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" Development of Pseudocapacitive Properties in Nanostructured LiMn2O4 as a Fast Charging Cathode for Lithium Ion Batteries "
Lesel, Benjamin Kalman
Tolbert, Sarah H.
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Latin Dissertation
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English
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| Record Number
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897930
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TL5wh6t57d
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| Main Entry
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Adeleye, Adeyemi S.
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| Title & Author
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Development of Pseudocapacitive Properties in Nanostructured LiMn2O4 as a Fast Charging Cathode for Lithium Ion Batteries\ Lesel, Benjamin KalmanTolbert, Sarah H.
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2017
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2017
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| Abstract
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Pseudocapacitive materials provide a high energy density solution to fast charging, long cycle life energy storage. This work explores the pseudocapacitive characteristics and attempts to optimize nanostructured LiMn2O4 for use as a cathode material in fast charging, long cycle lifetime lithium ion batteries. Because slow kinetics in traditional batteries is linked to long lithium ion diffusion lengths through micron sized grains, the key to achieving pseudocapacitance in most materials is through nanostructuring to reduced diffusion distance. One of the most effective methods for producing nanostructures is through nanocrystal/polymer templating, which produces a porous structure with interconnected nanoscale walls capable of intercalating lithium ions at pseudocapactive rates. To make a full pseudocapacitive lithium ion battery a reality, however, a pseudocapacitive material of each electrode type, anode and cathode, must be paired. To date, many pseudocapacitive materials have been identified, but nearly all of them are redox active in a voltage range more suitable for anode materials. Recently, we identified a pseudocapacitive cathode material, nanostructured LiMn2O4 which shows impressive rate capabilities. Unfortunately, the improvements came at the cost of energy density, which decreased significantly with decreasing crystallite size. Kinetics for different crystallite sizes, however, increased suddenly below a certain critical crystallite size. We found that this critical crystallite size, below which pseudocapacitance occurred, was linked to a suppression of phase transition in nanoscale LiMn2O4. To address the capacity loss due to dissolution in high surface area nanostructured LiMn2O4 powders, a sol-gel templating method which formed dissolution resistant surfaces was employed. The resulting materials had long needle-like morphology and showed higher capacity and less dissolution than a similarly sized material synthesized with a different structure. It was concluded that the needles of the higher capacity structure were dissolution resistant surfaces along their lengths and therefore maintained higher energy density. In another approach, higher capacity was achieved in nanostructured LiMn2O4 with the addition of magnesium into the crystal structure. It was theorized that the increased capacity came from the magnesium ions stabilizing the surface from dissolution, therefore increasing capacity. This understanding and optimization of nanostructured LiMn2O4 has led to the first scalable pseudocapacitive cathode material that can be effectively used in fast charging, long cycle lifetime lithium ion batteries.
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Lesel, Benjamin Kalman
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UCLA
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