Before changing the battery, find out the difference between the two batteries.
Battery energy density
Ternary Lithium>Lithium Iron Phosphate/LiFePo4
The most critical indicator for evaluating battery performance is battery energy density. The concept of battery energy density is the same as that of other material densities. Simply put, it is the electric energy contained in the battery per unit weight or volume.
To make an analogy, two more of the same size and weight, one with more impurities and one with high content, there is no doubt that the one with the high content is obviously more valuable.
The energy density of the battery is the same as the content of the ore. Under the same volume or weight, the higher the energy density, the more electric energy is provided, and the longer the battery life. Increasing the battery energy density is equivalent to increasing the vehicle battery life.
A lithium iron phosphate battery (LFP) is a lithium-ion battery that uses lithium iron phosphate as a positive electrode material, while a ternary lithium battery is a lithium battery that uses nickel and cobalt as the positive electrode material and uses manganese or aluminum salts to stabilize the chemical structure. There are mainly NCM (nickel cobalt manganese) and NCA (nickel cobalt aluminum).
Due to chemical characteristics, the voltage platform of lithium iron phosphate batteries is low, and the energy density of lithium iron phosphate batteries is about 140Wh/kg. The ternary lithium battery has a high voltage and an energy density of 240Wh/kg. In other words, under the same battery weight, the energy density of ternary lithium is 1.7 times the energy density of lithium iron phosphate materials.
There is no doubt that ternary lithium batteries have obvious advantages in energy density, but the energy density of ternary lithium batteries with different "formulations" will also be different (different ratios of nickel, cobalt, and manganese/aluminum).
The 21700 NCA ternary lithium battery cell used by Tesla has an energy density of up to 260Wh/kg, which is the highest among mass-produced electric vehicles. Its nickel-cobalt-aluminum ratio is 8:1.5:0.5, which is a “high nickel battery”. ".
NCM batteries can be divided into NCM111, NCM523, NCM622, NCM811 (the number represents the ratio of nickel, cobalt, and manganese) according to the content of nickel, cobalt and manganese.
According to the current requirements for battery life, the high-nickel NCM811 is the key breakthrough direction. Because as the nickel content increases, the specific capacity of the ternary cathode material gradually increases, and the energy density of the battery will also increase.
But from the table, it is obvious that the former of the two types of NCA811 and NCM811 has better performance. So should we take the NCA route or the NCM route?
In fact, it is not difficult to choose. Nickel-cobalt-aluminum batteries have high manufacturing process requirements, high costs, and the technology is in the hands of Japan and South Korea. On the other hand, it is easy to cause thermal runaway at higher temperatures.
The battery life performance of nickel-cobalt-manganese batteries is not as good as that of nickel-cobalt-aluminum batteries, but the advantage is that the manganese-containing ternary system has better thermal stability and safety. Therefore, the main domestic research and development of nickel-cobalt-manganese batteries are.
Safety
Lithium Iron Phosphate>Ternary Lithium
The thermal stability of lithium iron phosphate is currently the best among lithium batteries for vehicles. The peak value of electric heating is greater than 350°C. When the battery temperature is at a high temperature of 500-600°C, its internal chemical components begin to decompose.
The thermal stability of the ternary lithium battery is poor, and it starts to decompose at about 300°C. Therefore, the requirements for the battery management system are very high, and the over-temperature protection device and the battery management system are needed to protect the safety of the battery. Therefore, in high-temperature conditions, lithium iron phosphate is relatively safe.
Low-temperature performance
Ternary Lithium>Lithium Iron Phosphate
It is commonplace for electric vehicles to lose their cruising range in winter, and the low-temperature performance of lithium iron phosphate batteries is worse than that of ternary lithium batteries. The lower limit of the use temperature of lithium iron phosphate battery is -20℃, and the discharge performance in a low-temperature environment is poor. The capacity retention rate at 0℃ is about 60～70%, at -10℃ it is 40～55%, and at -20℃ it is 20-40%. The lower limit of low-temperature use of ternary lithium battery is -30℃, and the low-temperature discharge performance is good. Under the same low-temperature conditions as lithium iron phosphate battery, the mileage attenuation in winter is less than 15%, which is significantly higher than that of lithium iron phosphate battery.
Of course, in order to avoid significant mileage degradation, most vehicles now have corresponding thermal management to ensure the winter performance of electric vehicles.
Life
Lithium Iron Phosphate>Ternary Lithium Battery
Life is the attenuation of the battery after several times full charge and discharge. Generally, the electric vehicle battery decays to 80% of its original capacity after being fully charged, which means the battery should be replaced. Only after the number of full charges and discharge cycles of lithium iron phosphate battery is greater than 3500 times will the power decay to 80% of the original. That is to say, if it is charged and discharged once a day, it will take nearly 10 years for the lithium iron phosphate battery to show a significant attenuation phenomenon.
The ternary lithium battery has a shorter lifespan than the lithium iron phosphate battery. The decay phenomenon will begin to occur after a complete charge and discharge cycle greater than 2000 times, which is about 6 years. Of course, the battery management and vehicle electronic control system can also be slightly extended. Battery life, but it can only be delayed slightly.
Of course, the electric vehicle battery is made up of multiple single batteries in series, and its working state is similar to the barrel effect. How much water a wooden barrel can hold does not depend on the longest piece of wood but on the shortest. Of the board. The battery pack is similar, only when the battery performance is highly consistent, the life span can be close to the level of a single battery.
Cost
Ternary Lithium>Lithium Iron Phosphate
In terms of battery cost, the lithium iron phosphate battery also has a huge advantage. It has no precious metals (nickel and cobalt metal elements), so the production cost is lower.
Ternary lithium batteries use a variety of materials such as nickel, cobalt, and manganese, and the production of high nickel batteries requires a relatively strict process environment, and the current cost is relatively high.
And after several years of development, metal resources such as lithium, cobalt, etc., as key materials, have become tight, especially the price of the metal cobalt, whose prices have soared, and the quotation is above 200,000 yuan/ton. The price of one ton of electrolytic nickel is currently only over 110,000. Therefore, it is also forcing battery companies to go to the 811 route to increase the content of nickel and reduce the content of cobalt, which can also bring about a reduction in costs.
