Boosting Cathode Activity and Anode Stability of Lithium–Sulfur Batteries with Vigorous Iodic Species Triggered by Nitrate

An iodine-nitrate (I₂−LiNO₃)-containing ether-based electrolyte has been applied to Li−S battery with a sulfurized polyacrylonitrile cathode. The I⁻/HI-induced polymerization of 1,3-dioxolane is inhibited in the presence of nitrate. The nitrate can chemically oxidize I⁻/HI to I₃ ⁻/IO₃ ⁻, which play a crucial role to accelerate cathode conversion reaction and rejuvenate anode dead Li simultaneously. With the modified electrolyte, Li−S battery demonstrates long calendar life, high energy density and power efficiency.

Abstract

Lithium–sulfur (Li−S) battery with a sulfurized polyacrylonitrile cathode is a promising alternative to Li-ion systems. However, the sluggish charge transfer of cathode and accumulation of inactive Li on anode remain persistent challenges. An advanced electrolyte additive with function towards both cathode and anode holds great promise to address these issues. Herein, we present a new strategy to boost sulfur activity and rejuvenate dead Li simultaneously. In the polar electrolyte containing I₂−LiNO₃ additives, I₃ ⁻/IO₃ ⁻ are triggered significantly by the reaction between NO₃ ⁻ and I⁻ ions. The I₃ ⁻/IO₃ ⁻ are reactive to insulated Li₂S product of cathode and inactive Li on anode, thus accelerating the conversion reaction of sulfur and recovering Li sources back to battery cycling. The in situ/ex situ spectroscopic and morphologic monitoring reveal the crucial role of iodine in promoting Li₂S dissociation and inhibiting dendritic Li growth. With the modified electrolyte, the symmetric Li||Li cells deliver a lifespan of 4000 h with an overpotential less than 12 mV at 0.5 mA cm⁻². For Li−S cells, 100 % capacity retention up to thousands of cycles and enhanced rate capability are available. This work demonstrates a feasible strategy on electrolyte engineering for practical applications of Li−S batteries.

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