(Georgia Institute of Technology, 2023-05-03)
Chandra, Vismay
In the wake of global transition to renewable energy, the demand for energy storage devices has grown exponentially. With electric vehicles (EVs) becoming mainstream, energy dense lithium-ion batteries (LIBs) are the need of the hour. Conventional liquid electrolyte batteries for LIBs may pose a safety hazard due to the use of flammable organic electrolytes with high vapor pressure. Solid state batteries (SSB) may become a solution to this problem if they mitigate the flammability issue and offer sufficiently high energy and power densities required for applications in the electric mobility sector. Conventional methods of processing solid polymer electrolytes (SPEs) and their incorporation into LIBs involve fabricating the electrode(s) and the separator membrane separately. These methods are heavily reliant on toxic solvents and are time and energy intensive processes, which makes a hurdle to commercialization. This thesis employs in-situ polymerization process, which is a one-step process of infiltration of SPE precursors into LIB stack followed by the polymerization and formation of the SPEs. Eliminating the use of solvents and reducing fabrication time makes this technique more attractive for a commercial deployment. A novel SPE is being explored in this thesis. The synthesis of the polymer has been explained and characterizations have been performed to understand thermal and electrochemical stability of the SPE. Systematic studies have been performed to investigate the evolution of resistance and stability of the solid electrolyte interphase (SEI) in contact with electrodes. Finally, the long-term cycling and rate performance of the SPE incorporated into commercial battery materials, such as lithium iron phosphate (LFP) and lithium titanate (LTO) have been evaluated.
(Georgia Institute of Technology, 2023-05-02)
Jakhar, Rishika
Sodium-ion batteries (SIBs) are an attractive alternative to lithium-ion batteries (LIBs) given sodium’s (Na) abundant availability, lower cost, and comparable energy storage characteristics. There is an increasing impetus to increase the energy densities and specific energies of SIBs. One of the ways to achieve this is to produce thicker electrodes with higher areal mass and capacity loadings in order to reduce the relative weight and volume fractions of inactive SIB components, such as current collectors and separators. Unfortunately, fabricating thicker electrodes by conventional slurry-casting methods presents two challenges – (i) avoiding the loss of mechanical strength and (ii) retaining fast ion transport within thick electrodes. In our proof-of-concept studies, SIB cathodes were fabricated using a phase inversion technique to be free-standing, exhibit over 100 µm thickness and possess vertically aligned pores. The electrochemical performance of such electrodes was investigated by studying their charge-discharge (C-D) profiles at different current densities and conducting cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements in half cell configurations. The effects of electrolyte composition and solid electrolyte interphase (SEI) additives were additionally investigated in symmetric cell configurations. The performance characteristics attained suggest a promise of this approach for a broad range of SIB and other battery chemistries. Further work on optimizing the pore shape, pore size distribution and pore volume is expected to further boost cell performance.