Novel Way to Turn Spent Li-Ion Battery Graphite into Valuable and Active Catalyst for Electrochemical Oxygen Reduction

Abstract

Battery technology has been recognized as one of the main driving forces and key technologies required to create a carbon-neutral economy and, therefore, batteries are currently one of the most rapidly growing technology sectors due to the rapid rise in the number of electric vehicles (EV´s). Additionally, the employment of Li-ion batteries (LIBs) in portable electronics has become a necessity in the modern world. This produces spend Li-ion batteries (SLIBs) in substantial volumes, it was estimated that in 2019 188,000 tonnes of SLIBs were available for recycling and it is expected that this number will rise to 125 million in 2030.1,2 To obtain the full benefits of electrification the value chain associated with batteries needs to become more sustainable, which strongly depends on the ability of SLIBs recycling to maximize the components return back to materials circulation. However, current SLIBs recycling strategies has been focused on cathode materials alone while largely overlooking the anode of the battery. In turn, anode recycling has so far concentrated mostly on the metal in the electrode and only very recently has the focus shifted towards the recycling of graphite powders.In this work, a novel strategy for recycling SLIB graphite and reforming it as a valuable catalyst material for electrochemical oxygen reduction reaction (ORR) is proposed. A modified Hummers method was applied to fabricate graphene oxide (GO) from SLIB graphite powder. The GO reduction and doping with nitrogen was achieved by pyrolyzing sample at 800 °C in the presence of DCDA. The prepared nitrogen-doped graphene (NG-Bat) was characterised by various physicochemical (SEM, TEM, XRD, Raman and XPS) and electrochemical characterization methods (LSV, EIS, chronoamperometry). For electrochemical characterisation RDE setup with the glassy carbon working electrode, modified with studied catalyst, in 0.1 M KOH solution was used. The physical and electrochemical characteristics of NG-Bat were compared with commercially available nitrogen doped graphene (NG-Com) sample.Based on XRD and Raman data, SLIB-derived graphite maintains its high quality, even after intense exploitation in the batteries and is therefore a valuable material that is worth recycling.3 Homogeneous distribution of carbon, nitrogen, and oxygen in NG-Bat sample was achieved and the overall nitrogen content was found to be 18.4 at%, based on XPS analysis. The onset potential of the ORR for the NG-Bat catalyst material is 0.867 V, and for the NG-Com catalyst 0.797 V. The NG-Bat shows a larger oxygen reduction current and higher electrocatalytic activity than the catalyst based on NG-Com (Figure 1). Based on EIS fitting very different charge transfer resistance and double-layer capacitance values are found, probably caused by different conductivities of the catalyst materials. NG-Bat showed much high electrocatalytic activity towards the ORR than commercial NG-Com based-catalyst material, caused probably by a higher content of active nitrogen species and the presence of carbon vacancies on the surface of graphene, as confirmed by XRD, Raman and XPS experiments.The findings demonstrate that SLIB graphite is still a valuable material and a promising precursor for GO fabrication. One of the potential applications of the SLIB-derived graphene could be the production of catalyst material for the oxygen reduction reaction (ORR), thereby open new avenues to the fuel cell, metal-air battery, and sensor industries.