Flexible and efficient supercapacitor devices based on inkjet-printed Ni–Co layered double hydroxides

Abstract

Abstract This study presents a novel strategy for producing the spinel phase of nickel cobaltite (NiCo 2 O 4 ) by annealing inkjet-printed nickel–cobalt layered double hydroxide (Ni-Co LDH) patterns at 300 °C. The drop-on-demand technique was used to print interdigitated microsupercapacitors (µSCs) in different layers (1, 3, 5, 7, 10, and 15 layers) of Ni-Co LDH ink over a printed 10-layer liquid-phase exfoliated graphene (LPEG) layer on a flexible polyimide substrate. Next, the post-printed Ni-Co LDH@LPEG devices were annealed at 300 °C to obtain a highly durable pseudocapacitive NiCo 2 O 4 . The 7L printed NiCo 2 O 4 @LPEG symmetric electrodes outperformed the LPEG electrodes, demonstrating a higher areal capacitance of 119 F m −2 compared to 3.1 F m −2 . NiCo 2 O 4 showed a longer charge–discharge time, leading to a higher energy density (1.65 mWh m −2 ). An asymmetric planar microsupercapacitor (AµSC) configuration was printed as NiCo 2 O 4 @LPEG//LPEG interdigitated device and tested at a potential window of 1.2 V. The device demonstrated high cyclic stability, retaining 97.4% of its initial capacitance after 2000 cycles. The AµSC demonstrated exceptional flexibility, maintaining a stable retention rate of 98.1% after 2000 cycles at a bending radius of 0.8 cm. For the practical integration, we prepared a laser-induced graphene strain gauge sensor (LIG-SGS) powered by AµSC. The LIG-SGS device has response time of around 300 ms at a 90° bending angle, while LIG-SGS/AµSC has response time of around 200 ms at the same angle. This approach has the potential to inspire fully integrated flexible energy storage systems with exceptional performance for wearable electronics, opening new possibilities for practical applications in the field. Graphical abstract