Which one is better, lithium ternary or lithium iron phosphate?

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. As the source of electric vehicle power, all the uses of electric vehicles, such as battery life, charge and discharge, are also inextricably linked with the performance of the battery.

At present, the domestic power battery is mainly divided into two factions, which are divided into lithium iron phosphate pie and ternary material pie according to the different 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.

Ternary material or lithium iron phosphate

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). 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 material 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 also have great advantages in terms of large rate charging and low temperature resistance.

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.

Battery ternary material more suitable for passenger cars

low-temperature discharge performance 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 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.

Higher energy density

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 much.

Unlike the huge 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.

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 in measuring the charging efficiency of a group of batteries during charging. Generally, the higher the percentage, the higher 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.

Guaranteed cycle life

For household vehicles, the rated cycle life of ternary materials and lithium iron phosphate power batteries far exceeds the actual user habits, so you can be completely assured of the service life.

Taking the current high-capacity 18650 battery of the BAK battery as an example, after 1000 charge and discharge cycles, 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, which is basically more than the average change cycle of Chinese consumers.

Safe materials and processes

most harmful part of the traditional internal combustion engine car 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 perfect battery management system (BMS), and each battery can get the most accurate control to prevent accidents.

Take the BAK 18650 battery product as an example. In the single cell process, Bick chooses to arrange protective additives and reactive additives 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 group mode maintains a sufficient safety distance between each battery to ensure that the accident of a single battery does not affect other batteries.

Ternary materials are the future direction

In the field of electric vehicles, Tesla in the United States has always been the benchmark for many domestic car companies. When it comes to the strength of traditional car companies to develop new energy vehicles, the launch of the BMW i3 has become a model for textbooks. Interestingly, both cars have chosen a ternary lithium battery as the power battery. In contrast to the domestic market, many automakers such as Jianghuai, BYD, and Beiqi have also begun to replace their ternary lithium batteries with their original lithium iron phosphate batteries.

Technology is good or bad, only suitable or not suitable. It is no coincidence that domestic and foreign car companies are "complex" for the choice of battery types. It is believed that in the near future, the battery market of electric vehicles will be reshuffled. The ternary lithium battery will also be characterized by its low temperature resistance, high energy density, high charging efficiency, good cycle life and enhanced safety. Stand firm in the new market.