Demystifying the popular BYD blade battery in the lithium battery circle

by:CTECHi     2021-08-06

Lithium Grid News: I want to write about the market situation of square-shell batteries. In fact, they are mainly divided into CATL, BYD and the following square-shell lithium battery companies. This is the homework to be done before the holiday. But this time BYD has done a lot of work on the square shell batteries, and it is also very worthy of tracking and attention. I want to divide it into three articles, from the blade battery, the blade battery group and the PACK program, and whether this set of BYD's program can carry on the past and make some deductions.

1) BYD’s blade batteries

In 2018 and 2019, BYD’s power battery installed capacity was 11.4GWh and 10.8GWh, respectively. After the decline, BYD's installed capacity in 2019 decreased by 5.7% year-on-year. Among them, iron-lithium used in passenger cars and special vehicles dropped significantly. The use of iron-lithium batteries decreased from 4.5GWh to 2.8GWh, a year-on-year decrease of 37.3%.

Figure 1 BYD blade battery concept

From the perspective of cost, BYD has made changes to the battery size on the original basis, showing 'Flat' and 'Long' shapes. Since this matter is highly confidential, we have no way of knowing the details of the product. We can only find it from public channels. A valuable place is the patent channel. Since mass production is going to happen soon, BYD also needs to get it in terms of intellectual property rights. protection. As shown in the figure below, it is generally a critical path for key patents at the core of China to be named as leaders. The following three patents are like this, especially the two patents have a very short time from application to publication, and they are also the core patents that BYD is very fond of and hope to be protected.

Table 1 BYD’s three key patents

From the third patent, we can see that BYD’s blade battery is a long battery cell The solution (a battery made of a square aluminum shell) is based on the size of BYD's original battery cell (the two that BYD used to be 173 and 148 before) are reduced by reducing the thickness of the battery. , And increase the length of the battery core, and the battery core is designed to be elongated and thinned.

2) BYD blade battery information

From this battery cell, in fact, the height of 118 is based on the current normal winding core. , The thickness of 13.5 is actually not much more than the thickness of the soft bag. Mainly from 435mm to 905mm, or even higher to 2500, how is the battery connected inside? This is actually a bit similar to the very hot Combo before. The battery cell includes a very long battery 'module, Can also be made in parallel.

Figure 2 The size of the blade cell

Under the series scheme, a partition is set between two adjacent pole core groups, and the The space of the electric core is divided into a number of accommodating cavities, which form a similar honeycomb structure and are equipped with sealing and liquid injection channels.

Figure 3 The structure of the blade cell

In the series structure, a cell is formed by series connection 3.2V*3u003d9.6V small module. There are many design points in the series design:

1) In the series design, the different voltages between different pole core groups will cause the local potential of the aluminum shell to be too low, which can easily cause lithium ions to be embedded in the shell. The formation of lithium aluminum alloy corrodes the aluminum shell, and an isolation film is set between the shell and the pole core group to isolate the contact between the electrolyte and the shell

2) The electrolytes in different pole core groups are in communication In the case of, there is an internal short circuit problem; there is a high potential difference between different pole core groups (the LFP potential difference is about 4.0 ~ 7.6V), the electrolyte will decompose due to the large potential difference, which affects the battery performance, so Separator is designed.

3) The pole core connector includes a copper connection part and an aluminum connection part. There is a potential difference between copper and aluminum and lithium, and the electrolyte contacts at the contact position of the copper connection part and the aluminum connection part. The location is prone to corrosion, so an isolation plate is used in the design, and a packaging structure is set to encapsulate the pole core connector in the connection through hole. Because the capacity is not large due to the series connection, this is estimated to have some benefits in PHEV, plus BYD The voltage can indeed be increased, not limited to 400V, so the battery capacity can be smaller.

Figure 4 Structure design of series connection

The structure of parallel connection is more powerful. This is to make the single end of the battery cell out of two taps and two taps out of both sides. Combining them together is equivalent to using two series paths, but connecting them in series in one segment, so that the cells are connected one by one. The details of this battery core have to be digested. I believe that the first version of the battery core we can see is this, which is more reliable than the series connection above, and can increase the capacity.

Figure 5 Parallel structure

Summary: I think BYD’s steps are a bit big this time, but it’s actually a bit similar to the previous Combo module concept. I think the two square-shell lithium battery companies in China have really big brains, and I have time tomorrow to discuss the grouping under this blade.

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