacity and lifetime. Here, we investigate pre-saturating the KOH electrolyte with ZnO as a strategy to mitigate this issue, utilizing rechargeable Ni-Zn cells. In contrast to previous reports featuring this approach, we use more practical limited-electrolyte cells and systematically study ZnO saturation at different levels of zinc depth-of-discharge (DODZn), where the pre-dissolved ZnO is included in the total system capacity. Starting with 32 wt. % KOH, cells tested at 14%, 21%, and 35% DODZn with ZnO-saturated electrolyte exhibit 191%, 235%, and 110% longer cycle life respectively over identically tested cells with ZnO-free electrolyte, with similar energy efficiency and no voltage-related energy losses. Furthermore, anodes cycled in ZnO-saturated electrolyte develop more favorable compact zinc deposits with less overall mass loss. The effect of initial KOH concentration was also studied, with ZnO saturation enhancing cycle life for 32 wt % and 45 wt % KOH but not for 25 wt % KOH, likely due to cell failure by passivation rather than shorting. The simplicity of ZnO addition and its beneficial effect at high zinc utilization make it a promising means to make secondary alkaline zinc batteries more commercially viable.

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Batteries for grid storage applications must be inexpensive, safe, reliable, as well as have a high energy density. Here, we utilize the high capacity of sulfur (S) (1675 mAh g^–1, based on the idealized redox couple of S^2–/S) in order to demonstrate for the first time, a reversible high capacity solid-state S-based cathode for alkaline batteries. To maintain S in the solid-state, it is bound to copper (Cu), initially in its fully reduced state as the sulfide.

Batteries for grid storage applications must be inexpensive, safe, reliable, as well as have a high energy density. Here, we utilize the high capacity of sulfur (S) (1675 mAh g-1, based on the idealized redox couple of S2./S) in order to demonstrate for the first time, a reversible high capacity solid-state S-based cathode for alkaline batteries. To maintain S in the solid-state, it is bound to copper (Cu), initially in its fully reduced state as the sulfide. Upon charging, the sulfide is oxidized to a polysulfide species which is captured and maintained in the solid-state by the Cu ions. This solid-state sulfide/polysulfide cathode was analyzed versus a zinc (Zn) anode which gives a nominal >1.2 V cell voltage based on the sulfide/polysulfide redox cathode chemistry. It was found that in order for the S cathode to have the best cycle life in the solid-state it must not only be bound to Cu ions but bound to Cu ions in the +1 valence state, forming Cu2S as a discharge product. Zn/Cu2S batteries cycled between 1.45 V and 0.4 V vs. Zn displayed capacities of 1500 mAh g-1 (based on mass of S) or i300 mAh g-1 (based on mass of Cu2S) and high areal (>23 mAh cm.2) and energy densities (>135 Wh L-1), but suffered from moderate cycle lifes (<250 cycles). The failure mechanism of this electrode was found to be disproportionation of the charged S species into irreversible sulfite releasing the bound Cu ions. The Cu ions become free to perform Cu specific redox reactions which slowly changes the battery redox chemistry from that of S to that of Cu with a S additive. Batteries utilizing the Cu2S cathode and a 50% depth of charge (DOC) cathode cycling protocol, with 5 wt% Na2S added to the electrolyte, retained a cathode capacity of 838 mAh g-1 (based on the mass of S) or 169 mA h g-1 (based on mass of Cu2S) after 450 cycles with >99.7% coulombic efficiency. These Zn/Cu2S batteries provided a grid storage relevant energy density of >42Wh L-1 (at 65 wt% Cu2S loading), despite only using a 3% depth of discharge (DOD) for the Zn anode. This work opens the way to a new class of energy dense grid storage batteries based on high capacity solid-state S-based cathodes.

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Rechargeable Zn/MnO2 alkaline batteries are a promising technology for grid storage applications since they are safe, low cost, and considered environmentally friendly. Here, a commercial ceramic sodium ion conductor which is impervious to zincate [Zn(OH)42−], a contributor to MnO2 cathode failure, is evaluated as the battery separator. As received, the ionic conductivity of this separator was measured with electrochemical impedance spectroscopy to be 3.5 mS cm−1, while its thickness is 1.0 mm, resulting in large total membrane resistance of 25.3 Ω. Reducing the thickness of the ceramic to 0.5 mm provided for a decreased resistance of 9.8 Ω. Crossover experiments conducted using inductively coupled plasma - mass spectrometry measurements failed to measure any Zn(OH)42− transport indicating a diffusion coefficient that is at least two orders of magnitude less than that for the commercial cellophane and Celgard separators. For 5% DOD at a C/5 rate, the cycle lifetime was increased by over 22% using the 0.5 mm thick ceramic separator compared to traditional Celgard and cellophane separators. Scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray diffraction characterization of cycled electrodes showed limited amounts of zinc species on the cathode utilizing the ceramic separator, consistent with its prevention of Zn(OH)42− transport.

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At a low depth of discharge, the performance of rechargeable alkaline Zn/MnO2 batteries is determined by the concomitant processes of hydrogen ion insertion and electro-reduction in the solid phase of γ-MnO2. Ab initio computational methods based on density functional theory (DFT) were applied to study the mechanism of hydrogen ion insertion into the pyrolusite (β), ramsdellite (R), and nsutite (γ) MnO2 polymorphs. It was found that hydrogen ion insertion induced significant distortion in the crystal structures of MnO2 polymorphs. Calculations demonstrated that the hydrogen ions inserted into γ-MnO2 initially occupied the larger 2×1 ramsdellite tunnels. The protonated form of γ-MnO2 was found to be stable over the discharge range during which up to two hydrogen ions were inserted into each 2×1 tunnel. At the same time, the study showed that the insertion of hydrogen ions into the 1×1 pyrolusite tunnels of γ-MnO2 created instability leading to the structural breakdown of γ-MnO2. The results of this study explain the presence of groutite (α-MnOOH) and the absence of manganite (γ-MnOOH) among the reaction products of partially reduced γ-MnO2

Anodic stripping voltammetry (ASV) is an analysis technique that permits the selective and quantitative analysis of metal ion species in solution. It is most commonly applied in neutral to acidic electrolyte largely due to inherent metal ion solubility. Bismuth (Bi) is a common film used for ASV due to its good sensitivity, overall stability and insensitivity to O2. ASV, utilizing a Bi film, along with cadmium (Cd) and lead (Pb) as the plating mediators, has recently been adapted to determine zinc (Zn) concentrations in highly alkaline environments (30 % NaOH or 35 % M KOH). Successful analysis of Zn in alkaline relies on the ability of the hydroxide to form soluble metal anion species, such as Bi(OH)4 − and Zn(OH)4 2−. Here, we look to extend this technique to detect and quantify copper (Cu) ions in these highly basic electrolytes. However, in general, the use of ASV to detect and quantify Cu ion concentrations is notoriously difficult as the Cu stripping peak potential overlays with that of Bi from the common Bi film electrode. Here, an ASV method for determining Cu concentration in alkaline solutions is developed utilizing Pb as a deposition mediator. As such, it was found that when analyzing Cu solutions in the presence of Pb, the stripping voltammetry curves present separate and defined Cu stripping peaks. Different analyzes were made to find the best stripping voltammetry performance conditions. As such, an accumulation time of 5 minutes, an accumulation potential of≤−1.45 V vs. Hg/HgO, and a concentration of 35 wt% KOH were determined to be the conditions that presented the best ASV results. Utilizing these conditions, calibration curves in the presence of 5.0 ppm Pb showed the best linear stripping signal correlation with an r-squared value of 0.991 and a limit of detection (LOD) of 0.67 ppm. These results give way to evaluating Cu concentrations using ASV in aqueous alkaline solutions.

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Physical stress relaxation in rubbery, thermoset polymers is limited by cross-links, which impede segmental motion and restrict relaxation to network defects, such as chain ends. In parallel, the cure shrinkage associated with thermoset polymerizations leads to the development of internal residual stress that cannot be effectively relaxed. Recent strategies have reduced or eliminated such cure stress in thermoset polymers largely by exploiting chemical relaxation processes, wherein temporary cross-links or otherwise transient bonds are incorporated into the polymer network. Here, we explore an alternative approach, wherein physical relaxation is enhanced by the incorporation of organometallic sandwich moieties into the backbone of the polymer network. A standard epoxy resin is cured with a diamine derivative of ferrocene and compared to conventional diamine curing agents. The ferrocene-based thermoset is clearly distinguished from the conventional materials by reduced cure stress with increasing cure temperature as well as unique stress relaxation behavior above its glass transition in the fully cured state. The relaxation experiments exhibit features characteristic of a physical relaxation process. Furthermore, the cure stress is observed to vanish precipitously upon deliberate introduction of network defects through an increasing imbalance of epoxy and amine functional groups. We postulate that these beneficial properties arise from fluxional motion of the cyclopentadienyl ligands on the polymer backbone.

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Nickel-doped α-MnO2 nanowires (Ni-α-MnO2) were prepared with 3.4% or 4.9% Ni using a hydrothermal method. A comparison of the electrocatalytic data for the oxygen reduction reaction (ORR) in alkaline electrolyte versus that obtained with α-MnO2 or Cu-α-MnO2 is provided. In general, Ni-α-MnO2 (e.g., Ni-4.9%) had higher n values (n = 3.6), faster kinetics (k = 0.015 cm s-1), and lower charge transfer resistance (RCT = 2264 Ω at half-wave) values than MnO2 (n = 3.0, k = 0.006 cm s-1, RCT = 6104 Ω at half-wave) or Cu-α-MnO2 (Cu-2.9%, n = 3.5, k = 0.015 cm s-1, RCT = 3412 Ω at half-wave), and the overall activity for Ni-α-MnO2 trended with increasing Ni content, i.e., Ni-4.9% > Ni-3.4%. As observed for Cu-α-MnO2, the increase in ORR activity correlates with the amount of Mn3+ at the surface of the Ni-α-MnO2 nanowire. Examining the activity for both Ni-α-MnO2 and Cu-α-MnO2 materials indicates that the Mn3+ at the surface of the electrocatalysts dictates the activity trends within the overall series. Single nanowire resistance measurements conducted on 47 nanowire devices (15 of α-MnO2, 16 of Cu-α-MnO2-2.9%, and 16 of Ni-α-MnO2-4.9%) demonstrated that Cu-doping leads to a slightly lower resistance value than Ni-doping, although both were considerably improved relative to the undoped α-MnO2. The data also suggest that the ORR charge transfer resistance value, as determined by electrochemical impedance spectroscopy, is a better indicator of the cation-doping effect on ORR catalysis than the electrical resistance of the nanowire. (Figure Presented).

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Rechargeable alkaline Zn/MnO2 batteries are being developed for use as cost-effective grid-scale energy storage devices. Previous studies have shown that limiting the depth of discharge (DOD) of the MnO2 cathode extends cell lifetime while still providing a cost-effective battery system. Herein, a comprehensive study of triethanolamine (TEA) as an additive in Zn/MnO2 limited DOD batteries is provided by examining the effect of TEA in full cells as well as independently on the cathode, anode, separator, and electrolyte. Improvement in cycle-ability of the cathode (on average, 80% of cycled capacity remains after 191 cycles without TEA, 568 cycles with TEA) and a decrease in ionic zinc mobility across Celgard 3501 (7.91 × 10-5 cm2/min without TEA, 3.56 × 10-5 cm2/min with TEA) and Cellophane 350P00 (3.26 × 10-5 cm2/min without TEA, 4.74 × 10-6 cm2/min with TEA) separators upon the addition of TEA are demonstrated. However, TEA increased both the reduction potential of Zn (-0.68 V vs. Hg/HgO without TEA, -0.76 V with TEA) and the solubility of Zn2+ (0.813 M without TEA, 1.023 M with TEA). Overall, the addition of TEA extended the lifetime of limited DOD cells on average by 297%.

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Manganese oxide/poly(3,4-ethylene-dioxythiophene) (MnO_x/ PEDOT) nanostructured hybrid thin films were prepared using a simple anodic electrodeposition process from aqueous solution, and then tested for oxygen reduction reaction (ORR) activity in alkaline electrolyte using rotating disk electrode and rotating ring disk electrode methods. MnO_x/PEDOT provided improvements over MnO_x-only and PEDOT-only control films, with > 0.2 V decrease in onset and half-wave overpotentials, and > 1.5 times increase in terminal current density. The MnO_x/PEDOT film exhibited only a slightly lower n value (n = 3.86-3.92) than the 20% Pt/C benchmark electrocatalyst (n = 3.98) across all potentials. MnO_x/PEDOT also displayed a more positive half-wave potential and superior electrocatalytic selectivity for the ORR upon methanol exposure than 20% Pt/C. Here, the high activity and synergism of MnO_x/PEDOT towards the ORR is attributed to effective intermixing/dispersion of the two materials, intimate substrate contact with improved charge transfer processes attained by co-electrodepositing MnO_x with PEDOT and due to the increase in Mn³⁺ content at the surface of the oxide.

Cobalt phosphide based thin films and nanoparticles were prepared by the thermal phosphidation of spinel Co₃O₄ precursor films and nanoparticles, respectively. CoP films were prepared with overall retention of the Co₃O₄ nanoplatelet morphology while the spherical/cubic Co₃O₄ and Ni_0.15Co_2.85O₄ nanoparticles were converted to nanorods or nanoparticles, respectively. The inclusion of nickel in the nanoparticles resulted in a 2.5 fold higher surface area leading to higher gravimetric performance. In each case high surface area structures were obtained with CoP as the primary phase. All materials were found to act as effective bifunctional electrocatalysts for both the HER and the OER and compared well to commercial precious metal benchmark materials in alkaline electrolyte. As a result, a symmetrical water electrolysis cell prepared from the CoP-based film operated at a low overpotential of 0.41-0.51 V.

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The contribution of each component of a power generation plant to the levelized cost of energy (LCOE) can be estimated and used to increase the power output while reducing system operation and maintenance costs. The LCOE is used in order to quantify solar receiver coating influence on the LCOE of solar power towers. Two new parameters are introduced: the absolute levelized cost of coating (LCOC) and the LCOC efficiency. Depending on the material properties, aging, costs, and temperature, the absolute LCOC enables quantifying the cost-effectiveness of absorber coatings, as well as finding optimal operating conditions. The absolute LCOC is investigated for different hypothetic coatings and is demonstrated on Pyromark 2500 paint. Results show that absorber coatings yield lower LCOE values in most cases, even at significant costs. Optimal reapplication intervals range from one to five years. At receiver temperatures greater than 700 °C, non-selective coatings are not always worthwhile while durable selective coatings consistently reduce the LCOE-up to 12% of the value obtained for an uncoated receiver. The absolute LCOC is a powerful tool to characterize and compare different coatings, not only considering their initial efficiencies but also including their durability.

The electroreduction of Er3+ in propylene carbonate, N,N-dimethylformamide, or a variety of quaternary ammonium ionic liquids (ILs) was investigated using [Er(OTf)3] and [Er(NTf2)3]. Systematic variation of the ILs' cation and anion, Er3+ salt, and electrode material revealed a disparity in electrochemical interactions not previously seen. For most ILs at a platinum electrode, cyclic voltammetry exhibits irreversible interactions between Er3+ salts and the electrode at potentials significantly less than the theoretical reduction potential for Er3+. Throughout all solvent-salt systems tested, a deposit could be formed on the electrode, though obtaining a high purity, crystalline Er0 deposit is challenging due to the extreme reactivity of the deposit and resulting chemical interactions, often resulting in the formation of a complex, amorphous solid-electrolyte interface that slowed deposition rates. Comparison of platinum, gold, nickel, and glassy carbon (GC) working electrodes revealed oxidation processes unique to the platinum surface. While no appreciable reduction current was observed on GC at the potentials investigated, deposits were seen on platinum, gold, and nickel electrodes.

Cobalt phosphide based thin films and nanoparticles were prepared by the thermal phosphidation of spinel Co3O4 precursor films and nanoparticles, respectively. CoP films were prepared with overall retention of the Co3O4 nanoplatelet morphology while the spherical/cubic Co3O4 and Ni0.15Co2.85O4 nanoparticles were converted to nanorods or nanoparticles, respectively. The inclusion of nickel in the nanoparticles resulted in a 2.5 fold higher surface area leading to higher gravimetric performance. In each case high surface area structures were obtained with CoP as the primary phase. All materials were found to act as effective bifunctional electrocatalysts for both the HER and the OER and compared well to commercial precious metal benchmark materials in alkaline electrolyte. A symmetrical water electrolysis cell prepared from the CoP-based film operated at a low overpotential of 0.41-0.51 V.

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In this study, the use of maltodextrin supramolecular structures (MD SMS) as a reducing agent and colloidal stabilizing agent for the synthesis of Ag nanoparticles (Ag NPs) identified three key points. First, the maltodextrin (MD) solutions are effective in the formation of well-dispersed Ag NPs utilizing alkaline solution conditions, with the resulting Ag NPs ranging in size from 5 to 50 nm diameter. Second, in situ characterization by Raman spectroscopy and small angle X-ray scattering (SAXS) are consistent with initial nucleation of Ag NPs within the MD SMS up to a critical size of ca. 1 nm, followed by a transition to more rapid growth by aggregation and fusion between MD SMS, similar to micelle aggregation reactions. Third, the stabilization of larger Ag NPs by adsorbed MD SMS is similar to hemi-micelle stabilization, and monomodal size distributions are proposed to relate to integer surface coverage of the Ag NPs. Conditions were identified for preparing Ag NPs with monomodal distributions centered at 30–35 nm Ag NPs.

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Electro-optical organic materials hold great promise for the development of high-efficiency devices based on exciton formation and dissociation, such as organic photovoltaics (OPV) and organic light-emitting devices (OLEDs). However, the external quantum efficiency (EQE) of both OPV and OLEDs must be improved to make these technologies economical. Efficiency rolloff in OLEDs and inability to control morphology at key OPV interfaces both reduce EQE. Only by creating materials that allow manipulation and control of the intimate assembly and communication between various nanoscale excitonic components can we hope to first understand and then engineer the system to allow these materials to reach their potential. The aims of this proposal are to: 1) develop a paradigm-changing platform for probing excitonic processes composed of Crystalline Nanoporous Frameworks (CNFs) infiltrated with secondary materials (such as a complimentary semiconductor); 2) use them to probe fundamental aspects of excitonic processes; and 3) create prototype OPVs and OLEDs using infiltrated CNF as active device components. These functional platforms will allow detailed control of key interactions at the nanoscale, overcoming the disorder and limited synthetic control inherent in conventional organic materials. CNFs are revolutionary inorganic-organic hybrid materials boasting unmatched synthetic flexibility that allow tuning of chemical, geometric, electrical, and light absorption/generation properties. For example, bandgap engineering is feasible and polyaromatic linkers provide tunable photon antennae; rigid 1-5 nm pores provide an oriented, intimate host for triplet emitters (to improve light emission in OLEDs) or secondary semiconducting polymers (creating a charge-separation interface in OPV). These atomically engineered, ordered structures will enable critical fundamental questions to be answered concerning charge transport, nanoscale interfaces, and exciton behavior that are inaccessible in disordered systems. Implementing this concept also creates entirely new dimensions for device fabrication that could both improve performance, increase durability, and reduce costs with unprecedented control of over properties. This report summarizes the key results of this project and is divided into sections based on publications that resulted from the work. We begin in Section 2 with an investigation of light harvesting and energy transfer in a MOF infiltrated with donor and acceptor molecules of the type typically used in OPV devices (thiophenes and fullerenes, respectively). The results show that MOFs can provide multiple functions: as a light harvester, as a stabilizer and organizer or the infiltrated molecules, and as a facilitator of energy transfer. Section 3 describes computational design of MOF linker groups to accomplish light harvesting in the visible and facilitate charge separation and transport. The predictions were validated by UV-visible absorption spectroscopy, demonstrating that rational design of MOFs for light-harvesting purposes is feasible. Section 4 extends the infiltration concept discussed in Section to, which we now designate as "Molecule@MOF" to create an electrically conducting framework. The tailorability and high conductivity of this material are unprecedented, meriting publication in the journal Science and spawning several Technical Advances. Section 5 discusses processes we developed for depositing MOFs as thin films on substrates, a critical enabling technology for fabricating MOF-based electronic devices. Finally, in Section 6 we summarize results showing that a MOF thin film can be used as a sensitizer in a DSSC, demonstrating that MOFs can serve as active layers in excitonic devices. Overall, this project provides several crucial proofs-of- concept that the potential of MOFs for use in optoelectronic devices that we predicted several years ago [ 3 ] can be realized in practice.

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This work aims to address the failure modes in lithium-ion batteries that can be directly attributed to separator failure at temperatures well below the onset of thermal runaway. Polyester-based separators have been developed by an ambient temperature electro-spinning process shown in the SEM image. Resulting separators have electrochemical performance comparable to commercial polyolefin separators with greatly improved thermal stability. © 2013 WILEY-VCH Verlag GmbH & Co.

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Pyromark 2500 is a silicone-based high-temperature paint that has been used on central receivers to increase solar absorptance. The cost, application, curing methods, radiative properties, and absorber efficiency of Pyromark 2500 are presented in this paper for use as a baseline for comparison to high-temperature solar selective absorber coatings currently being developed. The directional solar absorptance was calculated from directional spectral absorptance data, and values for pristine samples of Pyromark 2500 were as high as 0.96-0.97 at near normal incidence angles. At higher irradiance angles (>40° - 60°), the solar absorptance decreased. The total hemispherical emittance of Pyromark 2500 was calculated from spectral directional emittance data measured at room temperature and 600°C. The total hemispherical emittance values ranged from ∼0.80-0.89 at surface temperatures ranging from 100°C - 1,000°C. The aging and degradation of Pyromark 2500 with exposure at elevated temperatures were also examined. Previous tests showed that solar receiver panels had to be repainted after three years due to a decrease in solar absorptance to 0.88 at the Solar One central receiver pilot plant. Laboratory studies also showed that exposure of Pyromark 2500 at high temperatures (750°C and higher) resulted in significant decreases in solar absorptance within a few days. However, at 650°C and below, the solar absorptance did not decrease appreciably after several thousand hours of testing. Finally, the absorber efficiency of Pyromark 2500 was determined as a function of temperature and irradiance using the calculated solar absorptance and emittance values presented in this paper. Copyright © 2012 by ASME.

Pyromark 2500 is a silicone-based high-temperature paint that has been used on central receivers to increase solar absorptance. The cost, application, curing methods, radiative properties, and absorber efficiency of Pyromark 2500 are presented in this paper for use as a baseline for comparison to high-temperature solar selective absorber coatings currently being developed. The directional solar absorptance was calculated from directional spectral absorptance data, and values for pristine samples of Pyromark 2500 were as high as 0.96-0.97 at near normal incidence angles. At higher irradiance angles (>40° - 60°), the solar absorptance decreased. The total hemispherical emittance of Pyromark 2500 was calculated from spectral directional emittance data measured at room temperature and 600°C. The total hemispherical emittance values ranged from ∼0.80-0.89 at surface temperatures ranging from 100°C - 1,000°C. The aging and degradation of Pyromark 2500 with exposure at elevated temperatures were also examined. Previous tests showed that solar receiver panels had to be repainted after three years due to a decrease in solar absorptance to 0.88 at the Solar One central receiver pilot plant. Laboratory studies also showed that exposure of Pyromark 2500 at high temperatures (750°C and higher) resulted in significant decreases in solar absorptance within a few days. However, at 650°C and below, the solar absorptance did not decrease appreciably after several thousand hours of testing. Finally, the absorber efficiency of Pyromark 2500 was determined as a function of temperature and irradiance using the calculated solar absorptance and emittance values presented in this paper. Copyright © 2012 by ASME.

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Silver nanomaterials have significant application resulting from their optical properties related to surface enhanced Raman spectroscopy, high electrical conductivity, and anti-microbial impact. A 'green chemistry' synthetic approach for silver nanomaterials minimizes the environmental impact of silver synthesis, as well as lowers the toxicity of the reactive agents. Biopolymers have long been used for stabilization of silver nanomaterials during synthesis, and include gum Arabic, heparin, and common starch. Maltodextrin is a processed derivative of starch with lower molecular weight and an increase in the number of reactive reducing aldehyde groups, and serves as a suitable single reactant for the formation of metallic silver. Silver nanomaterials can be formed under either a thermal route at neutral pH in water or by reaction at room temperature under more alkaline conditions. Deposited silver materials are formed on substrates from near neutral pH solutions at low temperatures near 50 C. Experimental conditions based on material concentrations, pH and reaction time are investigated for development of deposited films. Deposit morphology and optical properties are characterized using SEM and UV-vis techniques. Silver nanoparticles are generated under alkaline conditions by a dissolution-reduction method from precipitated silver (II) oxide. Synthesis conditions were explored for the rapid development of stable silver nanoparticle dispersions. UV-vis absorption spectra, powder X-ray diffraction (PXRD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques were used to characterize the nanoparticle formation kinetics and the influence of reaction conditions. The adsorbed content of the maltodextrin was characterized using thermogravimetric analysis (TGA).

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Concentrating solar power (CSP) systems use solar absorbers to convert the heat from sunlight to electric power. Increased operating temperatures are necessary to lower the cost of solar-generated electricity by improving efficiencies and reducing thermal energy storage costs. Durable new materials are needed to cope with operating temperatures >600 C. The current coating technology (Pyromark High Temperature paint) has a solar absorptance in excess of 0.95 but a thermal emittance greater than 0.8, which results in large thermal losses at high temperatures. In addition, because solar receivers operate in air, these coatings have long term stability issues that add to the operating costs of CSP facilities. Ideal absorbers must have high solar absorptance (>0.95) and low thermal emittance (<0.05) in the IR region, be stable in air, and be low-cost and readily manufacturable. We propose to utilize solution-based synthesis techniques to prepare intrinsic absorbers for use in central receiver applications.

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The global market for wireless sensor networks in 2010 will be valued close to $10 B, or 200 M units. TPL, Inc. is a small Albuquerque based business that has positioned itself to be a leader in providing uninterruptible power supplies in this growing market with projected revenues expected to exceed $26 M in 5 years. This project focused on improving TPL, Inc.'s patent-pending EnerPak{trademark} device which converts small amounts of energy from the environment (e.g., vibrations, light or temperature differences) into electrical energy that can be used to charge small energy storage devices. A critical component of the EnerPak{trademark} is the supercapacitor that handles high power delivery for wireless communications; however, optimization and miniaturization of this critical component is required. This proposal aimed to produce prototype microsupercapacitors through the integration of novel materials and fabrication processes developed at New Mexico Technology Research Collaborative (NMTRC) member institutions. In particular, we focused on developing novel ruthenium oxide nanomaterials and placed them into carbon supports to significantly increase the energy density of the supercapacitor. These improvements were expected to reduce maintenance costs and expand the utility of the TPL, Inc.'s device, enabling New Mexico to become the leader in the growing global wireless power supply market. By dominating this niche, new customers were expected to be attracted to TPL, Inc. yielding new technical opportunities and increased job opportunities for New Mexico.