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

Abstract

Employing Li-ion batteries (LIBs) in portable electronics has become a necessity in the modern world but, due to the short application time for any given battery (1-3 years) [1], the quantity of spent LIBs (SLIBs) waste is becoming substantial. As LIBs contain different valuable materials (the cathode layer holds Li, Co, Ni, Mn, Al and the anode layer graphite and Cu), the recycling of SLIBs is economically and environmentally beneficial. Additionally, the potential resource strain, as well of the geographical limitations found in the mining/production of the raw materials, will make recycling crucial for sustainable production of LIBs. However, current SLIBs recycling strategies has been focused on cathode materials alone while largely overlooking the anode of the battery [1–3]. 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 used to fabricate graphene oxide (GO) from SLIB graphite powder. The GO doping was done by pyrolyzing at 800 °C in the presence of dicyandiamide (DCDA). The mass ratio of GO-to-DCDA was 1:20. The prepared nitrogen-doped graphene, from SLIB graphite powder, (NG-Bat) was characterised by various physical (XRD, Raman, XPS, SEM, TEM) and electrochemical characterization methods. Electrochemical properties of the catalyst material was investigated by using the rotation disc electrode voltammetry and electrochemical impedance methods. For electrochemical characterisation the glassy carbon (CG) electrodes were modified with synthesized catalyst and the experiments were carried out in 0.1 M KOH solution. The GC disc electrodes were modified with NG ethanol suspensions (4 mgcatalyst ml-1) containing 6 µl aQAPS-S14 (2%) ionomer from Hephas Energy per 1ml ethanol. The physical and electrochemical characteristics of NG-Bat were compared with commercially available nitrogen doped graphene (NG-Com).Based on XRD and Raman data, it was shown that SLIB-derived graphite maintains its high quality, even after intense exploitation in the batteries and is therefore a valuable material that is worth recycling. The homogeneous distribution of carbon, nitrogen, and oxygen in NG-Bat was demonstrated by elemental mapping. The overall nitrogen content in NG-Bat was found to be 18.4 at%, from which pyridinic N constitutes 55.5 at%, graphitic N 21.7 at%, pyrrolic N 17.8 at% and oxidized N 5.0 at%. The onset potential of the ORR for the NG-Bat catalyst material is −0.11 V, and for the NG-Com catalyst −0.18V (Figure 1). The NG-Bat shows a larger oxygen reduction current and higher electrocatalytic activity than the catalyst based on NG-Com. Based on EIS fitting results very different charge transfer resistance and double-layer capacitance values are achived, probably caused by different conductivities of the catalyst materials. Catalyst material NG-Bat showed much high electrocatalytic activity towards the ORR than did a NG-Com, 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.These findings demonstrate that SLIB graphite is still a valuable material and a very suitable precursor for GO fabrication and SLIB anode layer needs to be recycled and returned to usage in a new form. Based on the result of this work, 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.