Spindle‐Shaped Ni‐Fe‐Layered Double Hydroxide: Effect of Etching Time on Flexible Energy Storage

The rising demand for efficient energy storage in flexible electronics is driving the search for materials that are well-suited for the fabrication of these devices. Layered Double Hydroxides (LDHs) stand out as a remarkable material with a layered structure that embodies exceptional electrochemical properties. In this study, both double-shelled and single-shelled NiFe-Layered Double Hydroxide (LDH) particles are prepared using spindle-shaped MIL-101(Fe) as the template. These NiFe-LDH particles are then utilized to develop a flexible energy storage device. Transmission electron microscopy(TEM) analysis revealed that the as-synthesized NiFe-LDH particles transformed into hollow single-shells from a double-shelled structure as the aging time increased, which significantly influenced the electrochemical performances. Despite the decreasing specific capacitance and energy density with longer etching times, the sample etched for 2 h (NiFe-LDH 2h) demonstrated the highest capacitance of 9.24 mF·cm⁻² and an energy density of 0.46 µW·h·cm⁻², highlighting its promising performance for energy storage applications. X-ray photoelectron spectroscopy (XPS) analysis revealed the highest Ni²⁺: Ni³⁺ ratio, and Fe: Ni ratio for NiFe- LDH 2h samples, which further influences the energy storage properties. The ability to maintain the high performance of these materials across different bending angles further emphasizes its versatility and relevance in emerging flexible electronics markets.