Non-uniform temperature distribution in Li-ion batteries during discharge e A combined thermal imaging, X-ray micro-tomography and electrochemical impedance approach James B. Robinson a , Jawwad A. Darr b , David S. Eastwood c , Gareth Hinds d , Peter D. Lee c , Paul R. Shearing a , Oluwadamilola O. Taiwo a , Dan J.L. Brett a, * a Electrochemical Innovation Lab, Department of Chemical Engineering, UCL, London WC1E 7JE, UK b Department of Chemistry, UCL, London WC1H 0AJ, UK c The Manchester X-Ray Imaging Facility, School of Materials, The University of Manchester, Oxford Rd., M13 9PL, UK d National Physical Laboratory, Teddington, Middlesex TW110LW, UK highlights graphical abstract  X-ray tomography provides 3D structural map of 18650 battery.  Heterogeneous temperature distri- bution above 0.75C.  Localised heat generation from posi- tive cap containing PTC and safety valve. article info Article history: Received 17 July 2013 Received in revised form 28 October 2013 Accepted 1 November 2013 Available online 1 December 2013 Keywords: Positive temperature coefficient Thermal imaging Infrared thermography Temperature distribution X-ray tomography 18650 Battery abstract Thermal runaway is a major cause of failure in Li-ion batteries (LIBs), and of particular concern for high energy density transport applications, where safety concerns have hampered commercialisation. A clear understanding of electro-thermal properties and how these relate to structure and operation is vital to improving thermal management of LIBs. Here a combined thermal imaging, X-ray tomography and electrochemical impedance spectroscopy (EIS) approach was applied to commercially available 18650 cells to study their thermal characteristics. Thermal imaging was used to characterise heterogeneous temperature distributions during discharge above 0.75C; the complementary information provided by 3D X-ray tomography was utilised to evaluate the internal structure of the battery and identify the re- gions causing heating, specifically the components of the battery cap. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Effective operation of Li-ion battery systems requires careful thermal management in order to ensure stable performance, du- rable operation and prevent thermal runaway which can lead to catastrophic failure [1]. Poorly designed battery packs can also * Corresponding author. Tel.: þ44(0)20 7679 3310. E-mail address: d.brett@ucl.ac.uk (D.J.L. Brett). URL: http://www.ucl.ac.uk/electrochemical-innovation-lab Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2013.11.059 Journal of Power Sources 252 (2014) 51e57