The Development, current status & Prospect of China power battery Safety Standards
Authors: Ji Ran, Li Hongwei
China Automotive Technology & Research Center, China-Auto Data Co., Ltd.
As the power source of new energy vehicles, the safety of power batteries cannot be ignored. The composition and reaction principle of lithium-ion batteries determine that they have certain dangers during use: the electrolyte mainly uses organic solvents, which are mostly flammable and explosive. If leakage occurs due to external force collisions and other situations, it is very likely to cause fires and explosions, endangering lives in car. During the cycling process, lithium ions are prone to deposit on the electrode surface to form "dendrites". If "dendrites" continue to grow, they may pierce the separator and cause local short circuits, leading to serious consequences such as thermal runaway. Hence China launched a lot rules and regulations per battery development since 2000.
The evolution of China's battery safety standards for new energy vehicles has gone through three stages:
Phase 1: 2006 - 2014
By early 2000, The expert group of China 863 Program's Major Project on Electric Vehicles proposed and established the "Three Verticals and Three Horizontals" technical route, laying the foundation for the development strategy of China's energy-saving and new energy vehicle industry. In 2006, QC/T 743-2006 "Lithium-ion Batteries for Electric Road Vehicles" was released and implemented, providing explanations on the classification, requirements, and testing methods of lithium-ion power batteries. The testing objects of QC/T 743-2006 include single cells and Battery Modules, and it specifies the basic conditions, electrical performance, and safety-related requirements and testing methods for each type of testing object. The safety testing items in the standard include electrical safety (overcharging, overdischarging, short circuit, needle puncture), mechanical safety (drop, crush), and environmental safety (heating), among which the drop test is only applicable to single cells, while the other items need to be tested for both single cells and modules.
QC/T 743-2006 was one of the earliest standards worldwide to address safety requirements for power batteries and was of great significance during the nascent stage of China's new energy vehicle industry. However, as the large-scale promotion of new energy vehicles had not yet been achieved at the time of its release, and the industry lacked practical experience, further improvements were needed.
Phase 2: 2015 - 2019
In 2015, China's production and sales of new energy vehicles-NEV ranked first globally, with a vehicle inventory approaching 600,000 units. China's new energy vehicles entered the industrialization period. Therefore, China simultaneously issued and implemented two standards:
GB/T 31485-2015 "Safety Requirements and Test Methods for Electric Vehicle Power Batteries"
GB/T 31467.3-2015 "Electric Vehicle Lithium-Ion Power Battery Packs and Systems - Part 3: Safety Requirements and Test Methods"
Among them, GB/T 31485-2015 stipulated and explained the safety requirements, test methods, and inspection rules for individual power batteries and modules. The test items for individual batteries and modules were the same, including electrical safety items (overcharging, overdischarging, short circuit, puncture), mechanical safety items (drop, compression), and environmental safety items (seawater immersion, temperature cycling, low pressure, heating) etc.
GB/T 31467.3-2015 was the first national standard specifically targeting the safety of power battery systems. The test items included electrical safety (overcharging, overdischarging, overtemperature, short circuit), mechanical safety (drop, compression, vibration, mechanical impact, overturning, simulated collision), and environmental safety (seawater immersion, temperature shock, wet heat cycling, external fire, salt fog, high altitude) etc. Compared with GB/T 31485-2015, the test items were more comprehensive, and conducting more dimensional and stricter tests on the power battery system was more in line with actual usage scenarios.
Phase 3: 2020 - Present
Based on GB/T 31485 and GB/T 31467.3, China has comprehensively summarized the innovative achievements and practical experiences of the development of China's new energy vehicle industry, and has fully coordinated multiple international standards in related fields. In 2021-1-1, GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles" was released and implemented. This is the first mandatory national standard that covers safety requirements and test methods for individual batteries, modules, and systems of power batteries. It is fully in line with the global regulations on electric vehicle safety of the United Nations (UN GTR 20).
The test objects of GB 38031-2020 include individual batteries, modules, and systems (among which modules are not mandatory tests), and the test items for individual batteries include electrical safety (overcharging, overdischarging, short circuit), mechanical safety (compression), and environmental safety (temperature cycling, heating), while the test items for systems include electrical safety (overcharging, overdischarging, overcurrent, overtemperature, short circuit), mechanical safety (compression, vibration, mechanical impact, simulation collision), and environmental safety (temperature shock, wet heat cycling, salt fog, high altitude, immersion in water, heat diffusion). Compared with the previous version of the standard, GB 38031-2020 further strengthens the safety requirements for the power battery system, which is also in line with the consensus of the industry on the safety requirements of the power battery system:
- To meet the demands of product development, new technologies such as CTP(cell to pack) , CTC(cell to chassis), CTB(cell to body)have emerged in the field of battery power. The original three-level structure of battery power (cell - module - system) has been simplified in practical applications. Therefore, the module safety requirements are no longer mandatory inspection items, and for battery packs or systems that are encapsulated by the vehicle body and form the battery box, box or vehicle body testing can be conducted. The testing objects and methods are more flexible and in line with actual situations, laying the foundation for the compliance and healthy development of new technologies;
- GB 38031 focuses on the safety issues during the use of battery power. Therefore, in the setting of test items, safety test items for other aspects such as production, transportation, maintenance, and recycling of battery power (such as drop test, low pressure test, etc.) have been removed, and new test items such as overcurrent and temperature shock that are more in line with the scenarios prone to failure in actual use have been added;
- In response to the frequent occurrence of thermal runaway problems that cause battery fires and endanger the personal safety of passengers in recent years, GB 38031-2020 has added the thermal diffusion test of battery power system, and has adjusted the controversial puncture test in recent years to one of the ways to trigger thermal diffusion. It requires that the battery power system should provide an alarm signal 5 minutes before the passenger cabin is endangered due to thermal diffusion, in order to more comprehensively and effectively evaluate the safety of the battery power system.
Prospects for China power Battery Safety Standards development:
- Safety requirements over the battery life cycle:
With the rapid development of the new energy vehicle industry, the technological progress of battery products has accelerated, and their performance such as energy density and cycle life have significantly improved. The life cycle of battery cells has gradually extended. Currently, the safety standards and related testing procedures for battery cells in their initial stage are mainly applicable. However, studies have shown that the decomposition temperature of the SEI film in lithium-ion batteries decreases with the increase in the number of cycles, and the thermal stability of battery cells gradually declines [1]. Therefore, from the perspective of the entire life cycle, the middle and later stages may be the "peak period" for thermal runaway reactions of battery cells, and special prevention and control measures are needed. To better enhance the safety of battery cells, it is necessary to formulate scientific, reasonable and feasible safety standards for battery cells throughout their entire life cycle.
- Criteria for determining the results by quantitative tests
Based on the provisions in GB 38031-2020 after the battery test, the status is only defined as leakage (the phenomenon where visible substances leak out from the battery cell, module battery pack or system to the outside of the test object), shell rupture (mechanical damage to the battery cell, module, battery pack or system shell due to internal or external factors, resulting in the exposure or overflow of internal substances), fire (continuous burning in any part of the battery cell, module, battery pack or system (single flame duration greater than 1 second). Spark and arc do not belong to combustion), and explosion (sudden release of sufficient energy to generate pressure waves or projectiles, which may cause structural or physical damage to the surrounding area). These definitions and descriptions are relatively broad vague and mostly rely on subjective judgment through visual observation, lacking quantifiable determination criteria. In contrast, foreign standards provide more detailed descriptions for the evaluation of test results, introducing more parameters to make the result determination more rigorous. For example, IEC 62660 divides the test results into 8 grades, and provides more detailed descriptions of the phenomena after each grade of testing; UL1642 and UN38.3 introduce the battery shell temperature as an indicator in the requirements for external short-circuit tests, which can effectively quantify and compare the test results.
Conclusion:
The power batteries safety is the foundation for NEV industry sustained and healthy development. The safety standard system for power batteries in China has undergone development over more than a decade, with more comprehensive testing items and ones that are more in line with actual operating conditions. With the advancement of technology and the continuous accumulation of practical experience, the system safety of power batteries has become an industry consensus. Looking to the future, the requirements for the full life cycle safety and the quantification of test results determination basis are expected to become the next development direction of the power battery safety standards.
https://leva-eu.com/china-introduces-worlds-first-ev-battery-safety-law-requiring-fire-prevention/