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The safety, energy density and temperature influence of lithium iron phosphate battery on discharge

by:dcfpower     2021-03-17
The safety of lithium iron phosphate batteries The chemical properties of lithium iron phosphate materials are very stable, especially high temperature stability is very good, even at very high temperatures can not liberate oxygen, so the safety performance of lithium iron phosphate batteries is very good, not easy to happen Dangers such as burning and explosion. Coupled with a reasonable structural design, its safety has been further improved, so the battery will not burn or explode under impact, needle stick, short circuit, etc. Figure 4 shows that after a 20 Ah lithium iron phosphate battery is fully charged, the battery is quickly pierced with a steel nail with a diameter of 8 mm, and the voltage and temperature changes of the battery are recorded at the same time. It can be seen from Figure 4 that at the initial stage of the nail piercing, the battery voltage drops rapidly due to the internal short circuit, and a certain amount of heat is released, and the battery temperature rises. However, since the internal vacuum of the battery drops significantly after being pierced, the short-circuit contact part is deformed and poor contact occurs. At this time, no more heat is released, so the voltage tends to stabilize, and the battery temperature only rises slightly. Energy density of lithium iron phosphate batteries Weight energy density is an important indicator of battery performance. Figure 5 shows that a 20 Ah lithium iron phosphate battery is fully charged and discharged to 2.0 V at a rate of 0.3 c. The energy released by the battery can be obtained by integrating the discharge curve. After the integral calculation, the 20 Ah lithium iron phosphate battery released 70.7 Wh of energy, and the weight of the battery is 580 g, so the weight energy density of the lithium iron phosphate battery can be calculated to be 121.90 Wh/kg. Discharge of lithium iron phosphate batteries at different temperatures Due to the large geographical differences in the use of electric vehicles, there are cold weather conditions in the northern winter, and the lower temperature will inevitably have a certain impact on the performance of the battery. Therefore, in order to understand the low-temperature discharge performance of lithium iron phosphate batteries, a 20 Ah lithium iron phosphate power battery was stored at -20 ℃, -10 ℃, 0 ℃, 25 ℃ and 55 ℃ for 20 h in the test, and then stored there Discharge at a rate of 0.3 c in a low temperature environment (with a discharge capacity of 0-3 c at room temperature as 100%), the results are shown in Figure 6. It can be seen from Figure 6 that the lithium iron magnetic acid battery can only discharge about 55% of its capacity at room temperature at a temperature of 20°C, so it may have an adverse effect on electric vehicles during use. But in fact, it is obvious that the discharge capacity of a single battery decreases more with the decrease of temperature. For electric vehicles, hundreds of batteries are usually combined together. When the battery is working, a certain amount of heat will be released. The temperature of the battery will inevitably rise, so for the battery pack in practical applications, the problem of low-temperature discharge is not very serious. During the test, due to the large exposed specific surface area of u200bu200ba single battery, the temperature during the entire test process is basically the same as the environment, so the discharge capacity is greatly affected. At higher temperatures, lithium iron phosphate batteries are less affected. For example, the discharge capacity of the battery at 55°C is only slightly increased compared to that at 25°C. The above research shows that lithium iron phosphate batteries have long cycle life, high safety and energy density. At the same time, lithium iron phosphate batteries do not use lead, cadmium, mercury, hexavalent chromium and other toxic heavy metal elements in the entire production process. Materials, battery packaging materials do not contain polybrominated biphenyls and polybrominated diphenyl ethers, lithium iron phosphate batteries are also more environmentally friendly. Therefore, lithium iron phosphate batteries will have broader applications in the fields of electric vehicles and large-scale chemical energy storage. Other experimental results of lithium iron phosphate battery are attached: 1. Cycle performance of lithium iron phosphate battery 2. Discharge performance of lithium iron phosphate battery at different ratesu003c/pu003e
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