Electrolytes and interphases in Li-ion batteries and beyond.

In this comprehensive review, recent progress and developments on perfluorinated sulfonic-acid (PFSA) membranes have been summarized on many key topics. Although quite well investigated for decades, PFSA ionomers’ complex behavior, along with their key role in many emerging technologies, have presented significant scientific challenges but also helped create a unique cross-disciplinary research field to overcome such challenges. Research and progress on PFSAs, especially when considered with their applications, are at the forefront of bridging electrochemistry and polymer (physics), which have also opened up development of state-of-the-art in situ characterization techniques as well as multiphysics computation models. Topics reviewed stem from correlating the various physical (e.g., mechanical) and transport properties with morphology and structure across time and length scales. In addition, topics of recent interest such as structure/transport correlations and modeling, composite PFSA membranes, degradat...

New Insights into Perfluorinated Sulfonic-Acid Ionomers

Unlike the revolutionary advances in the anodes of lithium-ion batteries from Li intercalation materials to Li alloy and/or conversion reaction materials, the development of the cathode is still dominated by the Li intercalation compounds. Transition metal ions are essential in these cathodes as the rapid redox reaction centers, and one of the biggest challenges for the TM-based cathodes is the capacity and power fading especially at an elevated temperature, which is directly associated with the dissolution–migration–deposition (DMD) process of TMs from the cathode materials. This process not only alters the surface structure of the cathode materials, but more importantly, changes the SEI composition at the anode side. There is no doubt that the TM-DMD issue should be addressed thoroughly to unlock the potential of these compounds to enable a prolonged battery lifetime. This review article mainly focuses on research activities with regard to the DMD process in TM-based cathode materials. In the first four sections, we choose Mn-based cathodes as an example to discuss how Mn DMD relates to the capacity fade of the cell, and what possible approaches might suppress the DMD process by modification of the electrode or electrolyte. In the fifth section, we discuss the TM DMD process in Ni-, Co-, Fe- and V-containing cathode materials. This article reviews the frontier electrochemical research on TM-based cathodes and summarizes the progress and challenges, thereby helping to advance future R&D of LIBs.

Dissolution, migration, and deposition of transition metal ions in Li-ion batteries exemplified by Mn-based cathodes – a critical review

Lithium-ion batteries are nowadays playing a pivotal role in our everyday life thanks to their excellent rechargeability, suitable power density, and outstanding energy density. A key component that has paved the way for this success story in the past almost 30 years is graphite, which has served as a lithium-ion host structure for the negative electrode. And despite extensive research efforts to find suitable alternatives with enhanced power and/or energy density, while maintaining the excellent cycling stability, graphite is still used in the great majority of presently available commercial lithium-ion batteries. A comprehensive review article focusing on graphite as lithium-ion intercalation host, however, appeared to be missing so far. Thus, herein, we provide an overview on the relevant fundamental aspects for the de-/lithiation mechanism, the already overcome and remaining challenges (including, for instance, the potential fast charging and the recycling), as well as recent progress in the field such as the trade-off between relatively cheaper natural graphite and comparably purer synthetic graphite and the introduction of relevant amounts of silicon (oxide) to boost the energy and power density. The latter, in fact, comes with its own challenges and the different approaches to overcome these in graphite/silicon (oxide) composites are discussed herein as well.

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The success story of graphite as a lithium-ion anode material – fundamentals, remaining challenges, and recent developments including silicon (oxide) composites

A perspective on nickel-rich layered oxide cathodes for lithium-ion batteries

Effect of Manganese Contamination on the Solid-Electrolyte-Interphase Properties in Li-Ion Batteries

Light-weight aluminum (Al) alloys have widespread applications. However, most Al alloys have inherently low mechanical strength. Nanotwins can induce high strength and ductility in metallic materials. Yet, introducing high-density growth twins into Al remains difficult due to its ultrahigh stacking-fault energy. In this study, it is shown that incorporating merely several atomic percent of Fe solutes into Al enables the formation of nanotwinned (nt) columnar grains with high-density 9R phase in Al(Fe) solid solutions. The nt Al-Fe alloy coatings reach a maximum hardness of ≈5.5 GPa, one of the strongest binary Al alloys ever created. In situ uniaxial compressions show that the nt Al-Fe alloys populated with 9R phase have flow stress exceeding 1.5 GPa, comparable to high-strength steels. Molecular dynamics simulations reveal that high strength and hardening ability of Al-Fe alloys arise mainly from the high-density 9R phase and nanoscale grain sizes.

High-Strength Nanotwinned Al Alloys with 9R Phase

https://iopscience.iop.org/article/10.1149/2.031209jes/pdf

Water Uptake of Fuel-Cell Catalyst Layers

Optimal water management in proton-exchange-membrane fuel cells at lower temperatures requires the efficient removal of liquid water from the cell. This pathway is intimately linked with liquid-water-droplet removal from the surface of the gas-diffusion layer (GDL) and into the flow channel. In this study, these liquid-water phenomena are investigated experimentally to improve the understandingofwatertransportthrough,andremovalfrom,theGDL.Specifically,anexperimentusingasliding-anglemeasurement is designed and used to quantify and measure directly the adhesion force for liquid-water droplets and to understand the droplets’ growth and detachment from the GDL. The results show that unlike the static contact angle, the adhesion force, as measured by sliding angles, provides a good indicator of water-droplet removal as it is a direct measure of the dominating force that is holding a droplet on the GDL surface and preventing its detachment. It is also observed that injection through the GDL, as is representative of operating fuel cells, results in a higher adhesion force than a droplet placed on the top surface. Finally, it is shown that aged GDLs demonstrate higher adhesion forces, which dominate GDL degradation response and fuel-cell water holdup.

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Liquid-Water-Droplet Adhesion-Force Measurements on Fresh and Aged Fuel-Cell Gas-Diffusion Layers

Due to their favorable materials properties including direct bandgap and high electron mobilities, epitaxially grown III–V compound semiconductors such as gallium arsenide (GaAs) provide unmatched performance over silicon in solar energy harvesting. Nonetheless, their large-scale deployment in terrestrial photovoltaics remains challenging mainly due to the high cost of growing device quality epitaxial materials. In this regard, reducing the thickness of constituent active materials under appropriate light management schemes is a conceptually viable option to lower the cost of GaAs solar cells. Here, we present a type of high efficiency, ultrathin GaAs solar cell that incorporates bifacial photon management enabled by techniques of transfer printing to maximize the absorption and photovoltaic performance without compromising the optimized electronic configuration of planar devices. Nanoimprint lithography and dry etching of titanium dioxide (TiO2) deposited directly on the window layer of GaAs solar cells ...

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Anthony Kwong

Papers

Effect of Manganese Contamination on the Solid-Electrolyte-Interphase Properties in Li-Ion Batteries

High-Strength Nanotwinned Al Alloys with 9R Phase

Water Uptake of Fuel-Cell Catalyst Layers

Liquid-Water-Droplet Adhesion-Force Measurements on Fresh and Aged Fuel-Cell Gas-Diffusion Layers

High Performance Ultrathin GaAs Solar Cells Enabled with Heterogeneously Integrated Dielectric Periodic Nanostructures