Investigation of Fe-Ni Battery/Module for Grid Service Duty Cycles.

Iron-nickel (Fe-Ni) batteries are renowned for their durability and resilience against overcharging and operating temperatures. However, they encounter challenges in achieving widespread adoption for energy storage applications due to their low efficiency and the need for regular maintenance and electrolyte replacement, which adds to maintenance costs. This study evaluates and demonstrates the capabilities of Fe-Ni batteries for participating in grid energy storage applications. Stable performance was observed frequency regulation (FR) testing at 100% and 50% state of charge (SOC)s, while at 50% SOC, there was a 14% increase in efficiency compared to 100% SOC. Although 25% SOC achieved higher efficiency, limited cyclability was observed due to reaching the discharge cutoff voltage. Optimal SOC selection, battery monitoring, maintenance, and appropriate charging strategies of Fe-Ni batteries seem to be crucial for their FR applications. Fe-Ni batteries exhibit stable peak shaving (PS) results, indicating their suitability and reliability under various load conditions for PS testing. Extended cycling tests confirm their potential for long-term grid-scale energy storage, enhancing their appeal for PS and FR applications.

Phosphonate-based iron complex for a cost-effective and long cycling aqueous iron redox flow battery.

A promising metal-organic complex, iron (Fe)-NTMPA2, consisting of Fe(III) chloride and nitrilotri-(methylphosphonic acid) (NTMPA), is designed for use in aqueous iron redox flow batteries. A full-cell testing, where a concentrated Fe-NTMPA2 anolyte (0.67 M) is paired with a Fe-CN catholyte, demonstrates exceptional cycling stability over 1000 charge/discharge cycles, and noteworthy performances, including 96% capacity utilization, a minimal capacity fade rate of 0.0013% per cycle (1.3% over 1,000 cycles), high Coulombic efficiency and energy efficiency near 100% and 87%, respectively, all achieved under a current density of 20 mA·cm-². Furthermore, density functional theory unveils two potential coordination structures for Fe-NTMPA2 complexes, improving the understanding between the ligand coordination environment and electron transfer kinetics. When paired with a high redox potential Fe-Dcbpy/CN catholyte, 2,2'-bipyridine-4,4'-dicarboxylic (Dcbpy) acid and cyanide (CN) ligands, Fe-NTMPA2 demonstrates a notably elevated cell voltage of 1 V, enabling a practical energy density of up to 9 Wh/L.

Stabilizing Metallic Na Anodes via Sodiophilicity Regulation: A Review.

This review focuses on the Na wetting challenges and relevant strategies regarding stabilizing sodium-metal anodes in sodium-metal batteries (SMBs). The Na anode is the essential component of three key energy storage systems, including molten SMBs (i.e., intermediate-temperature Na-S and ZEBRA batteries), all-solid-state SMBs, and conventional SMBs using liquid electrolytes. We begin with a general description of issues encountered by different SMB systems and point out the common challenge in Na wetting. We detail the emerging strategies of improving Na wettability and stabilizing Na metal anodes for the three types of batteries, with the emphasis on discussing various types of tactics developed for SMBs using liquid electrolytes. We conclude with a discussion of the overlooked yet critical aspects (Na metal utilization, N/P ratio, critical current density, etc.) in the existing strategies for an individual battery system and propose promising areas (anolyte incorporation and catholyte modifications for lower-temperature molten SMBs, cell evaluation under practically relevant current density and areal capacity, etc.) that we believe to be the most urgent for further pursuit. Comprehensive investigations combining complementary post-mortem, in situ, and operando analyses to elucidate cell-level structure-performance relations are advocated.

Interfacial Engineering with a Nanoparticle-Decorated Porous Carbon Structure on ß″-Alumina Solid-State Electrolytes for Molten Sodium Batteries.

We present a novel anode interface modification on the ß″-alumina solid-state electrolyte that improves the wetting behavior of molten sodium in battery applications. Heat treating a simple slurry, composed only of water, acetone, carbon black, and lead acetate, formed a porous carbon network decorated with PbOx (0 ≤ x ≤ 2) nanoparticles between 10 and 50 nm. Extensive performance analysis, through impedance spectroscopy and symmetric cycling, shows a stable, low-resistance interface for close to 6000 cycles. Furthermore, an intermediate temperature Na-S cell with a modified ß″-alumina solid-state electrolyte could achieve an average stable cycling capacity as high as 509 mA h/g. This modification drastically decreases the amount of Pb content to approximately 3% in the anode interface (6 wt % or 0.4 mol %) and could further eliminate the need for toxic Pb altogether by replacing it with environmentally benign Sn. Overall, in situ reduction of oxide nanoparticles created a high-performance anode interface, further enabling large-scale applications of liquid metal anodes with solid-state electrolytes.

Interfacial-engineering-enabled practical low-temperature sodium metal battery.

Solid-state sodium (Na) batteries have received extensive attention as a promising alternative to room-temperature liquid electrolyte Na-ion batteries and high-temperature liquid electrode Na-S batteries because of safety concerns. However, the major issues for solid-state Na batteries are a high interfacial resistance between solid electrolytes and electrodes, and Na dendrite growth. Here we report that a yttria-stabilized zirconia (YSZ)-enhanced beta-alumina solid electrolyte (YSZ@BASE) has an extremely low interface impedance of 3.6 Ω cm2 with the Na metal anode at 80 °C, and also exhibits an extremely high critical current density of ~7.0 mA cm-2 compared with those of other Li- and Na-ion solid electrolytes reported so far. With a trace amount of eutectic NaFSI-KFSI molten salt at the electrolyte/cathode interface, a quasi-solid-state Na/YSZ@BASE/NaNi0.45Cu0.05Mn0.4Ti0.1O2 full cell achieves a high capacity of 110 mAh g-1 with a Coulombic efficiency >99.99% and retains 73% of the cell capacity over 500 cycles at 4C and 80 °C. Extensive characterizations and theoretical calculations prove that the stable ß-NaAlO2-rich solid-electrolyte interphase and strong YSZ support matrix play a critical role in suppressing the Na dendrite as they maintain robust interfacial contacts, lower electronic conduction and prevent the continual reduction of BASE through oxygen-ion compensation.

Uncommon Behavior of Li Doping Suppresses Oxygen Redox in P2-Type Manganese-Rich Sodium Cathodes.

Utilizing both cationic and anionic oxygen redox reactions is regarded as an important approach to exploit high-capacity layered cathode materials with earth abundant elements. It has been popular strategies to effectively elevate the oxygen redox activities by Li-doping to introduce unhybridized O 2p orbitals in Nax MnO2 -based chemistries or enabling high covalency transition metals in P2-Na0.66 Mnx TM1- x O2 (TM = Fe, Cu, Ni) materials. Here, the effect of Li doping on regulating the oxygen redox activities P2-structured Na0.66 Ni0.25 Mn0.75 O2 materials is investigated. Systematic X-ray characterizations and ab initio simulations have shown that the doped Li has uncommon behavior in modulating the density of states of the neighboring Ni, Mn, and O, leading to the suppression of the existing oxygen and Mn redox reactivities and the promotion of the Ni redox. The findings provide a complementary scenario to current oxygen redox mechanisms and shed lights on developing new routes for high-performance cathodes.

Recent Progress in Cathode Materials for Sodium-Metal Halide Batteries.

Transitioning from fossil fuels to renewable energy sources is a critical goal to address greenhouse gas emissions and climate change. Major improvements have made wind and solar power increasingly cost-competitive with fossil fuels. However, the inherent intermittency of renewable power sources motivates pairing these resources with energy storage. Electrochemical energy storage in batteries is widely used in many fields and increasingly for grid-level storage, but current battery technologies still fall short of performance, safety, and cost. This review focuses on sodium metal halide (Na-MH) batteries, such as the well-known Na-NiCl2 battery, as a promising solution to safe and economical grid-level energy storage. Important features of conventional Na-MH batteries are discussed, and recent literature on the development of intermediate-temperature, low-cost cathodes for Na-MH batteries is highlighted. By employing lower cost metal halides (e.g., FeCl2, and ZnCl2, etc.) in the cathode and operating at lower temperatures (e.g., 190 °C vs. 280 °C), new Na-MH batteries have the potential to offer comparable performance at much lower overall costs, providing an exciting alternative technology to enable widespread adoption of renewables-plus-storage for the grid.

Evaluating ZEBRA Battery Module under the Peak-Shaving Duty Cycles.

With the recent rapid increase in demand for reliable, long-cycle life, and safe battery technologies for large-scale energy-storage applications, a battery module based on ZEBRA battery chemistry is extensively evaluated for its application in peak shaving duty cycles. First, this module is tested with a full capacity cycle consisting of a charging process (factory default) and a discharging process with a current of 40 A. The battery energy efficiency (discharge vs. charge) is about 90%, and the overall energy efficiency is 80.9%, which includes the auxiliary power used to run the battery management system electronics and self-heating to maintain the module operating temperature (265 °C). Generally, because of the increased self-heating during the holding times that exist for the peak shaving duty cycles, the overall module efficiency decreases slightly for the peak-shaving duty cycles (70.7-71.8%) compared to the full-capacity duty cycle. With a 6 h, peak-shaving duty cycle, the overall energy efficiency increases from 71.8% for 7.5 kWh energy utilization to 74.1% for 8.5 kWh. We conducted long-term cycling tests of the module at a 6 h, peak-shaving duty cycle with 7.5 kWh energy utilization, and the module exhibited a capacity degradation rate of 0.0046%/cycle over 150 cycles (>150 days).

High performance sodium-sulfur batteries at low temperature enabled by superior molten Na wettability.

Reducing the operating temperature of conventional molten sodium-sulfur batteries (∼350 °C) is critical to create safe and cost-effective large-scale storage devices. By raising the surface treatment temperature of lead acetate trihydrate, the sodium wettability on ß''-Al2O3 improved significantly at 120 °C. The low temperature Na-S cell can reach a capacity as high as 520.2 mA h g-1 and stable cycling over 1000 cycles.

Elastic NaxMoS2-Carbon-BASE Triple Interface Direct Robust Solid-Solid Interface for All-Solid-State Na-S Batteries.

The developments of all-solid-state sodium batteries are severely constrained by poor Na-ion transport across incompatible solid-solid interfaces. We demonstrate here a triple NaxMoS2-carbon-BASE nanojunction interface strategy to address this challenge using the ß″-Al2O3 solid electrolyte (BASE). Such an interface was constructed by adhering ternary Na electrodes containing 3 wt % MoS2 and 3 wt % carbon on BASE and reducing contact angles of molten Na to ∼45°. The ternary Na electrodes exhibited twice improved elasticity for flexible deformation and intimate solid contact, whereas NaxMoS2 and carbon synergistically provide durable ionic/electronic diffusion paths, which effectively resist premature interface failure due to loss of contact and improved Na stripping utilization to over 90%. Na metal hosted via triple junctions exhibited much smaller charge-transfer resistance and 200 h of stable cycling. The novel interface architecture enabled 1100 mAh/g cycling of all-solid-state Na-S batteries when using advanced sulfur cathodes with Na-ion conductive PEO10-NaFSI binder and NaxMo6S8 redox catalytic mediator.

Revealing the Atomic Origin of Heterogeneous Li-Ion Diffusion by Probing Na.

Tracing the dynamic process of Li-ion transport at the atomic scale has long been attempted in solid state ionics and is essential for battery material engineering. Approaches via phase change, strain, and valence states of redox species have been developed to circumvent the technical challenge of direct imaging Li; however, all are limited by poor spatial resolution and weak correlation with state-of-charge (SOC). An ion-exchange approach is adopted by sodiating the delithiated cathode and probing Na distribution to trace the Li deintercalation, which enables the visualization of heterogeneous Li-ion diffusion down to the atomic level. In a model LiNi1/3 Mn1/3 Co1/3 O2 cathode, dislocation-mediated ion diffusion is kinetically favorable at low SOC and planar diffusion along (003) layers dominates at high SOC. These processes work synergistically to determine the overall ion-diffusion dynamics. The heterogeneous nature of ion diffusion in battery materials is unveiled and the role of defect engineering in tailoring ion-transport kinetics is stressed.

A comparative study of pomegranate Sb@C yolk-shell microspheres as Li and Na-ion battery anodes.

Alloy-based nanostructure anodes have the privilege of alleviating the challenges of large volume expansion and improving the cycling stability and rate performance for high energy lithium- and sodium-ion batteries (LIBs and SIBs). Yet, they face the dilemma of worsening the parasitic reactions at the electrode-electrolyte interface and low packing density for the fabrication of practical electrodes. Here, pomegranate Sb@C yolk-shell microspheres were developed as a high-performance anode for LIBs and SIBs with controlled interfacial properties and enhanced packing density. Although the same yolk-shell nanostructure (primary particle size, porosity) and three-dimensional architecture alleviated the volume change induced stress and swelling in both batteries, the SIBs show 99% capacity retention over 200 cycles, much better than the 78% capacity retention of the LIBs. The comparative electrochemical study and X-ray photoelectron spectroscopy characterization revealed that the different SEIs, besides the distinct phase transition mechanism, played a critical role in the divergent cycling performance.

An Intermediate-Temperature High-Performance Na-ZnCl2 Battery.

The Na-ß-alumina battery (NBB) is one of the most promising energy storage technologies for integrating renewable energy resources into the grid. In the family of NBBs, Na-NiCl2 battery has been extensively studied during the past decade because it has a lower operating temperature, better safety, and good battery performance. One of the major issues with the Na-NiCl2 battery is material cost, which is primarily from Ni metal in the battery cathode. As an alternative, Zn is much cheaper than Ni, and replacing Ni with Zn in the cathode can significantly reduce the cost. In this work, we investigate the performance and reaction mechanism for a Na-ZnCl2 battery at 190 °C. Two-step reversible reactions are identified. During the first step of charging, NaCl reacts with Zn to produce a ribbon-type Na2ZnCl4 layer. This layer is formed at the NaCl-Zn interface rather than covering the surface of the Zn particles, which leads to an excellent cell rate capability. During the second step, the produced Na2ZnCl4 is gradually consumed to form ZnCl2 on the surface of Zn particles. The formed ZnCl2 covers most of the surface area of the Zn particles and shows a limited rate capability compared to that of the first step. We conclude that this limited performance of the second step is due to the passivation of Zn particles by ZnCl2, which blocks the electron pathway of the NaCl-Zn cathodes.

Tuning the Solid Electrolyte Interphase for Selective Li- and Na-Ion Storage in Hard Carbon.

Solid-electrolyte interphase (SEI) films with controllable properties are highly desirable for improving battery performance. In this paper, a combined experimental and theoretical approach is used to study SEI films formed on hard carbon in Li- and Na-ion batteries. It is shown that a stable SEI layer can be designed by precycling an electrode in a desired Li- or Na-based electrolyte, and that ionic transport can be kinetically controlled. Selective Li- and Na-based SEI membranes are produced using Li- or Na-based electrolytes, respectively. The Na-based SEI allows easy transport of Li ions, while the Li-based SEI shuts off Na-ion transport. Na-ion storage can be manipulated by tuning the SEI layer with film-forming electrolyte additives, or by preforming an SEI layer on the electrode surface. The Na specific capacity can be controlled to < 25 mAh g-1 ; ≈ 1/10 of the normal capacity (250 mAh g-1 ). Unusual selective/preferential transport of Li ions is demonstrated by preforming an SEI layer on the electrode surface and corroborated with a mixed electrolyte. This work may provide new guidance for preparing good ion-selective conductors using electrochemical approaches.

Advanced Na-NiCl2 Battery Using Nickel-Coated Graphite with Core-Shell Microarchitecture.

Stationary electric energy storage devices (rechargeable batteries) have gained increasing prominence due to great market needs, such as smoothing the fluctuation of renewable energy resources and supporting the reliability of the electric grid. With regard to raw materials availability, sodium-based batteries are better positioned than lithium batteries due to the abundant resource of sodium in Earth's crust. However, the sodium-nickel chloride (Na-NiCl2) battery, one of the most attractive stationary battery technologies, is hindered from further market penetration by its high material cost (Ni cost) and fast material degradation at its high operating temperature. Here, we demonstrate the design of a core-shell microarchitecture, nickel-coated graphite, with a graphite core to maintain electrochemically active surface area and structural integrity of the electron percolation pathway while using 40% less Ni than conventional Na-NiCl2 batteries. An initial energy density of 133 Wh/kg (at ∼C/4) and energy efficiency of 94% are achieved at an intermediate temperature of 190 °C.

New Mechanism for the Reduction of Vanadyl Acetylacetonate to Vanadium Acetylacetonate for Room Temperature Flow Batteries.

In this study, a new mechanism for the reduction of vanadyl acetylacetonate, VO(acac)2 , to vanadium acetylacetonate, V(acac)3 , is introduced. V(acac)3 has been studied for use in redox flow batteries (RFBs) for some time; however, contamination by moisture leads to the formation of VO(acac)2 . In previous work, once this transformation occurs, it is no longer reversible because there is a requirement for extreme low potentials for the reduction to occur. Here, we propose that, in the presence of excess acetylacetone (Hacac) and free protons (H+ ), the reduction can take place between 2.25 and 1.5 V versus Na/Na+ via a one-electron-transfer reduction. This reduction can take place in situ during discharge in a novel hybrid Na-based flow battery (HNFB) with a molten Na-Cs alloy as the anode. The in situ recovery of V(acac)3 during discharge is shown to allow the Coulombic efficiency of the HNFB to be ≈100 % with little or no capacity decay over cycles. In addition, utilizing two-electron-transfer redox reactions (i.e., V3+ /V4+ and V2+ /V3+ redox couples) per V ion to increase the energy density of RFBs becomes possible owing to the in situ recovery of V(acac)3 during discharge. The concept of in situ recovery of material can lead to more advances in maintaining the cycle life of RFBs in the future.

Tuning the Perfluorosulfonic Acid Membrane Morphology for Vanadium Redox-Flow Batteries.

The microstructure of perfluorinated sulfonic acid proton-exchange membranes such as Nafion significantly affects their transport properties and performance in a vanadium redox-flow battery (VRB). In this work, Nafion membranes with various equivalent weights ranging from 1000 to 1500 are prepared and the morphology-property-performance relationship is investigated. NMR and small-angle X-ray scattering studies revealed their composition and morphology variances, which lead to major differences in key transport properties related to proton conduction and vanadium-ion permeation. Their performances are further characterized as VRB membranes. On the basis of this understanding, a new perfluorosulfonic acid membrane is designed with optimal pore geometry and thickness, leading to higher ion selectivity and lower cost compared with the widely used Nafion 115. Excellent VRB single-cell performance (89.3% energy efficiency at 50 mA·cm-2) was achieved along with a stable cyclical capacity over prolonged cycling.

LiCoPO4 cathode from a CoHPO4·xH2O nanoplate precursor for high voltage Li-ion batteries.

A highly crystalline LiCoPO4/C cathode material has been synthesized without noticeable impurities via a single step solid-state reaction using CoHPO4·xH2O nanoplate as a precursor obtained by a simple precipitation route. The LiCoPO4/C cathode delivered a specific capacity of 125 mAhg(-1) at a charge/discharge rate of C/10. The nanoplate precursor and final LiCoPO4/C cathode have been characterized using X-ray diffraction, thermogravimetric analysis - differential scanning calorimetry (TGA-DSC), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) and the electrochemical cycling stability has been investigated using different electrolytes, additives and separators.

Metal-Organic Frameworks as Highly Active Electrocatalysts for High-Energy Density, Aqueous Zinc-Polyiodide Redox Flow Batteries.

The new aqueous zinc-polyiodide redox flow battery (RFB) system with highly soluble active materials as well as ambipolar and bifunctional designs demonstrated significantly enhanced energy density, which shows great potential to reduce RFB cost. However, the poor kinetic reversibility and electrochemical activity of the redox reaction of I3(-)/I(-) couples on graphite felts (GFs) electrode can result in low energy efficiency. Two nanoporous metal-organic frameworks (MOFs), MIL-125-NH2 and UiO-66-CH3, that have high surface areas when introduced to GF surfaces accelerated the I3(-)/I(-) redox reaction. The flow cell with MOF-modified GFs serving as a positive electrode showed higher energy efficiency than the pristine GFs; increases of about 6.4% and 2.7% occurred at the current density of 30 mA/cm(2) for MIL-125-NH2 and UiO-66-CH3, respectively. Moreover, UiO-66-CH3 is more promising due to its excellent chemical stability in the weakly acidic electrolyte. This letter highlights a way for MOFs to be used in the field of RFBs.

Highly Reversible Zinc-Ion Intercalation into Chevrel Phase Mo6S8 Nanocubes and Applications for Advanced Zinc-Ion Batteries.

This work describes the synthesis of Chevrel phase Mo6S8 nanocubes and its application as the anode material for rechargeable Zn-ion batteries. Mo6S8 can host Zn(2+) ions reversibly in both aqueous and nonaqueous electrolytes with specific capacities around 90 mAh/g, and exhibited remarkable intercalation kinetics and cyclic stability. In addition, we assembled full cells by integrating Mo6S8 anodes with zinc-polyiodide (I(-)/I3(-))-based catholytes, and demonstrated that such full cells were also able to deliver outstanding rate performance and cyclic stability. This first demonstration of a zinc-intercalating anode could inspire the design of advanced Zn-ion batteries.