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

Abstract

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 ZnCo 2O 4 nanocrystals. The mesoscale assembly with distinctively sharp edges was formed by close-packing the ZnCo 2O 4 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 ZnCo 2O 4 nanoparticles, an active lithium ion storage compound, into a dense organized structure is an effective way to increase the volumetric capacity of ZnCo 2O 4 nanoparticles for reversible lithium ion storage. The highly ordered 3D assembly of ZnCo 2O 4 demonstrated excellent reversible lithium ion storage properties and a specific capacity (∼800mAhg -1) much higher than that of carbon (typically ∼ 350mAhg -1). © 2011 IOP Publishing Ltd.