Differences between ternary batteries and lithium iron phosphate batteries from 5 perspectives.
Although there have been recent reports of solid-state batteries, there are still many challenges that need to be addressed. The commercialization and application of solid-state batteries in new energy vehicles still have a long way to go.
The mainstream of current power batteries are still ternary batteries and lithium iron phosphate batteries. In the past period of time, lithium iron phosphate batteries have been in the limelight, with more and more new energy passenger vehicles shifting from ternary batteries to lithium iron phosphate batteries.
This article examines the differences between ternary batteries and lithium iron phosphate batteries from five perspectives: safety, energy density, low-temperature discharge, charging efficiency, and cycle life.
1. Security
The blade battery is a lithium iron phosphate battery. Blade batteries have been proven to pass rigorous needle tests, while ternary batteries cannot. Therefore, lithium iron phosphate batteries are safer than ternary batteries.
In addition, the thermal stability of lithium iron phosphate cathode material itself is much better than that of ternary lithium. It has extremely high stability within 500 degrees Celsius, and thermal runaway only occurs above 800 degrees Celsius. In addition, even if thermal runaway occurs, the heat release of lithium iron phosphate batteries is very slow, and oxygen is not released during decomposition, reducing the risk of fire.
In contrast, ternary lithium batteries begin to dissolve at around 300 degrees Celsius, and indeed, ternary lithium battery models account for a larger proportion in the spontaneous combustion events of new energy vehicles.
2. Energy density
According to public information from various domestic enterprises, it is quite common for the energy density of high-end ternary batteries to reach or exceed 250Wh/kg, while the energy density of lithium iron phosphate batteries in China is currently around 180Wh/kg.
At this point, ternary batteries have better energy density than lithium iron phosphate batteries.
Although BYD's development of blade batteries has improved the recombination efficiency of battery cells and increased the volumetric energy density by up to 50%, this is a structural change, and the individual energy density of lithium iron phosphate batteries has not increased.
3. Low temperature discharge
Compared to lithium iron phosphate batteries, ternary lithium batteries have significant advantages at minus 20 degrees Celsius.
As shown in the following figure:
4. Charging efficiency
The most common charging method currently on the market is constant current and constant voltage charging. Generally, constant current charging is used at the beginning of charging. At this time, the current is larger and the charging efficiency is relatively higher. After the voltage reaches a certain value, the current is reduced and changed to constant voltage charging, which can make the battery fully charged.
In this process, the ratio of constant current charging capacity to total battery capacity is called constant current ratio, which is a key value to measure the charging efficiency of a group of batteries during charging. Generally, the larger the percentage, the higher the amount of electricity charged during the constant current stage, which proves that the charging efficiency of the battery is higher.
The ratio of charging and discharging current to the total amount of the battery is the charging and discharging rate. From the data, it can be seen that there is no significant difference in constant current ratio between ternary lithium batteries and lithium iron phosphate batteries when charged below ten rates. When charged above ten rates, the constant current ratio of lithium iron phosphate batteries rapidly decreases, and the charging efficiency rapidly decreases. Therefore, it can be seen that ternary lithium batteries have a greater advantage in charging efficiency.
5. Cycle life
If the remaining capacity of 80% of the initial capacity is taken as the end point of the test, currently, lithium iron phosphate batteries have been tested in the laboratory and have a cycle life of over 3500 times, with some reaching 5000 times.
The test cycle life of ternary lithium batteries is around 2500 times. In terms of cycle life, lithium iron phosphate batteries have a much longer actual life than ternary lithium batteries.
At the same number of cycles, the remaining capacity of lithium iron phosphate batteries is only significantly higher than that of ternary lithium batteries. Ternary lithium batteries have been cycled 3900 times with a remaining capacity of 66%, while lithium iron phosphate batteries have been cycled 5000 times with a remaining capacity of 84%. The advantages of lithium iron phosphate batteries are obvious.
From the above analysis, it can be seen that lithium iron phosphate has significant advantages in safety and cycle life; Ternary batteries have advantages in energy density, low-temperature discharge, and charging efficiency.
Of course, it is not to say which battery is better among the two, as they both have their own excellent application scenarios.
