Biomimetic Bipolar Microcapsules Derived From Staphylococcus Aureus For Enhanced Properties Of Lithium-Sulfur Battery Cathodes

Lithium-sulfur(Li-S)batteries are receiving the increasing attention because of their high theoretical capacity and energy density,environmental friendliness,low cost,as well as natural abundance of sulfur resources.These advantages make Li-S batteries expected to be the next generation commercial batteries.Although Li-S batteries demonstrate very promising properties,the practical application of Li-S batteries are still hindered by several scientific and technologic issues,such as the insulating properties of sulfur and discharged products(Li2S2/Li2S),the large volume changes,and the dissolution of polysulfide intermediates.These issues will lead to poor cycling stability,inferior rate capability,and low Coulombic efficiency.To improve these electrochemical properties,we need to design a mechanically stable electrode structure,which is able to accommodate the volume change,prevent polysulfides migration,and retain the continuous networks for both electron and ion transports during cycling.Given that the charged and discharged products have the opposite polarities,insulating properties,changing volume,and varying solubilities in electrolytes,in this paper,we proposed a biomimetic bipolar microcapsule for Li-S battery cathode based on the previous studies and inspired by cell structures,which have "selective"membranes.The external membranes of cells control the mass transport of substances in and out.Only necessary nutrients are allowed into cells and metabolites released to the environment through the membrane protein interaction with substances.The selective transport and confined reaction are desired for the ideal Li-S batteries.The biomimetic biplar microcapsule uses polar TiO2 as the model chemical to build the biomimetic membrane,which allows lithium ion diffusion and mitigates polysulfides migration by means of the strong adsorption.The carbonaceous interior is derived from Staphylococcus aureus via a microbial fermentation and heat treatment route.The sulfur cathode with biomimetic bipolar microcapsule confinement demonstrate a high capacity of 1202 mA h g-1 at 0.1 A g-1 and an improved rate capability as well as Coulombic efficiency.Besides,the cathode shows a good cycling property over 1500 cycles at 1.5 A g'1 and a low capacity decay rate.What's more,TiO2 is only used as a model adsorbent in this paper.If some stronger adsorbents or higher efficiency electrocatalysts are introduced into the microcapsule,the biomimetic capsule-like concept will perform even better as particulate microreactors.It's worth noting that the biomimetic approach combines the biologic fermentation and chemical syntheses.On the one hand,the current approach could utilize the microorganism dead bodies,which are produced in the fermentation industries of medicines and some fine chemicals,for sulfur batteries cathodes and make wastes profitable,reduce the environment pollution.On the other hand,the route will open a new avenue to advance the preparation of new battery electrode materials.