Vertically grown and intertwined Co(OH)₂ nanosheet@Ni-mesh network for transparent flexible supercapacitor

Pseudo-capacitive materials have attracted great attention as electrode materials for supercapacitor owing to their high specific capacitance, high energy densities, and high rate capability. However, performances of pseudo-capacitive materials as transparent flexible supercapacitors are limited due to their non-transparent characteristics and brittleness in nature. Herein, we report a scalable, low-cost, and opto-electrochemical tunable, high-performance core-shell Co(OH)₂@Ni-mesh network transparent flexible supercapacitor electrode using a simple cracked silica template method in combination with metal deposition and electrochemical deposition technique. A seamless highly-conducting (~24 Ω/sq), transparent Ni-mesh network (~87%) was first fabricated using cracked silica template and etching method. In particular, a cracked silica template enables fabrication of a junction-less, high-aspect-ratio Ni-mesh network which substantially improves conductivity without considerably sacrificing transparency. The Ni-mesh network as flexible transparent current collector high pseudo-capacitive material, Co(OH)₂ nanosheets were then electrodeposited over Ni-mesh network electrode. The growth of vertically aligned and intertwined Co(OH)₂ nanosheets over Ni-mesh network electrodes results in high electrochemical performance of the electrode at high transparency. The core-shell Co(OH)₂@Ni-mesh network electrode with the transparency of ~75% demonstrated an areal capacitance of 22.9 mF/cm² at 5 mV/s scan rate, exhibiting excellent mechanical flexibility along with high rate capability. Moreover, the fabricated symmetric transparent flexible supercapacitor device exhibited a high areal cell capacitance of 5.32 mF/cm² at 5 mV/s scan rate at a transparency of ~54%, showing high rate capability, long cycling stability, excellent mechanical bendability along with high energy density of 0.42 μWh/cm² and power density of 8.33 μW/cm².