Characterization of Thermal Behavior of Commercial NCR 18650B Batteries under Varying Cycling Conditions
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Characterization of Thermal Behavior of Commercial NCR 18650B Batteries under Varying Cycling Conditions Bo Dong1, Kazi Ahmed1, Yige Li2,3, Cengiz Sinan Ozkan2,3, and Mihrimah Ozkan1 1 Electrical and Computer Engineering, University of California, Riverside, Riverside, CA, United States. 2 Mechanical Engineering, University of California, Riverside, Riverside, CA, United States. 3 Materials Science and Engineering, University of California, Riverside, Riverside, CA, United States. ABSTRACT To better understand the condition of commercial batteries used in Tesla EVs and stationary applications under real performing situations, this article focuses on tracking the temperature of commercial batteries during varying cycling conditions. We have found evidence of significant impact of cycling methods on batteries in ionic conductivity, inner impedance development, and structural change in both cathode and anode electrodes, which will be further analyzed by electrochemical impedance spectroscopy technique in the following research. INTRODUCTION Human society has relied on fossil fuels for thousands of years. In recent years, due to limited resources and CO2 pollution, modern society has been seeking for renewable energy sources. However, many renewable sources such as solar and wind are intermittent in nature and must be coupled with capable energy storage technology. The answer to this challenge may lie within lithium-ion battery (LIB) technology [1,2]. More than two decades have passed since the first commercial Lithium-ion battery was produced in 1991. Compared with traditional lead-acid, Ni-Cd, or Ni-MH batteries, LIBs have 3 to 5 times larger energy storage capability ( 180Wh kg1 ) with an average voltage of 3.8V, and better behavior in real applications [3]. Individual cells use lithium cobalt oxide as the cathode material, graphite as the anode material, and organic solution as the electrolyte. After decades of research in this novel area, different kinds of cathode materials (LiFePO4, LiMn2O4, NMC, NCA) and anode materials (Si) have been synthesized and investigated, and the energy storage capability also increased to a much higher level. An 800Wh/kg LiCoPO4 battery has been reported by Daniele di Lecce, et al [4]. However, safety issues constitute the main barrier to more widespread adoption of Lithium-ion batteries in the market. The hazard of using lithium-ion batteries compel most companies to select mature commercial batteries instead of novel ones, including Tesla. All Tesla EVs use NCR 18650 series cylindrical cells from Panasonic, which uses NCA as the cathode material and graphite as the anode material. However, since the battery pack of Tesla EV contains over 7000 cylindrical batteries, it is impossible to keep all individual cells in the same condition, and is hard to find out the real states of charge and states of health of them. But two Tesla battery-related accidents on August and October of 2016 have proven the significance of investigating these commercial batteries in depth. Most of the recent re
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