Linker-free 3D assembly of nanocrystals with tunable unit size for reversible lithium ion storage

A simple and scalable procedure combining hydrothermal synthesis with post-synthesis calcination was developed to produce a linker-free, thermally stable, mesoscale 3D ordered assembly of spinel-type ZnCo2O4 nanocrystals. The mesoscale assembly with distinctively sharp edges was formed by close-packing the ZnCo2O4 nanocrystal building blocks with a unit size changeable by the synthesis temperature. A self-templating mechanism based on the topotactic transformation of an oxalato-bridged precursor coordination compound was proposed for the assembly. The packaging of crystalline ZnCo2O4 nanoparticles, an active lithium ion storage compound, into a dense organized structure is an effective way to increase the volumetric capacity of ZnCo2O4 nanoparticles for reversible lithium ion storage. The highly ordered 3D assembly of ZnCo2O4 demonstrated excellent reversible lithium ion storage properties and a specific capacity (similar to 800 mAh g(-1)) much higher than that of carbon (typically similar to 350 mAh g(-1)).