Thermotolerant and Li2Sn-trapped/converted separators enabled by NiFe2O4 quantum dots/g-C3N4 nanofiber interlayers: toward more practical Li–S batteries

Abstract

The battery redox kinetics and operational reliability are two overriding concerns for current Li–S batteries (LSBs). When built up from the coin type to larger cells, LSBs are subjected to major issues of severe Li₂S_n polysulfide shuttling and safety hazards if working in overheated conditions. To effectively intercept/solidify these shuttled molecules and elevate the LSB thermostability, we herein propose to make thermotolerant and Li₂S_n-trapped/converted separators with functionalized interlayers, where highly catalytic NiFe₂O₄ quantum dots (QDs) are evenly distributed on intertwined g-C₃N₄ networks. In resulting separators, fluffy g-C₃N₄ nanofibers can impede the polysulfide shuttling well via physical confinement and chemisorption as well as enabling smooth charge transfer, while bimetallic QDs facilitate the catalytic conversion of intercepted polysulfides; in addition, using this interlayer will benefit the uniform deposition of Li at anode interfaces. Besides promotion in battery kinetics, our modified separators exhibit a reasonably high heat-resistance temperature beyond 170 °C. As evaluated, LSBs made using the designed separators achieve a large reversible capacity (1483.23 mA h g⁻¹ at 0.2C), salient cycling stability (a capacity decay rate of less than 0.08% in 500 cycles) and good rate capabilities. Even with a higher S loading of ∼6.24 mg cm⁻², full LSBs still deliver a remarkable capacity of ∼544 mA h g⁻¹ (84% of initial discharging capacity) after cycling. Our work may trigger great research enthusiasm in making more efficient separators for LSBs with extended storage capacities and improve safety.