The key to LiFePO4 (lithium iron phosphate) batteries’ over 4,000 times cycle life lies in the stability of their olivine crystal structure. During the charging and discharging process, the volume change rate of this structure is merely 2-3% (6-8% for ternary materials), which reduces the stress fluctuation range of the electrode by 67%. According to the “2023 White Paper on Power Battery Technology”, CATL’s third-generation LiFePO4 battery employs nano-scale carbon coating technology (coating thickness ≤50nm), which increases the rate of lithium-ion diffusion to 1.2×10⁻⁸ cm²/s, an increase of 40% from the traditional process. Meanwhile, under 1C charging and discharging conditions (25℃ environment), The 0-100% deep cycle test shows that the rate of capacity retention is as high as 95.6% after 2000 cycles and still as high as 82.3% after 4000 cycles (the industry standard is ≥80%). The actual operating data of the lifepo4 battery pack (3MWh capacity) used in Tesla’s Megapack energy storage system at the Hornsdale power plant in Australia show that with an average of 1.2 full cycles per day, the rate of capacity fading after 4 years is as low as 0.0085%/cycle, much lower than the 0.02%/cycle of NMC batteries.
As far as material innovation, BYD’s Blade Battery has ensured the electrode sheets’ expansion pressure remains in between 15MPa through lamination process (25-30 mpa through winding process) and by applying the lithium bis (fluorosulfonyl) imide (LiFSI) electrolyte additive (with concentration of 1.2mol/L), the interface impedance is reduced from 38Ω·cm² to 12Ω·cm². Low-temperature (-20℃) efficiency of discharge has been enhanced to 91% (compared to 78% for the standard formula). A third-party laboratory also performed an accelerated aging test on CATL’s LiFePO4 cells (280Ah capacity) and concluded that at a high-temperature condition of 45 ° C when cycled at 1.5C rate, the rate of electrolyte decomposition was as low as 0.003mL/Ah·cycle, which is equal to a total gas yield of less than 5mL after 4000 cycles. Much lower than 15mL for NCA batteries. UL 1973 test results suggest that the high-temperature triggering temperature of LiFePO4 batteries of high quality can reach up to 486℃ (210-250℃ for ternary batteries), and the heat diffusion failure probability can be below 0.17ppm (0.17 parts per million).
In the manufacturing process, Ewatt Lithium Energy uses laser welding technology to reduce the range of fluctuation of TAB contact resistance to ±0.05mΩ (±0.2mΩ for manual welding), and with a formation equipment having a precision of 0.3%, the voltage difference of individual cells in the battery pack is below 10mV (industry average: 30mV). The operation data of an electric bus of a certain type show that the vehicle equipped with LiFePO4 batteries (with a capacity of 350kWh in its battery pack) has only a capacity decrease of 18.7% after the cumulative mileage reaches 600,000 kilometers within an 8-year operation period (at an average rate of 1.8 charges per day), which corresponds to a capacity loss of 0.031% for every 10,000 kilometers, which is 58% lower than lithium manganate batteries under the same condition. From a cost-effectiveness point of view, the life-cycle cost of electricity (LCOE) of LiFePO4 batteries is 0.08/kWh (using 4,000 cycles as a reference), 33% lower than NMC battery’s 0.12/kWh. Moreover, following secondary applications, they can provide more than 2,000 energy storage cycles (capacity retention rate ≥70%).
Optimization of the intelligent management system (BMS) is crucial as well. Huawei Digital Energy’s intelligent string-based BMS reduces the temperature gradient of the battery pack within ±1.5℃ (±5℃ in the traditional plan), and along with a 0.5mV precision voltage sampling chip, lowers the SOC calculation error from ±3% to ±0.8%. In Qinghai photovoltaic energy storage, a certain 2MW/8MWh LiFePO4 energy storage system controlled capacity dispersion between individual cells from the initial 2.1% to 4.3% after 4,000 cycles (≤8% as per national standard) through a dynamic balancing strategy (balancing current 5A). Patent data shows that CATL’s self-healing SEI film technology can reduce active lithium loss in each cycle from 0.0005g/Ah to 0.0001g/Ah, and the lithium inventory retention rate is still 96.4% at 4,000 cycles. It is one of the significant achievements of achieving ultra-long cycles.