Energy efficiency of lithium-ion battery used as energy storage devices in micro-grid

This paper investigates the energy efficiency of Li-ion battery used as energy storage devices in a micro-grid. The overall energy efficiency of Li-ion battery depends on the energy efficiency under charging, discharging, and charging-discharging conditions. These three types of energy efficiency of single battery cell have been calculated under different current rates. The relations of the energy efficiencies with current rate are analyzed using non-linear curve fitting and polynomial equations. Moreover, the Li-ion battery used in the present study has been verified to have low cell imbalance when 10 cells are connected in series without any cell equalizers, and the charging-discharging energy efficiency of the battery pack has been obtained through hardware experiments.