Nasim Azimi

Bis(2,2,2-trifluoroethyl) ether as an electrolyte co-solvent for mitigating self-discharge in lithium-sulfur batteries.

Lithium-sulfur batteries suffer from severe self-discharge because of polysulfide dissolution and side reaction. In this work, a novel electrolyte containing bis(2,2,2-trifluoroethyl) ether (BTFE) was used to mitigate self-discharge of Li-S cells having both low- and high-sulfur-loading sulfur cathodes. This electrolyte meaningfully decreased self-discharge at elevated temperature, though differences in behavior of cells with high- and low-sulfur-loading were also noted. Further investigation showed that this effect likely stems from the formation of a more robust protective film on the anode surface.

Insight into lithium–metal anodes in lithium–sulfur batteries with a fluorinated ether electrolyte

High energy density Li–S batteries are a promising green battery chemistry, but polysulfide shuttling and lithium anode degradation hinder the practical use of Li–S batteries. Tremendous efforts have been made including confining sulfur in a closed cathode porous matrix and stabilizing lithium–metal anodes with additives; however, satisfactory confinement is challenging to achieve and electrolyte additives could be electrochemically unstable, deteriorating the long-term cyclability of Li–S batteries. Here, we demonstrate the control of polysulfide shuttling and stabilization of the lithium–metal anode with a fluorinated ether electrolyte without either cathode confinement or additives, which can be beneficial for both the efficient use of electrolytes and safe operation of Li–S batteries. Moreover, a solid-electrolyte interphase (SEI) layer with a hierarchical chemical composition of LiF and sulfate/sulfite/sulfide was identified on lithium anodes, which suppresses parasitic reactions and helps preserve the anode quality.

Understanding the Effect of a Fluorinated Ether on the Performance of Lithium–Sulfur Batteries

A high performance Li-S battery with novel fluoroether-based electrolyte was reported. The fluorinated electrolyte prevents the polysulfide shuttling effect and improves the Coulombic efficiency and capacity retention of the Li-S battery. Reversible redox reaction of the sulfur electrode in the presence of fluoroether TTE was systematically investigated. Electrochemical tests and post-test analysis using HPLC, XPS, and SEM/EDS were performed to examine the electrode and the electrolyte after cycling. The results demonstrate that TTE as a cosolvent mitigates polysulfide dissolution and promotes conversion kinetics from polysulfides to Li2S/Li2S2. Furthermore, TTE participates in a redox reaction on both electrodes, forming a solid electrolyte interphase (SEI) which further prevents parasitic reactions and thus improves the utilization of the active material.

An organophosphine oxide redox shuttle additive that delivers long-term overcharge protection for 4 V lithium-ion batteries

Redox shuttle additives are used to protect Li-ion batteries from overcharge. Increased operating voltage requires striking a balance between a high redox potential and electrochemical stability. 1,4-Bis[bis(1-methylethyl)phosphinyl]-2,5-dimethoxybenzene (BPDB) exhibits a redox potential of 4.5 V vs. Li/Li+ and provides stable overcharge protection for 4 V cells delivering 95 cycles of 100% overcharge ratio.

Improved cyclability of a lithium–sulfur battery using POP–Sulfur composite materials

The microporous nature of the porous organic polymer (POP) successfully limits the crystallization of sulfur and hence restrains the dissolution and diffusion of lithium polysulfides formed during the repeated charge and discharge process of lithium–sulfur batteries. In this study, we demonstrated for the first time that a POP–sulfur nanocomposite can lead to high coulombic efficiency and superior reversibility in lithium–sulfur batteries.

Materials and technologies for rechargeable lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are one of the most promising energy storage systems being developed as an alternative to conventional intercalation-type lithium-ion batteries. This chapter first discusses the fundamental chemistry and existing issues associated with Li–S system. It then consolidates significant advances in the Li–S battery, including the development of sulfur composite cathodes, binders, and electrolytes, as well as several notable new concepts in materials and cell design.