Ag decorated $ZnCo_2O_4$ hollow spheres originated from metal-organic framework for a high-rate and long-cycle lithium ion battery anode

Abstract

Huge volume expansion during discharge is always a critical problem of high capacity conversion anodes for next generation lithium-ion (Li-ion) batteries. Although extensive efforts have been devoted to controlling the volume expansion using nanostructuring and surface engineering till now, more simple and facile approaches have to be considered due to the complicated and inefficient synthetic methods. Here, we report a straightforward synthesis of Ag coated $ZnCo_2O_4$ porous hollow spheres ($ZnCo_2O_4$@Ag HSs): (i) immobilization of metal-organic frameworks (MOFs) including Zn and Co metal nodes onto polystrene sphere templates, (ii) calcination ($~450^\circ C$) for removal of core polystryre sphere templates and oxidation of MOFs to produce mesoporous ZnCo2O4 polyhedron structure, and (iii) subsequent Ag-mirror reaction for 10 min, resulting in formation of $ZnCo_2O_4$@Ag HSs. This porous hollow mophology not only effectively relieves the strain stemming from volume expansion of transition metal, but also facilitates the efficient electron transport for Li+ diffusion by shortening the Li-ion diffusion path during lithiation/delithiation process. Moreover, uniformly decorated Ag nanoparticles are beneficial to formation of stable solid electrolyte interface (SEI) layer as well as increased electrical conductivity of $ZnCo_2O_4$. The MOFs derived porous $ZnCo_2O_4$@Ag HSs exhibited remarkably stable cycling performance (a capacity value of $616 mAh g^{-1}$ after 900 cycles at a current density of $1 A g^{-1}$) and excellent capacity retention of 80% under very high current density of $20.0 A g^{-1}$.