With the continuous increase in the market share of domestic new energy vehicles, consumers are paying more attention to the safety issues of using new energy vehicles. As the most core component in the three electric systems of new energy vehicles, the power battery directly affects the main performance indicators of new energy vehicles, and its safety often determines the reliability of the entire vehicle. Therefore, it has become the focus of attention for battery manufacturers, vehicle manufacturers, and even consumers.

　　1、 What is power battery safety?

　　For the daily use of new energy vehicles, the safety of power batteries mainly includes structural safety, electrical safety, thermal safety, and environmental safety. Among them, structural safety refers to the internal structural change caused by the external mechanical shock of the power battery, which leads to the risk of runaway heating; Electrical safety refers to the risk of electric shock caused by short circuits in power batteries caused by dust pollution, wading, flooding, etc; Thermal safety refers to the thermal runaway caused by external high temperature or high impedance of power batteries, leading to combustion or explosion accidents; Environmental safety refers to the risk of thermal runaway caused by external temperature changes and altitude impacts on power batteries.

　　It is not difficult to find that although the factors that affect the safety of power batteries are very complex, the most core factors are electrical safety and thermal safety, mainly reflected in short circuit electric shock, thermal runaway combustion or explosion. Therefore, strengthening the waterproof performance of batteries and curbing thermal runaway have become the key to improving the safety of power batteries.

　　2、 What are the safety standards for regulating the safety of power batteries both domestically and internationally?

　　Due to the early development of new energy vehicles in China, the relevant national standards for the safety of power batteries are also relatively complete. In addition to the early six recommended standards for the safety of battery cells, modules, and battery packs, in 2020, the Ministry of Industry and Information Technology also organized the development of three mandatory national standards, including GB 18384-2020 "Safety Requirements for Power Batteries Used in Electric Vehicles", GB 30381-2020 "Safety Requirements for Electric Vehicles", and GB 38032-2020 "Safety Requirements for Electric Vehicles". On the basis of ensuring the basic safety performance requirements of power batteries, the three mandatory national standards have added the requirement for thermal event alarm signals of power battery systems. At the same time, they require that after a single power battery unit experiences thermal runaway, the system will not fire or explode within 5 minutes, and reserve safe escape time for passengers.

　　In addition, for the dust and water resistance performance of power batteries, according to the GB4208  IEC  EN60529 standard, it is recommended that the dust and water resistance level of power batteries throughout their entire life cycle should not be lower than IP67. Among them, 6 represents the dust prevention level, which is completely preventing dust intrusion; 7 represents the waterproof level, which means soaking in water at a depth of 1 meter for no less than 30 minutes.

　　The international standard for the safety of power batteries is based on the standards published by ISO (International Organization for Standardization), IEC (International Electrotechnical Commission), and SAE International (Society of Automotive Engineers), and is formulated by countries and regions according to specific circumstances. Among them, ISO has developed standards in the field of power batteries, including ISO 12405-3:2014 "Electric drive vehicles - Lithium ion power battery packs and systems testing procedures - Part 3: Safety requirements". In response to the safety performance requirements of power batteries, it provides vehicle manufacturers with optional testing items and methods. The mandatory safety standard of the EU for power batteries is UN ECE R100, which includes the requirements for Electrical safety of the whole vehicle and the safety requirements for the part level on-board rechargeable energy storage system (REESS).

　　3、 How strict is the safety testing of power batteries in domestic vehicle manufacturers?

　　Although domestic/foreign safety standards have comprehensive regulations on the safety of power batteries, current testing is more focused on the battery itself, with less testing at the vehicle level. In order to strengthen the testing of power batteries, many vehicle manufacturers are also actively participating in safety testing, and compared to national standard requirements, the testing of power batteries by top domestic vehicle manufacturers is more rigorous and complex.

　　As early as March 2020, BYD announced for the first time the complete test video of the "blade battery" successfully passing the "needle test". According to the video, under the same test conditions, the ternary lithium battery experienced a drastic temperature change at the moment of puncture, with the surface temperature rapidly exceeding 500 ℃ and starting to burn violently; Traditional lithium iron phosphate block batteries have no open flames or smoke, and their surface temperature can reach 200 ℃ -400 ℃. Although there is no obvious ignition, this high temperature may ignite nearby combustibles. In contrast, "blade batteries" have no open flames or smoke after penetration, and the surface temperature of the battery is only 60 ℃. This means that the 'blade battery' will not catch fire even in the event of severe damage.

　　Compared to BYD's "acupuncture test", the Euler Lightning Cat conducted a "high-speed spiral rolling and falling challenge" in October 2022 to test the safety performance of the battery from more accident scenarios that may be encountered in daily life. Challenge The simulated vehicle runs out of control and crashes out of the guardrail on the expressway or urban express ring elevated road, falls from the elevated road and hits the ground, causing the vehicle to roll over, and the battery pack suffers from crushing, deformation, puncture and other injuries. During the experiment, the Euler Lightning Cat experienced violent impact, landing, and spiral rolling, and the "worry free battery" quickly lost power at high voltage. In the end, there were no electrolyte leakage, spontaneous ignition, or vehicle leakage, and the electrical safety evaluation project passed smoothly.

　　The latest test related to battery safety performance came from GAC Aian. In March 2023, GAC Aian conducted a "Magazine Battery 2.0" shooting test, firing a full charged battery pack with a reserved shooting opening at a distance of 15 meters. When the bullet penetrated the battery cell, the speed could reach 975000 times that of the needle, and the diameter of the wound was 7-8 times that of the needle. In this experiment, the entire package of "Magazine Battery 2.0" did not catch fire or explode after being shot. After disassembling the battery system casing, the overall structure was intact, with only three battery cells being explosively damaged. After standing for 24 hours, the temperature returned to normal temperature and successfully passed the shooting test.

　　4、 How to ensure and improve the safety of power batteries?

　　Being able to pass rigorous safety tests proves that the safety of power batteries has made remarkable progress today. So, how do battery manufacturers and vehicle manufacturers ensure the safety of power batteries?

　　1. In terms of hardware, from the perspective of power battery structure, it mainly includes cell materials, module design, package design, and passive protection.

　　The first is the selection of battery cell materials. Generally speaking, lithium iron phosphate and lithium titanate have relatively high safety factors, followed by ternary materials, lithium manganese oxide, and lithium cobalt oxide. Taking BYD's "blade battery" as an example, it uses lithium iron phosphate cells, which have the advantage of high temperature resistance and high safety.

　　Next is module design. The safety design of modules is usually based on blocking heat transfer. For example, heat insulation materials with low thermal conductivity and high chemical stability are added in the middle of the cell to prevent heat spread. Currently, the commonly used fire insulation materials include aerogel, mica, fire retardant coating, thermal ceramics, etc. Among them, aerogel is the most ideal material for insulation of electric core. It is not only light in weight and high in strength, but also has 2-5 times the thermal insulation effect of traditional thermal insulation materials.

　　The third is the design of the entire package. When assembling a battery module, a layer of insulation board (usually made of mica sheets) will be adhered to its upper and lower surfaces to prevent thermal runaway. Mica board has high-temperature insulation performance, with a maximum temperature resistance of up to 1000 ℃, and has good cost-effectiveness. In addition, the entire pack design also needs to have corrosion resistance characteristics to ensure sealing and sufficient strength. GAC's "magazine battery" is a super strong thermal insulation safety cabin formed by using mesh nanoporous insulation materials and high-temperature resistant upper shell, achieving thermal runaway of ternary cells without spreading to adjacent cells. The temperature resistance of the upper shell of the battery pack can reach over 1400 ℃.

　　Finally, there are passive protective measures. In addition to the safety effects achieved based on the design of the power battery body, the vehicle body structure can also be used to protect the power battery. For example, adding a protective shell to enhance the impact resistance of the battery, or adding a chassis protective beam to prevent deformation and compression of the power battery, or adding bottom armor to prevent damage to the power battery, etc.

　　2. In terms of software, the battery management system BMS is mainly used to ensure the safety of the escort power battery. During the operation of the power battery, BMS monitors or calculates a series of related parameters such as voltage, temperature, working current, and battery capacity in real-time, which can prevent overcharging or discharging of the power battery. It also monitors the insulation status of the high-voltage system in real-time by measuring the voltage and temperature changes of individual cells collected by internal sensors.

　　In addition, in the daily use of new energy vehicles, it is also necessary for car owners to always pay attention to the safety of power batteries. For example, avoiding prolonged connection between vehicles and charging stations reduces the safety risk of thermal runaway of power batteries caused by overcharging; Try to avoid frequent rapid acceleration or deceleration during driving, as this may cause the power battery temperature to be too high. Once a power battery overheat alarm occurs, the vehicle should be stopped to cool down the battery, and the driving can only continue after the overheat warning light goes out. If the battery overheat alarm or battery failure warning light remains on, professional personnel should be asked to promptly troubleshoot the problem. Non professional personnel are strictly prohibited from disassembling the battery pack on their own to avoid personal injury.

　　Summary: The safety of power batteries is a complex and systematic issue, covering various factors such as battery material selection, manufacturing process, safety testing, and daily use. Under the guidance of relevant national standards, battery manufacturers and vehicle manufacturers have further clarified the safety goals of power batteries. By continuously optimizing battery cell materials, manufacturing processes, and software algorithms, and increasing testing efforts and difficulties, significant progress has been made in power battery safety, and the reliability of new energy vehicle vehicles has also been further improved. As car owners, we cannot ignore the impact of daily use on the safety of power batteries. We suggest that everyone develop good driving habits and work together to create an environmentally friendly, energy-saving, and safe environment for using new energy vehicles.