In Situ Liquid-Cell TEM Observation of Multiphase Classical and Nonclassical Nucleation of Calcium Oxalate

Calcium oxalate (CaOx) is the major phase in kidney stones and the primary calcium storage medium in plants. CaOx can form crystals with different lattice types, water contents, and crystal structures. However, the conditions and mechanisms leading to nucleation of particular CaOx crystals are unclear. Here, liquid-cell transmission electron microscopy and atomistic molecular dynamics simulations are used to study in situ CaOx nucleation at different conditions. The observations reveal that rhombohedral CaOx monohydrate (COM) can nucleate via a classical pathway, while square COM can nucleate via a non-classical multiphase pathway. Citrate, a kidney stone inhibitor, increases the solubility of calcium by forming calcium-citrate complexes and blocks oxalate ions from approaching calcium. The presence of multiple hydrated ionic species draws additional water molecules into nucleating CaOx dihydrate crystals. These findings reveal that by controlling the nucleation pathways one can determine the macroscale crystal structure, hydration state, and morphology of CaOx.     

Anti‐Oxygen Leaking LiCoO2

LiCoO₂ is a prime example of widely used cathodes that suffer from the structural/thermal instability issues that lead to the release of their lattice oxygen under nonequilibrium conditions and safety concerns in Li‐ion batteries. Here, it is shown that an atomically thin layer of reduced graphene oxide can suppress oxygen release from Li_xCoO₂ particles and improve their structural stability. Electrochemical cycling, differential electrochemical mass spectroscopy, differential scanning calorimetry, and in situ heating transmission electron microscopy are performed to characterize the effectiveness of the graphene‐coating on the abusive tolerance of Li_xCoO₂. Electrochemical cycling mass spectroscopy results suggest that oxygen release is hindered at high cutoff voltage cycling when the cathode is coated with reduced graphene oxide. Thermal analysis, in situ heating transmission electron microscopy, and electron energy loss spectroscopy results show that the reduction of Co species from the graphene‐coated samples is delayed when compared with bare cathodes. Finally, density functional theory and ab initio molecular dynamics calculations show that the rGO layers could suppress O₂ formation more effectively due to the strong C? O_cathode bond formation at the interface of rGO/LCO where low coordination oxygens exist. This investigation uncovers a reliable approach for hindering the oxygen release reaction and improving the thermal stability of battery cathodes.     

Synergistic Effect of Graphene Oxide for Impeding the Dendritic Plating of Li

Dendritic growth of lithium (Li) has severely impeded the practical application of Li‐metal batteries. Herein, a 3D conformal graphene oxide nanosheet (GOn) coating, confined into the woven structure of a glass fiber separator, is reported, which permits facile transport of Li‐ions thought its structure, meanwhile regulating the Li deposition. Electrochemical measurements illustrate a remarkably enhanced cycle life and stability of the Li‐metal anode, which is explained by various microscopy and modeling results. Utilizing scanning electron microscopy, focused ion beam, and optical imaging, the formation of an uniform Li film on the electrode surface in the case of GO‐modified samples is revealed. Ab initio molecular dynamics (AIMD) simulations suggest that Li‐ions initially get adsorbed to the lithiophilic GOn and then diffuse through defect sites. This delayed Li transfer eliminates the “tip effect” leading to a more homogeneous Li nucleation. Meanwhile, C? C bonds rupture observed in the GO during AIMD simulations creates more pathways for faster Li‐ions transport. In addition, phase‐field modeling demonstrates that mechanically rigid GOn coating with proper defect size (smaller than 25 nm) can physically block the anisotropic growth of Li. This new understanding is a significant step toward the employment of 2D materials for regulating the Li deposition.     

Improving broadcast performance by traffic isolation in wireless ad hoc networks

In this paper we propose a new broadcasting algorithm. In the proposed method we significantly reduce the broadcast overhead and also improve the broadcast delivery ratio in mobile networks. A novel traffic isolation method has been used which reduces the control message exchange. The proposed broadcasting method is based on a clustering method called ‘stability‐based clustering algorithm’ which had been proposed before. The broadcasting traffic is divided into internal (flow inside a cluster) and external traffic (flow among the clusters). For internal flooding traffic, cluster‐heads and gateways are responsible for re‐broadcasting but for external type, border nodes may perform the forwarding function as well. This simplifies the gateway selection method through the local selection of gateway nodes by its cluster head. Therefore, a cluster head selects gateway in its own cluster without any knowledge of other clusters. Considering the effect of mobility and node density, simulations have been conducted in a number of wireless environments. Simulation results show the broadcast coverage is close to 100% at different node speeds. Moreover, we study the broadcast parameters in light and dense networks and show improvement of the overhead and the number of forward nodes in comparison to other broadcasting methods. Copyright © 2005 John Wiley & Sons, Ltd.     

Direct Ink Writing of Polymer Composite Electrolytes with Enhanced Thermal Conductivities

Proper distribution of thermally conductive nanomaterials in polymer batteries offers new opportunities to mitigate performance degradations associated with local hot spots and safety concerns in batteries. Herein, a direct ink writing (DIW) method is utilized to fabricate polyethylene oxide (PEO) composite polymers electrolytes (CPE) embedded with silane-treated hexagonal boron nitride (S-hBN) platelets and free of any volatile organic solvents. It is observed that the S-hBN platelets are well aligned in the printed CPE during the DIW process. The in-plane thermal conductivity of the printed CPE with the aligned S-hBN platelets is 1.031 W ⁻¹ K⁻¹, which is about 1.7 times that of the pristine CPE with the randomly dispersed S-hBN platelets (0.612 W ⁻¹ K⁻¹). Thermal imaging shows that the peak temperature (°C) of the printed electrolytes is 24.2% lower than that of the CPE without S-hBN, and 10.6% lower than that of the CPE with the randomly dispersed S-hBN, indicating a superior thermal transport property. Lithium-ion half-cells made with the printed CPE and LiFePO₄ cathode displayed high specific discharge capacity of 146.0 mAh g⁻¹ and stable Coulombic efficiency of 91% for 100 cycles at room temperature. This work facilitates the development of printable thermally-conductive polymers for safer battery operations.     

The Quantitative Effect of Drying on the Surface Color Change of Reaction Woods: Spruce Compression Wood (Picea abies L.) and Poplar Tension Wood (Populus nigra L.)

The surface color change of compression wood in spruce (Picea abies L.) and tension wood in poplar (Populus nigra L.) due to drying was investigated using CIE LAB and CIELCh colorimetry techniques. The results showed that the compression wood was lighter, yellower, less red, and more statured in color with a deeper hue after drying. Similar changes were also seen with the tension wood, except that it was less yellow and less statured in the dry condition. The color change (ΔE) of compression wood was found to be more remarkable than that of tension wood. Overall, the difference in the colorimetric parameters between the reaction woods and their corresponding normal woods was less significant after drying.     

A New Lightweight User Authentication and Key Agreement Scheme for WSN

The Internet of Things (IoT) is one of the most up-to-date and newest technologies that allows remote control of heterogeneous networks and has a good outlook for industrial applications. Wireless sensor networks (or in brief WSNs) have a key role on the Internet of industrial objects. Due to the limited resources of the sensor nodes, designing a balanced authentication scheme to provide security in reasonable performance in wireless sensor networks is a major challenge in these applications. So far, several security schemes have been presented in this context, but unfortunately, none of these schemes have provided desired security in reasonable cost. In 2017, Khemissa et al. proposed a security protocol for mutual authentication between sensor node and user in WSNs, however, in this paper we show that this protocol is not safe enough in the confrontation of desynchronization, user impersonation and gateway impersonation attacks. The proposed attacks succeed with the probability of one and to be realized only require an execution of the protocol. Given merits of the Khemissa et al.’s protocol, we also improved their protocol in such a way that provides suitable level of security, and also we prove its security using two formal ways, i.e. BAN logic and also the Scyther tool. We also argue informally about the improved protocol’s security.

     

Elevated‐Temperature 3D Printing of Hybrid Solid‐State Electrolyte for Li‐Ion Batteries

While 3D printing of rechargeable batteries has received immense interest in advancing the next generation of 3D energy storage devices, challenges with the 3D printing of electrolytes still remain. Additional processing steps such as solvent evaporation were required for earlier studies of electrolyte fabrication, which hindered the simultaneous production of electrode and electrolyte in an all‐3D‐printed battery. Here, a novel method is demonstrated to fabricate hybrid solid‐state electrolytes using an elevated‐temperature direct ink writing technique without any additional processing steps. The hybrid solid‐state electrolyte consists of solid poly(vinylidene fluoride‐hexafluoropropylene) matrices and a Li⁺‐conducting ionic‐liquid electrolyte. The ink is modified by adding nanosized ceramic fillers to achieve the desired rheological properties. The ionic conductivity of the inks is 0.78 × 10 ^?3 S cm^?1. Interestingly, a continuous, thin, and dense layer is discovered to form between the porous electrolyte layer and the electrode, which effectively reduces the interfacial resistance of the solid‐state battery. Compared to the traditional methods of solid‐state battery assembly, the directly printed electrolyte helps to achieve higher capacities and a better rate performance. The direct fabrication of electrolyte from printable inks at an elevated temperature will shed new light on the design of all‐3D‐printed batteries for next‐generation electronic devices.     

Direct Growth of High Mobility and Low‐Noise Lateral MoS2–Graphene Heterostructure Electronics

Reliable fabrication of lateral interfaces between conducting and semiconducting 2D materials is considered a major technological advancement for the next generation of highly packed all‐2D electronic circuitry. This study employs seed‐free consecutive chemical vapor deposition processes to synthesize high‐quality lateral MoS₂–graphene heterostructures and comprehensively investigated their electronic properties through a combination of various experimental techniques and theoretical modeling. These results show that the MoS₂–graphene devices exhibit an order of magnitude higher mobility and lower noise metrics compared to conventional MoS₂–metal devices as a result of energy band rearrangement and smaller Schottky barrier height at the contacts. These findings suggest that MoS₂–graphene in‐plane heterostructures are promising materials for the scale‐up of all‐2D circuitry with superlative electrical performance.