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Studies of viewing-angle-switching display devices with all-direction-switching characteristicChung, Chia-Hung 05 September 2011 (has links)
In this study, a liquid crystal display (LCD) is proposed to have a capability of viewing-angle-switching in all directions. In the proposed LCD, a three-electrode structure is used to control the viewing angle of the LCD. By using a bi-direction slit type electrode, fringe fields with two different directions are generated. The fringe fields cause a light leakage of the dark state in all directions. Experimental results reveal that the proposed LCD has viewing angle within 40o in both vertical and horizontal directions when the area ratio of the vertical and horizontal slit is 1:1. Furthermore, contrast ratio (CR) of the proposed LCD increases as cell gap increases. When the angle between polarizer axis and LC is 0, the proposed LCD has the highest CR in the normal direction. The personal privacy is protected based on the proposed LCD due to the all-direction light leakage in the dark state.
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Operando Degradation Diagnostics and Fast Charging Analytics in Lithium-Ion BatteriesAmy M Bohinsky (10710579) 06 May 2021 (has links)
<p>Fast charging is crucial to the proliferation of electric vehicles.
Fast charging is limited by lithium plating, which is the deposition of lithium
metal on the anode surface instead of intercalation of lithium into the anode. Lithium
plating causes capacity fade, increases cell resistance, and presents safety
issues. A fast charging strategy was implemented using a battery management
system (BMS) that avoided lithium plating by predicting the anode impedance. Commercial
pouch cells modified with a reference electrode were cycled with and without
the BMS. Cells cycled with the BMS avoided lithium plating but experienced
significant degradation at the cathode. Cells cycled without the BMS underwent
extensive lithium plating at the anode. Capacity loss was differentiated into
irreversible and irretrievable capacity to understand electrode-based
degradation mechanisms. Post-mortem analysis on harvested electrodes showed
that the BMS cycled cells exhibited minimal anode degradation and had a
two-times higher capacity loss on the cathode. The cells cycled without the BMS
had extensive anode degradation caused by lithium plating and a seven-times
higher capacity loss on the anode. </p>
<p> </p>
<p>Understanding and preventing the aging mechanisms of lithium-ion
batteries is necessary to prolong battery life. Traditional full cell measurements
are limited because they cannot differentiate between degradation processes
that occur separately on anode and cathode. A reference electrode was inserted
into commercial cylindrical lithium-ion cells to deconvolute the anode and
cathode performance from the overall cell performance. Two configurations of
the reference electrode placement inside the cell were tested to find a
location that was stable and had minimal interference on the full cell
performance. The reference electrode inside the mandrel of the cylindrical cell
had stable potential measurements for 80 cycles and at different C-rates and
had minimal impact on the full cell performance.<b></b></p>
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Diagnosis of the Lifetime Performance Degradation of Lithium-Ion Batteries : Focus on Power-Assist Hybrid Electric Vehicle and Low-Earth-Orbit Satellite ApplicationsBrown, Shelley January 2008 (has links)
Lithium-ion batteries are a possible choice for the energy storage system onboard hybrid electric vehicles and low-earth-orbit satellites, but lifetime performance remains an issue. The challenge is to diagnose the effects of ageing and then investigate the dependence of the magnitude of the deterioration on different accelerating factors (e.g. state-of-charge (SOC), depth-of-discharge (DOD) and temperature). Lifetime studies were undertaken incorporating different accelerating factors for two different applications: (1) coin cells with a LixNi0.8Co0.15Al0.05O2-based positive electrode were studied with a EUCAR power-assist HEV cycle, and (2) laminated commercial cells with a LixMn2O4-based positive electrode were studied with a low-earth-orbit (LEO) satellite cycle. Cells were disassembled and the electrochemical performance of harvested electrodes measured with two- and three-electrode cells. The LixNi0.8Co0.15Al0.05O2-based electrode impedance results were interpreted with a physically-based three-electrode model incorporating justifiable effects of ageing. The performance degradation of the cells with nickelate chemistry was independent of the cycling condition or target SOC, but strongly dependent on the temperature. The positive electrode was identified as the main source of impedance increase, with surface films having a composition that was independent of the target SOC, but with more of the same species present at higher temperatures. Furthermore, impedance results were shown to be highly dependent on both the electrode SOC during the measurement and the pressure applied to the electrode surface. An ageing hypothesis incorporating a resistive layer on the current collector and a local contact resistance (dependent on SOC) between the carbon and active material, both possibly leading to particle isolation, was found to be adequate in fitting the harvested aged electrode impedance data. The performance degradation of the cells with manganese chemistry was accelerated by both higher temperatures and larger DODs. The impedance increase was small, manifested in a SOC-dependent increase of the high-frequency semicircle and a noticeable increase of the high-frequency real axis intercept. The positive electrode had a larger decrease in capacity and increase in the magnitude of the high-frequency semi-circle (particularly at high intercalated lithium-ion concentrations) in comparison with the negative electrode. This SOC-dependent change was associated with cells cycled for either extended periods of time or at higher temperatures with a large DOD. An observed change of the cycling behaviour in the second potential plateau for the LixMn2O4-based electrode provided a possible kinetic-based explanation for the change of the high-frequency semi-circle. / Litiumjonbatteriet är en möjlig kandidat för energilagring i hybridfordon och i satelliter i låg omloppsbana, men än så länge är livslängden på batterierna ett problem. Utmaningen ligger i att kunna förstå hur batteriet åldras genom att utforska hur åldringsprocessen accelereras av faktorer som laddningstillstånd, urladdningsdjup och temperatur. Livslängdsstudier för två olika typer av batterier tänkta för olika applikationer utfördes: (1) knappceller med positiva LixNi0,8Co0,15Al0,05O2-baserade elektroder studerades med en effektstödd (power-assist) hybridcykel från EUCAR, och (2) laminerade kommersiella celler med positiva LixMn2O4-baserade elektroder studerades med en satellitcykel, avsedd för en satellit med låg omloppsbana. Cellerna öppnades och de uttagna elektrodernas elektrokemiska egenskaper utvärderades i två- och tre-elektroduppställningar. Resultaten från elektrokemiska impedansmätningar för den positiva LixNi0,8Co0,15Al0,05O2-baserade elektroden tolkades med hjälp av en fysikalisk tre-elektrod modell som tog hänsyn till de i litteraturen främst föreslagna effekterna av åldring. Prestandadegraderingen av celler med nickelkemi var oberoende av cykel och laddningstillståndet där åldringen skedde, men starkt beroende av temperaturen. Den positiva elektroden visade sig vara den största orsaken till impedansökningen i batteriet. Ytfilmerna på den positiva elektroden hade en sammansättning som var oberoende av laddningstillståndet men beroende av temperaturen. Impedansresultaten från de uttagna elektroderna var starkt beroende av både laddningstillstånd och yttre tryck på elektrodytan. Det visade sig att det var tillräckligt att ta hänsyn till ett resistivt skikt på strömtilledaren och en lokal kontaktresistans mellan kolet och det aktiva materialet (som är beroende av laddningstillståndet) för att anpassa modellen till impedansdata mätt på de uttagna elektroderna. Prestandadegraderingen av celler med mangankemi påskyndades av både högre temperaturer och högre urladdningsdjup. Impedansen ökade något, då både högfrekvenshalvcirkeln och högfrekvensintercepten ändrades. Positiva elektroden hade en större degradering i kapaciteten och en större ökning i magnituden av högfrekvenshalvcirkeln (speciellt vid högre litiumjon koncentrationer i elektroden) jämfört med den negativa elektroden. Denna laddningstillståndsberoende impedans-ökning var kopplad till celler som hade cyklats under en längre tid eller vid en högre temperatur och med ett högt urladdningsdjup. Ökningen i magnituden av högfrekvenshalvcirkeln skulle kunna vara relaterad till kinetiska begränsningar eftersom cyklingsbeteendet vid andra spänningsplatån ändrades samtidigt för de LixMn2O4-baserade elektroderna. / QC 20100621
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