RATIONAL DESIGN OF NANOSTRUCTURED POLYMER ELECTROLYTES AND SOLID - LIQUID INTERPHASES FOR LITHIUM BATTERIES

Abstract

Advances in understanding of the basic science and engineering principles the underpin performance of electrochemical storage technologies is imperative for significant progress in portable electrical storage. In this regard, metal based batteries comprising of a reactive metal (like Li, Na, Al) as anode have attracted significant attention because of their promise of improving the anode-specific capacity by as much 10-fold, compared to the current state-of-art Li-ion battery using graphitic anode. Perhaps their greatest advantage lies in the possibility of using of a Li-free high-capacity cathode like oxygen that can improve the gravimetric energy density of batteries from ~0.3kWh/kg to ~12kWh/kg (i.e. comparable to the useful energy available from combustion of hydrocarbons). A persistent challenge with batteries based on metallic anodes, concerns their propensity to fail by short-circuits produced by dendrite growth during battery recharge, as well as by runaway of the cell resistance due to internal side reactions with liquid electrolytes. The work reported in this thesis utilizes multiscale transport modeling and experiments to fundamentally understand and to thereby develop rational designs for polymer electrolytes and electrode – electrolyte interphases that overcome these challenges . On the basis of a linear stability analysis of dendrite growth during metal electrodeposition, it is shown that the length – scale on which transport occurs near the electrodes can be as important as electrolyte modulus in stabilizing metals against dendrite formation. To evaluate this proposal, cross-linked polymer electrolytes were designed with tunable pore size and the stability of metal electrodeposition was quantified in these systems. Direct visualization of electrodeposition using these electrolytes showed remarkable agreement with the theoretical predictions. Furthermore, when operated in a battery, the crosslinked membrane demonstrated stable galvanostatic cycling of lithium metal anodes for several hundreds of hours. Importantly, these studies showed that while the tendency for battery failure by dendrite-induced short-circuits can be reduced, the issue of capacity-fading as a result of continuous reactions of the metal with liquid electrolyte persists. Through multiscale modeling of ion transport, artificial solid electrolyte interphase designs are proposed for lithium-oxygen batteries to enable stable recharge and low overpotentials even with chemically reactive liquid electrolytes.