Search

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 1.0molL−1LiPF6 -EC/EMC/DMC (1:1:1, weight ratio) with 0.5wt.% MMDS additive keeps 79.2% of initial capacity after100 cycles at 60°C, whereas it is only 52.7% for the cell without additive. After the storage at 85°C for 24h, the cell with 0.5wt.% 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. [ABSTRACT FROM AUTHOR]

Abstract: A novel electrolyte applied in electrochemical double-layer capacitors (EDLCs) has been prepared based on lithium hexafluorophosphate (LiPF6) and acetamide and subsequently characterized by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), electrochemical techniques and so on. The mixtures of LiPF6 and acetamide at the molar ratios of 1:4 to 1:6 exist as liquids below 25°C, which is attributed to the melting point depression of mixture and the coordination of the polar groups (Cgroups) of acetamide with Li+ and PF6 − ions. The strong interaction between LiPF6 and acetamide results in the rupture of the electrovalent bond of LiPF6 and the breakage of hydrogen bonds among the acetamide molecules, leading to the formation of a liquid electrolyte. The LiPF6/acetamide electrolyte with a molar ratio of 1:5.5 exhibits a 5.2V electrochemical window and suitable ionic conductivity at room temperature. In particular, the coin-type cells with carbon electrodes and LiPF6/acetamide electrolyte possess high thermal stability and electrochemical properties, showing that the as-prepared LiPF6/acetamide electrolyte is a promising candidate for EDLCs. [Copyright &y& Elsevier]