Car power battery is still inseparable from lithium iron phosphate
On September 26-27, China Electric Vehicles 100 People held the latest industry training in Shanghai Jiading Automobile City. The theme of this issue is “Technology Breakthrough and Innovation of Electric Vehiclesâ€, Researcher and Doctoral Supervisor of Institute of Physics, Chinese Academy of Sciences Huang Xuejie, professor and doctoral supervisor of the School of Chemistry and Molecular Sciences of Wuhan University, Ai Xinping, as a representative of industry experts, gave a detailed and in-depth explanation of the power battery and key components, core technologies, and next-generation battery technology routes.
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Zhou Peng, general manager of Huasheng (Hefei) Power Technology Co., Ltd., Zhang Zhouyun, deputy general manager of Shanghai Electric Drive Co., Ltd., chairman of Jingjin Electric Technology Co., Ltd., chief engineer Yu Ping, engineering department of Shanghai Jiexin Power Battery System Co., Ltd. Zhu Yulong, deputy chief engineer, Wang Ying, new energy vehicle power system expert, and Song Zhihuan, senior manager of motor design of Huayu Automotive Electric Systems Co., Ltd. shared their practical experience in the development trend of electric drive and cutting-edge technology.
As the core component of electric vehicles, power battery affects the speed and driving range of the whole vehicle. Therefore, the research on battery technology has never stopped. Due to the influence of different materials on the performance of the battery, which material is the most suitable power battery for the vehicle is the focus of the industry, and it is also a difficult point for tackling the problem.
Is lithium iron phosphate obsolete?
Huang Xuejie, an expert in the electric vehicle steering group of the “12th Five-Year Plan†National 863 Program, is mainly engaged in research on lithium secondary batteries and related materials, processes and equipment technologies. He pointed out that there are mainly two technical routes for the development of power batteries in China. For commercial vehicles and passenger cars, commercial vehicles mainly choose lithium iron phosphate batteries, which are expected to exceed 160 Wh/kg this year. Because passenger cars have higher requirements for comparative energy, ternary material batteries are more favored. The specific energy of the battery cell can reach 220 Wh/kg, and the battery pack system can reach 150 Wh/kg.
Researcher and doctoral supervisor Huang Xuejie, Institute of Physics, Chinese Academy of Sciences
However, such specific energy does not meet people's requirements for longer driving range, so people are constantly trying different materials. Huang Xuejie introduced that in addition to the application of lithium cobalt oxide on mobile phones, other lithium manganate, lithium iron phosphate, ternary materials, high nickel and lithium rich have certain advantages to varying degrees.
Among them, NCA ternary materials are favored by some of them because of their high specific energy and long storage life. SAFT of France used the battery of this material on satellites. Now, Tesla is also equipped with NCA battery. On the other hand, the cycle life of NCA is low, and more importantly, its safety performance is poor. Although the specific energy of the monomer is high, the specific energy after the group is greatly reduced. In order to ensure a longer driving range, a certain amount of monomers will be required, and there will be certain hidden dangers in terms of safety.
Huang Xuejie made a detailed comparison of the batteries of the above materials. Although the performance of lithium cobaltate is good, but the cost is high, it is only used in mobile phones; the cost of lithium manganate is relatively low, and currently there is more demand in the field of commercial vehicles. However, its specific energy is lower, so low-speed cars and two-wheelers are more suitable. From a comprehensive comparison, Huang Xuejie believes that lithium iron phosphate has a long cycle life, strong safety and stability, and the cost is gradually decreasing, so it is still the current mainstream choice.
For this point of view, Ai Xinping holds the same attitude. He has participated in the preparation of the "New Energy Vehicle Steering" guide of the Ministry of Science and Technology. He firmly opposes the practice of blindly increasing the weight of the battery in order to increase the driving range. Because this method will cause the overall weight of the vehicle to rise, the energy consumption will also increase. Making electric vehicles anti-environmental, and this practice has led to a significant increase in costs, which is not conducive to market promotion.
Therefore, Ai Xinping emphasized that the overall development direction of power batteries must significantly increase the specific energy under the criteria of safety, long life and cycle life. Comprehensive comparison of various materials batteries, he also believes that lithium-ion batteries are still the focus of power battery development.
How to increase the specific energy of lithium iron phosphate?
Huang Xuejie proposed that the focus of research and development of lithium iron phosphate is not the improvement of the material itself, but the design of the battery and the supporting anode material. In his view, after years of development, lithium iron phosphate has formed an annual production capacity of more than 100,000 tons, and the technology of materials is very mature. Then the next thing to focus on is to give lithium iron phosphate what kind of negative electrode material to better play its excellent performance.
Huang Xuejie takes two materials as an example. One can be quickly charged at low temperatures, and the other can have higher specific energy. Graphene materials can be quickly charged at low temperatures, silicon-carbon materials with higher specific energy, and must be nano-scale silicon.
In this regard, Ai Xinping said that in order to improve the specific energy of lithium iron phosphate, it is necessary to solve the problem of low cycle coulombic efficiency of silicon negative electrode and voltage decay of lithium-rich manganese-based, and it is expected to develop advanced lithium with a specific energy exceeding 400 Wh/kg. Ion power batteries; from a long-term perspective, innovative lithium-ion batteries are more realistic than lithium-sulfur and lithium-ion. He proposed to develop a high-capacity lithium-rich oxide anode (≥350mAh/g) based on an anion charge compensation mechanism to develop a power battery with a specific energy greater than 500Wh/kg.
Professor Ai Xinping, Professor and Doctoral Supervisor, School of Chemistry and Molecular Sciences, Wuhan University
Ai Xinping emphasized that safety determines the prospect of high-energy battery loading applications. Developing self-heating control technology and all-solid-state batteries is a viable solution, so it is necessary to step up the research. The high-capacity electrode is the basis for realizing the high specific energy of the battery. According to the polarization model, the development of the gradient porosity electrode has an important role and significance for the development of high-energy batteries.
The advantage of lithium iron phosphate is increasingly apparent
According to Huang Xuejie, the specific energy of the new generation of lithium iron phosphate battery cells can reach 175Wh/kg, which can meet the requirements of 150Wh/kg for commercial vehicles. In his view, continue to develop along the above route, by 2020, the goal of achieving a 180Wh/kg lithium iron phosphate battery pack is achievable, and there is still more room for development. Huang Xuejie also pointed out that lithium iron phosphate not only has a strong industrial base in China, but more importantly, it also has application space in commercial and energy storage.
In addition, Ai Xinping mentioned that solid-state batteries are an inevitable trend in the future, while solid-state batteries have high requirements for anti-oxidation capability and low-temperature conductivity. However, the popular ternary materials and lithium cobalt oxide cannot be realized. Only lithium iron phosphate batteries can be satisfied.
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