Bristol-Myers Squibb and lithium battery technology

Currently, nickel-cobalt-aluminum hydride (NCA) batteries, although dominant in the electric vehicle sector, may be replaced by other technologies. Because battery management systems (BMS) are often the weak link in electric vehicle batteries.

Although lithium cobalt oxide is cheap and has high specific energy, it cannot provide the peak current of 14 - 18 amps required for the bicycle. Although nickel-metal hydride batteries have been used, their ratio is less than half that of nickel-cobalt-aluminum hydride 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 the lithium iron phosphate battery league is higher than 250°C, which makes it a very safe battery, and its life is very long. However, its low specific energy (less than half of the NCA) makes its use on small mopeds not common.

Nickel-cobalt-aluminum hydride (NCA) has the highest specific energy ratio with its ratio of 250 - 290 wh / kg, but its cost is high and its safety is low, its service life is also different, and the frequency of repetitive charging is generally Between 500 and 1000 times, it is only about half of the lithium-ion battery. Tesla uses thousands of 18650 nickel-cobalt lithium batteries and uses a more rigorous test (ensuring equal quality of each battery in the battery pack) to increase service life to avoid full discharge and full charge. Like other brands of electric cars, Tesla offers an 8-year warranty to keep battery capacity within 80% and unlimited charge times. However, the battery of an electric bicycle is rarely fully tested, even if it will increase production.

Lithium nickel cobalt manganese oxide (NMC) batteries have been used in Renault and BMW for their electric vehicles. According to Samsung's news, the current ratio is 130 wh / kg (about half of NCA) but will reach 250 - 300 wh / kg between 2019/2020. The cost of NMC is currently 12% to 19% higher than the NCA. %. As it gradually becomes the mainstream battery for electric vehicles, its cost will also decrease. However, the cost of NCA can hardly be reduced. NMC has a lot of life and safety higher than NCA, so it will become strong competition for electric bicycle batteries in the future. By.

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 said that it and the GP battery company have been "ready to go", but it seems that there is no sign of mass production. At present, the price of a 300 wh version of lithium-sulfur battery per kilogram is the same as that of a high-end nickel-aluminum aluminate battery, but its life is slightly insufficient. According to industry forums, Tesla is willing to evaluate new compounds after they get prototypes, but they have not yet received any products. Lithium-sulfur batteries have their advantages, but it will take time to mature.

Battery management system

A good battery management system has a temperature sensor that monitors the voltage of a single battery pack and detects a poorly performing battery before the battery pack is packaged. This 100% test guarantees higher throughput, higher battery capacity, and reduced warranty commitments. A good battery management system also records mechanical shocks, deep discharge dates, and information, so you can avoid false claims. Excellent BMS can also detect the humidity of the battery pack to avoid accidents.

The BetterBMS Group (recognized by the CALCE Electronic Products and Systems Research Center of the University of Maryland, high-tech electronics specialist ErigineeringSpiirit and I) published the BBM specification at the 2014 Eurobike show based on the above information. A large electric bicycle system company asked EngineerSpirit (BCT member) to design this BMS. In particular, they do not charge for research and development and allow third parties to produce

4 Under the discharge current, the difference in capacity between good battery resistance (0.1 ohms) and a poor battery (0.4 ohms) is not obvious. The low discharge current on the warranty makes the poor battery a good battery. After the voltage is reduced, the poor battery (0.4 ohms) is 30% faster than the good battery power-off time. A good BMS can monitor internal resistance and actively reduce current to delay power outages. But the acceleration also dropped significantly: it was time to change the battery.

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