Stabilizing Transition Metal Vacancy Induced Oxygen Redox by Co 2+ /Co 3+ Redox and Sodium-Site Doping for Layered Cathode Materials
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99 GENERAL AND MISCELLANEOUS↗
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Harnessing Redox-Active Molecules in Alkylammonium Halide-Based Eutectic Solvents for Redox Flow Batteries
Redox flow batteries (RFBs) are promising for large-scale energy storage, however, advancements in performance and cost-effectiveness are critical factors for adoption. Here we report on alkylammonium halide based eutectic solvents (ESs) and found that a ESs comprising of diethylammonium chloride or bromide, in ethylene glycol demonstrated exceptional stability and a wide electrochemical stability window, making it a promising candidate for RFB applications. The electrochemical stability and redox behavior of the alkylammonium halide-based ESs are significantly influenced by hydrogen-bonding interactions, modulated by the alkyl chain length of the cation and the nature of the anion. A redox-active eutectic electrolyte containing 0.45 M methyl viologen dichloride (MV 2+ ) paired with acetylferrocene exhibited reversible redox behavior with a maximum open-circuit voltage of ∼1.34 V. The first redox couple, representing the viologen dication to radical cation transition, exhibited remarkable stability with consistent performance, achieving an energy efficiency near 70% at charge-discharge current densities of 10 mA cm −2 over 160 cycles with about 3% loss of the initial capacity. This study highlights the potential of alkylammonium halide DES systems for implementing eutectic-based RFB technologies in the future.
25 ENERGY STORAGE↗
Carbon dioxide reduction in solid oxide electrolyzer cells using transition metals infiltrated into Gd 0.1 Ce 0.9 O 1.95 (GDC10) scaffolds
Here, this study reports the catalytic activity of transition metal electrocatalysts (Co, Ni, and Cu) incorporated into Gd 0.1 Ce 0.9 O 1.95 (GDC10) cathodes for the electroreduction of CO 2 in solid oxide electrolyzer cells (SOECs). CO 2 electroreduction performance of cells having porous and non-infiltrated GDC10 cathodes was compared with the performance of cells containing transition metal electrocatalysts infiltrated into porous GDC10 cathodes at 750, 800, and 850°C. Results showed that cells with Co infiltrated cathodes had the best catalytic activity towards CO 2 electroreduction. Furthermore, these cells displayed good stability towards CO electroreduction, having a faradaic efficiency value close to 100% with insignificant voltage increase when tested for 48h at 750 and 850°C under the current densities of 0.2, and 0.4Acm -2 , respectively.
25 ENERGY STORAGE↗
Selecting the Optimal Fluorinated Ether Co-Solvent for Lithium Metal Batteries
To guide the selection of a suitable fluorinated ether (FE) co -solvent for lithium metal batteries, it is crucial to understand the relationship between the organic structures of the FEs and the electrochemical performance of an FE-containing electrolyte. In this work, 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane (FEE), 1,1,2,2-tetrafluoro-3-(1,1,2,2-tetrafluoroethoxy)-propane (TTE), and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (OFDEE) were chosen as representative FE co-solvents because of their distinct structural properties. The structure-activity relationship between the FEs and the electrochemical performance of Li||LiNi 0.6 Mn 0.2 Co 0.2 O 2 (Li||NMC622) cells was correlated and quantified by Fourier-transform infrared and multi-dimensional nuclear magnetic resonance techniques. Sand's model was also employed to assess the extent of lithium dendrite formation in the cells using various FE electrolytes. The cycling performance of Li||NMC622 cells using different FE co-solvents follows the order FEE > TTE > OFDEE. Further, since the direct measurement of Sand's time is difficult, we introduced relative Sand's time to probe the diffusion behavior of each electrolyte, and the results showed that the best performance was obtained in the electrolyte with the longest relative Sand's time. Moreover, the lithium metal cell using the electrolyte with FEE co-solvent showed similar capacity retention compared with the baseline electrolyte at room temperature, but it demonstrated significantly improved low-temperature performance. The results indicate that FEE is a promising co-solvent candidate for improving the low-temperature performance of lithium metal batteries because it possesses not only non-solvating behavior but also very low viscosity and non-flammability. The advanced electrolyte LiPF 6 -FEC-DMC-FEE enables very stable cycling of lithium metal batteries at various temperatures.
25 ENERGY STORAGE↗
Mitigation of rapid capacity decay in silicon-LiNi 0.6 Mn 0.2 Co 0.2 O 2 full batteries
Silicon (Si)-based materials have been considered as the most promising anode materials for high-energy-density lithium-ion batteries because of their higher storage capacity and similar operating voltage, as compared to the commercial graphite (Gr) anode. But the use of Si anodes including silicon-graphite (Si-Gr) blended anodes often leads to rapid capacity decay in Si-Gr/LiNixMnyCo z O 2 (x+y+z=1) full cells, which has been attributed to surface instability of the Si component. In addition to stabilizing the surface, this work investigates the potential of the Si-Gr blended anodes in a full-cell configuration and its impact on the capacity contribution from active components. Using dQ/dV plots of the full cells, a powerful but simple-to-implement differential potential approach is developed to decouple the capacity contribution and degradation from the graphite and silicon components. Data collected from three-electrode cells confirm the results from the differential potential approach, which suggests a voltage slippage to a higher voltage at the blended anode side. Additionally, the voltage slippage causes a reduced utilization of the Gr component and exacerbates side reactions between the Si-Gr anode and carbonate electrolytes. Furthermore, based on these failure mechanisms, we adopted a mitigation strategy to tune the open circuit voltage of the prelithiated anode while stabilizing the surface. As a result, the full cells with the modified Si-Gr anodes (mass loading, 2.5 mAh/cm 2 ) offer a highly reversible full-cell energy density of 390 Wh/kg (based on the mass of both anode and cathode materials in a full cell) with a cycling CE of 99.9% over 200 cycles.
25 ENERGY STORAGE↗
Tailoring the Reaction Heterogeneity for Robust Li‐Rich Cathodes
The practical application of Li-rich Mn-based layered oxides (LLO) cathode is hindered by severe capacity and voltage degradation resulting from severe oxygen release and irreversible phase transition. In this work, the reaction heterogeneity, which describes the spatially resolved electrochemical divergence within individual cathode particles, is engineered through compositional gradient design to couple Li + transport kinetics and the anion redox activity between particle interiors and surfaces. It is revealed that Co/Mn concentration gradient within particles creates heterogeneous phase content distribution and structural ordering, inducing surface-bulk reaction heterogeneity that significantly impacts the overall electrochemical performance. Specifically, Li 2 MnO 3 -poor and Co-enriched surface effectively mitigates the oxygen loss and enhances electrochemical reaction kinetics, benefited from the reduced surface redox reactivity and induced highly ordered intra-layered cationic arrangement. Meanwhile, the Li 2 MnO 3 -enriched core with slight Li/Ni intermixing provides high reversible capacity and strong mechanical stability. Consequently, the greatly enhanced anion redox reversibility, Li + diffusion dynamics, and structure stability endow LLO with exceptional electrochemical properties, showing a capacity retention of 86.0% and a reduced voltage decay of 0.518 mV per cycle after 500 cycles at 1 C. This work provides a valuable strategy to tailor the redox chemistry and achieve robust LLO.
25 ENERGY STORAGE↗
Coulombically-stabilized oxygen hole polarons enable fully reversible oxygen redox
Stabilizing high-valent redox couples and exotic electronic states necessitates an understanding of the stabilization mechanism. In oxides, whether they are being considered for energy storage or computing, highly oxidized oxide-anion species rehybridize to form short covalent bonds and are related to significant local structural distortions. In intercalation oxide electrodes for batteries, while such reorganization partially stabilizes oxygen redox, it also gives rise to substantial hysteresis. In this work, we investigate oxygen redox in layered Na 2-x Mn 3 O 7 , a positive electrode material with ordered Mn vacancies. We prove that coulombic interactions between oxidized oxide-anions and the interlayer Na vacancies can disfavor rehybridization and stabilize hole polarons on oxygen (O-) at 4.2 V vs. Na/Na + . These coulombic interactions provide thermodynamic energy saving as large as O–O covalent bonding and enable ~40 mV voltage hysteresis over multiple electrochemical cycles with negligible voltage fade. As such, our results establish a complete picture of redox energetics by highlighting the role of coulombic interactions across several atomic distances and suggest avenues to stabilize highly oxidized oxygen for applications in energy storage and beyond.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
High Performance SrFe 0.2 Co 0.4 Mo 0.4 O 3–δ Ceramic Anode Supported Low-Temperature SOFCs
The development of alternative ceramic anodes for low-temperature solid oxide fuel cells (LT-SOFCs) is essential to overcome the inherent challenges such as redox instability and coking associated with Ni-based cermet anodes. Moreover, due to the large electrolyte ohmic loss at low temperature, it is critical to developing an electrode supported cell that allows electrolyte thickness reduction. Here we successfully demonstrated a high performance SrFe 0.2 Co 0.4 Mo 0.4 O 3–δ (SFCM) ceramic anode supported LT-SOFC with a peak power density of 730 mW cm –2 and 300 mW cm –2 at ambitious low temperatures of 550 °C and 450 °C, respectively, in humidified H 2 . The new anode material SFCM exhibits exceptional conductivity of over 30 S cm –1 at 450 °C in humidified H 2 , providing essential current collection capability as an anode backbone appropriate for the infiltration of Ni-gadolinia doped ceria (GDC) electrocatalysts. Compared to conventional Ni-cermet anodes, the nano-sized Ni-GDC particles in our SFCM based electrode significantly improves the cell stability in hydrocarbon gases. We demonstrated a stable long-term operation over a period of 380 h in CH 4 –containing gas mixtures at 450 °C with a voltage degradation rate of 4% per 1000 h at a constant current of 0.2 A*cm –2 . Furthermore, our results demonstrate a high performance ceramic anode with high stability for low temperature operation.
25 ENERGY STORAGE↗
Power-Hardware-in-the-Loop Experiments of a Microgrid with a Grid-Forming Battery Inverter
Microgrids continue to proliferate, and they are transitioning away from using conventional generating resources to increasingly relying on inverter-based resources (IBRs) as the voltage and frequency leaders. It is crucial to evaluate the capability of IBRs to provide microgrid stability and resilience. Hardware-in-the-loop (HIL) experiments were conducted to de-risk the field deployment of the San Diego Gas & Electric Company Borrego Springs Microgrid, where a battery inverter was upgraded with grid-forming (GFM) capability to serve as the island leader. This paper presents the HIL experimental results from an HIL test bed that uses a power-hardware-in-the-loop (PHIL) interface with a power inductor that was previously developed for PHIL simulations of microgrids where the inverters need to switch modes, i.e., between grid-following and GFM as the microgrid transitions between grid-connected and islanded operation. This paper presents more details on the interface and HIL simulation results of the planned islanding and load steps in islanded operation to show the effectiveness of the inverters in managing the voltage and frequency.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Power-Hardware-in-the-Loop Experiments of a Microgrid With a Grid-Forming Battery Inverter: Preprint
Microgrids continue to proliferate, and they are transitioning away from using conventional generating resources to increasingly relying on inverter-based resources (IBRs) as the voltage and frequency leaders. It is crucial to evaluate the capability of IBRs to provide microgrid stability and resilience. Hardware-in-the-loop (HIL) experiments were conducted to de-risk the field deployment of the San Diego Gas & Electric Company Borrego Springs Microgrid, where a battery inverter was upgraded with grid-forming (GFM) capability to serve as the island leader. This paper presents the HIL experimental results from an HIL test bed that uses a power-hardware-in-the-loop (PHIL) interface with a power inductor that was previously developed for PHIL simulations of microgrids where the inverters need to switch modes, i.e., between grid-following and GFM as the microgrid transitions between grid-connected and islanded operation. This paper presents more details on the interface and HIL simulation results of the planned islanding and load steps in islanded operation to show the effectiveness of the inverters in managing the voltage and frequency.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Passivity-Based Control of Grid Forming and Grid Following Converters in Microgrids
With the integration of more and more power electronics devices into the grid, it is not easy to guarantee the stability of the whole system due to the complexity of the control structure of various power converters. In this paper, we consider grid-forming and grid-following converters in one microgrid, in which the grid-forming converters support the voltage and frequency of the microgrid and the grid-following converters inject their maximum power into the microgrid. To handle the stability issue, the passivity principle is applied to guarantee the stability of the whole microgrid. We ensure every grid-following converter satisfies the passivity via the port-controlled Hamiltonian method. In addition, we apply the passivity-based proportional-resonant controller to the grid-forming converter. One of the advantages of the proposed method is that the phase lock loop system is eliminated, which may cause stability issues. Simulation results show that the proposed method can control the microgrid effectively.
Gui, Yonghao (Young)↗
Engineering Na‐Rich P2‐Type Layered Oxides Through Li/Ti Dual Doping for Oxygen Redox Activation and Superior Structural Stability
Sodium layered oxides Na x MO 2 (x ≤ 1 and M = transition metal ions) have gained significant interest as sodium-ion battery (NIB) cathodes owing to their high operating voltages and potential for higher energy density compared with polyanion and Prussian blue–type cathodes. However, their practical applications are often hindered by the irreversible structural transitions leading to capacity fading during cycling. The nature and substitution of transition metal ions define the material properties and electrochemical performance. In this study, through comprehensive electrochemical characterization combined with multi-scale structural and spectroscopical analyses, we demonstrate the synergistic impacts of Lithium and Titanium doping, which not only increases overall capacity by boosting cation and anion cooperative redox contributions but also improves the rate capability and cycling stability. Specifically, Li + doping enhances the available sodium inventory for extraction, while Ti 4+ disrupts Na + /vacancy ordering at lower voltages (< 4 V) and mitigates the detrimental P2→OP4/O2 phase transition during cycling. The combined effect of Lithium and Titanium doping promotes more charge localization on Oxygen, which activates reversible lattice oxygen redox reactions at elevated voltages, contributing additional capacity beyond conventional cationic redox. This work provides crucial insights into the design of high-performance, high-capacity P2-type layered cathode materials for sodium-ion batteries.
36 MATERIALS SCIENCE↗
Impact of dipolar molecules on the reliability of organic photovoltaic cells
Blending two non-fullerene acceptors (NFAs) to form bulk heterojunctions (BHJs) in ternary organic photovoltaics (OPVs) has been shown to lead to an end-capping exchange reaction that results in the generation of several new dipolar species whose impact on OPV operational stability remains uncertain. Here, we investigate the reliability of a ternary OPV system intentionally blended with dipolar NFA molecules. We reveal that an intrinsic contribution to OPV degradation is the reorganization and reorientation of the dipolar molecules during operation, which leads to an increased dielectric constant (ε r ) of the BHJ. Consequently, the electric field across the BHJ with dipolar molecules decreases compared with that of a non-dipolar BHJ under the same applied voltage, leading to a larger reduction in charge collection efficiency over time. This result has implications on the stability of a range of organic electronic devices containing dipolar molecules.
14 SOLAR ENERGY↗
Operationalizing Synchrophasors for Enhanced Grid Reliability and Asset Utilization
The report discusses the development of production-grade synchrophasor software applications. The objective is to improve system reliability and asset utilization for offline as well as real-time considerations, as per the Department of Energy (DOE) guidelines specified by Funding Opportunity Announcement (FOA) DE-FOA-0001492. On the one hand, we have developed grid management applications on how to transform synchrophasor-based monitoring into operator guidance, and commercial grade tools addressing industry needs such as NERC Reliability Standards (MOD 26, MOD 27 and MOD 33). On the other hand, with the wide industrial adoption in mind, the developed applications have been fully discussed with utility partners and installed in the utility partners site including 6 field tests. The Model Validation and Calibration software module has been integrated into GE’s PhasorAnalyticsTM. The first commercial contract has been signed even before the close date of this project. The Angle-based Grid Management (AGM), Fast Voltage Security Assessment (FastVSA), Enhanced Islanding Monitoring(EIM) and Enhanced Disturbance Management (EDM) have been integrated into GE’s Grid Stability Assessment line of applications in e-terra Suite of EMS product.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Enabling high areal capacity for Co-free high voltage spinel materials in next-generation Li-ion batteries
The rapidly growing technological demand for lithium-ion batteries has prompted the development of novel cathode materials with high energy density, low cost, and improved safety. High voltage spinel, LiNi 0.5 Mn 1.5 O 4 (LNMO), is one of the most promising candidates yet to be commercialized. The two primary obstacles for this material are the inferior electronic conductivity and fast capacity degradation in full cells due to the high operating voltage. By systematically addressing these limitations, we successfully develop a thick LNMO electrode with areal capacity loadings up to 3 mAh·cm –2 . The optimized thick electrode is paired with a commercial graphite anode at both the coin cell and pouch cell level, achieving a full cell capacity retention as high as 72% and 78%, respectively, after 300 cycles. We attribute this superior cycling stability to careful optimizations of cell components and testing conditions, with a specific focus improving electronic conductivity and high voltage compatibility. These results suggest precise control of materials quality, electrode architecture and electrolyte optimization can soon support the development of a cobalt-free battery system based on a thick LNMO cathode (>4 mAh·cm 2 ), which will eventually meet the needs of next-generation Li-ion batteries with reduced cost, improved safety, and assured sustainability.
25 ENERGY STORAGE↗
Air‐Stable High‐Voltage Li‐Ion Organic Cathode Enabled by Localized High‐Concentration Electrolyte
While lithium‐ion batteries have revolutionized the field of energy storage, their reliance on critical minerals such as cobalt and nickel raises significant concerns over resource availability and supply chain uncertainty. In this study, we revisit dithiin‐fused dilithium naphthazarin (5,8‐dihydroxy‐1,4‐naphthoquinone) (DNP‐Li) as a high‐voltage Li‐ion organic cathode and evaluate its performance in conjunction with localized high‐concentration electrolyte (LHCE). DNP‐Li exhibits remarkable air and thermal stability, a high operating potential of 3.55 V vs. Li + /Li, and a specific capacity of 232 mAh g −1 , positioning it as one of the most promising candidates among Li‐ion organic cathodes. Furthermore, the electrochemical behavior of DNP‐Li is strongly influenced by the electrolyte composition, giving distinct two‐plateau or four‐plateau voltage profiles accompanied by reversible or irreversible phase transitions in carbonate‐based or LHCE electrolyte formulations, respectively. The reduced solubility of DNP‐Li‐based redox intermediates in LHCE enhances cycling stability, achieving a capacity retention of 85% after 50 cycles at 0.1C and 75% after 160 cycles at 0.5C, demonstrating a significant improvement compared to the carbonate‐based electrolyte. This work highlights the critical role of solute–electrolyte interactions in modulating the electrochemical performance of multielectron small‐molecule organic cathodes, offering new pathways for advancing sustainable and high‐efficiency energy storage technologies.
Lakraychi, Alae Eddine [Department of Electrical a↗
Control Design of Passive Grid-Forming Inverters in Port-Hamiltonian Framework
This article presents a modified dispatchable virtual oscillator control approach for achieving the passivity of gridforming inverters (GFMs), without assuming constant voltage and constant frequency. The proposed control framework utilizes the Port-Hamiltonian (PH) based structure that mimics the behaviors of coupled harmonic oscillators, along with an energy ‘pumpingor-damping’ block and the Control by Interconnection (CbI) technique, to render the inverter passive. Once passivity is achieved, transient stability of the system will be guaranteed. The proposed control framework is composed of three loops: an outer power dispatching loop that generates the voltage and frequency references, a virtual oscillator loop that emulates the spontaneous synchronization of oscillators, and an inductor current loop that maintains lossless interconnection in PH systems. In conclusion, the study shows that the proposed control approach ensures the passivity of GFMs, facilitating the transient stability design of multi-inverter systems, as interconnections of passive systems remain passive and stable.
42 ENGINEERING↗