Untreated Natural Graphite as a Graphene Source for High-Performance Li-Ion Batteries

Abstract

Graphene nanosheets (GNS) are synthesized from untreated natural graphite (NG) foruse as electroactive materials in Li-ion batteries (LIBs), which avoids the pollution-generating stepsof purifying graphite. Through a modified Hummer method and subsequent thermal exfoliation,graphitic oxide and graphene were synthesized and characterized structurally, morphologicallyand chemically. Untreated natural graphite samples contain 45–50% carbon by weight; the rest iscomposed of different elements such as aluminium, calcium, iron, silicon and oxygen, which arepresent as calcium carbonate and silicates of aluminium and iron. Our results confirm that in the GOand GNS synthesized, calcium is removed due to oxidation, though other impurities are maintainedbecause they are not affected by the synthesis. Despite the remaining mineral phases, the energystorage capacity of GNS electrodes is very promising. In addition, an electrochemical comparisonbetween GNS and NG demonstrated that the specific capacity in GNS is higher during the wholecycling process, 770 mA·g−1at 100th cycle, which is twice that of graphite.