Energy efficiency of Li-ion battery packs re-used in stationary power applications

The effects of capacity fade, energy efficiency fade, failure rate, and charge/discharge profile are investigated for lithium-ion (Li-ion) batteries based on first use in electric vehicles (EVs) and second-use in energy storage systems (ESS). The research supports the feasibility of re-purposing used Li-ion batteries from EVs for use in ESS. Based on data extrapolation from previous studies with a low number of charge/discharge cycles, it is estimated that the EV battery loses 20% of its capacity during its first use in the vehicle and a further 15% after its second use in the ESS over 10 years. As energy efficiency decreases with increased charge/discharge cycles, a capacity fade model is used to approximate the effect of the relationship between cycles and capacity fade over the life of the battery. The performance of the battery in its second use is represented using a model of degradation modes, assuming a 0.01% cell failure rate and a non-symmetric charge/discharge profile. Finally, an accurate modeling of battery performance is used to examine energy savings and greenhouse gas (GHG) emission reduction benefits from using a Li-ion battery first in an EV and then in an ESS connected to the Ontario electrical grid.