Exploring the electrochemical properties and lithium insertion mechanisms in akaganeite (β-FeOOH) – a combined DFT/experimental study

Abstract

Akaganeite (β-FeOOH) has been intensely investigated to be used in different electrochemical applications as a cathode material in Li-ion batteries owing to its unique structural characteristics, including channels capable of accommodating and reversibly extracting charged species such as lithium or sodium ions. We revisited the synthesis, and its electrochemical properties based on a combined experimental/theoretical approach aiming to understand the mechanism of the electron transfer in this material. Electrochemical investigations, employing Li₂SO₄ aqueous electrolyte, unveiled notable alterations in the charge/discharge profiles. The initial discharge curve revealed distinct plateaus at 3.4 V and 2.9 V, with the absence of the former in subsequent cycles, indicating irreversible reactions in the initial cycle. Furthermore, density functional theory (DFT) calculations were employed to elucidate the impact of lithium atom insertion on the electronic and structural properties of akaganeite. We gained insights into the underlying electrochemical processes calculating band structures, density of states, and topological analysis based on Bader's theory. The calculated oxidation potentials (3.2 V) closely matched experimental observations, attributing the 3.2 V plateau to lithium insertion into the akaganeite structure.