In recent years, lithium-ion battery energy storage systems have become increasingly prevalent in the global power industry, thanks to their notable advantages, including high energy density, large discharge rates, and cost reduction. This article conducts a systematic analysis and comparison of the specific safety requirements outlined in UL, IEC, and Chinese national standards for lithium-ion batteries used in major energy storage systems. By examining the strengths and weaknesses of each standard, the article aims to propose recommendations for enhancing and upgrading safety standards in new storage systems.
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1 Background of Safety Standards in China, US, EU
Lithium-ion battery energy storage systems are gaining widespread adoption in the global power industry due to their high energy density, rapid discharge rates, and cost-effectiveness. This article systematically analyzes and compares safety standards for lithium-ion battery systems from China, the US (represented by UL), and the EU (represented by IEC). Through a detailed examination of specific requirements, the article aims to identify the strengths and weaknesses of each standard and offer recommendations for enhancing safety standards in emerging energy storage systems. This analysis provides valuable insights for improving system safety standards across different regions.
2 Characteristics of Energy Storage System Safety Standards: China, US, EU
International Standards: Energy storage system safety standards are primarily overseen by international organizations such as the International Electrotechnical Commission (IEC) and Underwriters Laboratories (UL). In Europe and Japan, safety regulations often align with IEC standards, with standards like EN 62619 and JIS C 8715-2 directly derived from IEC 62619. In North America, UL standards are widely adopted due to their comprehensive and strict battery safety criteria. Australia takes a dual approach, incorporating both UL and IEC standards, with ongoing development reflected in the AS/NZS 5139 draft. South Korea introduced its energy storage standards in 2015, drawing primarily from IEC standards but with notable modifications to meet local requirements.
Chinese Domestic Standards: National energy storage standards within countries are usually led by power-related authorities. While the process of setting standards is thorough, the specifications often allow for some flexibility, serving as minimum safety requirements. Several industry group standards have surfaced, including those from the China Electricity Council (CEC), China Energy Storage Alliance (CNESA), and China Industrial Association of Power Sources (CIPAS), demonstrating diverse approaches tailored to domestic contexts.
Lithium Battery Transportation Safety: For lithium battery transportation safety, the UN 38.3 standard establishes stringent tests that simulate transportation conditions. These tests encompass height simulation, thermal, vibration, and impact tests, among others, guaranteeing safety throughout the transportation process. Adopted worldwide, this standard plays a critical role in ensuring the secure transport of lithium batteries. Similarly, IEC 62281 mirrors UN 38.3 in test items, although it differs in sample numbers and charged state requirements.
2.1 IEC Safety Standards For Energy Storage Systems
IEC safety standards for energy storage system products are primarily developed and disseminated by the International Electrotechnical Commission (IEC) Standards Working Groups TC21/SC21A and TC120. TC21/SC21A focuses on safety standards for all secondary batteries, while TC120 focuses on electrochemical energy storage for grid applications (EES) system-related standards. The main safety standards for IEC energy storage systems include:
- IEC 62619: Outlines safety requirements for secondary lithium cells and batteries used in industrial applications. This standard serves as an umbrella covering various industrial uses, such as communication base stations, UPS systems, and maritime transportation.
- IEC 62485-5: Focuses on the safe operation of stationary lithium-ion batteries, ensuring operational safety in stationary applications.
- IEC 62933-5-1: Addresses safety considerations for grid-integrated EES systems, providing general specifications for grid-integrated energy storage systems.
- IEC 62933-5-2: Specifies safety requirements for grid-integrated EES systems with electrochemical-based systems, ensuring system safety during integration into the power grid.
- IEC 63056: Specifies safety requirements for secondary lithium batteries and battery packs in energy storage systems, particularly those with DC rated voltage below 1500V.
- IEC 62281: Outlines safety requirements for primary and secondary lithium cells and batteries during transportation, ensuring safe transportation of lithium batteries.
IEC 62619 serves as a foundational standard, encompassing common test items and minimum safety requirements for secondary lithium batteries in industrial applications. Additional standards like IEC 63056 and IEC 62485-5 focus on specific applications and operational safety aspects.
While IEC energy storage safety standards offer comprehensive guidelines, complexities arise due to the involvement of diverse organizations and members, leading to disputes over national interests and slower progress compared to industry development. Despite the release of standards like IEC 62619 and IEC 62281, ongoing preparations for other safety standards are underway to address emerging energy storage system needs.
2.2 UL Safety Standards for Energy Storage Systems
UL (Underwriters Laboratories Inc.) Safety Laboratory stands as the foremost authoritative, independent, for-profit organization dedicated to safety testing and identification in the United States. Its key safety standards for electrochemical energy storage include:
- UL 1973: Standard for Safety for Batteries for Use in Stationary, Vehicle Auxiliary Power, and Light Electric Rail (LER) Applications. This standard addresses battery systems for stationary energy storage applications such as photovoltaics, wind power storage, UPS, and stationary railway substations. Similar to IEC 62619, it outlines common safety requirements for various battery types, including lithium-ion, sodium-β, and flow batteries. The 2019 revision of UL 1973 details safety-related requirements and test methods, covering structural, electrical, mechanical, environmental, cell failure, and production line testing.
- UL 9540: Standard for Energy Storage Systems and Equipment. This safety standard encompasses a wide range of energy storage technologies, including electrochemical, mechanical, and thermal storage systems. It covers various aspects such as charge and discharge systems, control and protection systems, power conversion systems, communication, heating and cooling management, fire protection, and system installations.
- UL 9540A: Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems. UL 9540A specifically evaluates the thermal runaway characteristics and fire protection mechanisms of battery energy storage systems, aiding in system design and fire safety.
UL energy storage safety standards are known for their comprehensiveness, specificity, and maturity, serving as robust benchmarks for product safety in the industry.
2.3 China Safety Standards For Energy Storage System Products
In contrast to the delineation in IEC and UL standards, China’s national standards do not segregate safety standards for energy storage systems into standalone documents but incorporate them within chapters of technical specifications or operation management guidelines. The following national standards encompass safety requirements for lithium battery energy storage systems:
- GB/T 34131: Technical Specifications for Lithium-Ion Battery Management Systems for Electrochemical Energy Storage Power Stations
- GB/T 36276: Lithium-Ion Batteries for Electric Energy Storage
- GB/T 36547: Technical Regulations for Connecting Electrochemical Energy Storage Systems to the Power Grid
- GB/T 36548: Test Specifications for Electrochemical Energy Storage Systems Connected to the Power Grid
- GB/T 36558: General Technical Conditions for Electrochemical Energy Storage Systems in Power Systems
- GB/T 36549: Operation Indicators and Evaluation of Electrochemical Energy Storage Power Stations
- GB/T 51048: Design Specifications for Electrochemical Energy Storage Power Stations
Primarily, GB/T 34131, GB/T 36276, and GB/T 36558 stand out as standards related to battery system safety. These standards establish common terminology, symbols, test items, and methods within the functional energy storage industry, significantly influencing the domestic energy storage sector. Safety tests encompass a wide range of scenarios including overcharge, over-discharge, external short-circuit, physical stress, and environmental factors like temperature and humidity.
Industry alliances such as the National Energy Administration’s Energy Industry, China Electricity Council (CEC), Zhongguancun Energy Storage Industry Technology Alliance (CNESA), and China Chemical and Physical Power Industry Association (CIPAS) have also issued industry (group) standards alongside national standards, including:
- NB/T 42091: Technical Specifications for Lithium-Ion Batteries for Electrochemical Energy Storage Power Stations
- TCIAPS0003: Safety Requirements for Secondary Lithium-Ion Single Cells and Battery Systems Used in Power Energy Storage Systems
- T/CEC 172: Safety Requirements and Test Methods for Lithium-Ion Batteries for Electric Energy Storage
- T/CNESA 1000: Electrochemical Energy Storage System Evaluation Specification
- T/CNESA 1001: General Technical Requirements for DC Power Connectors for Electric Energy Storage
- T/CNESA 1002: Technical Specifications for Battery Management Systems for Electrochemical Energy Storage Systems
These standards, while diverse in origin and focus, collectively contribute to bolstering the safety and reliability of energy storage systems within China’s rapidly evolving energy landscape.
3 Comparative Analysis: Lithium-Ion Battery Safety Standards in China, US, EU
Safety considerations in energy storage systems extend beyond batteries to encompass external integrated components like the Power Conversion System (PCS). However, due to significant variations in global grid access requirements, direct comparisons in this area are impractical. Therefore, this study focuses on common safety standards for lithium-ion battery systems, including UL 1973, IEC 62619, GB/T 36276, and GB/T 34131. This article excludes considerations regarding the interface between energy storage and the grid, particularly the connection between PCS and the grid, and instead examines safety standards relevant to lithium-ion battery systems.
To facilitate comparison, these standards are categorized into four aspects: structural safety, battery safety, system safety, and environmental safety, with UL standards as the reference point. The subsequent table presents a comparative analysis of UL, IEC, and GB safety standards for lithium-ion battery systems, with a focus on structural requirements.
3.1 Comparison of structural safety requirements
UL 1973 provides detailed specifications for product enclosures, including non-metallic and metal enclosures, wall-mounted brackets/handles, cables, and terminals. In contrast, IEC and GB standards focus on ensuring the enclosure remains intact during tests, without specific requirements for these components. UL also standardizes protective grounding, which is not detailed in IEC and GB standards, potentially leading to oversight in inspections.
Here’s a condensed version of the comparison of lithium-ion battery safety requirements for UL, IEC, and GB standards:
This summary provides a concise overview of the battery safety requirements outlined by UL, IEC, and GB standards.
3.2 Comparison of battery safety requirements
Comparison of battery safety requirements involves test specifications directly related to the battery, such as overcharge and overdischarge tests. National standards delineate test requirements and methods for battery cells, modules, and clusters (systems). UL and IEC designate the test objects for each test, with minimal disparities in battery safety requisites. UL’s standards typically set rigorous qualifications, demanding no fire, explosion, leakage, toxic gas accumulation, exposed electric shock hazards, or loss of control post-testing. Temperature-related safety mandates vary among standards. UL’s temperature tests ensure conditions remain within specified limits, with accessible surface temperatures not surpassing safety thresholds. In contrast, IEC and GB standards focus on thermal abuse, with GB specifying higher test temperatures. UL includes unbalanced charging tests for battery modules, lacking in IEC and GB standards. Drop tests in UL and IEC are weight-based classifications, while GB employs a uniform free-fall method. All standards address thermal runaway diffusion, with IEC providing a battery core short-circuit test alternative.
In the US, UL 9540A evaluates thermal runaway characteristics in battery energy storage systems, aiding in selecting fire and explosion protection mechanisms. This standard assists suppliers in clarifying isolation requirements, calorific value, combustible components, gas types produced by combustion, and fire extinguisher selection. Comparable standards have yet to be developed by IEC and GB.
This summary highlights the environmental impact requirements outlined by UL, IEC, and GB standards for lithium-ion battery systems.
3.3 Comparison of environmental impact requirements
Comparison of environmental impact requirements reveals differences in mandated tests across UL, GB, and IEC standards. UL standards prescribe environmental tests such as salt spray, moisture-proof, and external fire tests. In contrast, GB standards require the salt spray test and high temperature and high humidity test. Notably, these tests are tailored to specific product application environments and are not obligatory. IEC 62619 does not incorporate environmental testing, likely due to its universal scope, while the forthcoming IEC 62485-5 may include such provisions, although it remains uncertain.
Regarding electromagnetic compatibility, the national standard outlines test items and levels in the BMS technical specification GB/T 34131. UL and IEC standards mandate functional safety analysis for control systems crucial for safety, encompassing electricity, circuits, and software, including BMS tests. Additionally, IEC 60730-1 Appendix H, a reference standard in both UL and IEC, encompasses more electromagnetic compatibility test items and methods compared to the national standard. The testing method focuses on evaluating various controller modes (BMS falls under the electronic controller category) to assess their impact on the safety of controlled equipment.
Here’s a condensed version of the comparison of lithium-ion battery safety standards for system requirements under UL, IEC, and GB standards:
This summary provides an overview of the system requirements outlined by UL, IEC, and GB standards for lithium-ion battery systems.
3.4 Comparison of system requirements
Both UL and IEC mandate functional safety assessments of electronic circuit software for system safety analysis. UL goes further by requiring a risk analysis of the system and the provision of reports such as FMEA or fault tree analysis, facilitating the investigation of various risks like electric shock, fire hazards, and mechanical risks, aiming to control risks to a sufficiently low probability. However, the GB standard does not specifically address this aspect. Regarding system component safety, the UL standard specifies the standards and specifications that key components must adhere to, whereas the IEC and GB standards do not have direct requirements in this regard.
4 Conclusion
In conclusion, this article provides a thorough exploration of lithium-ion battery safety standards for major energy storage systems worldwide, offering a comprehensive comparison of their similarities, differences, strengths, and weaknesses. It highlights that while IEC standards are well-designed, their progress is hindered by a slower pace. Conversely, UL standards are detailed and exhaustive, necessitating stringent compliance verification during implementation. Domestic standards, influenced by both national and IEC standards, are developed by various industry groups, resulting in diverse organizational structures and implementation complexities.
Concerning lithium battery energy storage systems in China, several areas for improvement are identified:
- The national standard lacks a comprehensive system-level safety assessment, including system risk identification and assessment, BMS functional safety assessment, and integration of BMS into the overall system evaluation.
- There is a deficiency in detailed specifications or clear guidance for critical components such as enclosures, protective grounding, terminals, cables, and documentation information.
The article suggests several measures for enhancement, including:
- Separating safety-related standards from functional performance standards.
- Implementing relevant certification for safety standards.
- Establishing mandatory regulations for product access to foster fair competition and industry development in China’s energy storage sector.