【Times Hi-Tech Battery Column】Innovative aviation power battery safety strategy

summary

Relying on a deep understanding of battery safety, Sino-Singapore Airlines has jointly created a complete battery safety system in five aspects: rigorous manufacturing, stable materials, system matching, structural system and effective early warning.

Power battery safety is becoming the biggest "gray rhinoceros" in the process of electrification, and it is also the direction in which battery companies overcome difficulties.

As a strong player with the top three installed capacity, China Innovation Aviation (AVIC Lithium Battery) relies on a deep understanding of battery safety, and jointly creates a complete battery safety system in five aspects, such as rigorous manufacturing, stable materials, system matching, structural system and effective early warning, forming a unique safety technology advantage of "excellent manufacturing, few defects", "anti-defect, strong heat resistance", "slow heat production, less heat release", "thermal insulation, fast heat dissipation", "accurate prediction, early detection".

Guo Qixin, head of the battery research and development department of China Innovation Airlines (AVIC Lithium Battery), said that through the engineering method, the complexity is simplified, and the company has found a way to deal with the key problems in the power battery fire.

The first is the root cause of thermal safety problems in electric vehicles.

In simple terms, thermal safety issues originate from abnormal thermogenesis. An abnormal concentrated hot spot may lead to a chain reaction inside the battery, and in the absence of effective blocking measures, the chain reaction will continue to occur on the entire battery pack, which will eventually lead to a safety accident in the whole vehicle.

The occurrence of abnormal heat production is caused by battery defects, and is often the ultimate source of a series of chain reactions. This defect mainly comes from three aspects, first, the manufacturing process exists, the manufacturing defects that are not detected at the factory; second, the deterioration defects caused by reliability problems in the use process; and the third, the abuse defects caused by accidents or incorrect use.

Then how the defect causes safety problems, you need to focus on understanding the heat production or failure mechanism. Abnormal heat sources include joule heat caused by internal short circuit and external short circuit, and chemical heat caused by material decomposition and interface reaction, and under the current material system, most of the initial abnormal heat production is caused by internal short circuit, especially the short circuit mode of lithium graphite-aluminum foil embedded in the negative electrode.

The heat production rate and hazard of this short-circuit mode are much higher than other types, which is also the most important reason for the current safety problem, including foreign bodies in the shell, polar ear folding, and poor die-cutting may lead to this short-circuit mode. Therefore, many of the work of China Innovation Airlines is to carry out analysis and prevention with this focus.

The second is a multi-dimensional thermal safety solution.

To completely avoid thermal safety problems, it is necessary to carry out comprehensive defense from multiple dimensions such as starting point prevention, battery cell reinforcement, system blocking and prediction and early warning.

The first dimension is "starting point prevention", which refers to how to avoid the occurrence of initial defects, especially manufacturing defects, and thus avoid initial abnormal production hotspots.

According to the manufacturing process, China Innovation Airlines looks for the path that the defect may produce, analyzes the severity of the consequences caused by the defect from the failure mechanism, and then decomposes and determines the control point.

With thousands of control points per cell production process, China Innovation Avionics relies on industry-leading manufacturing and testing capabilities and the most rigorous management methods to ensure the quality of shipped products. Its strategy is to rely on design innovation from the source to reduce the need to control the points, and to solve and avoid problems at the starting point.

In 2020, the company launched the "DBW" full pole ear pole simply connected technology, eliminating the extreme ear die-cutting process, avoiding defects such as die-cutting residues from the design, and helping to improve the strength of the polar ear glue, which has been introduced in the laminated whole series of products, and the customer application feedback is very good.

In 2021, the company released "One-Stop Bettery" to implement the innovative design concept to the end, returning to the goal and functional essence of the battery redesign and integration. The first generation of "One-Stop Bettery" integrates ten processes in the assembly section such as lamination, shelling, welding, and coating into three processes through design optimization, completely avoiding defects such as foreign matter in the shell and battery cell pinch injury, and improving the safety performance of battery products from the starting point.

The second dimension is "cell reinforcement", which refers to how to improve the cell material and chemical system level to make the battery more thermally stable and more tolerant of defects.

First of all, in the design of cathode materials, it is well known that the thermal stability of high nickel materials is poor, and the thermal stability of medium and low nickel materials is good. However, the factors affecting the thermal properties of cathode materials are far more than the proportion of elements, including the particle design of precursors, the doping and coating design of various elements such as aluminum- titanium, tungsten, zirconium, and sintering process, which will have a great impact on the structural stability and interfacial stability of the material.

Zhongxin Aviation cathode materials are based on these fine custom designs and have excellent safety performance.

The same nickel,cobalt-manganese proportional battery, its product tolerance for micro-short circuit, the starting point of severe heat production temperature have been significantly improved, and the total out-of-control heat production has also been greatly reduced. It is based on a deep understanding of material design, to find a safe solution for high nickel materials, Zhongxin Hang firmly proposed the next generation of high energy density 9 series cathode materials, pushing the battery energy density to 350Wh/kg.

In addition to the cathode material, the combination of electrolyte and material system is also crucial for battery safety.

A reasonable system combination will increase the initial thermogenesis temperature, reduce the total exothermic heat of the reaction, and delay or even block the cascading exothermic reaction. To this end, the company has done a lot of analysis and experiments to decouple the influence relationship between positive and negative electrode materials, electrolyte solvents, and additives on thermal properties, find the key influencing factors inside, and then according to these influencing factors, forward the best system collocation design.

Through the measures of the first two dimensions, China Innovation Airlines can already reduce the probability of thermal safety problems of batteries to a very low level, but if it pursues complete zero safety accidents, it also needs a barrier, that is, the third dimension - system blocking.

The third dimension is "system blocking", the main body lies in the "combination of dredging and blocking", that is, heat insulation and heat dissipation jointly realize the heat chain reaction blockade.

Cartridge batteries, Dayu batteries, etc. are based on the concept and scheme of unblocking combination. In 2019, Zhongxin Hang clearly put forward the idea of "dayu governing water, there is looseness and blockage", and used it as a solution to the thermal runaway inhibition of high-energy density ternary batteries.

In the third quarter of 2020, it has come up with a mature plan to support the main engine factory, and the main engine factories that have cooperated deeply with China Innovation Airlines have been introduced into the entire series of new models.

After the blocking scheme is realized, Zhongxin Airlines further pursues how to be more efficient, that is, how to formulate the most reasonable blocking scheme, through the lowest energy density loss and the lowest additional cost, which requires the company to have a very deep positive quantitative design capability.

In 2021, based on the flexible application of the basic theory of heat transfer, the understanding of the mechanism of thermal runaway, the analysis of the material system level, the development of new evaluation methods at the battery level and the accumulation of a large amount of experimental data, Zhongxin Aviation has built a dedicated thermal runaway suppression simulation calculation tool, as well as a full set of simulation, design and verification methods from the material level to the battery cell level and the system level.

It is precisely because of this quantitative forward design capability that Sino-Singapore Airlines can provide the most efficient thermal suppression solution.

The fourth dimension is "prediction and early warning", through the measures of the first three dimensions, it has been possible to reduce the "thermal safety accident" to a general failure, but China Innovation Airlines hopes to find the fault earlier, and implement maintenance measures before the failure occurs to improve the user experience.

To this end, China Innovation Airlines has established its own big data platform, which has access to the operating data of more than 80,000 vehicles.

Based on the platform, it detects the corresponding data performance of different defects by conducting a large number of positive defect implantation and anomaly simulation experiments, and develops the corresponding fault algorithm based on this. Next, we will continue to correct and correct based on model training, and develop new algorithms to achieve more accurate prediction and early warning.

At the same time, China Innovation Aviation is also establishing a digital battery platform to realize the data chain from raw materials to the whole process of manufacturing to the whole process of application, and more efficiently and accurately realize the fault prevention and value expansion of the whole life cycle of the battery.