01 – lithium iron phosphate shows a rising trend

Lithium battery has the advantages of small size, light weight, fast charging and durability. It can be seen from mobile phone battery and automobile battery. Among them, lithium iron phosphate battery and ternary material battery are two major branches of lithium battery at present.

For the safety requirements, in the field of passenger cars and special purpose vehicles, the lithium iron phosphate power battery with lower cost, relatively more mature and safe product technology has been used at a higher rate. The ternary lithium battery with higher specific energy is widely used in the field of passenger cars. In a new batch of announcements, the proportion of lithium iron phosphate batteries in the field of passenger vehicles has increased from less than 20% before to about 30%.

Lithium iron phosphate (LiFePO4) is one of the commonly used cathode materials for lithium-ion batteries. It has good thermal stability, less moisture absorption and excellent charge discharge cycle performance under fully charged state. It is the focus of research, production and development in the field of power and energy storage lithium-ion batteries. However, due to the limitation of its own structure, the lithium-ion battery with lithium iron phosphate as the positive material has poor conductivity, slow diffusion rate of lithium ion, and poor discharge performance at low temperature. This results in the low mileage of the early vehicles equipped with lithium iron phosphate battery, especially in the low temperature condition.

In order to seek the breakthrough of endurance mileage, especially after the subsidy policy of new energy vehicles put forward higher requirements for vehicle endurance mileage, energy density, energy consumption and other aspects, although lithium iron phosphate battery occupies the market earlier, the ternary lithium battery with higher energy density has gradually become the mainstream of new energy passenger vehicle market. It can be seen from the latest announcement that although the proportion of lithium iron phosphate battery in the field of passenger vehicles has rebounded, the proportion of lithium ternary battery is still about 70%.

 02 – safety is the biggest advantage

Nickel cobalt aluminum or nickel cobalt manganese are generally used as anode materials for ternary lithium batteries, but the high activity of the materials not only brings high energy density, but also brings high security risks. Incomplete statistics show that in 2019, the number of self ignition accidents of new energy vehicles was mentioned 14 times more than that in 2018, and brands such as Tesla, Weilai, BAIC and Weima have successively erupted self ignition accidents.

It can be seen from the accident that the fire mainly occurs in the charging process, or just after the charging, because the battery will rise in temperature during long-term operation. When the temperature of ternary lithium battery is over 200 ° C, the positive material is easy to decompose, and the oxidation reaction leads to rapid thermal runaway and violent combustion. The olivine structure of lithium iron phosphate brings about high temperature stability, and its runaway temperature reaches 800 ° C, and less gas production, so it is relatively safer. This is also why, based on safety considerations, new energy buses generally use lithium iron phosphate batteries, while new energy buses using ternary lithium batteries are temporarily unable to enter the catalogue of new energy vehicles for promotion and application.

Recently, two electric vehicles of Changan Auchan have adopted lithium iron phosphate battery, which is different from the general vehicle enterprises that focus on cars. The two models of Changan Auchan are SUV and MPV. Xiong zewei, deputy general manager of Chang’an Auchan Research Institute, told the reporter: “this marks that Auchan has officially entered the era of electric power after two years of efforts.”

As for why lithium iron phosphate battery is used, Xiong said that the safety of new energy vehicles has always been one of the “pain points” of users, and also the most concerned by enterprises. In consideration of this, the lithium iron phosphate battery pack carried by the new car has completed the limit test of over 1300 ° C flame baking, – 20 ° C low temperature standing, 3.5% salt solution standing, 11 kn external pressure impact, etc., and achieved the “four not afraid” battery safety solution of “not afraid of heat, not afraid of cold, not afraid of water, not afraid of impact”.

According to reports, Changan Auchan x7ev is equipped with a permanent magnet synchronous motor with a maximum power of 150KW, with a endurance mileage of more than 405 km and a super long life battery with 3000 times of cyclic charging. At normal temperature, it only takes half an hour to supplement the endurance mileage of more than 300 km. “In fact, due to the existence of braking energy recovery system, the vehicle’s endurance can reach about 420 km under urban working conditions.” Xiong added.

According to the new energy vehicle industry development plan (2021-2035) (Draft for comments) issued by the Ministry of industry and information technology, new energy vehicle sales will account for about 25% by 2025. It can be seen that the proportion of new energy vehicles will continue to increase in the future. In this context, including Chang’an Automobile, traditional independent brand vehicle enterprises are accelerating the layout of new energy vehicle market.