Analysis of integrated heating approaches for cold-start conditions in 21700 lithium-ion battery modules using thermal system simulation

Abstract

Cold ambient conditions significantly reduce discharge capacity and slow the thermal response of lithium-ion cells, particularly at low state of charge (SOC). To address these challenges, this research studies the feasibility of heating strategies to improve cold-start performance in 21700 lithium-ion battery modules using thermal system simulation. Both experimental and simulation-based approaches were employed. At the cell level, experimental tests were conducted to evaluate thermal and capacity behavior under sub-zero temperatures. These results were compared against thermal system simulation simulations under convective or adiabatic conditions, revealing that experimental test setups introduce additional resistances not captured in idealized models. And adiabatic conditions could allow faster cell heating compared to convective conditions due to internal heat accumulation, which shows the effect of insulation. In fact, the temperature rise simulated under adiabatic conditions is approximately 2.3 to 2.9 times greater than under simulated convective conditions. Building on these findings, a module design was developed to enable system-level simulation of thermal strategies. The design considered safety, structural integrity, and thermal performance, balancing insulation with heat flow pathways. Then the study focuses on evaluating the feasibility of external and battery-powered heating strategies. Four heating configurations were simulated, external heating, battery discharge, or combined configurations. Simulations were carried out across below zero ambient temperatures of -20 °C, -10 °C, and 0 °C and different initial SOC values of 80%, 50% and 20%. Results show that in the absence of heating, the battery was unable to complete discharge at low SOC, particularly at -20 °C and 20% initial SOC. Yet when external surface heating was applied, the module achieved a faster temperature rise enabling full discharge even under these extreme conditions. Furthermore, when external heating is applied without discharge, the heating rate slows down, highlighting the added benefit of internal heat generation during battery operation. Lastly, the study evaluated whether the battery could power its own heating system. At 20% SOC and -20 °C, the energy required for heating exceeded the battery’s usable output, rendering self-heating unfeasible. In contrast, at 0 °C and moderate SOC levels, it remained viable, with heating demands as low as 2 to 3% of the available capacity. Overall, the findings support the integration of targeted heating strategies into electric vehicle (EV) thermal management systems, showing that a combination of external heating and internal heat generation enables reliable cold-start performance while minimizing energy consumption for battery heating in sub-zero conditions.