Exceptional Performance of Li-ion Battery Cells with Liquid Electrolyte at 100 C

Single crystal NMC640/artificial graphite cells balanced for low voltage operation (<= 4.1 V) and using electrolyte salts rich in lithium bis(fluorosulfonyl)imide are demonstrated to have exceptional lifetime during continuous operation at 100 degrees C. Cells tested to an upper cutoff voltage of 4.0 V retained >80% of their original capacity for 600 cycles and 4300 h at 100 degrees C and 1200 cycles and 1 year cycling to 3.9 V at 85 degrees C. The cells exhibited minimal gassing, no transition metal dissolution from the positive electrode, and no detectable corrosion of the aluminum current collector. Ultra-high precision coulometry measurements from 20 to 100 degrees C suggest an Arrhenius-type relationship for the coulombic inefficiency and capacity fade of these cells. The possibility of exploiting this relationship to project ambient temperature lifetime from high-temperature measurements is suggested. However, cell performance at the highest temperatures is most likely reduced by the permeation of electrolyte through the seals of the pouch cell.