Energy Storage Kinetics of Hierarchically Designed Co9S8@CoNiO2 Hollow Cubic Supercapacitors with Improved Stability and Energy Density

Thedelicate design and rational preparation of core-shellheterostructures are effective in improving the energy conversionand storage characteristics in supercapacitors. Herein, we designedand constructed cobalt metal-organic framework (Co-MOF) hollowcore-shell nanocubes decorated with abundant Co9S8 and CoNiO2 nanofeatures. The synergisticallycomposed Co9S8@CoNiO2-120 exhibitshigh electrical conductivity, high cycling stability, and excellentenergy density compared to others with different Ni contents. Theimprovement of structural stability originated from the pseudocapacitivenature of Co9S8. The conversion of CoNi-LDHto CoNiO2 increases the cycle stability by 8.7 times (specificcapacity retention of 587.3 C g(-1) after 10 000cycles at a high current density of 10 A g(-1)) withthe specific capacity (652.6 C g(-1) at 1 A g(-1)) 3.4-fold higher than that of Co9S8. Mechanism analysis reveals that the dissociation processof OH- is more detrimental to the cycle stability.Furthermore, the assembled asymmetric supercapacitor (ASC) devicedemonstrates a maximum energy density of 50 Wh kg(-1) (49.4 Wh kg(-1) after consideration of iR loss)at a corresponding power density of 800 W kg(-1) (790W kg(-1) after consideration of iR loss), with 82%capacity retention over 5000 cycles at 5 A g(-1).Our work provides a novel approach for MOF derivative supercapacitorsin practical energy storage applications.

Automated summary

A novel core-shell heterostructure composed of cobalt metal-organic framework hollow core-shell nanocubes decorated with Co9S8 and CoNiO2 nanofeatures was designed and constructed, exhibiting high electrical conductivity, cycling stability, and energy density in supercapacitors.