The traditional way of integrating battery packs is to form a module from the cells, then the module forms the battery pack. At present, the CTC battery can be arranged in the same space, thus increasing the power and achieving the purpose of increasing the cruising range.
This article analyses the advantages and disadvantages of each technology path by comparing the technology development plans of mainstream enterprises in the market. At the same time, the development trend of batteries integration was analyzed, and finally the batteries integration scheme of CTC battery was used to continue the analysis work.
1. Comparative analysis of the typical battery integration
The trend of CTC battery integration can be analyzed from the trend of CTC battery module changes. For the top 10 lithium battery companies in the world, they want to pack more cells in a limited space. And through modularization and scale to achieve cost reduction, there is an evolution process from small modules, medium modules, large modules to ultra-long modules.
It can be seen that the evolution process is a trend from small modules to large modules or even no modules. Therefore, consider increasing the maximum space utilization of vehicle and batteries integration to further achieve the purpose of increasing power.
① Traditional battery solutions
The traditional battery pack consists of cells composed of modules, which are then assembled from the lower part and the body floor. The height of the battery cover is the same as the floor surface, which can replace part of the floor structure.
The advantages are: The lifepo4 batteries pack consists of multiple modules, each with a separate housing protection and control. The batteries module can be replaced separately, and maintenance costs and convenience are high.
The disadvantages are: Due to the housing and safety clearance between the modules, the overall weight is higher and the space utilization is low. Each module is configured with a separate control unit, resulting in a relatively high cost.
② CTP battery solutions
The integration scheme eliminates the module structure, and the battery pack is directly composed of battery cells, and also it is integrated into the body floor as part of the entire vehicle structural parts.
There are many advantages: Reduced spacing between modules and increased number of cells. The module structure is reduced, which reduces the weight of the overall battery pack.
There are many disadvantages: The battery pack will carry the load as part of the structural part. Higher requirements are put forward for the structural design of the batteries.
③ CTC battery scheme
The CTC battery solution is to integrate the cells directly inside the floor frame, and the upper and lower floor plates are used as CTC battery housings. It is a further step in the CTP scheme, using entirely the upper and lower floors instead of the CTC battery housing and cover.
It is not only integrated with the body floor and chassis, but also fundamentally changes the installation form of the CTC battery. Previously, the CTC battery cell played only one role, that is, the unit of energy storage and release, and now the CTC battery cell will add a function as part of the structural parts of the entire vehicle.
The merits lie in: Greatly improve space utilization, which can increase battery life by 15%–25%. The structural parts of the CTC battery pack have been eliminated, and the weight has been reduced. It can achieve a high degree of integration and modularity.
The demerits lie in: The cell needs to consider how to secure the cell to the upper and lower structural parts to cope with the most demanding shear forces. Higher requirements for the process, if the manufacturer is not qualified, will lead to the scrapping of the entire batteries and low maintainability.
● Comparison of the different schemes
From the comparison of the above table, it can be seen that the CTC battery scheme has the highest space utilization rate, which has a significant effect on the improvement of battery power.
At the same time, it is necessary to consider how to achieve sealing and CTC battery loading. However, CTC battery is also the most effective solution to increase power, provided that the existing CTC battery technology itself remains unchanged.
2. Introduction of CTC battery technology
In order to achieve higher power, the integration trend of batteries has developed from small modules to large modules, ultra-long modules, and even no module solutions, which has improved space utilization and increased power to a certain extent.
But in order to pursue more demanding needs, it is proposed to make the battery itself a part of the body, that is, Cell to Chassis abbreviated as CTC, also known as the body integration concept.
● Key point analysis of CTC battery
Taking the load-bearing body as an example, the CTC battery integration solution needs to focus on solving the installation scheme of the batteries and body.
For example, the waterproof sealing scheme of the batteries, the packaging scheme of the cell, the batteries cooling scheme, and how to solve the problem of the load bearing of the cell as a structural part. Finally, consider the battery's serviceability. This paper mainly analyses the feasibility of the following aspects.
3. Integration of CTC battery and car
● The main problems with batteries and bodies are:
- It is necessary to ensure the sealing performance and safety of the battery itself.
- It is necessary to ensure the sealing performance of the member compartment after the battery is integrated with the body.
- Sealed batteries seriously increase the risk of battery cell short circuit fire caused by water ingress, and serious safety hazards.
All parts and components of the body interface must be tested for 100% airtightness: inspection lines and rework lines need to be developed in the final assembly shop, resulting in a significant reduction in production cycle times, increased costs, and man-hours.
If there is a problem, it is difficult to check the air leakage point, it cannot be repaired in a short time, and there is a risk of line stoppage. Failure to return the vehicle will result in the entire body being scrapped.
● CTC battery structural strength explanation
Because the batteries cell in the CTC battery carries the load as a structural part. From the perspective of Tesla 4680 battery vs CATL CTP battery, glue is still the most suitable connection means between the cell and the box. Tesla will use a multi-functional glue that takes structural glue and fire-resistant flame retardant glue into account to fix the batteries cell with the upper and lower structural parts.
The adhesive is hard enough to handle the harshest shear forces when cured. The structured batteries has a high probability of continuing to boil the design, so that the entire batteries cell is glued to the box to form a structure with very high strength and rigidity.
4. CTC battery cooling analysis
At present, most electric vehicles are cooled by liquid cooling, and the coolant takes the heat of individual batteries modules through the lines between the cells. The CTC battery scheme directly forms the batteries pack because the batteries cells are directly formed, and the space in the pack is almost completely occupied.
The space left for the cooling system setup is very limited, so the batteries cooling system setup is somewhat difficult. In addition to the use of condensation plates, when a mechanical failure occurs in a certain area of the batteries, the circuit can be automatically broken.
This avoids the failure of one cell, which causes damage to other cells. In order to form effective protection for the entire batteries pack and reduce the safety hazards of the batteries.
The cooling plate is a combination of an aluminum substrate and an aluminum stamping plate. The main channel at the edge and four groups of branch channels intelligently control the batteries through the water pump and controller driving the coolant flow.
5. CTC battery serviceability analysis
The purpose of CTC battery technology is to be highly integrated and modular, simplifying the final assembly process and reducing costs. At the same time, it is also a technology that abandons power exchange and pursues an integrated design.
For the CTC battery cells, they are directly assembled into a battery pack, and the cells are encapsulated by glue to form a high-strength whole, while at the same time being wrapped in multiple layers of protective materials.
Therefore, it is impossible to repair and replace individual cells, and if there is a problem, the CTC battery pack can only be replaced as a whole. For the installation of the CTC battery pack and body, if the CTC battery pack needs to be repaired or replaced, It is necessary to remove the seat beam and sealant. Maintenance is relatively complex, and the convenience of maintenance requires further research.
The CTC battery scheme is the current development trend of pure electric vehicle batteries and vehicle integration, and according to the mainstream body form of passenger cars, the feasibility of adopting the CTC battery scheme for load-bearing bodies is mainly analyzed.
After analyzing the integration scheme, sealing scheme, structural strength, cooling scheme and maintenance convenience of the CTC battery pack and the body. It was confirmed that the pack itself was integrated first, and then the battery shell and the floor in the body were combined and integrated.