Waste Hemp Hurd as a Sustainable Precursor for Affordable and High-Rate Hard Carbon-Based Anodes in Sodium-Ion Batteries

The present studyreports the promising potential of waste hemp-hurd-derivedcarbons as anodes in sodium-ion batteries (SIBs). Carbons were producedthrough an easily scalable process consisting of pyrolysis of rawbiomass at 500 degrees C followed by mild chemical activation of theresulting char through wet impregnation with K2CO3 and subsequent heating of the solid phase (after filtration anddrying) up to 700 or 800 degrees C under nitrogen. The best electrochemicalperformance was observed for the hard carbon activated at a char-K2CO3 mass ratio of 1:4 and heated up to 800 degrees C,which exhibited an excellent initial coulombic efficiency (73%) andachieved reversible charge capacities of 267 and 79 mAh g(-1) at 0.03 and 1 A g(-1), respectively. This materialalso exhibited an impressive cyclic stability and rate capability,with a capacity retention of 96% after 300 cycles at a current densityof 2 A g(-1). This more than satisfactory performancecould be related to the textural and structural features of the hardcarbon, which include moderate interconnected microporosity (withpore sizes below 1 nm), an appropriate concentration of defects inthe carbon structure, relatively large interplanar distances, anda certain number of closed pores.