Mechanistic Study of Structural Evolution and Lithium-Ion Transport in Water-in-Polymer-Salt Electrolyte with Rigid-Rod Polyanion

Abstract

Conventional aqueous electrolytes are often restricted by a narrow electrochemical stability window (∼1.23 V), while water-in-salt electrolytes alleviate this limitation at the cost of excessive salt consumption and sluggish Li+ transport. To address this trade-off, poly(2,2′-disulfonyl-4,4′-biphenyline terephthalamide) (PBDT), a rigid-rod polyanion, is introduced to regulate Li+ solvation structure and transport behavior in water-in-polymer-salt electrolytes. All-atom molecular dynamics simulations reveal how incorporation of PBDT restricts free-water mobility and alters Li+ solvation environments through direct coordination of sulfonate groups. As a result, Li+ exists in three ion-association states (contact ion pairs (CIPs), solvent-separated ion pairs (SSIPs), and solvated Li+ ions), among which SSIP-Li+ participates in polymer-associated hopping pathways involving both along-chain and interchain migration, thereby providing molecular insight into Li+ transport regulation in concentrated electrolytes. These findings contribute to a molecular-level understanding of polyanion-regulated Li+ transport in aqueous electrolytes.