Heat generation and surrogate model for large-capacity nickel-rich prismatic lithium-ion battery as against 18650 battery

Large-capacity lithium batteries are being widely used as the power sources of new energy vehicles due to the advantages of easy assembly and simplified electrical connections. However, the temperature rise and thermal safety issues would become more severe for larger capacity batteries with smaller specific areas due to more concentrated heat generation and accumulation thereof. In this paper, an experimental study is presented for the thermal characteristics and thermal performance of a commercial large-capacity lithium battery over 100 Ah. The orthogonal experiment protocol was designed to obtain the direct current internal resistance and entropy coefficient of battery under varying working conditions involving the temperature and depth of discharge. It was found that the discharge rate had little effect on the entropy coefficient and direct current internal resistance, and the average entropy coefficient of a battery with high nickel content and specific energy was lower. Meanwhile, the electrochemical impedance spectroscopy of a battery in different placement orientations was also tested. The results indicated that the ohmic impedance and charge transfer impedance of the battery in the upright orientation were slightly smaller than that in the lying-down orientation, which is preferred in practical operation. The battery heat generation rate is gained by combining the measured internal resistance and entropy coefficient terms. A third-order surrogate model of heat generation rate is correlated under different working conditions with the depth of discharge, temperature, and discharge rate by the response surface analysis (RSA). In addition, the volumetric heat generation rate of the present large-capacity prismatic battery is compared with a smaller 18650 battery. The battery temperature rise under natural convection condition was experimentally measured, together with the measured specific heat, to examine the validity of the present heat generation model. Finally, the heat generation surrogate model was applied in WLTC conditions, and the temperature rises of the battery under different depths of discharge were obtained and discussed.