Toyota bZ4X cell and module design

bZ4X?is the first?pure electric model that Toyota really began to do with heart, although it brought us not so many shocks and surprises, and the response of the car was mediocre, but this is the first step for Toyota who turned around.

Some of its designs in electrification are also worth scrutinizing and studying in detail, such as charging, such as power inverter, such as battery systems. The overall design of its battery is similar to the square style we used around 2019-2020, which not only retains traces of traditional design concepts (such as maintainability, assembly, recyclability, redundancy), but also wants to break forward, such as the scheme of using large cells and large modules.

1. Types and design of bZ4X cells

The basic battery system parameters of the bZ4X are shown in the following table:

▲Comparison of Toyota bZ4X and UX300e battery pack parameters

There are two versions in terms of electricity, the Panasonic version with 71.4 kWh and the CATL version with 72.8 kWh. The integration method of these two versions is the same, but there are differences in the way the cells are placed.

From the comparison between the Panasonic version of the battery system and the UX300e, the mass specific energy of the bZ4X system is 148.44Wh/kg, an increase of 13%. The comparison of the parameters of the two cells of the bZ4X is as follows.

▲Comparison of basic parameters of Toyota bZ4X Panasonic battery cells and Ningde version cells

On the bZ4X model, Toyota uses two batteries, one is Panasonic's 201Ah cell, and the other is the 205Ah cell of the Ningde era. From the perspective of battery parameters, the biggest difference between the two is that the Panasonic version is an energy and power cell, and its fast charge almost reaches 2C, while the Ningde version does not support this degree of fast charging. In terms of actual usage, the Panasonic version of the bZ4X fast charging power reaches 150kW, while the Ningde version is about 100kW. According to the current technical reserves of Panasonic and CATL, completion can provide better cell choices than this, and it is not clear why Toyota does not pursue better performance cells.

One aspect that may be one of the reasons is that Toyota's life requirement for bZ4X cells is 10 years of capacity decay of no less than 10%.

Here I take a detailed look at the Panasonic version of the bZ4X cell, the following is its structural composition, there are 3 bare cells,?and?there is an insulating film between the bare cell and the aluminum shell. The positive and negative output poles are at one end of the cover plate, and the middle of the cover plate is a safety explosion relief valve, next to which is a liquid injection hole.

▲Toyota bZ4X Panasonic version battery cell composition explosion diagram

In terms of size, this cell is similar to the BMW ix3 cell, but the Z height is higher than the ix3, the cell shoulder height is 103mm, plus the size of the output electrode, the height is almost 106.5mm. The specific volume energy is 589Wh/L, which is 300% higher than that of the UX11e cell. Its positive and negative electrodes and diaphragms are composed as follows:

▲Toyota bZ4X Panasonic battery cell positive and negative electrodes and diaphragm composition

The diaphragm of the Toyota bZ4X Panasonic battery cell has been coated with a heat-resistant coating on both sides to enhance the performance against the damage of short circuits in the cell.

▲?Comparison of C-HR battery cell cathode material and bZ4X Panasonic version battery cell cathode material

In order to increase the capacity of the cells, the bZ4X cells have upgraded the cathode material to increase the nickel content relative to the C-HR cells. Moreover, the small particles in the bZ4X cathode material are changed to single crystals, which improves the attenuation performance of the capacity. At the same time, the large and small particles of the bZ4X battery cell cathode material are surface treated to inhibit the reaction between the cathode material and the electrolyte, and further improve the attenuation performance of the cell capacity.

The surface of the active material is treated to reduce the reaction with the electrolyte, and this measure is also applied to the negative electrode material, and the negative electrode also optimizes the distribution of the binder and active material to improve the diffusion of lithium ions on the surface of the electrode and the negative active material. In this way, not only improves the cycle life of the cell, but also improves the fast charging ability of the cell.

▲?Comparison of life of C-HR cells and bZ4X Panasonic cells

2. Design of bZ4X module

▲The?module of the Toyota bZ4X constitutes an explosion diagram

The bZ4X module is a large sandwich-style module with a length of about 1186mm. From the perspective of structural design, this module is between the traditional module and the strap-type large module. It actually has 4 steel belts/plates, which are side panels on both sides, upper and lower straps. Used to fasten modules and provide preload to the cells.

The biggest highlight of this module is that it uses two spacers between its cells: one is a rubber pad of EPDM rubber and the other is a silica aerogel pad. Aerogel mat is mainly used for thermal runaway heat insulation, EPDM is mainly used to cope with the expansion force of the cell, through the control of the expansion force of the cell, so that the cell is in a more comfortable state of force, reduce the increase of internal resistance, improve the life of the cell.