Showing papers on "Ion published in 2017"
TL;DR: Here, cationic control of the interlayer spacing of graphene oxide membranes with ångström precision is demonstrated using K+, Na+, Ca2+, Li+ or Mg2+ ions, suggesting that other ions could be used to produce a wider range of interlayer spacings.
Abstract: Graphene oxide membranes-partially oxidized, stacked sheets of graphene-can provide ultrathin, high-flux and energy-efficient membranes for precise ionic and molecular sieving in aqueous solution. These materials have shown potential in a variety of applications, including water desalination and purification, gas and ion separation, biosensors, proton conductors, lithium-based batteries and super-capacitors. Unlike the pores of carbon nanotube membranes, which have fixed sizes, the pores of graphene oxide membranes-that is, the interlayer spacing between graphene oxide sheets (a sheet is a single flake inside the membrane)-are of variable size. Furthermore, it is difficult to reduce the interlayer spacing sufficiently to exclude small ions and to maintain this spacing against the tendency of graphene oxide membranes to swell when immersed in aqueous solution. These challenges hinder the potential ion filtration applications of graphene oxide membranes. Here we demonstrate cationic control of the interlayer spacing of graphene oxide membranes with angstrom precision using K+, Na+, Ca2+, Li+ or Mg2+ ions. Moreover, membrane spacings controlled by one type of cation can efficiently and selectively exclude other cations that have larger hydrated volumes. First-principles calculations and ultraviolet absorption spectroscopy reveal that the location of the most stable cation adsorption is where oxide groups and aromatic rings coexist. Previous density functional theory computations show that other cations (Fe2+, Co2+, Cu2+, Cd2+, Cr2+ and Pb2+) should have a much stronger cation-π interaction with the graphene sheet than Na+ has, suggesting that other ions could be used to produce a wider range of interlayer spacings.
1,082 citations
TL;DR: It is demonstrated that under reaction conditions, mobilized Cu ions can travel through zeolite windows and form transient ion pairs that participate in an oxygen (O2)–mediated CuI→CuII redox step integral to SCR.
Abstract: Copper ions exchanged into zeolites are active for the selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with ammonia (NH3), but the low-temperature rate dependence on copper (Cu) volumetric density is inconsistent with reaction at single sites. We combine steady-state and transient kinetic measurements, x-ray absorption spectroscopy, and first-principles calculations to demonstrate that under reaction conditions, mobilized Cu ions can travel through zeolite windows and form transient ion pairs that participate in an oxygen (O2)-mediated CuI→CuII redox step integral to SCR. Electrostatic tethering to framework aluminum centers limits the volume that each ion can explore and thus its capacity to form an ion pair. The dynamic, reversible formation of multinuclear sites from mobilized single atoms represents a distinct phenomenon that falls outside the conventional boundaries of a heterogeneous or homogeneous catalyst.
594 citations
TL;DR: Using ab initio modelling, it is shown that fast diffusion in super-ionic conductors does not occur through isolated ion hopping as is typical in solids, but instead proceeds through concerted migrations of multiple ions with low energy barriers.
Abstract: Ab initio atomistic modelling reveals that fast ion diffusion in super-ionic conductors is mediated by concerted migration of multiple ions. On the basis of this understanding, a universal strategy for designing fast ion conductors is proposed and demonstrated.…
528 citations
TL;DR: These results show that the lattice softness has a striking influence on the ionic transport: the softer bonds lower the activation barrier and simultaneously decrease the prefactor of the moving ion.
Abstract: In the search for novel solid electrolytes for solid-state batteries, thiophosphate ionic conductors have been in recent focus owing to their high ionic conductivities, which are believed to stem from a softer, more polarizable anion framework. Inspired by the oft-cited connection between a soft anion lattice and ionic transport, this work aims to provide evidence on how changing the polarizability of the anion sublattice in one structure affects ionic transport. Here, we systematically alter the anion framework polarizability of the superionic argyrodites Li6PS5X by controlling the fractional occupancy of the halide anions (X = Cl, Br, I). Ultrasonic speed of sound measurements are used to quantify the variation in the lattice stiffness and Debye frequencies. In combination with electrochemical impedance spectroscopy and neutron diffraction, these results show that the lattice softness has a striking influence on the ionic transport: the softer bonds lower the activation barrier and simultaneously decrea...
413 citations
TL;DR: In this article, a 2D-material-based nanofluidic reverse electrodialysis system, containing cascading lamellar nanochannels in oppositely charged graphene oxide membrane (GOM) pairs, is reported for efficient osmotic energy conversion.
Abstract: In nature, hierarchically assembled nanoscale ionic conductors, such as ion channels and ion pumps, become the structural and functional basis of bioelectric phenomena Recently, ion-channel-mimetic nanofluidic systems have been built into reconstructed 2D nanomaterials for energy conversion and storage as effective as the electrogenic cells Here, a 2D-material-based nanofluidic reverse electrodialysis system, containing cascading lamellar nanochannels in oppositely charged graphene oxide membrane (GOM) pairs, is reported for efficient osmotic energy conversion Through preassembly modification, the surface charge polarity of the 2D nanochannels can be efficiently tuned from negative (−123 mC m−2) to positive (+147 mC m−2), yielding strongly cation- or anion-selective GOMs The complementary two-way ion diffusion leads to an efficient charge separation process, creating superposed electrochemical potential difference and ionic flux An output power density of 077 W m−2 is achieved by controlled mixing concentrated (05 m) and diluted ionic solutions (001 m), which is about 54% higher than using commercial ion exchange membranes Tandem alternating GOM pairs produce high voltage up to 27 V to power electronic devices Besides simple salt solutions, various complex electrolyte solutions can be used as energy sources These findings provide insights to construct cascading nanofluidic circuits for energy, environmental, and healthcare applications
300 citations
TL;DR: In this paper, the authors use in situ pulsed field gradient NMR spectroscopy to measure ionic diffusion in supercapacitors directly and find that confinement in the nanoporous electrode structures decreases the effective self-diffusion coefficients of ions by over two orders of magnitude compared with neat electrolyte, and in pore diffusion is modulated by changes in ion populations at the electrode/electrolyte interface during charging.
Abstract: Ionic transport inside porous carbon electrodes underpins the storage of energy in supercapacitors and the rate at which they can charge and discharge, yet few studies have elucidated the materials properties that influence ion dynamics. Here we use in situ pulsed field gradient NMR spectroscopy to measure ionic diffusion in supercapacitors directly. We find that confinement in the nanoporous electrode structures decreases the effective self-diffusion coefficients of ions by over two orders of magnitude compared with neat electrolyte, and in-pore diffusion is modulated by changes in ion populations at the electrode/electrolyte interface during charging. Electrolyte concentration and carbon pore size distributions also affect in-pore diffusion and the movement of ions in and out of the nanopores. In light of our findings we propose that controlling the charging mechanism may allow the tuning of the energy and power performances of supercapacitors for a range of different applications. It is challenging to probe ion dynamics in supercapacitor electrodes, which has significant implications in optimizing their performance. Here, the authors develop in situ diffusion NMR spectroscopy to measure and illustrate the diffusion of the charge-storing ions in working supercapacitors.
278 citations
TL;DR: It is shown that a NaBr enriched solid–electrolyte interphase can lower the surface diffusion barrier for sodium ions, enabling stable electrodeposition, and this prediction is evaluated by means of electrochemical measurements and direct visualization studies.
Abstract: Secondary batteries based on earth-abundant sodium metal anodes are desirable for both stationary and portable electrical energy storage. Room-temperature sodium metal batteries are impractical today because morphological instability during recharge drives rough, dendritic electrodeposition. Chemical instability of liquid electrolytes also leads to premature cell failure as a result of parasitic reactions with the anode. Here we use joint density-functional theoretical analysis to show that the surface diffusion barrier for sodium ion transport is a sensitive function of the chemistry of solid–electrolyte interphase. In particular, we find that a sodium bromide interphase presents an exceptionally low energy barrier to ion transport, comparable to that of metallic magnesium. We evaluate this prediction by means of electrochemical measurements and direct visualization studies. These experiments reveal an approximately three-fold reduction in activation energy for ion transport at a sodium bromide interphase. Direct visualization of sodium electrodeposition confirms large improvements in stability of sodium deposition at sodium bromide-rich interphases. The chemistry at the interface between electrolyte and electrode plays a critical role in determining battery performance. Here, the authors show that a NaBr enriched solid–electrolyte interphase can lower the surface diffusion barrier for sodium ions, enabling stable electrodeposition.
271 citations
265 citations
TL;DR: In this paper, the authors investigated the interactions between K ions and organic electrolyte solvents for application in nonaqueous K-ion batteries, which have recently drawn interest as novel rechargeable batteries.
Abstract: Ion–solvent interactions play a crucial role in secondary battery systems: the desolvation of ions at an electrode/electrolyte interface can be the rate-determining step of a battery reaction, for instance. The present theoretical study investigates the interactions between K ions and organic electrolyte solvents for application in non-aqueous K-ion batteries, which have recently drawn interest as novel rechargeable batteries. Compared to Li, Na, and Mg ions, K ions display the lowest interaction energy, reflecting the large ionic radius and weak Lewis acidity of K. The weak interaction of K ions with solvents is consistent with the high rate capability exhibited by K-ion batteries and the relatively low solubility of K-ion salts observed experimentally.
248 citations
TL;DR: In this article, the metallic 1T MoS2 sandwich grown on graphene tube was used as a freestanding intercalation anode for promising sodium-ion batteries (SIBs).
Abstract: This work studies for the first time the metallic 1T MoS2 sandwich grown on graphene tube as a freestanding intercalation anode for promising sodium-ion batteries (SIBs). Sodium is earth-abundant and readily accessible. Compared to lithium, the main challenge of sodium-ion batteries is its sluggish ion diffusion kinetic. The freestanding, porous, hollow structure of the electrode allows maximum electrolyte accessibility to benefit the transportation of Na+ ions. Meanwhile, the metallic MoS2 provides excellent electron conductivity. The obtained 1T MoS2 electrode exhibits excellent electrochemical performance: a high reversible capacity of 313 mAh g−1 at a current density of 0.05 A g−1 after 200 cycles and a high rate capability of 175 mAh g−1 at 2 A g−1. The underlying mechanism of high rate performance of 1T MoS2 for SIBs is the high electrical conductivity and excellent ion accessibility. This study sheds light on using the 1T MoS2 as a novel anode for SIBs.
241 citations
TL;DR: In this paper, the elementary composition and crystal structure of P2-Na0.67O2 powders were studied in detail using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and X-ray diffraction (XRD).
Abstract: P2-Na0.67Ni0.33−x Cu
x
Mn0.67O2 (x = 0, 0.02, 0.04, 0.06, 0.08) cathode materials have been synthesized via acetate decomposition method. The elementary composition and crystal structure of the powders are studied in detail using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and X-ray diffraction (XRD). XRD results demonstrate that Cu2+ ions have been incorporated into the crystal structure successfully and the P2-type structure remains unchanged after substitution. According to XPS data, Cu substitution does not change the valence states of Ni and Mn, whose predominant oxidation states in Na-Ni-Mn-O structure remains +2 and +4. The introduction of Cu2+ can effectively suppress P2-O2 phase transformation when charging to 4.5 V, and significantly improve rate performance and cyclic stability compared to the undoped material. The P2-Na0.67Ni0.27Cu0.06Mn0.67O2 sample can deliver an initial discharge capacity of 211.6 mAh g−1 at 10 mAh g−1 between 1.5 and 4.5 V, and a capacity retention of 93.9% after 10 cycles. Moreover, it can also deliver a discharge capacity of 115.2 mAh g−1 at 100 mAh g−1. In addition, electrochemical impedance spectroscopy (EIS) reveals that P2-Na0.67Ni0.27Cu0.06Mn0.67O2 cathode exhibits a higher electronic conductivity and faster sodium ion diffusion velocity than that of undoped sample. These results show that P2-Na0.67Ni0.27Cu0.06Mn0.67O2 is a promising high-voltage cathode material for sodium-ion batteries.
TL;DR: It is shown that the output of triboelectric nanogenerators (TENGs) can quantitatively control the total ionization charges in mass spectrometry, and that native protein conformation is conserved in TENG-ESI.
Abstract: Ion sources for molecular mass spectrometry are usually driven by direct current power supplies with no user control over the total charges generated. Here, we show that the output of triboelectric nanogenerators (TENGs) can quantitatively control the total ionization charges in mass spectrometry. The high output voltage of TENGs can generate single- or alternating-polarity ion pulses, and is ideal for inducing nanoelectrospray ionization (nanoESI) and plasma discharge ionization. For a given nanoESI emitter, accurately controlled ion pulses ranging from 1.0 to 5.5 nC were delivered with an onset charge of 1.0 nC. Spray pulses can be generated at a high frequency of 17 Hz (60 ms in period) and the pulse duration is adjustable on-demand between 60 ms and 5.5 s. Highly sensitive (∼0.6 zeptomole) mass spectrometry analysis using minimal sample (18 pl per pulse) was achieved with a 10 pg ml−1 cocaine sample. We also show that native protein conformation is conserved in TENG-ESI, and that patterned ion deposition on conductive and insulating surfaces is possible. The high output voltage of triboelectric nanogenerators enables well-controlled ion pulses for nanoelectrospray molecular mass spectrometry and surface modification.
TL;DR: Iodine ions are unambiguously shown to be the mobile species in CH3NH3PbI3, with iodine vacancies shown to represent the mechanistic centers under equilibrium conditions, and local variations of the iodine stoichiometry may be fast and enable light effects on ion transport.
Abstract: By applying a multitude of experimental techniques including 1 H, 14 N, 207 Pb NMR and 127 I NMR/NQR, tracer diffusion, reaction cell and doping experiments, as well as stoichiometric variation, conductivity, and polarization experiments, iodine ions are unambiguously shown to be the mobile species in CH3 NH3 PbI3 , with iodine vacancies shown to represent the mechanistic centers under equilibrium conditions Pb2+ and CH3 NH3+ ions do not significantly contribute to the long range transport (upper limits for their contributions are given), whereby the latter exhibit substantial local motion The decisive electronic contribution to the mixed conductivity in the experimental window stems from electron holes As holes can be associated with iodine orbitals, local variations of the iodine stoichiometry may be fast and enable light effects on ion transport
TL;DR: It is shown that Coulombic ordering reduces when the pores can only accommodate a single layer of ions, and equally-charged ion pairs are formed due to the induction of an electric potential of opposite sign in the carbon pore walls.
Abstract: Ionic liquids are composed of equal quantities of positive and negative ions. In the bulk, electrical neutrality occurs in these liquids due to Coulombic ordering, in which ion shells of alternating charge form around a central ion. Their structure under confinement is far less well understood. This hinders the widespread application of ionic liquids in technological applications. Here we use scattering experiments to resolve the structure of a widely used ionic liquid (EMI–TFSI) when it is confined inside nanoporous carbons. We show that Coulombic ordering reduces when the pores can accommodate only a single layer of ions. Instead, equally charged ion pairs are formed due to the induction of an electric potential of opposite sign in the carbon pore walls. This non-Coulombic ordering is further enhanced in the presence of an applied external electric potential. This finding opens the door for the design of better materials for electrochemical applications.
TL;DR: In this paper, an efficient activated carbon was prepared using palm oil mill effluent as a precursor, and the adsorption capacity of activated carbon for lead ion and zinc ion from aqueous media was investigated under equilibrium conditions between 303.15 and 353.15 K.
TL;DR: It is shown that ions can quickly pass through interlayer spaces in hydrated boron nitride (BN) membranes and remain fully functional at temperatures up to 90 °C, which makes the BN ionic conduits attractive for applications in nanofluidic devices and membrane separation.
Abstract: Achieving a high rate of ionic transport through porous membranes and ionic channels is important in numerous applications ranging from energy storage to water desalination, but it still remains a challenge. Herein we show that ions can quickly pass through interlayer spaces in hydrated boron nitride (BN) membranes. Measurements of surface-charge governed ionic currents between BN nanosheets in a variety of salt solutions (KCl, NaCl and CaCl2) at low salt concentrations (<10–4 M) showed several orders of magnitude higher ionic conductivity compared to that of the bulk solution. Moreover, due to the outstanding chemical and thermal stability of BN, the ionic conduits remain fully functional at temperatures up to 90 °C. The BN conduits can operate in acidic and basic environments and do not degrade after immersing in solutions with extreme pH (pH ∼ 0 or 14) for 1 week. Those excellent properties make the BN ionic conduits attractive for applications in nanofluidic devices and membrane separation.
TL;DR: In this article, the ability of argon cluster ions (Arn+) to etch metal oxides and other technologically important inorganic compounds has been reported, but no depth profiles have previously been reported.
TL;DR: In this article, a high performance anode material, MnNCN, is synthesized through a facile and low-cost method, and the relationship between electrochemical properties and chemical composition is explored on the scientific considerations that can provide an insight on designing expected materials.
Abstract: A high-performance anode material, MnNCN, is synthesized through a facile and low-cost method. The relationship between electrochemical properties and chemical composition is explored on the scientific considerations that can provide an insight on designing expected materials. MnNCN with the long bonding length of 2.262 A in MnN and weak electronegativity of 3.04 Pauling units in N leads to a lower charge/discharge potential than that of MnO owing to the character of chemical bonds transformed to covalent dominating from ionic dominating in MnO. Covalent character increases the ratio of sharing electrons that decreases the migration energy of electrons in electrochemical reaction, which enhances the reactive reversibility and stability of electrode material. MnNCN delivered a reversibly specific capacity of 385 mA h g−1 at 5 A g−1 in a Li-ion half cell. Besides, a Li-ion hybrid capacitor with a high voltage of 4 V presents energy and power densities of respective 103 Wh kg−1 and 8533 W kg−1 and cycles at 5 A g−1 without detectable degradation after 5000 cycles.
TL;DR: Endohedral metallofullerenes Y2@C80 and Dy2@ C80 are obtained in the form of air-stable benzyl monoadducts, both of which feature an unpaired electron trapped between metal ions, thus forming a single-electron metal-metal bond.
Abstract: Increasing the temperature at which molecules behave as single-molecule magnets is a serious challenge in molecular magnetism. One of the ways to address this problem is to create the molecules with strongly coupled lanthanide ions. In this work, endohedral metallofullerenes Y2@C80 and Dy2@C80 are obtained in the form of air-stable benzyl monoadducts. Both feature an unpaired electron trapped between metal ions, thus forming a single-electron metal-metal bond. Giant exchange interactions between lanthanide ions and the unpaired electron result in single-molecule magnetism of Dy2@C80(CH2Ph) with a record-high 100 s blocking temperature of 18 K. All magnetic moments in Dy2@C80(CH2Ph) are parallel and couple ferromagnetically to form a single spin unit of 21 μB with a dysprosium-electron exchange constant of 32 cm−1. The barrier of the magnetization reversal of 613 K is assigned to the state in which the spin of one Dy centre is flipped. Single molecule magnets have demonstrated promise for information storage, molecular spintronics and quantum computing, but are limited by their low operational temperatures. Here, Popov and coworkers prepare a SMM with a high blocking temperature of 18 K by trapping two lanthanide ions with a single-electron bond inside a fullerene.
TL;DR: The charge-selectivity allows us to rationally design membranes with increased ionic rejection and opens up the field of ion exchange and electrodialysis to the GO membranes.
Abstract: Nanostructured graphene-oxide (GO) laminate membranes, exhibiting ultrahigh water flux, are excellent candidates for next generation nanofiltration and desalination membranes, provided the ionic rejection could be further increased without compromising the water flux. Using microscopic drift–diffusion experiments, we demonstrated the ultrahigh charge selectivity for GO membranes, with more than order of magnitude difference in the permeabilities of cationic and anionic species of equivalent hydration radii. Measuring diffusion of a wide range of ions of different size and charge, we were able to clearly disentangle different physical mechanisms contributing to the ionic sieving in GO membranes: electrostatic repulsion between ions and charged chemical groups; and the compression of the ionic hydration shell within the membrane’s nanochannels, following the activated behavior. The charge-selectivity allows us to rationally design membranes with increased ionic rejection and opens up the field of ion exchan...
TL;DR: In this paper, the sodiation kinetics and phase evolution behavior of the van der Waals stacked Sb2S3 nanorods (SSNR/C) were unraveled by coupling in situ transmission electron microscopy analysis with first-principles calculations.
Abstract: Carbon-coated van der Waals stacked Sb2S3 nanorods (SSNR/C) are synthesized by facile hydrothermal growth as anodes for sodium ion batteries (SIBs). The sodiation kinetics and phase evolution behavior of the SSNR/C anode during the first and subsequent cycles are unraveled by coupling in situ transmission electron microscopy analysis with first-principles calculations. During the first sodiation process, Na+ ions intercalate into the Sb2S3 crystals with an ultrafast speed of 146 nm s−1. The resulting amorphous NaxSb2S3 intermediate phases undergo sequential conversion and alloying reactions to form crystalline Na2S, Na3Sb, and minor metallic Sb. Upon desodiation, Na+ ions extract from the nanocrystalline phases to leave behind the fully desodiated Sb2S3 in an amorphous state. Such unique phase evolution behavior gives rise to superb electrochemical performance and leads to an unexpectedly small volume expansion of ≈54%. The first-principles calculations reveal distinctive phase evolution arising from the synergy between the extremely low Na+ ion diffusion barrier of 190 meV and the sharply increased electronic conductivity upon the formation of amorphous NaxSb2S3 intermediate phases. These findings highlight an anomalous Na+ ion storage mechanism and shed new light on the development of high performance SIB anodes based on van der Waals crystals.
TL;DR: The methodology employed here utilizes the sodium super ion conductor type sodium iron phosphate wrapped with conducting carbon network to generate a stable Fe3+ /Fe4+ redox couple, thereby exhibiting higher operating voltage and energy density of sodium-ion batteries.
Abstract: The methodology employed here utilizes the sodium super ion conductor type sodium iron phosphate wrapped with conducting carbon network to generate a stable Fe3+ /Fe4+ redox couple, thereby exhibiting higher operating voltage and energy density of sodium-ion batteries. This new class of sodium iron phosphate wrapped by carbon also displays a cycling stability with >96% capacity retention after 200 cycles.
TL;DR: Evidence of oxygen ion migration and accumulation in HfO2 is shown by in situ measurements of electrostatic force gradient between the probe and the sample, as systematically verified by the charge duration, oxygen gas eruption and controlled studies utilizing different electrolytes, field directions and environments.
Abstract: Ion transport is an essential process for various applications including energy storage, sensing, display, memory and so on, however direct visualization of oxygen ion motion has been a challenging task, which lies in the fact that the normally used electron microscopy imaging mainly focuses on the mass attribute of ions. The lack of appropriate understandings and analytic approaches on oxygen ion motion has caused significant difficulties in disclosing the mechanism of oxides-based memristors. Here we show evidence of oxygen ion migration and accumulation in HfO2 by in situ measurements of electrostatic force gradient between the probe and the sample, as systematically verified by the charge duration, oxygen gas eruption and controlled studies utilizing different electrolytes, field directions and environments. At higher voltages, oxygen-deficient nano-filaments are formed, as directly identified employing a CS-corrected transmission electron microscope. This study could provide a generalized approach for probing ion motions at the nanoscale. Ion transport in solid-state materials is a fundamental process for many modern technologies. Utilizing electrostatic force microscopy, Yanget al. directly visualize ion motion and verify the oxygen ion dynamics within HfO2—a common metal-oxide based memristive material.
28 Apr 2017
TL;DR: In this paper, the authors study the production of defects in free-standing metal dichalcogenides (TMDs) under noble gas ion irradiation for a wide range of ion energies when nuclear stopping dominates, and assess the probabilities for different defects to appear.
Abstract: Two-dimensional (2D) transition metal dichalcogenides (TMDs), like MoS2, have unique electronic and optical properties, which can further be tuned using ion bombardment and post-synthesis ion-beam mediated methods combined with exposure of the irradiated sample to precursor gases. The optimization of these techniques requires a complete understanding of the response of 2D TMDs to ion irradiation, which is affected by the reduced dimensionality of the system. By combining analytical potential molecular dynamics with first-principles calculations, we study the production of defects in free-standing MoS2 sheets under noble gas ion irradiation for a wide range of ion energies when nuclear stopping dominates, and assess the probabilities for different defects to appear. We show that depending on the incident angle, ion type and energy, sulfur atoms can be sputtered away predominantly from the top or bottom layers, creating unique opportunities for engineering mixed MoSX compounds where X are chemical elements from group V or VII. We study the electronic structure of such systems, demonstrate that they can be metals, and finally discuss how metal/semiconductor/metal junctions, which exhibit negative differential resistance, can be designed using focused ion beams combined with the exposure of the system to fluorine.
TL;DR: In this article, the authors show that the photocurrent transients are reversed in sign (i.e. inverted), and the magnitude of the inverted transients can be used to find an upper bound on the width of the space charge layers adjacent to the electrodes.
Abstract: In Methyl Ammonium Lead Iodide (MAPI) perovskite solar cells, screening of the built-in field by mobile ions has been proposed as part of the cause of the large hysteresis observed in the current/voltage scans in many cells. We show that photocurrent transients measured immediately (e.g. 100 μs) after a voltage step can provide direct evidence that this field screening exists. Just after a step to forward bias, the photocurrent transients are reversed in sign (i.e. inverted), and the magnitude of the inverted transients can be used to find an upper bound on the width of the space charge layers adjacent to the electrodes. This in turn provides a lower bound on the mobile charge concentration, which we find to be ≳1 × 1017 cm−3. Using a new photocurrent transient experiment, we show that the space charge layer thickness remains approximately constant as a function of bias, as expected for mobile ions in a solid electrolyte. We also discuss additional characteristics of the inverted photocurrent transients that imply either an unusually stable deep trapping, or a photo effect on the mobile ion conductivity.
TL;DR: It is shown that crystalline 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), an organic solid, is highly amenable to host divalent metal ions, i.e., Mg2+ and Ca2+, in aqueous electrolytes, where the van der Waals structure is intrinsically superior in hosting charge-dense ions.
Abstract: We report that crystalline 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), an organic solid, is highly amenable to host divalent metal ions, i.e., Mg2+ and Ca2+, in aqueous electrolytes, where the van der Waals structure is intrinsically superior in hosting charge-dense ions. We observe that the divalent nature of Mg2+ causes unique squeezing deformation of the electrode structure, where it contracts and expands in different crystallographic directions when hosting the inserted Mg-ions. This phenomenon is revealed experimentally by ex situ X-ray diffraction and transmission electron microscopy, and is investigated theoretically by first-principles calculations. Interestingly, hosting one Mg2+ ion requires the coordination from three PTCDA molecules in adjacent columns of stacked molecules, which rotates the columns, thus reducing the (011) spacing but increasing the (021) spacing. We demonstrate that a PTCDA Mg-ion electrode delivers a reversible capacity of 125 mA h g–1, which may include a minor c...
TL;DR: Spectroscopic evidence demonstrate that the Li+ and Na+ cations share a number of similar ion-solvent interaction trends, such as a preference in the gas and liquid phase for a solvation shell rich in cyclic carbonates over linear carbonates and fluorinated carbonates.
Abstract: Sodium ion batteries are on the cusp of being a commercially available technology. Compared to lithium ion batteries, sodium ion batteries can potentially offer an attractive dollar-per-kilowatt-hour value, though at the penalty of reduced energy density. As a materials system, sodium ion batteries present a unique opportunity to apply lessons learned in the study of electrolytes for lithium ion batteries; specifically, the behavior of the sodium ion in an organic carbonate solution and the relationship of ion solvation with electrode surface passivation. In this work the Li+ and Na+-based solvates were characterized using electrospray mass spectrometry, infrared and Raman spectroscopy, 17O, 23Na and pulse field gradient double-stimulated-echo pulse sequence nuclear magnetic resonance (NMR), and conductivity measurements. Spectroscopic evidence demonstrate that the Li+ and Na+ cations share a number of similar ion–solvent interaction trends, such as a preference in the gas and liquid phase for a solvation shell rich in cyclic carbonates over linear carbonates and fluorinated carbonates. However, quite different IR spectra due to the PF6− anion interactions with the Na+ and Li+ cations were observed and were rationalized with the help of density functional theory (DFT) calculations that were also used to examine the relative free energies of solvates using cluster – continuum models. Ion–solvent distances for Na+ were longer than Li+, and Na+ had a greater tendency towards forming contact pairs compared to Li+ in linear carbonate solvents. In tests of hard carbon Na-ion batteries, performance was not well correlated to Na+ solvent preference, leading to the possibility that Na+ solvent preference may play a reduced role in the passivation of anode surfaces and overall Na-ion battery performance.
TL;DR: This work highlights that Ni ions, though acting as the dominant redox species in many LTMO, are labile to migrate to cause lattice disordering upon battery cycling, while the Mn ions are more stable as compared with Ni and Co and can act as pillar to stabilize layered structure.
Abstract: Layered lithium transition metal oxides (LTMO) are promising candidate cathode materials for next-generation high-energy density lithium ion battery. The challenge for using this category of cathode is the capacity and voltage fading, which is believed to be associated with the layered structure disordering, a process that is initiated from the surface or solid-electrolyte interface and facilitated by transition metal (TM) reduction and oxygen vacancy formation. However, the atomic level dynamic mechanism of such a layered structure disordering is still not fully clear. In this work, utilizing atomic resolution electron energy loss spectroscopy (EELS), we map, for the first time at atomic scale, the spatial evolution of Ni, Co and Mn in a cycled LiNi1/3Mn1/3Co1/3O2 layered cathode. In combination with atomic level structural imaging, we discovered the direct correlation of TM ions migration behavior with lattice disordering, featuring the residing of TM ions in the tetrahedral site and a sequential migrat...
TL;DR: In this article, the intrinsic lead ion (Pb2+) emissions in zero-dimensional (0D) perovskite nanocrystals (NCs) using a combination of experimental and theoretical approaches were investigated.
Abstract: We investigate the intrinsic lead ion (Pb2+) emissions in zero-dimensional (0D) perovskite nanocrystals (NCs) using a combination of experimental and theoretical approaches. The temperature-dependent photoluminescence experiments for both “nonemissive” (highly suppressed green emission) and emissive (bright green emission) Cs4PbBr6 NCs show a splitting of emission spectra into high- and low-energy transitions in the ultraviolet (UV) spectral range. In the nonemissive case, we attribute the high-energy UV emission at approximately 350 nm to the allowed optical transition of 3P1 to 1S0 in Pb2+ ions and the low-energy UV emission at approximately 400 nm to the charge-transfer state involved in the 0D NC host lattice (D-state). In the emissive Cs4PbBr6 NCs, in addition to the broad UV emission, we demonstrate that energy transfer occurs from Pb2+ ions to green luminescent centers. The optical phonon modes in Cs4PbBr6 NCs can be assigned to both Pb–Br stretching and rocking motions from density functional theo...