In the process of fighting with contemporary Amperex Technology Co., Ltd., BYD directly invited the media to broadcast the acupuncture experiment of two batteries live. Compared with NCM ternary battery, lithium iron phosphate battery with blade is still very calm, and the safety of blade battery greatly exceeds that of ternary battery. In terms of safety, lithium iron phosphate battery is really the pillar.
Acupuncture experiment is the process of short circuit inside the battery. Acupuncture breaks the diaphragm, resulting in contact between anode and cathode, and intense heat erupts. A series of subsequent reactions of the battery were observed. At this high temperature, the cathode material of the battery will decompose, which will lead to the collapse of the battery material structure and affect the normal use of the battery.
When the ternary lithium battery is short-circuited in the battery, the decomposition temperature of the cathode material is at? What is the decomposition temperature of cathode material of lithium iron phosphate battery at about 200℃? 500℃? Above. In lithium iron phosphate battery, when the cathode material has a side reaction, the phosphorus-oxygen bond energy of lithium iron phosphate material is very high, and the energy required to break this chemical bond is also very high, which means that it is difficult for this material to release oxygen, which greatly reduces the possibility that the electrolyte will catch fire when it meets oxygen. Today we will talk about the structure of BYD blade battery.
The most powerful technology used by BYD in blade batteries is actually lamination technology. Although this technology is not a patent of BYD, BYD is definitely the leading brand in mass production. At present, the most commonly used process in battery assembly is winding process. Although it is convenient and has high yield, one of the disadvantages of the winding process is the low capacity density.
As you can imagine, putting a cylinder into a square container will definitely have a lot of wasted space; The arrangement sequence of laminated batteries in cross section is the cycle of shell-aluminum foil-diaphragm-positive electrode-diaphragm-negative electrode-positive electrode-diaphragm-negative electrode, which is similar to the shape of a thousand-layer cake and just fits into a rectangular battery pack.
The battery pack of blade battery adopts CTP module-free technology, which saves the intermediate assembly process of battery modules. In this case, I take the zongzi gift box as an example. A zongzi is a single battery, the packaging box of zongzi is a module, and the battery bag is a handbag outside the packaging box. If I leave out the box, I can put more zongzi in my handbag. Now the blade battery and the zongzi itself are assembled into a gift box. BYD directly connects the batteries together to make a battery pack, which improves the space utilization, which is equivalent to improving the battery capacity.
The shape of the blade battery can also explain why it doesn't suddenly heat up like NCM battery. The blade battery has a slender shape and a large area. When a single point is out of control, it will dissipate heat quickly, and it will not accumulate heat like a square shell battery, and there will be no obvious temperature rise. The unique design and technology make the energy per unit area on the panel smaller, which further controls the calorific value of the battery.
On the other hand, the blade battery actually flattens the wound electrode for assembly. Compared with wound battery, the number of punctured layers is less, and the heat in generate is less.
Everyone knows that laminated batteries are well designed, so why not design them as laminated batteries? Lamination, in fact, anyone can do it, but other lamination is very expensive, friends! The output is not reached, the output speed is slow and the cost is high. Isn't this a bit of a loss? BYD's wide lamination technology can now be completed quickly and well. This is not Chinese cabbage, it is easy to buy. At present, the coating speed of BYD production line is 70 meters per minute, the width is 1.3 meters, and the laminating speed can reach 0.3 seconds. As far as this process is concerned, BYD is too good at playing.
One of the patents applied by BYD is about the new design of battery structure. A single leaf battery is composed of a plurality of cells, and each cell or cell group is located in an isolated accommodating cavity, and the accommodating cavity is provided with a switch system, and if a single cavity is short-circuited, the system will discharge the electrolyte in the cavity. To be precise, it is to open the switch to exhaust and release pressure. Because each accommodating cavity is relatively independent, one problem will not affect other batteries.
This is actually very similar to the design of modern cabins. There are many sealed cabins at the bottom of the ship. When one capsule was smashed into the water, the others remained intact. Even if two or three pieces are broken, the ship will not sink. This design ensures enough safety, so does the battery design.
BYD official said that the blade battery has not used this technology, and the length of a single electrode is 960 mm I have reservations about this. Maybe Mimi used it, but she didn't admit it and it didn't hurt.
However, the national standard requirements that have been cancelled actually have corresponding standards for the breakdown of single cells and battery packs. Some people will think that the battery pack is used in cars, which has no reference significance for the breakdown experiment of single cells. But! The acupuncture experiment itself simulates the situation that lithium dendrites are produced inside the battery to puncture the diaphragm, so it is meaningless to use the battery pack to puncture. In the national standard test, the battery pack has to undergo mechanical collision and other tests. In essence, it is the same as the steel needle piercing the battery pack, in order to test the firmness of the battery pack shell rather than the internal short circuit.
However, if the lithium iron phosphate battery really only has the advantages mentioned above, it will not be eliminated by many car companies now. Safety comes from the characteristics of lithium ferrous phosphate itself, as does low capacity density. The electrolyte and binder of lithium iron phosphate battery will deteriorate at low temperature, which greatly reduces the capacity and performance of the battery. At MINUS 20℃, the electrochemical activity of lithium iron phosphate battery is only 50%-60%, while the electrochemical activity of ternary lithium battery can be maintained at about 70%-80%, which is why many northern car owners react to the shrinking battery life in winter.
Furthermore, another essential problem of lithium iron phosphate battery is the poor consistency of the battery, and some people may have no concept of this consistency. If the consistency of the battery is poor, the failure rate of the battery will increase, and the maintenance difficulty of the battery pack is directly proportional, which also puts forward high requirements for material preparation and manufacturing technology. Structurally, the blade battery adopts a safer lamination process, but more reactions will occur at the part that first contacts the electrolyte, which will affect the synchronization of battery reactions. The winding process is more convenient for the uniform distribution of electrolyte and the consistent reaction degree of each part of the battery.
Therefore, people who advocate lithium ferrous phosphate do not need to save new energy. On these two most critical issues, the distance between lithium ferrous phosphate and lithium ternary is probably all roads lead to Rome, but lithium ternary was born in Rome. Why use your own shortcomings to attack each other?
Some people may ask whether it is possible to combine the high capacity advantages of ternary materials with the safety of lamination process to make a blade NCM battery. The official explanation given by BYD is that ternary materials are generally not as safe as lithium ferrous phosphate, and even if they are made into blade shapes, the calorific value cannot be controlled at a very low level.
Neither the battery BMS management system, the more exquisite internal structure of the battery, nor the customization on demand can fundamentally solve the contradiction between lithium iron phosphate battery and ternary lithium battery. The nature of chemical materials is innate. Only by modifying the material or structure from the chemical level can we really make up for the shortcomings of lithium iron phosphate batteries and ternary lithium batteries and become hexagonal fighters who can fight and resist.
This article comes from car home, the author of the car manufacturer, and does not represent car home's position.