PNNL

Abstract

The charging voltage limits of mixed carbonate solvents for Li-ion batteries have been systematically investigated from 4.9 to 5.3 V in half cells using Cr-doped spinel cathode material LiNi0.45Cr0.05Mn1.5O4. We found that the stability of conventional carbonate electrolytes is strongly related to the stability and properties of the cathode materials at both lithiated and de-lithiated states. It is the first time to report that the conventional electrolytes based on mixtures of ethylene carbonate (EC) and linear carbonate (dimethyl carbonate – DMC, ethyl methyl carbonate – EMC, and diethyl carbonate – DEC) have shown very similar long-term cycling performance when cycled up to 5.2 V on LiNi0.45Cr0.05Mn1.5O4. The discharge capacity increases with the charge cutoff voltage and reaches the highest discharge capacity at 5.2 V. The capacity retention is about 87% after 500 cycles at 1C rate for all three carbonate mixtures when cycled between 3.0 V and 5.2V. The first-cycle efficiency has a maximum value at 5.1 V, with an average from 83% to 85% at C/10 rate. When cycled to 5.3 V, EC-DMC still shows good cycling performance but EC-EMC and EC-DEC show faster capacity fading. EC-DMC and EC-EMC have much better rate capability than EC-DEC. In addition, the first-cycle irreversible capacity loss increases with the cutoff voltage and the “inactive” conductive carbon has also been found to be partly associated with the low first-cycle Coulombic efficiency at high voltages due to electrolyte decomposition and probably the PF6- anion irreversible intercalation.