The thermal stability of LiFePO4 lithium iron phosphate batteries in high-temperature environments is far greater than that of other lithium battery technologies. Compared to ternary lithium batteries (NMC), the starting temperature of thermal runaway of LiFePO4 cells is 270°C, while that of NMC is 150°C-210°C. The U.S. test data show. Department of Energy in 2022, where ambient temperature was raised to 45°C, capacity degradation rate of LiFePO4 battery was as low as 0.8% per month and that of NMC batteries up to 2.5%. For instance, in a photovoltaic energy storage project in Arizona, the LiFePO4 system was under average daily temperature of 40°C in summer for three consecutive years, and the capacity retention rate was still 85%, while the NMC group declined to 68% in the same years.
In terms of high-temperature charging and discharging efficiency, LiFePO4 battery can still maintain a 93% energy efficiency conversion rate at 50°C, 11 percentage points higher than that of NMC batteries (efficiency down to 82%). Its unique olivine crystal structure is capable of retarding the rate of thickening of the SEI film (solid electrolyte interface film) at high temperature, thereby reducing the increase in internal resistance. In comparison with LiFePO4 batterie of the same capacity, when Tesla Powerwall (NMC) is charged and discharged at full power in a 35°C environment, its temperature rise is 12°C, whereas that of the latter is only 5° C. The temperature difference control capability is enhanced by 58%. Real test of 2023 Saudi Arabian Desert energy storage project reveals that LiFePO4 system ran 8 hours continuously with a surface temperature of 55°C, and cell temperature remained below 60°C constantly without triggering any overheat protection mode.
From cycle life dimension aspect, LiFePO4 batterie’s attenuation rate is lower under conditions of high-temperature and high-load. If the surrounding temperature raises from 25°C to 45°C, its 2000 cycle (100% deep discharge) capacity retention ratio will be 80%, while that of the NMC battery will be 65% under the same condition. For instance, a fleet of electric tricycles in Mumbai, India, utilized LiFePO4 batterie. For the battery state of health (SOH) under the harsh operation conditions of 45°C average daily temperature and three charge and discharge cycles, the SOH was even 92% after two years, whereas the SOH of the NMC battery pack was down to 78% under the same operating condition. According to UL-certified lab data, LiFePO4 at 45°C 3.2%/year static storage calendar life (decay) is just 37.6% of the 8.5% maximum of the NMC batteries.
Safety hazard control is the inherent advantage of LiFePO4 batterie. The thermal runaway energy released by it is 90kJ/kg, which is much lower than that of NMC’s 750kJ/kg. Furthermore, no oxygen is released in the process of decomposition, reducing the fire risk by 80%. In the 2021 Florida hurricane season, thermal spread was triggered by high temperature in an NMC battery at a community energy storage station, which also burnt three modules with a direct loss of 120,000 US dollars. However, in closer LiFePO4 batterie systems under the same ambient temperature condition, only a single cell failed and didn’t propagate. In addition, its BMS can automatically limit the charging current during the high-temperature regime (>50°C) to 0.3C, which is more conservative than the 0.5C limit of NMC batteries, avoiding the risk of lithium evolution at the electrode.
Cost-benefit analysis shows the entire life cycle cost of LiFePO4 batterie to be more favorable in hot conditions. Consider an example of a 10kWh energy storage system. LiFePO4 costs around $6,000 upfront, 15% greater than that of NMC. But its replacement cycle in high-temperature applications is 10 years (NMC is 6 years), and its average yearly cost is only $600, 28% less than NMC’s $833. If the air conditioning cooling energy consumption is considered (the cooling power needed for LiFePO4 is 40% smaller than that of NMC), the operation and maintenance cost over 10 years can be lowered another 1,200 US dollars. According to Bloomberg New Energy Finance estimates, in which the average annual temperature is over 30°C, LiFePO4 batterie’s return on investment (IRR) is 5.8 percentage points higher than that of NMC.
Real-world application examples also verify its superiority. LiFePO4 batterie has been applied in 2022 at the frequency-regulated energy storage station of the Queensland electricity network in Australia. When the summer maximum temperature was as high as 48°C, the system operated 15 cycles of charge and discharge per day with a system efficiency of 95%, while the annual system failure rate of 0.07% coexisted, whereas the same period saw a failure rate in the NMC system of as much as 0.35%. Furthermore, as its weight energy density (160Wh/kg) is only 27% lower than NMC (220Wh/kg), due to structural optimization (for instance, CTP grouping technology), the energy density difference between the system can be lowered to just 15% in account both high-temperature performance and spatial efficiency. The Global Energy Storage Alliance predicts that by 2025, the proportion of LiFePO4 batterie in the high-temperature region will increase from 32% in 2020 to 55%, and it will be an essential technical method to counter climate warming.