Carbonized polydopamine wrapping layered KNb₃O₈ nanoflakes based on alkaline hydrothermal for enhanced and discrepant lithium storage

Although the photochemical and ion exchange properties of layered KNb₃O₈ (KN) have been extensively studied, its potential lithium storage applications were ignored. Unlike typical acid hydrothermal method, this work demonstrate that interlayer-controlled KN nanoflakes can be prepared based on alkaline hydrothermal conditions. Pristine KN performs a high first-discharge capacity and superior cyclic stability. Moreover, polydopamine derived carbon as a conductive coating shell was firstly applied to modify KN for enhancing its lithium insertion ability. It performs outstanding rate character (310, 255, 110 mA h g⁻¹ at the current density of 0.2, 1, 10 A g⁻¹, respectively), as compared with pristine KN (96, 51, 13 mA h g⁻¹). It also shows excellent long-term cycling feature (209 mA h g⁻¹ after 3000 cycles, corresponds to 95% capacity retention). In addition, relevant energy storage mechanisms have been expounded. The present work could be helpful in developing potential multifunctional applications of KN-based and other similar niobates.