The Role of Air–Electrode Structure on the Incorporation of Immiscible PFCs in Nonaqueous Li–O₂ Battery

Perfluorocarbons (PFCs) are considered advantageous additives to nonaqueous Li–O₂ battery due to their superior oxygen solubility and diffusivity compared to common battery electrolytes. Up to now, the main focus was concentrated on PFCs–electrolyte investigation; however, no special attention was granted to the role of carbon structure in the PFCs–Li–O₂ system. In our current research, immiscible PFCs, rather than miscible fluorinated ethers, were added to activated carbon class air electrode due to their higher susceptibility toward O₂^•– attack and to their ability to shift the reaction from two-phase to an artificial three-phase reaction zone. The results showed superior battery performance upon PFCs addition at lower current density (0.05 mA cm^–2) but unexpectedly failed to do so at higher current density (0.1 and 0.2 mA cm^–2), where oxygen transport limitation is best illustrated. The last was a direct result of liquid–liquid displacement phenomenon occurring when the two immiscible liquids were introduced into the porous carbon medium. The investigation and role of carbon structure on the mechanism upon PFCs addition to Li–O₂ system are suggested based on electrochemical characterization, wettability behavior studies, and the physical adsorption technique. Finally, we suggest an optimum air–electrode structure enabling the incorporation of immiscible PFCs in a nonaqueous Li–O₂ battery

Investigation of Rechargeable Poly(ethylene oxide)-Based Solid Lithium–Oxygen Batteries

Liquid-free solid polymer electrolyte (SPE) Li–O₂ batteries are considered advantageous power sources for multiple applications, albeit their cycle performance is far from being acceptable. A most challenging SPE stability in Li–O₂ battery operating at 80 °C is described here, presenting possible directions for this battery type future development. Hereby, we investigated poly­(ethylene oxide) (PEO) stability in Li–O₂ batteries after cycling and determined that the polymer instability is originated from an accumulation of formate-based species, which required high decomposition potential and showed low decomposition efficiency. This poses a key challenging issue of unfavorable round-trip efficiency, dictating a poor cycle performance

PFC and Triglyme for Li–Air Batteries: A Molecular Dynamics Study

In this work, we present an all-atom molecular dynamics (MD) study of triglyme and perfluorinated carbons (PFCs) using classical atomistic force fields. Triglyme is a typical solvent used in nonaqueous Li–air battery cells. PFCs were recently reported to increase oxygen availability in such cells. We show that O₂ diffusion in two specific PFC molecules (C₆F₁₄ and C₈F₁₈) is significantly faster than in triglyme. Furthermore, by starting with two very different initial configurations for our MD simulation, we demonstrate that C₈F₁₈ and triglyme do not mix. The mutual solubility of these molecules is evaluated both theoretically and experimentally, and a qualitative agreement is found. Finally, we show that the solubility of O₂ in C₈F₁₈ is considerably higher than in triglyme. The significance of these results to Li–air batteries is discussed

Comprehensive Route to the Formation of Alloy Interface in Core/Shell Colloidal Quantum Dots

The electronic properties of colloidal quantum dots (CQDs) have shown intriguing potential in recent years for implementation in various optoelectronic applications. However, their chemical and photochemical stabilities, mainly derived from surface properties, have remained a major concern. This paper reports a new strategic route for the synthesis of surface-treated CQDs, the CdSe/CdS core/shell heterostructures, based on low-temperature coating of a shell constituent, followed by a programmed annealing process. A comprehensive follow-up of the stability and the optical properties through the various synthesis stages is reported, suggesting that the low-temperature coating is responsible for the formation of a sharp interface between the core and the shell, whereas a postcoating annealing process leads to the generation of a thin alloy interfacial layer. At the end of the process, the CdSe/CdS CQDs show a significant improvement of the photoluminescence quantum yield, as well as an exceptional photostability. Consequently, the work reported here provides a convenient generic route to the formation of core/shell CQDs to be employed as a procedure for achieving various other heterostructures