Due to the rapid depletion of fossil fuels and severe environmental pollution, more advanced energy storage systems need to possess dramatically improved performance and be produced on a large scale with high-efficiency while maintaining low-enough costs to ensure the higher and wider requirements. A facile, energy-saving process was successfully adopted for the synthesis of ethylene glycol intercalated cobalt nickel layered double hydroxide (EG-Co-Ni LDH) nanosheet assemblies variants with higher interlayer distance and tunable transitional-metal composition. At an optimized starting Co/Ni ratio of 1, the nanosheet assemblies display a three-dimensional, sponge-like network, affording a high specific surface area with advantageous mesopore structure in 2-5 nm containing large numbers of about 1.2 nm micropores for promoting electrochemical reaction. An unprecedented electrochemical performance was achieved, with a specific capacitance of 4160 F g-1 at a discharge current density of 1 A g-1 and 1313 F g-1 even at 50 A g-1, as well as excellent cycling ability. The design and optimization of EG-Co-Ni LDH nanosheets in compositions, structures and performances, in conjunction with the easy and relatively "green" synthetic process, will play a pivotal role to meet the needs of large scale manufacture and widespread application for advanced electrochemical storage.