The temperature of electric vehicle batteries needs to be controlled through a thermal management system to ensure working performance, service life, and safety. In this paper, TAFEL-LAE895 100Ah ternary Li-ion batteries were used, and discharging experiments at different rates were conducted to study the surface temperature increasing characteristics of the battery. To dissipate heat, heat pipes with high thermal conductivity were used to accelerate dissipating heat on the surface of the battery. We found that the heat pipe was sufficient to keep the battery temperature within the desired range with a midlevel discharge rate. For further improvement, an additional thermoelectric cooler was needed for a high discharge rate. Simulations were completed with a battery management system based on a heat pipe and with a combined heat pipe and thermoelectric cooler, and the results were in line with the experimental results. The findings show that the combined system can effectively reduce the surface temperature of a battery within the full range of discharge rates expected in the battery used.
Scientific and reasonable battery thermal management systems contribute to improve the performance of a power battery, prolong its life of service, and improve its safety. Based on TAFEL-LAE895 type 100Ah ternary lithium ion power battery, this paper is conducted on charging and discharging experiments at different rates to study the rise of temperature and the uniformity of the battery. Paraffin can be used to reduce the surface temperature of the battery, while expanded graphite (EG) is added to improve the thermal conductivity and viscosity of the composite phase change material (CPCM), and to reduce the fluidity after melting. With the increase of graphite content, the heat storage capacity of phase change material (PCM) decreases, which affects the thermal management effect directly. Therefore, this paper combines heat pipe and semiconductor refrigeration technology to transform heat from the inner CPCM to the thermoelectric cooling sheet for heat dissipation. The results show that the surface temperature of the battery can be kept within a reasonable range when discharging at high rate. The temperature uniformity of the battery is improved and the energy of the battery is saved.
Lithium-ion batteries which are used in electric vehicles cannot be charged to their maximum capacity at the end of the charging period, a situation which is caused by inconsistency between the battery cells. This paper takes the 18650 ternary lithium battery as the research object and proposes an alternate equalization control system in the charging process. This system takes SOC consistency to be the equalization variable. Through controlling the relay, this system realizes the alternate recombination between different batteries in order to form a series battery group for charging, which achieves the goal of SOC equalization of the entire battery group. The simulation result of charge equalization, based on Matlab/Simulink, shows that at the end of the charging simulation, the SOC inconsistency of the battery group reduced from 10% to 1%. Finally, an experimental platform was built in order to verify the experiment. During the charge balance experiment, the maximum SOC inconsistency between the batteries reduced from 1.542% to 1.035%. The SOC inconsistency at the end of charging reduced from 1.214% to 0.8%, which represents an improvement of the equalization effect of the control system. The experimental results are consistent with the simulation results, which proves the effectiveness of the system’s ability to control the battery SOC balance during the charging process.
The spontaneous combustion of electric vehicles occurs frequently, and the main reason is the thermal runaway of a lithium-ion battery. In order to prevent the heat that is produced in the use of a lithium-ion battery out of control, this study proposed a coolant circulation cooling system, that is, the heat generated by the lithium-ion battery is transferred to heat sinks through aluminum plates and copper rods, and then dissipated through the coolant. Based on a CALB-LB5F73 LiFePO4 battery pack, experiments with the coolant circulation cooling system were conducted to study the temperature rise characteristics at different ambient temperatures. The temperature of the battery pack was still close to the upper limit of permitted temperature when the ambient temperature reached 313 K. Further improvement, increasing the diameter of copper rod of the system was proposed to enhance heat dissipation and simulations with this scheme were completed. The findings show that the cooling system can clearly reduce the temperature of a lithium-ion battery pack and control the temperature within the safe temperature range.
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