The power battery of electric vehicles is actually a general term, including three levels battery cells, modules and battery packs.Cell is the basic unit of a lithium-ion battery that can be charged and discharged. It includes positive and negative electrodes, separators and electrolytes. It is the space where the redox reaction of the battery takes place. According to different packaging forms of battery cells, they can be divided into cylindrical batteries, square batteries and soft-packed batteries. Currently, the vast majority of electric vehicles use cylindrical batteries. There are two ways to increase the power of a battery pack, using high-capacity cells and using more cells. Generally, the higher the battery capacity, the higher the cost. Therefore, optimizing the structure of the power battery pack and using as many cells as possible have become important factors to consider in the power battery design process.
In order to protect the battery cells from external heat, vibration and other impacts, the module connects a certain number of battery cells together and places them in a frame to form the components of the battery. Module optimization design can start from many aspects. For cylinders, the industry has newly developed 21700 battery cells. Compared with 18650, when the battery core diameter becomes larger, the power battery bracket plate and current collector holes become larger, and the corresponding weight Reduced, the number of cells in the power battery pack is reduced, and the number of welding accessories is also reduced accordingly.
The battery pack is the final form of the battery installed in an electric vehicle. Based on the module, it is assembled with a battery management system (BMS), a battery thermal management system, a battery structural system composed of components such as wiring harnesses, brackets, and casings.
Power Battery Management System
The power battery management system can be divided into a master control module and a slave control module in terms of hardware. It mainly consists of a data acquisition unit (acquisition module), a central processing unit (main control module), a display unit, and a balancing unit detection module (current sensor, voltage sensor , temperature sensor, leakage detection), control components (fuse device, relay), etc. The central processing unit is composed of a high-voltage control loop, a main control board, etc., and the data acquisition unit is composed of a temperature acquisition module, a voltage acquisition module, etc. Generally, CAN fieldbus technology is used to realize mutual information communication.
Battery Thermal Management System
The battery thermal management system is the battery cooling system, which is equivalent to installing an "air conditioner" on the power battery PACK, because the process of charging and discharging the power battery is actually a chemical reaction process. The chemical reaction will release a large amount of heat, and the heat needs to be taken away. Keep the power battery within a reasonable operating temperature range to improve the life and reliability of the power battery
Battery Structural System
The battery structure system mainly consists of the power battery PACK upper cover, tray, various metal brackets, end plates and bolts. It can be regarded as the "skeleton" of the power battery PACK, providing support, resistance to mechanical impact, mechanical vibration, and waterproof and dustproof role. When a power battery pack is installed in a car, it must first consider and meet the mechanical characteristics. The product needs to have sufficient strength and stiffness, and will not deform or function abnormally under mechanical loads such as vibration and impact. There is adequate safety protection in case of accidents such as collision, squeezing, rolling and falling,ect.
In short, the relationship between the three is that multiple cells form a module, multiple modules form a battery pack, and then the battery pack is assembled into an electric vehicle.
