Quasi-2D Bi0.775Ln0.225O1.5 (Ln = La, Pr, Nd, Sm, Eu): reversible iodine intercalation and their evaluation as the anode in the lithium-ion battery system

Abstract

Layered materials with a robust structure and reversible intercalation behavior are highly sought-after in applications involving energy conversion and storage systems, energy converting devices, supercapacitors, batteries, superconductors, photonic materials, and catalysis involving hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), solar cells and sensors. In the current study, quasi-2D rhombohedral Bi_0.775Ln_0.225O_1.5 (Ln = La, Pr, Nd, Sm, and Eu) samples, synthesized by a solution combustion route, have been demonstrated to intercalate iodine reversibly. A solid–vapor reaction was employed to intercalate iodine at moderate temperatures, and deintercalation occurred on heating at higher temperatures. Expansion of the rhombohedral c-axis by ∼10 Å occurred, and the iodine between the interlayers existed as triiodide ions (I₃⁻) in an unsymmetrical fashion. The amount of intercalated iodide has been determined from thermogravimetric analysis. Electron microscopic analysis confirmed these systems’ intercalation and subsequent lattice expansion. In the diffuse reflectance spectra, charge transfer from the triiodide ions to the host oxide was noticed, and it caused the absorption edge to fall beyond the visible region for the intercalated samples. XPS analysis of iodine intercalated Bi_0.775Pr_0.225O_1.5 has shown the mixed valence states for Pr and the existence of I₃⁻ along with some IO₃⁻ species. The quasi-2D structure was stable during the thermal deintercalation process. The evaluation of iodine intercalated Bi_0.775Ln_0.225O_1.5 (Ln = La, Pr, Nd, Sm, and Eu) samples as anode material in the lithium-ion battery system has given quite promising results, exhibiting fast Li⁺-ion diffusion, low charge transfer resistance, good reversible capacity, capacity retention (after cycling back to 10 mA g⁻¹), and structural stability (after long cycles).