Nonlithium metals such as sodium have attracted wide attention as a potential charge carrying ion for rechargeable batteries. Using in situ transmission electron microscopy in combination with ...density functional theory calculations, we probed the structural and chemical evolution of SnO2 nanowire anodes in Na-ion batteries and compared them quantitatively with results from Li-ion batteries ( Huang J. Y. Science 2010, 330, 1515−1520 ). Upon Na insertion into SnO2, a displacement reaction occurs, leading to the formation of amorphous Na x Sn nanoparticles dispersed in Na2O matrix. With further Na insertion, the Na x Sn crystallized into Na15Sn4 (x = 3.75). Upon extraction of Na (desodiation), the Na x Sn transforms to Sn nanoparticles. Associated with the dealloying, pores are found to form, leading to a structure of Sn particles confined in a hollow matrix of Na2O. These pores greatly increase electrical impedance, therefore accounting for the poor cyclability of SnO2. DFT calculations indicate that Na+ diffuses 30 times slower than Li+ in SnO2, in agreement with in situ TEM measurement. Insertion of Na can chemomechanically soften the reaction product to a greater extent than in lithiation. Therefore, in contrast to the lithiation of SnO2 significantly less dislocation plasticity was seen ahead of the sodiation front. This direct comparison of the results from Na and Li highlights the critical role of ionic size and electronic structure of different ionic species on the charge/discharge rate and failure mechanisms in these batteries.
Rechargeable magnesium batteries have attracted wide attention for energy storage. Currently, most studies focus on Mg metal as the anode, but this approach is still limited by the properties of the ...electrolyte and poor control of the Mg plating/stripping processes. This paper reports the synthesis and application of Bi nanotubes as a high-performance anode material for rechargeable Mg ion batteries. The nanostructured Bi anode delivers a high reversible specific capacity (350 mAh/gBi or 3430 mAh/cm3 Bi), excellent stability, and high Coulombic efficiency (95% initial and very close to 100% afterward). The good performance is attributed to the unique properties of in situ formed, interconnected nanoporous bismuth. Such nanostructures can effectively accommodate the large volume change without losing electric contact and significantly reduce diffusion length for Mg2+. Significantly, the nanostructured Bi anode can be used with conventional electrolytes which will open new opportunities to study Mg ion battery chemistry and further improve its properties.
Silicon has been identified as a highly promising anode for next-generation lithium-ion batteries (LIBs). The key challenge for Si anodes is large volume change during the lithiation/delithiation ...cycle that results in chemomechanical degradation and subsequent rapid capacity fading. Here we report a novel fabrication method for hierarchically porous Si nanospheres (hp-SiNSs), which consist of a porous shell and a hollow core. On charge/discharge cycling, the hp-SiNSs accommodate the volume change through reversible inward Li breathing with negligible particle-level outward expansion. Our mechanics analysis revealed that such inward expansion is enabled by the much stiffer lithiated layer than the unlithiated porous layer. LIBs assembled with the hp-SiNSs exhibit high capacity, high power and long cycle life, which is superior to the current commercial Si-based anode materials. The low-cost synthesis approach provides a new avenue for the rational design of hierarchically porous structures with unique materials properties.
Rational design of silicon and carbon nanocomposite with a special topological feature has been demonstrated to be a feasible way for mitigating the capacity fading associated with the large volume ...change of silicon anode in lithium ion batteries. Although the lithiation behavior of silicon and carbon as individual components has been well understood, lithium ion transport behavior across a network of silicon and carbon is still lacking. In this paper, we probe the lithiation behavior of silicon nanoparticles attached to and embedded in a carbon nanofiber using in situ TEM and continuum mechanical calculation. We found that aggregated silicon nanoparticles show contact flattening upon initial lithiation, which is characteristically analogous to the classic sintering of powder particles by a neck-growth mechanism. As compared with the surface-attached silicon particles, particles embedded in the carbon matrix show delayed lithiation. Depending on the strength of the carbon matrix, lithiation of the embedded silicon nanoparticles can lead to the fracture of the carbon fiber. These observations provide insights on lithium ion transport in the network-structured composite of silicon and carbon and ultimately provide fundamental guidance for mitigating the failure of batteries due to the large volume change of silicon anodes.
A number of butadiynylene-strapped O6-corona6arenes were synthesized straightforwardly through intramolecular oxidative homocoupling of O6-corona6arenes, which contained at least two ...N-propargyl-phthalimide segments. The mono-macrocyclic reactants were prepared from the reaction between 3,6-dichlorotetrazine and N-propargyl-3,6-dihydroxyphthalimide and another 1,4-dihydroxybenzene derivative with roughly a 3:2:1.3–1.5 ratio in a one-pot reaction manner. The synthesized butadiynylene-strapped corona3arene3tetrazines acted as highly selective electron-deficient macrocyclic hosts to form 1:1 complexes with thiocyanate in solution, and the association constant (K a) was up to 1390 M–1. The anion−π noncovalent interactions provided the driving force for host–guest complexation.
Sodium ion (Na+) batteries have attracted increased attention for energy storage due to the natural abundance of sodium, but their development is hindered by poor intercalation property of Na+ in ...electrodes. This paper reports a detailed study of high capacity, high rate sodium ion energy storage in functionalized high-surface-area nanocellular carbon foams (NCCF). The energy storage mechanism is surface-driven reactions between Na+ and oxygen-containing functional groups on the surface of NCCF. The surface reaction, rather than a Na+ bulk intercalation reaction, leads to high rate performance and cycling stability due to the enhanced reaction kinetics and the absence of electrode structure change. The NCCF makes more surface area and surface functional groups available for the Na+ reaction. It delivers 152 mAh/g capacity at the rate of 0.1 A/g and a capacity retention of 90% for over 1600 cycles.
The metastable hexagonal 4H-phase gold has recently attracted extensive interest due to its exceptional performance in catalysis. However, gold usually crystallizes to its lowest free energy ...structure called face-centered cubic (fcc). The phase transformation from the stable fcc phase to the metastable 4H phase is thus of great significance in crystal phase engineering. Herein, we report this unusual phenomenon on a 4H gold nanorod template with the aid of CO gas and an electron beam. In situ transmission electron microscopy was used to directly visualize the interface propagation kinetics between the 4H-Au-nanorod and fcc-Au nanoparticle. Epitaxial growth was initiated at the contact interface, and then propagated to convert all parts of these fcc nanoparticles to 4H phase. Density functional theory calculations and ab initio molecular dynamics simulations show that the CO molecules can assist the Au diffusion process and promote the flexibility of Au particles during the epitaxial growth. The phase transformation was driven by the reduction of Gibbs free energy by eliminating the interface between fcc and 4H phases.
In this study, a novel composite flow channel was proposed to address issues of gas transport obstruction, poor water removal performance, high pressure drop, and low current density within the ...cathode flow channel of proton exchange membrane fuel cells (PEMFCs). The flow channel could optimize performance by combining a tapered design with a 3D wave structure. Based on a controlled variable method and three-dimensional (3D) multiphase computational fluid dynamics (CFD) simulations, the effects of the flow channel inlet and outlet side length ratio LD/d, amplitude A, and wavelength λ on PEMFC performance were investigated. As shown by results, appropriate decrease of LD/d, increase of A, and reduction of λ could increase convective mass transfer in the flow channel, improve the uniformity of the reaction gas distribution, and enhance the Water removal performance. Moreover, the optimal performance was achieved when LD/d=1/3, A = 0.3 mm and λ=4 mm for PEMFC. Finally, when the cell output voltage was 0.4 V, the current density of the novel composite flow channel was up to 6.26% higher than that of the traditional 3D wave-shaped flow channel.
•A novel composite channel considering a tapered-3D wavy structure is proposed.•Impact of structural parameters on PEMFC performance studied for novel channels.•Optimal parameter combination for the novel composite flow channel achieved.•The current density of the novel composite channel can increase by up to 6.26%.
Reliable trajectory prediction methods are critical in providing predictive safety intelligence for vital decision making in intelligent transportation systems to further enhance the safety of ...drivers and passengers. To tackle complicated maneuvering and interactions between objects, learning-based algorithms were used to replace classic model-based trajectory prediction algorithms. However, most algorithms implicitly presume that they are executed at centralized processing units after gathering data from edge sensors and delivering the results back to the on-board units. This causes an increase in computation time and latency; thus, reducing the reaction time of the drivers. To reduce the computation time and latency and consider the robustness of local sensors, we propose a decentralized radar-dedicated framework with a deep-learning (DL) model, called predictive RadarNet, to predict future trajectories over binary range angle (RA) maps with a probabilistic representation according to the original radar RA maps for presenting the uncertainty of the estimated trajectories. In addition, to reduce the model size for low-complexity, we designed a prepossessing technique that can largely reduce the size of the input tensors without losing information. Moreover, we found that the functions of the DL-model consist of two operations: future inference of original radar RA maps and transformation to binary RA maps. Thus, we designed two models with different kernels that are suitable for dealing with the two operations. Simulations show that the proposed decentralized framework using predictive RadarNet can provide reliable prediction results with a low computation time.
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