Comparison of the advantages and disadvantages of three types of power batteries

Since the first rechargeable battery was invented in 1859, batteries have been developed for a century and a half. With the improvement of human science and technology and the advancement of manufacturing level, batteries have gradually grown in technological changes and their performance has been continuously improved. Unfortunately, facing the urgent demand for power batteries in electric vehicles today, it seems that no battery is fully suitable for use as the main energy source in cars.

At present, there are three types of power batteries that are commonly used in electric vehicles and have great development potential: lead-acid batteries, nickel-metal hydride batteries and lithium batteries. To talk about their respective comprehensive performance, we have to mention two concepts, one is specific energy and the other is specific power. To put it simply, they refer to the durability and power of the battery respectively. A power battery with high specific energy is like the tortoise in the tortoise and the hare race, with good endurance, can work for a long time, continuously release more energy, and have a long driving range; a power battery with high specific power is like Bolt in the 100-meter race, with fast speed, great power, and strong explosive power, which can ensure good acceleration performance of the car. Obviously, only power batteries with high specific energy, high specific power, low price and easy maintenance are the first choice for the main energy source of electric vehicles.

Lead-acid batteries

It is the most widely used battery in electric vehicles. According to incomplete statistics, 90% of the electric vehicles that have been produced use lead-acid batteries. This is mainly due to its many advantages: long history of development, relatively mature technology, high specific power, cycle life of about 800 to 1,000 times, and low cost. However, the specific energy of lead-acid batteries is very low, only about 40W·h/kg, and the fast charging technology is not yet mature (generally slow charging takes more than 8 hours), and it is seriously polluting.

NiMH battery

Its advantages are high specific energy and specific power (relatively speaking), good fast charging performance, 40% to 80% of capacity can be fully charged in 15 minutes, and wide operating temperature range. However, the cycle life of nickel-metal hydride batteries is short, at 600 times, and the price is expensive, at about $600 to $800 for 1000W·h. Only with mass production can the price be reduced to $250.

Lithium-ion battery

Its specific energy and specific power are both very high, reaching 150W·h/kg and 1600W/kg respectively, and its cycle life is long, about 1200 times, and its charging time is short, 2~4h, and its operating voltage can reach 4V, and its safety is relatively good. However, lithium-ion batteries are relatively expensive, have poor fast charging and discharging performance, and have overcharge and discharge protection problems, which have affected the further application and development of lithium batteries.

Conclusion

From the above data, we can know that the use of each battery has problems of one kind or another, and relevant experts also said that in general, the current power battery has a low specific energy. Take the lithium battery with the best performance among the three batteries as an example. In terms of energy density, it is still far behind the gasoline that reaches 10,000~12,000W·h/kg. Let's calculate. 1L of gasoline weighs about 0.742kg. Calculated based on 50L on board, it is a full load of 37.1kg of gasoline, which is approximately equivalent to the amount of electricity contained in 2,968~3,091kg of lithium batteries. If the lower efficiency of gasoline engines is taken into account, there is also a gap of about 50 times between the two. No wonder hundreds of kilograms of batteries are installed on electric vehicles at any time. With such a large amount of battery usage, coupled with the high price of lithium batteries, it is inevitable that electric vehicles will form a high price threshold.

In addition, different electric vehicles have different requirements for batteries. Pure electric vehicles (PEV) require higher specific energy because they are only powered by batteries, while in general hybrid electric vehicles (HEV), batteries often play the role of braking energy recovery and assisting starting acceleration, so the specific power of the battery is demanding. The batteries in plug-in hybrid electric vehicles (PHEV) such as Toyota Prius are of the type that take both energy and power into consideration but have low requirements. It seems that it is indeed difficult to design suitable power batteries for different models according to their needs.