Higher performance of Lithium-Sulfur Batteries by tuning the chemical structure of multifunctional NaPSS-PEGA copolymer binders

Addressing the multiple challenges associated with sulfur chemistry is imperative to unlock the full theoretical capacity of sulfur (1675 mAh·g−1) in Lithium-Sulfur Batteries. In pursuit of this objective, two linear copolymers were meticulously designed to serve as binders, exhibiting various capabilities such as polysulfides trapping, improved ionic conductivity, and adaptation to extreme volume changes. The synthesis of these polymers via RAFT polymerization ensured uniform molecular weight and enabled control over the chemical structure's organization—whether random or block copolymers. While the inclusion of distinct moieties, namely sodium polystyrene sulfonate and polyacrylates with pendant oligoethers groups, played a pivotal role in addressing the challenges associated with sulfur chemistry, the chemical structure emerged as the key factor significantly influencing the physicochemical properties. Insights gathered from tensile tests, polysulfide trapping assessments, swelling rates, electrochemical characterizations, and ab initio simulations underscored the profound impact of the chemical structure. Triblock copolymer demonstrated superior outcomes, including enhanced capacity retention (500 mAh·g−1 at 1C and ~ 800 mAh·g−1 at C/10), lower cell polarization (118 mV), and very high stable capacity at 100 cycles, compared to the random copolymer and overpassing traditional PVDF binders. This enhancement is attributed to the formation of predominant ionic conductive regions, which, owing to the specific chemical structure, remains unaffected by swelling upon interaction with the electrolyte. Schematization of segregated conductive regions (shaded in yellow) and polysulfides entrapment regions (shaded in purple) caused by the varying swelling degree for a) triblock and b) random copolymers. Copolymers are represented in bicolor curved lines; red and blue indicate NaPSS and PEGA respectively, and lithium polysulfides depicted as yellow happy faces. [Display omitted] •The primary structure of copolymer binders (block or random) affects Li-Sulfur batteries performance.•Block copolymer demonstrates exceptional performance, a low polarization (118 mV) with discharge capacity of 700 mAh·g-1.•The block copolymer architecture exhibits superior stability during long-term cycling tests.•The block copolymer binder reduces swelling rates, enhances polysulfide trapping and improve ionic conduction.