Strongly coupled carbon quantum dots/NiCo-LDHs nanosheets on carbon cloth as electrode for high performance flexible supercapacitors

Highlight • CQDs/NiCo-LDHs heterostructures on carbon cloth (CC) were constructed. • CQDs/NiCo-LDHs exhibited compact structure with high structural stability. • The coupling effect and unique structure improve the rate capability and long-term cycle stability. • The assemble flexible device exhibited an energy density of 117.8 Wh kg−1 with a power density of 528.3 W kg−1 at 2 mA cm−2. NiCo-LDHs is one of the most promising electrode materials for supercapacitors. However, the intrinsic low conductivity and the volume expansion/contraction still seriously limit the application of NiCo-LDHs in supercapacitors. Herein, we constructed carbon quantum dots (CQDs)/NiCo-LDHs nanosheets heterostructures on carbon cloth (CQDs/NiCo-LDHs@CC) through a simple solvothermal method using CQDs-embedded Co-MOF as precursor. The in-situ implanting of CQDs not only can effectively improve the conductivity of the NiCo-LDHs but also boost the long-term structural stability of the flexible electrode through the morphological optimization of NiCo-LDHs. Benefit from the ingenious structural design and strong coupling between CQDs and NiCo-LDHs, the CQDs/NiCo-LDHs@CC electrode delivered a much-enhanced capacitance performance in 6 M KOH, including a large reversible specific capacitance of 2023 F g−1 (5.22 F cm−2) at 5 mA cm−2, superior rate capability with 84.3% capacitance retention at 30 mA cm−2 and excellent cycle life. The flexible asymmetric supercapacitor device exhibited an energy density of 117.8 Wh kg−1 with a power density of 528.3 W kg−1 at 2 mA cm−2 using CQDs/NiCo-LDHs@CC as positive electrode and activated CC as negative electrode. This work provides a new opportunity for the development of nanocomposites with the in-situ implanting of CQDs to construct high-performance electrodes for flexible supercapacitors.