New energy vehicle knowledge
Because the country vigorously promotes sustainable development strategies, many automobile manufacturers have launched new energy vehicles one after another. But do you know what is happening with the batteries of new energy vehicles? Lead-acid batteries are currently widely used batteries. Their main advantages are stable voltage and low price; their disadvantages are low specific energy (that is, the amount of electricity stored per kilogram of battery), short service life, and frequent daily maintenance. Old-fashioned batteries generally have a lifespan of about 2 years, and the electrolyte level needs to be checked regularly and distilled water added. However, with the development of technology, the lifespan of lead-acid batteries has become longer and maintenance has become easier. The same goes for lead-acid batteries, which are bulky due to their low energy density. In addition, because its component is sulfuric acid electrolyte, the environmental pollution after disposal is relatively serious.
The biggest disadvantage is that its driving endurance is relatively low, so its application in pure electric vehicles cannot meet people's daily needs. From the current point of view, lead-acid batteries are mostly used in low-speed electric vehicles, especially scooters and electric bicycles for the elderly. Lithium iron phosphate battery is a type of lithium-ion battery. Its characteristic is that it does not contain precious metal elements such as cobalt. The raw materials used are phosphorus and iron. These elements are not only abundant in resources, but also relatively cheap. The safety of lithium iron phosphate battery is second to none among lithium batteries. It only decomposes at 700℃~800℃, but it will not be as violent as the chemical reaction of ternary lithium material, nor will it release oxygen molecules. It has good Security. Because of this, it has become one of the main categories of electric vehicle batteries.
In addition, high charging and discharging efficiency and no pollution to the environment are also its advantages. However, it also has its own shortcomings. Due to the low energy density of the battery, its volume is relatively large; the battery capacity is small, so its driving endurance is also relatively low; after it is scrapped, its recyclable value is very low; Moreover, due to its poor low-temperature performance, research shows that if a battery with a capacity of 3500mAh is operated in an environment of -10°C, after less than 100 charge and discharge cycles, the power will sharply decrease to 500mAh, and it will basically be scrapped. The energy density of the ternary lithium battery used in Tesla MODEL S is greater than that of the lithium iron phosphate battery, which means that the ternary lithium battery of the same weight has a longer driving range than the lithium iron phosphate battery.
However, when the temperature of the ternary lithium battery itself is 250-350°C, its internal chemical components begin to decompose, which puts higher requirements on the battery management system, and the cost of the battery is also relatively high. . To put it simply, ternary lithium materials are more likely to catch fire than lithium iron phosphate materials. However, as consumers have increasingly higher requirements for driving range, they have attracted more and more attention from car companies in recent years. They take certain technical and design measures to avoid their flaws as much as possible.
Japanese manufacturers choose lithium manganate batteries because their overall performance is relatively balanced, and they are not as technically radical as ternary lithium batteries.
Since it does not require the precious metal cobalt, the cost is much lower, and there are no patent restrictions. This sounds like a continuation of Japan’s economical strategy for electrification. Lithium manganate is a cathode material with low cost, safety and good low-temperature performance. However, the material itself is not very stable and easily decomposes to produce gas. Therefore, it is often mixed with other materials to reduce the cost of the battery core, but its cycle life is It decays quickly, is prone to bulging, has poor high-temperature performance, and has a relatively short life. It is mainly used for large and medium-sized batteries. In terms of power batteries, its nominal voltage is 3.7V. Although its energy density is not as good as ternary lithium battery, its other comprehensive performance is quite excellent.
The high cost and safety of lithium batteries are the main reasons why Toyota mainly uses nickel-metal hydride batteries in its vehicles.
Nickel-metal hydride batteries have been gradually developed since the 1990s. Many hybrid vehicles, such as the Toyota Prius, use such batteries as energy storage components. Its main advantage is that it can adapt to large current discharge, and is more suitable for occasions that require larger power output requirements. Its energy density is larger, which increases the cruising range. The electricity released by the nickel-metal hydride battery is relatively stable and the heat generation is small. Its main disadvantage is that it has a "memory effect", that is, the battery capacity will decay during the cycle of charging and discharging, and overcharging or discharging may aggravate the battery's capacity loss.
Therefore, for manufacturers, the nickel-metal hydride battery control system will actively avoid excessive charging and discharging in setting, such as artificially controlling the charging and discharging interval of the battery within a certain percentage of the total capacity to reduce the capacity fading rate.