How to improve the efficiency of power battery grouping

With the increasing demand for new energy vehicles, the system energy density of power batteries and energy consumption, the weight reduction of power batteries has become a topic of great concern. To achieve lightweight power batteries, it is extremely urgent to improve the efficiency of the power battery.

Power battery: How to improve group efficiency?

Battery group efficiency comparison

For irregular battery compartments, cylindrical batteries make the most of space, and are more advantageous than squares and soft packs. By reducing the cell spacing and the weight of the module, the efficiency of the mold group can be greatly improved.

The individual energy density of the soft-packed battery has higher lifting space than the cylinder and the square, but the module design requirements are high, and the safety is not easy to control.

The square type battery core is more suitable for the regular box body. The larger the volume of the battery core is beneficial to increase the energy density of the battery core. The space efficiency of the subsequent mold group is limited, which depends on the energy density of the single cell.

It is understood that at present, the efficiency of the modular group of the cylindrical core in the industry is about 87%, the system group efficiency is about 65%; the soft pack core mold group efficiency is about 85%, and the system group efficiency is about 60%. The square cell has a mode group efficiency of about 89% and a system group efficiency of about 70%.

According to the current system grouping efficiency calculation, in order to achieve the energy density of 260Wh/kg of the new lithium-ion battery system proposed in the 2020 Promotion of Automotive Power Battery Industry Action Plan, the cylindrical unit cell needs to reach 400Wh. /kg, the energy density of the single cell of the soft pack should reach 433Wh/kg, and the energy density of the square cell should reach 371Wh/kg. Obviously, it is difficult to achieve the energy density of the single cell in 2020. Therefore, it is necessary and urgent to further improve the group efficiency of the power battery.

At the "Innovative Future of the New Energy Industry Summit and the 2018 New Situation of Power Battery Development Direction Seminar", Ruiwen Xie, Assistant President of Huasheng (Hefei) Power Technology Co., Ltd., said that improving the efficiency of power battery grouping can be obtained from the module. Optimization and lightweight design start with two aspects.

Module optimization design

Module optimization can start from many aspects. For the cylinder, the industry has newly developed 21,700 batteries. Compared with 18650, after the diameter of the battery becomes larger, the battery holder plate and the collector hole become larger, the corresponding weight is reduced, the number of cells in the battery system is reduced, and welding is performed. The number of accessories has also been reduced accordingly.

Improving space utilization is also an important way to optimize modules. Power battery PACK companies can improve the module space and heat management system design, reduce the cell spacing, thereby improving the utilization of the space inside the battery box.

There is also a solution that uses new materials. For example, the bus bar in the power battery system (the bus in the parallel circuit usually made of copper) is replaced by copper into aluminum, and the module fixing parts are replaced by high-strength steel and aluminum by sheet metal materials, which can also reduce the weight of the power battery. .

Lightweight design of the housing

Compared with other components of new energy vehicles, the power battery housing is particularly demanding in terms of anti-collision, waterproof, fireproof and dustproof. In addition to securing and accommodating the battery, the power battery case also effectively isolates the operator, the passenger and the battery from contact, so the power battery case has a high degree of protection. Therefore, the weight reduction of the power battery case has certain difficulty, and it is necessary to ensure the safety of the power battery and the passenger, and to ensure the weight reduction.

According to estimates, if the power battery sheet metal shell is replaced by an all-aluminum shell, the weight can be reduced by about 30%. In addition, carbon fiber materials are also considered to be more promising shell materials. The carbon fiber material has low density, light weight, tensile strength of 3400MPa or more, corrosion resistance and high temperature resistance, and also has great advantages in absorbing impact force, and is a superior material for realizing light weight of automobiles. However, due to technical difficulties and other reasons, the price of carbon fiber battery boxes is higher than that of ordinary materials, and it will take time to popularize. With the continuous maturity of carbon fiber production technology and the rapid development of new energy vehicles, the demand for carbon fiber battery boxes will further increase.

From the current point of view, there are not many ways to improve the energy density of the power battery system, and nothing is done from the aspects of improving the energy density of the unit and the optimization of the module and the weight reduction of the casing. In short, in the case of a certain amount of power battery charge, try to improve its group efficiency.

The page contains the contents of the machine translation.