Large-scale Stationary Energy Storage Research Articles

Fatal Impurity for Electrochemical Mg Deposition/Dissolution

Rechargeable magnesium batteries (RMBs) are promising large-scale stationary energy storage devices. A manufacturing system similar to that used for lithium-ion batteries should be adoptable to the fabrication of RMBs. However, the compatibility of RMB components with atmospheric components other than moisture has not been studied yet. This might be due to the uncertain preconception and misunderstanding of the passivation characteristics of magnesium. In this study, we investigated the effects of atmospheric conditions on the electrochemical dissolution–deposition behavior of magnesium in non-aqueous electrolytes.1 The compatibility of magnesium metal and electrolytes incorporating air-stable weakly-coordinated anions [B(HFIP)4]− or [Al(HFIP)4]− (HFIP: hexafluoro-iso-propoxyl) with dry air was investigated. The results of a simple cyclic voltammetry (CV) clearly demonstrate the far excessive care of magnesium metals against atmospheric O2, because reversible magnesium deposition/dissolution is possible using magnesium metals polished under dry air. However, cells assembled under a dry-air atmosphere show no features of electrochemical magnesium deposition/dissolution. To identify which component of a dry air has a significant detrimental effect on the electrochemical characteristics, systematic CV and open-circuit potential (OCP) measurements were conducted under certain atmospheric conditions with Ar, N2, and O2 and an air-tight voltammetry cell equipped with gas-inlet lines. The platinum and magnesium working electrodes show characteristic responses dependent on the inlet gases, and O2 gas is found to be detrimental for the electrochemical activities of magnesium (Figure 1). The time-profile of OCP and that of O2 content in the electrolyte under steady flow of O2 gas are correlated well, suggesting passivation of magnesium metal upon uptake of O2 in the electrolyte. The electrochemical impedance spectra of symmetric magnesium metal cells using oxygenated and deoxygenated electrolytes and X-ray photoelectron spectra further corroborate inactivation of magnesium by even miniscule amount, ca., 10 ppm, of O2 impurity. Acknowledgement This work was financially supported by the Advanced Low-Carbon Technology-Specially Promoted Research for Innovative Next Generation Batteries Program (ALCA-SPRING, Grant Number JPMJAL1301), NEXT Center of Innovation Program (COI-NEXT, Grant Number JPMJPF2016) of the Japan Science and Technology Agency, and KAKENHI (Grant No. 21K05263) of the Japan Society for the Promotion of Science. Reference T. Mandai and M. Watanabe, under revision. Figure 1

X-Ray Absorption Spectroscopy Studies of Ti-Mn Redox Flow Battery to Clarify the Redox Reaction

Redox flow battery (RFB) is a promising candidate of large-scale stationary energy storage which is necessary to utilize renewable energy. For RFBs, the capability to easily increase the capacity by enlarging the electrolyte tank, high charge-discharge cycle performance, and wide flexibility to high- and low-frequency fluctuations are highly advantageous.Nowadays vanadium RFBs are used for practical use, but the material cost of vanadium is problematic to further spread them. An alternative candidate for commercial use is titanium-manganese (Ti-Mn) RFBs [1] whose material cost should be lower. On the other hand, the stability of the electrolyte for positive electrode (catholyte) need to be improved, because precipitates are created by a charge disproportionation reaction of Mn ions in the charged catholyte [2]. The formation of precipitates decreases the energy density and degrades the cyclability. To improve the characteristics, the chemical state and redox reaction of the electrolytes of Ti-Mn RFBs should be clarified by precise analyses.We performed synchrotron radiation X-ray absorption spectroscopy (XAS) for the electrolytes of a Ti-Mn RFB to directly observe the redox reaction [3]. In this study, the same Ti-Mn RFB electrolyte was used for both positive and negative electrodes. The Ti K-edge XAS of the electrolyte for negative electrode (anolyte) revealed gradual reduction reaction of Ti from Ti4+ on the charge process. The Ti L 2,3-edge XAS spectrum for the anolyte at state of charge (SOC) of 80% was mostly attributed to Ti3+ state. The results for Ti are consistent with electrochemical views in previous reports [2]. The Mn K-edge XAS of the catholyte gradually shifted to higher energy-side up to SOC of 50%, indicating a slight oxidation reaction of Mn from Mn2+. However, the Mn L 2,3-edge XAS spectrum for the catholyte solution at SOC of 80% was of Mn2+ state that was not changed from the initial state. Instead, scanning transmission X-ray microscopy (STXM; XAS mapping with a high spatial resolution) at the Mn L 3-edge unveiled that the precipitates mostly consist of Mn4+. Thus, the charge disproportionation reaction of 2Mn3+ -> Mn2+ (solution) + Mn4+ (precipitates) in the charged catholyte was confirmed. In the presentation, the electronic-structure change of the Ti and Mn ions in both catholyte and anolyte will be discussed in detail.

Li2GeS3: Lithium Ionic Conductor with an Unprecedented Structural Type.

Lithium-ion batteries (LIBs) are widely used in electric vehicles, mobile electronic devices, and large-scale stationary energy storage systems. However, their liquid electrolytes present significant safety concerns due to their inherent flammability. To address this, the focus has shifted toward all-solid-state batteries (ASSBs) utilizing inorganic solid electrolytes that promise enhanced safety. In this work, we report the discovery of a new crystal structural type of Li-ion conductor, Li2GeS3, with a unique structure, synthesized by a solid-state reaction from Li2S and GeS2. It was first reported in 2000 with an orthorhombic unit cell, but its detailed crystal structure remains veiled. We have unveiled its structure for the first time, employing an ab initio structure determination technique from powder X-ray and time-of-flight neutron diffraction data. The compound has an unprecedented crystal structural type with a hexagonal P61 symmetry and a unit cell of a = 6.79364(4) Å and c = 17.90724(14) Å. Its structure is comprised of a distorted hexagonal close-packed arrangement of sulfur anions with three asymmetric metal atoms: Li1, Li2, and Ge are in tetrahedral cavities surrounded by sulfur atoms. The ionic conductivity of Li2GeS3 was measured to be 1.63 × 10-8 S cm-1 at 303 K and 2.45 × 10-7 S cm-1 at 383 K. Bond valence energy landscape calculations revealed three-dimensional lithium diffusion pathways within the structure. This novel crystal structure in Li2GeS3 holds the potential for developing high-performance ionic conductors through suitable chemical substitution and offers valuable insights into designing new ionic conductors for ASSBs.

Advanced and sustainable functional materials for potassium-ion batteries

Rechargeable potassium-ion batteries (PIBs) have gained attention as sustainable, environmentally friendly, and cost-effective large-scale stationary energy storage technology. However, although this technology was assumed to perform in a manner similar to that of its monovalent counterparts, huge anode volume expansion and sluggish kinetics are posing challenges in up-scaling it. Apart from the efforts to develop and optimise electrode materials, recent research endeavours have also focussed on the essential role of sustainability. These attempts have often relied on bio-derived and bio-inspired materials to mimic the effectiveness of nature. Furthermore, the use of materials with self-healing properties can alleviate electrode degradation after cycling and augment its electrochemical performance. This review summarises the development of smart materials with self-healing properties that aid in overcoming the present issues of PIBs and highlights the relevance of the interphases. In addition, state-of-the-art design strategies for bio-derived and bio-inspired materials are presented and discussed. The incorporation of recycled and sustainable materials into the manufacturing of PIBs is expected to contribute towards the ultimate goal of achieving truly circular economy ecosystems. Finally, perspectives for further advancements are provided to kindle new ideas and open questions regarding the use of new-generation materials in the development of PIBs.

High Performance Zinc-Based Anodes for Aqueous Zinc Batteries

In the past thirty years, there has been significant development in the search for alternative energy sources such as secondary battery systems. Zinc (fourth-most mined material) has attracted much attention due to its abundance, low-cost, and recyclability. Moreover, as zinc-based batteries can be manufactured with aqueous-based electrolytes that benefits from many advantages of Zn anode, such as low redox protentional (-0.76V vs SHE), high theoretical capacity (820mAh/g), and enhanced safety. These features allow for high applicability in large-scale stationary energy storage system. Zinc-based batteries (MnO2/Zinc) have been previously commercialized and are one of the dominant technologies in the primary battery market. However, the alkaline MnO2/Zn battery is not currently considered re-chargeable due to the formation of zinc-dendrites, passivation of Zn metal, and cathode poisoning. In contrast to the alkaline system, the mild acidic system does not suffer from zinc passivation as there is negligible generation of zinc oxide/zinc hydroxide.In this work, we report a proof-of concept work where electrodeposited zinc-based anodes (zinc and zinc-alloys) are used in mild acidic aqueous electrolyte. The study provides a comparison of commercial zinc foil, and electrodeposited zinc/zinc-alloy. The anodes are further analyzed structurally through X-ray diffraction and scanning electron microscopy. To evaluate the feasibility of each anode. further electrochemical characterization was carried out in coin cells as symmetric and full cells. The electrodeposited zinc-based anodes exhibit low electrode polarization (~0.030-0.045V), and more stable cycling performance at 10 mA cm-2 compared to commercial zinc foil. Furthermore, full cells with an electrodeposited zinc or zinc-alloy anode, DTT cathode, in 2M ZnSO4 delivered comparable capacities but higher stability compared to commercial zinc. Consequently, this work points toward a further development for anode materials in rechargeable aqueous zinc batteries for scalable applications.

Performance of Several Excellent Oxide-Based Intercalation Cathodes for Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have garnered significant interest in recent years due to their advantages in safety, cost, and energy density, which make them suitable for large-scale stationary energy storage. Cathode materials have been a primary research focus in the early stage of ZIBs development since they are widely deemed a limiting factor to the performance. In general, good ZIB cathode materials are found in oxides with layered and open framework structures, and inorganic/organic hybrids, and follow mechanisms of “intercalation”, “conversion” or a combination of both to store Zn2+ and H+ during discharge. However, dissolution of these cathodes into aqueous electrolytes has been a major cause of the performance degradation of aqueous ZIBs. In this presentation, we first show our fundamental understanding of cathode dissolution mechanisms and development of engineering solutions to address the dissolution and instability issues. We then show through several examples how specially engineered V-oxides based cathodes achieve better dissolution resistance and performance stability using aqueous Zn(OTf)2 and ZnSO4 electrolytes as examples. We expect that the insights in this presentation will advance the understanding of dissolution mechanisms and provide design principles for better cathode materials.

The Future of Energy Storage: Detailed Description of Layered Structure and Porosity of Hard Carbons

The effort of commissioning green and renewable energy with the growing list of critical raw materials demands innovations in energy storage and conversion [1]. The research on sodium-ion batteries (SIBs) has proved promising for large-scale stationary energy storage. Therefore, the crucial need for material research for SIB applications has motivated the studies on hard carbon anodes that have shown high reversible capacity and low working potential[2]. Nevertheless, the exact sodium storage mechanism in hard carbons remains uncertain, inspiring the detailed study of the structure of non-graphitized carbons. Yet, the structure of hard carbons has no long-range order, which complicates the exact characterization. Thus, we present a study focusing on the chemically activated hard carbons' porous and graphite-like structures with complementary wide- and small-angle scattering methods (Figure 1). The current presentation examines the exact impact of the ratio of activating agents on the structure of hard carbons and how the structure affects the ability to store sodium ions. The studied materials were synthesized from D-glycose via hydrothermal carbonization and activated with zinc chloride with different ratios[3]. The evaluation of the layered structure of carbons from wide-angle x-ray scattering (WAXS) data was carried out with Ruland and Smarsly algorithm[4], which is more suitable for non-graphitic carbons than the typically used approaches. The porous structure was described with small-angle neutron scattering (SANS) data model-free analysis, combining Schiller, Mering, Perret, and Ruland approaches[5].This presentation reveals exciting results from the detailed data analysis that opens new perspectives to the material development for SIB hard carbon anodes. During activation of the hard carbon materials activated with zinc chloride with ratios 1:1.5 and 1:2 significant differences in the interlayer arrangement, pore sizes, and the degree of disorder appeared. The presented results indicate the role of different structural parameters on the charge-discharge plateau and sloping regions, guiding to the better understanding of the sodium storage mechanism in hard carbon anode. The presentation demonstrates the interpretation of the results with a focus on improving energy storage capability. It is discussed: is the detailed structural analysis for the non-graphitic carbons a comprehensive and new sight into the future of energy storage?[1] Critical Raw Materials for Strategic Technologies and Sectors in the EU A Foresight Study, (2020).[2] A. Adamson, R. Väli, M. Paalo, J. Aruväli, M. Koppel, R. Palm, E. Hark, J. Nerut, T. Romann, E. Lust, A. Jänes, Peat-Derived Hard Carbons for High Capacity Sodium-Ion Batteries: Synthesis and Characterization, ECS Meet. Abstr., MA2020-02 (2020) 78.[3] M. Härmas, T. Thomberg, A. Jänes, Effect of Zinc Chloride Activation on D-Glucose Derived Carbons Based Capacitors Performance in Ionic Liquid, J. Electrochem. Soc., 167 (2020) 080533.[4] W. Ruland, B. Smarsly, X-ray scattering of non-graphitic carbon: an improved method of evaluation, J. Appl. Crystallogr., 35 (2002) 624–633.[5] E. Härk, M. Ballauff, Carbonaceous Materials Investigated by Small-Angle X-ray and Neutron Scattering, C, 6 (2020) 82. Figure 1

AlCl3-NaCl-ZnCl2 Secondary Electrolyte in Next-Generation ZEBRA (Na-ZnCl2) Battery

Increasing demand to store intermittent renewable electricity from, e.g., photovoltaic and wind energy, has led to much research and development in large-scale stationary energy storage, for example, ZEBRA batteries (Na-NiCl2 solid electrolyte batteries). Replacing Ni with abundant and low-cost Zn makes the ZEBRA battery more cost-effective. However, few studies were performed on this next-generation ZEBRA (Na-ZnCl2) battery system, particularly on its AlCl3-NaCl-ZnCl2 secondary electrolyte. Its properties such as phase diagrams and vapor pressures are vital for the cell design and optimization. In our previous work, a simulation-assisted method for molten salt electrolyte selection has shown its successful application in development of molten salt batteries. The same method is used here to in-depth study the AlCl3-NaCl-ZnCl2 salt electrolyte in terms of its phase diagrams and vapor pressures via FactSageTM and thermo-analytical techniques (Differential Scanning Calorimetry (DSC) and OptiMeltTM), and their effects on battery performance such as operation safety and charging/discharging reaction mechanism. The DSC and OptiMelt results show that the experimental data such as melting temperatures and phase changes agree well with the simulated phase diagrams. Moreover, the FactSageTM simulation shows that the salt vapor pressure increases significantly with increasing temperature and molar fraction of AlCl3. The obtained phase diagrams and vapor pressures will be used in the secondary electrolyte selection, cell design and battery operation.

Scientific issues of zinc-bromine flow batteries and mitigation strategies.

Zinc-bromine flow batteries (ZBFBs) are promising candidates for the large-scale stationary energy storage application due to their inherent scalability and flexibility, low cost, green, and environmentally friendly characteristics. ZBFBs have been commercially available for several years in both grid scale and residential energy storage applications. Nevertheless, their continued development still presents challenges associated with electrodes, separators, electrolyte, as well as their operational chemistry. Therefore, rational design of these components in ZBFBs is of utmost importance to further improve the overall device performance. In this review, the focus is on the scientific understanding of the fundamental electrochemistry and functional components of ZBFBs, with an emphasis on the technical challenges of reaction chemistry, development of functional materials, and their application in ZBFBs. Current limitations of ZBFBs with future research directions in the development of high performance ZBFBs are suggested.

Power curves of megawatt-scale battery storage technologies for frequency regulation and energy trading

Large-scale stationary battery energy storage systems (BESS) continue to increase in number and size. Most systems have been put into operation for grid services because of their technical capabilities. With increasing and more dynamic energy prices, their use in short-term energy trading such as day-ahead and intraday trading has also been gaining importance. In current technical and economic simulations and trading models, batteries are often used as an energy reservoir that can charge and discharge a constant power specified by the energy over a certain time. However, this simplification can lead to wrong results and makes economic assessments difficult. In order to successfully use BESS in energy trading, their real operating ranges and limits must be investigated, since batteries respectively BESS cannot deliver the same power over the entire state of charge (SOC) range. With a performance test of our hybrid BESS M5BAT, we show the characteristic performance curves for different battery technologies and consequently suitable operating ranges in a large-scale system configuration. The results show the wide range of challenges such as battery aging and balancing states that occur in the real-world implementation of BESS. The lithium-ion batteries of the system under test have a remaining usable energy between 75 % and 90 %, depending on the type of lithium-ion battery, while the usable energy of the lead acid batteries is only 60 %. The lithium-ion batteries were able to deliver a constant power output in the SOC range between 10 % and 80 %, which is a necessary requirement in short-term energy trading. The lead-acid batteries could only be discharged at full power in the range of 100 %–50 % SOC and charged at full power between 0 % and 50 %. In the performance test, balancing was a limiting factor for lithium-ion batteries, while aging was the limiting factor for lead-acid batteries. Based on our findings, estimates for other existing BESS can be made to determine feasible operating ranges of these batteries for short-term energy trading. This also provides a guideline for individual tests that should be carried out on other BESS for verification.

Prospect and Challenges of Hydrate-Based Hydrogen Storage in the Low-Carbon Future

Hydrogen hydrate is a promising material for safe and potentially cost-effective hydrogen storage. In particular, hydrogen hydrate has potential for applications in large-scale stationary energy storage to dampen the temporal variation of renewable energy, for example, in the form of hydrogen-ready gas-fired power plants for generating energy when the renewable power is not available. Preliminary SWOT (strengths, weaknesses, opportunities, threats) analysis indicates that such hydrate-based hydrogen storage (HBHS) has intrinsic competitive edges. However, while the theoretical hydrogen density of the hydrate could reach ∼5 wt %, experiments have not achieved such a high hydrogen storage capacity under practical conditions. This low gravimetric hydrogen density, plus the slow kinetics of hydrogen inclusion in the hydrate, presents an outstanding challenge for commercializing the HBHS. Future research is urged to resolve both the gaps in knowledge and technological barriers for realizing this unconventional technology. Particular future directions include the elucidation of the working mechanism of hydrate promoters, rational designs of new promoters, upscaled experiments and demonstrations, the assessment of long-term stability of hydrogen hydrates, and systematic SWOT analysis. This paper offers an insightful view of the HBHS in low-emission economies.

Graphene oxide-assisted fabrication of mesoporous oxygen-deficient VO2 nanobelts for enhanced Zn2+ storage

Rechargeable aqueous zinc-ion batteries (ZIBs) are regarded as promising devices for large-scale stationary energy storage. However, developing ideal cathode materials confronts great challenges. Herein, a novel graphene oxide (GO)-assisted strategy is proposed to synthesis mesoporous VO2/G nanobelts with abundant oxygen defects for high-performance Zn2+ storage. The oxygen vacancies and mesopores facilitate Zn2+ insertion/extraction process. After an in-situ electrochemical activation at around 1.5 V, the monoclinic VO2 transforms to layered V2O5·nH2O, delivering an extremely high reversible capacity of 731 mAh/g (0.1 A/g). In addition, superior high-rate and cycling performances are also achieved.

To flow or not to flow. A perspective on large-scale stationary electrochemical energy storage

Schematic comparative diagram of the stages involved in moving from compact solid electrode materials to dilute nanofluids and RFB solutions.

Mixed Integer Linear Program model for optimized scheduling of a vanadium redox flow battery with variable efficiencies, capacity fade, and electrolyte maintenance

Redox Flow Batteries are a versatile and durable type of electrochemical storage and a promising option for large-scale stationary energy storage. The vanadium redox flow battery represents the most mature chemistry for the technology, and it is the most widely commercialized system thanks to its high chemical stability and performance. This work aims to optimize the scheduling of a vanadium redox flow battery that stores energy produced by a renewable power plant, keeping into account a thorough characterization of the battery performance, with variable efficiencies and capacity fade effects. A detailed characterization of the battery performance improves the calculation of the optimal number of cycles and revenue associated with the battery use if compared to the results obtained using simpler models, which take into account constant efficiencies and no capacity fade effects. The presented problem is nonlinear due to the functions of the battery efficiency, which depend upon charging and discharging powers and state of charge with nonlinear, non-convex correlations. Therefore, as per the state of the art of operation research, the problem is linearized using convex hulls in three dimensions. The optimization program also calculates the progressive battery capacity fade due to undesired secondary electrochemical reactions and the economic impact of capacity restoration through periodic maintenance. The final problem is solved as a Mixed-Integer Linear Program (MILP) to guarantee the global optimality of the linearized problem. The proposed optimization model has been applied to two different case studies. The first is a case of energy arbitrage, where the electric energy produced by a renewable plant is stored when the energy price is low and sold to the grid when the energy price is high to maximize the profit. The second is a case of load-shifting, balancing electric energy generation and demand from a grid-connected renewable energy community, where storage minimizes the expenses for the energy purchased from the grid. The optimization results have been compared to those obtained with constant battery efficiency models, which do not consider the capacity fade effects. Results show that simpler models overestimate the optimal number of cycles of the battery and the revenue by up to 15% if they do not take into account the degradation model of the battery, and respectively up to 32% and 42% if they also assume constant efficiency for the battery.

Environmental trade-offs and externalities of electrochemical-based batteries: Quantitative analysis between lithium-ion and vanadium redox flow units

This study aims to increase the scientific knowledge of the environmental impacts and externalities of two promising electrochemical-based techniques for large-scale stationary energy storage: lithium nickel cobalt manganese (NCM) and vanadium redox flow (VRF) batteries. The global warming potential (GWP) and cumulative energy demand (CED) for NCM and VRF batteries are 28 kg CO2eq and 410 MJ and 186 kg CO2eq and 3080 MJ, respectively, for the provision of 1 MWh of electricity. While the trend of the environmental externality results is proportional to the environmental impact results, the environmental costs from GWP and terrestrial ecotoxicity impacts contribute the largest share of the total environmental costs for both batteries. Overall, NCM batteries have favorable environmental performance in terms of their impact values and externalities but still show relatively higher contributions in human toxicity and ozone layer depletion impacts, based on their high resource uses. The VRF batteries, on the other hand, report higher impacts in abiotic depletion, GWP and terrestrial ecotoxicity, mainly due to their great mass of the electrolyte. Our results highlight the importance of substituting the active metals with low-impact metals or carefully considering the origin of key materials while also taking advantage of the properties of the battery to carefully assess possible advancements in battery design. The environmental externality results also provide essential information for the future development of battery industries for stationary applications with energy and environmental benefits.

Clean preparation of mixed trivalent and quadrivalent vanadium electrolyte for vanadium redox flow batteries by catalytic reduction with hydrogen

The vanadium redox flow battery (VRFB) is a promising technology for large-scale stationary energy storage systems. However, the high preparation cost of mixed valent vanadium electrolyte hinders the large-scale commercial application of VRFB. In this work, a simple, green and low-cost method is proposed to prepare the mixed valent vanadium electrolyte for VRFB. The clean hydrogen is chosen as the reducing agent to obtain trivalent vanadium ions from quadrivalent vanadium ions. The Pt/C material is used as the catalyst to accelerate the reduction rate at atmospheric pressure. The impurity-free mixed valent vanadium electrolyte, with a mean valence number of 3.5, prepared by the catalytic reduction process exhibits excellent battery performance with CE of 93% and EE of 85%. Furthermore, a catalytic reactor using Pt/C decorated graphite felt is designed and used to continuously produce the mixed valent vanadium electrolyte. According to the result of simple cost analysis, the proposed catalytic hydrogen reduction process can reduce theoretically the manufacturing cost by approximately 22.6% compared with the present industrial electrolytic process. As a consequence, the simple, clean and low-cost manufacture method of the mixed valent vanadium electrolyte exhibits remarkable competitiveness and promising potential for the practical production application of VRFB.

Insights into Chemical and Electrochemical Interactions between Zn Anode and Electrolytes in Aqueous Zn−ion Batteries

Aqueous Zn-ion batteries (ZIBs) have garnered significant interest in recent years due to their potential applications in large-scale stationary energy storage. Early ZIBs research has primarily focused on searching for better cathodes and understanding cathodic Zn2+ storage mechanisms. Only very recently has ZIBs research shifted to Zn anode. Here in this study, we report on insights into the interactions between Zn anode and aqueous Zn-salt electrolytes gained by a systematic investigation of bulk properties of electrolytes, surface properties of the reacted Zn, electrokinetics of Zn/Zn2+ redox reaction and cycle stability of Zn/electrolyte/Zn symmetrical cells. We found that Zn metal surface, regardless of electrolyte, are always covered by a layer of Zn-containing layered double hydroxides (Zn-LDHs) upon contact with aqueous Zn-electrolytes. We show that “OH− production” pathway resulted from the dissolved oxygen in Zn-electrolytes is the root cause for the Zn-LDHs formation. The electrokinetic studies reveal that Zn/Zn(ClO4)2 interface has the highest exchange current density, while the symmetrical cell tests show that Zn(OTf)2 is the most stable electrolyte for Zn-metal anode.

Modelling Nickel Metal Hydride Batteries for System Integrated Applications

The NiMH battery is resilient against mistreatment and can be charged in a large temperature window. It also has a high power-capability, which has made it popular in for instance power tools. Today, the battery is often found in large scale stationary energy storage, as well as applications which require high power capability.In large scale energy storage, small differences in run cycles can have large total effects on power efficiency and safety. It is therefore desirable to develop better methods of battery management. In recent years, development in system hardware has made it possible to implement on-line models in battery management systems. Such an implementation requires a model capable of working in dynamic conditions simulating voltage, temperature, and pressure. In this study, a model for this purpose is developed and verified.There are two major features that present a challenge when modelling a NiMH-system dynamically: Open Circuit Voltage (OCV) hysteresis and pressure build-up. Handling the hysteresis effect is important to accurately predict voltage and OCV.[1] OCV is especially important, as OCV is used to estimate the battery state of charge (SOC). Pressure build-up can be an important tool for charge termination, as it is the build-up of oxygen pressure and subsequent temperature increase that signal end of charge, Figure 1. In addition, the hydrogen pressure behavior changes with battery age and can be used to estimate end-of-life.OCV hysteresis is when the open circuit voltage at a certain SOC depends on the path taken to reach that charge state. This mean that a battery that has been charged to 50% will have a drastically different OCV than when the same battery has been discharged to 50%. This effect is believed to arise primarily from structural changes in the positive electrode, where the potential of the electrode surface is dependent on the material structure of the surface. An example of open circuit voltage hysteresis in a NiMH cell is found in Figure 1.The gas phase in the battery consists of four gases: nitrogen, hydrogen, oxygen and water. Nitrogen is an inert remnant from the battery manufacture.[2] Water is in equilibrium with the aqueous electrolyte. Hydrogen is in equilibrium with intercalated hydrogen in the negative metal hydride (MH) electrode. Finally, oxygen is the product of a side reaction that occurs at high potentials on the positive electrode. The production of oxygen at the positive electrode and ensuing oxygen recombination on the negative electrode produces a great deal of heat, which heats the battery and produces the temperature response that can be used to set a temperature derivative determined end of charge criteria. However, the presence of oxygen and high temperatures also drives the major aging mechanism: oxidation of the negative electrode. As the negative electrode is consumed, the capacity decreases. This leads to a difference in the hydrogen equilibrium pressure, as reaching a higher intercalation fraction increases the equilibrium pressure. [3]An implementation of a model for system battery management could help improve the following functions for a NiMH system: SOC estimation, SOH estimation, charge termination, fault detection and aging prevention. Therefore, development of a fully dynamic NiMH model has great value in improving over all system function for large scale energy storage applications. This study presents a fully dynamic and experimentally verified model for the NiMH battery that takes both pressure and OCV hysteresis into consideration. References Axén, J. B.; Ekström, H.; Zetterström, E. W.; Lindbergh, G. Evaluation of Hysteresis Expressions in a Lumped Voltage Prediction Model of a NiMH Battery System in Stationary Storage Applications. J. Energy Storage 2022, 48 (January). https://doi.org/10.1016/j.est.2022.103985.Mank, A. J. G.; Belfadhel-Ayeb, A.; Krüsemann, P. V. E.; Notten, P. H. L. In Situ Raman Analysis of Gas Formation in NiMH Batteries. Appl. Spectrosc. 2005, 59 (1), 109–114. https://doi.org/10.1366/0003702052940503.Tserolas, V.; Katagiri, M.; Onodera, H.; Ogawa, H. Thermodynamical Modeling of P-C Isotherms for Metal Hydride Materials. Trans. Mater. Res. Soc. Japan 2010, 35 (2), 221–226. https://doi.org/10.14723/tmrsj.35.221. Figure 1 Left: Open Circuit Voltage of a NiMH cell with exhibited hysteresis behavior. Right: Pressure and Temperature behavior of a NiMH module during a charge discharge cycle. Figure 1

Phase-manipulated hierarchically core-shell Na3(VO1-xPO4)2F1+2x (0≤x≤1)@Na3V2(PO4)3 and its synergistic effect with conformally wrapped reduced graphene oxide framework towards high-performance cathode for sodium-ion batteries

Sodium-ion batteries (SIBs) are regarded as promising candidates for large-scale stationary energy storage systems because of the high abundance of Na resources. Na superionic conductor polyanionic cathode (NASICON), such as Na3(VO1-xPO4)2F1+2x (0 ≤ x ≤ 1, NVPF1+2x) and Na3V2(PO4)3 (NVP), shows intriguing electrochemical performances due to their robust open structure and superior cycle stability. Inspired by phase manipulation and conductive reduced graphene oxide (rGO) incorporation, a hierarchical NVPF1+2x@NVP core-shell structure is elaborately synthesized and conformally wrapped by rGO via a facial microwave-assisted hydrothermal approach. F-free surface of NVPF1+2x@NVP particle possesses intimate contact with rGO framework without strong mutual repulsive force while conductive rGO endows NVPF1+2x@NVP with high electronic conductivity to ensure fast electron transport. Combining the synergistic effect between delicate design of core-shell structure and conductive rGO framework, the NVPF1+2x@NVP/rGO-600 °C electrode achieves a high discharge capacity of 105.9 mAh g−1 at 0.5 C with an impressive capacity retention of 99.1% after 200 cycles, delivering an excellent rate capability of 90.6 mAh g−1 at 10 C. Moreover, the NVPF1+2x@NVP/rGO-600 °C electrode possesses an alleviated polarization, small impedance and fast electron/Na + diffusion properties due to this synergistic effect. The full cell using NVPF1+2x@NVP/rGO-600 °C cathode and hard carbon (HC) anode shows an initial discharge capacity of 80.0 mAh g−1 at 0.2 C and rate capability of 45.2 mAh g−1 at 10 C, which could light an LED lamp and manifest its prospective application. Our findings provide new insights into a broadly applicable material design combining morphological phase manipulation with conductive rGO framework incorporation, which synergistically boosts the electrochemical performance of NASICON cathode towards advanced SIBs with a higher energy density, faster charging rate and more practical applications.

Comparison of Zinc Bromine and Zinc Iodine Flow Batteries: From Electrolde to Electrolyte

Research in flow batteries and their application in large scale energy storage has received a growing amount of attention and promise over the past two decades. Although the energy density of flow batteries is low relative to the Li-ion battery, their comparatively lower costs, preferred safety, and ease of scalability has made flow batteries some of the most promising contenders for large-scale stationary energy storage, and are currently commercially available for this purpose. The zinc-bromine flow battery (ZBFB), despite being one of the first proposed flow batteries in the 1980s, has only recently gained enough traction to compete with the well established all-vanadium redox flow batteries. This is largely due to the high solubility of the bromine redox species in aqueous electrolytes, which has allowed the ZBFB is achieve double the energy density of the all-vanadium technology. Recently, an analogue to the zinc-bromine flow battery was introduced: the zinc-iodine flow battery (ZIFB). Similar to the ZBFB, the main advantages of this technology arose from the high solubility of the electroactive species in the electrolyte (iodine/tri-iodide). The solubility of the iodine redox species is even higher than that of analogous bromine electrolytes, and accordingly, the highest energy densities of all aqueous flow batteries to date has been for the ZIFB.Despite the similarities between the two technologies, they are held back by different issues, and so different approaches have been taken to improving the performances of the ZBFB and ZIFB. The ZBFB primarily suffers from a low power-density due to the sluggish kinetics of the bromine redox couple. Therefore, a majority of research on the ZBFB has focused on identifying new, low cost electrode materials that minimize kinetic losses at the bromine half-cell. In contrast, a majority of research on the ZIFB has been on improvements to the electrolyte composition. The ZIFB is plagued by issues of a thick, high impedance iodine film that forms at the positive electrode on charge. Due to the strong Lewis acid nature of the iodine species, a variety of charge-transfer complexes can be formed in the electrolyte, having a variety of effects on the battery performance.This presentation provides an overview on the similarities and differences between the ZBFB and ZIFB technologies. We performed a variety of half-cell and flow battery tests varying the electrode and electrolyte compositions. A number of low cost carbon materials are used as electrode materials, along with a variety of modifications to the bromine and iodine electrolytes. Through the use of high-surface area carbon blacks, the exchange current of the bromine redox couple is able to be increased by two orders to magnitude in comparison to glassy carbon. Additions of MSA or other acids to the ZBFB increases the oxidation kinetics greatly, and accordingly the overall energy efficiency of the ZBFB. For the ZIFB, the presence of high surface area catalysts have little to no effect on the overall performance. We found that in aqueous electrolytes, the iodine electrode is largely held back by the iodine film that forms on charge. Therefore, by adding ions to the electrolyte such as Br-, Cl-, and SO4 2-, we were able to increase the solubility of the iodine film and the reversibility of the battery, and accordingly its efficiency. Although the ZIFB initially performs better than the ZBFB, after making systematic adjustments to both the electrode and electrolyte compositions, the discrepancy between their performances is largely minimized, demonstrating both can be viable for the future of large-scale energy storage. Figure 1