Reversible Anionic Redox Activities in Conventional LiNi1/3 Co1/3 Mn1/3 O2 Cathodes.

Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium-excessive layered-oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi1/3 Co1/3 Mn1/3 O2 . The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high-capacity lithium-ion batteries

An asymptotic analysis of composite beams with kinematically corrected end effects

AbstractA finite element-based beam analysis for anisotropic beams with arbitrary-shaped cross-sections is developed with the aid of a formal asymptotic expansion method. From the equilibrium equations of the linear three-dimensional (3D) elasticity, a set of the microscopic 2D and macroscopic 1D equations are systematically derived by introducing the virtual work concept. Displacements at each order are split into two parts, such as fundamental and warping solutions. First we seek the warping solutions via the microscopic 2D cross-sectional analyses that will be smeared into the macroscopic 1D beam equations. The variations of fundamental solutions enable us to formulate the macroscopic 1D beam problems. By introducing the orthogonality of asymptotic displacements to six beam fundamental solutions, the end effects of a clamped boundary are kinematically corrected without applying the sophisticated decay analysis method. The boundary conditions obtained herein are applied to composite beams with solid and thin-walled cross-sections in order to demonstrate the efficiency and accuracy of the formal asymptotic method-based beam analysis (FAMBA) presented in this paper. The numerical results are compared to those reported in literature as well as 3D FEM solutions

Manganese based layered oxides with modulated electronic and thermodynamic properties for sodium ion batteries

Manganese based layered oxides have received increasing attention as cathode materials for sodium ion batteries due to their high theoretical capacities and good sodium ion conductivities. However, the Jahn–Teller distortion arising from the manganese (III) centers destabilizes the host structure and deteriorates the cycling life. Herein, we report that zinc-doped Na0.833[Li0.25Mn0.75]O2 can not only suppress the Jahn–Teller effect but also reduce the inherent phase separations. The reduction of manganese (III) amount in the zinc-doped sample, as predicted by first-principles calculations, has been confirmed by its high binding energies and the reduced octahedral structural variations. In the viewpoint of thermodynamics, the zinc-doped sample has lower formation energy, more stable ground states, and fewer spinodal decomposition regions than those of the undoped sample, all of which make it charge or discharge without any phase transition. Hence, the zinc-doped sample shows superior cycling performance, demonstrating that zinc doping is an effective strategy for developing high-performance layered cathode materials

Cyclic performance of silicon as anode material in lithium ion batteries

Silicon is a promising anode material owing to its high energy density which is an important aspect of the -performance metric for lithium ion batteries. In this study, the cyclic behavior of silicon as the anode material in lithium ion batteries is investigated. Chemical–mechanical coupling is considered to analyze the interactions between diffusion and factors influencing the mechanical response of materials. Galvanostatic–potentiostatic -charging/discharging cycles are used to investigate the cyclic performance of the material in terms of response time, stress generation, and energy dissipation. The effects of plasticity, c-rate, and maximum state of charge are analyzed. In particular, energy losses due to diffusion dissipation and plasticity are calculated. Contributions of concentration -inhomogeneity and stress-induced chemical potential shift on energy loss are quantified. This study yields -guidelines for achieving faster charge/discharge by tailoring plasticity, mechanical-to-chemical coupling and limiting SOC

Thermal conductivity prediction for GaN nanowires from atomistic potential Additional information on AIP Advances Thermal conductivity prediction for GaN nanowires from atomistic potential

A model is developed to evaluate the thermal conductivity of semiconducting compounds as a function of their atomistic structures during phase transformations induced by mechanical loading. The approach uses atomistic configurational information and interatomic interactions as input. The harmonic and anharmonic behaviors of phonons are captured through force constants which are sensitive to structural changes. The calculations focus on changes in thermal conductivity of GaN nanowires in response to deformation and phase transformation. Results show that the model yields results consistent with data obtained using the Green-Kubo method and is 50 times more efficient than calculations based on molecular dynamics. C 2013 Author(

Effect of packing density on maximum stretch ratio of stretchable wavy circuit

A wavy circuit is one of the structures used in flexible devices, which endure high stretch ratios during operation. In this study, we focus on the importance of the section tilting angle of the wavy circuit. Both simulation and experiment reveal that the plane wavy circuit is highly affected by the buckling of the circuit, and buckling is influenced by the gap between circuits. On the other hand, the buckling effect tends to decrease when the tilting angle of the circuit section increases. We conclude that increasing the tilting angle of the wavy circuit provides an advantage in designing a flexible device that nullifies the gap-buckling tendency of the wavy circuit, and gives extra margin in the design process.N

Combined coarse-grained molecular dynamics and finite-element study of light-activated deformation of photoresponsive polymers

The azobenzene-containing crosslinked liquid crystalline polymer is a potential candidate for a stimuli-responsive soft robot, as it provides contactless actuation without the implementation of any separate component. For facilitating practical applications of this novel material, complicated and predefined motions have been realized by tailoring the chemical structure of the polymer network. However, conventional multiscale mechanical analysis, which utilizes the all-atom molecular dynamics to represent a microscopic model, is unsuitable for handling diverse material design parameters due to excessive computational costs. Hence, a multiscale optomechanical simulation framework, which combines the coarse-grained molecular dynamics (CG MD) and the finite-element (FE) method, is developed in this study. The CG MD simulation satisfactorily reproduces the light-induced phase transition and photosoftening effect on the mechanical properties. In particular, using the mesoscale analysis, the presented methodology can treat diverse morphology parameters (liquid crystal phase, spacer length, and crosslinking density) to observe the associated photodeformations. The photostrain and elastic modulus profiles in terms of photoisomerization ratio are implemented into the continuum-scale governing equation, which is based on the neoclassical elasticity theory. To efficiently reflect the light-induced large rotations of liquid crystal mesogens and the corresponding geometric nonlinearity, a corotational formulation is employed in the FE shell model. We examine the mesostructural-morphology-dependent photobending deformations of the nematic and smectic photoresponsive polymers (PRPs). In addition, the mesoscopic-texture-mediated unique 3D deformations are investigated by modeling the topological defects. This study offers insight into the engineering of PRP materials for designing the mechanical motions of smart actuators

Length and boundary effects on a nanorod

We investigate length and boundary effects on the equilibrium strain of a < 100 > copper nanorod with {100} or {110} surfaces. Unlike a nanowire, a free-edged nanorod has finite length and has two more surfaces at both tip and root. Although the area of these two edge surfaces is generally much smaller than that of side surfaces, the effect of the edge surfaces should not be ignored in the equilibrium configuration of a nanorod. In this letter, an analytical model to estimate the equilibrium strain of the nanorod is proposed, and molecular statics simulations are performed to prove the proposed model. As the length of a nanorod increases, the equilibrium strain increases and converges to that of a nanowire. As for the boundary effect, we compare the equilibrium strain of a clamped nanorod with that of a free-edged nanorod