Discussion on the technical requirements for the preparation of 1.2V Ni-MH battery

The relative molecular mass of nitrogen is 28, the boiling point is about -1960C, and the condensation point is -210℃. The content of nitrogen (N2) in the air is about 78%. At present, the precursor lithium battery preparation technology requires that the reaction process be completed under nitrogen protection, and the source of nitrogen can be compressed nitrogen or liquid nitrogen. If the demand for nitrogen is large, large liquid nitrogen tanks or nitrogen generators can also be used. Generally, the compressed nitrogen pressure on the market is 12.5MPa and the volume is 6m3. The unit price is high and the gas volume is small, but the footprint is small and the management is convenient. It is suitable for schools, R&D institutions or factory R&D departments; bottled liquid nitrogen has many volume specifications, the most common is l20m3/bottle, the price is moderate, and the gas volume can also meet the needs of small production; the gas supply of large liquid nitrogen tanks is hundreds of times that of small bottles of liquid nitrogen, the price is cheap, but it requires initial investment and later maintenance, which is suitable for medium-sized production needs; nitrogen generators can choose different types of equipment according to the actual gas consumption. The larger the gas production volume, the lower the operating cost and nitrogen cost, which is suitable for large-scale production needs. There are two types of nitrogen generators: liquid nitrogen generators and PSA nitrogen generators. Liquid nitrogen is produced by cryogenic method, and the equipment investment and operation costs are relatively high, so this book will not discuss this. Here we will only introduce the PSA nitrogen generator. PSA stands for Pressure Swing Adsorption, which is pressure swing adsorption. The volume of various gases in the air is 78.0840%, oxygen 20.9476%, argon 0.9364%, carbon dioxide 0.0314%, and others include H2, CH4, N20, 0, SO4, N02, etc., but the content is very small. The core part of PSA is the adsorbent, and carbon molecular sieve is generally selected as the adsorbent. It adsorbs oxygen, carbon dioxide, moisture, etc. in the air, but does not adsorb nitrogen. The adsorption amount of oxygen, carbon dioxide, and moisture by carbon molecular sieve increases with the increase of pressure, and finally high-purity and low-dew point nitrogen can be obtained. The PSA nitrogen production system is generally composed of several parts such as compressed air device, compressed air purification device, pressure swing adsorption oxygen production device, and gas storage tank. The ambient air is compressed by the air compressor and then enters the buffer tank. After the gas in the buffer tank is removed of oil, water and dust by the chemical device, it enters the pressure swing adsorption device consisting of two adsorption towers filled with carbon molecular sieves. The compressed air flows through the adsorption tower from bottom to top, during which the oxygen molecules are adsorbed on the surface of the carbon molecular sieve, and the nitrogen flows out from the upper end of the adsorption tower and enters the nitrogen buffer tank to be provided to the nitrogen user department. The following is a brief introduction to the functions of each device in the PSA nitrogen production system. (1) Compressed air system The compressed air system consists of a compressor and an air buffer tank, which provides the gas source required by the pressure swing adsorption nitrogen production device. The system provides stable output pressure and sufficient gas volume. The air compressor generally uses a screw air compressor with reliable operation, simple maintenance and low noise. The air buffer tank is mainly used as a buffer for the gas source, which plays a stabilizing and storage role. In addition, it can also collect and remove most of the oil and water condensate entering the compressed air source. The buffer tank is equipped with a pressure gauge, a safety valve and a drain port. The exhaust capacity of the air compressor needs to be slightly greater than the air consumption under the rated output of the oxygen generator. Since its start and stop are controlled by the exhaust pressure, when the exhaust volume is greater than the gas consumption, the exhaust pressure rises and the air compressor stops; otherwise, the air compressor starts. Through such a cycle of start and stop, the exhaust volume of the air compressor is suitable for the gas consumption requirements of the oxygen generator and adapts to the operation needs of the production line under variable conditions (lower than the rated output). (2) Air purification system The main function of this system is dust removal and oil removal. The compressed air coming out of the buffer tank first enters the C-class filter for coarse filtration, and then enters the refrigerated dryer to force the compressed air to cool down and condense the water vapor in the air. (3) Pressure swing adsorption nitrogen production system There are two adsorption towers filled with molecular sieves in the PSA nitrogen production device. Clean and dry compressed air enters the pressure swing adsorption nitrogen production device and flows through the adsorption tower filled with molecular sieves. Compressed air flows through the adsorption tower from bottom to top. The molecular sieve has different adsorption forces for oxygen and nitrogen at different pressures. Oxygen, water and other components are adsorbed on the surface of the molecular sieve. The unadsorbed nitrogen is collected at the outlet and becomes product gas, which flows out from the upper end of the adsorption tower and enters the buffer tank. After a period of time, the oxygen adsorbed by the molecular sieve in the adsorption tower reaches saturation and needs to be regenerated. Regeneration is achieved by stopping the adsorption step and reducing the pressure of the adsorption tower. The adsorption tower that has completed adsorption begins to reduce the pressure after a short period of equalization, removes the adsorbed oxygen, water and other components, and completes the regeneration process. The two adsorption towers alternately adsorb and regenerate, thereby producing product nitrogen with stable flow and purity.

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