Enhanced electrochemical performance of Li-S battery via structural transformation of N,O dual-doped carbon host material

Abstract

Poor electronic conductivity and “shuttle effect” as well as large volume change during cycling hinder the further practical applications of lithium-sulfur batteries (LSBs). Here, N,O dual-doped carbons were developed as sulfur host with adjustable porosity, graphited degree and surficial chemistry by simply changing molten inorganic salts (none, NaCl, NaCl/FeCl3) during sintering with aniline-pyrrole copolymer. NaCl promotes the graphitization and porosity with multi-scaled porous carbon host (CH2). NaCl/FeCl3 boosts doping content and facilitates transformation of both chemical state of doping elements and morphology to micro-meso pores dominated nanosheet (CH3) from little porous bulk (CH1). The flexible CH3 nanosheet with micro-mesopores could physically block dissolved Li2Sn (4 ≤ n ≤ 8) and provide large interfacial area to guarantee good electronic conductivity and ionic transport of the sulfur cathode for improving the electrochemical reactions kinetics. Furthermore, the high content doped pyrrolic N and epoxidized O in CH3 enhance chemical adsorption of soluble Li2Sn and accelerate the conversion process between Li2Sn and Li2S2/Li2S. Hence, CH3/S system exhibits ∼30% and ∼167% higher capacity than CH2/S and CH1/S after 200 cycles at 0.2 C. Our results clarify the working mechanism of carbon morphology and nitrogen, oxygen co-doping state tuning and promote the development of high-electrochemical performance LSBs.