Engineering topics
Irshad, Ahamed
Publications and source records attributed to Irshad, Ahamed.
Room-Temperature Electrochemical Fluoride (De)insertion into CsMnFeF[subscript 6]
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Promoting Reversibility of Multielectron Redox in Alkali-Rich Sulfide Cathodes through Cryomilling
We report conventional cathodes for Li-ion batteries (LIBs) are reaching their theoretical capacity limits. One way to meet the growing demands for high-capacity LIBs is by developing so-called Li-rich cathode materials that greatly benefit from additional capacities from anionic moieties in the structure. Li-rich materials are intrinsically subject to higher degrees of (de)intercalation, leaving the particles more prone to fractures and thus rapid capacity fade. Alkali-rich LiNaFeS 2 reversibly cycles with capacities exceeding 300 mAh g -1 , but its capacity fades faster than an isostructural material Li 2 FeS 2 . Using synchrotron-based transmission X-ray microscopy (TXM), we demonstrate that the capacity fade of LiNaFeS 2 stems from particle fractures in the first charge cycle. We improve the cycling performance of LiNaFeS 2 by means of cryomilling, which enhances capacity retention at cycle 50 by 76%. Through crystallographic and morphological characterization techniques, we confirm that cryomilling not only decreases particle and crystallite size while increasing microstrain but also prevents particles from fracturing. Cryomilling is a powerful tool to engineer nanoscale battery materials, and TXM allows the direct observation of morphological changes of the particles, which can be leveraged to develop next-generation cathode materials for LIBs.
Electrochemical Oxidative Fluorination of an Oxide Perovskite
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Controlling Covalency and Anion Redox Potentials through Anion Substitution in Li-Rich Chalcogenides
Development of next-generation battery technologies is imperative in the pursuit of a clean energy future. Toward that end, battery chemistries capable of multielectron redox processes are at the forefront of studies on Li-based systems to increase the gravimetric capacity of the cathode. Multielectron processes rely either on the iterative redox of transition metal cations or redox involving both the transition metal cations and the anionic framework. Targeting coupled cation and anion redox to achieve multielectron charge storage is difficult, however, because the structure–property relationships that govern reversibility are poorly understood. In an effort to develop fundamental understanding of anion redox, we have developed a materials family that displays tunable anion redox over a range of potentials that are dependent on a systematic modification of the stoichiometry. We report anion redox in the chalcogenide solid solution Li 2 FeS 2–y Se y , wherein the mixing of the sulfide and selenide anions yields a controllable shift in the high voltage oxidation plateau. Electrochemical measurements indicate that reversible multielectron redox occurs across the solid solution. X-ray absorption spectroscopy supports the oxidation of both iron and selenium at high states of charge, while Raman spectroscopy indicates the formation of Se–Se dimers in Li 2 FeSe 2 upon Li deintercalation, providing insight into the charge mechanism of the Li-rich iron chalcogenides. Anion substitution presents direct control over the functional properties of multielectron redox materials for next generation battery technologies.
A Low-Cost Iron-Based Current Collector for Alkaline Battery Electrodes
The use of three-dimensional porous nickel foam as the current collector of the nickel hydroxide electrode adds significantly to the cost of the nickel-based alkaline rechargeable batteries. Although iron is considerably less expensive than nickel, iron corrodes at the operating potential of the nickel hydroxide electrode. We have found that a 70–100 nm thick thermal coating of cobalt ferrite spinel protects the iron from corrosion. Such a coated iron substrate was found to be stable against corrosion even when polarized anodically at 10 mA cm -2 in 30% potassium hydroxide electrolyte for 1000 h. While the thermal coating of cobalt ferrite protected iron against corrosion, incorporation of lithium ions into the coating was found to enhance the electrical conductivity of the coating. XPS and EXAFS studies confirmed that the enhanced conductivity resulted from an increase in the population of Co 3+ in the ferrite spinel lattice. An inexpensive iron (steel) substrate protected by such a coating when used as a nickel hydroxide battery electrode exhibited a specific capacity of 0.25 Ah g -1 at C/5 discharge rate, comparable to a nickel hydroxide electrode based on a relatively expensive nickel foam substrate. The steel-based electrode also exhibited no noticeable degradation over 150 cycles at C/2 rate. This demonstration of a robust and economical steel substrate presents a unique opportunity for reducing the cost of the nickel hydroxide battery electrode in alkaline batteries