Tailoring crosslinked gelled electrolyte and probing its synergistic performance with polymer-ceramic hybrid separators for high energy density lithium-sulfur battery systems

Shah, Vaidik Rashesh

Tailoring crosslinked gelled electrolyte and probing its synergistic performance with polymer-ceramic hybrid separators for high energy density lithium-sulfur battery systems

Abstract

The last two decades have seen an instrumental increase in the favor for renewable energy and the demand for electrical transport has significantly strengthened. With ever increasing demand for longer device duration especially for long-range electric transport, the existing Li-ion technology has eventually reached its limit. Meanwhile, Lithium Sulphur (Li-S) batteries, owing to their ultrahigh theoretical energy density of about 2600 Whkg-1, low-cost, Earth abundant and environmentally friendly sulfur (S) cathode, are seen as promising replacements to realize energy densities beyond 500 Whkg-1. However, Li-S batteries still suffer from several challenges. (1) The loss of coulombic efficiency due to ‘polysulfide shuttling’ wherein lithium polysulfide intermediates formed during cell discharge, dissolve into the battery electrolyte and migrate and undergo side reactions at the Li anode. The instability caused due to (2) significant cathodic volume changes, (2) lithium dendritic formation and (3) the formation of an ionically insulating ‘rough’ passivation layer after repeated charge/discharge operations, limit the practical utility of Li-S batteries. In this work, a novel solution in the form a facile, in-situ fabricated crosslinked Gel Electrolyte (GE) system has been proposed to tackle all the above issues. First, we present a comprehensive comparative analysis of the performance of GE cells with traditional liquid electrolyte (LE). The performance of GE cells was further enhanced using Polyethylene Glycol (PEG) as an additive. It was observed that the GE cells had substantially lower capacity fade and performed better than LE cells at high-rate cycling. Next, the GE system was paired with high-performance hybrid Polyimide (PI) / Organopolysilazane (OPSZ) separators. The synergistic performance of these two components in Li-S cell was probed and comparative analysis was conducted with conventional Celgard 2400 separator. The hybrid separator systems exhibit a ten-fold improvement in electrolyte uptake, a marked improvement in ionic conductivity and a high first cycle discharge capacity – close to that of LE cells.Finally, to investigate the effectivity of the gelled separators at trapping the lithium polysulfide (LPS) intermediates, a diffusivity analysis was carried out using gel crosslinked and non-crosslinked Celgard 2400 and PI/OPSZ separators. Experimental analysis showed that the gelled separators were more effective at entrapping LPS migration. We have also built a numerical model solved using Finite Element Method on a mapped mesh grid using COMSOL Multiphysics 5.5 to supplement the experimental analysis.

Description

146 pages

Date Issued

2021-08

Keywords

Gelled Electrolyte; Lithium-Sulfur Batteries; Polymer-Ceramic Hybrid Separators

Committee Chair

Joo, Yong L.

Committee Member

Suntivich, Jin

Degree Discipline

Chemical Engineering

Degree Name

M.S., Chemical Engineering

Degree Level

Master of Science

Types

dissertation or thesis