NiMH No. 7 battery

Chemical Engineering and Equipment Research on NiMH No. 7 battery Formation Process

Lithium-ion batteries are green, high-energy and environmentally friendly batteries that appeared in the 1990s. They have outstanding advantages such as high energy density, environmental friendliness, no memory effect, long cycle life, and low self-discharge. They are ideal power sources for small and lightweight electronic devices such as cameras, mobile phones, laptops, and portable measuring instruments. They are also ideal lightweight and high-energy power sources for future electric vehicles and special equipment. Therefore, lithium-ion batteries have become a hot topic in the battery industry in recent years.

Formation is an important process in the production of lithium batteries. During formation, a passivation layer, namely the solid electrolyte interface film (SEI film), is formed on the surface of the negative electrode. The quality of the SEI film directly affects the electrochemical properties of the battery, such as cycle life, stability, self-discharge, and safety, and meets the requirements of "maintenance-free" sealing of secondary batteries. Different SEI films formed by different formation processes have different effects on battery performance. The traditional low-current pre-charging method is conducive to the formation of a stable SEI film, but long-term low-current charging will increase the impedance of the formed SEI film, thereby affecting the rate discharge performance of lithium-ion batteries. The long process time affects the production efficiency. In addition, for the lithium iron phosphate system, when the charging voltage is greater than 3.7V, the lattice structure of lithium iron phosphate may be damaged, thereby affecting the cycle performance of the battery. Therefore, it is necessary to explore an efficient lithium battery formation process. This paper examines the effects of four formation processes on battery performance and selects an efficient NiMH No. 7 battery formation process, which can improve production efficiency and improve the performance of lithium-ion batteries.

1 Experiment 1.1 Main raw materials and instruments and equipment The main raw materials and instruments and equipment used in the formation and cycle test are shown in Table 1. Table 1 Main raw materials and instruments and equipment Name Specification Origin Formation test machine Shenzhen Constant temperature box United States 40Ah power lithium ion Luoyang 1.2 Battery preparation company The production process of lithium-ion batteries is shown in the production process of lithium-ion batteries.

NiMH No. 7 battery production process. 3 Test 1.3.1 Formation Take 12 40AH batteries from the same batch after injection, divide them into four groups, and test them on the machine separately. The formation process of the four groups of batteries is shown in Table 2.

Formation process Battery label Process content 0.1C constant current charge to 4.2V4.2V constant voltage charge to current of 1000mA Let stand for 20 minutes 0.1C constant current discharge to 2.5V0.05C constant current charge to 2.7V0.3C constant current charge to 3.7V3.7V constant voltage charge to current of 1000mA Let stand for 20 minutes 0.1C constant current discharge to 2.50.1C constant current charge to battery charge Let stand for 20 minutes 0.1C constant current discharge to 2.5V Let stand for 20 minutes 0.1C constant current charge to 3.7V3.7V constant voltage charge to current of 1000mA Let stand for 20 minutes 0.1C constant current discharge to 2.5V Let stand for 20 minutes 0.1C constant current charge to battery charge Let stand for 20 minutes C constant current discharge to 2.5V cycle 1 time 1.3.2 Cycle test After formation, the battery is left to age for 7 days. In a constant temperature box, the four groups of batteries are charged and discharged with I3 current using a formation tester. The constant temperature cycle at 25°C 2 Results and discussion 2.1 Formation A-1, 2, 3, B-1, 2, 3, C-1, 2, 3, D-1, 2, 3 are formed according to the above formation process. The formation test data are shown in Table 3. Table 3 Formation time data Formation process Battery label Formation time/h Average formation time/h It can be seen from the data in Table 3 that formation process 2 takes the shortest time, which is about 10 hours shorter than formation process 1; formation process 3 takes the longest time, which is about 10 hours longer than formation process 1; formation process 4 is about 3 hours shorter than formation process 1. By comparing the above data, the improvement of production efficiency between formation processes 2 and 4 is quite significant. Further cycle tests are needed to compare the influence of the above formation processes on battery performance in depth.

2.2 Cycle test After formation, the battery was aged for 7 days, and the four groups of batteries were charged and discharged with I3 current, and cycled at 25C constant temperature for 30 weeks. The cycle curves of the four groups of batteries were fitted as shown: After 30 cycles, the average decay rate of discharge capacity of the batteries formed by process 1, process 2, process 3, and process 4 was the best. (Continued on page 40) Middle cone part Lower cone/tube part 1.5 Calculation results Evaluation degree analysis design method: Primary local film stress: 31.5; Primary plus secondary stress strength S<3.0SmN meets the above three conditions, the equipment strength meets the requirements and can operate normally.

The analysis results show that the maximum peak stress of the storage tank under the design condition is located at the transition fillet where the upper head/pipe part head and the cylinder are connected. According to the maximum peak stress under the internal and external pressure conditions at this position, the number of cycles allowed in B4732-95 is; considering the cumulative damage, the storage tank bears two kinds of + (n2/N2) +, and the cumulative use coefficient is required not to be greater than 1. The cumulative use coefficient of this storage tank is <1, so the equipment meets the fatigue strength requirements.

2 Conclusion The maximum alternating stress amplitude of the thin-walled container subjected to alternating loads occurs at the transition fillet where the head and the cylinder are connected under the action of internal and external pressures, and is on the inner surface.

Peak stress is the stress increase caused by local structural discontinuity and local thermal stress superimposed on the primary and secondary stresses, which will not cause obvious deformation, and its harm is only fatigue or brittle fracture.

Proper adjustment of the fillet radius size can improve the ability of the equipment to withstand alternating loads, thereby avoiding the occurrence of fatigue damage.

The fatigue design method of the equipment has been standardized, but it is very convenient to use the stress results obtained by the ANSYS post-processor to determine the fatigue life consumption coefficient of the solid unit or shell unit model.

The formation time of formation process 2 is about 10 hours shorter than that of formation process 1, which can greatly improve the production efficiency, and the battery capacity decays slowly, but the discharge capacity of the battery is low.

The battery formed by formation process 3 has a faster capacity decay, and the formation time is about 10 hours longer than that of formation process 1, and the production efficiency is low.

The three batteries formed by formation process 4 have a higher discharge capacity, slow capacity decay, and the formation time is about 3 hours shorter than that of formation process 1, which can improve production efficiency.

3 Conclusion Comprehensively compare the four formation processes, and investigate the effects of the four formation processes on battery performance. From the analysis of formation and cycle data, it can be seen that formation process 4 is better. This formation process can improve production efficiency, increase the discharge capacity of lithium-ion batteries, and improve the cycle performance of lithium-ion batteries. The formation process is: 0.1C constant current charging to 0.65 of the battery charge, then 0.1C constant current discharge to 2.5V, and continuous cycle twice.

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