Myth: The greater the energy density of the power battery, the better? The answer is not

Guide: After the electric vehicle mileage is refreshed again and again, it means that the energy density of the battery is also increasing again and again. The breakthrough in technology is certainly good, but is the energy density of the battery as high as possible? Is there an optimal value?

Recently, BAIC New Energy launched the EU400 with a driving range of 460km. It became the electric car with a driving range of more than 400km after the BYD e6400 listed last year and the Tengshi 400 listed in February this year. According to the latest news, the Chery Arrizo 5e, which will be launched in September, will also have a driving range of more than 400km.

Behind the fact that the mileage of electric vehicles is refreshed again and again, it means that the energy density of the battery is also increasing again and again. The breakthrough in technology is certainly good, but is the energy density of the battery as high as possible? Is there an optimal value?

Although the mileage of electric vehicles has exceeded 400km, people are still eager to have higher mileage vehicles. "The driving mileage is of course as long as possible. I drive an electric car and normally only drive in the city, but if I have a longer range, I can safely drive to the suburbs. In the reporter's interview process, a consumer spoke his heartfelt wishes. This also means that the energy density of existing batteries cannot meet the needs of consumers. The national policy also requires that the mass energy density of the pure electric passenger car power battery system is not less than 90Wh/kg, and the subsidy is 1.1 times higher than 120Wh/kg. It is foreseeable that how to increase the energy density of the battery will still be the main direction in the future.

Among the many types of lithium batteries, ternary materials have significant advantages due to their high cost performance and potential for development. Compared with other types of lithium batteries, ternary lithium batteries have obvious advantages.

First, the policy requires that the power cell's specific energy exceeds 300watt-hours/kg by 2020, the system's specific energy strives to reach 260watt-hours/kg, and the cost falls below 1 Yuan/watt-hour. The technical route has potential;

The second is policy incentives and subsidy guidance. The points system uses different points for models with different power consumption and cruising range. Pure electric passenger cars vary with the cruising range; energy density becomes an important consideration for the amount of subsidies.

In the first six months of this year, the share of domestic ternary lithium-ion batteries has reached 73%, and lithium iron phosphate batteries are only 14%. This is mainly because the advantages of the ternary battery relative to lithium iron phosphate in terms of energy density and cycle life are prominent, which is also an important reason for selecting a ternary lithium battery.

"Although domestic and foreign countries use ternary lithium batteries, but in terms of technology, there is still much room for improvement in domestic battery technology." Xu Liang (a pseudonym), an engineer engaged in battery system research at a new energy automobile company, said. At present, most battery monomers in China are cuboids, and the battery stability is relatively poor. When batteries are connected in series or in parallel, copper plates need to be installed, as well as cooling and heating systems, etc., all of which need to occupy a certain space, thus limiting the capacity of the battery pack.

It is understood that the current foreign new energy vehicle manufacturers use more cylindrical ternary lithium batteries, such as 18650 ternary lithium batteries. These batteries are more stable and have a higher energy density. Under the same space conditions, the battery pack releases more battery power than domestically produced batteries. Even so, due to the limitation of battery materials, the energy density of any battery has its limit. Under the fixed volume space, if the battery material is not changed, the energy density of the battery cannot be improved.

Due to space and material constraints, future battery energy densities will not increase much. Simply increasing the number and weight of the battery cells not only increases the price of the vehicle, but also increases the weight of the vehicle and reduces the economy of the vehicle.

In the future, the energy density of the battery is not required to be infinite, as long as the normal mileage of the car is met. As far as 2015 is concerned, some experts have put forward their views on the issue of the driving range of electric vehicles. Minggao Ouyang, executive vice president of China Electric Vehicles 100, said that he does not support the development of pure electric passenger vehicles with a driving range of more than 500km. The reason is not that the technology cannot be met, but the price is not high.

At the recent lithium industry international summit forum, Minggao Ouyang proposed that with  increase of battery capacity and electric vehicle driving range, the safety challenge of electric vehicles will also be multiplied in all directions, giving complete vehicle electrical safety and battery safety. Charging safety and grid security pose significant technical challenges.

Experts say that for some time in the future, electric vehicle manufacturers will focus their research and development on car safety and smart interconnection.

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