Ion Exchange-Mediated 3D Cross-Linked ZIF-L Superstructure for Flexible Electrochemical Energy Storage

Metal-organic frameworks (MOFs) are considered as a promising candidate for advancing energy storage owing to their intrinsic multi-channel architecture, high theoretical capacity, and precise adjustability. However, the low conductivity and poor structural stability lead to unsatisfactory rate and cycling performance, greatly hindering their practical application. Herein, we propose a sea urchin-like Co-ZIF-L superstructure using molecular template to induce self-assembly followed by ion exchange method, which shows improved conductivity, successive channels, and high stability. The ion exchange can gradually etch the superstructure, leading to the reconstruction of Co-ZIF-L with three-dimensional (3D) cross-linked ultrathin porous nanosheets. Moreover, the precise control of Co to Ni ratios can construct effective micro-electric field and synergistically enhance the rapid transfer of electrons and electrolyte ions, improving the conductivity and stability of CoNi-ZIF-L. The Co_6.53Ni-ZIF-L electrode exhibits a high specific capacity (602 F g^-1 at 1 A g^-1) and long cycling stability (95.3 % retention after 4,000 cycles at 5 A g^-1). The Co_6.53Ni-ZIF-L//AC asymmetric flexible supercapacitor employing gel electrolyte also exhibits excellent cycling stability (93.3 % retention after 4000 cycles at 5 A g^-1). This discovery provides valuable insights for electrode material selection and energy storage efficiency improvement.