Mitigating polysulfide crossover in lithium–sulfur batteries with polymer-coated separators†

Abstract

Lithium–sulfur (Li–S) batteries promise high energy density and sustainability advantages by using earth-abundant sulfur as a key component, yet practical performance is limited by the complexity of sulfur-based redox reactions. One key challenge is the dissolution and redistribution of soluble lithium polysulfide (LiPS) intermediates from the sulfur cathode, which leads to irreversible loss of active material, poor cycle life, and high self-discharge rates. To ameliorate this issue, we use initiated chemical vapor deposition (iCVD) to conformally coat conventional polyolefin separators with an ultrathin (40–400 nm) copolymer, poly(divinylbenzene-co-(dimethylaminomethyl)styrene). This pDVB-co-DMAMS copolymer is designed with amine functionalities to interact with LiPSs and mitigate cathode-to-anode crossover, while DVB comonomer units serve as cross-linkers that improve mechanical integrity. We evaluate the electrochemical properties of prototype Li–S cells that include pDVB-co-DMAMS-coated separators and sulfur-infused carbon nanofoam paper cathodes. Separators with the thickest pDVB-co-DMAMS coating (400 nm) provide extended protection against self-discharge, while 40 nm pDVB-co-DMAMS coatings enable the highest overall rate capability and cycling stability while still maintaining reasonably low self-discharge rates. Post-cycling analysis of anode, separator, and cathode components, in conjunction with computational efforts, confirms that pDVB-co-DMAMS delays LiPSs crossover through chemical adsorption in the polymer-coated separator. The pDVB-co-DMAMS-coated separators also interact with Li metal anode to form favorable chemical speciation at the solid-electrolyte interphase that stabilizes the Li surface for Li–S cell operation.