Abstract: Flexible supercapacitors with high mechanical strength, excellent flexibility, and high performance are highly desired to meet the increasing demands of flexible electronics. However, the trade-off between mechanical and electrochemical properties remains challenging. In this context, an interface-engineered strategy approach was proposed to construct polylactic acid (PLA)/polyaniline (PANI)/MXene (PPM) film electrodes for flexible supercapacitor applications. In the PPM electrode, the porous PLA prepared from the nonsolvent-induced-phase-separation method served as an ideal flexible substrate, providing excellent flexibility and high mechanical strength, whereas PANI as the coupling agent, enhanced the interfacial strength between PLA and the electroactive MXene that was firmly anchored and deposited on PLA through a facile layer-by-layer dip coating method. The tensile strength at break, elongation at break, and toughness of PPM are 53.09 MPa, 11.09 %, and 4.12 MJ/m³, respectively, much higher than those of pure MXene (29.36 MPa, 4.62 %, and 0.75 MJ/m³). At an optimum mass loading density of 3 mg cm^-2 for MXene, the fabricated PPM3 film electrode achieved a high specific capacitance of 290.8 F g^-1 at a current density of 1 A g^-1 in the three-electrode setup, approximately 1.5 times that of 190.8 F g^-1 for pure MXene. Meanwhile, the symmetric all-solid-state supercapacitor based on PPM3 film electrodes delivers a high specific capacitance of 193.7 F g^-1 at a current density of 0.25 A g^-1, with a corresponding high energy density of 9.3 Wh kg^-1 at a power density of 291.3 W kg^-1. The SC retains 86 % of its original capacitance even bent at 120° and also possesses an excellent fire-retardant ability, demonstrating its great potential for flexible and safe wearable electronics.

Key words: Flexible supercapacitors, Porous polylactic acid, MXene, Interface engineering