Synthesis,Modification Of MnO₂ Nanostructures For Application In Lithium-Sulfur Battery

The development of new energy technology is of great significance to catch up the progress of society.This makes the research of high-performance energy storage devices play important roles to satisfy the demand.Therefore,as a kind of promising energy storage system with high theoretical specific capacity and energy density,lithium-sulfur(Li-S)batteries have attracted considerable attention recently.Apart from that,sulfur as a cathode material also enjoys many advantages--low cost,naturally abundant,non-toxic and environmental friendliness.However,the insulation of the S/Li₂S,volume expansion and shuttle effect in Li-S battery largely hamper its commercialization.These inherent problems make the capacity of Li-S battery in practical test and fast-charging far from the theoretical value.In view of these problems,we attempted to overcome the shuttle effect of polysulfides and improve the redox kinetics of active substances.The main contents are as follows:(1)Polyaniline in-situ modifying MnO₂ nanoparticles(PANI-MnO₂)were used to form a three dimensional(3D)hierarchically porous network as sulfur host for lithium-sulfur battery.The key point of this strategy is that the outer PANI layer leads to form an ultra-thin flexible 3D network skeleton with fast channels;and the birnessite MnO₂nanoparticles provide extraordinary chemical process via maximizing the oxidation of polysulfides to thiosulfates to largely alleviate the shuttle effect.Consequently,when evaluated as the cathode host for Li-S battery,the PANI-MnO₂-S electrode demonstrates excellent electrochemical performance,with a sustainable cycling capacity up to 1195 m A h·g^-1 at 0.5 C after 100 cycles.Even at a high current density of 2 C,the discharge capacity of 640 m A h·g^-1 after 500 cycles is accomplished.(2)The ultra-thin and lightweight mesoporous MnO₂ layer double-sided modified separator was synthesized by in-situ chemical self-assembly method.The mesoporous MnO₂ layer can not only act as an effective barrier for LIPS but as a chemical catalyst to improve the redox kinetics of electrochemical reactions,thereby effectively inhibiting LIPS shuttling.Furthermore,the polar MnO₂ layer facilitates the conductivity at the sulfur cathode and the wettability of electrolyte to improve Li⁺/e^-transport.When using pure sulfur as cathode,the mesoporous MnO₂ double-sided modified separator exhibits an initial capacity of 923 m Ah·g^-1 and 665 m Ah·g^-1after1000 cycles at 1 C,equivalent to only 0.028%attenuation per cycle.