The discharge capacity of lifepo4 batteries in a low-temperature environment of -20℃ decreased to 65% of the nominal value (tested by Harbin Institute of Technology in 2023), a reduction of 35 percentage points compared to the 25℃ working condition. The internal resistance soared by 180% (from 0.8mΩ to 2.24mΩ), resulting in a 12% drop in the starting voltage. The operational data of the Norwegian electric vehicle fleet shows that the range reduction rate at -15℃ in winter is as high as 41%, while that of ternary lithium batteries only drops by 28%. However, the high-temperature performance advantage is significant. The capacity retention rate of continuous 1C discharge at 45℃ still reaches 96% (GB/T 31486 standard), and the initial temperature of thermal runaway is maintained at 270℃ (UL 1642 certification), which is 70℃ higher than the safety threshold of ternary batteries.
Temperature has an exponential influence on the cycle life. The calculation of the Arrhenius equation indicates that an environment of 40 ° C increases the electrochemical reaction rate by 150%, resulting in a reduction of the 6,000-cycle life (25 ° C /80% DOD) to 3,800 cycles (IEC 62619 data). Empirical evidence from BYD’s energy storage project shows that the capacity attenuation rate of lifepo4 after three years of operation in a 35℃ area is 12.7%, which is 3.8 times higher than that in temperate regions. What is even more serious is the high-temperature storage at 60℃. The accelerated aging test confirmed that for every 10℃ increase, the rate of calendar life decline doubles. When stored in a fully charged state for one year, the capacity loss reaches 24% (only 5% at 25℃).
The charging characteristics are strictly restricted by temperature. When charging at 0.3C below 0℃, the probability of lithium dendrite growth surges to 8.3 times that of the environment at 25℃ (electron microscope observation data from Tsinghua University). The MIL-STD-810G standard of the US military requires that the charging current at -30℃ shall not exceed 1/3C; otherwise, the permanent capacity loss rate exceeds 5% per time. The risk of high-temperature charging also exists. At 55℃, 1C fast charging will increase the decomposition rate of the SEI film by 300%. Tests by CATL show that the capacity drops sharply by 19% after 300 cycles (compared to the 7% attenuation at 25℃).
Thermal management energy consumption significantly affects system efficiency. The power consumption of the self-heating system that maintains lifepo4 operating at -20℃ accounts for 18% of the output energy (Tesla Heat Pump Technology White Paper), while the power consumption of active cooling in a 45℃ environment reaches 5.3%. The actual measurement of the Sahara photovoltaic storage project shows that the temperature control system of the battery compartment consumes an average of 127kWh/kWh of electricity annually, reducing the overall efficiency by 7.2 percentage points. Temperature uniformity is even more crucial. A temperature difference of more than 5℃ inside the module will shorten the lifespan by 37% (UL 1973 standard). Therefore, the liquid cooling system needs to control the temperature difference within ±2℃ (the temperature difference in the natural convection scheme reaches ±8℃).