li ion 18650 battery pack

　　BYD blade li ion 18650 battery packand GCTP technology

　　BYD's blade li ion 18650 battery packis a long li ion 18650 battery packcell solution (mainly refers to a square aluminum shell). It is a method of further improving the li ion 18650 battery packpack by increasing the length of the li ion 18650 battery packcell (the maximum length is equivalent to the width of the li ion 18650 battery packpack) and making the li ion 18650 battery packcell flat and elongated. Technology that integrates efficiency. It is not a li ion 18650 battery packcell of a specific size, but a series of li ion 18650 battery packcells of different sizes based on different needs. The specific shapes are as follows:

　　The positive and negative poles are at both ends, and there are explosion-proof valves at both ends (or one end). It feels like a soft package with tabs at both ends + a square aluminum shell. Compared with the existing square aluminum shell li ion 18650 battery packcell solution, the most obvious advantage of this li ion 18650 battery packcell is its good heat dissipation effect. The difficulty lies in the structural stability of the entire li ion 18650 battery packcell, internal resistance, liquid injection, etc., especially in terms of structural strength. In the subsequent CTP In the plan, the li ion 18650 battery packcore needs to rely on itself to achieve support.

　　For this, BYD mainly improves the support strength of the shell through improvements in molding technology, structural design, etc., while controlling the aspect ratio of the shell within a predetermined range. In addition, the internal resistance of the single cell can be reduced by optimizing the current collection path, and can also be supplemented by the improvement of the liquid injection process to solve the problem of long liquid injection time caused by the long size of the single cell.

　　Regarding specific energy, there is no clear information yet, and it has not been disclosed in the patent. However, based on BYD's speech yesterday, we can roughly infer an overall specific energy trend.

　　Next, let’s focus on BYD’s CTP solution from the perspective of patents.

　　(1) Structurally, the figure below is an exploded diagram of a CTP solution.

　　It can be seen that a single row of cells is directly laid on the bottom plate. Both ends of the cells are fixed on the end plates. The frames at both ends provide support for the cells. In order to increase the support force, a support step can be added to the bottom plate. ; There is a buffer plate (side plate) between the li ion 18650 battery packpack frame and the large surface of the li ion 18650 battery packcore to provide clamping force to the li ion 18650 battery packcore. There are no vertical and horizontal beams in this plan. You can also add vertical and horizontal beams or flame-retardant heat insulation pads to form multiple sub-modules, as follows:

　　BYD seems to be planning to use the strength of the li ion 18650 battery packcells themselves to achieve self-support, and at the same time rely on the strength of the integrated li ion 18650 battery packcells to increase the structural strength of the entire li ion 18650 battery packpack, that is, the li ion 18650 battery packcells and the box are tightly integrated into one. This needs to be finalized for product inspection, and the strength requirements for the li ion 18650 battery packshell are very high.

　　(2) Thermal management

　　BYD has provided two cooling solutions for the CTP. The picture above shows a liquid cooling design. This solution is to place the water-cooling plate on top of the entire li ion 18650 battery packpack, in direct contact with the module top plate, to cool the narrow sides of the li ion 18650 battery packcore; in order to improve the thermal conductivity efficiency, there is a thermal conductive plate between the module top plate and the li ion 18650 battery packcore side (possibly Thermal conductive glue or thermal pad is more reasonable), and the temperature difference of the entire package is controlled within 1°C. Water cooling adopts U-shaped water channel design or parallel design.

　　At the same time, there is an insulation layer between the other side of the li ion 18650 battery packcore and the bottom of the module to isolate the heat exchange between the li ion 18650 battery packcore and the outside world and play a thermal insulation role. Insulation cotton can be used.

　　This picture also shows the basic idea of BYD's CTP thermal runaway. The air inlet is designed directly opposite the explosion-proof valve to guide the gas and flame after the thermal runaway occurs to the exhaust channel, and then discharge it to the surrounding environment through the exhaust channel. In addition, if there are multiple modules, physical isolation will be formed between the modules; there should be a balanced explosion-proof valve on the outside of the entire li ion 18650 battery packpack; this idea is consistent with the design of Model S. The difficulty lies in IP67 and water corrosion in the thermal runaway channel. question.

　　The other one is designed for air cooling, and also has air ducts on the li ion 18650 battery packpack, as shown below.

　　The air duct is located between the li ion 18650 battery packupper cover and the chassis. It is designed with thermal conductive fins to enhance the heat dissipation area of the upper cover to improve the heat conduction efficiency between the thermal conductive plate and the single battery. There is a thermal conductive fin between the bottom plate and the li ion 18650 battery packcore. Insulating layer to increase heat dissipation at the bottom.

　　Whether it is liquid cooling or air cooling, the location is above the li ion 18650 battery packpack, that is, between the li ion 18650 battery packpack and the car chassis. I have never seen this solution before, and I don’t know how to handle the fastening of the li ion 18650 battery packpack and the car body. In addition, Air cooling also needs to deal with the problem of the air inlet.

　　(3) CTP solution configuration

　　Judging from the patent, BYD CTP has more than 8 solutions, corresponding to different sizes of cells and different arrangements, and also takes into account the double-layer li ion 18650 battery packsolution; for the integration of the box, CTP will have a traditional car chassis and box There are traditional solutions where the body is separated, and there are also integrated chassis solutions where the two are integrated into one.

　　The entire design also lacks another core electrical connection and high-voltage power distribution solution. Electrical connection should use FPC technology, which BYD has also pioneered relatively early. High-voltage power distribution may use the space circled in red below, which is somewhat similar to the idea of the Audi e-tron, as well as a space in the air at the front end, see the above section. 4 graphs, similar to ModelS.

　　I personally feel that BYD's CTP idea is more beautiful, more scalable and iterative. The only regret is that other parts of the vehicle have not been integrated yet. This is an advantage that BYD can achieve over CATL.

　　The above is a general summary of what we can learn from the patents. It can be seen from the PPT shared yesterday that the integration efficiency of BYD CTP (seemingly called GCTP) can reach more than 86%. In addition to the large module solution, there is also a group form of using adhesive to replace structural parts; in addition to functions Integrated aluminum tray (I personally feel that the water-cooling design is still possible at the bottom of the li ion 18650 battery packpack), and functionally integrated composite tray. Sufficient attention should be paid here, because the two solution trends pointed out have the tendency to subvert part of the upstream supply chain: that is, bonding replaces welding, etc., and composite materials replace metal materials. This is very important for structural parts, boxes, Welding and forming equipment companies are hit hard. At present, it is not known how fast this trend is and how many proportions within BYD are changing.

　　BYD’s CTP technology contains a lot of information. Let me briefly summarize the key points in my opinion (except for the inside of the li ion 18650 battery packcell):

　　(1) Large li ion 18650 battery packcells, large modules, and li ion 18650 battery packshell materials/processes are areas where there is a need for new technologies;

　　(2) Regarding the CTP structure, how to fix the li ion 18650 battery packcore is difficult;

　　(3) In terms of CTP thermal management, the design of cooling the top of the li ion 18650 battery packpack was proposed for the first time. Thermal conductive glue, thermal insulation cotton and the like are the areas of improvement;

　　(4) Regarding CTP thermal runaway, the reliability of the solution is not very good (this solution has already had failure cases), and more PACK explosion-proof valves may be needed;

　　(5) In terms of connection technology, high-strength structural adhesive may be the future growth area;

　　(6) The industrialization of multifunctional composite material boxes should be accelerated, which is a good thing for those engaged in materials.

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