Phase and morphology evolution of CoAl LDH nanosheets towards advanced supercapacitor applications

Abstract

Al-Based LDH materials have been considered as promising active electrode materials for pseudocapacitors due to their structural tunability. In this work, we employed a hydrothermal method, alkali etching treatment, calcination and sulfofication to achieve crystalline phase transformation. According to 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 (ASC) devices are characterized, respectively. As the electrode materials in supercapacitors, the specific capacitances are in the order CoAl LDH > Co₄S₃ > Co₂AlO₄ > Co₃O₄ > Co(OH)₂. The CoAl LDH exhibits the maximum specific capacitance due to the intercalation/deintercalation of electrolyte ions which is attributed to its unique layer structure. The CoAl LDH exhibits a high specific capacitance of 983.71 F g⁻¹ at 1 A g⁻¹, a superior rate capability of 79.00% at 20 A g⁻¹ and excellent cycling stability with a capacitance retention of 89.10% after 15 000 cycles. After assembling the ASC device, a maximum energy density of 16.275 W h kg⁻¹ and a high power density of 3500 W kg⁻¹ are achieved in a potential window of 1.4 V. In a word, the study not only provides a dependable pathway for materials modification, but also promotes the development of cobalt-based electrode materials for energy storage.