Iron pyrite (FeS 2 ) is a promising lithium-ion battery cathode material because of its low cost and ultrahigh energy density (1671 Wh kg −1 ). However, its reaction mechanisms are still controversial. In this work, we find that different from the conventional belief that an intermediate phase Li 2 FeS 2 is formed followed by Fe/Li 2 S composites at the initial discharge, it undergoes a one-step reaction (FeS 2 → Fe + Li 2 S) or a two-step reaction (FeS 2 → FeS + Li 2 S → Fe + Li 2 S), which depends on the current rate and temperature. In the charge process, it undergoes a two-step reaction: phase transition Fe + Li 2 S → FeS at about 1.74 V and generation of elemental sulfur (Li 2 S → S, 2.30 V). FeS is a mackinawite phase that is formed on the interface of Li 2 S via heteroepitaxial growth. Subsequent cycles involves a combination reaction of FeS and S. The reaction mechanism suggests that FeS 2 suffers from the demerits of both FeS and S, such as a large volume change, voltage hysteresis, and polysulfide dissolution. These findings would help us to understand the intrinsic capacity fading of FeS 2 and provide guidelines to improve its electrochemical performances.
We focus this review on the theoretical description, at the density functional theory level, of two key processes that are common to electronic devices based on organic semiconductors (such as organic light-emitting diodes, field-effect transistors, and solar cells), namely charge transport and charge injection from electrodes. By using representative examples of current interest, our main goal is to introduce some of the reliable theoretical methodologies that can best depict these processes. We first discuss the evaluation of the microscopic parameters that determine charge-carrier transport in organic molecular crystals, i.e., electronic couplings and electron-vibration couplings. We then examine the electronic structure at interfaces between an organic layer and a metal or conducting oxide electrode, with an emphasis on the work-function modifications induced by the organic layer and on the interfacial energy-level alignments.
Li2Ru0.5Mn0.5O3, a
high capacity lithium-rich layered cathode material for lithium-ion
batteries, was subject to comprehensive diagnostic studies, including
in situ/ex situ X-ray diffraction, X-ray absorption spectroscopy (XAS),
pair distribution function, and high resolution scanning transmission
electron microscopy analysis, to understand the correlations between
transition-metal chemistry, structure, and lithium storage electrochemical
behavior. Ru–Ru dimers were identified in the as-prepared sample
and found to be preserved upon prolonged cycling. Presence of these
dimers, which are likely caused by the delocalized nature of 4d electrons,
is found to favor the stabilization of the structure in a layered
phase. The in situ XAS results confirm the participation of oxygen
redox into the charge compensation at high charge voltage, and the
great flexibility of the covalent bond between Ru and O may provide
great reversibility of the global structure despite the significant
local distortion around Ru. In contrast, the local distortion around
Mn occurs at low discharge voltage and is accompanied by a layered
to 1T phase transformation, which is found to be detrimental to the
cycle performances. It is clear that the changes of local structure
around individual transition-metal cations respond separately and
differently to lithium intercalation/deintercalation. Cations with
the capability to tolerate the lattice distortion will be beneficial
for maintaining the integrality of the crystal structure and therefore
is able to enhance the long-term cycling performance of the electrode
materials.
The Debye sheath has a significant effect on the performance of Hall thrusters. The dynamic characteristics of the two-dimensional sheath is investigated using the 2D-3V particle-in-cell method in this paper. The numerical results show that while the sheath exhibits the one-dimensional stability when the electron temperature is relatively low, it behaves as a two-dimensional (both in time and space) oscillating characteristic when the electron temperature is high. Moreover, it is found that the oscillating frequency is the same order as the electron plasma frequency and the spatial wavelength is equal to the length of the electrostatic wave.
We report on terahertz emission from a single layer ferromagnet which involves the generation of backflow nonthermal charge current from the ferromagnet/dielectric interface by femtosecond laser excitation and subsequent conversion of the charge current to a transverse transient charge current via the anomalous Hall effect, thereby generating the THz radiation. The THz emission can be either enhanced or suppressed, or even the polarity can be reversed, by introducing a magnetization gradient in the thickness direction of the ferromagnet. Unlike spintronic THz emitters reported previously, it does not require additional non-magnetic layer or Rashba interface.
The
soil environment is an important sink for penicillin antibiotics
released from animal manure and wastewater, but the mineral-catalyzed
transformation of penicillins in soil has not been well studied. To
simulate this environmental process, we systematically investigated
the behavior of penicillin G and amoxicillin, the two most widely-used
penicillin antibiotics, in the presence of goethite and metal ions.
The results demonstrated that Zn ions significantly promoted the hydrolysis
of penicillins in goethite suspensions, as evidenced by the degradation
rate nearly 3 orders of magnitude higher than that of the non-Zn-containing
control. The spectroscopic analysis indicated that the specific complexation
between penicillins, adsorbed Zn, and goethite was responsible for
the enhanced degradation. Metastable interactions, involving hydrogen
bonds between carbonyl groups in the β-lactam ring and the double/triple
hydroxyl groups on goethite surface, and coordination bonding between
carboxyl groups and surface irons were proposed to stabilize the ternary
reaction intermediates. Moreover, the surface zinc-hydroxide might
act as powerful nucleophile to rapidly rupture the β-lactam
ring in penicillins. This study is among the first to identify the
synergic roles of Zn ion and goethite in facilitating penicillin degradation
and provides insights into β-lactam antibiotics to assess their
environmental risk in soil.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.