Experimental Investigation of AC Pulse Heating Method for NMC Lithium-Ion Battery at Subzero Temperatures 2017-01-1217
An alternating current (AC) heating method for a NMC lithium-ion battery with 8Ah capacity is proposed. The effects of excitation frequency, current amplitudes, and voltage limit condition on the temperature evolution are investigated experimentally. Current amplitudes are set to 24A(3C), 40(5C), and 64A(8C), and excitation frequencies are set to 300Hz, 100Hz, 30Hz, 10Hz, 5Hz, and 1Hz respectively. The voltage limitations are necessary to protect cells from overcharge and over-discharge. Therefore the voltage limit condition (4.2V/2.75V, 4.3V/2.65V, and 4.4V/2.55V) are also considered in depth to verify the feasibility of the AC heating method. The temperature rises prominently as the current increases, and the decrement of frequencies also lead to the obvious growth of battery temperature. The battery obtain the maximum temperature rise at 64A and 1Hz, which takes 1800s to heat up the battery from -25°C to 18°C. When at low frequencies (5Hz, 1Hz) and low temperature, the heating rate deteriorates because of the calibration of voltage limit protection to current amplitude. But even with different voltage limitations, the battery can almost achieve same temperature results in 1800s. Therefore, the temperature rise is determined by the current amplitude, voltage limitations, and excitation frequency comprehensively. The capacity, DC (Direct Current) resistance and EIS (Electrochemical Impedance Spectroscopy) of cells are calibrated to assess the SOH (State of Health) of cells during the heating cycle tests. The results show that the capacity deteriorates at low frequency (1Hz) even with different current amplitudes, but its impedance is almost not influenced during the AC heating process. We can speculate that the SOH is mainly relevant to excitation frequency during the AC heating process.