Defocusing-Controlled Morphology and Electrochemical Performance of Laser-Induced Graphene Electrodes for Microsupercapacitors.

Laser-induced graphene (LIG) is a promising porous carbon electrode for flexible microsupercapacitors (MSCs), and defocusing is an established means of tuning its morphology. Here, a defocusing series was evaluated as a complete process-to-device chain with the CO2 laser power and scan speed fixed at 5.0 W and 46 mm s-1. A polyimide substrate was positioned 0-3 mm below the focal plane to produce laser-induced graphene fibers (LIGFs), LIG-1, LIG-2, and LIG-3. Increasing the defocusing distance lowered the peak fluence per pulse from 16.7 to 2.1 J cm-2, transforming a fibrous network into porous LIG, an open-cell-like network, and a film whose smooth, oxygen-rich surface skin covered a porous interior. LIG-2 showed the lowest sheet resistance (15.3 Ω sq-1), ID/IG ratio (0.29), and equivalent series resistance (78 Ω), delivering 2.88 mF cm-2 at 0.05 mA cm-2 and 97.4% retention after 2000 cycles. LIGF showed the lowest contact angle (12.1°), retained 57.3% of its capacitance at 0.25 mA cm-2, and surpassed LIG-2 at ≥0.10 mA cm-2. Both electrodes retained their cyclic voltammetry (CV) response under a single 180° bend. Thus, substrate-height adjustment tunes LIG morphology and rate-dependent MSC performance without changing laser power or scan speed.