Alexander Warnecke

Batteries 2020 – Lithium - ion battery first and second life ageing, validated battery models, lifetime modelling and ageing assessment of thermal parameters

The European Project “Batteries 2020” unites nine partners jointly working on research and the development of competitive European automotive batteries. The project aims at increasing both the energy density and lifetime of large format pouch lithium-ion batteries towards the goals targeted for automotive batteries (250 Wh/kg at cell level, over 4000 cycles at 80% depth of discharge). Three parallel strategies are followed in order to achieve those targets: (i) Highly focused materials development; two improved generations of NMC cathode materials allows to improve the performance, stability and cyclability of state of the art battery cells. (ii) Better understanding of the ageing phenomena; a robust and realistic testing methodology has been developed and was carried out. Combined accelerated, real driving cycle tests, real field data, post-mortem analysis, modelling and validation with real driving profiles was used to obtain a thorough understanding of the degradation processes occurring in the battery cells. (iii) Reduction of battery cost; a way to reduce costs, increase battery residual value and improve sustainability is to consider second life uses of batteries used in electric vehicle application. These batteries are still operational and suitable to less restrictive conditions, such as those for stationary and renewable energy application. Therefore, possible second life opportunities have been identified and further assessed. In this paper, the main ageing effects of lithium ion batteries are explained. Next, an overview of different validated battery models will be discussed. Finally, a methodology for assessing the performance of the battery cells in a second life application is presented.

Evaluation of lithium-ion battery second life performance and degradation

Reusing electric vehicle batteries once they have been retired from the automotive application is stated as one of the possible solutions to reduce electric vehicle costs. Many publications in the literature have analyzed the economic viability of such a solution, and some car manufacturers have recently started running several projects to demonstrate the technical viability of the so-called battery second life. Nevertheless, the performance and degradation of second life batteries remain an unknown topic and one of the biggest gaps in the literature. The present work aims at evaluating the effects of lithium-ion (Li-ion) battery State of Health (SOH) and ageing history over the second life performance on two different applications: a residential demand management application and a power smoothing renewable integration application. The performance and degradation of second life batteries are assessed both at the cell level and at stack level. Homogeneous and heterogeneous stacks are analyzed in order to evaluate the impact of cell-to-cell history and SOH differences over the stack level battery cell performance and degradation behaviour.