Grid-level Energy Storage Research Articles

Performance and cost characteristics of multi-electron transfer, common ion exchange non-aqueous redox flow batteries

Abstract Non-aqueous redox flow batteries (NAqRFBs) have recently received considerable attention as promising high energy density, low cost grid-level energy storage technologies. Despite these attractive features, NAqRFBs are still at an early stage of development and innovative design techniques are necessary to improve performance and decrease costs. In this work, we investigate multi-electron transfer, common ion exchange NAqRFBs. Common ion systems decrease the supporting electrolyte requirement, which subsequently improves active material solubility and decreases electrolyte cost. Voltammetric and electrolytic techniques are used to study the electrochemical performance and chemical compatibility of model redox active materials, iron (II) tris(2,2′-bipyridine) tetrafluoroborate (Fe(bpy) 3 (BF 4 ) 2 ) and ferrocenylmethyl dimethyl ethyl ammonium tetrafluoroborate (Fc1N112-BF 4 ). These results help disentangle complex cycling behavior observed in flow cell experiments. Further, a simple techno-economic model demonstrates the cost benefits of employing common ion exchange NAqRFBs, afforded by decreasing the salt and solvent contributions to total chemical cost. This study highlights two new concepts, common ion exchange and multi-electron transfer, for NAqRFBs through a demonstration flow cell employing model active species. In addition, the compatibility analysis developed for asymmetric chemistries can apply to other promising species, including organics, metal coordination complexes (MCCs) and mixed MCC/organic systems, enabling the design of low cost NAqRFBs.

Probing the Aging Effects on Nanomechanical Properties of a Thin Film LiFePO4 Cathode

Despite widespread usage of Li-ion batteries in portable electronics, large scale utilization of Li-ion batteries in electric vehicles and grid-level energy storage is only possible if cost, safety, energy density, specific power and cycle life of Li-ion batteries are further improved. Enhancing the cycle life is especially critical for wider market penetration of Li-ion batteries which requires detailed understanding of the degradation mechanisms. The interplay between various battery subcomponents such as cathode, anode, separator, electrolyte and current collector determines the degradation mechanisms of Li-ion batteries that can have both chemical and mechanical origins that are closely interrelated. Chemical degradation mechanisms such as solid electrolyte interphase formation and electrolyte decomposition have been studied extensively; however, mechanical degradation mechanisms attracted less attention. Mechanical degradation is associated with the volume changes and stress generated during Li de-/intercalation in an active material which can result in formation of cracks, delamination and isolation of the active particles causing capacity and power losses. Our previous work on composite LiFePO4 cathode by nanoindentation revealed that elastic modulus deteriorates by aging as well as shows spatial variation on the electrode surface [1]. Binder is the compliant component in a composite electrode; therefore, degradation in elastic modulus is associated with the binder not the active material. To determine the mechanical degradation in the active material, thin film LiFePO4 cathode (i.e., no binder or carbon coating/additive as in a composite electrode) was synthesized by physical vapor deposition, and employed in determining the changes in the mechanical properties of the active material due to aging. The preliminary AFM experiments on thin film LiFePO4 cathode showed significant changes in particle morphology and roughness upon cycling as shown in Fig. 1. On the other hand, mechanical properties of the thin film LiFePO4 did not show as significant deterioration as in a composite LiFePO4 cathode indicating mechanical degradation in binder is more problematic than the mechanical degradation in the active material.

Efficiency and Long-Term Cycling Study of Carbon Anode Materials in Sodium-Ion Batteries

Recently, there has been much discussion about Na-ion batteries (NIBs) emerging as one ideal technology for grid-level energy storage. Large-scale usage of NIBs can be sustainable as the raw materials involved in making such batteries are cheap, plentiful and non-toxic. Thus far, they have demonstrated very promising electrochemical performances in prototype experiments. Despite the aforementioned benefits, there still remain technical issues associated with the electrode materials, which is currently hindering their development as a fully-functional commercial battery. One of these pressing problems is the efficiency and cyclability of the anode material: an ideal material must possess both a high 1st cycle coulombic efficiency and a stable long-term cycling life—as both of these are crucial to the performance of the battery. However, most candidate materials currently proposed in the literature do not meet such criteria. Herein, we study self-standing cellulose-derived carbon as a model carbon, where we attempt to understand factors affecting coulombic efficiency and long-term cycling. This material displays one of the highest reported coulombic efficiencies for carbon-based anodes in the literature, with values averaging near 90% for the first cycle with a deep-sodiation in a half-cell. On the other hand, the carbon material also displays extremely poor rate and long-term cycling performances, which leads us to an in-depth investigation of the fading mechanism of carbon materials used as NIB anodes. Through the course of our investigation on the fading mechanism, we are able to uncover some structural-property relationships to understand the capacity loss during long-term cycling. This was elucidated through the use of traditional characterization methods such as XRD, Raman spectroscopy and XPS measurements along with more advanced TEM characterization, using sample “lift-outs” to probe the structural effects of long-term cycling on the carbon material. These claims are also further supported through electrochemical data including diffusivity tests, CV and EIS measurements. Using the information learned on the efficiency/long-term decay mechanism, we were able to devise ‘proof-of-concept’ solutions to increase long-term cycling of carbon anode materials utilized in NIBs.

Targeted Molecular Engineering of Dimethoxybenzenes for Non-Aqueous Redox Flow Batteries

Technical advances in grid-level energy storage are of critical importance in enabling the widespread penetration of renewable resources that meet consumer requirements for on-demand, safe, and uninterrupted power provided at a reasonable cost. Redox flow batteries (RFBs) are electrochemical systems well-suited for multi-hour storage at the low system costs needed for economically viable grid storage. While aqueous RFBs utilizing inorganic active species have been traditionally studied1, 2, non-aqueous redox flow batteries (NRFBs) utilizing organic active species offer the advantages of a larger electrolyte voltage window and the ability to tailor the molecular structure of the active species to achieve desired properties. Recently, Darling et al. outlined materials-level benchmarks for NRFBs which align with aggressive cost targets established by the U.S. Department of Energy.3 Specifically, for economic feasibility, NRFBs require active materials with disparate redox potentials (Vcell > 3 V), high solubility in electrolyte solutions (4-5 M charge carriers), and high gravimetric capacity (< 150 g/mol e-).3 Overcharge protection redox shuttles for lithium-ion batteries provide a good basis for molecular derivatization as the materials developed over the past 30 years share many of the same desired properties, including a high potential, high solubility, and long-term stability4, 5. Using a dimethoxybenzene core4, we combine molecular engineering, electrochemical analysis, and materials characterization to understand the role of structure in redox performance and to develop design principles. In this presentation, we will report on key findings based on studies of several different dimethoxybenzene-based derivatives. Specifically, we will highlight means of improving solubility6, increasing intrinsic capacity7, and raising redox potential, all of which lead to enhanced energy density. For example, Figure 1 shows the impact of halidization on the redox behavior of a series of dimethoxybenzene derivatives. Further, unintended consequences of these derivatizations, such as changes in active species stability, will be contemplated with a focus on improving the success of molecular design campaigns. Acknowledgments We gratefully acknowledge the financial support of the Joint Center for Energy Storage Research.

NSTF Advances for PEM Electrolysis - the Effect of Alloying on Activity of NSTF Electrolyzer Catalysts and Performance of NSTF Based PEM Electrolyzers

Recent resurgence of interest in harnessing energy from renewable sources, and a push to achieve environmental cleanliness in the energy industry has rekindled interest in hydrogen as a clean and environmentally benign energy carrier. This is done with the ultimate goal of supplanting the current hydrocarbon based economy by hydrogen economy as means to achieve environmentally friendly energy industry and energy independence. The rising star of hydrogen enabled mobility i.e. recent accomplishments in (automotive) fuel cells adds further impetus to advance renewable and at the same time economical means to generate hydrogen – i.e., which is the ultimate key to success for hydrogen as fuel in societal everyday transportation solutions. As such, this rekindled interest in the age-old water electrolysis process spawned new approaches to generate hydrogen with increased efficiency and lower cost. Polymer electrolyte membrane (PEM) water electrolysis, while one of those relatively new approaches, has been used for quite a few years now without undergoing any substantial improvements over those years. Solutions based on Nafion 117 and high loadings of Platinum-Group Metals (PGM) worked well enough and were sufficiently durable. Now, however, with the new focus on hydrogen as the energy carrier (as opposed to a chemical reactant, mobile phase, or coolant – its major applications at present), there is much more interest in low cost/high efficiency H2 production. This explains the renewed interest and recent increase in R&D activity in this fertile and promising area. As a matter of fact it is quite possible the success (or lack of) in achieving lower cost of hydrogen production may make or break the success of fuel cell as grid-level energy storage solution and personal transportation technology of choice. There are two main ways to lower the cost of hydrogen production via PEM water electrolysis: to lower the capital expenses (CAPEX) and/or to lower the operating expenses (OPEX). We at 3M have recently addressed reducing the first (high CAPEX ) by widening the range of current densities where electrolyzers can operate from a maximum of about 2.0 A/cm2, as used today in commercial electrolyzers, to as much as 20 A/cm2. While the research on high power density operation of PEM water electrolysis still continues, and many questions remain as yet unanswered, the NSTF catalyst, with its highly conductive, compact, and hydrophilic catalyst layer seems uniquely fitting to the task. Indeed, its hydrophilicity that is a major weakness in fuel cells is a tremendous strength in water electrolysis and one of the features enabling the extremely high mass transport free current densities we reported previously1. Currently, we intend to tackle the second means for reduction of cost of hydrogen production by increasing the intrinsic activity of the catalyst as means to increase the kinetics of oxygen evolution and hence the efficiency of water electrolysis (thus reducing the OPEX). We will show the effect of alloying on the performance of typical PGM based NSTF anode catalysts. One such example will be exploration of the Pt/Ir compositional parameter space (in the NSTF alloy catalyst format) and the compositional effects on fundamental catalyst activity, as determined by RDE measurements. Subsequently, we will correlate this to the in-situ performance measurements in a PEM electrolysis cell. Finally, we will discuss the possibilities in other promising alloying compositions and structures. Krzysztof A. Lewinski, Sean M. Luopa, “High Power Water Electrolysis as a New Paradigm for Operation of PEM Electrolyzer.”, Spring ECS Meeting, Chicago, IL, May 2015.

ChemInform Abstract: Recent Development on Anodes for Na‐Ion Batteries

AbstractReview: [124 refs.

An Electrochemical Cell for Selective Lithium Capture from Seawater.

Lithium (Li) is a core element of Li-ion batteries (LIBs). Recent developments in mobile electronics such as smartphones and tablet PCs as well as advent of large-scale LIB applications including electrical vehicles and grid-level energy storage systems have led to an increase in demand for LIBs, giving rise to a concern on the availability and market price of Li resources. However, the current Lime-Soda process that is responsible for greater than 80% of worldwide Li resource supply is applicable only in certain regions on earth where the Li concentrations are sufficiently high (salt lakes or salt pans). Moreover, not only is the process time-consuming (12-18 months), but post-treatments are also required for the purification of Li. Here, we have devised a location-independent electrochemical system for Li capture, which can operate within a short time period (a few hours to days). By engaging olivine LiFePO4 active electrode that improves interfacial properties via polydopamine coating, the electrochemical cell achieves 4330 times amplification in Li/Na ion selectivity (Li/Na molar ratio of initial solution = 0.01 and Li/Na molar ratio of final electrode = 43.3). In addition, the electrochemical system engages an I(-)/I3(-) redox couple in the other electrode for balancing of the redox states on both electrode sides and sustainable operations of the entire cell. Based on the electrochemical results, key material and interfacial properties that affect the selectivity in Li capture are identified.

Optimization of MnO2 Cathodes for Aqueous Battery Applications

Grid-level energy storage demands a low-cost, safe, long cycle life battery chemistry. The Zn-MnO2 alkaline battery chemistry hits the first two targets. This type of battery has high energy density (comparable to that of a Li-ion battery) and low cost per kilowatt-hour. However, their rechargeability is limited by phase transformations which occur in the MnO2 cathode during discharge of close to one electron, which transforms it into an spinel phase, generally considered to be electrochemically inert. As a result, depth of discharge is limited to no more than 70% of the 1e- capacity of MnO2 at best, and in a large format cell typically no more than 0.5 e-. We have extensively studied the MnO2 alkaline system and have developed a variety of techniques to extend this depth of discharge window, improving the capacity and cyclability of the cell dramatically. We have also developed novel nanostructured forms of MnO2 for use as a cathode material in this system. Using these techniques, we have achieved capacities of over 350 mAh/g (1.2 e-) for more than 150 cycles. In this presentation, we will discuss the various failure modes of the MnO2 alkaline system, and the techniques our group has developed to overcome them. We will describe the crystal structure and electrochemical performance of the nanomaterials we have synthesized, as well as the structural changes occurring during their use as an electrode material as characterized via synchrotron radiation and other techniques. With further development, this material, combined with either a zinc anode or an earth abundant, insoluble anode such as Fe or Cd, may allow for over 1000 cycles at a cost of less that $100/kWhr for a packed out cell. Figure: a) MnO2 electrode before cycling; b) MnO2 electrode after 1st-electron discharge; c) MnO2 electrode after full discharge; d) MnO2 electrode after full recharge; e) MnO2 electrode after 3 cycles (discharged state); f) MnO2 electrode after 15 cycles (discharged state) Figure 1

Mixed ionic electronic conducting powder bed for grid level energy storage and release: A study of tungsten oxide reduction kinetics

The reduction kinetics of tungsten trioxide (WO3) powder using hydrogen gas was studied with titanium dioxide (TiO2) or 8 mol% yttria-stabilized zirconia (8YSZ) mixed into the powder bed. TiO2 was selected as an inert volume filler, and 8YSZ was selected to increase the ionic conductivity of the powder bed. The reduction sequence of tungsten trioxide in hydrogen is known to take place in the following steps: WO3 → WO2.9 → WO2.72 → WO2 → W. When the electronic and ionic conductivities of the mixed powder bed were both sufficiently high, reduction rates were found to increase. Specifically, reaction kinetics improved with the addition of 8YSZ to the WO3 when compared to experiments in which TiO2 was added to the WO3 powder bed. Chemical reaction rates were determined by first recording changes in mass as a function of time during reduction using thermogravimetry, and then reaction rates were calculated using relevant kinetic theory.

Recent Development on Anodes for Na‐Ion Batteries

AbstractNew discoveries in anode materials for sodium ion batteries (NIBs) are highly necessary to achieve the goals of widespread applications, such as electric vehicles (EVs) and grid‐level energy storage. Carbon‐based materials are critical for this task as they are inexpensive, abundant, and versatile. They contain a plethora of structures and morphologies, ranging from highly ordered graphite or nanotubes to highly disordered amorphous carbon, thus making them very attractive for electrochemical energy storage. This review attempts to cover past and recent progress in the development of carbon‐based anode materials for NIBs. To give a larger context, the article will briefly cover other anode materials for NIBs as well. The aim of this paper is to provide a timely update for researchers currently involved in the respective fields or to serve as a starting point for individuals who would like to gain a greater knowledge of new NIB anode materials.

A Comparison of the Capital Costs of a Vanadium Redox-Flow Battery and a Regenerative Hydrogen-Vanadium Fuel Cell

The capital costs of a Regenerative Hydrogen-Vanadium Fuel Cell and a Vanadium Redox-Flow Battery are compared for grid level energy storage. The bulk of the capital costs for a Vanadium Redox-Flow Battery lie in the costs of the vanadium electrolyte, while the Regenerative Hydrogen-Vanadium Fuel Cell presents a potential for savings by eliminating the need for half of the vanadium electrolyte required by a Vanadium Redox-Flow Battery. It was found that the Regenerative Hydrogen-Vanadium Fuel Cell would cost $57 less per kWh than the Vanadium Redox-Flow Battery, with savings garnered from the elimination of half of the electrolyte somewhat mitigated by the costs of the catalyst and air compressor required. If the capital costs are annualized through straight line depreciation, and the operation costs are included, the Vanadium Redox-Flow Battery is $5 per kWh less per year than the Regenerative Hydrogen-Vanadium Fuel Cell.

Lithium-antimony-lead liquid metal battery for grid-level energy storage.

The ability to store energy on the electric grid would greatly improve its efficiency and reliability while enabling the integration of intermittent renewable energy technologies (such as wind and solar) into baseload supply. Batteries have long been considered strong candidate solutions owing to their small spatial footprint, mechanical simplicity and flexibility in siting. However, the barrier to widespread adoption of batteries is their high cost. Here we describe a lithium-antimony-lead liquid metal battery that potentially meets the performance specifications for stationary energy storage applications. This Li||Sb-Pb battery comprises a liquid lithium negative electrode, a molten salt electrolyte, and a liquid antimony-lead alloy positive electrode, which self-segregate by density into three distinct layers owing to the immiscibility of the contiguous salt and metal phases. The all-liquid construction confers the advantages of higher current density, longer cycle life and simpler manufacturing of large-scale storage systems (because no membranes or separators are involved) relative to those of conventional batteries. At charge-discharge current densities of 275milliamperes per square centimetre, the cells cycled at 450 degrees Celsius with 98 per cent Coulombic efficiency and 73 per cent round-trip energy efficiency. To provide evidence of their high power capability, the cells were discharged and charged at current densities as high as 1,000milliamperes per square centimetre. Measured capacity loss after operation for 1,800hours (more than 450 charge-discharge cycles at 100 per cent depth of discharge) projects retention of over 85 per cent of initial capacity after ten years of daily cycling. Our results demonstrate that alloying a high-melting-point, high-voltage metal (antimony) with a low-melting-point, low-cost metal (lead) advantageously decreases the operating temperature while maintaining a high cell voltage. Apart from the fact that this finding puts us on a desirable cost trajectory, this approach may well be more broadly applicable to other battery chemistries.

The Role of Mixed Conduction in W-WO3 Redox Kinetics

The tungsten - tungsten trioxide (W-WO3) materials system has recently shown excellent promise as a medium for grid level energy storage and for solar energy conversion. In both these applications the thermal energy transfer is accompanied by a redox reaction in the W-WO3 couple. For viability of this system as an energy storage medium, it is important to have facile redox kinetics that allows us to rapidly store and release energy. Facile kinetics are also required in the utilization of this system in solar syngas production. In this paper we show that the addition of an ionic conducting phase, namely yttria stabilized zirconia (YSZ) greatly enhances the redox kinetics of the W-WO3 couple. Specifically, the reduction kinetics of the WO3-W reaction are facilitiated by the addition of YSZ. As a control experiment, a redox experiment with a filler material that is not an ionic conductor did not show such an enhancement in the kinetics. Chemical reaction rates were determined by transient thermogravimetry, and the data were analyzed using relevant kinetic and transport theory.

ChemInform Abstract: Nanostructured Sulfur Cathodes

AbstractReview: 109 refs.

Nanostructured sulfur cathodes

Rechargeable Li/S batteries have attracted significant attention lately due to their high specific energy and low cost. They are promising candidates for applications, including portable electronics, electric vehicles and grid-level energy storage. However, poor cycle life and low power capability are major technical obstacles. Various nanostructured sulfur cathodes have been developed to address these issues, as they provide greater resistance to pulverization, faster reaction kinetics and better trapping of soluble polysulfides. In this review, recent developments on nanostructured sulfur cathodes and mechanisms behind their operation are presented and discussed. Moreover, progress on novel characterization of sulfur cathodes is also summarized, as it has deepened the understanding of sulfur cathodes and will guide further rational design of sulfur electrodes.

Synchrophasors, Active Transformers, and Energy Storage in the Context of Fast Charge EV Infrastructure

Electric vehicle (EV) fast charging capabilities, and availability of fast charge infrastructure, are perhaps the greatest remaining obstacles in the future widespread use of EVs. Solving fast charging paradigms and issues will enhance driver and electric utility acceptance of EVs. Potential impact to the grid is one of the perceived issues. The technologies to transform EV fast chargers, a grid load, into a valuable grid asset, exist in the form of components and a system approach that includes: Synchrophasors Active Transformers Grid-Level Energy Storage Demand Response and Time of Use pricing Many of these technologies and strategies are in place or in the advanced stages of development. This would allow this system approach to become commercial as the widespread adoption of EVs unfolds.