Whether the power battery should use a ternary lithium battery or a lithium iron phosphate battery

Although domestic subsidies for new energy vehicles have begun to decline, the gradual enrichment of infrastructure and the growing number of optional models have also allowed consumers to embrace the popularity of new energy vehicles. In addition to being an alternative solution to the purchase of fuel vehicles as a restricted area, new energy vehicles also have many unique advantages. Quiet driving environment, clean energy type and low cost of using the car, even the super-torque output instantaneously at the start, can let many friends who drive fuel cars envy.

The battery that is the source of electric vehicle power is naturally one of the most important parts. All the uses of electric vehicles, such as battery life, charge and discharge, are also inextricably linked to the performance of the battery. At present, the domestic power battery is mainly divided into two factions, which are divided into lithium iron phosphate and ternary materials according to the difference of the positive electrode materials. Although both of them belong to the secondary battery, they can be repeatedly used for charging and discharging, but due to the difference in materials, there is still a big difference in the performance that is finally reflected to the use level.

Is the ternary lithium battery or lithium iron phosphate battery?

To figure out which battery is better, we should first have a simple understanding of the difference between the two.

The lithium iron phosphate battery refers to a lithium ion battery using lithium iron phosphate as a positive electrode material. This type of battery is characterized by the absence of precious metal elements (such as cobalt). Since the precious metal material is not contained, the raw material cost of the lithium iron phosphate battery can be compressed very low. In actual use, the lithium iron phosphate battery has the advantages of high temperature resistance, strong safety and stability, low price and better cycle performance.

The ternary lithium battery refers to a lithium battery using lithium cobalt cobalt manganate as a positive electrode material and graphite as a negative electrode material. Unlike lithium iron phosphate, the voltage platform of the ternary lithium battery is very high, which means that the specific energy and specific power of the ternary lithium battery are larger under the same volume or weight. In addition, ternary lithium batteries have great advantages in terms of large rate charging and low temperature resistance.

The author has always believed that technology is not good or bad, and it is only applicable to different products or environments. On the single battery, there is no such thing as who is better and who is worse. Just applied to the actual use of the scene, the ternary lithium battery is more suitable for the current and future home electric vehicles than the lithium iron phosphate battery.

Why is the ternary lithium battery more suitable for household electric vehicles?

First, the low temperature discharge performance is better

China has a vast territory and a complex climate. The temperature changes from the northernmost three northeastern provinces to the southernmost Hainan islands are very rich. Taking Beijing as an example, as the main market for electric vehicles, the highest summer temperature in Beijing is around 40 °C, while in winter it is basically at around 16 °C, or even lower. Such a temperature range is obviously suitable for a ternary lithium battery having a better low temperature performance. The lithium iron phosphate battery, which focuses on high temperature resistance, appears to be somewhat weak in winter in Beijing.

The "relative 25 ° C capacity" refers to the ratio of the discharge capacity at different temperature conditions to the discharge capacity at 25 ° C. This value can accurately reflect the battery's battery life attenuation under different temperature conditions. The closer to 100%, the better is the battery performance.

It can be seen from the above figure that the two types of batteries are discharged at a high temperature of 55 ° C and discharged at a normal temperature of 25 ° C at a normal temperature of 25 ° C, and there is almost no difference in discharge capacity. However, at minus 20 ° C, the ternary lithium battery has a clear advantage compared with the lithium iron phosphate battery.

Second, the energy density is higher

According to the information provided by the domestic ternary material 18650 cylindrical battery leading company - BAK battery, the energy density of its 18650 battery has reached 232Wh / kg, and will be further increased to 293Wh / kg. In contrast, the current domestic mainstream lithium iron phosphate battery energy density is only about 150Wh / kg, according to domestic battery industry experts, in the next few years, the energy density of lithium iron phosphate battery can reach 300Wh / kg I hope very embarrassed

Unlike a large electric bus, space is always the first for home electric cars. Lithium iron phosphate batteries with lower energy density will occupy less space in the car, and due to the heavier quality, the battery life during use will also be greatly affected. Relatively speaking, the ternary lithium battery with higher energy density also saves space for the family car while solving the weight problem.

Third, the charging efficiency is higher

In addition to battery life, charging is also an important part of the actual use of electric vehicles, and ternary lithium batteries have a very large advantage over lithium iron phosphate batteries in terms of charging efficiency.

At present, the more common charging method on the market is constant current and constant voltage charging. Generally, constant current charging is used at the beginning of charging, and the current at this time is large, and the charging efficiency is relatively higher. After the voltage reaches a certain value, the current is reduced to constant voltage charging, which can make the battery charge more full. In this process, the ratio of the constant current charging capacity to the total battery capacity is called the constant current ratio. It is a key figure that measures the charging efficiency of a group of batteries during charging. Generally, the higher the percentage, the higher is the charge in the constant current phase, which proves that the battery is more efficient.

It can be seen from the table that when the ternary lithium battery and the lithium iron phosphate battery are charged below 10C, there is no significant difference in the constant current ratio. When charging at 10C or higher, the constant current ratio of the lithium iron phosphate battery is rapidly decreased, and the charging efficiency is rapidly lowered.

Fourth, the cycle life can be assured

For the family car, the rated cycle life of the ternary material and the lithium iron phosphate power battery far exceeds the actual user's usage habits, so the service life can be completely assured. Taking the current high-capacity 18650 battery of the BAK battery as an example, after 1000 cycles of charge and discharge, the battery capacity can still remain above 90%. Since the author is also the owner of an electric car, it is only the coldest in winter for more than one month. When the warm air is frequently turned on, it can reach 2 days and one charge, and the rest of the time is basically 3-4 days. Assuming an average of 3 days a year to calculate the charge, it takes about 6 times to charge for 1 year, and it takes about 8 years to complete the cycle life of 1000 times. This also basically exceeds the current average change cycle of Chinese consumers.

5. Materials and processes sufficiently safe

The most harmful part of the traditional internal combustion engine vehicle is the fuel with huge energy. The low-explosive liquid fuel like gasoline can easily cause great safety hazard once it leaks. The power battery of the new energy vehicle is monitored by a comprehensive battery management system (BMS), and each battery can get the most accurate control to prevent accidents.

Ternary lithium battery, lithium iron phosphate battery, power battery

Take the BAK 18650 battery product as an example. In the single cell process, BAK chooses to configure a protective additive and a reactive additive on the positive and negative electrodes to prevent the safety problem caused by the decomposition of the electrolyte. At the same time, safety protection measures such as ceramic diaphragm and negative ceramic coating are added to control the accident from the root cause. In addition, the BAK small cylindrical 18650 battery pack mode maintains a sufficient safety distance between each battery to ensure that a single battery accident does not affect other batteries.

The page contains the contents of the machine translation.