China Electric Vehicles 100 People’s Association held the first phase of industrial training (East China Class) in Anting, Shanghai. The theme of this issue is “Technology Breakthrough and Innovation of Electric Vehicles”, Huang Xuejie, Research Fellow, Institute of Physics, Chinese Academy of Sciences, Professor Ai Xinping, Huaying, Wuhan University Power General Manager Zhou Peng, Shanghai Electric Drive Deputy General Manager Zhang Zhouyun, Jingjin Electric Founder Yu Ping, SAIC Jiexin Power Battery System Co., Ltd. Deputy Chief Engineer Zhu Yulong, New Energy Vehicle Power System Expert Wang Ying, Huayu Automotive Electric Song Yuhuan and other scholars and experts and business representatives gave a detailed and in-depth explanation of the core technology and development trend of power batteries, advanced drive technology development and practical achievements.
Professor Ai Xinping, professor at the School of Chemistry and Molecular Sciences, Wuhan University, doctoral tutor. Director of Hubei Provincial Key Laboratory of Chemical Power Materials and Technology, Ministry of Science and Technology “New Energy Vehicle Special” guide expert and general expert group power battery responsibility expert. His main research areas include lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, and battery safety technologies. He has presided over more than 10 national 973 project projects, national 863 projects and National Natural Science Foundation projects, and has published more than 100 academic papers. He has won the second prize of national technology invention and two provincial and ministerial level scientific and technological achievements awards.
The following is the speech of Professor Ai Xinping:
Before analyzing the technical development route of power batteries, first discuss the impact of battery specific energy on the development of electric vehicles.
The specific energy of the battery is an important factor in determining the cruising range of the vehicle, thus determining the convenience of driving and having an important influence on the market acceptance of the electric vehicle. Of course, like Tesla, the increase in battery load can also achieve a significant increase in cruising range, but I do not agree with this approach.
Here is a simple calculation: for a battery system with an energy density of only 120 watt-hours/kg, if we design the cruising range of the car to 150 km, the total weight of the battery is only 100 kg, and the battery cost is based on the current price. More than 20,000 yuan; but if we have to design the car’s cruising range to 300 kilometers, the weight of the entire battery system will become 340 kg. For a most economical car, 800 kilometers of self-weight to more than 300 kilograms of battery, I think the battery weight is still too heavy.
Let’s look at energy consumption, because most people don’t need to use so many batteries, which is why Tesla is not accepted and fined in Singapore because it is not environmentally friendly and increases energy consumption. It also increased emissions.
In addition, too many batteries will double the cost of the entire vehicle. Assume that according to our current plan, the battery system can reach 200 watt-hours/kg in 2020 and the unit reaches 300 watt-hours/kg or more. It is a normal configuration to design the cruising range of 300 km. However, if the 200 watt-hour/kg battery pack is designed to be designed for 500 kilometers, the energy consumption will increase by about 17%, and the battery cost of the vehicle will increase.
Therefore, regardless of the energy density of the battery, blindly increasing the battery weight to increase the cruising range will lead to an increase in energy consumption, a reduction in manned space and load capacity, and a substantial increase in the cost of the entire vehicle. Conducive to the development of electric vehicles. The overall development direction of the power battery should be to greatly increase the energy density while meeting the safety and life indicators. In fact, the increase in energy density will also bring about a significant reduction in cost, because for the manufacture of the same size of the battery, the battery wattage is high, and the manufacturing cost per watt hour is reduced.
I have given a correspondence here. If the energy density of the single unit reaches 300 watt-hours/kg, the cruising range is designed to 300 km, and 400 is equivalent to 400 cruising range. If the battery unit is 500 watt-hours per day, In kilograms, we design a car with a cruising range of 500 km.
How to improve the specific energy of the battery? The recent target is high nickel ternary positive electrode, silicon carbon negative electrode to achieve 300 watt-hour / kg; medium-term (2025) target is based on lithium-rich manganese-based / high-capacity Si-C negative electrode, achieving monomer 400 watt / kg; The period is to develop lithium-sulfur and lithium-air batteries to achieve a monomer specific energy of 500 watt-hours/kg.
Is this route not feasible? From the current technical conditions, in addition to the safety is not certain, there is no technical risk in the 2020 battery than the energy of 300 watts / kg.
According to the calculation results, the 400 watt hour/kg battery requires a positive electrode capacity of 250 mAh/g and a negative electrode capacity of 800 mAh/g. This requirement also has a clear material system, such as lithium-rich manganese. With a capacity of 250, 280 or even 300 mAh/g, it is no problem to have a silicon carbon of 800. Therefore, it is generally accepted that the near-mid-term technical route is generally feasible. In the long-term goal, theoretically, lithium sulphur and lithium vacancies have no problem in achieving specific energy index. For example, the theoretical specific energy of lithium sulphur is 2,600 watt-hours/kg. Lithium air can achieve theoretical specific energy without considering air quality. 11,000 watt-hours/kg, close to gasoline. If we only achieve 20% of the theoretical energy density, we can also reach 500-600Wh/kg, which is why everyone regards lithium sulfur and lithium space as the key points for future development.
Can these two systems be not feasible? Now let’s analyze the field of automotive power battery: such as lithium space, it is a battery system using metal lithium as the negative electrode and oxygen in the air as the positive electrode. Of course, the oxygen electrode requires porous carbon as the reaction carrier. Through such many years of development, it should be said that great progress has been made in catalyst selection, mechanism research, electrolyte selection, and chargeability. However, no matter how advanced, I feel that as an application product, we must face The following questions:
First, it is an open system, which is different from lithium-ion batteries. Lithium air uses oxygen in the air, and air contains water. Lithium reacts with water. It needs to be both oxygen-permeable and waterproof. A problem that is difficult to solve. Why is the zinc empty battery not successfully developed because of this problem? In the 1990s, we did a lot of work, including opening a small company to industrialize zinc-air batteries, but in the end it died. The biggest problem encountered was the control of water. Zinc air battery uses lye as electrolyte. If the humidity in Shanghai is so high in the past few days, the lye will absorb water and the battery will “suddenly die”. If it is in a relatively dry environment in Xinjiang, the lye will lose water. The battery is “dry”. This problem has not been a good solution, and now Li Kong has encountered the same problem.
The second problem is the catalytic reduction of oxygen. The reaction rate of oxygen is very slow. To increase the reactivity of oxygen, it is necessary to use a highly efficient catalyst. The present catalysts are all precious metals. Therefore, efficient and inexpensive catalysts must be developed, which has been a shortcoming that constrains the development of fuel cells.
The third problem is the chargeability of the metallic lithium negative electrode. In fact, lithium secondary batteries appeared earlier than lithium primary batteries. In the 1960s and 1960s, lithium primary batteries were not the first, but lithium secondary batteries. Everyone knows that there is a famous battery company in the world – Canada Moli company, why is this company basically no longer exist? The main reason is that they pioneered the introduction of lithium secondary batteries in the 1980s. Due to the growth of lithium dendrites, the battery exploded, the users were injured in the market, the batteries were recalled, and the battery was not lost, so the chargeability of lithium has been Is a problem. Up to now, there has been no great progress in the world, and it is very difficult to solve this problem in a short time.
Another problem is that its discharge product is lithium oxide, which is difficult to re-catalyze the decomposition of solid lithium oxide into oxygen and lithium.
I have summarized that lithium-ion batteries have gathered the most difficult problems encountered in multiple battery systems, including zinc-air batteries, fuel cells, and lithium secondary batteries, in addition to their own unique problems. Therefore, I think that the practical use of lithium-ion batteries is very hopeful.