Chunjing Lin

Vapor injection (VPI) can significantly enhance the heating performance of electric vehicle (EV) heat pump systems under low ambient temperatures, making the integrated design and control of the VPI loop essential. This study uses R290 as the working fluid and investigates the gas–liquid flow characteristics of the vapor-injection electronic expansion valve (VPI-EXV) in the VPI loop. The evaporation coefficient in the Lee model is calibrated using four typical operating conditions, keeping the relative errors of both total mass flow rate and injection ratio predictions within 10%. Results show that valve opening is the dominant factor: as the opening increases from 10% to 100%, the injection ratio rises from 0.24 to 0.83, while increasing outlet pressure from 0.58 MPa to 0.78 MPa and inlet subcooling from 0 °C to 10 °C reduces it by about 18% and 9%, respectively. The 90° turning structure inside the VPI-EXV induces recirculation and high turbulent kinetic energy downstream of the throttling region, modifying the outlet gas-liquid distribution, based on which an injection ratio control strategy with valve opening as the primary variable is proposed.

During the production process of lithium‐ion batteries, there exists a scenario of excessive water inside the battery due to poor water control in the factory environment. In addition, the battery housing may be damaged by corrosion, external vibration etc., which would cause water to enter the battery. To the best of the authors’ knowledge, there is little literature to reveal the influencing mechanism related to the above issue. The effects of excessive water on battery performance and safety were discussed. The results show that when the battery absorbs excessive water, the capacity decreases and the self‐discharging rate increases rapidly. The self‐heating temperature of the battery shows an increasing trend. The thermal runaway temperature decreases significantly with the time from self‐heating to thermal runaway dramatically shortened. The thermal stability of the battery deteriorates throughout the reaction process. This is mainly due to the mechanisms by which the water absorbed in the battery reacts with the electrolyte and the electrode material, resulting in the decrease of the electrolyte conductivity and the corrosion of the electrode material, as well as the thickening of the Solid Electrolyte Interface film and the accumulation of impurities. The findings are of positive significance in demonstrating the quantitative relationship between excessive water and the performance and safety of batteries. Also, it can add to the understanding of the complex scenarios of battery spontaneous failure, which is vital for solving battery self‐thermal runaways.

With the rapid development of electric vehicles, the safety accidents caused by the damage and failure of lithium-ion batteries under mechanical load are increasing gradually, which increases the significance of collision safety in lithium-ion batteries. The failure threshold of the cell in a free state is different from that of the cells in the module. Therefore, the safety characteristics of cells and modules under vertical dynamic impact conditions were studied in this paper. Lithium iron phosphate (LiFePO₄) batteries and assembled 2-in-10 series modules with a 100% state of charge (SOC) were tested. Analyses included the voltage, temperature, and mechanical behavior of test samples under different impact loads, extrusion positions, and indenter shapes. The results showed that the damage behavior of a battery was closely related to the contact shape, contact area, and contact position. A smaller contact area led to greater deformation; moreover, the contact area being closer to the edge position meant greater deformation and weaker load-carrying capacity. The load-carrying capacity of the cell in a free state was weaker than that of the module, but the failure threshold of the cell in a free state was higher than that of the module. It can be concluded that the failure threshold of the cell cannot reflect the failure threshold of the module.