Preparation of Porous Yolk–Shell S@Poly(vinyl alcohol) (PVA) Particles for a Lithium–Sulfur Battery Cathode with High Cycling and Rate Performances via a Self-Emulsification Process

Large volume expansion, the shuttling effect of polysulfides, and the low electronic conductivity of sulfur (S) largely deteriorate the cycling and rate performances of a lithium–sulfur battery. Premade yolk–shell particles with a S core and a carbon or conductive polymer shell are proven to be an effective way to alleviate all of the above three obstacles. Nevertheless, the reported preparation methods of yolk–shell particles with a S core and a polymer shell usually require complicated synthesis steps, which would severely inhibit their exploration in large-scale production. Here, a facile method to prepare S@polyvinyl alcohol (PVA) yolk–shell particles with the S core and PVA shell via a self-emulsification process is reported. On the one hand, the presence of abundant active hydroxyl groups along PVA chains enables PVA to act as a polymeric surfactant of S/CS₂ dispersed in water solution. On the other hand, these hydroxyl groups can be cross-linked by glutaraldehyde and form a robust shell. After the evaporation of CS₂, perfect S@PVA yolk–shell particles can be obtained. Meanwhile, along with the escape of CS₂ solvent, a lot of submicron-sized pores on the PVA shell can be formed, which will provide transporting paths for Li⁺ ions. Furthermore, the pore number on the shell is tunable by controlling the evaporation rate of CS₂. After adding carbon (C) into the S core to enhance its electronic conductivity, the initial specific capacity of the corresponding Li–S–C@PVA battery can reach 1117 mAh g^–1 at 0.1C, and the decay rate is only 0.036% per cycle at 1C for over 800 cycles.