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The influence of temperature on the internal resistance of lithium iron phosphate battery

by:dcfpower     2021-04-03
u003cpu003e  The internal resistance of a lithium iron phosphate battery, as the main parameter to measure the difficulty of the internal conductive ions and electrons in the battery, directly determines the power characteristics of the battery, and therefore has an important impact on the power of electric vehicles. At the same time, internal resistance also determines the amount of heat produced by the battery. For example, in the classic Bemardi battery heat generation model, internal resistance is one of the key parameters for battery heat generation estimation. u003c/pu003eu003cpu003e  The actual operating environment temperature range of electric vehicles is wide, and the internal resistance of the battery is different under different temperatures and working conditions. Grasp the internal relationship between battery internal resistance and temperature, SOC, charge and discharge rate, etc., which can better provide a basis for battery heat generation model simulation and thermal management system design. Li Zhe et al. studied power lithium iron phosphate batteries at 10, 25 and 25 The temperature characteristics at 40℃, the results show that as the temperature increases, the ohmic internal resistance and polarization internal resistance of the battery during charging and discharging decrease, and the rate of change of ohmic internal resistance at different temperatures is higher than that of polarization internal resistance. The rate of change of ohmic resistance is greater than the rate of change at high temperature. Guo Hongyu et al. studied the internal resistance changes of power lithium manganate batteries at different ambient temperatures (f-20~50℃) and SOC through experiments, and the results showed that the total internal resistance of the battery changes under low temperature f0℃) and lower SOC. obvious. Considering that electric vehicles need to operate in an environment below 0°C in winter, it is very necessary to fully study the low temperature characteristics of the internal resistance of lithium iron phosphate power batteries, and the current research on the internal resistance characteristics of batteries below 0°C is still less. In this paper, the internal resistance of 40 Ah square energy lithium iron phosphate power battery is tested at different temperatures by the hybrid pulse power characteristic method (HPPC), and the battery charging and discharging process at different temperatures at 20~40℃ is studied in detail. The internal resistance changes with SOC, and the reasons leading to this rule are analyzed. u003c/pu003eu003cpu003e   takes a square 40 Ah lithium iron phosphate power battery for electric vehicles as the research object. Among them, the positive electrode material is lithium iron phosphate, unmodified, and used as carbon coating; the negative electrode material is high-temperature mesophase carbon micro Ball (MCMB1; electrolyte is lithium salt electrolyte and organic solvent, diaphragm is polypropylene/polyethylene (PP/PE); battery cell parameters are shown in Table 1. Battery charging and discharging equipment is Arbin EVTS power battery test system. The constant temperature box is SETH.Z-040L ultra-low temperature humidity control experiment box, which provides a constant ambient temperature for battery charging and discharging experiments.u003c/pu003eu003cpu003eLithium iron phosphate power battery parameters:u003c/pu003eu003cpu003eSize/(mmxmmxmm ): 100x32xl80 minimum discharge voltage/V: 2.5 maximum charge voltage/v: 3.8 maximum charge current/A: 160 maximum discharge current/A: 200 (1min) working temperature (charging)/℃: 0~45 working temperature (discharging) /: -20~45 rated voltage / v: 3.2 rated capacity / Ah: 40 mass / g: 1250u003c/pu003eu003c/pu003e
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