Preparation and Supercapacitive Behaviors of the Porous Reduced Graphene Derived from the Graphite Anode of Spent Lithium-Ion Batteries

Taking full advantage of the waste graphite source from spent lithium-ion batteries to prepare graphene for the application of supercapacitors is a significant strategy. In this work, porous reduced graphene oxide was successfully synthesized from waste graphite through a freeze-drying technique and a modified Hummers method. The performances of as-prepared graphene as a supercapacitor electrode material are discussed in detail. It has been found that compared with conventional synthesis methods, this work is not only easy to obtain raw materials but also highly efficient and less polluted. The results have shown that after the KOH activation treatment, the as-prepared porous graphene has a high specific surface area of 1699.2 m2 g–1 and a high specific capacitance of 215.4 F g–1 (269.3 F cm–3) at a current density of 0.5 A g–1. Especially, a good rate capability and excellent cycling stability of 93% capacitance retention after 10,000 cycles at 2 A g–1 can be achieved in a 3 M KOH electrolyte. More importantly, the assembled symmetric supercapacitor delivers a high energy density of 11.4 W h kg–1 at a power density of 250 W kg–1. Therefore, this work provides a new exploration for the low-cost preparation of electrode materials for high-performance supercapacitors and high-value utilization of waste graphite derived from spent lithium-ion batteries.