The basic structure of lithium batteries is not “complex”. It is divided into four parts: positive electrode (anode), negative electrode (cathode), electrolyte and diaphragm. At present, the negative electrode material is basically graphite (currently developing towards silicon negative electrode material). The ternary lithium and lithium iron phosphate that everyone usually talks about are the differences in positive electrode materials. The electrolyte is currently mostly organic electrolyte, and is currently developing towards solid electrolyte. The diaphragm is a magical thing. Lithium ions can pass through, but other things cannot. In this way, when lithium ions pass through the diaphragm, the electron will pass through the wire to the other pole, and electricity will come~
The blade battery has the same structure:
Positive electrode material: lithium iron phosphate
Negative electrode material: graphite
Electrolyte: organic electrolyte
Diaphragm: still that magical thing
Shell: long and thin aluminum shell
So, some people say that there is no special innovation or progress, which is indeed reasonable: the battery principle is the same, and the positive electrode, negative electrode, and electrolyte materials have not changed.
However, engineering matters are not simply changing a formula or changing a material. There are also complex design and process issues. Otherwise, the atomic bomb in the world would not be so difficult to make. Theory is one thing, laboratory is another, engineering is another, and business is another.
The general structure of blade batteries
The traditional power battery structure is generally packaged step by step, such as cell-module-battery pack. The reason is that the cell is generally packaged in a very thin metal shell, and the structural strength is not high. If it is packaged separately in a battery pack, it is inconvenient to fix and wire it. Therefore, it is first placed in a module, fixed by the module, and then placed in the battery pack and connected with various cables. This step-by-step packaging idea is very intuitive and easy to control in terms of process. However, this will inevitably bring a little “waste” of materials and space, so everyone wants to remove the module and form a simplified structure of cell-battery pack, which is the so-called CTP. Cell To Pack, the cell is directly loaded into the battery pack.
The left side is a traditional CMP battery, and the right side is a blade battery
According to BYD’s blade battery patent, they referred to a structure similar to honeycomb aluminum (in fact, other companies also have similar ideas, but the structure is different). They boldly made the cell into a long strip to fill the entire pack and use the cell as part of the battery pack support structure. In this way, there is basically no need for a special module structure. At the same time, the long strip battery can make full use of the width of the vehicle (there can be no or very few partitions in the width direction of the vehicle, and the battery can be filled), further improving the energy density.
The battery cell structure of the blade battery
According to BYD’s patent, the battery cell in the blade is not actually a simple square aluminum shell battery cell (otherwise, it would not be patented, and it would not be patented just by flattening the square shell battery).
Each blade is actually a “micromodule”, and there are actually multiple unpackaged battery cells in this blade. (Why can’t you put one? Really, it’s too long, and it’s difficult to ensure the consistency of production.) They call this battery cell: pole core group (with multiple layers of pole pieces), and each has separate positive and negative leads. Then, use an isolation film bag to pack it inside the blade and encapsulate it inside the blade.
It is too difficult to directly produce such a long battery cell, so each blade actually has 3 pole cores.
In this way, the blade, as a structural component, is not only part of the structure of the entire battery pack (like the beam of a room), but also responsible for providing structural support for the internal battery cells. Killing two birds with one stone, saving materials and space, the energy density is naturally greatly improved.
It is also very beneficial when doing acupuncture experiments. The number of pole pieces punctured is small, the scope of short circuit is small, and the natural heat generation is small, which is conducive to the effective control of thermal runaway. (But the possibility of thermal runaway cannot be ruled out) Moreover, because it is made thin, the relative heat dissipation area is also large, and the problem of local heating of the battery can also be alleviated.
Of course, the content mentioned in the patent is far from that simple, and this is just a simple analysis.
