Humic acid-derived graphene–SnO2 nanocomposites for high capacity lithium-ion battery anodes

Humic acid obtained from wood, soil, and coal provides a naturally occurring highly oxidized carbonaceous two-dimensional material. Humic acid obtained from Leonardite coal and tin(II) chloride were used to synthesize graphene–SnO2 nanocomposites using scalable, thermal treatment processes. The humic acid-derived graphene–SnO2 nanocomposites showed the presence of graphene sheets with a unique crumpled and wrinkled morphology and SnO2 nanoparticles. The graphene–SnO2 nanocomposites were tested as anodes for lithium-ion batteries and showed high reversible specific capacities (641 mAh g−1). In addition, the graphene–SnO2 nanocomposites also exhibited high capacity retention upon cycling which is attributed to the interaction of SnO2 nanoparticles with the humic acid-derived graphene nanosheets that allows accommodation of highly reversible volumetric changes upon Li-ion insertion/de-insertion within the structure. In comparison, humic acid treated without the incorporation of SnCl2 during the synthesis process resulted in stacking of the nanosheets leading to low surface areas and low specific capacities. The scalable production of graphene nanocomposites from earth-abundant precursors opens up significant opportunities for low-cost and high performance materials for numerous energy storage and conversion devices.