Meaning
Thermal gradients represent the difference in degrees between the hottest internal part of a battery cell and its outer surface. A large temperature core-casing delta indicates that heat is being generated faster than it can be removed by the cooling system. Monitoring this value is essential for preventing thermal runaway in high power density packs.
Thermal Gradient
Internal resistance during fast charging or high current discharge generates heat deep within the jelly roll. The temperature core-casing delta grows when the thermal conductivity of the materials is low. Because plastic and electrolyte are poor conductors, the center of the cell can become much hotter than the skin.
Cooling Efficiency
Design of the thermal management system aims to minimize this difference to ensure uniform aging. If the temperature core-casing delta is too high, the center of the cell will degrade faster than the edges. This uneven wear leads to a reduction in the total usable life of the battery.
Risk Management
Safety sensors often measure only the surface temperature, which might hide a dangerous internal condition. Estimating the temperature core-casing delta using mathematical models allows the battery management system to throttle power before internal limits are reached. This proactive approach prevents the breakdown of the separator and stops the onset of chemical instability inside the electrode stack.
