8,536 research outputs found
Theory of layered-oxide cathode degradation in Li-ion batteries by oxidation-induced cation disorder
Disorder-driven degradation phenomena, such as structural phase
transformations and surface reconstructions, can significantly reduce the
lifetime of Li-ion batteries, especially those with nickel-rich layered-oxide
cathodes. We develop a general free energy model for layered-oxide
ion-intercalation materials as a function of the degree of disorder, which
represents the density of defects in the host crystal. The model accounts for
defect core energies, long-range dipolar electrostatic forces, and
configurational entropy of the solid solution. In the case of nickel-rich
oxides, we hypothesize that nickel with a high concentration of defects is
driven into the bulk by electrostatic forces as oxidation reactions at the
solid-electrolyte interface reduce nickel and either evolve oxygen gas or
oxidize the organic electrolyte at high potentials (>4.4V vs. Li/Li+). The
model is used in battery cycling simulations to describe the extent of cathode
degradation when using different voltage cutoffs, in agreement with
experimental observations that lower-voltage cycling can substantially reduce
cathode degradation. The theory provides a framework to guide the development
of cathode compositions, coatings and electrolytes to enhance rate capability
and enhance battery lifetime. The general theory of cation-disorder formation
may also find applications in electrochemical water treatment and ion
separations, such as lithium extraction from brines, based on competitive ion
intercalation in battery materials
Liquid Crystal-Solid Interface Structure at the Antiferroelectric-Ferroelectric Phase Transition
Total Internal Reflection (TIR) is used to probe the molecular organization
at the surface of a tilted chiral smectic liquid crystal at temperatures in the
vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are
interpreted using an exact analytical solution of a real model for
ferroelectric order at the surface. In the mixture T3, ferroelectric surface
order is expelled with the bulk ferroelectric-antiferroelectric transition. The
conditions for ferroelectric order at the surface of an antiferroelectric bulk
are presented
All roads lead to the places of your interest: An on-demand, ride-sharing visitor transport service
Successful visitor transport within large tourist sites should balance visitor experience and operating costs. Inspired by the model of sharing economy, we design a “user-centered” intelligent visitor transport system to improve the efficiency and quality of experience of transport service in large tourist sites. The system’s core approach is a three-stage heuristic model based on Pareto optimality. Results of the proposed service indicate a drastic reduction of visitor delay time and an improvement in energy efficiency. The proposed scheduling schemes for organizers are more diversified and adaptable than the existing service
Ultrathin MgB2 films fabricated on Al2O3 substrate by hybrid physical-chemical vapor deposition with high Tc and Jc
Ultrathin MgB2 superconducting films with a thickness down to 7.5 nm are
epitaxially grown on (0001) Al2O3 substrate by hybrid physical-chemical vapor
deposition method. The films are phase-pure, oxidation-free and continuous. The
7.5 nm thin film shows a Tc(0) of 34 K, which is so far the highest Tc(0)
reported in MgB2 with the same thickness. The critical current density of
ultrathin MgB2 films below 10 nm is demonstrated for the first time as Jc ~
10^6 A cm^{-2} for the above 7.5 nm sample at 16 K. Our results reveal the
excellent superconducting properties of ultrathin MgB2 films with thicknesses
between 7.5 and 40 nm on Al2O3 substrate.Comment: 7 pages, 4 figures, 2 table
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