Synergy strategy of heat preservation and preheating for lithium-ion battery pack operation under low temperature

The significant degradation of lithium-ion battery (LIB) discharge capacity at low temperature especially under subzero temperatures, results in the dramatical range attenuation of electric vehicles (EVs). Preheating LIBs before operation has emerged as a promising approach to improve low-temperature performance. However, prolonged parking allows batteries to equilibrate with ambient temperatures, necessitating extended heating durations and increased energy consumption. To address this challenge, this paper proposes a synergy strategy that integrates heat preservation and preheating to maintain optimal battery temperatures during operation. First, a three-dimensional numerical calculation model of heat preservation for the battery pack is developed and validated through the vehicle heat insulation experiments, effectively reducing the battery temperature decline rate in subzero environmental conditions. Second, a preheating control strategy is developed that considers the initial battery temperature, state of charge (SOC), and driving energy demands. This strategy integrates the sinusoidal alternating current (SAC) heating method with the optimization of the target heating temperature, enabling rapid and efficient warming batteries to optimal levels using the on-board SAC heater. Accordingly, effectively reducing heating energy consumption can be achieved by combining a reliable heat preservation scheme with an optimized preheating strategy. Finally, the experimental results demonstrated that the proposed synergy strategy could significantly enhance the battery discharge capability in low temperature environments, consequently extending the range of EVs. This paper highlights the importance of integrating heat preservation and preheating strategies to mitigate the adverse effects of low temperatures on LIB performance and EVs range.