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 H 2 and H 2 O to obtain high specific surface area, while increasing pyrolysis temperature could adjust the specific surface area of as-prepared carbon, ranging from 52 m 2 ·g −1 to as high as 890 m 2  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%.