Safety analysis of blade battery

Just because the battery cell shape is very special, BYD's blade battery has nothing to do with the knife. It is long and thin, just like the blade, so it is called the blade battery. The battery core used in BYD Han EV models is 1 meter in length, 10 cm in width, and only 2 cm in thickness. The single voltage is 3.34V and the capacity can reach 100Ah This is a shape that has never been seen before in the form of a battery cell. 1 External force kneading We have analyzed that the most serious safety problem that lithium-ion batteries will have is incineration or even explosion, as in the previous article. The root cause of these problems is the thermal runaway inside the battery, and the first requirement to prevent thermal runaway is to prevent the battery cell from being kneaded by external forces in the event of a collision. It can resist the impact to the battery pack body through deformation and energy absorption. BYD's blade battery is still planned with an energy-absorbing box structure similar to the anti-collision beam of a car on the outside of the battery pack. The blade batteries are directly placed vertically and tightly, and fixed on the frame of the battery pack, so that each battery cell itself becomes a structural member and a beam supporting the battery pack. A thin beam cannot serve any purpose, but when the number of beams is large, it will be a bit like a chopsticks for continuous use, and the largest area, the most likely to bend the part facing the front and rear of the car, the outside has More sufficient buffer area. The battery pack is only slightly deformed, and the blade battery is in the 100-800kN inspection specification. There is no smoke or fire. In the three-point pressure test, the blade battery can withstand a pressure of 445kN. The impact and kneading strength it can withstand is indeed stronger than the traditional battery pack structure. 2 The thermal runaway of the battery cell is caused by collision and kneading, or due to overcharge and overdischarge. Most of the new energy electric car incidents that have occurred are related to the thermal runaway of the power lithium battery. Eventually cause the battery core to overheat and catch fire. And the higher the nickel content of the positive electrode material, the more unstable (the NCM811 battery with the highest energy density now shows that the positive electrode ratio of nickel, cobalt, and manganese is 8:1:1 is theoretically the most unstable). The ternary lithium-ion battery of the company may experience thermal runaway when it exceeds 200°C. It is very prone to incineration. It has extremely high stability within 500℃, and the thermal stability of lithium iron phosphate cathode material is much better than that of ternary lithium ion. Thermal runaway may occur only when it exceeds 800°C. In addition, even if thermal runaway occurs, the heat release of the lithium iron phosphate battery is very slow, and oxygen will not be released during decomposition, reducing the risk of fire. The long strip structure of the blade battery has a large heat dissipation area, which is compared with the traditional battery of the same material. Accompanied by the long loop of the entire circuit, the heat generation capacity is low. In summary, the heat generation is low and the heat dissipation performance is good, so the probability of thermal runaway or spontaneous combustion is much smaller. BYD followed the GB/T31485-2015 acupuncture test method for the most difficult acupuncture test for lithium-ion batteries. Fully charge the battery, use a high temperature resistant steel needle with a diameter of 5mm, penetrate the entire battery from a direction perpendicular to the battery plate at a speed of (25±5mm/speed), artificially create a short-circuit environment under extreme conditions to test the battery's resistance Safety at the most severe damage. NCM622 ternary lithium-ion battery burns violently in an instant, and after puncture. The surface temperature exceeds 500℃. The traditional lithium iron phosphate bulk battery begins to expand and open after a short reaction time. The pressure relief valve is used to spray out the internal high-temperature liquid and gas. Although there is no open flame, the surface temperature also rises to 200℃-400℃. Although there is certain danger, it is still within the control scale as a whole. Smoke and fire phenomenon. Finally, the voltage of the blade battery only drops at a very slow rate after the puncture. The maximum temperature of the surface only stays at 30-60°C, which is very safe. Taking a step back, even if it shows thermal runaway under extreme conditions, Vehicles equipped with blade batteries can also provide longer escape and rescue time. Statement: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete the previous article: Analysis of the characteristics of lithium-ion batteries