What do you think of DM i’s blade battery design?

Today I saw a friend sharing information about the DM-I 120km battery version (previously the official statement was that it covers the battery power gradient of 8.3~46kWh), which is a picture stream. Combined with the information I know, I will sort out the design ideas, concepts and development of this thick blade battery. From the principle point of view, the thick blade is essentially an innovation based on soft-pack lithium iron phosphate, which may not be a wrong way in the long run.

Figure 1 Design of DM-I thick blade lithium iron phosphate battery system

Part 1 Thermal management of DM-i blade batteries

In Figure 1, we see something different from before - a heating film is embedded inside. In other words, there is an additional heating film in the displayed structure, and thermal conductive gel is used to reduce thermal resistance on the heating film as much as possible.

Figure 2 shows the DM-i battery structure

In BYD's previous promotional materials, two main modes were adopted: 1) Battery heat dissipation: using refrigerant direct cooling technology, the refrigerant is directly passed into the battery pack for cooling. Compared with liquid cooling, it reduces one level of energy exchange and improves the heat exchange efficiency by 20% compared to liquid cooling.

Figure 3 DM-i's refrigerant direct cooling technology

2) Battery heating: Pulse self-heating technology can not only heat the battery through high-frequency charging and discharging of the battery, but also heat it evenly. The efficiency of pulse self-heating is 10% higher than that of liquid heating.

Figure 4 Self-heating technology

But in reality, the rate of pulse self-heating is uncertain, so it is more direct to stick a heating film on the surface of thick blade batteries. As mentioned earlier, it is not easy to do, especially to evenly heat so many lithium iron phosphate batteries in series. The effect of high-frequency oscillation of self-heating is not so ideal.

Part 2 Design Concept of DM-i

My understanding is that the design of this thick blade is aimed at Toyota. This particularly long thick blade battery cell is actually similar to Toyota's method of putting multiple small standard NiMH batteries in a long and narrow NiMH battery. After multiple soft packs are made into finished products, they are put together by two insulators and then isolated, and then grouped into a long square shell.

Note: In this case, the shell may need special insulation treatment. We will look at it in detail later.

Figure 5 DM-i battery design, multiple soft packs are connected in series and then integrated into one battery cell.

The ultimate goal of doing this is to achieve a very high grouping rate for PHEVs, as shown in the figure below. This is a structure that battery system layout engineers like very much, and it is very simple and beautiful.

Figure 6: Vertically arranged modules

From the perspective of battery structure, it is indeed a good design. Of course, the disadvantage is that the operation of this shell is done on the battery module line (actually similar to the assembly of the module), and there are also operations such as sealing. Therefore, this soft pack battery cell has challenges in terms of manufacturing yield; especially after adding foam and pressure, once there is a self-discharge problem battery cell, the overall battery cell characteristics will be greatly affected. This kind of small-capacity lithium iron phosphate generally encounters a relatively large manufacturing challenge.

Figure 7 DM-i’s electrical connections and cooling are relatively simple

summary:

I actually like this design very much. The overall pack cost is still relatively low. However, whether there is potential for further cost reduction in the thick blade battery remains to be discussed.