Sr₂Nb₃O₁₀ nanosheet thin film grown via LB method for high-performance planar-type pseudocapacitor

The electrochemical properties of a two-dimensional metal-oxide Sr₂Nb₃O₁₀ (SNO) nanosheet thin film were investigated for application to pseudocapacitors. Smooth migration of cations was expected to occur in the SNO thin film because of a large gap between the SNO nanosheets along the [0 0 1] direction. A thin film with 10 SNO nanosheets was well deposited on a Pt/Ti/SiO₂/Si substrate using the Langmuir–Blodgett method, and it exhibited a large (0 0 1) interplanar distance of 1.83 nm owing to the presence of TBA⁺ ions. The TBA⁺ ions were removed from the SNO thin-film electrode after the second charge/discharge cycle in the LiCl electrolyte with a slight decrease in the (0 0 1) interplanar distance (1.65 nm). The Li⁺ ions were intercalated and deintercalated during the charge/discharge cycle, resulting in good capacitive behavior. The planar-type SNO pseudocapacitor exhibited rectangular cyclic-voltammetry curves and triangular charge/discharge curves. Moreover, capacity retention was 85% after 5000 cycles, indicating that the pseudocapacitor had ideal capacitive behavior with excellent cycling stability. The developed SNO pseudocapacitor exhibited a higher power density (0.2 W/cm³) and energy density (4.9 × 10^-3 W h/cm³) than previously reported thin-film capacitors. Therefore, the SNO thin film is a good candidate material for pseudocapacitors.