Wang Chuanfu, Chairman and President of BYD Group, said: "Blade battery reflects BYD's determination to completely end the safety pain point of new energy vehicles, and is more capable of leading the global power battery technology route back to the right path and completely erasing the word" spontaneous combustion "from the dictionary of new energy vehicles."
What is a "blade battery"?
Blade battery is a design patent of battery pack, which is called blade battery because it integrates many blade-like cells into a battery array. Compared with the traditional battery pack, the biggest change of blade battery is to change the shape of battery monomer, which can be directly installed in the battery pack without modules, simplifying the manufacturing process, assembly complexity, production cost and weight, and improving the energy density of the battery pack.
Traditional battery pack packaging mainly includes three parts: battery cell → battery module → battery pack.
The traditional single power battery generally adopts a cylindrical structure. Because of its small size, it is not easy to arrange, so it is necessary to put many single cells into a cube module first, and then into a battery pack. For example, the current mainstream 2 1700 ternary lithium battery refers to a cylindrical battery with a diameter of 2 1mm and a height of 70 mm. Tesla's old 85 kWh battery pack contains about 7 104 ternary lithium batteries.
(Traditional battery pack with module)
This modular battery pack has two main disadvantages:
First of all, the consumption of materials and space is high, and the assembly steps are complicated. Because the traditional power battery pack needs a battery module, it not only takes time to assemble the single battery into the module, but also needs to spend a lot of money on the module shell, the beam and longitudinal beam of the battery pack, and the wire harness and sensor needed by BMS battery management system to monitor each battery cell. In addition, there is a gap between the cylindrical battery cell and the battery module in the traditional power battery pack, so it is necessary to reserve a position for the structural beam. These wasted spaces have become the chief culprit in reducing the energy density of the battery pack.
Second, the failure rate and management and maintenance costs are high. There are a large number of batteries in the traditional power battery pack, and the hidden failure rate brings great working pressure to BMS battery management system. How to monitor and manage each battery in time has always been a difficult problem for car companies. Moreover, the complex internal structure of the traditional power battery pack has also become a burden for later maintenance and replacement of batteries.
BYD's blade battery is developed based on the concept of no module. It improves the battery cell, uses the blade-like hard shell to grow the battery cell, omits the step of assembling the module and directly installing the battery cell in the battery pack.
The packaging of blade battery (without modular battery pack) is divided into two parts: battery cell → battery pack.
The patent shows that the length of the blade cell can be between 600 mm and 2500 mm Because of its long size, this cell can be directly installed in the battery pack without forming a module, and it also adopts a hard shell structure, which can improve the rigidity of the battery pack through the cell itself, so that the battery pack is not easy to deform under the action of external force, thus reducing or even completely omitting the cross beam and longitudinal beam in the battery pack.
One of the advantages of modular battery pack is that it can improve the space utilization rate in battery pack. BYD official said that the space utilization rate of traditional modular battery pack is only 40%, and the space utilization rate of blade battery can reach 60%-80%, which has increased by more than 50%.
While greatly improving the mass energy density and volume energy density of the system, removing the intermediate structure of the module layer also greatly reduces the complexity of the battery pack, which also brings higher product stability and lower failure rate. He Long, vice president of BYD Co., Ltd. and chairman of Foday Battery Co., Ltd., introduced at the press conference that BYD's blade batteries only have 100 batteries.
Why did you choose "Ferrous lithium phosphate"?
At present, there are two mainstream power batteries used in new energy vehicles: ternary lithium batteries and lithium iron phosphate batteries.
Ternary lithium batteries are widely used because of their high specific energy, which can bring greater endurance and easily meet the national subsidy standards. However, its shortcomings are also obvious. Ternary lithium batteries have poor thermal stability, and will decompose to produce a large amount of free oxygen at high temperature of 250-300℃. Moreover, due to the particularly strong chemical reaction of ternary lithium materials, once oxygen molecules are released, the electrolyte will burn rapidly at high temperature, and then deflagration will occur.
In contrast, although the specific energy of lithium iron phosphate battery is relatively low, the P-O bond in its lithium iron phosphate crystal is relatively stable and difficult to decompose. Even in the case of high temperature or overcharge, it will not collapse and generate heat or form strong oxidizing substances like lithium cobaltate, and the safety is good.
Comparative test results of acupuncture for three kinds of power batteries;
Not long ago, BYD also conducted a comparative acupuncture test of ternary lithium battery, Ferrous lithium phosphate block battery and blade battery. This kind of test for battery thermal runaway has always been regarded as a nightmare by car companies, because it will cause short circuit inside the battery, which will lead to a rapid increase in the temperature and pressure inside the battery, and even lead to fire and explosion. There are even rumors that the latest draft of the compulsory national standard "Safety Requirements for Lithium-ion Power Batteries for Electric Vehicles" cancelled the battery core acupuncture test because the ternary lithium battery had poor thermal stability and could not pass the test.
BYD's test results are obviously different, which also proves the difference of thermal stability between the two cathode materials. The ternary lithium battery with poor thermal stability exploded and caught fire immediately after acupuncture, and the eggs on the battery surface were also blown up. Ferrous lithium phosphate bulk battery has no open flame and smoke, and its surface temperature is 200℃-400℃. BYD blade battery has no fire and smoke after acupuncture, and its surface temperature is 30℃-60℃, which is obviously better than ternary lithium battery and lithium iron phosphate battery.
Lithium iron phosphate battery has better thermal stability than ternary lithium battery. BYD leaf battery, which also uses LiFePO4 as cathode material, has better performance than LiFePO4 block battery, because its leaf-like structure makes the number of internal electrode coils obviously less than that of block battery, so the internal short circuit generates less heat when it is punctured, and the larger shell is also helpful for heat dissipation.
In addition, the life of lithium iron phosphate batteries is also longer, and the cycle life can generally reach more than 2000 times, while the cycle life of ternary lithium batteries is generally more than 1200 times. In other words, lithium iron phosphate battery can be used for 5.48 years even if it is charged and discharged once a day.
Write at the end:
Strictly speaking, BYD blade battery is more like an innovation in the form of battery pack than an innovation in battery monomer technology. Because the biggest change of the leaf battery is not the process, but the leaf-shaped battery monomer, it can save some processes and manufacturing costs, and has higher energy density and stability.
According to Wang Chuanfu, the blade battery is currently only planned to be used on BYD Korean EV models, and other models have no plans for the time being. Han EV is a pure electric medium and large vehicle that BYD plans to launch in the middle of this year, with a comprehensive cruising range of 605 kilometers and an acceleration time of 3.9 seconds per 100 kilometers.
This article comes from car home, the author of the car manufacturer, and does not represent car home's position.