The energy density of the ternary lithium-ion power battery has already seen the "ceiling". The energy density of the lithium battery with high nickel material and carbon silicon anode should be up to about 300Wh/kg, and the plus or minus should not exceed 20Wh. /kg.

——National“863”Planned energy-saving and new energy vehicle major project overall expert group expert Xiao Chengwei.

According to the plan of the national power battery technology roadmap, the single energy density target of lithium-ion batteries in 2020 is 350Wh/kg. From the current power battery technology, Xiao Chengwei believes that this goal may not be achieved.

And now there are still two years away from 2020, and the next generation of power batteries that can be industrialized has not surfaced.

At present, most of the power batteries carried by pure electric vehicles in my country's new energy vehicle market are ternary lithium materials and lithium iron phosphate materials. Although compared with lead-acid and nickel-metal hydride batteries, the energy density has been greatly improved, but it is still difficult to eliminate consumers' mileage anxiety.

There is no doubt that the bottleneck of power battery technology has hindered the industrialization of new energy vehicles for a long time.

So, can the density of lithium-ion batteries be increased?

Whether it is a ternary lithium battery or a lithium iron phosphate battery, it is basically composed of four key parts, namely the positive electrode, the negative electrode, the electrolyte and the membrane. Now based on these four components of lithium batteries, it is unlikely to increase the energy density and achieve industrial applications.

It often takes many years for a new technology to move from the laboratory to the application.

Miao Wenquan, deputy director of the Shanghai Motor Vehicle Inspection Center, believes that 2020 is not a distant future. No definitive solution has been seen yet, and there are only a handful of new generation power battery systems that can achieve the above goals.

Then the power battery fails to reach the goal of the technical route planning, will the development of my country's new energy vehicles be hindered?

Of course not!

Because it is not only the specific energy density that affects the performance of power batteries, but also the specific power density, safety, consistency, cycle life and other factors of power batteries. An industry can be found among many indicators and costs. The balance of chemical application is the key to supporting the development of new energy vehicles.

In addition, Japan and South Korea are currently studying gel batteries, which are a new type of battery without electrolyte and diaphragm, which may bring qualitative changes to the battery, but there is no news of industrialization.

In the view of Miao Wenquan, there are many technical ways to increase the specific energy of power batteries:

The first is technological progress, but now the battery process design is relatively mature, and there is not much room for increasing the specific energy of the battery;

The second is the improvement of material performance. Subject to its own physical and chemical properties, it is difficult for lithium-ion power batteries with lithium iron phosphate and ternary lithium as the positive electrode and carbon material as the negative electrode to have a major breakthrough in energy density;

The third is new materials and new systems, that is, the development of new materials with high specific energy and the development of new systems for power batteries are the main ways to greatly increase the specific energy of power batteries in the future.

If the energy density of the battery cannot be effectively increased, is it possible to consider increasing the energy density from the perspective of reducing the overall weight of the battery pack?

Dr. Zhang Minyu of China Battery Industry Association believes that this idea is completely feasible. She said that in the power battery battery pack, the weight of the battery cell is generally between 1/3-2/3, and the rest are accessories such as circuit boards and casings. If the weight of these accessories is effectively reduced while maintaining the energy density of the existing battery cells, the overall energy density of the battery pack will be significantly improved.

In 2010, power battery packs often use metal casings due to safety and other needs, and the overall energy density of the battery packs is very low. Later, after replacing the high polymer shell, the energy density has been greatly improved.

The energy density of the battery pack is a system problem. Increasing the energy density of the cells is a direct measure. However, if the cell layout and circuit planning are done well, the weight of the case is reduced, and the burden on the battery is reduced, which also improves the energy density of the battery. An effective means.

In practical applications, the lower box of the battery box of BAIC New Energy EV200 uses aluminum alloy material and the upper cover uses composite materials, which can effectively reduce the weight by tens of kilograms.

Wang Kefeng, deputy general manager of BAIC New Energy, said that by reducing the overall weight of the battery box, the weight of the vehicle can be reduced, which is an effective means to increase the energy density of the battery box. In addition, he said that the replacement of lighter materials will generally lead to an increase in battery costs. Now BAIC New Energy is also stepping up research in this area to strive for the application of lighter, stronger and lower-cost materials.

At present, in order to achieve the 350Wh/kg target, major battery companies not only need to develop new batteries, but also reduce the weight of battery packs. The two must be parallel.

Because the power battery is assembled on the car, it needs to be tested under various working conditions to ensure a certain structural safety. It is completely feasible to replace the steel shell with a carbon fiber shell or other material shell, as long as the strength requirements can be guaranteed.

In addition, another important indicator of the battery pack is the ability to dissipate heat and heat. If the battery pack is partially overheated, the internal resistance of the battery will be inconsistent, and the discharge capacity of the cells will decrease. In a sense, the cells that are not fully discharged will increase the weight of the battery pack.

Although the energy density of the battery pack reaches 350Wh/kg, it may not be possible to reduce the weight of the battery alone, but the power battery as a system cannot be ignored. Domestic companies are relatively lack of basic research and excessive pursuit of high specific energy batteries. This is wrong and should be developed in a balanced manner. While developing new material batteries, they should pay attention to the weight reduction of the existing battery system.