Improvement of the thermal stability of LiMn2O4/graphite cells with methylene methanedisulfonate as electrolyte additive

In order to overcome the severe capacity fading of LiMn2O4/graphite cells cycled at elevated temperature, methylene methanedisulfonate (MMDS) is newly evaluated as an electrolyte additive to improve the thermal stability of LiMn2O4 cathode. The cell using 1.0 mol L-1 LiPF6 -EC/EMC/DMC (1:1:1, weight ratio) with 0.5 wt.% MMDS additive keeps 79.2% of initial capacity after 100 cycles at 60 degrees C, whereas it is only 52.7% for the cell without additive. After the storage at 85 degrees C for 24 h, the cell with 0.5 wt.% MMDS additive exhibits higher discharge capacity retention (82.5%) than the cell without additive (71.8%), and the change of thickness, resistance and discharge voltage plateaus decrease. The effects of the additive are characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), transmission electron microscopy (TEM), as well as electrochemical performance tests. These results suggest that MMDS additive can form better electrochemical and thermal stability of surface film on the LiMn2O4 electrode, which reduces both the decomposition of the electrolyte and the dissolution of Mn ion in the electrolyte at elevated temperature, thus leads to the obvious improvement on the thermal stability of LiMn2O4 cathode. (C) 2014 Elsevier Ltd. All rights reserved.