Effect of Solvent Presoaking of FDM-Printed Conductive PLA Current Collectors in 3D-Printed Carbon Supercapacitors

The electrochemical response of symmetric carbon-based supercapacitor devices made using two 3D-printing techniques, Vat-P (vat polymerization) and FDM (fused deposition modeling), shows how the printing method dominates the overall cell response. Despite possessing excellent cycle life, the conductive poly(lactic acid) (PLA) FDM printed current collectors suffer from relatively high resistance and suppressed capacitance linked to current collector material resistivity. Here, we examine in situ methods to influence the interfacial conductivity of the FDM current collectors by surface modification. Both dimethylformamide (DMF) and aqueous potassium hydroxide (KOH) treatments are investigated to compare solvent decomposition and electrolyte presoaking for this purpose. Using a single-walled carbon nanotube and graphene nanoplatelet carbon composite slurry on FDM current collectors in Vat-P 3D-printed cell casings, the supercapacitor cells show that the DMF treatment method has worse capacitance but better retention over 1 million cycles compared to the untreated FDM current collector cells. Pretreatment in a solution of 6 M aqueous KOH, identical to the cell electrolyte, markedly improves the effective current collector conductivity and interface with the active material, with a five-fold improvement in capacitance at the expense of less cycling stability. This is possible because the KOH treatment provides a 10-fold reduction in the FDM current collector resistance, which correlates with the improved cyclic voltammetric response. Galvanostatic charge-discharge tests reveal a deteriorated long-term cycling stability and rate capability despite better interfacial conductivity with the active material. In-situ presoaking that allows a degree of depolymerization at the surface relieves the conductive additive within the PLA to improve electrochemical interfacial activity and identifies the trade-off between improved capacitance and long-term cycling stability for common electrolytes in PLA-based 3D printed aqueous supercapacitors.