Abstract
Lithium-ion batteries deteriorate in energy and power density over lifetime. Power density fades away with increasing internal resistance (Ri) and is generally monitored by pulse measurements, which do not describe details of the underlying loss contributions. Loss contributions as (i) ohmic resistance R0, (ii) contact resistance RCC and (iii) charge transfer resistance RCT are separated by electrochemical impedance spectroscopy (EIS) combined with the distribution of relaxation times method (DRT), and quantified using a simple equivalent-circuit model (Figure 1). This approach allows the systematic investigation of Li-ion batteries over lifetime, and gives more insight into the effect of temperature, cycling profiles and discharge/charge rates. We present a lifetime analysis of a high-energy pouch cell (KOKAM 560 mAh), using a wide set of procedures during cycling and calendar aging. The investigated cell consists of a NCA-LCO blend cathode and a graphite anode. The relationship between numerous test profiles (variation of temperature, charge/discharge rate and depth of discharge) and predominant aging mechanism of the cell resistance is quantified versus begin of life (BOL) and its origin is discussed in great detail. Figure 1
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