A Micelle Electrolyte Enabled by Fluorinated Ether Additives for Polysulfide Suppression and Li Metal Stabilization in Li-S Battery

Abstract

The Li-S battery is a promising next-generation technology due to its high theoretical energy density (2600 Wh kg −1) and low active material cost. However, poor cycling stability and coulombic efficiency caused by polysulfide dissolution have proven to be major obstacles for a practical Li-S battery implementation. In this work, we develop a novel strategy to suppress polysulfide dissolution using hydrofluoroethers (HFEs) with bi-functional, amphiphlic surfactant-like design: a polar lithiophilic "head" attached to a fluorinated lithiophobic "tail." A unique solvation mechanism is proposed for these solvents whereby dissociated lithium ions are readily coordinated with lithiophilic "head" to induce self-assembly into micelle-like complex structures. Complex formation is verified experimentally by changing the additive structure and concentration using small angle X-ray scattering (SAXS). These HFE-based electrolytes are found to prevent polysulfide dissolution and to have excellent chemical compatibility with lithium metal: Li||Cu stripping/plating tests reveal high coulombic efficiency (>99.5%), modest polarization, and smooth surface morphology of the uniformly deposited lithium. Li-S cells are demonstrated with 1395 mAh g −1 initial capacity and 71.9% retention over 100 cycles at >99.5% efficiency-evidence that the micelle structure of the amphiphilic additives in HFEs can prohibit polysulfide dissolution while enabling facile Li + transport and anode passivation.

An inverse vulcanized conductive polymer for Li–S battery cathodes

“…We note that there are several ways to prevent dissolution. First, there is a report of a new electrolyte (hydrofluoroethers with bi-functional, amphiphilic surfactant-like design) which significantly reduces the polysulfide dissolution 36 . Second, our theoretical calculations show Li x S y clusters anchored on the polymer can thermodynamically prevent such dissolution.…”

Highly Ordered Carbon Coating Prepared with Polyvinylidene Chloride Precursor for High‐Performance Silicon Anodes in Lithium‐Ion Batteries

“…Lithium‐ion batteries (LIBs) have long cycling life, high energy density, and high power capability, thus dominating the current energy storage market [1,2] . Significant research efforts have been devoted to development of next‐generation rechargeable batteries to meet the demand of the rapidly growing energy storage market, [3–7] as the graphite anodes in current LIBs have a rather limited theoretical capacity of 372 mAh/g. Silicon materials, with a nearly 10‐fold higher theoretical capacity of 3579 mAh/g, relatively low discharge potential (<0.5 V vs. Li/Li + ), and abundant resource, have been considered as promising anode materials for LIBs [8–10] .…”

Nitrogen‐Doped Hollow Carbon Polyhedrons with Carbon Nanotubes Surface Layers as Effective Sulfur Hosts for High‐Rate, Long‐Lifespan Lithium–Sulfur Batteries

“…Metal‐organic frameworks (MOFs), which have regular pores structures, are reported to be excellent scaffolds for preparation of porous carbon based electrode materials with a large specific surface area to maximize the electrode‐electrolyte interface. Further doping the neutral carbon skeleton with heteroatoms is considered as an effective method to polarize carbon basal planes, [21–23] which helps to enhance the adsorption ability towards lithium polysulfides [24–27] . As a highly conductive entity of carbon materials, CNTs can provide 1D continuous path for fast electron transport [28,29] .…”