Project Title: Materials architecture and charge transport in energy storage devices
Research overview. Modern portable and wearable devices require reliable, safe, compact, lightweight, and high-energy storage systems. Rechargeable power sources with high specific energy (>200 Wh/kg), high energy density (>300 Wh/l), maintenance free operation, architecture compatibility with human-safe operation and long operation time (> 8 hr) are the longer-term goals to meet the demands of future portable and wearable devices. Li-S batteries are promising candidates for long-term storage devices due to high theoretical specific capacity (~1675 mAh/g), high theoretical specific energy (~2600 Wh/kg), and high volumetric energy density (~2800 Wh/L). Li-S batteries differ from the conventional Li-ion cells, since these operate on multi-electronic processes (i.e., 16Li + S8 ↔ 8Li2S, Eo = 2.15 V vs Li+/Li). The major issues facing rechargeable Li-S batteries that impede their practical applications are: 1) undesirable surface reactions on the lithium electrode and 2) structural and morphological changes of the sulfur (S8) cathode during the charge-discharge processes which involves the formation of soluble lithium polysulfides, Li2Sx (x = 3 to 8) and insoluble sulfides Li2S2/Li2S in liquid electrolyte. Capacity fading is also caused by the accumulation of a net amount of the insoluble Li2S and Li2S2 on the Li anode. PR-CLIMB participants will study: 1) polymer-containing electrolytes including: polyethane oxide, polyethylene glycol-dimethylether (PEGDME), mixture of PEGDME or tetraethylene glycol-dimethoxyethane with ionic liquids that show longer cycle life and lower discharge; 2) additives containing N-O bonds, like LiNO3, into the cell, which can lead to the creation of a protective LixNOy and/or LixSOy on the Li anode; and 3) sulfur (S) composites either as C/S nano-composites with highly homogenous sulfur dispersion or as a C-core/S-shell structure using porous, graphitized carbons (C) like carbon nanotubes, graphene. It is expected that dispersion of the active sulfur in a highly conductive matrix, especially nanostructured carbon materials, will improve the electronic conductivity and enhance the discharge capacities as well as cycleability at high current densities.
Skills/Techniques: PR-CLIMB participants will learn to synthesize cathodes using co-precipitation methods and anodes using high energy mechanical milling (HEMM), microwave assisted, and chemical vapor deposition (CVD) techniques following laboratory published protocols.
Skills/Techniques: PR-CLIMB participants will learn to synthesize cathodes using co-precipitation methods and anodes using high energy mechanical milling (HEMM), microwave assisted, and chemical vapor deposition (CVD) techniques following laboratory published protocols.