A complete analysis of Geely's SEA platform battery system

Recently, Zeekr is doing marketing promotion, and the official has released a lot of detailed information. I will do an in-depth review of the battery part that I am interested in. As Geely shares the SEA platform with many projects, we will see its application in many models in the future, such as: Zeekr, Polestar, Volvo, Lynk & Co., and even Smart, as well as Jidu.

Title image: Cross-section of the SEA platform

At present, the battery platform solution has the following main features:

(1) The battery uses the Ni55 system battery that everyone uses. The Ni55 battery increases its energy by increasing the charging cut-off voltage. The charging cut-off voltage of Ni55 is 4.35V, which is 0.15V higher than the previous 4.2V. After adding insulation materials between the batteries and insulation above the module, this solution is generally called NTP non-heat propagation technology, as shown in Figure 2.

Figure 1 Battery system of SEA platform

NTP has the following main features: "Break" uses Pyrofuse to achieve millisecond breakpoints; "Exhaust" uses exhaust gas path design with a pressure relief valve; multi-layer insulation uses fire-proof materials (ceramic rubber, ceramic glass fiber and mica board), and the top cover is changed from the previous aluminum cover to a sheet metal cover; active cooling uses the control of an emergency water pump under the detection and wake-up of the air pressure sensor or CMU; early warning reminder methods mainly include ambient lights, central control screen, mobile phone apps, etc., covering driving and parking states.

Figure 2 NTP heat-free air defense technology

The verification of NTP uses the needle puncture test video that everyone uses now. After a steel needle is inserted into a single battery cell to trigger thermal runaway of the single battery cell, the battery pack BMS above promptly triggers the thermal event alarm signal. Here, through the infrared scanning, we can see that the maximum temperature of the battery cell reached 801.4℃ at that time, and the battery system discharged a large amount of smoke. What is shown here is that after the battery system has been stored for a period of time, the single cell voltage drops to 0V, the temperature returns to normal, the thermal isolation design and the whole package structure are intact, there is no obvious deformation, the battery shell is not charged, the internal fixed structure and high-voltage connection of the battery pack are intact, and there is no heat spread.

Figure 3 Thermal runaway situation

After removing the battery cover, we can see the condition of the entire module, which is basically burnt black.

Figure 4: Battery module status after the experiment

(2) The integration efficiency of the whole package is 72%, which shows the transition from the previous 590 to the current dual-module integration method. It is divided into 6 dual-row modules (16 cells) and 2 single-row modules (8 cells).

Figure 5 Module layout

Here, an integrated "S"-shaped parallel flat plate liquid cooling is used to achieve a pressure drop of 30kPa at 16L/min and reduce the energy consumption of the water pump. On the SEA platform, an inverter-controlled heating system is also added, and the specific data is to be checked.

Figure 6 Water cooling plate of SAE platformFigure 6 Water cooling plate of SAE platform

(3) In terms of fast charging, the maximum current is 600A at low SOC. In the actual demonstration, it is 552A at 5% SOC, 535A at 6% SOC, and 466A at 22% SOC. PyroFuse (PSS fuse) is also introduced here to solve the problem of heating of the blown fuse under high current charging, and the charging rate of this battery cell is still relatively high, according to current estimates, it is a 2.2C battery cell.

Geely also seems to have customized a 350kW charging station based on 400V, which uses liquid cooling with an outer diameter of 25mm.

The 600A charging capacity was tested inside the car, including all aspects including the charging cable, high-voltage connector, high-voltage contactor, etc.

Note: Geely will also build charging piles in the future, and it is expected to build 2,200 charging stations by 2023

Figure 7 Electrical fuse switching

The overall situation of this package is shown in the figure below. The line speed of electrical sampling goes around both sides. It can be seen that this platform is compatible with the previous 590 design. There may be two different ways abroad and domestically, and the battery cell can also be changed to iron-lithium battery cell.

Figure 8 Battery system design of SEA platform

summary

At present, with the development of automobile platforms and automobiles, the information released by manufacturers in the field of batteries is very detailed. I am looking forward to the subsequent actual disassembly for readers' reference.