No fire or explosion after thermal diffusion! Public comments on the national mandatory standard for power batteries

On May 27, the official website of the Ministry of Industry and Information Technology issued a document, publicly soliciting opinions on five mandatory national standards, including the "Safety Requirements for Power Batteries for Electric Vehicles" (hereinafter referred to as the "new power battery standards"). The deadline for soliciting opinions is July 27, 2024.

Its compilation instructions show that the new power battery standard will replace GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles", thereby further improving the safety requirements for power batteries, building a solid bottom line for power battery safety, and safeguarding the safety of consumers' lives and property.

This means that the safety requirements for power batteries will be further improved than before. Among them, the most concerned issue in the industry is that when power batteries undergo thermal diffusion under certain conditions, they will not catch fire or explode, which will become a new mandatory standard for power batteries.

According to the information, this time the Electric Vehicle Sub-Technical Committee of the National Technical Committee for Standardization of Automobiles (hereinafter referred to as the "Electric Vehicle Sub-Technical Committee") is responsible for organizing and carrying out the revision of relevant standards. The standard drafting group is led by Contemporary Amperex Technology Co., Ltd. and covers electric vehicle manufacturers, power battery companies, third-party testing agencies, scientific research institutes and other companies/institutions.

The new power battery standard stipulates the scope of application, safety requirements, test methods and other details of power batteries for electric vehicles.

The scope of application is clearly defined as power batteries, excluding batteries that do not provide power for electric vehicles, such as 12V low-voltage auxiliary power supplies. In addition, considering the development of industry technology, the scope of the standard should be able to cover new power batteries such as sodium-ion batteries and lithium metal batteries.

Compared with GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles", the new power battery standard has made new requirements for major technical standards in terms of temperature shock test, salt spray test, battery system protection test, battery pack or system extrusion test, external fire test, thermal diffusion analysis and verification, battery cell safety after charging, and battery pack or system bottom protection.

Among them, the power battery thermal diffusion analysis and verification details show that in terms of safety requirements, based on the industry consensus that the scope of thermal diffusion protection has been expanded from occupant safety to property safety, the power battery safety standard special research group discussed and decided to further improve the thermal diffusion requirements to "no fire, no explosion."

Statistics on the technical reserves of "no fire, no explosion" for power battery thermal diffusion in enterprises

Data source: Preparation instructions for the "Safety Requirements for Power Batteries for Electric Vehicles" (Draft for Comments)

It is worth noting that feedback from industry-related survey questionnaires shows that as of February 2024, 78% of companies have already possessed the technical reserves for "no fire and no explosion" (when power batteries diffuse thermally). Based on the above situation, the Power Battery Safety Standards Research Group unanimously believes that it is technically feasible to raise the thermal diffusion requirements to "no fire and no explosion".

The safety test methods for battery cells include: over-discharge, over-charge, external short circuit, heating, temperature cycle, extrusion, safety after fast cycle, etc.; the safety test methods for battery packs or systems include: vibration, mechanical shock, simulated collision, extrusion, wet heat cycle, immersion in water, thermal stability (including external fire, thermal diffusion), temperature shock, salt spray, high altitude, over-temperature protection, over-current protection, external short circuit protection, over-charge protection, over-discharge protection, bottom impact, etc.

Among them, the purpose of thermal diffusion analysis and verification is mainly to protect the safety of passengers and property. Therefore, the new standard for power batteries stipulates that the battery pack or system should not catch fire or explode after a thermal runaway caused by an internal short circuit in a single battery, and provide a thermal event alarm signal no later than 5 minutes after the thermal runaway occurs, and no visible smoke enters the passenger compartment before the thermal event alarm signal is issued and within 5 minutes after the thermal event alarm signal is issued.

In terms of verification methods, the new power battery standard recommends that manufacturers adopt three test methods to trigger thermal runaway, including needle puncture, external heating, and internal heating. Manufacturers can also choose other methods to trigger thermal runaway.

The new standard for power batteries recommends the following conditions for triggering thermal runaway: a) The trigger object generates a voltage drop, and the drop value exceeds 25% of the initial voltage; b) The temperature at the monitoring point reaches the maximum operating temperature specified by the manufacturer; c) The temperature rise rate dT/dt at the monitoring point is ≥1 ℃/s and lasts for more than 3 s. When a) and c) or b) and c) occur, thermal runaway is determined to have occurred.

The new power battery standard also stipulates: If the recommended method is used as the thermal runaway trigger method and thermal runaway does not occur, it is necessary to prove that thermal runaway will not occur using the above three recommended methods. After triggering the thermal runaway of the battery cell, observe at least 2 hours at the test environment temperature, and the temperature of all monitoring points is not higher than 60 ℃, and then end the test.

This means that during the test, if the manufacturer fails to trigger thermal runaway using any of the three recommended triggering methods, the battery product is considered unable to trigger thermal runaway and the test passes.

When thermal runaway is triggered, it is necessary to observe: the battery pack or system does not catch fire or explode, and a thermal event alarm signal is provided no later than 5 minutes after the occurrence of thermal runaway, and no visible smoke enters the passenger compartment before and within 5 minutes after the thermal event alarm signal is issued, the battery pack or system is judged to have passed the test; if any of the following situations occurs: fire, explosion, failure to issue an alarm within 5 minutes, or smoke enters the passenger compartment within 5 minutes before and after the alarm is issued, the test is judged to have failed.

Industry insiders believe that "safety is the highest luxury of electric vehicles", and the new power battery standard will undoubtedly further safeguard the safety of electric vehicles, while also putting forward more stringent safety standards for battery companies. In fact, leading battery companies including CATL, BYD, EVE Energy, Guoxuan High-tech, Xinwanda, Lishen Battery, Ruipu Lanjun, and Zhengli New Energy have already applied or possessed the "no fire, no explosion" technology and capabilities.

It is worth mentioning that the scope of application of the new power battery standard not only covers lithium batteries, but also includes new power batteries such as sodium batteries. It will further improve the safety technology level of my country's power batteries and lead the global power battery safety standards.