Phase and morphology evolution of CoAl LDH nanosheets towards advanced supercapacitor application
Al-based LDH materials have been considered as a promising active electrode material for pseudocapacitors due to its structural tunability. In this work, we employed the hydrothermal method, alkali etching treatment, calcination and sulfofication to achieve the crystalline phase transformation. According this pathway, five materials, including CoAl LDH, Co2AlO4, Co(OH)2, Co3O4 and Co4S3 have been prepared. The structural and physical/chemical properties are characterized by XRD, XPS, BET, SEM, TEM and FTIR. The electrochemical behaviors in supercapacitor and asymmetric supercapacitor device (ASC) are characterized, respectively. As the electrode materials in supercapacitor, the specific capacitances are at the order as CoAl LDH>Co4S3>Co2AlO4>Co3O4>Co(OH)2. The CoAl LDH possesses maximum specific capacitance due to the intercalation/deintercalation of electrolyte ions which is endowed by its unique layer structure. The CoAl LDH exhibits a high specific capacitance of 983.71 F g-1 at 1 A g-1, superior rate capability of 79.00% at 20 A g-1 and excellent cycling stability with capacitance retention of 89.10% after 15000 cycles. After assembling the ASC device, the maximum energy density of 16.275 Wh kg-1 and high power density of 3500 W kg-1 is achieved at the potential window of 1.4 V. In a word, the study not only provide a dependable pathway for materials modification, but also promote the development of cobalt-based electrode materials in energy storage.