978-1-7281-0653-3/19/$31.00 ©2019 IEEE Analysis of the main battery characterization techniques and experimental comparison of commercial 18650 Li-ion cells Adrian Soto, Alberto Berrueta, Pablo Sanchis, Alfredo Ursúa Department of Electrical, Electronic and Communication Engineering Institute of Smart Cities Public University of Navarre (UPNA) Pamplona, Spain adrian.soto@unavarra.es Abstract— Over the coming years, major growth in the use of Li-ion batteries is expected, both in electric mobility as well as in stationary applications, be it in self-consumption systems and micro grids or in large renewable power generation plants. The proper characterization of lithium-ion cells is of vital importance for the development of precise models that permit the simulation and prediction of their behavior, so as to suitably configure cell groupings for the resulting battery packs, and to properly select the most suitable cells from the extensive manufacturer offer. In this work, an analysis is conducted of the main techniques used in the literature to characterize batteries. Also, an experimental comparative is carried out on 18650 Li- ion cells from three large global manufacturers, focusing on the primary methodologies used to characterize capacity, internal resistance and open circuit voltage. Finally, the advantages and disadvantages are presented for the methodologies used, based on the experimental results obtained. Keywords— Battery, Characterization, Electrical energy storage, Lithium ion cell, Renewable energy. I. INTRODUCTION Applications using lithium-ion batteries have become increasingly popular, serving as the best solution in comparison to other energy storing technologies, given their high energetic density, long durability and ability to work at high powers. Over recent years, Li-ion batteries have undergone a significant reduction in manufacturing costs, thus becoming one of the most competitive electrical energy storing technologies on the market. But despite the fact that Li-ion batteries have been used in portable applications since the 1990s, this technology has yet to reach its full potential. Currently, it is difficult to make a clear comparative of the benefits of different Li-ion cells based only on manufacturer data sheets, since each of these offers functioning characteristics in distinct operating conditions. This is similar to what we find in the literature, where almost all authors work with distinct profiles and conditions, lacking a standardized methodology to characterize the Li-ion cells [1]–[3]. Therefore, characterization results are not typically comparable, since they tend to depend mainly on the charge and discharge profile and temperature. This lack of uniformity has hindered the analysis of the comparison of operational characteristics and features between different Li-ion cells. Distinct methodologies can be used to characterize Li-ion cells and to obtain their main functioning parameters and characteristics. The methodologies used to offer a detailed and precise characterization of Li-ion cells tend to demand extensive testing times [2]. Other methodologies, however, may offer similar results, although perhaps less detailed and less precise, but with a substantial reduction in the time necessary to complete the characterization tests [3]. This reduction in time is especially significant in the accelerated tests of calendar aging, where these procedures may influence the results that are obtained [4]. Based on the above, this article attempts to analyze and propose test techniques to characterize Li-ion cells that achieve an optimal relationship between the experimentation time used and the simplicity of the characterization. The work is presented as follows: Section II offers a brief description of the main Li-ion cells characterization methodologies found in the literature, as well as the most relevant parameters for cell analysis. Section III analyzes and compares the experimental results obtained for various 18650 Li-ion cells of some of the main global manufacturers (LG, Samsung and Panasonic) based on test type. Finally, in Section IV, the principal results obtained are summarized, as well as the study conclusions. II. METHODS OF CHARACTERIZATION When characterizing Li-ion cells, three fundamental parameters are relevant: capacity, open circuit voltage (VOC) and internal resistance (Ri). Both the open circuit voltage and the internal resistance depend on the cell’s state-of-charge (SOC). Appropriate cell characterization is essential in order to develop an electrical model that permits the analysis of the Li-ion cell behavior in simulation. This characterization must permit the creation of a simple cell model from which it is possible to simulate and optimize both the battery’s size and its management [1]. In order to group together the distinct cells in series and in parallel, thus forming battery packs, it is also necessary to determine the dispersion between the distinct cells when optimally grouped. Finally, in the case of subjecting commercially available cells to a selection criterion, based on the distinct applications and profiles in which they are to be used, a proper previous characterization is essential. A. Capacity characterization Capacity may be defined as the quantity of charge that can be stored in a cell. This parameter may, for instance, be related to the autonomy of an electric vehicle, the energy that can potentially be stored in an electric micro-grid, etc. Generally speaking, tests used to measure capacity consist of a continuous current charge, followed by a constant voltage charge phase until reaching a minimum current (CCCV 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.