Abstract
Research and/or Engineering Questions/Objective
The security performance and thermal behavior of the power lithium-ion battery, which proved to be the ideal power source for EV and HEV, have been widely investigated and reported. Evidently, the battery power and energy density deteriorate as the temperature decreases, and charging at low temperature could cause permanent damage. In the worst case scenario, lithium dendrites may pierce the separator and cause an internal short circuit leading to thermal runaway and battery explosion.
Methodology
Because of lithium ion battery poor performance at low temperature and based on the theory of lithium intercalation, an AC heating method is put forward. The cells adopted in experiments are commercial 18650 batteries and LiFePO4 batteries. The AC excitation has been performed using a BIPOLAR POWER SUPPLY. The amplitude of the perturbation current is set at 10A for 18650 and 40A for LiFePO4 battery and the frequency is set to 300Hz. The thermocouples are placed on both sides of the battery surface. The temperatures from both thermocouples are measured using a HIOKI temperature unit and recorded by a wireless logging station. The ARBIN serves the functionality of calibrating the battery capacity and direct current (DC) impedance at 25oC after every 20 times heating.
Results
The temperature of 18650 rises from -24oC to 4oC in 10 minutes. The heating effect for LiFePO4 battery is relatively badly, and it takes 30 minutes to warm up the cell from -24oC to -8oC. The main reason may be that the impedance of 18650 is greater than LiFePO4 battery at the same current amplitude and frequency. After 20 and 40 times heating, there is no existence of capacity fading and impedance growth for both batteries based on the capacity calibration and DC impedance analysis. It can provide an engineered basis for improving battery thermal performance and management system design.
Limitations of this study
Effects of current frequency, amplitudes, and waveforms on the temperature evolution and battery life should be respectively investigated and the results will be reported in a forthcoming communication. And engineering implementation method for EV and HEV also needs to be considered.
What does the paper offer that is new in the field including in comparison to other work by the authors?
The AC heating method is more efficient compared with traditional ones. The study in the paper could serve the function as a guidance to the design and development of the battery thermal management systems at low temperature.
Conclusions
A new AC heating method is proposed in the paper to improve the performance of the battery at low temperature. The feasibility of the method is proved by the experiments. The heating method may be more applicable to 18650 battery. The work has shown potential value in battery thermal management studies for EV/HEV applications at subzero temperatures.
Key Words : lithium-ion battery; low temperature; AC heating method; battery thermal management system