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[YesAuto New Energy] Super broadcast, every week. The rainy season across the country is approaching. This week, there were heavy rains in the north and south, and even accumulated water in many areas of Guangdong. Okay, the old question was brought up for discussion by everyone again: Are our cars afraid of driving on watery roads? With the increasing number of new energy vehicles, the battery in your car intensifies everyone’s attention to safety, especially when driving on watery roads or when the vehicle is parked in water. The word “electricity” makes Many people are afraid.

New energy vehicles and traditional fuel vehicles have different understandings on the issue of “water encounters”. In the past, the hidden dangers of water safety were basically on the “physical level.” The greatest threats were nothing more than the exhaust system, engine, and vehicle airtightness. Therefore, in the safety education of traditional automobiles, the wading height was the highest. A data that is valued by everyone. But when it comes to new energy vehicles, “the problem has risen to a higher level. In many people's minds, the existence of batteries may not only be as simple as “flooding in water”,” there have even been many alarmist rumors.

Regarding waterproofing, the safety of new energy vehicles can be divided into three parts, single battery, management system protection and battery pack. Many people now know that the battery pack in a new energy vehicle is composed of individual batteries arranged in series and finally connected in series. If water enters the car, the first step is the sealing protection of the outside of the battery pack, the second is the system management and protection between the battery series, and the innermost is the waterproof ability of each battery.

  The first protective monomer battery cell waterproof level

At present, in many product protection security levels, there is a clear index: IP protection level. Among them, we are most familiar with the IP67 standard, because this standard is also applied to mobile phones, watches and other mobile devices. This set of standards will be aimed at measuring the product's ability to protect against dust inhalation and protection against short-term soaking. At present, the highest level of some industrial products under this system is “IP68”, which mainly appears on military-grade and commercial-grade products. Most civilian-grade products have reached “IP67” as the highest standard. At present, every battery on a vehicle has at least reached the IP67 standard.

In the “Safety Requirements and Test Methods for Power Batteries for Electric Vehicles” issued by the General Administration of Quality Supervision, Inspection and Quarantine, the safety indicators and test methods for single power batteries and modules for new energy vehicles are clearly pointed out. In this test method, because salty seawater is more likely to cause corrosion to the product, the battery cell product must be immersed in a 3.5% NaCL (sodium chloride, simulated seawater) solution for 2 hours in a fully charged state. The battery is required to be free of charge. Phenomena such as fire and explosion.

In addition to strict waterproof testing, the battery cell products used in new energy vehicles have to go through other “naked tests”, such as puncture, extrusion, fire and other violent test procedures, to ensure that they do not rely on any protective measures. The core itself must also have a strong resistance to pressure. Therefore, the waterproof problem that users worry about is only one of the steps of battery cell testing, and other “hazardous hazards” that we may not consider have already had targeted management standards in the current standards.

● The second protection battery control system

Whether it is for waterproofing or fire prevention, it is the damage of the single cell caused by external force. If there is an irresistible external force, the single cell will have “flatulence bulge” caused by pressure, so control The most important safety measures inside the battery pack are: pressure and air release and temperature control.

Pressure relief, exhaust, and constant temperature. These responsibilities are the physical layout of the battery pack and the detection control system (BMS). This is why various brands are responding when they emphasize the uniqueness of their own battery control systems. The actual performance is “safe, safe, safe”. In last year's “Road to Electricity Search” column, we focused on explaining the internal structure of new energy vehicle batteries. Click to review: “The Road to Electricity: From Manufacturing to Recycling and Tracing the Life of Batteries”

But what we must also know is that the internal battery layout is also an important safety measure, just like in a fuel car, the safety of gasoline is defended by the protective structure of the fuel tank. The control system monitors the real-time status of each battery cell, but when a “danger” occurs, the physical structure in the battery pack provides an “escape space” for it. The internal layout and arrangement of the battery pack will shape the safety foundation of the structure and create a better heat dissipation and exhaust environment for the battery.

● The third protection: the battery pack is sealed and protected as a whole

Everyone knows that the “squatting nest” phenomenon of fuel vehicles wading is mainly due to the intake and exhaust systems, so the vehicle has a clear description of the height of the wading when it leaves the factory. However, because new energy vehicles do not require exhaust, after car companies have added additional hardware protection to the battery pack, the water wading capability will be better than that of fuel vehicles of the same level. At present, some new energy vehicles can reach the actual wading height of 70cm, but in the IPX7 standard we mentioned above, the maximum upper limit of the wading capacity of new energy vehicles can even be close to a height of 1 meter.

Therefore, in order to ensure the safety of the battery pack while the vehicle is driving, car companies will provide a protective frame for the battery pack, also known as a battery module frame. At present, most new energy vehicle battery packs are arranged on the chassis and are more likely to come into contact with water during driving. Therefore, the protection frame will provide special insulation protection for the high-voltage part of the battery pack to protect the battery pack from external forces such as wading, collisions, etc. Security impact. Moreover, the protective frame can achieve two benefits. While protecting the battery pack, it can also enhance the safety of the entire car body, especially the risk of car body deformation caused by side impact, and realize the safety protection of the whole car from the structural level.

At present, new energy vehicles also have wading test standards for complete vehicles. For example, there is a compulsory DB31T634-2012 standard in Shanghai’s admission policy for pure electric vehicles. This standard will simulate the wading environment of vehicles in driving, requiring pure electric vehicles to be in a water depth of 15 cm and greater than or equal to 30 km. /h, the total time for wading is 10 minutes. Then, in a water depth of 30 cm, drive forward and backward at a speed greater than or equal to 5 km/h, wading for a total of 10 minutes. Through this test, it can also further ensure that new energy vehicles have sufficient safe driving wading capabilities.

● The safety of the battery pack is still being strengthened

In summer, in addition to waterproofing, the issue of battery spontaneous combustion is also of great concern to the public. But as mentioned in the previous article, thermal runaway is the biggest safety hazard of the battery when it is affected by force majeure, because at present, the “acupuncture test” is regarded as the highest guarantee of battery safety from the industry to the car companies.

Previously, BYD had done a public acupuncture experiment on the latest “blade battery”. The results showed that the ternary lithium battery burned violently during the test, and the surface temperature exceeded 500 degrees Celsius; the lithium iron phosphate battery had no open flame or smoke. The surface temperature is 200-400 degrees Celsius; while the latest BYD blade battery has no open flame or smoke, and the surface temperature is 30-60 degrees Celsius. In the end, BYD used this to determine that the safety of blade batteries is higher than that of traditional ternary lithium batteries and lithium iron phosphate batteries.

But this week, Ningde Times “Acupuncture Test” made a point of view. Insiders of its brand said: The safety of power batteries is mainly manifested in system thermal safety, mechanical safety, electrical safety and functional safety, not just the safety of batteries. In reality, the battery cell will not be punctured by needles, and the “blunt puncture” and squeezing at the bottom of the battery pack are the test methods that are more in line with the real scenario.

The point of view is that lithium iron phosphate batteries are easier to pass through acupuncture not because of advanced technology, but because of the good thermal stability of the material itself; while the high energy density of ternary lithium batteries does pose a challenge for acupuncture, but it is not impossible to complete. In other words, a battery that passes the acupuncture test is not necessarily safe, and not doing the acupuncture test does not mean that the battery is unsafe.

Super broadcast comment:

In the past few years, battery safety issues have been guided by policies and regulations, as well as the continuous technological optimization of car companies and battery companies, and now have higher levels of protection in multiple dimensions. With the coming of summer, the safety issues of new energy vehicles must have attracted much attention. It is easy for everyone to instinctively associate various “vehicle failures” and “fires” with battery safety. Behind this is a blind spot in our technical knowledge, but At the same time, it also shows that the current car brands still cannot slacken their efforts to enhance product safety. Perhaps, if one day there is a brand that can promise “battery zero hidden danger”, it will also be a step for the people to trust the safety of new energy vehicles.