Biomass-derived Graphite-like Carbon as a Sustainable Cathode Material for Lithium Oxygen Batteries

Lithium–oxygen batteries (LOBs) offer the highest theoretical specific energy among metal–air chemistries, but their practical deployment is limited by the sluggish reversibility of Li2O2 formation/decomposition on the cathode, which requires a porous, electronically conductive carbon combining mesoporous transport with graphitic domains. Here, we report a two-step, KOH-assisted thermal treatment route for producing graphite-like porous carbon that converts spent mushroom substrate (SMS)—a lignin-rich agro-industrial waste generated at >5 million tonnes per year in East Asia—into a graphite-like porous carbon (G-SMS) for LOB cathodes. SMS derived from Pleurotus ostreatus cultivated on an oak–sawdust substrate was carbonized at 800 °C (1 h, 3 °C min−1), followed by KOH-assisted heat treatment at 1200–1800 °C. A KOH/C ratio of 0.5 was selected for the detailed graphitization series for its reagent economy and carbon yield: the 1.0 ratio gave ~10 wt% lower production yield and, at 1800 °C, lower carbon content (97.6 wt%) with residual ash (1.7 wt%), for no compensating benefit. Within the KOH/C = 0.5 series, G-SMS-1800/0.5 combined the smallest interlayer spacing (d002 = 0.347 nm), the lowest Raman I_D/I_G (0.69), the largest mesopore fraction (96.9%) and mesopore volume (0.31 cm3 g−1), and the highest powder conductivity (8607 S m−1 at 2000 kgf), giving the highest mesopore-volume-weighted conductivity descriptor of the matrix, V_Meso × σ = 2668 cm3 g−1 S m−1. This sample was identified as the most robust host, and its cycling stability was benchmarked against Super P in a modified CR2032 LOB cell (1 M LiTFSI in N,N-dimethylacetamide, 2.0 atm O2): G-SMS-1800/0.5 sustained 330 cycles, whereas Super P reached only 200 cycles under identical conditions, a ~1.65-fold improvement. KOH-mediated catalytic graphitization thus lowers the thermal budget of biomass graphitization while providing a conductive, mesopore-dominated host for Li2O2 deposition, providing a potential route for the valorization of spent mushroom substrate into graphite-like porous carbon for LOB cathodes.