Thermal characteristics of solid-state battery and its thermal management system based on flat heat pipe

Solid-state batteries (SSBs) offer promising potential for commercial applications due to their high energy density and elimination of the flammability associated with conventional liquid electrolyte batteries (LBs). Taking into account both experimental and simulated outcomes, the SSB generates more heat than LB, which leads to a higher temperature rise. To effectively address this issue, a hybrid battery thermal management system (BTMS) with micro heat pipe array (MHPA) and air-cooling was developed in this work for the solid-state battery pack (SSBP). In parallel, an electro-thermal coupling model at the pack level considering parallel branch current distribution and an equivalent thermal resistance-based MHPA model were developed. The models were verified by comparing the experimental and simulated results on the 2-parallel and 1-series connected (2P1S) battery pack and the BTMS. A maximum average absolute error (AEave) of 1.11 °C, an average relative error (REave) of 1.62 %, and a root mean square error (RMSE) of 0.88 °C were considered. The simulations were conducted to compare the temperature rise of the battery pack with MHAP and aluminum plate cooling. In the 35 °C-35 °C-6 m/s cooling condition and at 1.5C discharge, the pack temperature reached 52.21 °C with aluminum plate cooling, 8 °C higher than that with MHPA. Moreover, the simulations predicted the temperature, current, and state of charge distributions of 3P4S connected SSBP and LB pack (LBP) based on the hybrid BTMS at different cooling conditions. The results showed that the temperatures of SSBP and LBP were controlled within 43 °C even at 35 °C ambient temperature. Reducing the air temperature had a stronger cooling capacity than increasing the air speed. However, the temperature gradient was exacerbated to 3.29 °C and 1.54 °C in the SSBP and LBP. The impact of temperature difference on the resistance worsened the current inhomogeneity in the parallel branch and led to a maximum state of charge (SOC) difference of 5.59 % within the SSBP and 0.56 % in the LBP. Thus, to achieve an efficient cooling of SSBPs with higher heat loads, a more balanced consideration of the induced thermal-electrical homogeneities is required.