Rational Sulfur Cathode Design for Lithium–Sulfur Batteries: Sulfur-Embedded Benzoxazine Polymers

Abstract

A variety of advanced electrode structures have been developed lately to address the intrinsic drawbacks of lithium–sulfur batteries, such as polysulfide shuttling and low electrical conductivity of elemental sulfur. Nevertheless, it is still desired to find electrode structures that address those issues through an easy synthesis while securing large sulfur contents (i.e., > 70 wt %). Here, we report an orthogonal, “one-pot” synthetic approach to prepare a sulfur-embedded polybenzoxazine (S-BOP) with a high sulfur content of 72 wt %. This sulfur-embedded polymer was achieved via thermal ring-opening polymerization of benzoxazine in the presence of elemental sulfur, and the covalent attachment of sulfur to the polymer was rationally directed through the thiol group of benzoxazine. Also, the resulting S-BOP bears a homogeneous distribution of sulfur due to in situ formation of the polymer backbone. This unique internal structure endows S-BOP with high initial Coulombic efficiency (96.6%) and robust cyclability (92.7% retention after 1000 cycles) when tested as a sulfur cathode.

Recent Advances in Applying Vulcanization/Inverse Vulcanization Methods to Achieve High‐Performance Sulfur‐Containing Polymer Cathode Materials for Li–S Batteries

“…f) Rate performance of S‐BOP (0.9 mg sulfur cm −2 ). Reproduced with permission . Copyright 2016, American Chemical Society.…”

“…Je et al synthesized sulfur‐embedded polybenzoxazine (S‐BOP, as shown in Figure c) with 72 wt% sulfur. In S‐BOP, the sulfur chains were covalently bonded to the polymer framework through thiol groups present in the BZ monomer.…”

The Importance of Confined Sulfur Nanodomains and Adjoining Electron Conductive Pathways in Subreaction Regimes of Li‐S Batteries

“…Some representative electrode designs to avoid these fading mechanisms include encapsulating elemental sulfur (S) in conductive porous media or nanomaterial assemblies [35,36] or synthesizing sulfur-embedded polymers. [37][38][39][40][41][42] Both strategies have improved cyclability mainly by mitigating polysulfide dissolution. However, complete encapsulation remains a technical challenge for the former approach, where inevitable defects could lead to polysulfide dissolution especially Polysulfide dissolution into the electrolyte and poor electric conductivity of elemental sulfur are well-known origins for capacity fading in lithium-sulfur batteries.…”

Recent Advances in Cathode Materials for Room‐Temperature Sodium−Sulfur Batteries

“…Sulfur-organics copolymers have been wildly investigated in LiÀ S batteries. [41][42][43][44] These copolymers are usually prepared by heating sulfur and organics under controlled temperature and atmosphere. During the heating process, sulfur could copolymerize with the organics and form the sulfur-organics copolymers.…”