At low temperatures, lifepo4 (lithium iron phosphate battery) capacity release rate decreases exponentially with temperature: at -20°C, usable capacity drops to 70% of the nominal one (for lead-acid batteries, it drops to a mere 35%), and voltage decreases significantly by 12% at the 1C discharge rate (in comparison with a 25°C reference). Catl’s test data for 2023 in the Arctic show that, after 72 hours of continuous operation at -30°C, the charge and discharge efficiency of the lifepo4 module dropped from 98% to 65%, while the upgraded version with a self-heating function (power density 50W/kg) can recover the capacity to 85%. The actual verification of BYD Blade Battery shows that the charging time under the -10°C environment is extended to 2.3 times that under 25°C (6.5 hours for 0-100% SOC), and the variation of the charging cut-off voltage reaches up to ±0.15V (±0.05V at room temperature).
For high-temperature accelerated aging, lifepo4 cycle life at 45°C is reduced from 4,000 times at 25°C to 2,500 times (the rate of capacity decline is increased by 60%), and at 60°C, the decomposition rate of the electrolyte is three times greater (annual capacity loss is as much as 8%). Tesla Megapack heat dissipation design case shows that with every 10°C increase in ambient temperature, the standard deviation of the battery pack internal temperature difference increases from 1.5°C to 4.2°C, which causes the capacity dispersion to reach 7% (UL 1973 standard requires ≤5%). In the 2022 Australian grid energy storage project, lifepo4 arrays without liquid cooling systems, after six months of operation at a high temperature of 48°C, saw the cell expansion rate go over 2mm (0.5mm is the acceptable limit), and the possibility of safe shut-off increased to 1.2 times a month.
Temperature control technology is crucial. The lifepo4 system with active thermal management (liquid cooling +PTC heating) can keep the operating temperature within the ideal temperature range of 15-35°C. Northvolt’s field data in Sweden proves that this solution has increased the charging efficiency at -20°C to 92% (passive mode is only 65%), and has also extended the high-temperature cycle life by 38%. The BMS strategy of the BMW iX3 battery pack indicates that when the temperature gradient is within ±3°C, the capacity utilization rate of the battery pack increases by 11% and energy loss decreases by 19%. In terms of cost, the temperature control system increases the cost of lifepo4 energy storage units by 18% ($45/kWh) but decreases the life-cycle cost of electricity per kilowatt-hour (LCOE) by 26%.
In terms of safety risks under extreme temperatures, lifepo4’s thermal runaway initiation probability at 150°C is 10⁻⁶/ hour (10⁻⁴ for NMC batteries), and low-temperature overcharging (-10°C, 1.5 times the rated voltage) will render the growth rate of lithium dendrites 5 times larger. 2021 Qinghai Photovoltaic energy Storage station accident analysis shows that when the lifepo4 system without low-temperature protection function is overcharged at -25°C, the internal resistance of a single cell rises by 200%, and the risk of generating local hotspots increases to 0.7%. For comparison, CATL’s third-generation lifepo4 reduces thermal runaway propagation speed from 8cm/s to 0.5cm/s through the use of ceramic-coated diaphragms (300°C temperature resistance) and double closed-loop voltage and temperature control.
In terms of temperature sensitivity of charging and discharging performance, lifepo4’s maximum continuous discharge rate at 0°C decreased from 2C at 25°C to 0.5C (power output attenuation of 75%). Sandia National Laboratories of the United States tested and confirmed that when it is discharged at 1C rate at -10°C, the useful energy is only 58% of the nominal, and the voltage curve also changes by 8% (change <2% at room temperature). NIO’s 100kWh lifepo4 pack, which is installed with pulse preheating technology, is capable of increasing the cell temperature to -5°C by a 3-minute pulse current (300A peak) at an ambient temperature of -20°C, recovering 85% of its discharge capacity.