Search

Although most indoor positioning systems use radio waves, such as Wi-Fi, Bluetooth, or RFID, for application in department stores, exhibition halls, stations, and airports, the accuracy of such technology is easily affected by human shadowing and multipath propagation delay. This study combines the earth's magnetic field strength and Wi-Fi signals to obtain the indoor positioning information with high availability. Wi-Fi signals are first used to identify the user's area under several kinds of environment partitioning methods. Then, the signal pattern comparison is used for positioning calculations using the strength change in the earth's magnetic field among the east–west, north–south, and vertical directions at indoor area. Finally, the k-nearest neighbors (KNN) method and fingerprinting algorithm are used to calculate the fine-grained indoor positioning information. The experiment results show that the average positioning error is 0.57 m in 12-area partitioning, which is almost a 90% improvement in relation to that of one area partitioning. This study also considers the positioning error if the device is held at different angles by hand. A rotation matrix is used to convert the magnetic sensor coordinates from a mobile phone related coordinates into the geographic coordinates. The average positioning error is decreased by 68%, compared to the original coordinates in 12-area partitioning with a 30-degree pitch. In the offline procedure, only the northern direction data are used, which is reduced by 75%, to give an average positioning error of 1.38 m. If the number of reference points is collected every 2 m for reducing 50% of the database requirement, the average positioning error is 1.77 m. [ABSTRACT FROM AUTHOR]

Lithium iron silicate (LFS) attracts a lot of attention due to its 330 mAh g−1 theoretical capacity (2 Li+ per formula unit). However, inherently it exhibits poor Li‐ion intercalation kinetics, interfacial reactivity, and complex phase transitions resulting in lower than one Li+ capacity and poor retention. In this work, a core–shell architecture is devised largely overcoming these obstacles. At first, the nanostructure of Pmn21 LFS is annealed via mechanochemical processing enabling the activation of Li‐ion diffusion. Subsequently, the LFS nanocrystals are coated via in situ poly(3,4‐ethylenedioxythiophene) (PEDOT) polymerization involving partial chemical de‐lithiation/re‐lithiation, the latter catalyzed with FeCl3. As a result of the devised mechanochemical/interphasial engineering of the LFS@PEDOT nanocrystals, their Li‐ion storage capacity is augmented to > 1 Li, namely 200 mAh g−1 after 50 cycles or 1.2 Li+ units—the highest capacity reported for the Pmn21 LFS cathode. A key attribute of the new PEDOT coating technique is the generation of a Fe3+‐rich subsurface layer that contributes to structure stabilization via accelerated phase transition to inverse Pmn21 phase, in addition to rendering the nanocrystals electronically conductive and protected against reaction with electrolyte. Such core–shell engineered nanocrystals provide a powerful paradigm in developing viable high energy density cathodes for next‐generation Li‐ion batteries. [ABSTRACT FROM AUTHOR]

Lymphangiography can be useful for preoperative planning in chylothorax. Conventional ultrasound‐guided intranodal injection can be difficult in some cases and is dependent upon operator skill. Alternative methods have been proposed to simplify the procedure, but their feasibility has not been sufficiently evaluated in clinical cases. The primary purpose of this multicenter, retrospective, descriptive study was to assess the feasibility and describe the clinical findings of CT lymphangiography by intrametatarsal pad injection in dogs with naturally occurring chylothorax. Twenty dogs were analyzed, and enhancement of thoracic ducts (TDs) was successful in 18 (90%) dogs within 5‐14 min after initiating the injection, while successful enhancement of the lymphatic vessels cranial to the popliteal lymph nodes was seen in all dogs within 5 min after injection. The dose with good success to achieve TD enhancement was 1 mL/kg (concentration 350 mg I/kg). Only two dogs had mild discomfort after recovery from general anesthesia. Computed tomography lymphangiography by intrametatarsal pad injection is a feasible, easy, and safe procedure, which could provide adequate TD and cisterna chyli enhancement, identify TD number and cisterna chyli location and structure, and contribute to surgical planning. [ABSTRACT FROM AUTHOR]

The synthesis and processing of garnet-type conductors is usually done at temperatures above 1100 °C to reach the high Li-ion conducting cubic phase resulting in micron-sized particles and potential Li-loss, which are unfavorable for further processing and electrode-electrolyte assembly. Here, we tackle this problem and report a novel low-temperature aqueous synthesis route to stabilize the cubic phase of Li 6.1 Al 0.3 La 3 Zr 2 O 12 (c-Al-LLZO) at a temperature as low as 600 °C , while obtaining nano-crystallites at around 100 - 200 nm. Moreover, a dual-reaction mechanism was proposed to describe the process of c-Al-LLZO crystallization. The as-synthesized nanoscale c-Al-LLZO particles facilitate the densification of the solid-state electrolyte (SSE) pellets with less endowed grain boundaries (exhibiting a high relative density of 97.8 %). The ionic conductivity reaches 0.42 mS cm−1 at 21 °C and the low activation energy (half of the published values) is 0.17 eV. The results presented here show that symmetric cells with Li metal exhibit excellent stability at the current density of 0.2 mA/cm2 and 0.5 mA/cm2, and an improved critical current density (CCD) of 2.16 mA/cm2. This work provides a feasible method of low-temperature crystallization of nanoscale cubic garnet SSEs with good performance for the fabrication of stable SSLBs. [Display omitted] • Direct crystallization of cubic garnet (LLZO) solid-state electrolytes at 600 °C. • A new variety of near nanoscale cubic garnet solid electrolyte. • Excellent densification and high lithium-ion conductivity. • Symmetric cells with high CCD and Li metal plating-stripping stability. [ABSTRACT FROM AUTHOR]

Li2FeSiO4 (LFS) is a sustainable Li-ion cathode material composed of earth-abundant elements with potentially high energy density but suffers from limited reversible storage capacity (less than one Li), low intrinsic conductivities, and cycling instability. In search of deeper understanding of the structural chemistry of LFS towards overcoming some of these challenges, the viability of Fe-site doping by Co and other dopants in Pmn21 LFS is investigated using both first-principles calculations and experimental testing. Computational results suggest that the formation of Li2Fe1−xCoxSiO4 is energetically favorable, predictions confirmed by successful hydrothermal synthesis. Substitution of Co in LFS is revealed to have a dual effect; firstly catalyzing faster electrochemically induced phase transformation to the stable inverse-Pmn21 phase; and secondly enabling the formation of a low-resistant, uniform and stable fluorine-rich cathode-electrolyte interphase (CEI) layer that inhibits detrimental reactions between the cathode and electrolyte. As a result, Co-substituted LFS displays enhanced reversibility with 95% capacity retention after 50 cycles as compared to 80% of the undoped LFS. [ABSTRACT FROM AUTHOR]

In this work, a relatively inactive cathode material, βII orthorhombic Li2FeSiO4 with the Pmn21 space group, is shown to undergo crystal structural changes when subjected to nanosizing by high-energy milling that have a pronounced activation impact on Li-ion intercalation electrochemistry. In particular, we present evidence of mechanically induced structural annealing including lattice expansion, reduction of anti-site defects and preferred crystal orientation, opposite of what expected typically from nanosizing. As a result of this type of unreported structural activation for orthosilicates, a threefold increase of the accessible discharge (=intercalation) capacity of the high-energy milled Pmn21 material is attained, much higher than what would be expected solely from surface area increase due to nanosizing and surface area increase. Such mechanochemically induced structural annealing activates Li-ion diffusion (one order of magnitude enhancement in DLi) into less accessible sites via the combined effects of anti-site defect removal and modulation of the Fe–O coordination adjustment. Structural activation of intercalation materials via controlled mechanochemistry opens new possibilities in nanoengineering high energy density Li-ion storage electrodes. [ABSTRACT FROM AUTHOR]

Integration of solar‐energy harvesting and storage functions has attracted significant research attention, as it holds promise for ultimate development of light‐chargeable devices. In this context, a functional nanocomposite anode that not only permits electrochemical energy storage through Li‐ion photo‐intercalation, but also exhibits potential for photoelectrochromic applications, was investigated. The nanocomposite is made of the Li‐ion intercalation compound WO3, thinly coated with TiO2 and sensitized by the photoactive semiconductor CdS. During light exposure, the photoelectrons from CdS are transported to the WO3/electrolyte interface, where Li‐ion intercalation takes place. Photoelectron transport is facilitated by the interfacial TiO2 layer. The WO3 was shown to be functional in multiple photocharge–discharge cycles, but the CdS suffers from degradation and photocorrosion. Hence, the selection of compatible semiconductors and protective coating strategies should be pursued to overcome these issues. [ABSTRACT FROM AUTHOR]

Zero-strain and long-term stability of nanoscale lithium titanate (LTO) anode materials make possible the fabrication of exceptionally stable lithium ion batteries. But one issue must be considered that of nanostructure-induced relaxation in 2D LTO nanosheets which profoundly modifies their Li storage properties and structural stability. Excessively intercalated Li ions at both 8 a and 16 c sites trigger nucleation of the relaxed LTO structure in the near-surface region, which impedes Li-ion diffusion and causes the increasing polarization of LTO nanosheet electrodes. Nuclei of relaxed LTO then undergo isotropic growth along the 3D Li-ion pathways in LTO to completely convert near-surface regions into relaxed LTO. With increasing population of trapped Li ions, the enhanced conductivity due to Ti4+/Ti3+ reduction gradually eliminates the raised polarization. In the meantime, spontaneous electrolyte/LTO reduction to form the solid electrolyte interphase starts playing a major role in capacity loss once the transformation of near-surface region into relaxed LTO becomes saturated. Elucidation of these fundamental intercalation-induced surface structure transformations contribute greatly into the design of highly performing 2D nanoscaled LTO and other electrode materials. [ABSTRACT FROM AUTHOR]

Li 2 FeSiO 4 (LFS) has drawn much attention as cathode for high capacity Li-ion batteries. Even though significant volume of study has been devoted to its crystal chemistry and electrochemistry, many questions relating to its Li-ion storage dynamics remain yet to be fully elucidated. In this context, synchrotron-based X-ray diffraction and absorption spectroscopies are employed to characterize the phase stability and charge compensation mechanism in a metastable Li 2 FeSiO 4 nanostructured cathode as a function of state-of-charge (Li 2− x FeSiO 4 , x = 0, 0.25, 0.50, 0.75, 1.0) and cycling at very low current. The results demonstrate (i) no detectable phase transition from monoclinic to orthorhombic phase during the first charge-discharge cycle but rather formation of antisite defects that progressively induce phase transformation after several electrochemical cycles; (ii) characteristics of solid solution Li-ion storage (Li 2− x FeSiO 4 , x = 0–1); and (iii) the charge compensation for the first Li extraction does not come solely from the ferrous to ferric conversion, but interestingly from prominent participation of lattice oxygen as well that appears to destabilize the cycled LFS structure with significant performance implications. [ABSTRACT FROM AUTHOR]

Lithium iron orthosilicate (Li 2 FeSiO 4 ) is an important alternative cathode for next generation Li-ion batteries due to its high theoretical capacity (330 mA h/g). However, its development has faced great challenges arising from significant structural complexity, including the disordered arrangement/orientation of Fe/Si tetrahedra, polytypes and its poorly understood Li storage and transport properties. In this context, ab-initio calculations are employed to investigate the phase stability and Li diffusion profiles of both monoclinic ( P 2 1 ) and orthorhombic ( Pmn 2 1 ) Li 2 FeSiO 4 orthosilicates. The calculations demonstrate that formation of Li Fe antisites can induce a metastability competition between both phases, with neither dominating across nearly the entire discharging profile from Li 2 FeSiO 4 through to LiFeSiO 4 . Furthermore, structural instability is shown to be a serious concern at discharge concentrations below LiFeSiO 4 (1 Li extraction) due to the shared occupation of Li donated electrons with oxygen 2p orbitals – rather than the hypothesized transition to a tetravalent Fe 4+ state. This finding is further supported by diffusion calculations that have determined a high activation energy barrier towards fast charging and rapid phase transitions. In summary, these theoretical results provide critical and timely insight into the structural dynamics of lithium iron orthosilicate, in pursuit of high energy density cathodes. [ABSTRACT FROM AUTHOR]

The reaction between an uncharged Li2FeSiO4 (LFS) cathode and a LiPF6-EC/DMC electrolyte is revealed by in situ XANES in coin cells. This study shows clear evidence of delithiation and iron oxidation in LFS prior to cycling. Subsequent cycling appears to partially restore the original lithiation level, an observation that needs to be taken into consideration in future LFS development work. [ABSTRACT FROM AUTHOR]

Silicate Nanocrystals: PEDOT Encapsulated and Mechanochemically Engineered Silicate Nanocrystals for High Energy Density Cathodes (Adv. Keywords: interfacial engineering; Li-ion batteries; lithium iron silicate; mechanochemistry; PEDOT; surface modification EN interfacial engineering Li-ion batteries lithium iron silicate mechanochemistry PEDOT surface modification 1 1 1 07/13/20 20200709 NES 200709 In article number 2000226 Majid Rasool, George P. Demopoulos, and co-workers report the fabrication of a robust core-shell lithium iron silicate (Li SB 2 sb FeSiO SB 4 sb , LFS) cathode architecture, where nanocrystal's core is prepared via mechanochemical annealing and shell via PEDOT polymerization. Interfacial engineering, Li-ion batteries, lithium iron silicate, mechanochemistry, PEDOT, surface modification. [Extracted from the article]

Nanostructured lithium metal orthosilicate materials hold a lot of promise as next generation cathodes but their full potential realization is hampered by complex crystal and electrochemical behavior. In this work Li2FeSiO4 crystals are synthesized using organic-assisted precipitation method. By varying the annealing temperature different structures are obtained, namely the monoclinic phase at 400°C, the orthorhombic phase at 900°C, and a mixed phase at 700°C. The three Li2FeSiO4 crystal phases exhibit totally different charge/discharge profiles upon delithiation/lithiation. Thus the 400°C monoclinic nanocrystals exhibit initially one Li extraction via typical solid solution reaction, while the 900°C orthorhombic crystals are characterized by unacceptably high cell polarization. In the meantime the mixed phase Li2FeSiO4 crystals reveal a mixed cycling profile. We have found that the monoclinic nanocrystals undergo phase transition to orthorhombic structure resulting in significant progressive deterioration of the material's Li storage capability. By contrast, we discovered when the monoclinic nanocrystals are cycled initially at higher rate (C/20) and subsequently subjected to low rate (C/50) cycling the material's intercalation performance is stabilized. The discovered rate-dependent electrochemically-induced phase transition and stabilization of lithium metal silicate structure provides a novel and potentially rewarding avenue towards the development of high capacity Li-ion cathodes. [ABSTRACT FROM AUTHOR]