A facile route to synthesize multiporous MnCo2O4 and CoMn2O4 spinel quasi-hollow spheres with improved lithium storage properties

Abstract

A facile and general way for the synthesis of porous and hollow complex oxides is highly desirable owing to their significant applications for energy storage and other fields. In this contribution, uniform Mn_0.33Co_0.67CO₃ and Co_0.33Mn_0.67CO₃ microspheres are firstly fabricated solvothermally just by tuning the molar ratio of Mn and Co. Subsequently, the growth of multiporous MnCo₂O₄ and CoMn₂O₄ quasi-hollow microspheres by topotactic chemical transformation from the corresponding precursors are realized through a non-equilibrium heat treatment process. Topotactic conversion further demonstrated that the much larger CoMn₂O₄ pores than those of MnCo₂O₄ are possibly due to the longer transfer distance of ions. When evaluated as anode materials for LIBs (lithium ion batteries), after 25 cycles at a current density of 200 mA g⁻¹, the resultant MnCo₂O₄ and CoMn₂O₄ quasi-hollow microspheres possessed reversible capacities of 755 and 706 mA h g⁻¹, respectively. In particular, the MnCo₂O₄ samples could deliver a reversible capacity as high as 610 mA h g⁻¹ even at a higher current density of 400 mA g⁻¹ with excellent electrochemical stability after 100 cycles of testing, indicating its potential application in LIBs. We believe that such good performance results from the appropriate pore size and quasi-hollow nature of MnCo₂O₄ microspheres, which can effectively buffer the large volume variation of anodes based on the conversion reaction during Li⁺ insertion/extraction. The present strategy is simple but very effective, and due to its versatility, it can be extended to other binary, even ternary complex metal oxides with high-performance in LIBs.