Utilization Of Materials Research Articles

Revealing the Link between Morphological Heterogeneity and Reaction Behavior of Cathode in Solid-State Batteries

Structural heterogeneity within solid-state electrodes can have a significant impact on material utilization and reaction rates. This reaction heterogeneity is greater in solid state systems in comparison to conventional liquid electrolytes because it requires exquisite solid-solid contact between the active energy storage materials and the solid ion conducting phase (e.g. solid electrolyte) [1]. Electrode reaction behaviors encompass electrochemical lithiation and delithiation dynamics and chemo-mechanical processes such as volume change and fracture [2]. Understanding the connection between structural heterogeneity and reaction behavior is crucial for understanding degradation mechanisms and optimizing solid state battery architectures. Herein, we examine the implications of reaction heterogeneity in an additive-free, crystallographically textured electroplated lithium cobalt oxide (LCO) cathode [3]. The electroplated dense cathode alleviates the need for any solid electrolyte material in the cathode. A diverse set of synchrotron-based operando and ex situ experiments are combined with modeling to uncover the relationship between structural heterogeneity and reaction behavior. Operando energy dispersive X-ray diffraction and ex situ 3D XANES are used to identify reaction heterogeneity and X-ray nanotomography is used to probe nano-scale structural heterogeneity. Nanoindentation is utilized to determine the mechanical properties of LCO. To validate the results, we combine these experimental results with transport and mechanics modeling. Through this comprehensive characterization approach, we confirm that the reaction behavior of cathode in our model is mainly determined by the morphological heterogeneity rather than the Li diffusion within the electrode. Structural heterogeneity causes localized high stress and leads to fracture, which in turn limit the full utilization of the cathode. Reference [1] Jung, S.H., Kim, U.H., Kim, J.H., Jun, S., Yoon, C.S., Jung, Y.S. and Sun, Y.K., 2020. Ni‐rich layered cathode materials with electrochemo‐mechanically compliant microstructures for all‐solid‐state Li batteries. Advanced Energy Materials, 10(6), p.1903360.[2] Liu, X., Zheng, B., Zhao, J., Zhao, W., Liang, Z., Su, Y., Xie, C., Zhou, K., Xiang, Y., Zhu, J. and Wang, H., 2021. Electrochemo‐mechanical effects on structural integrity of Ni‐rich cathodes with different microstructures in all solid‐state batteries. Advanced Energy Materials, 11(8), p.2003583.[3] Zahiri, B., Patra, A., Kiggins, C., Yong, A.X.B., Ertekin, E., Cook, J.B. and Braun, P.V., 2021. Revealing the role of the cathode–electrolyte interface on solid-state batteries. Nature Materials, 20(10), pp.1392-1400. Figure 1

Sustainable Electrochemical Recycling of Spent Lithium-Ion Batteries: Selective Extraction of Lithium and Direct Regeneration of De-Lithiated Material

The recycling of spent lithium-ion batteries has become an urgent imperative. In recent years, the rising demand for lithium has sparked interest in the selective extraction of lithium from spent LIBs cathode materials. This process is of interest as it can streamline processes, improve lithium recovery efficiency, and reduce processing costs. Electrochemical methods for selectively extracting lithium from spent cathode materials have gained significant attention among various selective extraction methods due to their advantages, such as low energy consumption and environmental friendliness. Despite substantial progress in improving the efficiency of lithium recovery through electrochemical methods, the economic returns from lithium salt products, to some extent, are still insufficient to offset the processing costs of the entire process, thereby limiting the further development of this technology. Therefore, it is necessary to develop reasonable strategies for the utilization of such de-lithiated materials to further enhance product yields. One promising strategy among these approaches is direct regeneration of fresh cathode materials from the de-lithiated material. However, due to a lack of clear understanding of the structural evolution of transition metal oxides during the lithium extraction process, and the lithiation mechanisms of lithium-depleted materials, there is currently no research report on the direct regeneration of such de-lithiated materials into battery materials.Herein, an electrochemical method using LiCl aqueous as electrolyte is developed to realize the selective extraction of lithium from spent polycrystal LiNi0.55Co0.15Mn0.3O2 (NCM) cathode materials, with a maximum de-lithiation rate approaching 90%. Thorough characterizations were conducted to monitor the morphological, structural, and compositional evolution of NCM during the electrochemical de-lithiation process. These findings contribute to a profound understanding of the characteristics of the de-lithiated material and inform the rational design of regeneration pathways tailored to such materials. The results reveal that the deep de-lithiation of NCM in lithium-aqueous electrolyte triggers water-molecule intercalation, leading to an unusual phase transformation beyond H1→H2→H3. This phase transformation causes substantial lattice expansion along c-axis and introduces severe lattice distortion in de-lithiated material. The over-expanded lattice and the presence of bulk defects resulted in an unstable structure, posing huge challenge for the subsequent direct regeneration of de-lithiated material using conventional calcination methods. To address this, we employ a hydrothermal re-lithiation process, characterized by a milder, lithium-rich and water-based environment. This process is able to create a “lithium-water-balance” structure for de-lithiated materials by promoting the lithium diffusion into the lithium-deficiency structure and facilitating the exchange between lithium ions and water molecules. This process effectively enhances structural stability of the de-lithiated material. As a result, subsequent calcination successfully converts the degraded structure back into the original lithium-conductive layer structure by further eliminating the remaining lattice defects in material and promoting the cation rearrangement. The regenerated material exhibits decent electrochemical performances, which delivers a capacity of 153.2 mAh g−1 at 1C and 132.5 mAh g− 1 at 5C. This work provides insights into the electrochemical de-lithiation method and fills a gap in the utilization of de-lithiated NCM, paving the way for the sustainable recycling of spent LIBs.

Composite Ion-Exchange Membranes with High Specific Ion Selectivity for Efficient Electro-Membrane Processes

The advancement of ion-exchange membranes (IEMs) with heightened permselectivity for specific ions is pivotal for improving electro-membrane processes. Achieving targeted ion selectivity necessitates precise control over membrane surface characteristics, including electrostatic forces, ion transport channel size, and hydrophobicity. Utilization of diverse nanostructured materials, particularly metal-organic frameworks (MOFs), offers a pathway to modify these surface properties. MOFs, known for their structural diversity, adjustable pore sizes, and customizable frameworks, are widely applied in separation, catalysis, electrochemical, and biomedical fields. This study presents novel composite membranes, enhanced with various nanostructured materials including MOFs, demonstrating improved specific ion selectivity, robust physical strength, and superior electrochemical properties compared to standard commercial membranes. Notably, these membranes exhibit augmented performance in water-splitting electrodialysis for LiOH production, attributed to enhanced proton-blocking and monovalent ion permeability. This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MEST) (NRF-2022M3C1A3081178 and NRF-2022M3H4A4097521).

Efficient Direct Recycling of Spent Cathode Materials in Lithium-Ion Batteries

The demand for lithium-ion batteries (LIBs) has surged in recent years, driven by the rapid growth of electric vehicles (EVs) and emerging energy storage technologies. Yet, this surge in demand has also resulted from a significant increase in the number of spent batteries. Given the potential for environment pollution wastage, it is absolutely crucial to prioritize the recovery and recycling of these used lithium-ion batteries.The common techniques employed in large-scale industrial settings for battery recycling are pyrometallurgy and hydrometallurgy. These are pivotal multi-step processes, particularly suitable for materials containing Cobalt (Co) and Nickel (Ni), such as NMC (LiNixMnyCozO2). Aside from NMC, there has been a surge in the adoption of LFP (LiFePO4) as a cathode material target for lithium-ion batteries in electric vehicles worldwide over the past few decades. However, these established industrial recycling methods are not applicable to LFP due to the comparatively lower value of iron. This necessitates the pursuit of direct recycling approaches.In order to accomplish this goal, direct recycling stands out as the most suitable technique for regenerating spent batteries1. Unlike processes involving solution-based or high-temperature steps that entail potentially wasteful steps, thisapproach aims to reduce energy consumption and costs, all while maintaining environmental integrity through a judicious utilization of resources, materials, and energy. Consequently, our attention is directed towards this specific LFP material, prompting us to detail a direct recycling procedure for spent LFP cathodes via a chemical lithiation process at room temperature in a solution containing lithium iodide (LiI) and various solvents2 (Fig. 1).

Tuning the Bifunctional Properties of Cell Reversal-Tolerant Ir-Pt Electrocatalysts for HOR and Oer

Hydrogen starvation is still a big problem in PEM fuel cells [1]. In order to provide protons and electrons to the cathode during H2 starvation, the carbon oxidation reaction (COR) takes place at the anode [2]. To solve this issue, there are three main strategies: (i) utilization of corrosion resistant support materials, (ii) integration of extensive and complex system mitigation strategies and finally (iii) the addition of co-catalyst to promote the oxygen evolution reaction(OER) instead of COR. [3, 4]In this work, platinum-iridium (PtIr) nanoparticles (NPs) have been designed as a novel bifunctional electrocatalysts to accelerate either the hydrogen oxidation reaction (HOR) or the OER depending on the reaction conditions. Our catalyst concept is the combination of both functionality (HOR and OER) in single Pt-Ir alloy nanoparticles (NPs) deposited on the same support material. The Pt-Ir NPs with Pt:Ir ratios of 1:1 and 3:1 were prepared by two different (colloidal and wet-impregnation) routes. Very interestingly, the oxidation states of platinum and iridium as well as the particle size strongly vary depending on the synthesis route. More precisely, the wet-impregnation enables preparing Pt-Ir NPs of 3 – 4 nm size and mainly in the metallic state, while strongly oxidized NPs with ~2 nm size are produced by colloidal route. Despite the different oxidation states and particle sizes, the Pt-Ir NPs show considerable activity for HOR and OER compared to pure commercial Pt/C and IrOx catalysts. Very interestingly, the bifunctionality of these Pt-Ir is highly reversible and is robust during accelerated stress tests. Operando Quick-X-ray Absorption Near Edge Structure (XANES) spectroscopy were performed to provide fundamental insights into the reversibility and catalytically active states of these bifunctional catalysts under the working conditions by jumping with the potential between HER and OER within few seconds. The combination of operando XANES, RDE and MEA data show that the bifunctional approach is a promising way to improve the cell reversal-tolerant properties of anode catalyst materials compared to the state-of-the-art Pt-IrOx catalyst materials.

Modeling of Lithium-Ion Convection Cell Effects on Reaction Distribution and Different Cathode Active Materials

Li-ion batteries (LIBs) could play a substantial role in mitigating climate change if they become more widely adopted in transportation and stationary energy storage applications. Increasing this adoption requires improvement in both power density and energy density. At the cell level, this dual requirement calls for designs and active materials that overcome challenging trade-offs in nominal cell voltage, rate capability, and loaded capacity.In our previous research,1,2 we simulated that a convection cell with liquid electrolyte flow, using LCO, can overcome the trade-offs by enhancing accessed capacity under high-rate operation. Electrolyte flow achieves this enhancement by effectively addressing both bulk electrolyte mass transfer and thermal limitations. The flow of electrolyte raises cell voltage by promoting a uniform Li+ salt concentration and regulates temperature by removing heat and lowering heat-producing overpotentials.In our current work, we extend our macrohomogeneous modeling analysis of a Li-ion convection cell to explore the impact of concentration uniformity on charge-transfer reaction distribution and the flexibility of this approach to work with different active materials. Concentration uniformity evens the reaction distribution, facilitating spatially consistent and full utilization of the active material in the electrodes. Additionally, the use of flow enables the cell to maintain rate capability across various electrode thicknesses and areal capacity loadings. At high C rates, a convection cell with flow exhibits significantly higher output capacity than a closed cell without flow. The degree of increase in running voltage and delivered capacity depends on the choice of positive electrode active material—LFP, LCO, NCA, NMC, or LMO.Finally, simulations of net power density and net energy density account for pumping energy loss across the cell. The improvement in net energy density with flow becomes substantial at high power density. W. Gao, M.J. Orella, T.J. Carney, Y. Román-Leshkov, J. Drake, F.R. Brushett, J. Electrochem. Soc., 167, 140551 (2020).W. Gao, J. Drake, F.R. Brushett, J. Electrochem. Soc. 170, 090508 (2023).

Electromagnetically Enhanced Atomic Layer Deposition for Modification of Thin Film Properties through in Situ Substrate Biasing

Atomic layer deposition (ALD) is broadly used for thin, conformal film growth in microelectronics, photovoltaics, and other industries. Enhanced film properties are required for advancement of device performance. Use of electrical current in situ during deposition to drive material properties of films produced by ALD toward a desired state (such as higher conductivity) will increase the utility of thin film materials for device applications. In an ALD reactor bias is applied directly to substrates during ALD precursor pulses. Higher conductivity and growth rates were observed for samples grown with ALD enhanced by in situ substrate biasing. Thicknesses were determined via spectroscopic ellipsometry, uniformity was investigated by atomic force microscopy, and crystallinity by x-ray diffraction. These systems are computationally investigated to probe the mechanism by which the ALD processes are enhanced.

Enhanced Electrochemical Performance of Disordered Rocksalt Cathode in a Localized High Concentration Electrolyte

Lithium (Li) transition metal oxides with layered structure, commonly employed as cathodes in Li-ion batteries, exhibit limited capacity, and employ less abundant and costly materials, raising sustainability concerns amid surging battery demand. Addressing this, lithium rich cation disordered rock salt cathode (DRX) materials have garnered substantial attention as they offer high capacity and cost benefits. Manganese (Mn) based DRXs, in particular, show promise due to the utilization of earth abundant materials and good thermal stability of Mn. However, these cathodes often face challenges when cycled in state-of-the-art carbonate-based electrolytes. These include severe side reactions between the cathode and the electrolyte, transition metal dissolution and structural instability of the cathode particles all of which result in fast capacity fading. In this work, an advanced localized high concentration electrolyte (LHCE) is developed to mitigate these problems and enable stable cycling of Li1.2Mn0.6Ti0.2O2 (LMTO). The developed LHCE exhibits high voltage stability, forming an ultrathin and stable electrode/electrolyte interphase. Consequently, Li||LMTO half cells with the developed LHCE demonstrate increased capacity, enhanced cycling stability and superior rate capabilities compared to the cells with the conventional electrolyte. For instance, the Li||LMTO cells cycled in LHCE show higher initial capacity of 205.2 mAh/g, and a capacity retention of 72.5 % in contrast to an initial capacity of 187.7 mAh/g and a capacity retention of 19.9 % observed in Li||LMTO cells with the conventional electrolyte after 200 cycles at a current density of 20 mA/g. This work paves the way for the development of practical DRX cathode- based high-energy Li batteries.

Identification of Local Overpotentials and Their Spatial Distributions in Polymer Electrolyte Water Electrolyzers

Polymer electrolyte water electrolyzers (PEWEs) are pivotal in the transition to a clean energy economy, promising green and efficient hydrogen production. Understanding the complexities of overpotentials within PEWEs is crucial for optimizing their performance and efficiency1. For PEWEs to attain the highest possible system efficiency, considering a specific material set and operating parameters, meticulous design is imperative. The goal is to achieve a high reaction rate that is not only optimal but also uniform across the entire active surface area of the electrodes. This uniformity should ideally be maintained with minimal sensitivity to variations in operating conditions.This study focuses on the contribution of different overpotential categories and reveals their spatial variations through in-situ analysis to understand and overcome the issues caused by non-uniformity in reaction. Employing a segmented cell and printed circuit board (PCB) approach2, current density distribution (CDD) and distributed area-specific resistance (DASR) measurements are obtained, enabling a detailed examination of the mass transport overpotentials (as shown in Figure 1). Typically, in the fuel cell community, modeling mass transport limitations is thought of as diffusion-limited transport3. In the anode porous transport layer (PTL), oxygen accumulation (i.e. product transport limitation) can cause membrane dry-out and an increase in ASR4. The experimental results elucidate the intricate relationship between ohmic and mass transport losses, emphasizing the deep coupling induced by the two-phase nature of the system. Figure 1 shows that, as mass transport limitation grows, the highest increase in overpotential comes from mass transport-coupled ohmic losses. Beyond conventional diffusion limited mass transport losses, bubble dynamics significantly impact local hydration and ASR, highlighting the need for a holistic approach in device optimization5.This research contributes to the understanding of PEWE dynamics, providing a basis for informed engineering decisions. By unraveling the intricate interdependencies between overpotentials, this work empowers the efficient utilization of expensive catalyst materials. Moreover, it offers insights into mitigating the challenges associated with bubble removal, accomplishing this with lower pumping requirements that scale non-linearly. These insights enrich both theoretical understanding and are paramount for enhancing system efficiency and economic viability of PEWEs, thereby advancing the prospect of sustainable hydrogen production. Reference N. Danilovic and I. Zenyuk, Electrochem. Soc. Interface, 30 (2021).F. H. Roenning, A. Roy, D. S. Aaron, and M. M. Mench, J. Power Sources, 542, 231749 (2022) https://linkinghub.elsevier.com/retrieve/pii/S037877532200742X.A. Z. Weber et al., J. Electrochem. Soc., 161, F1254–F1299 (2014) https://iopscience.iop.org/article/10.1149/2.0751412jes.C. Immerz, B. Bensmann, P. Trinke, M. Suermann, and R. Hanke-Rauschenbach, J. Electrochem. Soc., 165, F1292–F1299 (2018).P. Satjaritanun et al., iScience, 23, 101783 (2020) https://doi.org/10.1016/j.isci.2020.101783. Figure 1

Enhanced Discharge Capacity in Carbon Felt Electrodes for Aqueous Aluminium-Ion Half-Cells

Diversifying the battery technology in use is an important step in ensuring a sustainable transition to a carbon neutral society, and reducing the emissions associated with lithium-ion cell manufacture. Aluminium is an attractive material for battery applications due to its high theoretical volumetric charge storage capacity of 8046 mA h cm−3 compared to lithium’s 2061 mAh cm-3 and relative abundance in the earth’s crust (1). Aqueous Al-ion batteries are one of many metal-ion systems being investigated utilising water as the electrolyte (2). Further, there are well-established mining, processing, and recycling routes for aluminium, with Li-ion battery recycling still in its infancy (3). Using aqueous electrolytes further provides improved safety as fire risk is reduced, and manufacturing costs are also reduced (4).The substrate on which the electrode material is applied impacts how it is utilised within an electrochemical system. The substrate provides both a shape to the electrode, as well as the material itself forming part of the system, and common substrates double as current collectors e.g. thin metal foils, but carbon polymers have also been explored as a substrate (5, 6). Carbon felt is a conductive substrate, with thin fibres of 5-10 μm diameter, providing a flexible porous structure and large surface area for the active material ‘ ink’ to adhere (0.4 m2 g-1 (7)) . Carbon based electrodes have been assessed in a non-aqueous Al-ion cathodes (8), with varying performance metrics based on the structure and make-up of the electrode, however, these were not investigated as a substrate for further electrode ink. In adding the ink to the carbon felt, the electrode becomes an effective 3D-matrix electrode.This poster explores the use of such 3D-matrix electrodes in order to increase the amount of active material utilised within the aq. Al-ion battery system (9) – a key requirement in reducing the environmental impacts of the battery overall (5), and a means for increasing the capacity of an individual electrode without increasing the overall volume. The cell described in (10) has a carbon-polymer electrode substrate, anatase TiO2 negative electrode and a copper hexacyanoferrate (CuHCF) positive electrode, with the electrolyte being 1 M AlCl3 + 1 M KCl. While the CuHCF redox reaction is partially understood, the negative electrode mechanism has not been fully elucidated. A theorised surface reaction, and pseudo-capacitance of the TiO2 electrode in the aq. Al-ion battery would benefit from an increased surface area of the electrode provided by the carbon felt. Therefore, a key factor in achieving the optimum utilisation of active material is not purely an increase of TiO2 in the electrode, but an increase in the surface area in contact with the electrolyte. Key findings presented show that the lower active material loadings result in a higher discharge capacity for both the positive and negative electrodes, with values reaching an order of magnitude higher than seen for the 2D electrodes studied in the past. For the TiO2 electrode, we see 205.0 mAh g-1 @978 mA g-1 (1.81 mg cm-2 active material loading) and for the CuHCF, 259 mA h g-1 @ 1256.8 mA g-1 (2.5 mg cm-2 active material loading). Elia GA, Kravchyk KV, Kovalenko MV, Chacón J, Holland A, Wills RGA. An overview and prospective on Al and Al-ion battery technologies. Journal of Power Sources. 2021;481:228870. Wu D, Li X, Liu X, Yi J, Acevedo-Peña P, Reguera E, et al. 2022 Roadmap on aqueous batteries. Journal of Physics: Energy. 2022;4(4):041501. Baum ZJ, Bird RE, Yu X, Ma J. Lithium-ion battery recycling─ overview of techniques and trends. ACS Publications; 2022. Chao D, Zhou W, Xie F, Ye C, Li H, Jaroniec M, et al. Roadmap for advanced aqueous batteries: From design of materials to applications. Science Advances. 2020;6:eaba4098. Melzack N. Advancing battery design based on environmental impacts using an aqueous Al-ion cell as a case study. Scientific Reports. 2022;12(1):8911. Holland A, Kimpton H, Cruden A, Wills R. CuHCF as an electrode material in an aqueous dual-ion Al3+/K+ ion battery. Energy Procedia. 2018 d;151:69-73. Sigracell. Speciality Graphites for Energy Storage. 2016. McKerracher RD, Holland A, Cruden A, Wills RGA. Comparison of carbon materials as cathodes for the aluminium-ion battery. Carbon. 2019;144:333-41. Holland A, McKerracher RD, Cruden A, Wills RGA. An aluminium battery operating with an aqueous electrolyte. Journal of Applied Electrochemistry. 2018;48(3):243-50. Melzack N, Wills R, Cruden A. Cleaner Energy Storage: Cradle-to-Gate Life Cycle Assessment of Aluminum-Ion Batteries With an Aqueous Electrolyte. Frontiers in Energy Research. 2021;9(290).

(Invited) Functional Complex Oxides for Next-Generation Logic, Memory, Sensing, and Beyond

Complex-oxide materials possess a range of interesting properties and phenomena that make them candidates for next-generation devices and applications. But before these materials can be integrated into state-of-the-art devices, it is important to understand how to control and engineer their response in a deterministic manner. In this talk, we will discuss some of the state-of-the-art science, engineering, and utilization of complex ferroic materials and their potential for emergent order and phenomena that can enable new device function. We will explore the role of the epitaxial thin-film growth process and the use of epitaxial constraints to engineer a range of systems with special attention to ferroelectric (i.e., materials with robust spontaneous polarization that can be switched with an electric field thereby producing a ferroelectric hysteresis loop), antiferroelectric (i.e., materials which have an antiparallel alignment of polarization (or are non-polar) in the ground state but can be switched to a polar (parallel) order by an external electric field producing a reversible antiferroelectric-to-ferroelectric phase transition and a characteristic double polarization-electric-field hysteresis loop), and relaxor (i.e., chemically complex materials that exhibit a competition between short- and long-range interactions such that it produces a complex, dynamic polarization structure and exotic properties) materials.In recent years, the use of epitaxial constraints has enabled the production of model versions of these complicated materials and the subsequent deterministic study of an array of physical phenomena that are now being widely considered for next-generation applications. Specifically, we will investigate the potential of ferroelectric materials for non-volatile, ultra-low voltage memory and logic applications including their use in ferroelectric-field-effect transistors, the realization of multi-state/neuromorphic function, and more. In turn, we will explore how antiferroelectric and relaxor thin-film materials can open the door to a new generation of thin-film based electromechanical, sensing, high-frequency, and capacitive-energy-storage devices. Along the way we will leverage advanced thin-film growth techniques to control the materials and to solicit new insights about their function, apply state-of-the-art characterization methods, including unique in operando studies under applied stimuli, to understand how materials function, and explore how such materials can be integrated and utilized in realistic device structures. We will try to introduce the listener to these complex materials and their potential for new applications – in effect working to motivate engineers to explore these materials. The discussion will range from the development of fundamental understanding of the physics that lies at the heart of the observed effects, to an illustration of routes to manipulate and control these effects, to the demonstration of rudimentary solid-state devices based on these materials.

Nature-Derived Sulfur Carbons for Highly-Efficient Room Temperature Sodium-Sulfur Energy Storage

In recent years, a growing interest in “beyond-Li-ion“ batteries has caused a speedy development of alternative battery technologies based on other alkali metals. Room temperature sodium sulfur (RT Na-S) batteries are potential candidate for sustainable large-scale energy storage systems. They offer low cost, nontoxicity and natural abundance of both cathode and anode materials combined with high theoretical energy density. However, rapid capacity fading related to the irreversible shuttling of soluble polysulfides, poor reaction kinetics and low sulfur utilisation in the cathode materials significantly limit their practical application.In this work, a microporous sulfur-carbon complex is produced from sustainable natural precursors in a one-pot synthesis via stepwise thermally-induced inverse vulcanisation and condensation. The material exhibits a unique structure, with sulfur chains covalently anchored to the conductive carbon matrix and physically confined in ultra-micropores. An increase in sulfur content in the sulfur-copolymer alters the morphology and chemical composition of the final sulfur-carbon material, enhancing the amount of long-chain sulfur. The combination of optimal microstructure, good electrical conductivity and high content of electrochemically active sulfur translates to an unprecedented ~99% utilisation of sulfur and the highest reported capacity for a room temperature Na-S cathode, along with high rate capability, coulombic efficiency and long-term stability. This study offers an innovative approach towards the understanding of the key chemico-physical properties of the sulfur-carbon composite materials for the development of high-performance cathodes in RT Na-S batteries with an atom-efficient utilisation of sulfur.

A Spray-Drying Approach for Highly Active Amorphous NiFe2O4 for AEM Water Electrolysis

Water electrolysis, a key process for hydrogen production, holds immense potential in mitigating carbon dioxide emissions when powered by renewable energy sources, thereby contributing to a sustainable and clean energy future. Commercially available and widely recognized technologies for water electrolysis include the proton exchange membrane water electrolysis (PEMWE) and the traditional alkaline water electrolysis (AWE). In order to use the benefits of both systems, the anion exchange membrane water electrolysis (AEMWE) method is proposed, enabling the utilization of non-noble catalyst materials and achieving high current densities at low cell voltages [1].In the present work, the influence of a spray-drying approach compared to a co-precipitation method on the bimetallic non-noble NiFe2O4 catalysts on the oxygen evolution reaction (OER) activity is systematically investigated. State of the art catalyst for OER is Iridium oxide and so far, the best non-noble catalyst has not been found yet. A widely used non-noble catalyst is NiFe- layered double hydroxide but it suffers from low electric conductivity [2]. Another promising catalyst is the NiFe2O4, which also provides low OER overvoltage. However, amorphous oxides are said to have a higher activity than crystalline [3]. Furthermore, the use of a spray drying approach is highly reproducible, with which the crystallinity can be set very easily [4, 5].The experimental study of the catalysts was carried out in a commercial Baltic-Fuel Cell with a geometrical area of 25 cm² at 60 °C in 1 M KOH electrolyte and a contact pressure of 1.25 MPa. The electrodes were prepared by directly spray coating the desired amount of catalyst onto the anode and cathode substrates. A Bekipor® 2NI 18-0.25 nickel felt was used as the substrate for the anode, while AvCarb MGL370 carbon paper was employed for the cathode. As cathode catalyst Pt/C from Tanaka (TEC10E40E, 37.2 % Pt) was used, while a loading of 0.5 mg cm-2 Pt was targeted during the spraying procedure. On the anode, the NiFe2O4 loading was set to 2 mg cm-2. Both electrodes were separated by a Sustainion® X37-50 Grade T membrane. For determination of relevant catalyst activity data chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) were carried out.Figure 1 reveals that the spray-dried NiFe2O4 (amorphous, red curve) has a superior performance compared to the precipitated NiFe2O4 (green curve), which is partly crystalline. With the spray-dried catalyst, a reduction in overvoltage of approx. 60 mV at 1 A cm-2 can be achieved. With a cell voltage of less than 1.7 V at a current density of 1 A cm-2, our recently developed catalyst ranks among the most outstandingly described in the literature to date [6]. These findings can contribute to a further development of amorphous catalysts with even higher activity.[1] Cossar, E., Murphy, F. and Baranova, E.A. (2022), Nickel-based anodes in anion exchange membrane water electrolysis: a review. J Chem Technol Biotechnol, 97: 1611-1624.[2] Jeon, S.S., Lim, J. Kang, P.W., Lee, J.W., Kang, G., Lee, H. (2021), Design Principles of NiFe-Layered Double Hydroxide Anode Catalysts for Anion Exchange Membrane Water Electrolyzers. ACS Appl Mater Interfaces,13 (31): 37179-37186.[3] Shi, G., Arata, C., Tryk, D., Tano, T., Yamaguchi, M., Iiyama, A., Uchia, M., Iida, K., Watanabe, S., Kakinuma, K. (2023), NiFe Alloy Integrated with Amorphous/Crystalline NiFe Oxide as an Electrocatalyst for Alkaline Hydrogen and Oxygen Evolution Reactions. ACS Omega, 8: 13068−13077.[4] Kreitz, B., Arias, A. M., Martin, J., Weber, A. P., Turek, T. (2020), Spray-Dried Ni Catalysts with Tailored Properties for CO2 Methanation, Catalysts, 10 (12): 1410.[5] Arias, A. M., Weber, A. P. (2019), Aerosol synthesis of porous SiO2-cobalt-catalyst with tailored pores and tunable metal particle size for Fischer-Tropsch synthesis (FTS), J Aerosol Sci, 131: 1-12.[6] Du, N., Roy, C. Peach, R., Turnbull, M., Thiele, S. and Bock, C. (2022), Anion-Exchange Membrane Water Electrolyzers. Chem Rev, 122: 11830-11895. Figure 1

Evaluation of Electrochemical Techniques for Characterizing the Kinetics of Porous Insertion-Type Electrodes

The composite-type porous electrode remains the most commonly used electrode for a wide variety of electrochemical energy storage devices, including lithium-ion batteries, electrochemical capacitors, Li-S/Li-air batteries, and even all-solid-state batteries. This is due to its ease of manufacturability and ability to maintain a high electrochemical surface area with adequate ion and electron transport. Understanding porous electrode kinetics is essential to maximize the active material utilization at high rates. A variety of electrochemical techniques exist to characterize the kinetic behavior of porous electrodes. The most popular ones include electrochemical impedance spectroscopy, galvanostatic charge/discharge, galvanostatic intermittent titration technique, and cyclic voltammetry. The purpose of this work was to evaluate which of these four techniques provides the most relevant kinetic information for understanding porous electrode kinetics. To do this, we utilized porous electrodes composed of LiCoO2 as a model insertion-type material, and with varying thicknesses (10 - 40 µm). We find that GITT is an accessible and reliable method for obtaining the effective diffusion coefficient of the porous electrode. It yields consistent results, regardless of electrode thickness and component ratio. On the other hand, the cyclic voltammetry peak current behavior can be easily compromised, even at slow scan rates of 0.01 - 0.1 mV/s, and when using a high conducting domain ratio. When comparing the dQ/dV plot and cyclic voltammetry for observing peaks indicating phase transitions in the insertion material, the dQ/dV plot is less kinetically limited. We utilized the differential relaxation time (DRT) method to analyze electrochemical impedance spectroscopy data. Our findings demonstrate that as thickness increases, charge transfer resistance decreases, while diffusion resistance increases. This study provides a comprehensive evaluation on the differences between electrochemical methods to characterize the kinetics of composite porous electrodes.

Guiding the Choice of Carbon Nanotubes Conductive Additives for Silicon Anode Electrode through Microstructure Scale Analysis

Silicon anode electrodes exhibit a large microstructure design space as several carbon additives are considered to improve its conductivity and thus electrochemical performance. Investigating each combination experimentally is time-consuming. In this work, microstructure scale modeling is used to discriminate between different carbon additives to accelerate electrode development [1]. Baseline spherical C45, single wall carbon nano tube (SWCNT, cf. Fig. 1), carbon nano rods (CNR), and mixed SWCNT-CNR are considered and their respective impact on connectivity, effective conductivity, specific surface area, pore size distributions, and effective diffusivity are calculated to provide design recommendations. To do so, microstructures are numerically generated using the NREL open-source Microstructure Analysis Toolbox (MATBOX) available to the battery community* [2].Additionally, the model is used to correlate material utilization and silicon particle size, in agreement with experimental data, to further guide the selection of silicon material.Lastly, the model is used to investigate the porosity specific surface area relationship in the low porosity range, for which the analytical expression 3ε/r (with ε the particle volume fraction and r the particle radius) is no longer valid due to the packing density limit, and revealed a non-monotonic correlation. Such result is very relevant for silicon anode development as one major hindrance to this chemistry is its limited calendar life due to SEI growth, for which the specific surface area is a key parameter. *Nanotube generation new feature will be released after article [1] publication. [1] F. L. E. Usseglio-Viretta, J. H. Kim, J. Preimesberger, N. Neale, P. Weddle, A. Verma, A. M. Colclasure, Guiding the Choice of Carbon Nanotubes Conductive Additives for Silicon Anode Electrode Through Microstructure Scale Analysis, in preparation[2] F. L. E. Usseglio-Viretta, P. Patel, E. Bernhardt, A. Mistry, P. P. Mukherjee, J. Allen, S. J. Cooper, J. Laurencin, K. Smith, MATBOX: An Open-source Microstructure Analysis Toolbox for microstructure generation, segmentation, characterization, visualization, correlation, and meshing, SoftwareX, 17 (2022) 100915. Figure 1

Modeling Metal Nitrides for Interface Design in Lithium-Sulfur Batteries with GPUs and CPUs

As current batteries reach their limits, finding new battery materials is crucial. Lithium-sulfur batteries are a promising next-generation technology but face three major issues: low active material utilization, cathode pulverization, and limited polysulfide conversion leading to anode corrosion. Nano-deposition of metal nitride (MNx, M = Ti, V, Zr, etc.) layers on the graphene sulfur cathodes could significantly improve conductivity and cycling performance. Nevertheless, the large number of potential metal candidates requires preliminary and efficient computational screening using density-functional theory (DFT). This modeling framework can be used to calculate many properties of the coatings and screen out poor candidates. Firstly, the surface-adsorption ability of metal nitride candidates for lithium polysulfide intermediates involved in the electrochemical cycle (Li2S, Li2S2, Li2S4, Li2S6, Li2S8, S8) must be greater than the adsorption by dioxolane and dimethyl ether electrolytes (>~0.99eV). Secondly, the electronic properties before and after adsorption must feature significant density of states near the Fermi level, as a possible indicator of good electrical conductivity. Lastly, the free-energy profiles for the sulfur reduction reaction (SRR) over the remaining candidates will be estimated to better understand the catalytic properties of the metals. Particular attention will be paid to the Li2S2 reduction to Li2S, the potential limiting step. The top catalyst candidates should allow for an exergonic reaction. Finally, this application serves as a case study for our modeling platform, and the relative merits of standard for CPUs and GPUs in terms of computation time and accuracy will be discussed. Careful analysis of binding energy results, densities of states, and energy profiles for the various metal candidates provides valuable insights into the design of experimentally viable lithium-sulfur batteries, as well as advanced interface design in the broader field of battery research.

Design and Characterization of Porous Electrodes for Redox Flow Batteries

The commercialization of redox flow batteries as large-scale energy storage systems depends on lowering the capital and operating costs which depend on achieving maximum power density. Optimizing electrode design parameters and flow field-electrode combinations is critical to minimize losses and maximize active material utilization. Modeling the current drawn from an electrode offers a means to interpret electrode structure based on the electrolyte distribution driven by internal design. However, direct imaging methods (such as in-situ fluorescence microscopy and X-ray tomography) and numerical methods for current to potential prediction (3D Lattice Boltzmann modeling) are specific to individual electrode structures and possess limited predictable value to obtain an ideal electrode design. In this work, we present an electrode impedance spectroscopy (EIS)-based approach for determining electrode design parameters and devise a general method for determination of effective diffusion layer thickness. Using COMSOL modeling we verified the development of slug flow behavior in highly randomized porous electrode systems, indicating that the mass transport properties are dictated by inter-fiber distance. An analytical model to predict current as a function of applied overpotential is presented which allows us to vary structural parameters of the porous electrodes to study the influence of surface area, inter-fiber distances and diffusion layer thickness on the RFB performance. This model is a highly flexible tool applicable to any electrochemical system using a porous electrode and identifies critical variables affecting electrode design to characterize optimal electrode structure to minimize mass transport losses and optimize operational parameters.

Fundamental Studies of Discharge Mechanism and Capacity Limits of Lead Acid Battery Electrodes

Long-duration energy storage provides key benefits such as consistent power supply during periods of high demand for grid reliability and flexibility. For environmental benefits, it allows for more renewable energy integration and helps reduce reliance on fossil fuels to lower greenhouse gas emission. Lead batteries have the economic potential to continue serving as an important energy storage technology for a decarbonized sustainable energy future given they are earth-abundant, inexpensive, and 99% recyclable. Advancing the design of lead batteries with higher material utilization, fast recharge rates, and long-cycle life requires a fundamental understanding of the electrochemical and chemical processes taking place at the atomic and molecular scales. In this work, we will discuss how the use of well-defined electrode interfaces allows us to gain insights into the fundamental limits of discharge capacity and recharge rates. We were able to unveil the relationships between discharge rates and PbSO4 particle size/layer thickness that ultimately governs the maximum discharge capacity accessible as a function of discharge rate on both the negative and positive lead electrodes. This data helped us develop a mathematical model that captures the key processes concerning lead ion and (bi)sulfate ion gradients coupled to nucleation and growth that explain, from first principles, the origin of the well-known empirical Peukert law. In this context, exploring how variables such as acid concentration, temperature, and the presence of lignosulfonate additives in the electrolyte further influence discharge capacity allows us to understand how thermodynamic, kinetic, and even mass transport play a huge role in governing the accessible capacity from the electrodes. This study paves the way for a deeper understanding of the variables that are most important in improving the discharge capacity of lead-acid batteries, and thus batteries that can be utilized at their full potential.

Microstructural Analysis of Lithium-Ion Battery Cathode Carbon-Binder Domain across Processing Conditions

Improvement of lithium-ion battery (LIB) energy density and rate capability is necessary to increase adoption of electric vehicles (EVs) and curb transportation emissions. The cathode structure must support facile ion and electron transport, enabling rapid charging while maintaining near-theoretical capacity. Much investigation focuses on active material design for fast-charging cathodes, [1] but less is understood about the effect of electrode processing on carbon-binder domain (CBD) structure and its impact on rate capability. As conductive carbon facilitates electron transfer, slow Li+ diffusion through cathode micropores is rate-limiting and prevents full active material utilization at high charge rates. [2,3] However, efforts to improve Li+ diffusion, such as increasing porosity, introduce charge-transfer limitations. [4] Thus, cathode processing conditions and resulting microstructure must be carefully designed to optimize for both electronic and ionic conductivity. For example, an increase in coating shear rate and decrease in slurry solid content improves long-range electronic pathways [5,6] and calendaring strengthens active material-carbon contacts to reduce charge-transfer resistance. [2] However, the impact of processing variations on ionic transport pathways, which can be described by CBD porosity and tortuosity, is not well understood. Further, because the CBD is traditionally characterized as a single phase, the distinct influences of insulating binder and conductive carbon distributions on structure and performance are poorly defined.In this talk, I will discuss how electrode coating conditions impact pathways available to Li+ and electrons within the CBD with the goal of identifying optimal microstructures for efficient transport. We fabricate cathodes with varying solid content, coating shear rate, and degree of calendaring to explore disparate CBD microstructures. We use electrochemical impedance spectroscopy (EIS) with a symmetric cell & blocking electrolyte to determine cathode resistivity and tortuosity and plasma focused ion beam scanning electron microscopy (PFIB-SEM) to examine CBD morphology over a representative cathode volume (~80 x 80 x 50 µm3). We then use small-angle neutron scattering (SANS) with solvent contrast variation to distinguish between binder and carbon distributions and determine the surface area of each component within the CBD. Relationships between processing conditions, structural variations, and rate capability will be discussed, informing the design of the CBD for facile transport and improved fast charging performance. Further, reducing ionic transport limitations through intentional design of LIB cathodes will enable thicker electrodes to increase cell energy density.

Shape Optimization for Lithium-Ion Battery with Porous Electrodes

In this presentation, we introduce a gradient-based shape optimization framework to design porous electrodes for maximum energy storage. Lithium-ion batteries are becoming an increasingly important energy source and storage device. Large surface area that advocates high reaction rates often leads to small porosities that deteriorate electrochemical transport, which significantly restricts ion penetration depth, limiting the material utilization in planar electrodes. Consequently, architected electrodes are required to optimize performance.We consider a model with two materials, namely porous electrode and pure electrolyte. Density-based topology optimization with continuous material volume fraction has previously been implemented on lithium-ion battery system for both half-cell and full-cell model to maximizes its energy storage. Despite the capability of producing complex interdigitated structures, an appropriate penalization scheme for intermediate materials is required for the optimizer to provide near binary designs. Setting up such a penalization is often time-consuming due to the large number of design-dependent variables that affect the forward model differently. Alternatively, the shape optimization approach used in this work produces binary designs naturally by morphing conformal meshes, circumventing inaccuracies associated with fuzzy interfaces. Shape sensitivities are computed via the adjoint method and leveraging automatic differentiation. The optimization problem is solved using a nonlinear programming technique.In this presentation, we perform shape optimization on a half-cell model to maximize its energy storage when a fixed charging current is applied. We study multiple arrangements of physical parameters and compare their performance against a monolithic electrode. Both 2D and 3D results are presented.