Thermal modeling and design considerations of lithium-ion batteries

A simplified one-dimensional thermal mathematical model with lumped parameters was used to simulate temperature profiles inside lithium-ion cells. The model makes use of heat-generation parameters established experimentally for the Sony (US18650) cell. The simulation results showed good agreement with temperature measurements at C/2, C/3, and C/6 discharge rates, while some deviation was noticed for the C/1 discharge rate. The model was used to simulate temperature profiles under different operating conditions and cooling rates for scaled-up cylindrical lithium-ion cells of 10 and 100 A h capacity. Results showed a strong effect of the cooling rate on cell temperature for all discharge rates. A significant temperature gradient inside the cell was found only at higher cooling rates, where the Blot number is expected to be > 0.1. At lower cooling rates, the cell behaves as a lumped system with uniform temperature. To establish the limit's of temperature allowable in scale-up by the simplified model, commercial lithium-ion cells at different open circuit potentials were tested inside an accelerated rate calorimeter (ARC) to determine the onset-of-thermal-runaway (OTR) temperatures. Sony (US18650) cells at 4.06, 3.0, and 2.8 V open circuit voltage (OCV) were tested and their measured OTR temperatures were found to be 104, 109, and 144 degrees C, respectively. A sharp drop in the OCV, indicating internal short circuit, was noticed at temperatures close to the melting point of the separator material for all open circuit voltages. (C) 1999 Elsevier Science S.A. All rights reserved.