Creation Of Intrinsic Pores In Transition Metal Nitrides And Use For Electrocatalytic Cathode Hosts In Li-S Batteries

As a new generation of energy storage devices,lithium-sulfur batteries have attracted extensive attention due to the high specific capacity,economical and environmental protection of the active material sulfur.However,as the cathode active material,the poor conductivity of sulfur leads to slow reaction kinetics;the dissolution of polysulfides in the electrolyte during charge and discharge causes"shuttle effect";the nearly 80%volume expansion of sulfur can easily causes the destruction of the electrode structure.These problems limit the rapid development of lithium-sulfur batteries.Porous metal nitrides possess excellent electrical conductivity and exceptional catalytic properties similar to noble metals,they also can adsorb polar polysulfides and their porous structure can overcome the issue of volume expansion.In a word,porous metal nitrides are ideal cathode materials for lithium-sulfur batteries.Therefore,an innovative experimental method for preparing porous nitrides（including porous TiN,VN,and CrN）in a hard template way was designed in this paper,and the porous metal nitrides were used as cathode materials for lithium-sulfur batteries.Firstly,nano-NaCl,KCl,and Na₂SO₄were prepared by recrystallization method with the solubility difference of inorganic salts in water and ethanol.Secondly,metal precursors porous TiN,VN,and CrN were prepared by sol-gel method with nano-NaCl as salt template,Ti Cl₄,VOCl₃,and Cr Cl₃·6H₂O as metal sources,and CO（NH₂）₂as nitrogen source,then the corresponding porous metal nitrides with NaCl were obtained by calcining at 750°C in a tube furnace under Ar atmosphere.Finally,porous metal nitrides were obtained by removal of NaCl with deionized water.By adjusting the content of NaCl and the molar ratio of CO（NH₂）₂to metal chlorides,we explored the optimal raw material ratio for the preparation of the three porous metal nitrides.CV,EIS,Li₂S deposition,and other electrochemical tests were used to compare the electrochemical properties of the three porous metal nitrides.The experimental results show that TiN has better electrochemical properies than VN and CrN.The lithium-sulfur batteries with S@TiN cathode material exhibit reversible capacity of above 500 m A h g^-1at current density of 4 C.XPS tests were carried out to explore the reaction mechanism of TiN and polysulfides,it was found that TiN has reinforcing chemical adsorption effect on polysulfides since Ti-S bond and N-Li bond are formed.What’s more,long-term cycling tests of lithium-sulfur batteries with S@TiN cathode material were performed at current densities of 0.5 C and 2 C,and the specific capacity remained above 600 m A h g^-1and 500 m A h g^-1after500 cycles separately,showing excellent electrochemical performances.