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Title: Oxidized bacterial cellulose functionalized with SiO2 nanoparticles as a separator for lithium-metal and lithium–sulfur batteries
Award ID(s):
2103582 2129983
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Page Range / eLocation ID:
481 to 493
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    Despite the potential to become the next‐generation energy storage technology, practical lithium–sulfur (Li–S) batteries are still plagued by the poor cyclability of the lithium‐metal anode and sluggish conversion kinetics of S species. In this study, lithium tritelluride (LiTe3), synthesized with a simple one‐step process, is introduced as a novel electrolyte additive for Li–S batteries. LiTe3quickly reacts with lithium polysulfides and functions as a redox mediator to greatly improve the cathode kinetics and the utilization of active materials in the cathode. Moreover, the formation of a Li2TeS3/Li2Te‐enriched interphase layer on the anode surface enhances ionic transport and stabilizes Li deposition. By regulating the chemistry on both the anode and cathode sides, this additive enables a stable operation of anode‐free Li–S batteries with only 0.1 mconcentration in conventional ether‐based electrolytes. The cell with the LiTe3additive retains 71% of the initial capacity after 100 cycles, while the control cell retains only 23%. More importantly, with high utilization of Te, the additive enables significantly better cyclability of anode‐free pouch full‐cells under lean electrolyte conditions.

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  2. Lithium metal batteries promise higher energy densities than current lithium-ion batteries but require novel electrolytes to extend their cycle life. Fluorinated solvents help stabilize the solid electrolyte interphase (SEI) with lithium metal, but are believed to have weaker solvation ability compared to their nonfluorinated counterparts and are deemed ‘poorer electrolytes’. In this work, we synthesize tris(2-fluoroethyl) borate (TFEB) as a new fluorinated borate ester solvent and show that TFEB unexpectedly has higher lithium salt solubility than its nonfluorinated counterpart (triethyl borate). Through experiments and simulations, we show that the partially fluorinated –CH2F group acts as the primary coordination site that promotes lithium salt dissolution. TFEB electrolyte has a higher lithium transference number and better rate capability compared to methoxy polyethyleneglycol borate esters reported in the literature. In addition, TFEB supports compact lithium deposition morphology, high lithium metal Coulombic efficiency, and stable cycling of lithium metal/LiFePO4 cells. This work ushers in a new electrolyte design paradigm where partially fluorinated moieties enable salt dissolution and can serve as primary ion coordination sites for next-generation electrolytes. 
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