A High-entropy Phosphate Cathode Host towards High-stability Lithium-sulfur Batteries

With the rapid development of portable electronic devices, electric vehicles and large-scale energy storage, higher energy density energy storage devices are needed to replace traditional lithium-ion batteries. Lithium-sulfur batteries (LSBs) are expected to be the next generation of high-specific capacity secondary batteries due to the high energy density (2600 Wh center dot kg(-1)) and low cost ($ 150 ton(-1)). However, LSBs also face serious problems, including poor rate performance and short cycle life. These problems are rooted in the insulating nature of sulfur, the shuttle effect of the intermediate phase lithium polysulfide (LiPSs), and sluggish reaction of sulfur redox reaction. Severe shuttle effects can cause LiPSs to diffuse into the lithium cathode and deposit on the Li metal surface, leading to the loss of active material; the insulating properties of sulfur and the reaction barrier also greatly limit the multiplier performance of lithium-sulfur batteries. The use of electrochemical catalysts to accelerate the conversion between LiPSs and lithium sulfide is currently an effective solution. Among them, high-entropy compounds have attracted a lot of attention. High entropy compounds are composed of multiple metallic elements uniformly distributed in the solid solution, and the catalytic activity and stability of these compounds are significantly enhanced due to the synergistic effect and high entropic stability. However, currently developed multi-elemental and high-entropy compounds are limited to single anion species such as oxides, carbides and sulfides, which have relatively simple molecular structures. Although the choice of combinatorial elements has been broadened by introducing the concept of high entropy, there is still a vast scope for development by extending the synthetic capabilities to more complex systems such as polyanionic materials. In this study, a high-entropy metal phosphate (HEPi) catalyst is obtained by one-step spray pyrolysis and applied to the sulfur cathode host. The rich porous structure of HEPi not only facilitates the encapsulation and domain-limiting of sulfur and ensures the sufficient infiltration of electrolyte, but also enhances the chemisorption of polysulfides and accelerates the rapid conversion of polysulfides, thus suppressing the shuttle effect of polysulfides and improving the utilization of sulfur. The results show that the assembled cell can obtain a high discharge capacity of 1477.3 mAh center dot g(-1) at a current density of 0.1 C. The capacity can be maintained at 782 mAh center dot g(-1) even at a high current density of 2 C. This work offers a prospect for the application of high-entropy materials in lithium-sulfur batteries.