Effects of Proton Irradiation on Structural and Electrochemical Charge Storage Properties of TiO\u3csub\u3e2 \u3c/sub\u3eNanotube Electrode for Lithium-Ion Batteries

The effects of proton irradiation on nanostructured metal oxides have been investigated. Recent studies suggest that the presence of structural defects (e.g. vacancies and interstitials) in metal oxides may enhance the material’s electrochemical charge storage capacity. A new approach to introduce defects in electrode materials is to use ion irradiation as it can produce a supersaturation of point defects in the target material. In this work we report the effect of low-energy proton irradiation on amorphous TiO2 nanotube electrodes at both room temperature and high temperature (250 ˚C). Upon room temperature irradiation the nanotubes demonstrate an irradiation-induced phase transformation to a mixture of amorphous, anatase, and rutile domains while showing a 35% reduction in capacity compared to anatase TiO2. On the other hand, the high temperature proton irradiation induced a disordered rutile phase within the nanotubes as characterized by Raman spectroscopy and transmission electron microscopy, which displays an improved capacity by 20% at ~ 240 mAh g-1 as well as improved rate capability compared to unirradiated anatase sample. Voltammetric sweep data was used to determine the contributions from diffusion-limited intercalation and capacitive processes and it was found that the electrodes after irradiation has more contributions from diffusion in lithium charge storage. Our work suggests that tailoring the defect generation through ion irradiation within metal oxide electrodes could present a new avenue for design of advanced electrode materials

Amorphous Boron Nanorod as an Anode Material for Lithium-Ion Batteries at Room Temperature

We report an amorphous boron nanorod anode material for lithium-ion batteries prepared through smelting non-toxic boron oxide in liquid lithium. Boron in theory can provide capacity as high as 3099 mAh g-1 by alloying with Li to form B4Li5. However, experimental studies of boron anode were rarely reported for room temperature lithium-ion batteries. Among the reported studies the electrochemical activity and cycling performance of bulk crystalline boron anode material are poor at room temperature. In this work, we utilized amorphous nanostructured one-dimensional (1D) boron material aiming at improving the electrochemical reactivity between boron and lithium ions at room temperature. The amorphous boron nanorod anode exhibited, at room temperature, a reversible capacity of 170 mAh g-1 at a current rate of 10 mA g-1 between 0.01 and 2 V. The anode also demonstrated good rate capability and cycling stability. Lithium storage mechanism was investigated by both sweep voltammetry measurements and galvanostatic intermittent titration technique (GITT). The sweep voltammetric analysis suggested that the contributions from lithium ions diffusion into boron as well as the capacitive process to the overall lithium charge storage are 57% and 43%, respectively. Results from GITT indicated that the discharge capacity at higher potentials (\u3e ~ 0.2 V vs, Li/Li+) could be ascribed to a capacitive process and at lower potentials (\u3c ~0.2 V vs, Li/Li+) to diffusion-controlled alloying reactions. Solid state nuclear magnetic resonance (NMR) measurement further confirmed that the capacity is from electrochemical reactions between lithium ions and the amorphous boron nanorod. This work provides new insights into designing nanostructured boron material for lithium-ion batteries

Carbon-Coated FeP Nanoparticles Anchored on Carbon Nanotube Networks as Anode for Long-Life Sodium-Ion Storage

A novel electrode design strategy of carbon-coated FeP particles anchored on a conducting carbon nanotube network (CNT@FePC) is designed to achieve a superior sodium ion storage. Such a unique structure demonstrated excellent long-life cycling stability (a 95% capacity retention for more than 1200 cycles at 3 A g-1) and rate capability (delivered 272 mAh g-1 at 8 A g-1)

Electrochemically Induced Amorphous-to-Rock-Salt Phase Transformation in Niobium Oxide Electrode for Li-Ion Batteries

Intercalation-type metal oxides are promising negative electrode materials for safe rechargeable lithium-ion batteries due to the reduced risk of Li plating at low voltages. Nevertheless, their lower energy and power density along with cycling instability remain bottlenecks for their implementation, especially for fast-charging applications. Here, we report a nanostructured rock-salt Nb2O5 electrode formed through an amorphous-to-crystalline transformation during repeated electrochemical cycling with Li+. This electrode can reversibly cycle three lithiums per Nb2O5, corresponding to a capacity of 269 mAh g−1 at 20 mA g−1, and retains a capacity of 191 mAh g−1 at a high rate of 1 A g−1. It exhibits superb cycling stability with a capacity of 225 mAh g−1 at 200 mA g−1 for 400 cycles, and a Coulombic efficiency of 99.93%. We attribute the enhanced performance to the cubic rock-salt framework, which promotes low-energy migration paths. Our work suggests that inducing crystallization of amorphous nanomaterials through electrochemical cycling is a promising avenue for creating unconventional high-performance metal oxide electrode materials

Significance of Photosynthetic Characters in the Evolution of Asian Gnetum (Gnetales)

Gnetum is a genus in the Gnetales that has a unique but ambiguous placement within seed plant phylogeny. Previous studies have shown that Gnetum has lower values of photosynthetic characters than those of other seed plants, but few Gnetum species have been studied, and those that have been studied are restricted to narrow taxonomic and geographic ranges. In addition, the mechanism underlying the lower values of photosynthetic characters in Gnetum remains poorly understood. Here, we investigated the photosynthetic characters of a Chinese lianoid species, i.e., Gnetum parvifolium, and co-occurring woody angiosperms growing in the wild, as well as seedlings of five Chinese Gnetum species cultivated in a greenhouse. The five Gnetum species had considerably lower values for photosynthesis parameters (net photosynthetic rate, transpiration rate, intercellular CO2 concentration, and stomatal conductance) than those of other seed plant representatives. Interrelated analyses revealed that the low photosynthetic capacity may be an intrinsic property of Gnetum, and may be associated with its evolutionary history. Comparison of the chloroplast genomes (cpDNAs) of Gnetum with those of other seed plant representatives revealed that 17 coding genes are absent from the cpDNAs of all species of Gnetum. This lack of multiple functional genes from the cpDNAs probably leads to the low photosynthetic rates of Gnetum. Our results provide a new perspective on the evolutionary history of the Gnetales, and on the ecophysiological and genomic attributes of tropical biomes in general. These results could also be useful for the breeding and cultivation of Gnetum

The Robustness Analysis of Wireless Sensor Networks under Uncertain Interference

Based on the complex network theory, robustness analysis of condition monitoring wireless sensor network under uncertain interference is present. In the evolution of the topology of sensor networks, the density weighted algebraic connectivity is taken into account, and the phenomenon of removing and repairing the link and node in the network is discussed. Numerical simulation is conducted to explore algebraic connectivity characteristics and network robustness performance. It is found that nodes density has the effect on algebraic connectivity distribution in the random graph model; high density nodes carry more connections, use more throughputs, and may be more unreliable. Moreover, the results show that, when network should be more error tolerant or robust by repairing nodes or adding new nodes, the network should be better clustered in median and high scale wireless sensor networks and be meshing topology in small scale networks

Understanding the Effect of Crystalline Structure and Atomic Arrangement in Metal Oxide Electrodes for Sodium Ion Batteries

This dissertation investigates the fundamental understanding in the influences of order-disorder and atomic arrangement on electrochemical properties of electrode materials for sodium ion batteries (SIBs). In specific, TiO2 anode and NaNixFeyMnxO2 cathode materials are studied. Due to their low cost and relatively high abundance of raw materials SIBs are attractive for large-scale energy storage systems for high round trip efficiency and long cycle life. Recent studies suggest that various polymorphs of TiO2 are suitable as anode material. However, the impact of crystallinity on the electrochemical properties of the material has not been explored. Meanwhile, the NaNixFeyMnxO2 cathode exhibits promising performance but detrimental irreversibility at high voltages as well as poor cycling stability and rate capability remain issues for its practical application. This dissertation presents the study which suggests that the increase of crystallinity in anatase TiO2 nanoparticle electrode leads to better electrochemical performance in terms of Coulombic efficiency, rate capability and cycle life. To understand the discrepancy in performance, various structural and electrochemical characterizations are conducted to explore the Na ion diffusion process and the local structural evolution of the material. Metal oxide cathode is also investigated. The atomic rearrangement of transition metals in NaNixFeyMnxO2 at high voltages attributes to irreversibility and instability. It becomes significant with the increase of either Fe composition or upper cut-off operation voltage. X-ray spectroscopy is used to investigate the oxidation state and local environment of the transition metals. The result suggests that vi the redox and bonding activity of Ni-O mainly attributes to irreversibility and instability. In addition, intergrown phases have been shown to improve structural stability and Na mobility in layered cathode materials. A new Li-substituted NaNixFeyMnxO2 intergrowth cathode is designed and synthesized. The improvement in stability and rate capability of the new intergrowth cathode is investigated, which is associated with the mixed layered-spinel phase that possibly offers improved ion diffusion and stability through direct channels between the 2D layered and 3D spinel component