Rechargeable Alkaline Batteries Research Articles

(Industrial Electrochemistry and Electrochemical Engineering Division New ElectrochemicalTechnology (NET) Award) Development and Commercialization of Rechargeable Zinc Manganese Alkaline Batteries to Enable a Sustainable Low-Carbon Energy Future

Urban Electric Power Inc. (UEP), a 2013 spinoff from the City University of New York Energy Institute (CUNY-EI), manufactures and markets rechargeable large-format zinc manganese dioxide (Zn-MnO2) alkaline battery cells in Pearl River, NY. The active materials in the UEP rechargeable cells are Zn and MnO2, both of which have high energy density, low cost, good safety characteristics, and are readily available with abundant supplies. These materials are key components of primary (non-rechargeable) alkaline batteries that presently dominate the disposable battery market, showing established commercial acceptability. This technology holds enormous potential to address a variety of energy storage applications, however the traditional chemistries used in primary alkaline batteries lead to irreversible degradation of the electroactive components which makes them unsuitable for the thousands of charge/discharge cycles desired for rechargeable grid-scale energy storage systems. UEP and the CUNY-EI have achieved several breakthroughs in addressing these challenges, utilizing chemical dopants and additives to stabilize both the Zn and MnO2 electrodes, which allow for more complete utilization of the battery capacity while maintaining hundreds to thousands of cycles.MnO2 and Zn deliver theoretical capacities, respectively, of 617mAh/g and 820mAh/g through a two-electron reaction in alkaline electrolyte (Figure 1). The theoretical energy density of this cell can be >400Wh/L, which is higher than many varieties of lithium-ion batteries. The Zn delivers its capacity through a dissolution-precipitation reaction, while MnO2 can exhibit solid-state proton insertion and dissolution-precipitation reactions depending on the type of MnO2 polymorph used. Electrolytic manganese dioxide (EMD, γ-MnO2), which is electrochemically synthesized in large quantities and used in primary batteries, exhibits proton insertion and dissolution-precipitation reactions. In batteries consisting of EMD, these two mechanisms each provide part of the two-electron capacity, where proton insertion delivers the first electron reaction (308mAh/g), and dissolution-precipitation delivers the second electron reaction. In contrast, birnessite(δ-MnO2), which has a layered crystal structure and is most commonly found in soils, exhibits only dissolution-precipitation reactions to deliver the two-electron capacity.The CUNY-EI made a breakthrough in 2014 and accessed the 2nd e- capacity of MnO2 reversibility. This was the first report of its complete reversibility for >6,000 cycles. EMD was used to make birnessite electrochemically in-situ, and also, because of ease of manufacturing, materials logistics and economic reasons. The additives, when mixed with EMD in the first discharge-charge formation process to make δ-MnO2, stabilized the layered cathode structure and prevented Mn3O4 formation. Bi2O3 prevented Mn3O4 formation electrochemically by complexing with the dissolved Mn(OH)6 3- and Mn(OH)4 2- ions. It also promoted δ-MnO2 formation in the charging process. The main discovery made at CUNY-EI involved recognizing that intercalating the MnO2 layers with Cu ions stabilized the cathode crystal structure and reduced the charge transfer resistance during the δ-MnO2’s electrochemical reactions. It was shown for the very first time in alkaline battery literature that energy densities approaching to 200Wh/L could be accessed from δ-MnO2 when paired with highly utilized Zn anodes.UEP’s current proton intercalation chemistry utilizes about 120-140 mAh/g-MnO2 and >160-200mAh/g-Zn. This creates an energy density of the cell of 150 Wh/L, which is comparable to existing lead-acid batteries, meaning UEP is competitive in many stationary battery applications including renewable integration, grid energy storage, backup power, including uninterruptible power supply (UPS), and residential backup applications. The company established a pilot scale manufacturing plant in Pearl River, NY with current production capacity of 100 MWh per year. Early production runs have gone to support battery systems for grid applications, backup power, and renewable integration projects. The batteries can be produced at cost lower than lead acid and lithium-ion batteries of comparable performance. Zn and MnO2 make up a small fraction of the cost per unit of storage capacity compared with costly or less environmentally friendly materials like cobalt, nickel, lithium, and lead that are used in other batteries. When manufactured in large volumes, UEP anticipates that its battery packs will cost less than $50’P3/kWh allowing building energy storage systems with a levelized cost of energy (LCOE) below the $0.05/kWh that ARPA-E has identified as the target for widespread adoption of energy storage on the electric grid. At $50/kWh, the technology becomes competitive for wide range grid applications including demand charge reductions, renewable load shifts and transmission and distribution upgrades. Moreover, these batteries offer a new level of inherent safety and environmental friendliness as they contain none of the flammable, toxic, or volatile electrolytes that have plagued other batteries considered for grid-scale storage. Figure 1

Enabling the fabrication of advanced NiCo/Bi alkaline battery via MOF-hydrolyzing derived cathode and anode

Rechargeable alkaline battery is a potential high-powered next-generation electrochemical energy storage equipment. However, the inferior energy density, compare with other electrochemical energy technologies, restrict its further practical applications. To address this, the rational design and optimization of electrode is of significance. Herein, we demonstrate the construction of high energy density NiCo/Bi alkaline battery by controllable MOF hydrolysis. Specifically, the hydrolysis conversion of Bi-MOF into Bi2O3 is performed on a large scale for the first time. The obtained flower-like Bi2O3 present large specific capacity, excellent rate capability and stable cycles life. And a series of ex-situ characterizations were employed to trace the phase transformation and morphological changes in charge-discharge. Meanwhile, Ni/Co layered double hydroxide hierarchical microspheres were also prepared via the hydrolysis of bimetallic Ni/Co-MOF. Furthermore, the assembled NiCo//Bi alkaline battery based on NiCo-LDH cathode and Bi2O3 anode perform a high energy density of 84.9 Wh/kg at 1600 W/kg, indicating its potential in practical applications.

Recent Advances and Prospects of Fiber‐Shaped Rechargeable Aqueous Alkaline Batteries

The prosperity in portable and wearable electronics has stimulated researchers to develop safe, environmentally friendly, and efficient energy‐storage technologies. Increased efforts have recently been made to fabricate high‐performance rechargeable aqueous alkaline batteries (RAABs) as the frontrunner to complement and even replace the dominant lithium‐ion batteries for large‐scale energy storage due to the limited lithium resources and the use of flammable and toxic organic electrolyte. Compared with the conventional planar RAABs, fiber‐shaped RAABs (FRAABs) manifest several intriguing features, such as miniaturization, adaptability, and weavability, making them an attractive candidate to power wearable and portable electronics. Herein, an overview of the recent progress in FRAABs by categories of fiber‐shaped aqueous rechargeable Zn‐based batteries, Fe−Ni batteries, and Bi−Ni batteries, with respect to the active electrode materials, device configurations, and battery properties, is comprehensively presented. Finally, the remaining challenges and possible solutions are emphasized as a useful guide for the further development of FRAABs.

Metallopolymer as a Solid Electrolyte for Rechargeable Zn-Metal Alkaline Batteries

Solid-electrolyte-based rechargeable metal-ion batteries hold great promise as low-cost, flexible, and high-safety energy storage devices. Zn-metal alkaline batteries, developed for more than a century, have dominated the market of primary batteries, but remain nonchargeable, because of serious side reactions and irreversible anodic reactions. A key component involved in these unfavorable reactions is the alkaline electrolyte. Here, we report a solid metallopolymer electrolyte (SME) with low alkaline solution uptake, high mechanical strength, exceptional stability, and excellent ion conductivity for rechargeable Zn-metal alkaline batteries. Compared to alkaline cells based on liquid and hydrogel electrolytes, SME-based Zn-metal alkaline batteries show dramatically enhanced cycling performance under harsh testing conditions by suppressing the electrolyte depletion and anode passivation.

Reducing Zinc Redistribution and Extending Cycle Life Via Electrochemical Synthesis of Zinc/Zinc Oxide Anodes in Rechargeable Alkaline Batteries

Redistribution of zinc over the electrode surface, also known as shape change, is a major problem and a cause of failure in alkaline zinc anode batteries. To mitigate this phenomenon, we propose a scalable approach based on an in situ formed, highly porous electrochemically synthesized ZnO matrix with uniformly electrodeposited zinc particles. This results in ∼70% improvement in cycle life performance at a rate of 10 mA cm−2 compared to control Zn anodes, which have not gone through the formation process. A quantitative electrolyte analysis revealed under-saturated zincate ion concentration in the electrochemically synthesized ZnO/Zn cells indicating reduced zincate movement. Post mortem analysis of the anodes indicated higher retention of both Zn and ZnO on the electrochemically synthesized ZnO anodes signifying reduced redistribution of active material. Image analysis of the cycled anodes revealed a narrower Zn particle size distribution (62−79 μm) in contrast to a wider particle size distribution of 51–96 μm observed in the control anodes. The formation approach results in electrochemically synthesized ZnO/Zn anodes providing a stable ZnO matrix in which Zn particles retain their localized distribution on cycling better than control electrodes conventionally made by pasting zinc particles together with a binder.

High Performance Iron Electrodes with Metal Sulfide Additives

Iron-based alkaline rechargeable batteries are promising candidates for large-scale energy storage applications owing to their low cost, robustness and environmental-friendliness. However, the widespread deployment of iron-based batteries has been limited by the low charging efficiency and poor discharge rate capability of the iron electrode. Our previous efforts on iron electrodes based on carbonyl iron powder and iron (II) sulfide have shown promise in overcoming these limitations. With the goal of understanding the role of sulfide additives, in this study, we have compared the performance of iron electrodes with iron (II) sulfide, iron (II) disulfide, copper (I) sulfide and zinc sulfide. The electrode containing zinc sulfide outperformed all other electrodes with a remarkable faradaic efficiency of 95% at C/2 rate and a specific discharge capacity close to 0.24 Ah g−1 at 1 C rate. The electrode did not lose any capacity for 750 cycles of repeated deep discharge at C/2 charge and discharge rates. Further, these electrodes could be cycled at 55 degrees Celsius with no noticeable change in performance. We attributed the excellent performance of zinc sulfide containing electrode to the low solubility of zinc sulfide in the electrolyte and the stability of zinc sulfide towards electro-reduction under the operating conditions of the iron electrode. These insights indicate that zinc sulfide is a promising additive for designing highly efficient and robust iron electrodes for alkaline nickel-iron and iron-air batteries.

An effective and accessible cell configuration for testing rechargeable zinc-based alkaline batteries

Rechargeable aqueous zinc-air batteries have received much attention due to their intrinsic safety, high theoretical volumetric energy density (6134 Wh/L), and low cost. However, zinc anodes suffer from severe hydrogen evolution reaction (HER) in alkaline electrolytes, which are kinetically favorable for air cathodes. Through an electrochemical cell–gas chromatography setup, we quantitatively identified that 99% of the capacity loss on the zinc anode was caused by HER. Most previous research has focused on material design to suppress HER, while less attention has been paid to the device. Here we demonstrate that the testing device has an apparent effect on the HER in alkaline electrolytes. Stainless-steel coin cells, as common devices used in research laboratories, accelerate HER due to synergistic effects of galvanic corrosion and a high HER activity. We designed an effective and accessible cell configuration for testing zinc-based alkaline batteries, which minimizes HER and demonstrates a higher Coulombic efficiency and longer cycling life than stainless-steel coin cells. Minimized HER and self-discharge of Zn were visualized through the operando optical microscopy. Specifically, the Ni–Zn battery with our cell configuration achieved stable long-term cycling for 816 cycles compared with ~100 cycles for the stainless-steel cell. The cell configuration shown here can be directly used or modified for future research on zinc-based aqueous batteries.

ELECTROCATALYSIS OF THE OXYGEN REACTION ON THE MULTICOMPONENT OXIDES OF TRANSITION METALS

The review presents the current state of research on oxides of transition metals as electrocatalysts for the both reactions of oxygen reduction and evolution, which are of key importance ones for electrochemical devices of alternative energy: metal-air rechargeable batteries and fuel cells with an oxygen electrode. The review includes the consideration of the thermodynamic, electronic and adsorption conditions for activation of the molecular oxygen by oxide surface, as well as the advantages of the oxide surfaces as catalysts in the alkaline electrolytes. The influence of the chemical composition and structural features of oxides of transition elements on the adsorption and chemisorption of water and oxygen, the formation of ionic forms at adsorption and the main factors, which influence on transfer of electrons, protons and oxygen, are considered. Synthesis of double and other multicomponent oxides and the usage of cationic doping expands the possibilities of forming the necessary properties of the electrocatalysts: porosity, thickness of hydrated layers, electronic and ionic conductivity, proton and electron-donor (acceptor) properties in a optimal combination. The oxide should have a metal with variable valence, and even better if there are two ones. Such oxides can be various structures based on Co2O3, MnO2, Ni2O3, Mn3O4, Fe2O3, and others. A qualitative leap in improving the performance of catalysts for electrode reactions with oxygen was made possible by the synthesis of nanoparticles, as well as nanocomposites with metallic and carbon materials. The some characteristics of the electroca­talytic activity of promising oxide electrocata­lysts, mainly, multicomponent ones, as well as the results of studies of oxide composites with carbon nanomaterials, are presented. Several of the most well-known oxide structures (spinel, perovskite, pyrochlor) are currently being studied as the most promising matrices for the efficient transfer of charge, oxygen, and metal ions. All of them are multicomponent. The most active non-platinum bifunctional catalysts for oxygen reactions concluded to be cobaltites with spinel structure. Nanocomposites based on cobalt and cobalt-manganese spinel are the most promising materials for use in alkaline rechargeable batteries, both in terms of cost and in terms of electrocatalytic activity as well as in terms of corrosion resistance.

Cerium-doped bimetal organic framework as a superhigh capacity cathode for rechargeable alkaline batteries.

In this work, cerium (Ce)-doped NiCo-MOF (metal organic framework) was investigated for its application as a cathode material of alkaline batteries. Inert substitution of Ni/Co by Ce in MOF can make Ce to become part of the backbone of the framework and then ensure structure stability during redox reaction, which greatly improved charge and discharge cycle stability. With dopant mole fraction up to 5%, the redox potential of NiCo-MOF increased by 85%. Adequate Ce doping can potentially enhance rate capacity dramatically due to the large ion radius that provided an extra space for electrolyte ion shutting channel. 1% Ce-doped NiCo-MOF, having a capacity of 286 mA h g-1 at 2 A g-1 and retaining 93% of its capacity (265 mA h g-1) at 20 A g-1, emerged as the best performing material among all the Ce-doped NiCo-MOFs presented in this study. A full cell coupling Ce-doped NiCo-MOF cathode and Fe2O3 anode was assembled to verify its practical application. The full cell showed an initial capacity of 280 mA h g-1 at 2 A g-1 and retained 92% after 1000 charge and discharge cycles. Therefore, Ce doping emerges as a powerful strategy for the designing of cathode materials used in advanced alkaline battery.

The Effect of Additives on the Performance and Failure Mechanisms of the Rechargeable, Low-Cost, Alkaline Zinc Electrode

Metallic zinc (Zn) is an attractive negative electrode material for rechargeable batteries because it is a non-toxic, non-flammable, earth abundant metal that is compatible with aqueous electrolytes. Zinc metal is also energy dense, exhibiting a high gravimetric discharge capacity of 820 mAh/g, a high volumetric discharge capacity of 5850 mAh/mL, and a low equilibrium potential of -1.35 V vs. mercury-mercuric oxide (Hg|HgO) in concentrated alkaline electrolyte. Rechargeable aqueous Zn alkaline batteries have thus recently been the subject of intense investigations for safe, low-cost, stationary electrochemical energy storage. Our research aims to achieve Zn depth-of-discharge (DOD) of 20% that is sustainable for 500 or more charge-discharge cycles, corresponding to an overall battery energy density of 200 Wh/L at the cell level.However, the cycle life of the porous Zn electrode in concentrated alkaline electrolyte is observed to decrease strongly with increasing Zn DOD. For example, we recently demonstrated that metallic Zn electrodes cycled in the range of 1% to 16% Zn DOD had an exponential decrease in cycle life with Zn DOD, which was attributed mostly to the loss of active Zn material. Here, we study the effect of additives to increase the Zn DOD and cycle life of Zn electrodes. Zinc oxide (ZnO) was used as a starting material from which metallic Zn was formed in zinc-nickel (Zn-Ni) batteries. Additives were incorporated into the ZnO electrodes for the tests done on Zn-Ni batteries and these electrodes were cycled in the range of 15% to 30% Zn DOD. The potential values of the Zn electrodes vs. Hg|HgO reference electrodes were recorded to identify failure due to Zn. At 15% Zn DOD, ZnO electrodes with certain additives or combinations of additives achieved an increased cycle life compared to Zn electrodes without additives. This highlights the need to perform electrochemical and spectroscopic studies to determine the effects of the additives on the mechanisms of the Zn electrode. These additives, with further understanding, could be implemented in low-cost, energy-dense, rechargeable Zn alkaline batteries for grid-scale energy storage.

(Invited) Bismuth Enables Formation of Disordered Birnessite in Rechargeable Alkaline Batteries

Recent advances in rechargeable Zn/MnO2 alkaline batteries have shown promise for scalable energy storage systems which provide a safe, low-cost alternative to current Li-ion technologies and have a demonstrated lifetime over thousands of cycles. This cathode technology is based on a 2-electron Mn redox process where a layered birnessite-type phase has been shown to form after the first cycle with excellent reversibility between the discharge product, Mn(OH)2 when Bi2O3 and Cu constituents were added to the electrode.1 For this system to reach costs < $100/kWh, the complete reduction to Mn2+ must be reversible with high mass loading (> 20 mAh/cm2). To get a complete understanding of the role of Bi2O3 in the reversible formation of a birnessite phase a multimodal structural characterization strategy is necessary to identify all the various intermediates formed during battery cycling. Spectroscopic evidence including Raman and X-ray absorption spectroscopy during cycling provide crucial insights into intermediate phases and variations in redox activity, with and without additives.Early demonstrations of Bi3+ containing constituents with MnO2 in alkaline batteries increased the cyclability of these systems up to hundreds of cycles with low mass loading.2,3 Later investigations followed up by hypothesizing the presence of Bi3+ could potentially catalyze the reduction of Mn3+ to Mn2+ and that upon subsequent charge promotes the formation of a layered, birnessite, MnO2 structure.4 The quick reduction of Mn3+/2+ is critical because the presence of Mn3+ is associated with the irreversible phase change to the Mn3O4 spinel structure.5,6 Figure 1 shows the birnessite vibrations at 510, 578 and 635 cm-1 form only at the top of charge with the Mn3O4 spinel vibration at 659 cm-1 present throughout the entire charging process. However, with the addition of the Bi2O3 a birnessite phase forms earlier in the charge process allowing for the facile conversion between the Mn(OH)2 and charged birnessite phase. This birnessite phase could not be identified through diffraction methods and is therefore considered a highly disordered phase that exists as a short-lived intermediate during battery operation. Using operando diffraction and X-ray near edge absorption spectroscopy (XANES) we characterize the disordered intermediate birnessite and the final crystalline phase formed as the final charge product. We expect the results will provide crucial insight into the development of aqueous, rechargeable battery systems utilizing MnO2. Figure 1 Operando Raman spectroscopy. (A) Individual Raman spectra, (B) contour map, and (C) corresponding voltage profile of the battery with a K-birnessite electrode. (D) Individual Raman spectra, (E) contour map, and (F) corresponding voltage profile of the battery with a K-birnessite with Bi2O3 electrode. Yadav, G. G.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Huang, J.; Wei, X.; Banerjee, S., Nature Communications 2017, 8, 14424.Dzieciuch, M. A.; Gupta, N.; Wroblowa, H. S., Journal of The Electrochemical Society 1988, 135 (10), 2415-2418.Wroblowa, H. S.; Gupta, N., Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1987, 238 (1), 93-102.Im, D.; Manthiram, A., Journal of The Electrochemical Society 2003, 150 (1), A68-A73.Gallaway, J. W.; Hertzberg, B. J.; Zhong, Z.; Croft, M.; Turney, D. E.; Yadav, G. G.; Steingart, D. A.; Erdonmez, C. K.; Banerjee, S., Power Sources 2016, 321, 135-142.Gallaway, J. W.; Yadav, G. G.; Turney, D. E.; Nyce, M.; Huang, J.; Chen-Wiegart, Y.-c. K.; Williams, G.; Thieme, J.; Okasinski, J. S.; Wei, X.; Banerjee, S., Journal of The Electrochemical Society 2018, 165 (13), A2935-A2947. Figure 1

Electrochemical Control and Understanding of the Electronic and Optical Properties of ZnO Formed in Rechargeable Zn-Alkaline Batteries

Rechargeable alkaline batteries using zinc metal (Zn) electrodes are of significant interest for next-generation energy storage because of their high energy density, low cost, environmental friendliness, and inherent safety. Rechargeable Zn-alkaline batteries, however, have not been widely commercialized in part due to the low cyclability of Zn electrodes. At high depths of discharge, zinc oxide (ZnO) discharge product accumulates in the electrode, passivating the zinc-electrolyte interface and ultimately leading to cell failure. While the ZnO discharge product has been studied for decades, there is no general consensus on its local structure, composition, and electrochemical properties, nor on how these properties are affected by the electrode potential or cycling conditions.In this work, we used in operando analytical techniques including X-Ray diffraction (XRD), confocal Raman spectroscopy, electrochemical impedance spectroscopy (EIS), and ultraviolet-visible (UV-vis) spectroscopy to demonstrate that the discharge product is proton-doped ZnO with oxygen vacancies, and that the electrical conductivity, band gap, and color vary systematically as a function of electrode potential. To investigate local hydrogen and zinc environments within the ZnO discharge product, we performed ex situ solid-state 1H, 2H, and 67Zn magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Solid-state 1H and 2H NMR measurements establish that hydrogen environments change as a function of potential, while solid-state 67Zn NMR spectra indicate that the local zinc environments are distorted compared to ZnO generated via conventional routes. We also performed 2D 1H-1H exchange (EXSY) NMR measurements to investigate proton mobility between defect environments and acquired 1D 1H-1H dipolar-mediated double quantum-filtered MAS NMR spectra to establish through-space molecular-level proximities between proton sites. This work provides insights into the dynamics of zinc electrodes in alkaline environments, as well as how to electrochemically control the defect structures and electronic and optical properties of ZnO in alkaline media, which are expected to aid the development of next-generation Zn alkaline batteries and electronic devices utilizing ZnO.

Charge Storage Mechanism of a Quinone Polymer Electrode for Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) offer a potentially stable alternative to alkaline rechargeable zinc batteries in utilizing zinc metals for low-cost and safe energy storage. Two fundamental features of AZIBs are (1) near-neutral aqueous electrolytes, in which zinc dendrites growth is apparently suppressed compared with that in alkaline electrolytes, and (2) Zn2+ -storing cathode materials, which do not store protons in cathodes and maintain the near-neutral pH of an electrolyte throughout charge-discharge processes. Because of the importance of stored species at the cathode for the viability of a battery, the charge storage mechanism in cathode materials has been under scrutinization. Among cathode materials proposed for high-energy AZIBs, many vanadium oxides seem to store zinc-ions, while manganese oxides more often than not involve proton storage which raises concerns of pH variation of the electrolyte. Quinones have been recently proposed as versatile electrode materials for aqueous batteries. Early attempts of quinones for AZIBs have resulted in promising specific energy and cycling stability. It is therefore interesting to investigate the charge storage mechanism in these materials and assess their viability for practical applications.This work focuses on the identification of stored ions in a quinone polymer, poly(benzoquinonyl sulfide) (PBQS), as an AZIB cathode material. Possible ions to be involved in the electrode reaction include zinc ions, protons, counter anions (in this case triflate), and their hydrated forms. Spectroscopic technologies suitable for qualitative and quantitative analyses of the electrode reaction of organic materials have undergone major development in recent years. Electrochemical quartz crystal microbalance (EQCM) is an established tool to quantitatively probe the stored ions in redox-active polymers and carbon materials. Recent advancement with dissipation monitoring (EQCM-D) further strengthened the technique for characterizing softer electrodes. On the other hand, Fourier transform infrared spectroscopy (FTIR) is a standard technique for qualitative detection of chemical groups, thus a useful tool to compliment EQCM-D which may lack chemical information. In-situ FTIR has been proven effective in monitoring the electrode reactions in organic carbonyl electrodes, though the use for detection of stored ions has not been reported. Here we combine EQCM-D and FTIR techniques for a comprehensive understanding of the charge storage mechanism of PBQS in a near-neutral zinc electrolyte.

Inexpensive and robust iron-based electrode substrates for water electrolysis and energy storage

The instability of iron under anodic conditions makes iron-based electrode substrates unsuitable for alkaline electrolyzers and rechargeable alkaline batteries. Therefore, significantly more expensive substrates such as nickel foam or sintered nickel are used. Nickel adds a significant cost to electrolysis and energy storage systems. We show that iron substrates can be stabilized using a unique protective thermal coating. These coatings can also yield some of the most electrocatalytically active electrodes in addition to showing no notable change in performance even after 1500 h of anodic polarization. Besides sintered iron, low-carbon steel mesh can be stabilized similarly. Low-carbon steel protected by a thin layer of lithium-doped cobalt spinel was found to be an excellent current collector for positive nickel hydroxide electrodes in alkaline batteries. Thus, surface-modified iron substrates, 40 times less expensive than nickel, are promising for lowering the material costs of alkaline water electrolyzers and rechargeable alkaline batteries.

Bridging the energy efficiency gap between quasi-neutral and alkaline rechargeable zinc-air batteries by an efficient hybrid battery design

The large-scale deployment of renewable energy is dependent on the accessibility of cost-effective and long cycle life energy storage solutions. Rechargeable Zn-air batteries are a good candidate, but the aggressiveness of their alkaline electrolyte reduces the battery life. Replacing the alkaline electrolyte with a neutral/quasi-neutral solution is a logical alternative. The energy efficiency of neutral/quasi-neutral Zn-air batteries is however lower than alkaline Zn-air batteries due to the more sluggish kinetics of the oxygen electrochemical reactions in pH-neutral solution. This article describes the development of an efficient hybrid battery design to close the performance gap between alkaline and neutral/quasi-neutral Zn-air batteries. Specifically, a Mn2+-containing electrolyte is used to complement the Zn-air chemistry with a facile MnO2/Mn2+ redox reaction. The quasi-neutral Zn-air battery formulated as such shows a record high round-trip energy efficiency of 63.2% by using only a low-cost phosphated MnO2 oxygen electrocatalyst; which is as energy efficient as the alkaline rechargeable Zn-air batteries but without the cycle life problem of the latter.

An Overview and Future Perspectives of Rechargeable Zinc Batteries.

Aqueous rechargeable zinc-based batteries have sparked a lot of enthusiasm in the energy storage field recently due to their inherent safety, low cost, and environmental friendliness. Although remarkable progress has been made in the exploration of performance so far, there are still many challenges such as low working voltage and dissolution of electrode materials at the material and system level. Herein, the central tenet is to establish a systematic summary for the construction and mechanism of different aqueous zinc-based batteries. Details for three major zinc-based battery systems, including alkaline rechargeable Zn-based batteries (ARZBs), aqueous Zn ion batteries (AZIBs), and dual-ion hybrid Zn batteries (DHZBs) are given. First, the electrode materials and energy storage mechanism of the three types of zinc-based batteries are discussed to provide universal guidance for these batteries. Then, the electrode behavior of zinc anodes and strategies to deal with problems such as dendrite and passivation are recommended. Finally, some challenge-oriented solutions are provided to facilitate the next development of zinc-based batteries. Combining the characteristics of zinc-based batteries with good use of concepts and ideas from other disciplines will surely pave the way for its commercialization.

Engineering ultrahigh-specific-capacity α-Fe2O3 nanoparticles and Ni(OH)2/Co0.85Se nanostructures separately anchored on N-doped graphene nanotubes toward alkaline rechargeable battery

In this paper, the N-doped graphene nanotubes (N-GNTs) are used as the scaffolds to grow α-Fe2O3 nanoparticles (NPs) and Ni(OH)2 nanosheets arrays (NAs)/Co0.85Se nanoparticles (NPs) respectively, which are directly acted as hybrid negative and positive electrodes for alkaline rechargeable battery (ARB). The synergistic merits from the supporters and active materials enable the N-GNTs@ α-Fe2O3 NPs to deliver an ultrahigh specific capacity of 309 mAh g−1 at 1 A g−1, and good rate performance. By paring with the N-GNTs@ Ni(OH)2 NAs/Co0.85Se NPs (268 mAh g−1 at 1 A g−1), an ARB configuration is assembled. Contributed by the particular electrode architectures, the device displays a high energy density of 78.8 Wh kg−1 at 2.47 kW kg−1 and robust cycling life (91.3% retention of the initial specific capacity over 10,000 cycles). This strategy reported here opens up a new avenue to construct unique hybrid electrodes and maximizes their superiority, which leads to the ultrahigh capacity for the fabrication of next-generation energy storage devices.

Breakdown and Reformation of Birnessite in Rechargeable, Bismuth Modified MnO2 Alkaline Batteries

Rechargeable Zn-MnO2 alkaline batteries have been identified as a viable option for the modernization of grid scale energy storage due to their projected cost (<$100/kWh), scalability, and safer components when compared to non-aqueous alternatives.1 For this system to reach its maximum capability, the full Mn4+/2+ redox couple must be reversible over thousands of cycles with high mass loading. This was successfully demonstrated with the incorporation of various electrode constituents which alter the fundamental discharge and charge process of MnO2 to Mn(OH)2.1 Using non-destructive, synchrotron diffraction techniques, we detail the effect of Bi on the breakdown and reformation of birnessite (\U0001d6ff-MnO2) during cycling. Further spectroscopic evidence including Raman and X-ray absorption spectroscopy during cycling also provides crucial insights into amorphous phases and variations in redox activity, with and without additives.Early demonstrations of Bi3+ containing constituents with MnO2 in alkaline batteries increased the cyclability of these systems up to hundreds of cycles with low mass loading.2,3 Later investigations followed up by hypothesizing the presence of Bi3+ could potentially catalyze the reduction of Mn3+ to Mn2+ and that upon subsequent charge promotes the formation of a layered, birnessite, MnO2 structure.4 The quick reduction of Mn3+/2+ is critical because the presence of Mn3+ is associated with the irreversible phase change to the Mn3O4 spinel structure.5 Figure 1 shows the birnessite (001) reflection at ~7.1 Å rapidly shift to lower d-spacings upon discharge until ~6.9 Å then directly convert to Mn(OH)2 where the corresponding ~4.8 Å reflection appears. Notably, no crystalline intermediates such as MnOOH or Mn3O4 form during cycling. Also, upon charge the birnessite (001) reflection does not appear until the third potential plateau even though the Mn(OH)2 (001) reflection fades linearly until the end of charge. Due to these observations, further spectroscopic techniques were used to probe these reactions. Using operando Raman spectroscopy we observed a limited formation of an amorphous Mn3O4 during discharge and a disordered birnessite phase formation occurring on the second plateau of charge in the presence of Bi3+. These investigations provide new insight into the intermediates and formation mechanisms of Mn-based alkaline battery electrodes in the presence of Bi2O3.The presence of both Cu and Bi additives are necessary to stabilize the reversible processes occurring during electrochemical cycling. However, the synergistic relationship between Cu and Bi is not extensively investigated. Previous synchrotron XANES and XRF mapping showed that the Cu2+/0 redox couple was occurring during the Mn3+/2+ reduction. It was hypothesized that the Cu acts as a redox mediator and rapidly forms the Mn2+ species during discharge.6 Here we use a X-ray absorption spectroscopy quick scanning to monitor the Mn, Bi, and Cu redox activity which are all relating to the possible mediation of Mn reduction and oxidation. Using multiple techniques, we provide a complete understanding of the role of both bismuth and copper containing constituents on the redox transitions of MnO2 in alkaline electrolyte. Wholistic investigations combining multiple operando techniques are critical to the development of rechargeable alkaline batteries by advancing the fundamental design of these systems. Figure 1 (a) Operando X-ray diffraction data between 3-7.5 Å of the first cycle of Bi2O3-modified birnessite electrode in KOH electrolyte. (b) Corresponding galvanostatic discharge and charge at a rate of C/3. (c) Lattice parameter ‘c’, the interlayer spacing, of the birnessite phase during the first cycle. (d) The relative peak intensities of the birnessite and Mn(OH)2 (001) reflection during the first cycle.

A Mechanistic Understanding of the Electrochemical Activity of Zinc Oxide in Alkaline Batteries

Rechargeable zinc alkaline batteries are of great interest for stationary storage applications because they are inherently safe, energy dense, environmentally friendly, and low-cost. However, these batteries have not been commercialized on a large scale because of their low cycle life at high depths of discharge. One cause is the buildup of ZnO on the electrode. It has been shown recently that ZnO produced in zinc alkaline electrodes inserts protons and electrons and undergoes electrochromic color changes as a function of electrode potential. This dynamic behavior increases hydrogen catalysis, contributes capacity to the electrode, and changes oxide conductivity as a function of electrode potential. In this work we investigate the disorder and nonstoichiometry of ZnO that allow the material to become electrochemically active. We used 1H, 2H, and 67Zn solid-state MAS NMR to better understand structure, defects, order, and the hydrogen insertion mechanism of the ZnO. Understanding the physical properties of the ZnO will enable better design of electrodes and additives for zinc alkaline batteries in the future.

Monolithic Nanoporous Zn Anode for Rechargeable Alkaline Batteries.

The fabrication of monolithic nanoporous zinc bears its significance in safe and inexpensive energy storage; it can provide the much needed electrical conductivity and specific area in a practical alkaline battery to extend the short cycle life of a zinc anode. Although this type of structure has been routinely fabricated by dealloying, that is, the selective dissolution of an alloy, it has not led to a rechargeable zinc anode largely because the need for more reactive metal as the dissolving component in dealloying limits the choices of alloy precursors. Here, we apply the mechanism of dealloying, percolation dissolution, to design a process of reduction-induced decomposition of a zinc compound (ZnCl2) for nanoporous zinc. Using naphthalenide solution, we confine the selective dissolution of chloride to the compound/electrolyte interface, triggering the spontaneous formation of a network of 70 nm wide percolating zinc ligaments that retain the shape of a 200 μm thick monolith. We further reveal that this structure, when electrochemically oxidized and reduced in an alkaline electrolyte, undergoes surface-diffusion-controlled coarsening toward a quasi-steady-state with a length scale of ∼500 nm. The coarsening dynamics preserves the continuous zinc phase, enabling its uniform reaction and 200 cycles of stable performance at 40% depth of discharge (328 mAh/g) in a Ni-Zn battery.