In recent years, China's new energy automobile industry has been moving forward under the dual favorable policies and markets, and the power battery as its core component has also received increasing market attention. As we all know, the core technology of new energy vehicles is “three powers”, namely batteries, electric controls and motors.
As one of the three core components of electric vehicles, batteries are responsible for the cruising range of electric vehicles, and lithium iron phosphate and ternary lithium batteries are the mainstream choices for power batteries in China. However, with the advancement of research and development technology, the ternary lithium battery broke out with greater potential. In the 8 batches of 296 new energy passenger cars announced by the Ministry of Industry and Information Technology in 2017, the most used are ternary lithium, a total of 221, and only 33 of the lithium iron phosphate.
Since the beginning of last year, BYD has been using the lithium iron phosphate battery to launch a variety of matching ternary lithium battery models such as Song EV300, Qin 80 and Tang 100. In October this year, BYD officially announced that it will continue to use lithium iron phosphate in the public transportation field in the future. Outside the battery, all PHEV passenger cars of the company use ternary lithium batteries; next year, E5, E6, Qin EV and other pure electric vehicles should also switch ternary lithium batteries. So, what are the advantages and disadvantages of lithium iron phosphate and ternary lithium batteries? In fact, consumers are concerned about the problem: which battery has a longer range, longer life and more safety. Let's take a look at each of these issues one by one.
Energy density (river mileage) comparison
Compared with the energy density of lithium iron phosphate battery, the ternary lithium battery has a higher energy density and a higher voltage, so the battery of the same weight has a larger capacity and the car can run farther. In addition, higher energy density can release more body space, which is a plus for home users.
At present, a large number of domestic ternary lithium battery production lines are closely related to the subsidy policy. According to the circulated new energy passenger car subsidy adjustment program, the energy density of the battery system must reach 140Wh/kg in 2018 to enjoy 1.1 times subsidy, while the low energy density (105-120Wh/kg) subsidy adjustment factor drops to 0.5, high-grade. The gap between subsidies and low-grade subsidies has further widened, and car companies will undoubtedly pursue the former.
The energy density of the lithium iron phosphate battery cell is usually between 90-120 Wh/kg, and the energy density of the ternary lithium battery cell can reach about 200 Wh/kg. As the world leader in lithium batteries for vehicles, the Ningde era plans to develop a ternary lithium battery with an energy density of 300-350Wh/kg by 2020, and the cruising range will have a qualitative leap. On the contrary, lithium iron phosphate battery has entered the bottleneck in the research and development of energy density, which also directly led to the abandonment of lithium iron phosphate batteries by some car manufacturers.
Charging efficiency comparison
Ternary lithium has a significant advantage over lithium iron phosphate in terms of charging efficiency. 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. For new energy vehicles, more efficient charging time can significantly improve the car experience. After all, it is quite helpless to wait for the car to be full.
In terms of service life, lithium iron phosphate has an advantage over ternary lithium in recycling rate, but for the average family, the rated cycle life of both is far beyond the actual use. In addition, the low temperature performance degradation of lithium iron phosphate batteries is a major drawback. Studies have shown that a battery with a capacity of 3,500 mAh, if operating in a -10 ° C environment, after less than 100 charge and discharge cycles, the power will be sharply attenuated to 500 mAh. As the main market for pure electric vehicles, Beijing's winter temperature is often around minus 16 °C, which will cause great trouble to the owner of the car.
As far as the material system is concerned, both batteries will decompose when they reach a certain temperature. The decomposition temperature of the lithium iron phosphate battery is higher than that of the ternary lithium battery, but this does not determine that the safety of the ternary lithium battery is poor. The safety design of the power battery system can also be upgraded through various aspects such as power connection structure, thermal management design, battery management system, etc. The design of the safety measures is more complete and scientific, and the battery can be operated in a safe state. For example, the ITCS battery temperature management system of Geely New Energy's electric vehicle configuration can turn on cooling at 38 degrees to ensure that the battery operates in a safe temperature range.
Through the above analysis, it is not difficult to find that although the lithium iron phosphate battery is slightly superior in high temperature resistance and cycle life, the ternary lithium battery has obvious advantages in terms of energy density, cruising range, low temperature performance and charging efficiency, and shows Greater development possibilities.