According to Lei Feng, there is no doubt that the power battery system is the most critical part of the electrification technology of new energy vehicles. At the same time, as the door to the electric vehicle market further opens, the frequent spontaneous combustion incidents of electric vehicles in recent years have also aroused public nerves.
"How to make batteries safer" has become a difficult problem that major manufacturers are trying to answer.
On August 20, Lei Feng.com had the honor to visit the SAIC-GM Power Battery Development Center. As an important part of the Buick brand's strategic layout of "Electrification, Networking, Intelligence, and Sharing", the mystery of the battery packs of Buick Weilan 7 and Weilan 6 PHEV models and the battery pack production line has also been revealed. Revealed.
In fact, in April 2019, Buick had officially launched the Weilan 6 pure electric model, which is Buick’s first pure electric product in China. However, the battery capacity of this car at that time was 35kwh, and the NEDC cruising range was only 301km.
In the past July, Buick launched the Weilan 6 PHEV, equipped with Buick’s new eMotin intelligent electric drive system. At the same time, the pure electric SUV Weilan 7 came out, based on GM's second-generation pure electric platform, equipped with a 55.6kwh battery pack, and an NEDC cruising range of 500km.
Unlike most car companies that simply purchase batteries from battery suppliers for assembly, SAIC General Motors prefers to be deeply involved in battery cell development and develop batteries through long-term cooperation with battery suppliers.
For example, the ternary lithium batteries used in the Buick Weilan 7 and Weilan 6 PHEVs mentioned above have further optimized the formula and design based on LG Chem’s technology, thus making the battery more efficient. Higher energy density and longer life.
Weilan 7 (left) and Weilan 6 PHEV (right) are equipped with a new generation of modular high-performance ternary lithium-ion battery packs
To some extent, the temperature is abnormal It is one of the biggest causes of battery safety accidents.
In this regard, the Buick Weilan 7 and Weilan 6 PHEV power battery systems adopt General Motors’ exclusive cell-level intelligent temperature management system, and based on the respective structures, shapes, performance and other characteristics of the two vehicles. Needs are tailored.
A thermal conductive sheet is placed between every two cells of Weilan 7. The thermal conductive sheet is directly connected to the water-cooling structure at the bottom of the battery pack, which can achieve active cooling or heating according to the battery working conditions. The inlet and outlet pipes of the water-cooling structure at the bottom of the battery pack adopt a double-flow channel snake design, which is more conducive to the temperature management of the battery module. Moreover, Buick Weilan 7's battery pack also uses foam between the cells to insulate heat dissipation to reduce the expansion of the cells during later charging, thus causing safety hazards.
The Weilan 6 PHEV battery pack uses General Motors’ patented lamellar liquid cooling technology. There is a thermal conductive sheet with capillary liquid cooling pipes sandwiched between each two cells, and the thickness is only 0.2 mm. , the flow of coolant in the capillary tube can speed up the conduction of heat.
Weilan 6 PHEV battery pack cooling plate
According to reports, the temperature adaptability range of these two battery packs is -35℃~55℃.
In terms of materials, the power batteries of Weilan 7 and Weilan 6 PHEV are made of lightweight composite materials, so the battery pack is relatively compact and thin. The IP67 sealing design ensures dustproof and safe operation of the vehicle. Battery pack operates safely while wading.
The bottom of the Weilan 7 battery pack also uses a steel tray design with reinforced ribs to reduce damage to the battery pack caused by collisions. In terms of the overall body, Weilan 7 adopts a high-performance BFI integrated body structure, with a high-strength steel application ratio of up to 78%, which also protects the safety of the battery pack to a great extent.
General Motors China Forward-looking Technology Research Center-Battery Laboratory
During the full-day visit, Lei Feng.com visited two locations in one day - General Motors China Forward-looking Technology and Research Center - Battery Laboratory and SAIC-GM Power Battery System Development Center - Weilan 7 and Weilan 6 PHEV battery pack production lines.
First let’s talk about the battery laboratory. General Motors has independent battery laboratories in the United States and China, where it has set up its own battery trial production line for battery prototype development and various types of test certification. Before each battery is put on the market, General Motors conducts 3-5 years of cell verification and testing in the battery laboratory.
According to staff, General Motors began investing in battery laboratories 10 years ago. Today, Weilan 7 and Weilan 6 PHEV batteries can pass more than 10 types of extreme tests here, including extrusion, collision, immersion, fire, overcharge, over-discharge, short circuit, and salt spray. In addition, the battery pack will undergo more than 100 system and vehicle tests covering various aspects such as mechanical, thermodynamics, electrical, life, and performance.
SAIC-GM Power Battery System Development Center was established in Jinqiao, Pudong, Shanghai in 2015. It is GM’s second battery assembly center in the world and the first outside North America.
SAIC-GM Power Battery System Development Center
It is here that the new generation of modular high-performance ternary lithium-ion battery packs equipped with Buick Weilan 7 and Weilan 6 PHEVs are located here Complete assembly production.
During the battery stacking and battery module assembly process, the entire process operations of battery cell and module loading, assembly, transportation and battery module testing are all completed intelligently by robots or manipulators, with a high automation rate Reaching 100; moreover, the accuracy of each loading/unloading/handling process of the robot is within 0.1mm.
According to engineers, there are not many manual inspectors on the entire production line, and they are only responsible for correcting machine misoperations. However, these two production lines are not busy at this stage, and were even "stopped" in the afternoon when Lei Feng.com visited.
Through the application of digital technology, the key components of Weilan 7 and Weilan 6 PHEV not only realize real-time data collection, monitoring and early warning during the assembly process, but also through a complete product information traceability system, Have their own "identity cards".
For example, a QR code will be printed on the outer packaging of battery cells that have undergone all-round correct operations. Only these battery products with QR codes can be offline. Moreover, by scanning the QR code It can also accurately trace the origin of the battery core, tracing where and when the product passed through whose hands.
Another technological highlight is ultrasonic welding. Engineers explained to us that the use of ultrasonic technology to weld battery tabs has no welding defects and will not cause high-temperature pollution or damage to materials such as aluminum, copper and other semiconductors, reducing the risk of tab tearing.
Ultrasonic tab welding
Specifically, this technology uses an industrial robot to accurately position and automatically operate the ultrasonic welding joint under the guidance of a visual system to complete the positive and negative tabs of the battery core. Welding to form a passage for the battery module. In addition, different ultrasonic welding technologies can be used for different materials.
In addition to cells, the evaluation of safety testing of modules and battery packs cannot be ignored. In order to ensure that there are no leaks in the sheet-layer liquid-cooling heat transfer fins of the Buick Weilan 6 PHEV and the liquid cooling circuit system of the Weilan 7, the module assembly line will use the mass flow method to conduct leakage tests to improve test accuracy and shorten test time.
In terms of module welding quality inspection, if there are weak welds, missing welds, etc. in the equipment welding, the points will be repaired by manual repair welding. As the engineer said before:
In fact, General Motors’ investment in new energy sources goes far beyond that.
As early as 1996, General Motors launched the pure electric model EV1. This car made General Motors a true pioneer in the field of electric vehicles. However, due to the inappropriate timing and immature market environment, it was Over the next decade or so, General Motors basically "gave up" on electric vehicles.
Although General Motors has begun to increase its investment in the research and development of pure electric vehicles in recent years, the NEDC cruising range of the Buick Weilan 6 released last year is only 301km. Four months later, General Motors has once again launched a new model of the Weilan 6 pure electric version, with a cruising range that has also been increased to 410km. Today, when electric vehicles have become mainstream, many new car-making forces have exceeded 600 kilometers of cruising range. Weilan 6 There is no competitiveness in this aspect.
However, General Motors has recently announced the launch of the Ultium battery system and the third-generation global electric vehicle platform. Buick Weilan 7 and Weilan 6 HEVP are also equipped with a new generation of modular ternary lithium battery packs—— General Motors has also taken a good step.