A study on capacity fading of lithium-ion battery with manganese spinel positive electrode during cycling

The capacity fading mechanism of lithium-ion cell was studied by disassembling the charge-discharged cells and analyzing their electrodes using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), etc. Cu ion dissolved from current collector of anode and Mn ion dissolved from LiMn₂O₄ spinel (cathode) were all existing in solid electrolyte interface (SEI) layer on carbon anode as Cu₂O and MnO or MnO₂, respectively. These depositions of Cu and Mn oxides did not uniformly deposited on the anode side, and most of them were detected on the carbon surface nearby to the separator side. The SEI layer is hard and about 0.3 μm in thickness. Furthermore, the cycling performance of the cells can be improved by adding 1,2,3-benzotrazole (a corrosion inhibitor of Cu) before assembling the cell, it then coordinates strongly with Cu ions into the electrolyte. From the results, it is obvious that the existing of Cu oxide as well as Mn oxide in the SEI layer, which blocks the normal intercalation of the lithium ions, is one of the factors for the capacity fading of the cells.