In the current era of new energy vehicles, battery safety and endurance have always been the issues that everyone pays close attention to. As the leader of domestic new energy vehicles, BYD's strength cannot be underestimated. In 1995, BYD was established and began to produce lithium batteries for mobile phones. By 2005, BYD began to engage in the research and development of new energy vehicle power batteries. The scary thing is that in the 15 years of power battery research and development and more than 500,000 installed capacity, there has not been a single battery safety incident.

　　How has BYD, which has always kept a low profile, never had a battery safety incident in 15 years? Let us uncover the secrets of BYD’s power battery safety technology. BYD's research direction of power batteries is mainly lithium iron phosphate batteries and ternary lithium batteries. The safety of lithium iron phosphate batteries is higher than that of ternary lithium batteries, so we will explore the relatively unsafe ternary lithium batteries.

　　Ternary lithium batteries have the advantages of high energy density and large output power. However, the shortcomings are also very prominent. The deoxidation temperature of the ternary material is 200°C. It has poor high-temperature stability and the exothermic energy exceeds 800J/g. It cannot pass the needle stick test. If the ternary battery is internally short-circuited, it is easy to cause serious damage. safety incident.

　　Regarding the safety issues of ternary lithium batteries, BYD conducted in-depth research from a technical perspective to resolve the conflicts one by one and seek solutions.

　　1. A well-thought-out choice - hard-shell prismatic battery

　　As we all know, the current selection of power battery packs mainly falls into three categories: cylindrical batteries, soft-pack batteries and hard-shell square batteries. The selection of battery pack is very important, as it determines the design and ease of arrangement of later battery pack accessories and the ability to control battery safety. After comparative analysis, BYD finally chose hard-shell square batteries for the following reasons.

　　Although the energy density of a soft-pack battery cell can be higher than that of a hard-shell rectangular battery, the entire battery system requires a battery thermal management module to heat and cool the battery to control the temperature range of the battery. The thermal management module of soft-pack batteries is more complex than that of hard-shell prismatic batteries, so the energy density of a group of soft-pack batteries is lower than that of hard-shell prismatic batteries.

　　Due to the application of high energy density materials, the safety of soft-pack batteries is uncontrollable, because soft-pack batteries are sealed by two layers of polymers pasted together; while hard-shell square batteries are sealed by welding of metal aluminum plates, so hard-shell square batteries The sealing of batteries is higher than that of soft pack batteries.

　　Thermal runaway is a very important risk factor in battery safety. When thermal runaway occurs, soft-pack batteries cannot release energy in a directional manner, but hard-shell rectangular batteries can have some specific exhaust and directional design in the module. Fire exhaust channel. This ensures that even if a cell goes out of control, the energy of the cell can be released along the fire exhaust channel, and the thermal insulation and fireproof materials between cells can protect other cells from being affected, thereby ensuring the safety of the entire system.

　　If you want to meet the vehicle's driving range of five to six hundred kilometers, the number of cylindrical batteries required will be particularly large. Tesla chose the cylindrical battery 18650. Model Large, it is difficult to achieve a high level of battery safety.

　　Therefore, BYD, which has always been known for its safety and technology, finally chose hard-shell prismatic batteries. The prerequisite for bringing consumers the wonderful driving experience of electric vehicles is to ensure the safety of passengers. This is BYD's consistent style.

　　 2. Battery Thermal Management System BMS

　　Similar to the "bad temper" of the engine, the power battery is very "delicate". Lithium batteries are not sensitive to the temperature range of 0°-40°. However, once the temperature exceeds this range, the life and capacity will be greatly reduced. The low-temperature attenuation of lithium batteries is more serious than that at high temperatures, so the problem of reduced cruising range of electric vehicles in winter is more serious in northern my country. In response to the adverse effects of temperature on batteries, battery manufacturers have developed a battery management system. BYD's battery thermal management system can effectively control the temperature of the battery and control it within a suitable temperature range, improving the vehicle's charge and discharge performance and delaying Battery degradation. The battery thermal management system can achieve battery cooling and battery heating.

　　Battery cooling is a battery thermal management system that reduces the temperature of the coolant in the battery water channel as needed by controlling the opening of the electronic expansion valve and the speed of the electric compressor, thereby taking away the heat generated during battery operation and the heat in the environment. The cooling tubes of the internal cooling circuit of the battery are arranged in an S-shape, which makes the contact area with the battery cells larger and is more conducive to the heat dissipation of the battery pack. Improve the charging and discharging performance of the vehicle and delay battery decay.

　　Battery heating: When the vehicle is in a low-temperature environment and the battery temperature is low, the battery thermal management system controls the PTC water heater to heat the coolant in the water channel during the charging process, and the high-temperature liquid in the water channel increases the battery temperature to achieve low-temperature charging and discharging functions.

　　3. “Technical means” to control security

　　Within BYD, battery safety is defined as the highest level, and no safety issues are allowed. BYD considers battery safety from 7 dimensions and 4 levels, and has corresponding protective measures in each dimension and level. From four levels of cells, modules, battery packs and systems, to seven dimensions of reliable connection, high voltage protection, collision, overcharge, short circuit and thermal runaway, battery safety is effectively protected in all aspects.

　　"Safety Guard" for CID overcharge protection

　　To prevent overcharging, BYD has multiple levels of protection: first, it accurately detects the voltage of the battery and monitors the status of the battery in real time. The second level is BMS layered protection. It charges to different voltages and executes different commands. It controls the charging status by limiting current and cutting off relays. If both levels fail, the third layer of protection is CID (Current Interrupt Device) technology. CID designs a flip piece on the battery cell. When the battery is overcharged, the internal pressure of the battery increases. CID uses the internal pressure of the battery to The high voltage turns over the flip piece to disconnect the circuit. The battery cells of the battery pack are connected in series. As long as one cell is disconnected, the entire circuit is cut off. As a pure hardware protection device, CID is BYD's patented technology.

　　FPC (flexible circuit board) simplifies the "friendship bridge" between modules

　　BYD uses flexible circuit boards to connect battery modules, which eliminates many connectors and wires, making the battery module layout more concise and the product layout more reasonable. BYD's FPC (flexible circuit board) has built-in fuses to avoid risks such as short circuits caused by accidental damage to the control circuit, further improving battery safety.

　　Explosion-proof valve-the "fireman" of battery safety

　　As a powerful line of defense at critical moments of battery safety, the explosion-proof valve is a "firefighter" that ensures vehicle safety. When the vehicle is in a fire or high-temperature environment, the high-temperature environment of the battery core will cause the electrolyte to vaporize. The vaporized electrolyte will cause excessive pressure inside the battery core. If it is not relieved in time, excessive pressure in the battery core will cause the conductive core to burst. The function of the explosion-proof valve is to release the high-pressure gas inside the battery core when the pressure inside the battery core exceeds the safe pressure to avoid battery core explosion and more serious consequences.

　　No amount can be done too much on safety issues. Compared with the profit-seeking behavior of American companies such as General Motors and Ford that did not modify design defects for the sake of profit, causing safety accidents and disregarding consumer safety, BYD is truly a conscientious company. Always put safety issues first. BYD has not had any safety accidents caused by battery problems in the past 15 years. In the field of electric vehicles, the battery life and safety that consumers are most concerned about have been initially solved by BYD. We look forward to BYD's further achievements in electrification and intelligence in the future. Good performance, stay true to your original intention and move forward.

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