Al doped Ni-Co layered double hydroxides with surface-sulphuration for highly stable flexible supercapacitors

In this work, a strategy of using fast co-precipitation method has been developed to synthesize stable Al doped α-phase NiCo layered double hydroxides (NCA-LDH). A subsequent surface sulphuration of NCA-LDH (S-NCA-LDH) was carried out to improve the conductivity. The as-synthesized S-NCA-LDH exhibits a good electrochemical performance with a specific capacity of 727.1C g^-1 at 1 A g^-1. At 20 A g^-1, the specific capacity still remains 556C g^-1. The capacity retention reaches 95.1 % after 10,000 cycles. Moreover, S-NCA-LDH as positive electrode, activated carbons (AC) as negative electrode and KOH doped polybenzimidazole (PBI-KOH) as solid polymer electrolyte have been employed to assemble flexible all-solid-state supercapacitors (S-NCA-LDH//PBI-KOH//AC). The device exhibits a specific capacitance of 182.6F g^-1 at 0.5 A g^-1 within 1.8 V. It corresponds to a specific energy of 82.2 Wh kg^-1 at 450 W kg^-1. It also shows a good cycling stability with capacitance retention of about 92.5 % after 10,000 cycles. Further considering the good mechanical performance under bending and folding deformation conditions, the S-NCA-LDH based flexible devices demonstrate the superiority in applications of flexible wearable electronics.