Enhancing the Capacitance of Flexible Supercapacitors by Utilizing Novel Li- and Co-Based Electrolytes Synthesized from Spent Lithium-Ion Battery Electrodes

Abstract To reduce the environmental damage caused by lithium-ion batteries (LIBs) and plastic waste, this study focused on the synthesis of Li-based (AME) and Co-based (PURE) electrolytes using electrodes recycled from spent LIBs obtained from cell phones. In addition, graphene (Gr) based supercapacitor (SC) electrodes were developed using recycled high-density polyethylene as the supporting material. First, reference SCs were made with AME (Gr-AME-SC) and PURE (Gr-PURE-SC) electrolytes, which exhibited specific capacitance/energy–density of 661.0 F g −1 /132.2 W·h kg −1 and 426.1 F g −1 /85.2 W·h kg −1 , respectively. Next, the TiO 2 /MoS 2 (TMS) composite was integrated into the SC electrodes, resulting in a 52.5% increase in specific capacitance for the SC fabricated with AME electrolyte (Gr/TMS-AME-SC) and a 20% increase in capacitance occurred for the device with PURE electrolyte (Gr/TMS-PURE-SC), respectively. Notably, the Gr/TMS-AME-SC device, which used the AME electrolyte, exhibited a specific capacitance that was 97% higher than that of the Gr/TMS-PURE-SC device, which employed the PURE electrolyte. Furthermore, both the Gr/TMS-AME-SC and Gr/TMS-PURE-SC devices exhibited remarkable electrochemical stability, attributed to the high decomposition voltages of the AME (1.51 V) and PURE (1.48 V) electrolytes. Additionally, analyses performed using UV–Vis, Raman, and XPS spectroscopies revealed that oxygen vacancies, together with Ti 3+ /Ti 4+ , Mo 4+ /Mo 6+ , and S 2− /S 6+ species, act as redox centers responsible for charge storage by redox reactions in the SC electrodes. Moreover, this study revealed that exposing the SC made with AME electrolyte to sunlight for 2 h enhanced the capacitance to the ultimate value of 1361.8 F g −1 . Hence, SCs studied here could help to reduce the environmental pollution because they were fabricated with materials recycled from spent LIBs.