Metal phosphides and borides as the catalytic host of sulfur cathode for lithium-sulfur batteries

Lithium-sulfur batteries are one of the most competitive high-energy batteries due to their high theoretical energy density of 2600 W center dot h center dot kg(-1). However, their commercialization is limited by poor cycle stability mainly due to the low intrinsic electrical conductivity of sulfur and its discharged products (Li2S2/Li2S), the sluggish reaction kinetics of sulfur cathode, and the "shuttle effect" of soluble intermediate lithium polysulfides in ether-based electrolyte. To address these challenges, catalytic hosts have recently been introduced in sulfur cathodes to enhance the conversion of soluble polysulfides to the final solid products and thus prevent the dissolution and loss of active-sulfur material. In this review, we summarize the recent progress on the use of metal phosphides and borides of different dimensions as the catalytic host of sulfur cathodes and demonstrate the catalytic conversion mechanism of sulfur cathodes with the help of metal phosphides and borides for high-energy and long-life lithium-sulfur batteries. Finally, future outlooks are proposed on developing advanced catalytic host materials to improve battery performance.