In the new energy vehicle market, the most common lithium-ion batteries are lithium iron phosphate batteries and ternary lithium-ion batteries. Today, Jin Jian will review the key characteristics, advantages, and disadvantages of ternary lithium-ion batteries and lithium iron phosphate batteries.
Lithium iron phosphate batteries: long cycle life and good safety.
Lithium-ion batteries using lithium iron phosphate as the cathode material are characterized by the absence of precious elements such as cobalt, low raw material costs, and abundant phosphorus and iron resources. They feature a moderate operating voltage (3.2V), high capacity per unit weight (170mAh/g), high discharge power, fast charging capability, long cycle life, and high stability under high temperature and high heat environments.
1. Lithium iron phosphate batteries are characterized by high safety, high-rate charge-discharge characteristics, and long cycle life. Literature shows that under the following conditions: charging at 1C to 3.65V, then switching to constant voltage until the current drops to 0.02C, followed by discharging at 1C to the cutoff voltage of 2.0V, after 1600 cycles, the battery capacity still retains 80% of its initial capacity.
2. Lithium iron phosphate batteries have excellent fast charging characteristics. Under 3C charging conditions, they can be charged to 55% in 15 minutes and to more than 95% in 30 minutes.
3. In addition to its long lifespan and excellent charge and discharge performance, the biggest advantage of lithium iron phosphate batteries is their safety. Lithium iron phosphate has stable chemical properties and good high-temperature stability. It only begins to decompose at 700-800℃. Furthermore, it does not release oxygen molecules or cause violent combustion when exposed to impacts, punctures, or short circuits, thus ensuring high safety performance.
4. The disadvantage of lithium iron phosphate batteries is that their performance is greatly affected by temperature, especially in low-temperature environments, where both discharge capacity and capacity will decrease significantly. Furthermore, lithium iron phosphate has a low energy density, with a weight energy density of only 120Wh/kg.
Ternary lithium-ion batteries: high energy density and low-temperature resistance
Ternary lithium-ion batteries, also known as ternary polymer lithium-ion batteries, are lithium-ion batteries that use lithium nickel cobalt manganese oxide (LCO) as the cathode material. This type of battery uses a transition metal lithium oxide composite cathode material containing nickel, cobalt, and manganese. This material combines the advantages of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, forming a three-phase eutectic system. Due to the synergistic effect of the ternary structure, its overall performance is superior to any single compound, achieving a gravimetric energy density of 200 Wh/kg.
1. Unlike lithium iron phosphate batteries, ternary lithium-ion batteries have a very high voltage platform, which means that for the same volume or weight, ternary lithium-ion batteries have higher specific energy and specific power. In addition, ternary lithium-ion batteries have significant advantages in high-rate charging and low-temperature performance. The temperature range of northern winters is more suitable for ternary lithium-ion batteries with better low-temperature performance, while lithium iron phosphate batteries, which emphasize high-temperature performance, may be less effective in northern winters.
2. Ternary lithium-ion batteries have relatively lower safety. They have poor thermal stability, decomposing at 250-300℃. Upon contact with flammable electrolytes or carbon materials within the battery, they ignite instantly, and the resulting heat further accelerates the decomposition of the positive electrode, leading to a rapid explosion. In a car accident, external impact can damage the battery separator, causing a short circuit. The heat generated during this short circuit can cause thermal runaway, rapidly raising the temperature above 300℃, posing a risk of spontaneous combustion. Therefore, the battery management system and cooling system are crucial for ternary lithium-ion batteries.
To improve product safety, materials with strong heat resistance are used, pressure relief valves are employed to control the pressure inside the battery, the battery current is actively controlled, and the battery charging status is monitored in real time. The ability to forcibly cut off the current circuit also enhances safety. These are all feasible measures to improve the safety of ternary lithium-ion batteries.
Overall comparison: Lithium iron phosphate batteries are superior.
With advancements in battery pack structure development technology, the energy density of lithium iron phosphate (LFP) battery packs has reached the level of ternary NCM523 batteries and continues to improve. Currently, Guoxuan High-Tech has completed the upgrade of its LFP cell energy density production line to 180Wh/kg, achieving a system energy density of nearly 130Wh/kg in passenger vehicles, sufficient for a driving range of approximately 400 kilometers. Guoxuan High-Tech plans to increase the energy density of its LFP cells to nearly 200Wh/kg in 2019.
Compared to ternary lithium-ion batteries, lithium iron phosphate (LFP) batteries have significant advantages due to their lower raw material costs, higher safety, and longer lifespan. Many battery manufacturers are confident in the larger market potential of LFP batteries. Hezhong Technology stated in its earnings conference that the company will continue to expand its LFP production. BYD's lithium battery division has also publicly expressed its belief in the strong resurgence of LFP batteries in certain specific sectors. Analysts point out that once fully marketized, the advantages of LFP batteries—low cost, long lifespan, and high safety—will gradually become apparent in the passenger car, commercial vehicle, and special-purpose vehicle sectors.
