Thermal and Mechanical Stress Degradation Mechanisms in Prismatic Formats
Constraining prismatic cells between 300 and 500 kPa prevents electrode delamination and suppresses localized lithium plating over long cycle life.
Core-to-Shell Delta T
Meaning
Temperature differences between the internal geometric center and the outer surface of a battery cell indicate internal thermal resistance and heat generation rates. Monitoring core-to-shell delta t provides critical data on heat conduction limits within large-format cylindrical and prismatic lithium cells during high-power operations. Rapid charging generates intense Joule heating deep within the electrode roll, where heat transfer is limited by cross-plane thermal resistance.
Exceeding safe internal temperature limits initiates local electrolyte degradation while the outer casing temperature remains within acceptable operational boundaries. This metric applies to active cells undergoing dynamic electrical loading, whereas thermal equilibrium conditions eliminate measurable temperature gradients across the cell body.
Internal Heating
High current flow through active electrode layers and internal current collectors generates continuous internal heat during fast charging. Core heat must travel through multiple layers of active materials, copper foils, aluminum current collectors and separators before reaching the outer shell. Low cross-plane thermal conductivity retards heat flow, causing internal core temperatures to rise far above surface readings.
Large-format prismatic and thick cylindrical cells exhibit the highest temperature splits due to long conduction paths from core to surface. Accumulating heat at the cell core accelerates chemical side reactions, accelerating solid electrolyte interphase breakdown. Physics-based thermal models calculate core temperatures using surface sensor data and known internal thermal resistances.
Cooling Constraints
External cooling systems lower outer shell temperatures effectively but cannot directly remove heat trapped deep inside the electrode roll. Surface cold plates create steep internal thermal gradients when forced liquid cooling chills the outer casing while high current continues generating core heat. Large temperature differences produce non-uniform current density distributions, forcing core regions to age faster than cooler outer layers.
Non-uniform degradation leads to localized capacity loss and uneven impedance growth across the cell roll. Thermal management strategies must moderate fast-charging current profiles when estimated core temperatures approach chemical safety thresholds. Balancing surface heat extraction with internal conduction prevents excessive core thermal buildup.
Safety Monitoring
Advanced battery management systems estimate internal core temperatures dynamically to prevent thermal runaway events. Standard surface thermistors fail to detect rapid core heat generation during aggressive pulse discharge events, delaying safety intervention. Incorporating real-time internal resistance measurements or thermal transfer algorithms allows management software to infer core-to-shell delta t continuously.
Lowering charge current when calculated core temperatures spike protects internal separator integrity and prevents hazardous thermal decomposition. Safety qualification testing validates these thermal algorithms under simulated coolant loss and extreme ambient conditions. Accurately predicting core heating protects cell integrity without imposing overly conservative performance limits.