The technology of automotive NiMH No.7 batteries power still needs to be improved

Internationally, NiMH No.7 batteriess have entered the market introduction stage, and the power of the engine has been greatly improved. A 70MPa hydrogen cylinder can run for more than 500 kilometers.

The power generation principle of NiMH No.7 batteriess is electrochemical, so the efficiency is relatively high; the working mode is an internal combustion engine, and the fuel is stored in the tank, so the safety is higher than that of lithium-ion batteries. Compared with electric vehicles and plug-in hybrid vehicles, NiMH No.7 batteries vehicles are more suitable for high-power and long-distance transportation, so they have obvious advantages in the application of buses and heavy-duty vehicles.

At present, hydrogen NiMH No.7 batteriess have basically met the requirements for vehicle use in terms of life, reliability and applicability, and the core technology of hydrogen NiMH No.7 batteriess has been mastered in China. At present, there are about 10 hydrogen refueling stations in operation in China, and it is expected that there will be about 100 next year. The most frequently operated ones are Zhangjiakou, Yunfu and Shanghai, and the amount of hydrogen refueling is also the largest. China has mastered the core technology of NiMH No.7 batteriess, and after a large number of demonstration operations, it has accumulated rich experience and has the conditions for large-scale demonstration operations.

But the current problem is that there is still no large-scale production line for NiMH No.7 batteriess, the cost is high, and it is restricted by hydrogen refueling stations. Therefore, from the perspective of stacks and NiMH No.7 batteriess, the current priority is to reduce the amount of platinum and the cost of catalysts. If China's automotive NiMH No.7 batteriess want to be competitive internationally, the core issue is to improve the working current density and specific power of the stack.

From an international perspective, NiMH No.7 batteries vehicles have reached the volume level of four-cylinder internal combustion engines. Honda announced that it has reached the level of six-cylinder internal combustion engines, with a power density of more than 3 kilowatts per liter. The stack installed in our country is now around 2.0 kilowatts per liter, so our stack specific power is about 1/3 lower than that of foreign countries.

At present, we must first realize the mass production of key materials, electrocatalysts, proton exchange membranes, membrane electrode three-in-ones, bipolar plates, etc. as soon as possible to lay the foundation for reducing the cost of stacks and improving the consistency of stacks. Secondly, we must reduce the amount of platinum and further improve the reliability and durability of stacks and battery systems.

To reduce the cost of NiMH No.7 batteries engines, especially the cost of stacks, we must first study how to increase the specific power of single cells and reduce chemical polarization, ohmic polarization and mass transfer polarization. In order to reduce chemical polarization, we need to develop more efficient electrocatalysts. The ultra-small platinum-copper alloy catalyst developed by the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences has a performance 3 to 5 times that of the current carbon-platinum catalyst; the performance of the platinum-nickel nanowire catalyst is also more than 3 times that of the carbon-platinum catalyst. With efficient electrocatalysts, the working current density of the battery stack can be increased and chemical polarization can be reduced. At the same time, a thin reinforced composite membrane should be used to reduce ohmic polarization.

At present, the single-cell research in domestic laboratories has reached 0.7V above 1 ampere per square centimeter, and 0.6V above 2 amperes per square centimeter. We are moving towards 2.5 amperes. In the future, we will develop to 2 to 2.5 amperes per square centimeter, so that our battery stack level can reach Toyota's level or even exceed Toyota's level.

From the perspective of the battery stack, the greater the flow field resistance, the better the consistency of the battery stack, but the increase in gas supply pressure will also increase the internal consumption of the air compressor. To this end, we need to study low-internal consumption air compressors to ensure the high power density output of the battery stack. In addition, the consistency of bipolar plate preparation should be improved, especially the flatness. Whether it is a metal plate or a graphite plate, flatness determines the consistency of the stack and is a key factor.

The stack is assembled by a press, and the main components are bipolar plates, MEA, and seals. Therefore, the assembly process of the stack should be further improved and strict positioning technology should be developed.

The life of the NiMH No.7 batteries is the result of the cooperation between the stack and the system, not the efforts of the stack itself. Therefore, we must also strengthen the research and development of key components of the stack and the system.

First, improve the industrial chain of NiMH No.7 batteriess as soon as possible and establish production lines for key materials such as diffusion layer carbon paper. In addition, attention should not only be focused on membrane electrodes and bipolar plates, but also on the development of air compressors and hydrogen circulation pumps.

Second, the working current density of the stack should be increased, the volume and weight-to-power ratio of the stack should be increased, and the cost of the stack should be reduced to lay the foundation for the development of passenger cars.

Third, we should deeply research the attenuation mechanism of the stack, develop new materials that are corrosion-resistant and stable, and greatly improve the reliability and durability of the engine. Reliability and durability are jointly determined by the system and the stack. If the stack is improved, the system can be simplified. Therefore, the stack and the system should cooperate with each other to simplify the battery system through the progress of key materials.

Fourth, it is necessary to carry out theoretical and applied research on ultra-low platinum and non-platinum electrocatalysts, and further reduce the platinum content of the battery to less than 0.1 grams per kilowatt, which is the basic requirement for the commercialization of automotive NiMH No.7 batteries engines internationally.

Fifth, establish a rapid evaluation method for testing and durability of key components, stacks and battery systems, which is also what the NiMH No.7 batteries Standardization Committee is doing. Therefore, we must establish a neutral testing agency as soon as possible, which will play a significant role in promoting the progress of my country's NiMH No.7 batteries technology and catching up with the world level.

It is hoped that NiMH No.7 batteries vehicles will achieve the rising stage of the S-curve of commercialization as soon as possible, and after reaching a certain level, they can get rid of subsidies and make profits. Some people predict that in terms of key materials, as long as the platinum content is reduced, the cost of NiMH No.7 batteries vehicles will be lower than that of lithium batteries, but this requires the joint efforts of our technicians.

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