Ž . Journal of Power Sources 87 2000 186–194 www.elsevier.comrlocaterjpowsour Characterization of commercial Li-ion batteries using electrochemical–calorimetric measurements S. Al Hallaj, J. Prakash, J.R. Selman ) Center for Electrochemical Science and Engineering, Department of Chemical and EnÕironmental Engineering, Illinois Institute of Technology, Chicago, IL 60616, USA Received 18 February 1999; accepted 22 October 1999 Abstract Commercial Li-ion cells of Type 18650 dimensions and prismatic designs from different manufacturers have been tested to evaluate their performance and to study their thermal behavior using electrochemical–calorimetric methods. All cells tested in this work showed good performance and cyclability under normal operating conditions. The measured heat effect for the cells were exothermic during discharge and partially endothermic during charge. Cell impedance was measured for selected cells and showed some dependence on the state of charge or depth of discharge, with significant increase at the end of discharge due to concentration polarization. The entropy Ž . Ž . Ž . coefficient d E rdT for the A & T 18650 and Panasonic CGR 18650 cells were measured using potentiometric methods at different eq Ž . depths of discharge DOD . The measured values for both cells showed some dependence on the DOD with some perturbation near 4.0 V, where the measured d E rdT for Panasonic cell had an unexpected positive value. This was found to be consistent with the measured eq endothermic heat effect during discharge for the Panasonic cell near E s4.0 V. This may be related to a phase change in the LiCoO eq 2 cathode material, as reported in the literature, and to structural transformation in the graphite used as anode material, in the Panasonic cell. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Li-ion batteries; Electrochemical measurements; Accelerated rate calorimeter 1. Introduction Lithium-ion batteries possess high energy density com- pared to other secondary batteries. Small Li-ion batteries with a capacity of 1300 to 1900 mA h are currently commercially available to power portable electronic de- vices such as camcorders, computers, cameras, etc. In addition, Li-ion batteries as power sources for electric Ž . vehicles EV are being developed to provide longer driv- ing range, higher acceleration, and long lifetime. However, safety concerns of the Li-ion batteries have limited their full utilization in EV applications. The primary challenge in designing an EV lithium-ion battery is its safety under abusive as well as normal operating conditions. The nor- mal operating conditions involve over-discharge, resistive andror forced over-discharge. Abuse conditions involve shorting, crushing, or excessive overcharging. ) Corresponding author. Tel.: q 1-312-567-3970; fax: q 1-312-567- 6914; e-mail: selman@charlie.cns.iit.edu Ž . Yoda and Ishihara 1997 described a significant role for Li-ion batteries in a battery-based society in the next century. Commercial Li-ion batteries from several manu- facturers such as Sony, A & T Battery, and Panasonic are available in the market. However, further development and cost reduction are required to design larger sizes of these Ž batteries suitable for EV and energy storage load condi- . tioner applications. w x Several researchers 3–6 have evaluated the effect of different designs and materials used in cells on the perfor- mance of commercial Li-ion cells. However, most of the work reported in the literature is limited to cylindrical cells and little research has been focused on the thermal behav- ior and its effect on the performance of these cells. In this work we present electrochemical–calorimetric measurements using a number of commercial Li-ion cells with different chemistries and designs, for different cycling rates at 358C operating temperature. Cells were taken from camcorder or cellular phone packs available in the market. The ARC–Arbin experimental set-up is used to measure the temperature, voltage and current of the cells at differ- 0378-7753r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. Ž . PII: S0378-7753 99 00472-3