Capacity fade study of lithium-ion batteries cycled at high discharge rates

Abstract

Capacity fade of Sony US 18650 Li-ion batteries cycled using different discharge rates was studied at ambient temperature. The capacity losses were estimated after 300 cycles at 2 C and 3 C discharge rates and were found to be 13.2 and 16.9% of the initial capacity, respectively. At 1 C discharge rate the capacity lost was only 9.5%. The cell cycled at high discharge rate (3 C) showed the largest internal resistance increase of 27.7% relative to the resistance of the fresh cells. The rate capability losses were proportional with the increase of discharge rates. Half-cell study and material and charge balances were used to quantify the capacity fade due to the losses of primary active material (Li +), the secondary active material (LiCoO 2/C)) and rate capability losses. It was found that carbon with 10.6% capacity loss after 300 cycles dominates the capacity fade of the whole cell at high discharge rates (3 C). A mechanism is proposed which explains the capacity fade at high discharge rates.