The safety of the lithium iron phosphate batteries, analysis of the influence of the discharge energy density and temperature

Source: 2020 - 04 - 12 21:37 hits: time to study the safety, energy density and temperature of the lithium iron phosphate battery discharge affects the safety of the lithium iron phosphate battery lithium iron phosphate material chemistry performance is very stable, especially the high temperature stability is very good, even at very high temperatures and not break out of oxygen, so the safety of the lithium iron phosphate battery is very good, not easy combustion explosion danger, etc. By reasonable structural design, to further improve the security and make a battery in the case of collision, needle, short circuit, etc will not burn or explosion. Can be seen from the figure 4, 20 ah lithium iron phosphate batteries, 8 mm diameter steel nail fast penetrate cells, at the same time record the change of the battery voltage and temperature. As can be seen from the figure 4, at the beginning of the steel nails piercing, due to internal short circuit, the battery voltage drops rapidly, certain heat make a battery temperature. But due to battery vacuum degree decreased obviously after the breakdown, cause a short-circuit contact part deformation, lead to poor contact. At this point, no more heat to be released, so the voltage stabilizing, battery temperature only slightly higher. Lithium iron phosphate battery energy density weight energy density is an important index to measure the battery performance. Figure 5 to 20 ah lithium iron phosphate batteries after a full charge from 0. 3 to 2 c. 0 v discharge conditions. Discharge curve can be integral energy release of the battery. After integral calculation, 20 - Ah energy release of the lithium iron phosphate battery for 70. 7 wh, battery weight is 580 g. Therefore, the weight of the lithium iron phosphate batteries and energy density can be calculated for 121. 9 wh /公斤。 Lithium iron phosphate battery discharge under different temperature due to the use of electric cars, large regional differences, the northern winter cold weather, cold the weather is bound to have influence on battery performance. Therefore, in order to understand the lithium iron phosphate battery discharge performance at low temperature, 20 ah lithium iron phosphate power battery storage in - 20℃、- 10 ℃ and 0 ℃, 25 ℃ and 55 ℃ 20 h respectively in the test, and then discharge rate is 0. Low temperature environment (3 degrees Celsius 0 - 3 c discharge capacity of 100%) at room temperature , as shown in figure 6. As can be seen from the figure 6, under the temperature of 20 ℃, ferromagnetic lithium battery at room temperature can only be released to about 55% of its capacity, which might be harmful to are using electric cars. But the fact is obvious individual cells discharge capacity decline and, more importantly, the temperature of the electric car, usually in the form of hundreds of batteries, battery when will release a certain amount of heat, the temperature of the battery will surely rise at this time, so the actual application of the battery pack, low temperature discharge problem is very serious. In the process of test, from a single cell exposure under the larger specific surface area, the whole test process in the same temperature and the environment, so the discharge capacity affected by a lot. At higher temperatures, the lithium iron phosphate battery less affected. Battery discharge capacity at the time of 55 ℃, for example, only a slight increase in the 25 ℃. Through the above studies show that the lithium iron phosphate battery long cycle life, high safety sui and energy density due to the lithium iron phosphate battery at the same time in the whole process does not use of lead, cadmium, mercury, hexavalent chromium toxic heavy metal elements, such as materials, battery packaging materials do not contain polybrominated biphenyls (PCBS) and polybrominated diphenyl ether ( Polychlorinated biphenyls (PCBS)) , lithium iron phosphate batteries are also more environmentally friendly. Therefore, lithium iron phosphate batteries in electric cars and large scale chemical storage areas have a wider range of application. Other results: lithium iron phosphate battery cycle performance of lithium iron phosphate battery 2. Lithium iron phosphate battery discharge performance under different rate