Inhibiting Polysulfide Shuttle in Lithium–Sulfur Batteries through Low‐Ion‐Pairing Salts and a Triflamide Solvent

Abstract

The step-change in gravimetric energy density needed for electrochemical energy storage devices to power unmanned autonomous vehicles, electric vehicles, and enable low-cost clean grid storage is unlikely to be provided by conventional lithium ion batteries. Lithium-sulfur batteries comprising lightweight elements provide a promising alternative, but the associated polysulfide shuttle in typical ether-based electrolytes generates loss in capacity and low coulombic efficiency. The first new electrolyte based on a unique combination of a relatively hydrophobic sulfonamide solvent and a low ion-pairing salt, which inhibits the polysulfide shuttle, is presented. This system behaves as a sparingly solvating electrolyte at slightly elevated temperatures, where it sustains reversible capacities as high as 1200-1500 mAh g over a wide range of current density (2C-C/5, respectively) when paired with a lithium metal anode, with a coulombic efficiency of >99.7 % in the absence of LiNO additive.

Towards Weakly Coordinating Anions with the Extremely Electron Withdrawing Perfluoropyridinoxy Ligand –OC5F4N

“…The measured ionicities of the [Al(OR HF ) 4 ] -WCA in a series of ionic liquids has been shown to reach 100 % and this high ionicity has recently been exploited in a lithium-sulfur battery. [11] The exceptionally weak coordination of the [Al(OR F ) 4 ] -WCA is further demonstrated by the formation and structural characterization of the weakly bound complexes [Ag(C 2 H 2 ) 4 ] + [12] or [Ag(P 4 ) 2 ] + . [13] In these, complexes, the weakly bound acetylene and white phosphorus ligands are in constant competition with the counterion and solvent molecules for a place in the coordination sphere of the metal.…”

“…They also represent some the most weakly coordinating WCAs currently reported. The measured ionicities of the [Al(OR HF ) 4 ] – WCA in a series of ionic liquids has been shown to reach 100 % and this high ionicity has recently been exploited in a lithium‐sulfur battery . The exceptionally weak coordination of the [Al(OR F ) 4 ] – WCA is further demonstrated by the formation and structural characterization of the weakly bound complexes [Ag(C 2 H 2 ) 4 ] +[12] or [Ag(P 4 ) 2 ] + .…”

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…[6,7] [6,[121][122][123] One of the most prominent aluminate anions is [Al-(OR F ) 4 ] À (where R F = C(CF 3 ) 3 )a nd this is due to its simple and scalable preparation, ease of conversion into other useful WCA precursors,and weak coordinative strength. [129] Furthermore,the [Al(OR F ) 4 ] À anion demonstrated excellent stability towards Brønsted acids,itisstable up to the level of protonated mesitylene [6,130] as well as against highly electrophilic cations such as [CX 3 ] + (where X = Cl, Br,o r I) [131] or the bulkier silylium ion [Si(C 6 Me 5 ) 3 ] + . [125][126][127][128] Thev ery weak coordinative strength of the [Al(OR F ) 4 ] À anions gives rise to electrolytes possessing high ionicities, which means that the extent of ion pairing is very low and results in more free ions to contribute to charge transport.…”

A Highly Conductive MOF of Graphene Analogue Ni3(HITP)2 as a Sulfur Host for High‐Performance Lithium–Sulfur Batteries

“…Lithium sulfur (Li–S) batteries that consist of sulfur cathode and lithium anode are of great interest in next generation energy storage systems due to their ultra‐high theoretical capacity of sulfur (1675 mAh g −1 ) and metallic Li (3840 mAh g −1 ), abundant reserves of sulfur, low‐cost and environmental benignity . However, these ambitious prospects are retarded by several intractable challenges before their practical realization: i) the insulating nature of sulfur and its reduction species endows a quite limited electronic contact, leading to a sluggish redox reaction and serious polarization; ii) the notorious shuttle effect of lithium polysulfides in electrolyte and disordered deposition of sulfur species on lithium anode bring about severely capacity decline and low coulombic efficiency on cycling; iii) almost 80% of volume change during operations may lead to significant structure degradations in a long run . Despite carbon and its derivatives with hierarchical pores can inexpensively ameliorate the conductivity of intermediate sulfides and confine polysulfides, the confinements by meso‐/micropores in simple carbon‐based hosts are less efficient in the extended operations due to the weak van der Waals interactions between their nonpolar surfaces and polar polysulfides …”