Quantification of the passive electrode effect explaining reversible capacity rise and decline during ageing of automotive lithium-ion batteries

<p>Meinert Lewerenz</p>

Quantification of the passive electrode effect explaining reversible capacity rise and decline during ageing of automotive lithium-ion batteries

Meinert Lewerenz

RWTH Aachen University, Germany

: J Nucl Ene Sci Power Generat Technol

Abstract

Batteries have become more and more important especially in the automotive sector. To increase lifetime and decrease costs, the loss of capacity needs to be well understood and separated in reversible and irreversible losses. State-of-the-art lithiumion batteries that are currently employed in electric vehicles exhibit an overhang of the anode compared to the cathode to prevent lithium plating at the edges of the anode. The percentage ratio of this overhang to the active anode is in the order of 5-10% for pouch, prismatic or cylindrical cells. In our previous publication, we could show that a potential difference between the overhang and the active anode is leading to a flow of active lithium slowly counterbalancing the potentials. Thus, the extractable capacity is rising or declining depending on the difference of the SOC prior to begin the test and the test SOC. With this knowledge, the reversible loss or gain of capacity can be separated from irreversible losses by simple linear extrapolation. The different SOC of the active anode and the overhang of the anode are visualized by Gyenes et al. in a post-mortem-study. In his PhD thesis Johannes Schmalstieg could model the lithium-flow from and to not directly chargeable parts of the anode. Unfortunately in literature the passive electrode effect is not known and capacity trends are misinterpreted. Thus, calendaric aging is fitted with a square root function although the irreversible aging follows a rather linear trend. Furthermore relaxation effects are reported where the capacity is increasing when it is repeated. With the theory of passive electrode effect, all these observations get explainable with a high storage SOC and a low SOC prior to begin of test. In this presentation, a quantification of the passive electrode effect will be shown for three different automotive cells with different cell designs.