Degradation analysis and state of health estimation on lithium nickel manganese cobalt oxide (NMC) battery

Battery ageing occurs throughout the entire life-time of the battery and limits its performance. Different operating conditions like working temperature, cycling depth, charge/discharge current rate, etc., lead to different degradation levels of the batteries. Having a profound understanding of battery ageing behaviour under various operating modes is helpful in improving battery life-time and hence making them economically more competitive. An accurate state of health (SoH) estimation of batteries is of great importance to the safety of entire systems, with this information we can adjust the operating modes to extend the battery lifetime as well as predict the time intervals for battery replacement. This work provides an ageing study of on commercialized high energy LiNi_xMn_yCo_1-x-yO₂(NMC)/graphite Li-ion pouch cell cycled under different depth of discharge (DoD). Incremental analysis (IC) was performed on It¹//25 test result to investigate the ageing mechanism and found loss of lithium inventory (LLI) was the main reason causing battery capacity fade. The linear regression observed between the battery state of health (SoH) and partial area loss in IC curves allows the SoH evaluation for cells under different cycling condition within 1%error bound. With the measurement results, the observed phenomena and possible battery degradation mechanism are discussed.