Aging mechanisms under different state-of-charge ranges and the multi indicators system of state-of-health for lithium-ion battery with Li(NiMnCo)O-2 cathode

Understanding the degradation of battery cycled under different state-of-charge ranges is important for the optimal control of operation state-of-charge range. Cycle life tests on 8 A h pouch batteries with Li(NiMnCo)O-2 cathode are conducted under 0-20%, 20%-40%, 40%-60%, 60%-80%, 80%-100% and 0-100% state-of-charge ranges with current and temperature at 6C and 25 degrees C. Results show that among the five ranges with 20% depth of-discharge, cycling under 0-20% causes more impedance increase and less capacity loss, cycling under 80%-100% cause more capacity loss. The degradation behaviors of batteries under the remaining three ranges are similar. Battery degradation under 20% depth-of-discharge is significantly slower than 100% depth-of-discharge. Battery aging mechanisms are investigated using incremental capacity analysis method. It is indicated that loss of active material in positive electrode and loss of lithium inventory are comparable during battery aging process under 100% depth-of-discharge. However, for the battery under 20% depth-of-discharge, the dominant factor causing aging is loss of lithium inventory. Moreover, six characteristic parameters corresponding to loss of lithium inventory and loss of electrode material respectively are extracted from incremental capacity curve to establish the multi-indicators system describing battery state-of-health, which enhances the convenience of incremental capacity analysis to identify battery aging mechanisms on-board.