——Xiao Chengwei, expert of the expert group of the national “863” program major project of energy saving and new energy vehicles.
According to the national power battery technology roadmap plan, the target of single-cell energy density for lithium-ion batteries in 2020 is 350Wh/kg. From current power battery technology, Xiao Chengwei believes that this target may not be reached.
And now there are 2 years from 2020, the next generation of power batteries that can be industrialized has not surfaced.
At present, most of the power batteries used in pure electric vehicles in China's new energy automotive market are ternary lithium materials and lithium iron phosphate materials. Although energy density is much greater than that of lead-acid and nickel-metal hydride batteries. Improve, but it is still difficult to dispel consumer anxiety.
Undoubtedly, the bottleneck of the power battery technology has hindered the industrialization of new energy vehicles for a long period of time.
So, can lithium-ion battery density be improved?
Whether it is a ternary lithium battery or a lithium iron phosphate battery, it basically consists of four key components: the positive electrode, the negative electrode, the electrolyte, and the membrane. Now based on these four components, the lithium-ion battery will increase energy density and achieve Industrial application is unlikely.
A new technology from the laboratory to the application, often goes through many years.
Wu Wenquan, deputy director of the Shanghai Motor Vehicle Inspection Center, believes that 2020 is not a distant future. At present, it has not seen any definitive solutions. Only a handful of new-generation power battery systems that can achieve these goals are also available.
Then, if the power battery fails to reach the target of the technical route, will the development of new energy vehicles in China be blocked?
of course not!
Because not only an index of specific energy density, but also the specific power density, safety, consistency, cycle life, and other factors affecting the performance of the power battery are found among many indicators and costs. The balance point is the key to supporting the development of new energy vehicles.
In addition, Japan and South Korea are currently studying colloidal batteries, which are new types of batteries without electrolyte and separators, which may bring qualitative changes to the batteries, but there is no news of industrialization.
In Min Wenquan's view, there are many technical ways to increase the specific energy of power batteries:
First, technological progress, but now the battery process design has been relatively mature, and there is little room for increasing the specific energy of the battery;
The second is the improvement of material properties, subject to its own physical and chemical properties. Lithium iron phosphate and ternary lithium are used as positive electrodes. Lithium-ion power batteries with carbon materials as the negative electrode are difficult to achieve a large breakthrough in energy density.
The third is new materials, new systems, that is, the development of new materials with high specific energy, and the development of a new battery power system is the main way to increase the specific energy of batteries in the future.
If the energy density of the battery cannot be effectively increased, can it be considered to increase the energy density from the perspective of reducing the overall weight of the battery pack?
Dr. Zhang Wei of the China Battery Industry Association told the “Electric Association” that this idea is entirely feasible. She stated that in a battery pack for a battery pack, the weight of the battery pack is generally between 1/ 3 and 2/3, and the rest is a circuit board. Such as accessories. If the weight of these accessories is effectively reduced, while maintaining the existing cell energy density, the overall energy density of the battery pack will have a significant increase.
Around 2010, power battery packs were often made of metal because of safety requirements. The overall energy density of the battery pack was very low. Later, after replacing the high polymer casing, the energy density had a substantial increase.
The energy density of the battery pack is a system problem. It is a direct measure to increase the energy density of the battery cell. However, if the layout of the battery core is properly planned, the circuit is lightened, the weight of the shell is lightened, and the burden on the battery is reduced. This is also an effective means to increase the energy density of the battery. .
In practical applications, the "Electric Association" learned that Beiqi New Energy EV200 models use aluminum alloy materials in the lower case of the battery box, and the cover is made of composite materials, which can effectively reduce weight by several tens of kilograms.
Wang Kefeng, deputy general manager of Beiqi New Energy, stated that by reducing the overall weight of the battery box, it is possible to realize weight reduction of the entire vehicle, which is an effective means to increase the energy density of the battery box. In addition, he said that replacing lighter materials will generally lead to rising battery costs. Now BAIC New Energy is also stepping up its research in this area and trying to apply lighter, stronger and lower-cost materials.
At present, for the major battery companies to achieve the target of 350Wh/kg, not only the development of new batteries, but also the weight reduction of the battery pack must be carried out in parallel.
Because the power battery is mounted on the automobile, it needs to pass various tests to ensure a certain degree of structural safety. Replacing the steel shell with a shell made of carbon fiber or other materials is only feasible if it can ensure the strength requirements.
In addition, another important indicator of the battery pack is the heat dissipation and soaking capacity. If the battery pack is overheated locally, it will cause the internal resistance of the battery to be inconsistent, and the discharge capacity of the cell will decrease. In some sense, those batteries that have insufficient discharge are: The battery pack has gained weight.
Although the energy density of the battery pack reaches 350Wh/kg, it may not be possible to achieve battery weight reduction. However, the role of the power battery as a system cannot be ignored. Domestic companies are relatively lack of basic research and excessive pursuit of high specific energy. The core, which is wrong, should be developed in a balanced manner. While developing a new type of material battery, it should pay attention to the weight reduction of the existing battery system.