Regulating NiCo-LDH’s morphology, loading, and capacitance: mixed use of anionic and cationic surfactants

Abstract

Improving capacitance performance and active material loading at the same time is essential for commercial electrode materials, e.g., layered double hydroxides (LDH). Mixed surfactants are more effective than single surfactants at reducing the surface tension of a solution and have a more significant impact on synthesis and modification. Mixed surfactants can also regulate interlayer spacing, morphology, and loading to acquire high capacitance performance. In this study, NiCo-LDH binder-free electrodes are fabricated on foam nickel using the hydrothermal method, with micelles formed by mixing sodium octyl sulfonate (SOS) and cetyltrimethylammonium bromide (CTAB) serving as soft templates. It is determined that by modifying the proportion of two surfactants, a worm-like morphology of NiCo-LDH could be achieved, with the specific surface area increasing by approximately twice the value observed for the no surfactants sample. After introducing octyl sulfonic acid groups (OS⁻), the maximum interlayer spacing reaches 2.85 nm, improving electrochemical performance. The maximum electrode load of 11.7 mg is obtained when adding 4 mmol SOS and 1 mmol CTAB. The maximum specific capacity of 1.73 mAh cm⁻² is obtained for the most loaded electrode at 3 mA cm⁻², and the capacity retention is 66.47% at 30 mA cm⁻². A hybrid device constructed using samples and AC has 2.22 mWh cm⁻² energy density at 1.70 mW cm⁻² and 66.67% capacity retention after 10,000 cycles at 100 mA cm⁻². The results indicate that the LDH electrode fabricated in this way has high load and high capacity and thus has great potential for application.