Browsing by Subject "Li-ion battery"
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Item Alloy-type and conversion-type anode materials for enhanced performance as lithium ion battery anode materials(2015-12) Klavetter, Kyle Christopher; Mullins, C. B.; Heller, Adam; Ellison, Chris; Hwang, Gyeong; Humphrey, SimonCharge storage in the contemporary lithium-ion battery is at an energy density too low to support the function of long-range electric vehicles and other electronically powered technologies. To obtain up to two times or greater higher energy density than what is available by intercalation of lithium ions into graphite, the prevalent anode material in commercial batteries, materials with a higher storage density of lithium may be used, including materials that alloy with lithium or undergo a reversible conversion reaction to form lithium oxide. In this work, several such materials are considered – Ge, SnO2, Co3O4, and Ge0.1Se0.9 – and focus is directed to first demonstrating significantly enhanced cycling stability and capacity retention at variable charge/discharge rates and, second, to explaining the electrochemical performance in terms of key physical and chemical properties. Particular attention is given to assessing the formation of the solid electrolyte interphase (SEI) formed upon the anode material during charge/discharge cycling by means of microscopy and chemical characterization.Item Computational, theoretical investigation of materials for a sustainable energy future(2016-08) Stauffer, Shannon Kaylie; Henkelman, Graeme; Mullins, Charles B; Crooks, Richard; Hwang, Gyeong; Milliron, DeliaOver the past several decades there has been significant progress in electronic structure theory, statistical sampling algorithms and computational resources which can be leveraged to calculate fundamental properties of materials and estimate rates of relevant chemical reactions. In the following dissertation, I use computational methods to address the materials problem of a sustainable energy future. Energy storage technologies have played a vital role in the mobile-technology revolution and the transition to utilize more sustainable energy sources; however improvements to the energy density, charge/discharge rate, and safety of rechargeable batteries are needed to realize the ambitious goals of fully electric vehicles and on-grid storage in areas with intermittent, renewable power sources. Li-ion batteries, in general, have a potential to fulfill these demands. In the following work, a new, high energy density electrode material with little capacity loss is considered. Additionally, the complex interaction between an electrode/electrolyte model system is considered in a potential dependent computational framework. Having a sustainable energy future also means utilizing energy-efficient processing in industrial scale applications. Separation processes use roughly 12% of all energy consumed in the United States due to energy-intensive thermal separation techniques. A final study looks at an alloy catalysts for the separation of ethylene from ethane/ethylene mixtures. A unique selectivity property was discovered that may help design catalysts to replace thermal separation of gases.Item The development of a battery management system with special focus on capacity estimation and thermal management(2016-08) Anyaegbunam, Ifedioranma; Chen, Dongmei, Ph. D.; Beaman, JosephLithium ion batteries are instrumental in tackling the challenges of global warming. They have shown great utility in electric and hybrid vehicles. However, challenges with regard to performance and safety such as capacity fade and thermal runaway need to be accounted for in the implementation of these battery systems. One way is through battery management systems that monitor and control various aspects of the battery’s operation. At the heart of the battery management system is an analytical model of the battery. This thesis proposes a battery management system which uses a “lowuses a “low-order” physics- based battery model that estimates capacity and optimally manages the temperature of the battery. A capacity estimation methodology is proposed that uses the state of charge estimate from an extended kalman filter and the inverse of the coulomb counting equation to estimates the “instant” capacity of the battery. This instant value is then used in an averaging calculation that uses saturation limits and a time delay to obtain a value for the capacity that is representative of the battery. This value is then feedback into the kalman filter. The capacity estimate obtained through this method was between 2 and 8 % off of the true value. A thermal management system is also proposed that optimally controls a fan to cool a lithium ion battery. The thermal management system was developed and tested in a simulated environment. First, the fan model was integrated with the battery model and simulations were run to test the open loop temperature response of the battery to the fan cooling while varying the input voltage of the fan the current demanded of the battery. From this data an operating point was chosen, the system was linearized, and a linear quadratic controller was designed and implemented. The controller was sluggish when faced with a temperature perturbation in the absence of a current demand increase but drove the temperature change to zero. In the presence of a current change controller drove the state to a nonzero steady state value. The same result occurred when a disturbance rejection mechanism was applied to the controller.