Enhanced polysulfide trapping in Li–S batteries by dipole alignment in ferroelectric BaTiO3

Abstract

Lithium sulfur (Li–S) batteries are a promising technology due to their high energy density and low cost. However, the polysulfide shuttle effect remains a significant cause of degradation in Li–S batteries and there is an urgent need for improved cathode materials that can effectively trap polysulfides to minimize this phenomenon. In this work, we propose a BaTiO₃ (BTO) cathode with controlled dipole alignment as a ferroelectric additive to improve polysulfide trapping. To evaluate the polysulfide adsorption on BTO with different degrees of dipole alignments, operando ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and optical microscopy were used to track the shuttling of polysulfides in cycling Li–S batteries. The poled BTO cathodes demonstrated not only superior initial capacity, but also lower concentrations of shuttling polysulfides during cycling, resulting in a 24% improvement in capacity after 500 cycles as compared with the unpoled material. These improvements were attributed to the relatively strong electrostatic field induced by the highly aligned dipoles on the poled BTO surface, confirmed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and density functional theory (DFT) modelling. We thus demonstrate, for the first time, the beneficial role of bulk aligned dipoles in ferroelectric materials for the suppression of polysulfide shuttling, and the resulting superior long-term cycling performance.