Recycling strategies for renewable graphite and other carbon nanomaterials from used batteries: A review

Recycling spent/used batteries can solve economic and environmental issues regarding the availability of graphite and resource depletion since the demand for graphite is growing with exponential technologies. Various batteries, including primary (manganese, alkaline) and secondary (lithium-ion, nickel-based batteries, vanadium redox flow batteries, sodium-sulfur batteries, lead acid batteries, electrochemical batteries, and supercapacitors), have been taken into consideration as a source of graphite. The graphite recovered must be converted to useable form like graphite oxide/graphene oxide or further as reduced graphene oxide for its high electrochemical property imparted to lithium-ion batteries (LIBs) via thermal, chemical and mechanical routes. The generated forms of graphite or carbon nanomaterials or carbon nanotubes (CNTs) have multiple merits viz., productivity, electrical conductivity and higher capacitance, over pristine, natural and synthetic graphite. These methods have shown high potential to prepare graphene oxide making it useful in photocatalysis, electronics, energy storage and sensors. Apart from the processing methods, mechanism, and property evaluation, a material flow analysis of recycling these batteries to recover graphite and the energy/cost savings are also illustrated.