Subnanometric CoSn clusters embedded in N-doped carbon nanoboxes (SN-CoSn@C NBs) realize high efficiency adsorption-conversion of polysulfides

Abstract

The currently available electrode materials with low conductivity and poor cycling stability have limited the further commercial applications of lithium-sulfur batteries (LSBs). In this work, the SN-CoSn@C NB composite electrode was prepared by embedding subnanometric CoSn clusters into N-doped carbon nanoboxes through the combined acid-etching and carbonization approach. The reaction mechanism of the prepared SN-CoSn@C NB composite electrode towards the adsorption-conversion of polysulfides was investigated by electrochemical in situ FTIR spectroscopy and density-functional theory (DFT) modelling. The results showed that the subnanometric CoSn clusters with abundant reactive sites were able to boost the chemisorption and electrocatalytic conversion dynamics of polysulfides. The porous carbon nanobox host buffered the potential volume expansion from the charge-discharge cycles while enhancing the conductivities of S and Li2S species. Thus, the optimal SN-CoSn@C NB composite electrode exhibited a discharge capacity of 557.3 mA h g−1 at 5 C, and a capacity of 305.2 mA h g−1 was retained after 800 charge-discharge cycles. The 0.056% capacity fading rate per cycle suggested the commercial potential of such composite electrodes.