Porous biochar nanosheets loaded with Fe3C particles accelerate electrochemical reactions and their applications in Li–S batteries

There is an urgent need for reasonably designed matrixes with strong adsorption for polysulfides, fast reaction kinetics, and simple preparation for lithium–sulfur battery (Li–S battery) applications. Therefore, in this study, potassium ferrate was used to carbonize the petals of a hibiscus flower, and the doping of Fe3C was realized at the same time as the carbonization to prepare in one step a porous biochar nanosheet (Fe3C-HSB) composite material loaded with Fe3C particles. Fe3C plays a key role in lithium polysulfide (LiPS) chemical adsorption and other aspects, which can greatly improve the cycle stability of Li–S batteries. Because the prepared composite material has a unique nanosheet structure, it can effectively shorten the ion diffusion length, improve the electron charge transfer ability, and accelerate the progress of the electrochemical reaction. When sulfur is injected at 80.0 wt%, the discharge capacity of the Fe3C-HSB@S composite material is 777.1 mA h g−1, and it is stable at a rate of 1C. After 500 cycles, its reversible capacity can still reach 451.3 mA h g−1, with a single-turn capacity attenuation rate of 0.083%. Therefore, the rational design of porous biochar nanosheets doped with Fe3C particles is of great significance for improving the electrochemical performance of Li–S batteries, realizing renewable energy technologies, and promoting industrial applications.