Brief analysis of lithium battery technology and BMS

At present, although nickel-cobalt lithium aluminum oxide (NCA) batteries dominate electric vehicles, they may be replaced by other technologies. Because the battery management system (BMS) is usually the weak link of the electric vehicle battery. Lithium cobalt oxide, although cheap and high in specific energy, does not supply the moped for 14-18 amps. Ni-MH batteries have been put into use, but their specific energy is less than half that of lithium nickel-cobalt aluminate batteries. The energy of lithium-titanium batteries is lower than that of lithium-manganese batteries, and the energy of lithium-manganese batteries is only slightly higher than that of lithium-titanium batteries. The thermal runaway temperature of the lithium iron phosphate battery (LFP) is higher than 250°C, which is a very safe and very long-life battery. However, its low specific energy (less than half of NCA) makes it less common in small motor vehicles. Lithium Nickel Cobalt Aluminum Oxide (NCA) has the highest specific energy, 250-290wh/kg, but it has high cost and low safety. Their service life is also different, the average number of recharges is between 500 and 1,000, which is only about half of that of lithium iron batteries. Tesla has used thousands of 18650 nickel-cobalt lithium batteries and conducted more stringent tests to ensure that each battery in the battery pack has the same quality, thereby increasing the battery life and preventing complete discharge and Fully charged. Like other brands of electric vehicles, Tesla also provides an 8-year warranty to ensure that the battery capacity is maintained at 80% and limit the number of recharges. However, e-bike batteries are rarely fully tested, even if this can increase production. Lithium nickel cobalt manganate (NMC) batteries have been used by Renault and BMW in their electric vehicles. According to Samsung, its current specific energy is 130 Wh/kg (about half of NCA), but it will reach 250-300 Wh/kg by 2019-2020. NMC costs are currently 12% to 19% higher than NCA. As it becomes the mainstream battery for electric vehicles, its cost will drop, but the cost of NCA will hardly drop further. The life and safety of NMC is much higher than NCA, so it will be a strong competitor for electric bicycle batteries in the future. Oxis Energy said that lithium-sulfur batteries are cheaper, have a longer life, and have the highest specific energy. In July 2013, the company's CEO stated that it and the GP battery are ready, but there is no sign of large-scale processing. At present, the price of 300Wh/kg lithium-sulfur battery is the same as that of high-end nickel diamond aluminate battery, but the lifespan is shorter. According to industry forums, Tesla is willing to evaluate the new compound after it gets a prototype, but they haven't got any. Lithium-sulfur batteries have their own advantages, but they will take some time to mature. A good battery management system has a temperature sensor that can monitor the voltage of a single battery and detect weak batteries before packaging. This 100% test guarantees higher yields, higher battery capacity and reduced warranty commitments. A good battery management system also records mechanical shocks, deep discharge dates and information, so it can prevent false warranty claims. A good BMS can also detect the humidity of the battery pack to prevent accidents. BetterBMS Group (funded by ErineneringSpiirit, who is a high-tech electronics expert at the CALCE Electronics and Systems Research Center of the University of Maryland, and himself) proposed the BBMS specification based on the above information at the 2014 European Bike Show. A large electric bicycle system company invited the engineer wizard (BCT member) to design the BMS. In particular, they do not charge research and development costs, nor do they allow third-party processing at a 4A discharge current. The capacity difference between a good battery resistance (0.1 ohm) and a poor battery (0.4 ohm) is not obvious. The low discharge current on the warranty can turn a bad battery into a good battery. When the voltage drops, the inferior battery (0.4 ohm) will cut off the power 30% faster than the high-quality battery. A good BMS can monitor the internal resistance and actively reduce the current to delay the power failure. But the acceleration has also dropped sharply: it's time to change the battery. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: The energy density of lithium-sulfur batteries is twice that of lithium batteries