Probability decomposition of lithium battery energy storage safety

As we all know, lithium battery is a good thing, but there are many factors that affect the normal operation of lithium battery, such as working temperature, environmental humidity, uneven heat dissipation, overcharge and overdischarge, BMS failure, vibration, system grouping, processing technology, etc. It may cause battery failure. The failure here does not necessarily have to explode and catch fire, but refers to the battery performance is no longer suitable for operation in the system, and must be replaced or removed, otherwise it will affect the system operation. So many factors are mixed together, like a mess, people feel that if the lithium battery system wants to run without failure, the difficulty is not a little bit, but it lacks data support. There is a saying in the Book of Changes: Dadao is easy to be simplified. So I went straight to the topic, taking the tip of the iceberg, and discussing the safety of lithium batteries from the company’s processing technology. My basis is: this influence is unprepared! No matter how good the processing technology is, no matter how accurate the test is, there will be fish that slip through the net. , Mixed into the product, bring risks to the system operation. It is assumed that the pass rate of each batch is a certain value, and the influence of series and parallel groups is not considered. I choose the following typical products, based on the probability calculation results, to discuss the impact of product qualification rate on the system failure rate: (1) mobile phone battery; (2) electric vehicle battery pack: Tesla battery pack, 7104 battery pack string ( 3) Large-scale energy storage series, 250kw×2h, 500kw×2h. 1 Mobile phone battery First of all, monolithic battery, due to the small capacity of monolithic battery (about 1000mAh) and mature technology, the qualification rate of domestic and foreign manufacturers is in the top 3 in the table, that is, the failure rate can be controlled at one hundred thousandths. Within. For example, Nanjing has a population of 8 million and a cell phone per capita. In Nanjing, the number of cell phone battery failures is about 100, which may actually be more. However, the calculation results seem to be consistent with daily life, that is, a single lithium battery is very safe. Sex. 2 The technical routes of different electric vehicles are different. The main points are the following aspects: (1) There are differences in battery types, ternary and iron-lithium; (2) There are differences in capacity and size, and small batteries of about 3AH are useful. For example, Tesla has a large battery of 26AH, such as BYD; (3) The shape is also different, there are cylindrical 18650 or 20700, which has a large heat dissipation area, which is convenient for thermal management, and there are also square battery packs for easy modularization and fixed installation. . I use Tesla Model S85 as an example to decompose. Tesla model S85 uses Panasonic ternary small-capacity batteries, a total of 7104 cells, the advantage is good consistency, high factory pass rate, up to 0.999999 (refer to the number 1 and 2 in the table). In this way, the pass rate of the S85 vehicle battery reaches 99.3%. As a consumer, I am satisfied with this result; assuming that Tesla purchases a battery with a pass rate of 0.9999, his vehicle pass rate will plummet to 50. %! It can be seen that the battery qualification rate is crucial to the entire vehicle! 3 Large-scale energy storage technology methods for large-scale energy storage are also different. Japanese and Korean companies mainly focus on ternary batteries, which have high energy density and good consistency, but they are more dangerous. The price is high, and the degree of reliance on BMS is higher. The ternary energy storage battery cell can achieve 100AH, which is very big. Lithium iron battery has low energy density, but it is safer, and the price is low and the capacity can be 120-200AH. There is no big problem. Large-scale energy storage will definitely not use small batteries such as 18650, whether it is ternary or iron lithium, according to my search, Samsung conventionally uses a single 68AH ternary, and BYD, Lishen or AVIC lithium battery is generally 120-180AH. Lithium iron. The larger the lithium battery capacity, the worse the safety performance. It is assumed that the 68AH ternary battery and the 150AH iron-lithium battery have a factory pass rate of 0.9999-0.99999 (refer to numbers 3 and 4 in the table). Although the qualification rate of energy storage battery cells of Samsung, LG and other Japanese and Korean companies cannot be found, based on the current industrialization level, it is considered an excellent level to single out one unqualified (0.99999) out of 100,000. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. 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