A candidate strategy for low-temperature preheating of lithium-ion batteries based on supercooling salt hydrates

Preheating is necessary for lithium-ion batteries to avoid severe performance degradation and potential safety hazards at temperatures below 283.15 K. Supercooling salt hydrates as latent heat storage materials provide a promising candidate to preheat batteries in an extremely low-temperature environment. This paper selects Na2S2O3 center dot 5H2O (STP) and CH3COONa center dot 3H2O (SAT) with deep supercooling properties and a prismatic LiFeO4 battery as the study objects. A parametric study is carried out to obtain an optimal design. The target preheating temperature of the battery is 293.15 K. After weighting the preheating time, effective utilization, specific energy, and specific power, the configuration that all the sides of the battery are covered with a salt hydrate thickness of 8.0 mm is considered to be the optimal design at 253.15 K. Heating rates are 0.236 K/s and 0.205 K/s for SAT and STP, respectively. However, when the ambient temperature increases to 273.15 K, the effective utilization of SAT and STP decreases by 30.46 % and 34.41 %, respectively. When the discharge rate increases from 1C to 5C, the state of charge (SOC) relative to the cut-off time of SAT and STP reduces from 85.45 % to 56.69 % and from 82.95 % to 57.46 %, respectively. This means a higher effective utilization is provided for a high discharge rate. Due to a higher melting point and higher fusion of heat, SAT shows a faster-preheating rate and higher effective utilization relative to STP, while the difference in average battery temperatures is slight.