Self-activated pyrolytic synthesis of S, N and O co-doped porous carbon derived from discarded COVID-19 masks for lithium sulfur batteries

The continuous spread of COVID-19 has produced a large number of abandoned disposable medical masks (DMMs), which have a greater negative impact on the environment and biosafety. In response to this issue, a method for rapid microwave sulfonation, nitrification and oxidation of DMMs was proposed to convert DMMs with low carbonization efficiency into aromatic carbon with good thermal stability, which not only maintained 51 wt% of initial mass at 1000 °C, but also achieved in situ co-doping of S, N and O. Subsequently, porous carbons derived from DMMs were synthesized by self-activation pyrolysis, which avoided consumption of alkali and metal salts in the traditional activation process. It was further found that low pyrolysis temperature was not enough to produce enough active material H2 and H2O to obtain high specific surface area, while increasing pyrolysis temperature could adjust the specific surface area of as-prepared carbon, ranging from 52 m2·g−1 to as high as 890 m2 g−1. Thanks to synergistic effect of S, N, and O co-doping and hierarchical porous structure, the first discharge specific capacity of sample synthesized by self-activated pyrolysis at 900 °C was 1459.8 mAh·g−1 at 0.1 C, and the discharge specific capacity retention at 0.5 C after 400 cycles was 52.3%.