Towards the harmonization of safety testing standards for lithium-ion batteries: A review and call to action

Rechargeable batteries have become an indispensable component of modern technology, serving as the primary energy source for applications ranging from consumer electronics to electric vehicles (EVs) and large-scale energy storage systems (ESS). Lithium-ion batteries (LIBs), in particular, dominate the market due to their high energy density and efficiency [1,2]. However, the increasing reliance on LIBs has brought their safety and reliability to the forefront. Thermal behavior and the risk of thermal runaway (TR) represent significant safety concerns, as even a single cell failure can trigger fires or explosions that propagate through battery packs. Ensuring battery safety across all use cases has thus become paramount. Despite numerous existing standards and testing protocols [3], the landscape of battery safety evaluation remains fragmented and inconsistent [4]. Different organizations and regions have developed their own methodologies, leading to a patchwork of guidelines that often use divergent procedures and criteria [5]. This lack of a unified framework for testing and evaluation poses a challenge, a battery deemed “safe” under one set of test conditions might behave unpredictably under another set used elsewhere. In practice, such inconsistencies undermine the comparability of results and can obscure true safety margins [6]. This review analyzes the current state of LIB safety testing protocols, identifies critical gaps caused by these inconsistencies, and proposes a framework for moving toward standardized, harmonized testing methods to enhance battery safety worldwide.

LIBs are central to multiple industries, each requiring tailored energy storage solutions. For instance, grid storage prioritizes long cycle life and energy capacity, while EVs and electric aircraft demand high power output and rapid charging capabilities. These application-specific requirements underscore the need for optimized battery performance, reliability, and safety [7]. The yellow section (in Fig. 1) focuses on industrial applications of LIBs, such as power tools, robotics, and remote sensing equipment. These sectors require batteries capable of withstanding high mechanical stress, temperature fluctuations, and prolonged heavy-duty use, further emphasizing the need for rigorous safety measures. The blue section in Fig. 1 shows the use of LIBs in ESS, such as home energy storage, grid backup, and telecommunications [8]. These energy solutions are vital for stabilizing renewable energy sources, demonstrating how LIBs contribute to the global transition toward sustainable energy. Furthermore, the green and red sections represent a diverse array of LIB applications, from consumer electronics, such as smartphones, wearables, and critical medical devices, to transportation systems, including EVs, aircraft, and bicycles [[9], [10], [11], [12], [13], [14]]. The wide-ranging utility of LIBs across these sectors highlights their versatility and importance in modern industries. However, as LIBs power everything from personal devices to electric aircraft, ensuring their safety, particularly in terms of thermal behavior and preventing TR, becomes a paramount concern. This extensive range of applications illustrates the adaptability of LIB technology and the varying safety requirements for each industry. Whether it is the high-power and high-energy demands of EVs or the operational consistency required in medical devices, the need for standardized testing protocols that ensure the reliability and safety of LIBs across these diverse applications is evident. Consequently, the introduction of universally accepted testing standards will play a crucial role in ensuring that LIBs continue to drive technological innovation while maintaining the highest levels of safety.

Safety concerns related to thermal behavior and TR pose significant challenges to the reliable and widespread use of LIBs [[15], [16], [17]]. Addressing these risks is essential to fully realize the potential of LIBs for modern technological and environmental advancements [18,19]. TR is a hazardous condition where an increase in temperature causes a reaction that further increases temperature, potentially leading to fires or explosions [20]. This phenomenon can be triggered by various events, such as overcharging, physical damage, internal short circuits (ISC), or high ambient temperatures [[21], [22], [23]]. The consequences of TR are severe, as evidenced by numerous incidents of battery fires in consumer electronics and EVs [24]. These incidents highlight the critical need for robust safety measures to prevent TR and ensure the safe operation of rechargeable batteries. Recent studies stress the importance of addressing these safety concerns. For example, research by Wang et al. [25] demonstrates that improving thermal management systems and incorporating advanced materials can significantly enhance the thermal stability of LIBs. These advancements help mitigate the risks of TR by effectively dissipating heat and maintaining stable temperatures during operation. Additionally, the development of solid-state batteries, which use solid electrolytes instead of flammable liquid electrolytes, represents a promising avenue for enhancing battery safety by reducing the risk of TR [25].

On the other hand, the benefits of LIBs outweigh their safety risks, especially given the advancements in safety technologies. While it is true that significant progress [25] has been made in improving battery safety, the risks associated with TR remain substantial and cannot be ignored. Incidents involving battery fires have severe implications for public safety and consumer confidence, necessitating continuous improvement and vigilance in safety measures. It is essential to recognize that ensuring the safety of rechargeable batteries is not an impediment but a crucial enabler of their broader adoption and acceptance. By addressing safety concerns comprehensively, we can build public trust and confidence in battery technologies, paving the way for their integration into more critical and widespread applications [26].

The absence of uniform testing methods for assessing the safety of LIBs presents a significant challenge, undermining the reliability and comparability of safety assessments across laboratories and industries. This inconsistency poses substantial risks, as batteries that meet safety criteria in one region may fail in another, potentially endangering consumers and affecting industries heavily reliant on rechargeable batteries. As illustrated in Fig. 2(a), the substantial increase in LIB demand from 2010 to 2030, coupled with declining prices, projects a growing need for standardized safety testing. The projected sector-wise breakdown in Fig. 2(b) further emphasizes this need, with EVs and stationary energy storage expected to lead the demand. However, current testing protocols vary significantly due to inconsistent heating rates, ambient conditions, and preconditioning methods, leading to variability in the onset and progression of TR events. For instance, studies by Lopez et al. [27] and Lamb et al. [28] highlight how these inconsistencies complicate the development of reliable safety benchmarks, while Ren et al. [29] demonstrated that overcharge tests yield different results under varying conditions. These discrepancies not only increase safety risks but also hinder international trade, regulatory effectiveness, and innovation [30,31].

This diversity in application contexts means that LIB safety testing must cover a wide range of scenarios, from extreme cold and heat, to physical impacts, to electrical abuse, to ensure batteries are safe in all envisaged conditions. Fragmented standards make it difficult for manufacturers and regulators to ensure that a battery tested in one context will perform safely in another. A globally harmonized approach to safety testing would help guarantee that, regardless of where or how a battery is used, it has been vetted against a comprehensive set of abuse conditions.

In the following sections, we review how LIBs behave thermally (including the mechanisms of TR) and survey the current testing methods used to induce and evaluate failures. We highlight the variations in mechanical, electrical, thermal, and chemical abuse tests employed by different standards and laboratories. We then examine existing industry standards and regulations to illustrate the gaps and overlaps in their coverage of safety scenarios. Notable case studies of battery failures in real-world devices are discussed to underscore why consistent testing is crucial. We also describe examples of effective safety protocols and diagnostic techniques that have improved outcomes. Finally, we provide recommendations for establishing unified testing standards. Rather than introducing prescriptive numeric criteria that lack broad validation, we advocate for a consensus-driven process to define test parameters, supported by collaborative research and gradual implementation. By addressing the current fragmentation with a unified framework, the industry can better mitigate safety risks while still encouraging innovation in battery technology.