In situ embedding of cobalt sulfide quantum dots among transition metal layered double hydroxides for high performance all-solid-state asymmetric supercapacitors

Layered double hydroxides (LDHs) are widely used as cathode materials for supercapacitors (SCs), thanks to their many advantages. However, the single metal species with limited active sites limit the further improvement of the electrochemical performance of LDH materials. We successfully in situ embedded cobalt sulfide quantum dots (Co9S8-QDs) between the layers of ternary metal LDHs derived from metal–organic-frameworks (MOFs) by selective vulcanization of Co. The prepared Ni3Mn1Co@Co9S8-QDs/NF nanocomposites retain the advantages of LDH materials, such as lower charge transfer resistance. At the same time, the selectively generated ultra-small sized Co9S8-QDs reveal more active sites, which complies with the size minimization strategy, leading to the largely enhanced electrochemical properties. Due to the cooperative effect of LDHs and Co9S8-QDs, the prepared electrode has an excellent capacity (492.1 mA h g−1 at 1 A g−1), remarkable equivalent series resistance (0.499 Ω) and superior capacity retention (90.4% after 10 000 charge–discharge cycles). In addition, the carbon coated Fe2O3 nanoarray is prepared on carbon cloth (CC) as the cathode electrode (Fe2O3@C/CC), and the prepared Ni3Mn1Co@Co9S8-QDs/NF//Fe2O3@C/CC all solid-state asymmetric supercapacitor (ASC) shows an outstanding energy density (71.48 W h kg−1) when the power density is 750 W kg−1 and excellent capacity retention (93.7% after 10 000 charge–discharge cycles). As a result, the construction of composite electrodes with polymetallic LDHs and in situ embedded quantum dots should envision broad prospects.