On March 29, BYD announced the official launch of the "Blade Battery". As the name suggests, the blade battery refers to a new battery pack whose internal battery cells are shaped like blades. The cathode material is still BYD's best lithium iron phosphate, which has the characteristics of long life and long battery life. At the same time, the special structural advantages of the blade battery also enable it to completely get rid of the "thermal runaway" nightmare that may occur in traditional power batteries during acupuncture penetration testing, redefining the safety standards of new energy vehicles, leading the world in power batteries A new level of safety.
Wang Chuanfu, Chairman and President of BYD Group, said: "The 'Blade Battery' reflects BYD's determination to completely end the safety pain points of new energy vehicles, and is more capable of leading the global power battery technology route back to the right path and putting ' The word "spontaneous combustion" has been completely erased from the dictionary of new energy vehicles."
What is a "blade battery"?
The blade battery is a patented design for a battery pack. Inside it, many blade-shaped battery cells are assembled into a battery array, so it is called a blade battery. Compared with traditional battery packs, the biggest change of blade batteries is that they change the shape of the battery cells. They do not require modules and can be placed directly in the battery pack, simplifying the manufacturing process, assembly complexity, production cost, weight, and Improve the energy density of battery packs.
Traditional battery pack packaging mainly consists of three parts: battery cell → battery module → battery pack.
Traditional single power batteries generally adopt a cylindrical structure. Because of their small size, they are difficult to arrange. Many single cells need to be installed into a cubic module first and then installed into the battery pack. For example, the current mainstream 21700 ternary lithium battery refers to a cylindrical battery with a diameter of 21 mm and a height of 70 mm. Tesla’s old 85 kWh battery pack contains approximately 7104 18650 ternary lithium batteries.
(Traditional battery pack with module)
This kind of battery pack with module has two major disadvantages:
First, the consumption of materials and space High, and the assembly steps are complicated. Because traditional power battery packs require battery modules, it not only takes time to assemble the single cells into the modules, but also requires the module casing, battery pack beams and longitudinal beams, and the BMS battery management system to monitor each battery cell. The wiring harness and sensors are a considerable expense. In addition, there are gaps between cylindrical battery cells and battery modules in traditional power battery packs, and space needs to be reserved for structural beams. These wasted spaces have become the culprit of reducing the energy density of the battery pack.
Second, the failure rate, management and maintenance costs are high. There are a large number of battery cells in traditional power battery packs, and the potential failure rate has brought huge work pressure to the BMS battery management system. How to monitor and manage each single cell in a timely manner has always been a problem that has troubled car companies. Moreover, the complex internal structure of traditional power battery packs has also become a burden for later maintenance and replacement of battery cells.
BYD's blade battery is developed based on the module-less concept. It improves the battery cells and uses long hard-shell battery cells shaped like blades, eliminating the need to assemble modules. Install the battery cells into the battery pack.
The packaging of blade batteries (module-less battery packs) can be divided into two parts: battery cells → battery packs.
The patent shows that the length of the blade battery cell can be between 600 mm and 2500 mm. Because this kind of battery cell is very long, it can be installed directly in the battery pack without forming a module. It also adopts a hard-shell structure, which can improve the stiffness of the battery pack through the battery cell itself, so that the battery pack can be protected from external forces. It is not easy to deform, thus reducing or even completely eliminating the cross beams and longitudinal beams in the battery pack.
A major advantage of the module-less battery pack that cannot be ignored is that it can improve the space utilization within the battery pack. BYD officials stated that the space utilization rate of traditional modular battery packs is only 40%, while the space utilization rate of blade batteries can reach 60-80%, an increase of more than 50%.
While greatly improving the system mass energy density and volume energy density, removing the intermediate structure of the module also significantly reduces the complexity of the battery pack, which also brings higher product stability. reliability and lower failure rate. He Long, vice president of BYD Co., Ltd. and chairman of Fudi Battery Co., Ltd., introduced at the press conference that there are only 100 battery cells in the BYD blade battery.
Why choose "lithium iron phosphate"?
There are currently two mainstream power batteries used in new energy vehicles: ternary lithium batteries and lithium iron phosphate batteries.
Because the battery has a high specific energy, ternary lithium batteries can bring greater endurance, are more likely to meet national subsidy standards, and are widely used. But its disadvantages are also obvious. Ternary lithium batteries have poor thermal stability. They will decompose at high temperatures of 250-300°C to produce a large amount of free oxygen. And because the chemical reaction of ternary lithium materials is particularly strong, once oxygen molecules are released, the electrolyte will It will burn quickly under the influence of high temperature, and deflagration will occur immediately.
In contrast, although the battery specific energy of lithium iron phosphate batteries is relatively low, the P-O bonds in the lithium iron phosphate crystals are stable and difficult to decompose. Even under high temperature or overcharge, the structure will not collapse and generate heat or form strong oxidizing substances like lithium cobalt oxide, so it has good safety.
Three types of power battery acupuncture control test results:
BYD also recently conducted a comparison of ternary lithium batteries, lithium iron phosphate block batteries, and blade batteries. Penetration test. This test for battery thermal runaway has always been regarded as a nightmare by car companies because it will cause a short circuit inside the battery, causing the temperature and pressure inside the battery to rise rapidly, and even trigger a fire and explosion. There are even rumors that the latest compulsory national standard "Safety Requirements for Lithium-Ion Power Batteries for Electric Vehicles" draft for comments has canceled the cell acupuncture test because ternary lithium batteries cannot pass this test due to poor thermal stability. .
BYD’s test results are significantly different this time, which also proves the difference in thermal stability of the two cathode materials. The ternary lithium battery with poor thermal stability exploded and caught fire immediately after being penetrated by a needle, and the eggs on the surface of the battery were also blown away; the lithium iron phosphate block battery had no open flames and smoke, and the surface temperature was 200℃-400℃; BYD After the blade battery is penetrated by acupuncture, there is no fire or smoke, and the surface temperature is 30℃-60℃, which is significantly better than ternary lithium battery and lithium iron phosphate battery.
Lithium iron phosphate batteries are better than ternary lithium batteries because they have better thermal stability. BYD's blade battery, which also uses lithium iron phosphate as the cathode material, is better than the lithium iron phosphate block battery. This is because its blade-shaped structure makes the number of internal electrode coils significantly smaller than that of the block battery, so when it is punctured, an internal short circuit will occur. There is less heat, and the larger shell also helps dissipate heat.
In addition, the life of lithium iron phosphate batteries is also longer, with a cycle life of more than 2,000 times, while the cycle life of ternary lithium batteries is generally more than 1,200 times. In other words, a lithium iron phosphate battery can be used for 5.48 years even if it is fully charged and discharged once a day.
Written at the end:
Strictly speaking, BYD Blade Battery is more like an innovation in battery pack form than an innovation in battery cell technology. Because the biggest change in blade batteries is not the technology, but the blade-shaped battery cells, which can save some processes and manufacturing costs and have higher energy density and stability.
According to Wang Chuanfu’s on-site disclosure, the blade battery is currently only planned to be installed on BYD Han EV models, and there are no plans for other models. Han EV is a pure electric medium and large sedan that BYD plans to launch in the middle of this year. It has a comprehensive cruising range of up to 605 kilometers and an acceleration time of 100 kilometers in 3.9 seconds.
This article comes from the author of Autohome Chejiahao and does not represent the views and positions of Autohome.