Porous core–shell CoMn2O4 microspheres as anode of lithium ion battery with excellent performances and their conversion reaction mechanism investigated by XAFS

Porous core–shell CoMn2O4 microspheres of ca. 3–5 μm in diameter were synthesized and served as anode of lithium ion battery. Results demonstrate that the as-synthesized CoMn2O4 materials exhibit excellent electrochemical properties. The CoMn2O4 anode can deliver a large capacity of 1070 mAh g–1 in the first discharge, a reversible capacity of 500 mAh g–1 after 100 cycles with a coulombic efficiency of 98.5% at a charge–discharge current density of 200 mA g–1, and a specific capacity of 385 mAh g–1 at a much higher charge-discharge current density of 1600 mA g–1. Synchrotron X–ray absorption fine structure (XAFS) techniques were applied to investigate the conversion reaction mechanism of the CoMn2O4 anode. The X–ray absorption near edge structure (XANES) spectra revealed that, in the first discharge–charge cycle, Co and Mn in CoMn2O4 were reduced to metallic Co and Mn when the electrode was discharged to 0.01 V, while they were oxidized respectively to CoO and MnO when the electrode was charged to 3.0 V. Experiments of both XANES and extended X–ray absorption fine structure (EXAFS) revealed that neither valence evolution nor phase transition of the porous core–shell CoMn2O4 microspheres could happen in the discharge plateau from 0.8 to 0.6 V, which demonstrates the formation of solid electrolyte interface (SEI) on the anode.