Flexible micro-supercapacitors from laser-induced graphene and gel polymer electrolytes

The rapid progress in the development and implementation of smart electronics and flexible devices has stimulated the need to produce energy storage units of high efficiency at low cost. In this work, we use laser-induced graphene to construct in-plane micro-supercapacitors (μ-SCs) and delve into the effects of inter-finger spacing, finger width, deformation state, and temperature on the electrochemical performance of the μ-SCs with five different gel polymer electrolytes made from H₂SO₄, H₃PO₄, KOH, NaOH, and NaCl, respectively. The μ-SCs with the electrolyte from the PVA/H₂SO₄ gel polymer exhibit the best performance under bending and torsion. Increasing temperature causes a slight increase of the specific areal capacitance. Increasing the inter-finger spacing reduces the specific areal capacitance, and the finger width has a limited effect on the specific areal capacitance. The capacitance retention of the μ-SCs with the electrolyte from the PVA/H₂SO₄ gel polymer is 94.24 % of the initial capacitance after 10,000 electrochemical cycles at a scan rate of 0.1 V/s. The specific areal capacitance of integrated μ-SCs constructed from individual μ-SCs with the PVA/H₂SO₄ gel polymer is inversely proportional to the number of μ-SCs for the series connection and proportional to the number of μ-SCs for the parallel connection. This study provides a feasible method to produce flexible μ-SCs of high efficiency at low cost.