BMS and lithium battery technology

　　Although nickel-cobalt lithium aluminum oxide (NCA) batteries dominate the field of electric vehicles, they may also be replaced by other technologies. Because the battery management system (BMS) is usually the weak link of the electric vehicle battery.

　　At present, although nickel-cobalt lithium aluminum oxide (NCA) batteries dominate the field of electric vehicles, they may also be replaced by other technologies. Because the battery management system (BMS) is usually the weak link of the electric vehicle battery.　　 Although lithium cobalt oxide is cheap and has a high specific energy, it cannot provide the 14-18 ampere peak current required by a moped. Although nickel-metal hydride batteries have been used, their specific energy is less than half of that of nickel-cobalt lithium-aluminate batteries. Lithium-titanium batteries have lower specific energy, while lithium-manganese batteries are only slightly higher than lithium-titanium batteries. The thermal runaway temperature of 　　 lithium iron phosphate battery (LFP) is higher than 250°C, which makes it a very safe battery with a very long life. However, its low specific energy (less than half of NCA) makes its application in small mopeds not universal.　　Nickel Cobalt Lithium Aluminum Oxide (NCA) is the compound with the highest specific energy with its specific energy of 250-290Wh/kg, but its cost is high and its safety is low. The service life is also different. Generally, the number of recharges is between 500 and 1000, which is only about half of that of lithium iron batteries. Tesla uses thousands of 18650 nickel-cobalt lithium batteries and uses more stringent tests (to ensure that the quality of each battery in the battery pack is equal) to improve the service life, so as to avoid full discharge and full charge. Like other brands of electric cars, Tesla provides an 8-year warranty to ensure that the battery capacity is maintained within 80% by then and there is no limit to the number of recharges. However, the batteries of electric bicycles are rarely fully tested, even if this will increase production.　　 Nickel Cobalt Manganese (NMC) batteries have been used by Renault and BMW in their electric vehicles. According to the information provided by Samsung, its specific energy is currently 130Wh/kg (about half of NCA), but it will reach 250-300Wh/kg in 2019/2020. The cost of NMC is currently 12% to 19% higher than NCA. As it gradually becomes the mainstream battery for electric vehicles, its cost will also be reduced, but the cost of NCA can hardly be reduced. NMC's life and safety are much higher than NCA, so it will become a strong competitor for electric bicycle batteries in the future.　　Oxis Energy claims that lithium-sulfur batteries will be cheaper, have a longer life and have the highest specific energy. In July 2013, the company's CEO stated that it and GP Battery Company are "ready to go", but it seems that there is no sign of mass production. Currently, the price of the 300Wh/kg version of lithium-sulfur batteries is the same as that of high-end nickel diamond aluminum aluminate batteries, but their lifespan is slightly insufficient. According to industry forum reports, Tesla is willing to evaluate new compounds after it has obtained prototype products, but they have not yet received any products. Lithium-sulfur batteries have their advantages, but it takes time to become mature.　　Battery Management System 　　A good battery management system has a temperature sensor that can monitor the voltage of a single battery pack and detect low-performance batteries before the battery pack is packaged. This 100% test guarantees higher production, higher battery capacity and reduces warranty commitments. A good battery management system also records mechanical shocks, deep discharge dates and information, so false warranty claims can be avoided. An excellent BMS can also detect the humidity of the battery pack to avoid accidents.　　 BetterBMS Group (funded by the University of Maryland CALCE Electronic Products and Systems Research Center, high-tech electronics expert EricineeringSpiirit and myself) based on the above information published the BBMS specifications at the 2014 Eurobike exhibition. A large electric bicycle system company asked EngineerSpirit (BCT member) to design this BMS. In particular, they do not charge R&D costs and allow third-party production. Under 4A discharge current, the difference in capacity between a good battery (0.1 ohm) and a poor battery (0.4 ohm) is not obvious. The low discharge current in the warranty can make a bad battery a good battery. After the voltage is reduced, a bad battery (0.4 ohm) has a 30% power-off time faster than a good battery. A good BMS can monitor the internal resistance and actively reduce the current in order to delay the power failure. But the acceleration has also dropped significantly: it's time to change the battery.