A Ti3C2Tx-Based Composite as Separator Coating for Stable Li-S Batteries.

The nitrogen-doped MXene carbon nanosheet-nickel (N-M@CNi) powder was successfully prepared by a combined process of electrostatic attraction and annealing strategy, and then applied as the separator coating in lithium-sulfur batteries. The morphology and structure of the N-M@CNi were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectrum, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption method. The strong LiPS adsorption ability and high conductivity are associated with the N-doped carbon nanosheet-Ni modified surface. The modified separator offers the cathode of Li-S cell with greater sulfur utilization, better high-rate adaptability, and more stable cycling performance compared with the pristine separator. At 0.2 C the cell with N-M@CNi separator delivers an initial capacity of 1309 mAh g-1. More importantly, the N-M@CNi separator is able to handle a cathode with 3.18 mg cm-2 sulfur loading, delivering a capacity decay rate of 0.043% with a high capacity retention of 95.8%. Therefore, this work may provide a feasible approach to separator modification materials towards improved Li-S cells with improved stability.

Practical Prelithiation of 4.5 V LiCoO2 ||Graphite Batteries by a Passivated Lithium-Carbon Composite.

Prelithiation can replenish active Li into the battery to compensate the Li consumption due to the formation of solid electrolyte interphase (SEI) on the electrode surface, therefore improving the energy density of Li-ion batteries (LIBs), especially for batteries using electrode materials with low initial Coulombic efficiency (ICE). However, practical prelithiation in LIBs is a challenge since most lithiated compounds with high specific capacity are unstable and industrially incompatible. Herein, an effective prelithiation strategy is demonstrated by using a lithium-carbon (Li-C) microsphere composite. These Li-C microspheres are passivated by a self-assembled monolayer of octadecylphosphonic acid, which suppresses the reaction between Li and commonly used slurry solvent 1-methyl-2-pyrrolidinone (NMP). After the addition of passivated Li-C into the NMP-based graphite slurry, the ICE of the graphite||Li half-cell boosts from 88.5% to 100.5%. In a 4.5 V LiCoO2 (LCO)||graphite full-cell, the supplementary Li source avoids excessive delithiation of LCO, thus suppressing the destructive phase transformation at high delithiation potential. As a result, the prelithiated LCO||graphite full-cell presents an initial discharge capacity of 201 mAh g-1 and the capacity retention after 100 cycles increases by 7.1 %. This work provides a practical approach for developing high energy density and long cycle life LIBs.

Self-Assembled Monolayers for Batteries.

Current studies in the Li-battery field are focusing on building systems with higher energy density than ever before. The path toward this goal, however, should not ignore aspects such as safety, stability, and cycling life. These issues frequently originate from interfacial instability, and therefore, precise surface chemistry that allows for accurate control of material surface and interfaces is much in demand for advanced battery research. Molecular self-assembly as a surface chemistry tool is considered to surpass many conventional coating techniques due to its intrinsic merits such as spontaneous organization, molecular-scale uniformity, and structural diversity. Recent publications have demonstrated the power of self-assembled monolayers (SAMs) in addressing pressing issues in the battery field such as the chemical stability of Li, but many more investigations are needed to fully explore the potential and impact of this technique on energy storage. This perspective is the first of its kind devoted to SAMs in batteries and related materials. Recent research progress on SAMs in batteries is reviewed and mainly falls in two categories, including the improvement of chemical stability and the regulation of nucleation in conversion electrode reactions. Future applications and consideration of SAMs in energy storage are discussed. We believe these summaries and outlooks are highly stimulative and may benefit future advancements in battery chemistry.

Nitrogen-Doped Hierarchical Porous Activated Carbon Derived from Paddy for High-Performance Supercapacitors.

A facile and environmentally friendly fabrication is proposed to prepare nitrogen-doped hierarchical porous activated carbon via normal-pressure popping, one-pot activation and nitrogen-doping process. The method adopts paddy as carbon precursor, KHCO3 and dicyandiamide as the safe activating agent and nitrogen dopant. The as-prepared activated carbon presents a large specific surface area of 3025 m2·g-1 resulting from the synergistic effect of KHCO3 and dicyandiamide. As an electrode material, it shows a maximum specific capacitance of 417 F·g-1 at a current density of 1 A·g-1 and very good rate performance. Furthermore, the assembled symmetric supercapacitor presents a large specific capacitance of 314.6 F·g-1 and a high energy density of 15.7 Wh·Kg-1 at 1 A·g-1, maintaining 14.4 Wh·Kg-1 even at 20 A·g-1 with the energy density retention of 91.7%. This research demonstrates that nitrogen-doped hierarchical porous activated carbon derived from paddy has a significant potential for developing a high-performance renewable supercapacitor and provides a new route for economical and large-scale production in supercapacitor application.

Fast and straightforward analysis approach of charge transport data in single molecule junctions.

In this study, we introduce an efficient data sorting algorithm, including filters for noisy signals, conductance mapping for analyzing the most dominant conductance group and sub-population groups. The capacity of our data analysis process has also been corroborated on real experimental data sets of Au-1,6-hexanedithiol-Au and Au-1,8-octanedithiol-Au molecular junctions. The fully automated and unsupervised program requires less than one minute on a standard PC to sort the data and generate histograms. The resulting one-dimensional and two-dimensional log histograms give conductance values in good agreement with previous studies. Our algorithm is a straightforward, fast and user-friendly tool for single molecule charge transport data analysis. We also analyze the data in a form of a conductance map which can offer evidence for diversity in molecular conductance. The code for automatic data analysis is openly available, well-documented and ready to use, thereby offering a useful new tool for single molecule electronics.

Symmetry Effects on Attenuation Factors in Graphene-Based Molecular Junctions.

The unique structural and electronic characteristics of graphene make it an attractive contact for fundamental single-molecule electrical studies. With this in mind, we have probed here the electrical conductance of a molecular junction based on α,ω-diaminoalkane chains sandwiched between a gold and a graphene electrode. Using an STM based I(s) method combined with density functional theory-based transport calculations, we demonstrate that the resulting attenuation factor turns out to be much lower when compared to the standard molecular junction between two gold electrodes. This effect is attributed to asymmetric coupling of the molecule through strong chemisorption at the gold electrode and weaker van der Waals contact at graphene. Moreover, this asymmetric coupling induces higher conductance than that in the same hybrid metal-graphene molecular junction using standard thiol anchoring groups.

Precipitation hardening and microstructure evolution of the Ti-7Nb-10Mo alloy during aging.

A biomedical ß titanium alloy (Ti-7Nb-10Mo) was designed and prepared by vacuum arc self-consumable melting. The ingot was forged and rolled to plates, followed by quenching and aging. Age-hardening behavior, microstructure evolution and its influence on mechanical properties of the alloy during aging were investigated, using X-ray diffraction, transmission electron microscopy, tensile and hardness measurements. The electrochemical behavior of the alloy was investigated in Ringer's solution. The microstructure of solution-treated (ST) alloy consists of the supersaturated solid solution ß phase and the ωath formed during athermal process. The ST alloy exhibits Young's modulus of 80 GPa, tensile strength of 774 MPa and elongation of 20%. The precipitation sequences during isothermal aging at different temperatures were determined as ß+ωath→ß+ωiso (144 h) at Taging=350-400 °C, ß+ωath→ß+ωiso+α→ß+α at Taging=500°C, and ß+ωath→ß+α at Taging=600-650 °C, where ωiso forms during isothermal process. The mechanical properties of the alloy can be tailored easily through controlling the phase transition during aging. Comparing with the conventional Ti-6Al-4V alloy, the Ti-7Nb-10Mo alloy is more resistant to corrosion in Ringer's solution. Results show that the Ti-7Nb-10Mo alloy is promising for biomedical applications.