Theoretical Design And Research Of Cathode Materials For Lithium-Sulfur Battreies

Lithium-sulfur batteries have become a favorable candidate for the next generation of green energy storage systems,owing to their high energy density,low material cost,and environmental friendliness.They also represent a new round of development opportunities for energy transformation.However,it is still in the stage of in-depth research.Therefore,rationally designing and developing functional materials with electrical conductivity,adsorption,and catalysis properties as sulfur cathode composites to effectively suppress the dissolution of polysulfides and the volume expansion of cathodes is the key to exerting their energy density advantages.In this paper,the method of density functional theory was used to study the following cathode composite materials:（1）The anchoring（adsorption）properties for polysulfides of boron（B）and nitrogen（N）co-doped graphene（BC₆NA,BC₆NM,BC₆NP）as sulfur cathode composite materials were studied.A systematic comparison was made with similar doping systems,and the complex adsorption mechanism was further analyzed.At the same time,the influence of the adsorption system on the battery performance was explored.The results show that BC₆NM and BC₆NP have relatively weaker anchoring properties,mainly contributed by physical interactions,and they proved not to be a good anchoring material due to their inability to efficiently adsorb Li₂S₄clusters.While BC₆NA has the best anchoring properties due to stronger chemical interactions.Furthermore,the enhanced electrical conductivity and reduced dissociation energy of the system after adsorption all indicate that BC₆NA is a promising cathode composite material with good effect.（2）In addition,the effect of ferroelectric polarization direction on the anchoring performance of polysulfides was also explored when the two-dimensional ferroelectric material In₂Se₃was used as the cathode composite material.The results showed that when the out-of-plane polarization direction was downward,the anchoring performance of the polysulfides was greater than that when the polarization direction was upward,which indicates that the ferroelectric polarization of ferroelectric films can effectively regulate the adsorption of polysulfides,and this conclusion provides a good idea for designing new high-efficiency lithium-sulfur batteries.These cathode composite materials play an important role in preventing the shuttle effect in lithium-sulfur batteries,improving the battery’s conductivity,and reducing volume expansion.At the same time,the different anchoring effect of lithium-sulfur battery can be regulated by adjusting the polarization direction of ferroelectric polarization during charge and discharge,so as to improve the charge and discharge rate and stability of the battery.These explorations of cathode composite materials for lithium-sulfur batteries have important implications for the development of commercial lithium-sulfur battery applications.