Discuss the optimization technology of power lithium battery system of Tesla pure electric vehicle

There are no absolutely safe batteries in the world, only risks that are not fully identified and prevented. Make full use of the people-oriented product safety development concept. Although the preventive measures are insufficient, the safety risks can be controlled.

Take the model accident on Seattle Expressway in 2013 as an example. There is a relatively independent space between the battery modules in the battery pack, which is isolated by the fireproof structure. When the car at the bottom of the battery protection cover is punctured by a hard object (the impact force reaches 25 t and the thickness of the disassembled bottom panel is about 6.35 mm, the hole diameter is 76.2 mm), which causes the battery module to lose control of heat and fire. At the same time, its three-level management system can activate the safety mechanism in time to warn the driver to leave the vehicle as soon as possible, so that the driver will not be injured finally. Details of the safety design for Tesla EVs are not clear. Therefore, we have consulted the relevant patents of Tesla Electric Vehicle Electric Energy Storage System, combined with the existing technical information, and made a preliminary understanding. I hope others are wrong. We hope that we can learn from their mistakes and prevent duplication of mistakes. At the same time, we can give full play to the spirit of copycat and achieve absorption and innovation.

Tesla Roadster battery pack

This sports car is Tesla's first pure electric sports car in mass production in 2008, with a global production limit of 2500 cars. The battery pack carried by this model is located in the trunk behind the seat (as shown in Figure 1). The weight of the entire battery pack is about 450kg, the volume is about 300L, the available energy is 53kWh, and the total voltage is 366V.

The Tesla Roadster series battery pack consists of 11 modules (as shown in Figure 2) Inside module, 69 individual cells are connected in parallel to form a brick (or "cell brick"), followed by nine bricks connected in series to form a battery pack with 6831 individual cells in one module. The module is a replaceable unit. If one of the batteries is broken, it must be replaced.

Replaceable modules containing batteries; At the same time, the independent module can separate the single battery according to the module. At present, its single cell is an important choice for Sanyo 18650 production in Japan.

In the words of Chen Liquan, academician of the Chinese Academy of Sciences, the argument about the single cell capacity selection of electric vehicle energy storage system is the argument about the development path of electric vehicles. At present, due to the limitation of battery management technology and other factors, electric vehicle energy storage systems in China mostly use large capacity square batteries. However, similar to Tesla, there are few electric vehicle energy storage systems assembled by small capacity single batteries, including Hangzhou Technology. Professor Li Gechen of Harbin University of Technology proposed a new term "intrinsic safety", which was recognized by some experts in the battery industry. Two conditions are met: one is the battery with the lowest capacity, and the energy limit is not enough to cause serious consequences. If it burns or explodes when used or stored alone; Second, in the battery module, if a battery with the lowest capacity burns or explodes, it will not cause other cell chains to burn or explode. Considering the current safety level of lithium batteries, Hangzhou Science and Technology also uses small capacity cylindrical lithium batteries to assemble battery packs in modular parallel and series connection (please refer to CN101369649). The battery connection device and assembly diagram are shown in Figure 3.

There is also a protrusion on the head of the battery pack (area P8 in Figure 5 corresponds to the protrusion on the right side of Figure 4). Install two battery modules for stacking and discharging. There are 5920 single batteries in the battery pack.

he 8 areas in the battery pack (including the projections) are completely isolated from each other. First of all, the isolation plate increases the overall structural strength of the battery pack, making the entire battery pack structure more solid. Second, when the battery in one area catches fire, it can effectively block and prevent the battery in other areas from catching fire. The gasket can be filled with materials with high melting point and low thermal conductivity (such as glass fiber) or water.

The battery module (as shown in Figure 6) is divided into seven areas (m1-M7 areas in Figure 6) by the s-shaped isolation plate. The s-type isolation plate provides a cooling channel for the battery module and is connected to the thermal management system of the battery pack.

Compared with the Roadster battery pack, although the appearance of the model battery pack has changed significantly, the structural design of independent partitions to prevent the spread of thermal runaway continues.

Unlike the Roadster battery pack, a single battery lies flat in the car, and the single batteries of the Model battery pack are arranged vertically. As the single battery is subjected to extrusion force during collision, the axial force is more likely to generate thermal stress along the core winding than the radial force. As the internal short circuit is out of control, theoretically, the sports car battery pack is more likely to generate thermal stress out of control during side collision than in other directions, and the model battery pack is more likely to generate thermal runaway during the bottom extrusion collision.

Three level battery management system

Unlike most manufacturers pursuing more advanced battery technology, Tesla, with its three-level battery management system, chose the more mature 18650 lithium battery instead of the larger square battery. The hierarchical management design can manage thousands of batteries at the same time. The framework of the battery management system is shown in Figure 7. Take Tesla oadster three-level battery management system as an example:

1) At the module level, set the Battery Monitor board (BMB) to monitor the voltage of the single battery in each brick of the module (as the minimum management unit), the temperature of each brick and the output voltage of the entire module.


2) The BatterySystemMonitor (BSM) is set at the battery pack level to monitor the operation status of the battery pack, including current, voltage, temperature, humidity, orientation, smoke, etc.

3) At the vehicle level, a VSM is set to monitor the BSM.