Damage of cells and battery packs due to ground impact Yong Xia a, b, * , Tomasz Wierzbicki a , Elham Sahraei a , Xiaowei Zhang a a Impact and Crashworthiness Lab, Massachusetts Institute of Technology, 77 Massachusetts Ave, Room 5-218A, Cambridge, MA 02139, USA b State Key Lab of Automotive Safety and Energy, Department of Automotive Engineering, Tsinghua University, Beijing 100084, China highlights  A general methodology is developed for analyzing ground impact of battery pack.  Scenarios of ground impact against battery pack of electric cars are discussed.  A hypothetic global FE model is developed for ground impact of battery pack.  Parametric study is carried out for ground impact of battery pack.  Failures of individual cell and shell casing are predicted with detailed models. article info Article history: Received 12 February 2014 Received in revised form 29 April 2014 Accepted 14 May 2014 Available online 23 May 2014 Keywords: Ground impact Battery pack Lithium-ion cell Multi-level modeling Fracture Electric short circuit abstract The present paper documents a comprehensive study on the ground impact of lithium-ion battery packs in electric vehicles. With the purpose of developing generic methodology, a hypothetic global finite element model is adopted. The forceedisplacement response of indentation process simulated by the global FE model is cross-validated with the earlier analytical solutions. The punching process after the armor plate perforation, the ensuing crack propagation of the armor plate as well as the local defor- mation modes of individual battery cells are clearly predicted by the global modeling. A parametric study is carried out, and a few underlying rules are revealed, providing important clues on the design of protective structure of battery packs against ground impact. In the next step, detailed FE models at the level of a single battery cell and shell casing are developed and simulations are performed using boundaries and loading conditions taken from the global solution. In the detailed modeling the failure of individual components is taken into account, which is an important indicator of electric short circuit of a battery cell and possible thermal runaway. The damage modes and the deformation tolerances of components in the battery cell under various loading conditions are observed and compared. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Protecting lithium-ion cells from crash related damage is a serious concern for vehicle manufacturers. Battery packs in hybrid vehicles are relatively small and they are usually placed in well- protected areas, away from crush zones and possible intrusion of foreign objects. Plug-in hybrids and pure electric cars have much larger battery packs which must be wisely integrated into the vehicle body structure. There are basically two main design con- cepts: the “T” architecture and the “Floor” architecture (see Fig. 1), each with its own advantages and limitations. In the “T” configu- ration battery modules are arranged along the tunnel between the seats and in the area of the real axel under the passenger seat, where most of gasoline cars place their fuel tanks. Such architec- ture, found for example in Fisker Karma, Chevy Volt and Opel Ampera ensures an excellent protection against frontal collision and side impact. But the “T” solution may sometimes compromise passenger comfort and interior space. Still it is not unconditionally safe, as one fire accident following a side collision test prompted NHTSA to launch a full investigation [1]. Placing the battery pack under a vehicle floor lowers the car's center of gravity and leaves an entire interior space for comfortable accommodation of occupants and luggage. It comes though at a price of lowering vehicle ground clearances that could have grave consequences. The “Floor” battery pack configuration is found, amongst others in the BMW i3, Nissan Leafs, Mitsubishi i-Miev, * Corresponding author. State Key Lab of Automotive Safety and Energy, Department of Automotive Engineering, Tsinghua University, Beijing 100084, China. Tel.: þ86 10 62789421. E-mail address: xiayong@tsinghua.edu.cn (Y. Xia). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour http://dx.doi.org/10.1016/j.jpowsour.2014.05.078 0378-7753/© 2014 Elsevier B.V. All rights reserved. Journal of Power Sources 267 (2014) 78e97