Atomic scale modulation strategies and crystal phase transition of flower-like CoAl layered double hydroxides for supercapacitors

Abstract

In the present work, a cobalt aluminum layered double hydroxide and its derivatives were synthesized via a hydrothermal method, an alkali-etching method and a phosphorization route to obtain different crystal phases. The structure, morphology and chemical composition of the four samples were characterized and their electrochemical performances were carefully investigated. All of them have a flower-like morphology, but their layered structures were destroyed after phase transition processes. The CoAl LDH electrode exhibited a superior capacitance performance of 983.1 F g⁻¹ at 1 A g⁻¹, a superior rate capability of 88.64% at 10 A g⁻¹ and excellent cycling stability (92.68% retention after 5000 cycles at 10 A g⁻¹), while the CoP_x has a lower electrochemical performance than CoAl LDH. The CoAl LDH and graphene (GR) were constructed as asymmetric capacitors with an energy density of 16.29 W h kg⁻¹ at a power density of 700 W kg⁻¹, excellent coulombic efficiency (90.85% at 5 A g⁻¹) and remarkable capacitance retention (82.84% after 10 000 cycles). Among the four samples, CoAl LDH shows the best electrochemical performance due to its unique layered structure allowing more electrolyte ions for redox reaction. Hence, the influence of original metallic element diversification is higher than the influence of mono-metallic oxide modification on improving electrochemical properties, which provides a good reference for follow-up studies to screen preliminary materials for energy storage and conversion.