Experimental Study on the Internal Resistance and Heat Generation Characteristics of Lithium Ion Power Battery with NCM/C Material System

Heat generation characteristics of lithium ion batteries are vital for both the optimization of the battery cells and thermal management system design of battery packs. Compared with other factors, internal resistance has great influence on the thermal behavior of Li-ion batteries. Focus on a 3 Ah pouch type battery cell with the NCM/C material system, this article quantitatively evaluates the battery heat generation behavior using an Extended Volume-Accelerating Rate Calorimeter in combination with a battery cycler. Also, internal resistances of the battery cell are measured using both the hybrid pulse power characteristic (HPPC) and electro-chemical impedance spectroscopy (EIS) methods. Experimental results show that the overall internal resistance obtained by the EIS method is close to the ohmic resistance measured by the HPPC method. Heat generation power of the battery cell is small during discharge processes lower than 0.5 C-rate. The curve of heat generation power vs. time shows a U-shaped characteristic that displays some symmetry when the current rate is high. Compared with the EIS method, internal resistances measured by the HPPC method have a more close relationship with the heat generation behavior. Influenced by the internal resistance, the battery heat generation power is much higher during the beginning period of charge process and the end period of discharge process. In addition, battery heat generation in this article is mainly composed of irreversible ohmic heat, while the reversible heat and side reaction heat are relatively small in quantity.