154 research outputs found
LT-LiMn0.5Ni0.5O2: A Unique Co-Free Cathode for High Energy Li-Ion Cells
No full textA new Li-ion battery cathode, ‘LT-LiMn0.5Ni0.5O2’, where LT refers to its relatively low synthesis temperature (400 oC), has been identified. Electrochemical data indicate that Li/LT-LiMn0.5Ni0.5O2 cells operate between 5.0 and 2.5 V with good cycling stability, yielding a cathode capacity of 225 mAh/g. The electrochemical reactions occur in two distinct steps centered at ~3.75 V and ~4.7 V during charge, and at ~4.6 V and ~3.5 V during discharge. High-angle, annular-dark-field (HAADF) scanning-transmission electron microscopy (STEM) provide evidence that LT-LiMn0.5Ni0.5O2 consists of a unique, partially-disordered LiMn0.5Ni0.5O2 structure with predominant lithiated-spinel- and layered-like character. Structural analysis of LT-LiMn0.5Ni0.5O2 with synchrotron X-ray diffraction data shows, surprisingly, that lithiated-spinel and layered models with approximately 16% (~1/6) disorder between the lithium and manganese/nickel ions, yield an identical fit to the data, complicating the determination of the exact nature and level of disorder in each structural model. We believe that this is the first report of a Mn-stabilized, lithium-nickel-oxide spinel-related structure in which the redox reactions occur almost entirely on the nickel ions, with the likelihood that oxygen redox also contributes to some capacity above 4.7 V
Electrochemical dynamics of nanoscale metallic inclusions in dielectrics
No full textNanoscale metal inclusions in or on solid-state dielectrics are an integral part of modern electrocatalysis, optoelectronics, capacitors, metamaterials and memory devices. The properties of these composite systems strongly depend on the size, dispersion of the inclusions and their chemical stability, and are usually considered constant. Here we demonstrate that nanoscale inclusions (for example, clusters) in dielectrics dynamically change their shape, size and position upon applied electric field. Through systematic in situ transmission electron microscopy studies, we show that fundamental electrochemical processes can lead to universally observed nucleation and growth of metal clusters, even for inert metals like platinum. The clusters exhibit diverse dynamic behaviours governed by kinetic factors including ion mobility and redox rates, leading to different filament growth modes and structures in memristive devices. These findings reveal the microscopic origin behind resistive switching, and also provide general guidance for the design of novel devices involving electronics and ionics
Fluorination‐Enhanced Surface Stability of Cation‐Disordered Rocksalt Cathodes for Li‐Ion Batteries
No full textAbstract Cation‐disordered rocksalt (DRX) materials have emerged as a class of novel high‐capacity cathodes for Li‐ion batteries. However, the commercialization of DRX cathodes will require reducing their capacity decay, which has been associated with oxygen loss during cycling. Recent studies show that fluorination of DRX cathodes can effectively reduce oxygen loss and improve cycling stability; however, the underlying atomic‐scale mechanisms remain elusive. Herein, using a combination of electrochemical measurements, scanning transmission electron microscopy, and electron energy loss spectroscopy, the correlation between the electrochemical properties and structural evolution in Mn‐redox‐based DRX cathodes, Li 1.2 Ti 0.4– x Mn 0.4+ x O 2.0‐ x F x ( x = 0 and 0.2) is examined. It is found that fluorination strongly suppresses structural amorphization and void formation initiated from the particle surface, therefore greatly enhancing the cyclability of the cathode. A novel rocksalt‐to‐spinel‐like structural transformation in the DRX bulk is further revealed, which surprisingly contributes to a gradual capacity increase during cycling. The results provide important insight for the design of novel DRX cathodes with high capacity and long cycle life
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Unlocking Li superionic conductivity in face-centred cubic oxides via face-sharing configurations
No full textOxides with a face-centred cubic (fcc) anion sublattice are generally not considered as solid-state electrolytes as the structural framework is thought to be unfavourable for lithium (Li) superionic conduction. Here we demonstrate Li superionic conductivity in fcc-type oxides in which face-sharing Li configurations have been created through cation over-stoichiometry in rocksalt-type lattices via excess Li. We find that the face-sharing Li configurations create a novel spinel with unconventional stoichiometry and raise the energy of Li, thereby promoting fast Li-ion conduction. The over-stoichiometric Li–In–Sn–O compound exhibits a total Li superionic conductivity of 3.38 × 10−4 S cm−1 at room temperature with a low migration barrier of 255 meV. Our work unlocks the potential of designing Li superionic conductors in a prototypical structural framework with vast chemical flexibility, providing fertile ground for discovering new solid-state electrolytes
Regime Shifts in the Hexi Oases over the Past Three Decades: The Case of the Linze Oasis in the Middle Reaches of the Heihe River
No full textOases regime shifts in the context of integrated water resource management have a significant impact on ecosystem functions and services and affect regional sustainable development and human wellbeing. Taking the Linze Oasis in the middle reaches of the Heihe River as a case study, we evaluated the regime shifts of the oases over the past 30 years from the two perspectives of scale and structure, considering the structural diversity index (H), water savings (Cn), productivity (WP), and other indicators. Furthermore, the driving factors of the socio-hydrological processes and the corresponding effects of the regime stages were discussed. The results indicate that the oases expanded concurrently with the increase in the regional water consumption from 1.09 × 108 m3 to 1.93 × 108 m3. The production of low-water-consumption and high-yield crops was found to be the main cause for the oases structure’s adjustment. The regime shifts in the oases comprised three main stages from 1990 to 2020, based on the interaction of socio-ecological elements. Water management policies promoted the regime shift process, while economic factors determined the long-term shifts. The improvement in water-saving practices driven by economic benefits is an effective way to realize the sustainable development of the Hexi oases
New Insight into the Role of Fluoro-ethylene Carbonate in Suppressing Li-Trapping for Si Anodes in Lithium-Ion Batteries
No full textFluoro-ethylene
carbonate (FEC) is widely adopted as a film-forming
electrolyte additive in Li-ion batteries and is believed to promote
the formation of a stable LiF-rich solid electrolyte interphase (SEI)
on silicon electrode surfaces. In this work, different from traditional
recognition, it is found that the role of FEC in suppressing Li-trapping
is more important than that of stabilizing the SEI film. In FEC-free
electrolyte, the growth and rearrangement of the SEI makes up for
47.8% of the capacity loss, and the remaining 52.2% is related to
Li-trapping within Si particles. In the presence of 10% FEC, capacity
loss related to SEI growth is reduced by 52.9%, while Li-trapping
within Si particles is reduced by 82.3%. Microscopic studies demonstrate
that LiF-doping in the bulk silicon phase is the main cause which
effectively inhibits the formation of crystalline Li15Si4 and thus reduces Li-trapping during electrochemical cycles.
This new insight discloses a hidden effect of FEC additive on the
Si anode in Li-ion batteries
Measurement on the Harmony Coefficient of Agro-eco-economic System in the Arid Region
No full textOn the basis of the present research progress of ecological agriculture, we take Minle County and Linze County located in the middle reaches of Heihe River as the typical research units. Based on the rural social and economic data during the period of 2000-2010, theory and method of mathematical statistics are used to establish the measure theory and model of agro-eco-economic system harmony coefficient, including efficacy function, function of harmony coefficient, harmony coefficient and level of harmony coefficient. Based on the actual situation of research region, evaluation indicator system of agro-eco-economic system is established and measurement is carried out. Results show that the regional agro-eco-economic system in research region was in a serious imbalance in 2000-2013. The harmony coefficient of Minle showed a slight rise from 2000 to 2004, and then presented a fluctuating decline. Its rank of harmony coefficient experienced serious imbalance-extreme imbalance-moderate imbalance-low imbalance-serious imbalance-high imbalance. At the same time, the similar tendency happened in Linze County. The measuring results of subsystem in 2000-2013 further indicated that except that the harmony coefficient of economic subsystem in Minle County and Linze County was moderate and high, the ecological subsystem was at Level II and Level III, and social subsystem was at Level IV and Level III, in high and low imbalance status. Finally, several recommendations were put forward for optimizing agro-eco-economic system
Atomic-scale Polarization Structures and Domain Dynamics in BiFeO3 Thin Films
No full textFerroelectric materials have been utilized in a broad range of electronic, optical, and electromechanical applications and hold the promise for the design of future high-density nonvolatile memories and multifunctional nanodevices. The applications of ferroelectric materials stem from the functional structures of domains and domain walls and the ability to switch them by applying an electric field. A fundamental understanding of the microscopic mechanism underlying the domain formation and the domain switching, therefore, is critical for design of practical ferroelectric devices. In this work, a systematic study of atomic-scale polarization structures and microscopic domain-switching processes in ferroelectric BiFeO3 thin films is performed by using atomic-resolution scanning transmission electron microscopy (STEM) and in situ transmission electron microscopy (TEM). The presented results, including structures and switching of strongly charged domain walls (sCDWs) and complex phenomena induced by nanoscale impurity defects, shed light on the interplay between ferroelectric polarization and bound charge, strain, or defect-induced local perturbations. This study opens up the possibility for developing novel ferroelectric nanodevices by control of sCDWs or through defect engineering.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135901/1/linze_1.pd
Transcategorial Shift in Mandarin Revisited: The Case of Nominalization
No full textThe article presents an analysis of transcategorial shift in Mandarin. Building on scholarly works conducted in the last century, this work sets out to present a new account of nominalization in terms of its underling cognitive mechanisms. A new notion, ontologicalization, is introduced into the study. It is argued that nominalization does exist in Mandarin and occurs on various levels, ranging from lexis to sentences. It may take on different forms, affix-derivation and zero-derivation. As detailed illustrations of the new approach, it is shown that structures like zhe ben shu de chuban (the publication of this book) and ta de bu lai (his not coming) are actually exocentric constructions and the possibility of defining de as a nominalizing infix
Optimering av taktil återkoppling i flera zoner : En beräkningseffektiv metod för fas- och aktiveringssekvensering
No full textDeafblindness has attracted more and more attention in recent years because it has a great impact on the quality of human daily life, and also affects their mental health. Some people get this kind of disability through illness or accident, while others are born with disability. This kind of condition, especially when they were born with deaf blindness, will lead to serious developmental and psychological problems and also will place a great burden on families. This study was initiated by the National Resource Centre for Deafblindness (Nationellt kunskapscenter för dövblindfrågor, Nkcdb), which wants to improve this situation and help those people. Haptic feedback systems have been developed to help deafblindness children to communicate with their parents. These systems usually use multi-zone vibration patterns to pass the information through touch. Linear resonant actuators (LRAs) are usually used in this kind of system to generate localized vibrations. However, LRAs are typically placed in a small area, which often causes mechanical and electrical interference that distorts the feedback signal and reduces tactile clarity, thereby reducing the accuracy of the device's vibration signal. So there is a need to solve this problem. A simulation-based case study was conducted using a 2×2 LRA array placed within a silicone pad interface, representing a wearable configuration for a congenitally deaf-blind child. The study simulated the electromechanical behavior and actuator interactions in optimized and unoptimized vibration modes. By evaluating parameters such as frequency energy distribution, phase coherence, and spatial interference, the case study validated the effectiveness of the proposed algorithm in reducing actuator interference and enhancing tactile clarity. This scenario can serve as a representative example for future deployment of optimized tactile systems in assistive communication devices. This study develops the Vibration Sequencing Algorithm (VSA) to address actuator interference. VSA is an algorithm based on the genetic algorithm framework. In this project, a mathematical model of the system is first established and then transformed into an optimization problem. Then, a method based on the non-dominated sorting genetic algorithm (NSGA) is used to generate the optimized vibration sequence. Experimental results show that the algorithm significantly reduces the mutual interference between actuators and improves the clarity of tactile feedback.Dövblindhet har fått allt mer uppmärksamhet de senaste åren eftersom det har en stor inverkan på människors dagliga liv och även påverkar deras psykiska hälsa. Vissa människor får denna typ av funktionsnedsättning genom sjukdom eller olycka, medan andra föds med funktionsnedsättning. Denna typ av tillstånd, särskilt när de föds med dövblindhet, leder till allvarliga utvecklings- och psykologiska problem och utgör en stor belastning för familjer. Denna studie initierades av Nationellt kunskapscenter för dövblindfrågor (Nkcdb), som vill förbättra denna situation och hjälpa dessa personer. Haptiska återkopplingssystem har utvecklats för att hjälpa dövblinda barn att kommunicera med sina föräldrar. Dessa system använder vanligtvis flerzonsvibrationsmönster för att förmedla informationen genom beröring. Linjära resonanta aktuatorer (LRA) används vanligtvis i denna typ av system för att generera lokaliserade vibrationer. LRA placeras dock vanligtvis i ett litet område, vilket ofta orsakar mekaniska och elektriska störningar som förvränger återkopplingssignalen och minskar den taktila tydligheten, vilket minskar noggrannheten i enhetens vibrationssignal. Så det finns ett behov av att lösa detta problem. En simuleringsbaserad fallstudie genomfördes med en 2×2 LRA-matris placerad i ett silikongränssnitt, vilket representerar en bärbar konfiguration för ett medfött dövblint barn. Studien simulerade det elektromekaniska beteendet och aktuatorinteraktioner i optimerade och ooptimerade vibrationslägen. Genom att utvärdera parametrar som frekvensenergifördelning, faskoherens och rumslig interferens validerade fallstudien effektiviteten hos den föreslagna algoritmen för att minska aktuatorinterferens och förbättra taktil tydlighet. Detta scenario kan fungera som ett representativt exempel för framtida användning av optimerade taktila system i kommunikationshjälpmedel. Denna studie utvecklar vibrationssekvenseringsalgoritmen (VSA) för att hantera aktuatorinterferens. VSA är en algoritm baserad på det genetiska algoritmramverket. I detta projekt etableras först en matematisk modell av systemet och omvandlas sedan till ett optimeringsproblem. Därefter används en metod baserad på den icke-dominerade sorteringsgenetiska algoritmen (NSGA) för att generera den optimerade vibrationssekvensen. Experimentella resultat visar att algoritmen avsevärt minskar den ömsesidiga interferensen mellan aktuatorer och förbättrar tydligheten i taktil återkoppling
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