Scale-up design of lithium-ion batteries: Electrochemical-calorimetric, thermal modeling, and safety studies

The heat effect of commercial Li-ion cells with cylindrical and prismatic design designs was studied under different operating conditions using an Accelerated rate Calorimeter (ARC) in combination with a battery cycler (Arbin). The measured heat effect was exothermic during discharge and partially endothermic during charge with strong dependence on the charge/discharge rate. The ARC-Arbin set-up was also used to measure the cell impedance and the entropy coefficient (dE_eq/dT) under normal operating conditions, and the onset of thermal runaway (OTR) temperature for selected cells under abusive conditions.; The DC-current interruption technique in combination with calorimetric measurements (DCIC) was used to study the unexpected endothermic heat effect during discharge for the Panasonic (CGR 18650H) cell. The heat effect was related to entropy change in the graphite used as anode in the cell. This conclusion was confirmed by measuring the entropy coefficient (dE_eq/dT) for a graphite/Li half-cell, which was found to be positive for all OCV > 0.1 V. The heat effect was complicated by the coexistence of a phase transition from hexagonal to monoclinic back to hexagonal again in the LiCoO₂ cathode material and a structural transformation in the graphite anode which take place at the same DOD.; A simplified 1-D thermal model was developed and used to simulate the thermal behavior of the Sony Type (US18650) cell under different operating conditions. Simulation results were in good agreement with experimental measurements at low to medium rates while some deviation was noted at higher rate. The model was used to simulate the thermal behavior of a 10 and 100 A-hr, scaled-up cells. Results showed that surface cooling has a significant effect on the temperature profile of the scaled-up cells and at high cooling rate a significant difference was found between the cell surface and center temperature.; A novel thermal management system that incorporates phase change material (PCM) was proposed and investigated for electric vehicle (EV) application. A commercial finite element (FE) software, PDEase2D™, was used to simulate the thermal behavior of the Sony ALTRA-EV™ battery Module with PCM thermal management system. Simulation results showed that the temperature profile of the cells integrated in the Module design was uniform during discharge at different rates. A major advantage of the PCM system is by storing the heat generated during discharge as latent heat. The stored heat will be rejected to the module when the battery is left to relax or when its temperature drops below the melting point of the PCM. This could be important for EV operation under cold conditions or in space application where the battery temperature drops significantly when an orbiting satellite moves from the light to the dark side of the earth.