Ceria-Spiderweb Nanosheets Unlock the Energy-Storage Properties in the “Sleeping” Triplite (Mn₂(PO₄)F)

Abstract

Rechargeable aqueous mobile-ion batteries (RAMIBs) are attractive next-generation battery technologies. Manganese fluorophosphate (triplite), Mn 2 (PO 4 )F (MFP), and its ceria-and carbon-coated composites (i.e., MFP-CeO 2 and MFP-C-CeO 2 ), have been synthesized using a microwave-assisted hydrothermal process. The materials are thoroughly characterized using powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, high-resolution scanning electron microscopy (field-emission scanning electron microscopy), and energy-dispersive X-ray spectroscopy elemental mapping to prove the successful synthesis of the materials and confirm their morphologies and elemental compositions. These materials have been used to introduce environmentally friendly and low-cost ceria-enabled rechargeable aqueous sodium-ion batteries (CERASIBs) using zinc foil as the anode and sodium perchlorate as the "water-in-salt" electrolyte. The batteries offer a high voltage window (1.6−2.2 V), with MFP-C-CeO 2 giving a higher specific capacity of ∼195 mAh g −1 than MFP-CeO 2 (∼100 mAh g −1 ). However, MFP-CeO 2 showed excellent cycling stability (ca. 99% capacity retention) compared to MFP-C-CeO 2 (ca. 78% capacity retention) after 300 cycles due to the impressive structural stability of the MFP material, aided by the ceria coating. The difference in the electrochemical properties of the two materials is related to their different morphologies: the MPF-CeO 2 material comprises micron-sized particles that consist of aggregated nanoparticles, while the MPF-C-CeO 2 material exhibits mostly a nanoporous structure. The remarkable properties of the CERASIB promise to open doors of opportunities for the design and manufacturing of various lanthanoid-or rare-earth metal compound-enabled triplite-based cathode materials for the large-scale development of affordable RAMIBs involving various mobile ions (such as Na, Li, K, Zn, Mg, and Al) and accompanying zinc anode materials. KEYWORDS: triplite, manganese fluorophosphate (Mn 2 (PO 4 )F), ceria (CeO 2 ) coating, microwave-assisted synthesis, water-in-salt electrolyte, aqueous sodium-ion batteries, energy storage

Advances in Mn-Based Electrode Materials for Aqueous Sodium-Ion Batteries

“…Charge–discharge curves at different current density of g MPF electrode, h MPF-CeO 2 electrode and i MPF-C-CeO 2 electrode. Cycling performance at 359.25 mA g − 1 of j MPF-CeO 2 electrode and k MPF-C-CeO 2 electrode [ 137 ]. Copyright 2021, American Chemical Society …”

“…Fluorophosphates, Mn 2 (PO 4 )F (MFP), as cathode material was reported by Nzimande et al [ 137 ]. MFP, ceria-coated MFP (MFP-CeO 2 ) and ceria- and carbon-coated MFP (MFP-C-CeO 2 ) were synthesized by microwave-assisted hydrothermal process.…”

“…For Mn-based polyanion compounds, their inferior electronic conductivity leads to low electrochemical performance. Surface-coating should be an effective way to enhance the electrochemical performance of Mn-based polyanion compounds [ 137 ]. Much attention should be devoted to these improvement strategies, which are related to material synthesis.…”