Power Battery Safety Starting From A Small Age

- Nov 20, 2019-

In 2019, the retreat of the subsidy policy for new energy vehicles really made the manufacturers feel awkward, and what is even more worrying is the power battery with frequent accidents. Seeing the electric cars burning and even exploding in the news, I don’t know what the car owners think. Do we drive a time bomb every day? Oh no, it’s an untimely bomb! When the battery turns into an angry bird, no one can touch it. It is really scary. In comparison, BYD, which has been low-key, has never had a battery safety accident. This is of course not by luck, but by a strong technical reserve.

As we all know, BYD power battery covers both lithium iron phosphate battery and ternary lithium battery, while the safer lithium iron phosphate battery is mostly used in large commercial vehicles, and the common safety problem is basically equipped with three on the passenger car. Yuan lithium battery. From the perspective of monomer structure, the ternary lithium battery is divided into three types: soft pack battery, hard shell square battery and cylindrical battery. Compared with the soft pack battery, the hard shell square battery has three advantages: First, its thermal management module is simpler than the soft pack battery, and the energy density of the set hard shell square battery is much higher than that of the soft pack battery; secondly, the soft pack The battery is sealed by two layers of polymer bonded together, while the hard-shell prismatic battery is sealed by a metal aluminum weld. Therefore, in terms of sealing, the hard-shell square battery is stronger than the soft-pack battery. Third, when there is thermal runaway, the hard-shell prismatic battery can be vented and ignited by directional design. Even if a single unit is out of control, the energy of the monomer can be released through the fire escape channel, and the soft pack battery cannot be realized. In contrast, Tesla's cylindrical battery cells are smaller in size, and the cylindrical battery requires much more than the hard-shell prism battery under the same cruising range, so the battery consistency is difficult. Assuring that the risk of control will also increase. For example, a modelx needs more than 7,000 18650 cylindrical batteries to be integrated. In addition, compared to the aluminum hard case of a prismatic battery, the cylindrical battery steel case is more heavy and has a larger gap between the cells, so it is more susceptible to energy density ceilings. Therefore, BYD chose to adopt a hard-shell square battery solution with better comprehensive safety.

In order to ensure the high integration of power battery and vehicle manufacturing, the quality is unified. BYD has formed a complete industrial chain from mineral development to raw material R&D, cell design and manufacturing process, BMS manufacturing, module and PACK R&D and manufacturing, and ladder utilization and recycling. It has successfully integrated 7 dimensions and 7 levels. The battery is safe overall. Let the battery research and development and the whole vehicle industry chain become more closely linked, and the feedback optimization work is more efficient. The most important thing is to ensure that the safety quality of the power battery can be tracked and controlled.

At the monomer level, the choice of a more reliable hard-shell prismatic battery does not mean that battery safety is safe, and the module-level link and isolation process design is closely related to battery safety. First of all, the single cells have to work together to output power and need to be linked. In this regard, BYD adopts the industry-leading soft connection plus laser welding process inside the module. The whole battery module is regular and reliable, bidding farewell to the original way of thick wire connection, completely eliminating the short circuit risk caused by friction. Between the modules, BYD also chose a more advanced and safe aluminum row of welding instead of a threaded connection. If the link technology is the active security of the battery module, the isolation technology is passive security. Through the "divide and rule" of the problem, it is a fire-proof design. Module thermal runaway management relies mainly on aerogels between individual cells. The aerogel is encapsulated by PET, and the overall thermal conductivity is less than 0.04w/K.m, which can delay the heat transfer between the monomers, isolate the individual cells with problems, and ensure the overall safety of the battery module.

If the module level security is also disabled, upgrade to the battery pack level. In response to the battery fire caused by violent impact, BYD ingeniously designed the aluminum alloy battery tray of the bee structure. Through a large number of experiments, it is proved that this structure will collapse when collision and smash occur, and better absorb the energy generated by external pressure. At the same time, the battery pack also uses insulation and fire insulation design, energy relief device and automatic fire extinguishing device. When the vehicle is in a fire caused by severe impact, the driver and passenger have enough escape time, and the automatic discharge of energy can also put the fire. Control is within a certain range.

In terms of software, BYD's battery management system BMS also plays a vital role in battery safety. The real-time status of each cell's voltage, current, temperature, etc. is collected, which achieves higher acquisition accuracy, synchronization and acquisition frequency, and provides a solid foundation for battery management optimization. Based on accurate data acquisition, BMS can accurately calculate the remaining battery capacity, the supported mileage and the safe life of the battery to guide the battery control, and it is convenient for the owner to master the vehicle status. It is also a guarantee for the safety of the entire system software and hardware functions. In addition, BMS, combined with the back-end cloud database, combined with the AI algorithm, enables smarter battery management and further optimizes battery performance.

For example, for the ubiquitous overcharging problem, BYD presets multiple levels of protection: first, the BMS accurately detects the voltage of the battery, monitors the state of the battery in real time, charges different voltages to execute different commands, passes current limiting and cuts off the relay. The way to control the state of charging. If this fails, a mechanical CID (Current InterruptDevice) device will be used. By designing a flip chip on the battery cell, the CID opens the circuit when the battery overcharge causes the internal pressure to rise. Since the cells of the battery pack are connected in series, as long as one unit is disconnected, the entire circuit is powered off. It is worth noting that CID as a pure hardware protection device is BYD's patented technology.

For new energy vehicles, the most important part is the power battery. In this regard, BYD has specialized in the industry for 15 years, not only in the energy density and battery management, but also in the industry, and more importantly, it has accumulated a complete set of logical and interlocking battery safety solutions. For the consumer, handling performance and cruising range are important, but all are based on safety. The safety of the power battery is not a problem. If you do not design the details that may involve safety in the battery system development stage, the hidden dangers will always exist. From the source of R&D, BYD has systematic thinking and overall control over all aspects of power battery safety. Providing users with safe and secure products is a real commitment.