The difference between ternary batteries and lithium iron phosphate batteries from 5 perspectives

Although there has been news about solid-state batteries recently, there are still quite a few difficulties that need to be solved, and there is still a long way to go before they can be commercially mass-produced and applied to new energy vehicles.

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, and more and more new energy passenger cars have switched 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

Blade batteries are lithium iron phosphate batteries. Blade batteries have proven that they can pass the harsh needle puncture test, while ternary batteries cannot. Therefore, lithium iron phosphate batteries are safer batteries than ternary batteries.

In addition, the thermal stability of the lithium iron phosphate positive electrode material itself is much better than that of ternary lithium. It has extremely high stability within 500 degrees Celsius, and thermal runaway only occurs when the temperature exceeds 800 degrees Celsius. In addition, even if thermal runaway occurs, the heat release of the lithium iron phosphate battery is very slow, and no oxygen is released during decomposition, reducing the risk of fire.

In comparison, ternary lithium batteries begin to dissolve at around 300 degrees Celsius. In the spontaneous combustion incidents of new energy vehicles, ternary lithium battery models do account for a larger proportion.

2. Energy density

According to public information from domestic companies, it is common for high-end ternary battery cells to have an energy density of 250Wh/kg or more, while the current energy density of domestic lithium iron phosphate battery cells is around 180Wh/kg.

From this point of view, ternary batteries have better energy density than lithium iron phosphate batteries.

Although the blade battery developed by BYD has improved the recombination efficiency of battery cells and increased the volume energy density by up to 50%, this is a structural change, and the single cell energy density of lithium iron phosphate batteries has not increased.

3. Low temperature discharge

In comparison, at minus 20 degrees Celsius, ternary lithium batteries have obvious advantages over lithium iron phosphate batteries.

The details are shown in the following figure:

Image source: Electronic Forum

4. Charging efficiency

At present, the more common charging method on the market is constant current and constant voltage charging. Generally, when charging starts, constant current charging is used first. 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. This allows the battery to be charged more fully.

In this process, the ratio of constant current charging capacity to the total amount of battery 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 in the constant current stage, which proves that the battery has a higher charging efficiency.

The ratio of the charge and discharge current to the total amount of the battery is the charge and discharge rate. From the data, we can see that when the ternary lithium battery and the lithium iron phosphate battery are charged at a rate below ten times, there is no obvious difference in the constant current ratio. When charging at a rate above ten times, the constant current ratio of the lithium iron phosphate battery decreases rapidly, and the charging efficiency also decreases rapidly. It can be seen that in terms of charging efficiency, the ternary lithium battery has a greater advantage.

5. Cycle life

If the remaining capacity is 80% of the initial capacity as the test end point, the current laboratory test shows that the cycle life of lithium iron phosphate batteries is more than 3,500 times, and some even reach 5,000 times.

The tested cycle life of the ternary lithium battery is about 2,500 times. In terms of cycle life, the actual life of the lithium iron phosphate battery is much longer than that of the ternary lithium battery.

Under the same number of cycles, the remaining capacity of the lithium iron phosphate battery is only slightly higher than that of the ternary lithium battery. The ternary lithium battery has a remaining capacity of 66% after 3,900 cycles, and the lithium iron phosphate battery has a remaining capacity of 84% after 5,000 cycles. The lithium iron phosphate battery has obvious advantages.

From the above analysis, it can be seen that lithium iron phosphate has obvious 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 of the two batteries is better, because they both have their own excellent application scenarios.