Analysis of the Configuration of CTP battery in CATL and BYD
Guide: As the exporter of new energy technologies in China, CATL and BYD have both released their own battery integration technologies on top of this trend.
Obviously, under the dual force of policy and cost competition, new energy technologies need to continuously evolve towards low cost, modularity and standardization. The decline in "technical costs" is not a bad thing at this time, including the reduction of precious metal material costs, R&D and manufacturing costs, which will greatly reduce the planning pressure of the entire vehicle. On the one hand, it will reserve more room for quality improvement and maintain the price advantage to improve the overall cost performance.
In fact, the 21700-based integrated large module used by Tesla Model 3 has shown the effect of this trend. Compared with the previous Model 3, the battery cost alone has been reduced by 35%, which has greatly helped Model 3 become a global market blockbuster.
Figure 1. Anatomical Diagram of Model 3 Large Module
As the exporters of domestic new energy technologies, CATL and BYD have both released their own battery integration technologies on top of this trend. The CATL CTP (CellToPack) technology route is based on the high nickel ternary lithium architecture. Its core is to reduce the number of modules, directly form a standardized battery pack from multiple large-capacity cells, and then flexibly stack to form a larger battery module to adapt to different energy storage needs for car models. BYD’s "blade" battery is based on its skilled lithium iron phosphate technology. The battery cell has also evolved to large capacity, but the shape of the cell is flatter and narrower (the long side can be customized and the maximum stable length of the cell can reach 2100mm), so the name "blade" is visualized. Multiple "blades" are bundled to form a battery pack module, and a few large modules are combined into a battery module.
Figure 2. Package Layout of CTP Batteries from CATL 、BYD "Blade" Batteries
The two technical states can be said to have the same goal in reducing the module structure and improving the packaging efficiency, greatly reducing the monomer connection wiring harness and related process cost, and greatly improving the group efficiency (energy density), but from the perspective of application , some differences can still be found.
From the perspective of structural durability
As a large-mass single component arranged under the vehicle, the battery module must consider the adaptability of the structural strength to the complex environment of the vehicle. The ability to withstand side collisions is the most obvious requirement, and manufacturers often improve this ability through the structure and material use of the battery pack casing. However, for long-term use of private cars, non-load-bearing bodies are generally used, without beams, and the battery structure needs to be able to withstand long-term stress changes brought about by repeated body deformation.
3. Simulation Model Diagram of Battery Pack Subjected to Torsion Force
Through structural analysis, we can see that the CTP technology of CATL takes into account the maximization of volume packaging efficiency, and the connection reliability between large modules is more susceptible to the influence of diagonal repeated shear stress. For high-voltage wiring harnesses and cooling systems, the connection challenge is relatively large, and the reliability of long-term use needs to be verified. The BYD "blade" battery actually still retains the overall configuration of the module package and the battery pack package. At the same time, it can be seen from the patent drawing that its battery pack package will be able to reserve deformation space according to the needs of the model to avoid ultra-thin and large batteries. The core is directly stressed. From the perspective of structural durability, BYD blade battery packaging is easier to make reliable products.
Figure 4. Internal Structure Diagram of CATL CTP Battery and BYD "Blade" Battery Pack
However, such an insurance structure will also bring other problems. Judging from the currently published data, BYD uses volumetric power density as a measurement index, instead of publishing the weight power density data that everyone has commonly used. It can be guessed that the specific energy of the battery of which the structural weight superimposed on iron is not very effective, resulting in no significant breakthrough in its weight power density on the standard measurement platform of the Ministry of Industry and Information Technology. According to previous information, it is estimated that the weight power density of the blade battery may reach about 180Wh/kg, which is at the current mainstream level.
From the perspective of structural matching
As a single battery and related technology supplier, CATL needs to consider more product matching. However, judging from the current patent details, the height of the large CTP module cannot be changed (and it is not thin enough), and a matching shell is required to fit and install on different models. Such a structure requires vehicle manufacturers to make corresponding adjustments in product planning. The relatively difficult problem is that there is currently no large-scale sales to support development. The risk of manufacturers making design adjustments for the matching of a single battery supplier is very high. This may also be one of the reasons why it has a loud voice, but the real plan to start production is less (currently it is known that BAIC will be sure to put into production).
Figure 5. Anatomical Diagram of the Large CTP Battery Module of CATL (the left
is the reference for the large module of commercial vehicles)
For BYD, which produces its own new energy vehicles, the "blade" battery may have taken into account the multi-specification adaptability needs of its own products from the beginning. The narrow side of the "blade" is made as small as possible, which means that the vertical height can be more easily adapted to the needs of high chassis and low chassis models. In the future, multi-purpose vehicles with ultra-thin chassis can be developed based on this, allowing users to use more space and tap the advantages of new energy vehicles. At the same time, we also see the possibility of stacking applications of this ultra-thin battery, which may be prepared for commercial and high-chassis large SUV products, which can store more energy.
From the monomer configuration characteristics
Another feature of the CATL CTP battery is the large capacity of the single cell. The single cell capacity has changed from 50Ah at the beginning to more than 200Ah now, which greatly reduces the proportion of the shell, and at the same time, the charging and discharging rate remains unchanged , a simple series structure can output or receive larger current (improve power and charging convenience). In addition, the current public information of CATL shows that CTP battery packs will still be packaged in a square shell. Considering the current stability of high nickel batteries, this package should be a better choice.
The single design of BYD's "blade" battery surprised me at first. First of all, such a large length of a single unit is not a stable mechanical structure, and its resistance to deformation when subjected to lateral force is very weak. Usually, the internal pressure caused by the operation of the battery will cause the shell to expand, and then press the surrounding battery. Therefore, we have to carefully consider the issue of clearance when forming a group. On the one hand, it is necessary to be shockproof and on the other hand to eliminate the lateral force. There is still a lack of evidence in this regard.
Figure 7. Blade Battery is Comparatively Weak to Resist Lateral Force
Another technical challenge may come from the internal winding method of the battery. It is guessed that it will use multiple electrodes + multiple independent winding units. In fact, it can be regarded as multiple small batteries forming a large battery nothing but these small batteries share one package, which poses a great challenge to the uniformity of each unit, because the battery performance will always follow the barrel principle, and the worst one determines the overall performance!
On the whole, CATL CTP batteries and BYD "blade" batteries have their own merits. CATL CTP has higher power density and higher group efficiency. It is more cost-controlling friendly for most OEMs, and it is easier to launch products with longer battery life under the premise of a certain weight; and BYD’s "blade" battery It is more valuable and imaginative in terms of structural flexibility and durability, greatly increasing the performance of iron batteries, allowing them to return to the mainstream from commercial or low-end products. This is also a considerable improvement.
From another point of view, the difference in the technical architecture of the two also shows the fact that although the two companies are both technology exporters of new energy vehicles, BYD itself has an advantage in technology accumulation as a vehicle manufacturer. The advantage may not depend on the improvement of a single indicator, but more on the understanding and rationalization of the user environment. I think it should also become the foothold of its long-term value.
Publisher: Car Research Society, from: http://www.batterycloud.com.cn/newsDetail?infoId=252