Sergei A. Ivanov

Iron metal has attracted great interest as an anode material for the development of aqueous rechargeable batteries due to its huge abundance in the earth's crust, offering significantly lower cost per cell. However, the intractable side reactions at the negative iron anode and parasitic hydrogen evolution in aqueous media hamper the technology being unattainable for practical evaluations. Herein, we demonstrate a nonaqueous, eutectic electrolyte based on triethylamine hydrochloride ((Et3NH)Cl) and FeCl3 as an efficient electrolyte for the application of rechargeable iron batteries (RIBs). The eutectic formation is achieved by dual intermolecular interactions, namely, Lewis acid-base interactions and hydrogen bonding, resulting in hybrid organic-inorganic active ionic complex species. The optimized eutectic electrolyte offers appreciably high ionic conductivity (similar to 1.2 mS cm(-1)) at room temperature, high plating and stripping efficiency (similar to 100%), a long cycling stability of congruent to 400 h in a symmetric iron cell, and a wide operating potential window (similar to 2.5 V on Mo or carbon-coat Al). Differential scanning calorimetry (DSC) reveals that the electrolyte renders the liquid phase at -11 degrees C. A hydrothermally synthesized V2O5 nanowire cathode paired against an iron anode in the optimized eutectic electrolyte renders a good capacity of similar to 140 mAh g(-1) at a current density of 10 mA g(-1). The charge storage mechanism of the cell is thoroughly investigated by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction on the galvanostatically cycled electrodes. The addition of AlCl3 extends the electrolyte stability window to 3.2 V on SS, resulting in enhanced cell performance that maintains stability for >100 cycles. This work introduces a eutectic electrolyte class that can enable safe RIBs at low-cost and a wide operating potential window.

Charged excited states can accumulate on the surface of colloidal quantum dots (QDs), affecting their optoelectronic properties. In experimental samples, QDs often have non-stoichiometric structures, giving rise to cation-rich and anion-rich nanostructures. We explore the effect of charge on the ground- and excited-state properties of CdSe non-stoichiometric QDs (NS-QDs) of similar to 1.5 nm in size using density functional theory calculations. We compare two cases: (i) NS-QDs with a charge introduced by direct hole or electron injection and (ii) neutral NS-QDs with one removed surface ligand (with a dangling bond). Our calculations reveal that a neutral dangling bond has an effect on the electronic structure similar to that of the electron injection for the Cd-rich NS-QDs or hole injection for the Se-rich NS-QDs. In Cd-rich structures, either the injection of an electron or the removal of a passivating ligand results in the surface-localized half-filled trap state inside the energy gap. For Se-rich structures, either the injection of a hole or the removal of a ligand introduces surface-localized unoccupied trap states inside the energy gap. As a result, the charge localization formed by these two approaches leads to an appearance of low-energy electronic transitions strongly red-shifted from the main excitonic band of NS-QDs. These transitions related to a negative charge or a dangling bond exhibit weak optical activity in Cd-rich NS-QDs. Transitions related to a positive charge or a dangling bond are optically forbidden in Se-rich NS-QDs. In contrast, electron injection in Se-rich NS-QDs strongly increases the optical activity of the lowest-red-shifted charge-originated states.

We have successfully synthesized near-infrared photoluminescent erbium-doped lithium yttrium fluoride nanocrystals using a facile coprecipitation approach. The nanocrystals are capped with oleic acid, enabling dispersion in nonpolar solvents such as toluene and cyclohexane. The relative amounts of yttrium and erbium precursors were adjusted during the synthesis to obtain different concentrations of Er between 1% and 15%. The composition and structure of the nanocrystals were studied via X-ray fluorescence spectroscopy and X-ray powder diffraction. The nanocrystals were optically characterized by extensive photoluminescence studies, including Stokes and anti-Stokes emission. When excited with 1.55-mu m light, the nanocrystals displayed strong anti-Stokes emission associated with the I-4(13/2) -> I-4(15/2) transition. These nanocrystals therefore have a high potential to be used in optical cooling applications with telecommunication-wavelength excitation.

Lithium-ion batteries are widely used in applications from consumer electronic devices to stationary energy storage. Appropriate management of batteries is challenging due to limited data on their performance and materials degradation. Previous studies have focused on characterization of single cells under specific operating conditions. In the present work, commercial 18650 lithium-ion cells with LiNixMnyCo1-x-yO2 (NMC) and LiNixCoyAl1-x-yO2 (NCA) positive electrodes were characterized by a wide range of electrochemical and materials techniques after cycling at 15, 25, or 35 degrees C to similar to 80% capacity. The NCA cells exhibit weak temperature dependence in their cycle aging and materials degradation. The NMC cells exhibited increased capacity fade and materials degradation as ambient temperature decreased. All cells exhibited loss of lithium inventory as their primary degradation mode. However, the NCA cells only showed evidence of solid electrolyte interphase (SEI) growth whereas the NMC cells showed signs of Li plating at 15 degrees C, transitioning to SEI growth at 35 degrees C. The NMC cells displayed signs of loss of active material at the positive electrode at lower temperatures, suggesting that Li plating is correlated to additional processes that increase the rate of degradation. These results highlight the importance of avoiding broad generalizations about Li-ion battery temperature dependence.

"Giant" or core/thick-shell quantum dots (gQDs) are an important class of solid-state quantum emitter characterized by strongly suppressed blinking and photobleaching under ambient conditions, and reduced nonradiative Auger processes. Together, these qualities provide distinguishing and useful functionality as single- and ensemble-photon sources. For many applications, operation at elevated temperatures and under intense photon flux is desired, but performance is strongly dependent on the synthetic method employed for thick-shell growth. Here, a comprehensive analysis of gQD structural properties "from the inside out" as a function of shell-growth method is reported: successive ionic layer adsorption and reaction (SILAR) and high-temperature continuous injection (HT-CI), or sequential combinations of the two. Key correlations across synthesis methods, structural features (interfacial alloying, stacking-fault density and surface-ligand identity), and performance metrics (quantum yield, single-gQD photoluminescence under thermal/photo stress, charging behavior and quantum-optical properties) are identified. Surprisingly, it is found that interfacial alloying is the strongest indicator of gQD stability under stress, but this parameter is not the determining factor for Auger suppression. Furthermore, quantum yield is strongly influenced by surface chemistry and can approach unity even in the case of high shell-defect density, while introduction of zinc-blende stacking faults increases the likelihood that a gQD exhibits charged-state emission. The functionally unique "giant" quantum dot-a nonblinking and nonphotobleaching room-temperature photon source-is the subject of numerous investigations of its optical properties and application demonstrations from 3D single-molecule tracking to light-emitting diodes. In this work, explicit synthesis-structure-function correlations are revealed as a blueprint for designing syntheses to produce nanoscale structures for long-term stability under harsh operating conditions of high-temperature and photon flux.image (c) 2023 WILEY-VCH GmbH