Electrospun Particle/Polymer Fiber Mat Electrodes for Li-ion Batteries

• Main Author: Self, Ethan Craig
• Other Authors: Bridget R. Rogers
• Format: Others
• Language: en
• Published: VANDERBILT 2017
• Subjects: Chemical Engineering
• Online Access: http://etd.library.vanderbilt.edu/available/etd-12222016-234907/

Since their commercial debut in 1991, Li-ion batteries (LIBs) have revolutionized the functionality of portable electronic devices, and the LIB industry continues to grow today due emerging applications such as electric vehicle propulsion. Despite the extraordinary success of LIBs, many devices are still limited by battery performance, and thus new batteries with higher energy density, faster rechargeability, and longer cycle life must be developed to satisfy the ever-increasing demands of consumers. This dissertation details the fabrication and characterization of electrospun particle/polymer fiber mats as LIB electrodes, including: (i) anodes containing titania nanoparticles, carbon powder, and poly(acrylic acid) (TiO2/C/PAA), (ii) anodes containing carbon powder and poly(vinylidene fluoride) (C/PVDF), (iii) anodes containing Si nanoparticles, carbon powder, and PAA (Si/C/PAA), and (iv) cathodes containing LiCoO2 nanoparticles, carbon powder, and PVDF (LiCoO2/C/PVDF). The composition, thickness, fiber volume fraction, and fiber interconnectivity of electrospun mats can be easily controlled to achieve high capacities at fast charge/discharge rates. An electrospun TiO2/C/PAA anode with a thickness of 600 µm had an areal capacity of 0.97 mAh cm-2 at 2C which is much greater than that of a slurry cast anode of the same composition and loading (0.53 mAh cm-2). Likewise, a C/PVDF anode with a fiber volume fraction of 0.85 had a high volumetric capacity of 55 mAh cm-3 at 2C compared to only 27 mAh cm-3 for a conventional slurry cast graphite anode. Si/C/PAA fiber mat anodes had extremely high gravimetric, areal, and volumetric capacities of 1,484 mAh g-1, 4.5 mAh cm-2, and 750 mAh cm-3, respectively. C/LiCoO2 and Si/LiCoO2 full cells prepared with an electrospun anode and electrospun cathode had high specific energy densities of 150 and 270 Wh kg-1, respectively, which are among the highest values reported in the literature to date. The excellent performance of electrospun particle/polymer fiber mat electrodes is attributed to their: (i) large electrode/electrolyte interfacial areas, (ii) short Li+ transport pathways, and (iii) good electrolyte infiltration throughout the intra- and interfiber void space of the mats. These results demonstrate that the intelligent organization of electroactive powders into fiber mat electrodes can enhance Li+ transport rates and improve LIB performance.