Effect of linear carboxylic ester on low temperature performance of LiMn2O4-graphite cells

To improve the low-temperature performances of Li-ion cells, three types of linear carboxylic ester-based electrolyte, such as EC/EMC/EA (1:1:2, mass ratio), EC/EMC/EP (1:1:2, mass ratio) and EC/EMC/EB (1:1:2, mass ratio), were prepared to substitute for industrial electrolyte (EC/EMC/DMC). Then, 18650-type LiMn2O4-graphite cells (nominal capacity of 1150 mA.h) were assembled and studied. Results show that the cells containing three types of electrolyte are able to undertake 5C discharging current with above 93% capacity retention at -20 degrees C. Electrochemical impedance spectra show that the discharge capacity fading of Li-ion cells at low temperature is mainly ascribed to the charge transfer resistance increasing with temperature decreasing. In comparison, the cells containing electrolyte of 1.0 mol/L LiPF6 in EC/EMC/EA (1:1:2, mass ratio) have the highest capacity retention of 90% at -40 degrees C and 44.41% at -60 degrees C, due to its lowest charge-transfer resistance.