Fish-scale-like NiMn-based layered double hydroxides for high-energy aqueous supercapacitors

Aqueous supercapacitors (SCs) exhibit exceptional electrochemical characteristics, including extended cycle stability and high-power density, making them highly promising. Though their practical application and commercialization are hindered by low energy density, we developed a high-performance, self-supporting SC electrode to address this limitation using nickel manganese layered double hydroxide (NiMn-LDH) directly synthesized on activated carbon cloth (ACC). This electrode achieved an extraordinary specific capacitance of 2838.8 F g⁻¹ at a current density of 1 A g⁻¹, with 70.3% retention at 30 A g⁻¹ and 86.1% retention after 6,000 cycles at 15 A g⁻¹, demonstrating its remarkable performance and durability. After being assembled into an asymmetric SCs (ASCs) device with the ACC negative electrode in 2M potassium hydroxide (KOH), a broad operating voltage window of 1.6 V with an energy density of up to 89.7 Wh kg⁻¹ was achieved at a power density of 800.0 W kg⁻¹. Furthermore, the device retained 89.30% of its initial capacitance after 10,000 cycles at 10 A g⁻¹, with a near-perfect Coulombic efficiency close to 100%. The fish-scale-like nanostructure effectively increases the active sites of the electrode to make sufficient full contact with the electrolyte, accelerating the transport of electrons/ions and enhancing its electrochemical performance. These findings emphasize the potential of NiMn-LDH for application in wearable and microscale energy storage devices.

Graphical abstract