Synthesis and properties of novel sulfonated polyimides from 4,4′-(biphenyl-4,4′-diyldi(oxo))bis(1,8-naphthalic anhydride)

Development of Membranes and Separators to Inhibit Cross-Shuttling of Sulfur in Polysulfide-Based Redox Flow Batteries: A Review

The global rapid transition from fossil fuels to renewable energy resources necessitates the implementation of long-duration energy storage technologies owing to the intermittent nature of renewable energy sources. Therefore, the deployment of grid-scale energy storage systems is inevitable. Sulfur-based batteries can be exploited as excellent energy storage devices owing to their intrinsic safety, low cost of raw materials, low risk of environmental hazards, and highest theoretical capacities (gravimetric: 2600 Wh/kg and volumetric: 2800 Wh/L). However, sulfur-based batteries exhibit certain scientific limitations, such as polysulfide crossover, which causes rapid capacity decay and low Coulombic efficiency, thereby hindering their implementation at a commercial scale. In this review article, we focus on the latest research developments between 2012-2023 to improve the separators/membranes and overcome the shuttle effect associated with them. Various categories of ion exchange membranes (IEMs) used in redox batteries, particularly polysulfide redox flow batteries and lithium-sulfur batteries, are discussed in detail. Furthermore, advances in IEM constituents are summarized to gain insights into different fundamental strategies for attaining targeted characteristics, and a critical analysis is proposed to highlight their efficiency in mitigating sulfur cross-shuttling issues. Finally, future prospects and recommendations are suggested for future research toward the fabrication of more effective membranes with desired properties.

Synthesis, freestanding membrane formation, and properties of novel sulfonated hyperbranched polyimides

A novel six-membered ring hyperbranched polyimide (HBPI) has been synthesized by condensation polymerization of a difunctional monomer, 9,9-fluorenylidenebis(4,1-phenylene)bis(oxy)-4,4′-bis(1,8-naphthalic anhydride) (FBPNA), and a trifunctional monomer, tris(4-aminophenyl)amine (TAPA), at the molar ratio of FBPNA/TAPA = 1:1 in m-cresol at 180°C for 20 h. The resultant HBPI is further modified via end-capping reaction with 4-phenoxy-1,8-anhydride naphthalene (PNA). Post-sulfonation is performed in concentrated sulfuric acid at different temperatures (50, 60, and 70°C) for the pristine HBPI and 50°C for the PNA-modified polyimides to give various sulfonated HBPIs. Freestanding and tough membranes have been successfully fabricated by casting the polymer solutions containing a cross-linker, bisphenol A epoxy resin, at 80°C. The ion exchange capacities of the resultant membranes are in the range of 1.35–2.21 meq g−1 depending on the degree of chemical modification and the sulfonation conditions. Membrane properties such as water uptake, swelling ratio, proton conductivity, and radical oxidative stability are investigated.