Characterization and capacity dispersion of lithium-ion second-life batteries from electric vehicles Elisa Braco, Idoia San Martín, Pablo Sanchis, Alfredo Ursúa Department of Electrical, Electronic and Communication Engineering Institute of Smart Cities Public University of Navarre Pamplona, Spain elisa.braco@unavarra.es Abstract— Nowadays, electric vehicle batteries reutilization is considered such as a feasible alternative to recycling, as it allows to benefit from their remaining energy and to enlarge their lifetime. Stationary applications as self-consumption or isolated systems support are examples of possible second life uses for these batteries. However, the modules that compose these batteries have very heterogeneous properties, and therefore condition their performance. This paper aims to characterize and analyze the existing capacity dispersion of Nissan Leaf modules that have reached the end of their lifetime on their original application and of new modules of this Electric Vehicle, in order to establish a comparison between them. Keywords— Characterization, Electric vehicle, Energy storage, Lithium-ion battery, Renewable energy, Second life batteries. I. INTRODUCTION Environmental problems caused by fossil fuels are placing the Electric Vehicle (EV) as an alternative for sustainable mobility. As reported by the International Energy Agency, in 2017 the total number of EVs in the world reached 3.1 million [1]. According to this source, the figure will continue to grow until 1.2 billion by 2060. One of the most critical elements of EVs are their lithium-ion batteries. The performance of these batteries undermines with ageing, due to multiple factors, such as temperature, charge and discharge current rate or voltage operation limits, inter alia. For this reason, several regulations establish the end of their useful life when their capacity reaches an 80% of its initial value [2]. Nevertheless, some authors question this limit, and consider it overly conservative [3-4]. In this context, the first Nissan Leaf EVs were introduced in Japan and USA in 2011. According to their manufacturer, after 8 years their capacity is considered to have attained the 80% threshold [5]. Thus, the time has come for numerous batteries from these EVs to be withdrawn. Being an important part of the EVs price, batteries reutilization emerges as a cost reduction alternative against other solutions as recycling. As reported by several authors, the salvage value of EVs batteries can lead to a reduction of their upfront costs up to a 20% [6,7]. It is in this background that the Second Life (SL) term appears, related to the post-EV use, in contrast to the so-called First Life (FL), in which they serve as energy storage device on the EV. The SL benefits from the remaining energy for less demanding applications, in which power and energy density are not as key as in EVs. There exist several examples of FL lithium-ion batteries used as storage systems on renewable energies applications [8-12]. In the case of SL batteries, one of the most promising uses is energy storage on residential photovoltaic installations [13]. Moreover, in the recent years, several OEM have supported demonstration projects with SL batteries [14- 16]. According to a report study by Bloomberg New Energy Finance, by 2025, 95GWh will be available from EVs batteries and the SL market for stationary storage could reach 26 GWh [17]. Today, there are many uncertainties with regard to economic viability on EV batteries reutilization [18, 19]. In principle, the cost of the SL batteries should be significantly lower than that of the new ones. The main drawbacks of SL with respect to FL batteries are their lower energy and power capacity, as well as their heterogeneity [4]. However, appropriate sizing, adapted to the specific SL application, can overcome limitations due to capacity and power fade. Furthermore, cells heterogeneity can be palliated with adequate association, and with specific control strategies, implemented in both Battery Management System (BMS) and power electronics converters, which are used to power conditioning [4]. Battery packs from EVs consist normally of series and/or parallel connected modules, in such a way that the desired voltage and capacity are achieved. These modules contain, in turn, series and/or parallel We would like to acknowledge the support of the Spanish State Research Agency (AEI) and FEDER-UE under grants DPI2016- 80641-R and DPI2016-80642-R and of Government of Navarra through research projects PI020 RENEWABLE STORAGE and 0011- 1411-2018-000029 GERA.