Chloride Insertion Enhances the Electrochemical Oxidation of Iron Hydroxide Double-Layer Hydroxide into Oxyhydroxide in Alkaline Iron Batteries

Abstract

Rechargeable alkaline iron batteries that constitute environmentally benign electrolytes and earth-abundant industrial materials are desirable green solutions for large-scale energy storage. As one of the most abundant metal elements in the earth’s crust, iron (Fe) can satisfy nearly all criteria for low-cost and safe battery electrodes. However, challenges in achieving reversible Fe redox impede their extensive implementation in modern energy supply systems. This study revealed that Cl-anion insertion into Fe­(OH)2 layered double hydroxide (LDH) formed a green rust intermediate phase with the formula [Fe2 2+Fe1 3+(HO–)6]+[Cl]−, which assisted a high Fe­(OH)2/FeOOH conversion reaction (64.7%) and improved cycling stability. This new iron redox chemistry was validated by operando X-ray diffraction, electrochemical testing, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) analysis, scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy (STEM-EDS) mapping, and molecular dynamics (MD) simulations. Our study provides new insight into designing LDH materials for high-capacity alkaline iron batteries.

Highlights from 2023 and Chemistry of Materials’ 35th Year

“…They were also the subject of the journal’s 2023 best paper award ( Devil is in the Defects: Electronic Conductivity in Solid Electrolytes by Canepa and collaborators) and are represented well here, with four papers making our list. The first two are studies of Ni-containing lithium transition metal oxides, important cathode materials, wherein in situ methods identified their formation pathways from hydroxide precursors and operando muon spectroscopy probed lithium-ion diffusion at the Å-length scale. , A suite of analytical methods and simulations were also used to study chloride insertion into iron hydroxide double-layer hydroxide, aiding in the design of layered double hydroxide materials for high-capacity alkaline iron batteries . Rounding out this topic is the study of divalent closo- type complex hydrides as electrolytes that seek to move the community beyond lithium battery electrolytes …”