Are Current Battery Safety Standards Ready for the Solid-State Revolution?

Solid-state batteries (SSBs) are hailed as the revolutionary next step in energy storage technology because of their potentially superior performance compared with conventional liquid-solvent-based electrolyte counterparts. SSBs are noted for their advantages in energy density, with a 2-4-fold increase depending on the cathode when paired with a pure lithium metal anode; cycle life, up to 10 times more cycles; charging time, up to 4 times faster; and operating temperature range, -30°C to 80°C compared with 0°C to 45°C [1,2]. Some also promote them as being intrinsically safe due to the lack of a flammable liquid electrolyte and have repeatedly passed nail penetration tests. However, independent research is beginning to highlight the thermal runaway hazards of SSBs, raising the question of whether current safety standards are equipped to address them.

In theory, SSBs have a lower probability of thermal runaway compared to lithium-ion alternatives. This is primarily attributed to their electrolyte having elevated activation temperatures (see table below for comparison) and the absence of flammable liquid electrolytes, which typically drive hazardous exothermic reactions. However, due to the use of lithium metal anodes, SSBs will contain significantly more lithium than traditional Li-ion batteries and therefore the severity of thermal runaway can be much greater, especially if all the lithium reacts [3]. As such, safety will have to be proven at a system level for the desired application.

Noted hazards of SSB thermal runaway include, as reviewed by [4], short-circuit failures triggering significantly higher temperature spikes, with potential reactions between the solid-state electrolyte and the cathode proving up to ten times more severe than those involving solvent-based electrolytes. These conditions can accelerate cell thermal runaway by a factor of 100, resulting in overpressures that compromise the integrity of the entire battery pack, while simultaneously causing cell-to-cell propagation to occur five times faster and releasing hazardous toxic gases. However, these substantial safety risks may be effectively mitigated through targeted design adaptations.

A real-world illustration of these mechanisms occurred in 2022, when two EV buses powered by Lithium Metal Polymer (LMP) batteries, with similar characteristics to SSBs, erupted in flames and emitted large amounts of molten lithium [5]. Following a root case analysis, BEA-TT determined that insulation sheets between cells were incorrectly positioned during manufacture, and therefore could not guarantee sufficient insulation between the cells, leading to an inter-cell short-circuit triggering thermal runaway.

With the similarities of these cells to SSB, the French National Institute for Industrial Environment and Risks (Ineris) assessed the performance of the LMP EV bus batteries against the R100 regulation propagation test [4]. Testing one of the LMP modules, constructed of an electrochemical bipolar cell stack housed within an air-tight aluminium casing filled with nitrogen, under standard localised heating conditions (600W), the cell remained stable – successfully passing the R100 criteria. This is attributed to the larger heat dissipation ability of the aluminium casing and the insulation of the electrochemical material from the housing by the nitrogen-filled void and electrical insulation. However, under high power heating (3.3kW), the module underwent thermal runaway, reaching 1000°C.

To analyse this further, the authors had the battery manufacturer construct unit cell LMP cells within a pouch cell form. In this scenario, under 600W heating, an increase in temperature rate was seen at 796°C, resulting in a rapid reaction culminating in a maximum temperature of 1200°C and the release of projectile lithium metal. If this behaviour were caused by a short, it is easy to understand how thermal runaway can progress so rapidly. However, additional nail penetration tests were undertaken on the custom-made pouch cell, which did not result in thermal runaway. These tests highlight how existing testing frameworks may prove inadequate for detecting the novel hazards intrinsic to technologies like SSBs.

Given these emerging risks, the adequacy of current safety standards becomes a pressing question. Several international bodies, such as Underwriters Laboratories, the International Organisation for Standards and the International Electrotechnical Commission, have established standards for battery safety of current technologies, including solvent-based Li-ion. Even across this rigorous body of standards, none currently address the specific hazards of SSBs. However, standardisation organisations are beginning to fill the SSB standards void.

China has issued the first draft SSB standard “GB/T Solid-State Battery for electric vehicle – Part 1: Terms and Classification”, the first of 4 parts to also cover performance, safety and service life [6,7]. Part 1 aims to clarify the core technical definitions and categorisation of SSBs. The main classifications include:

• Ion transfer methods: liquid, hybrid solid–liquid or solid-state electrolyte

• Solid electrolyte type: sulphide, oxide, polymer, halide or composite

• Ions conducted: lithium or sodium

• Fields: high energy or high power

The draft also addresses methods to verify the absence of liquid electrolyte components by ensuring that the mass loss rate of an SSB battery product is less than 0.5%. The China Automotive Technology and Research Center (CATARC) is expected to have reviewed the draft presented for public consultation and released the official version by July 2026 [8].

On the other side of the Pacific Ocean, the Underwriters Laboratory Standards & Engagement organisation is developing two standards in relation to SSBs: the “Standard for Performance and Reliability of Solid-State Batteries, UL 2286”; and “Standard for Safety for Solid-State Batteries, UL 2285” [9,10]. The former, UL 2286, is designed to provide battery manufacturers with explicit guidance to qualify the performance and reliability of secondary solid-state batteries, thereby confirming performance expectations for consumers and accelerating commercial innovation. Conversely, UL 2285 addresses a critical regulatory gap; current safety standards (such as UL 1642 and UL 2580) are built around liquid-electrolyte lithium-ion technology and fail to account for the unique architecture, degradation pathways, and distinct hazard profiles of SSBs. By establishing technology-neutral test methods and hazard mitigation criteria tailored to solid-state systems, UL 2285 aims to ensure safety tests remain effective while fostering consumer and regulatory confidence. Both joint US-Canadian standards will streamline regional compliance and establish a collaborative forum for a wide range of stakeholders—spanning manufacturers, end-users, and first responders—to continuously adapt safety and performance requirements as the technology evolves.

In short, SSBs are likely to be less prone to entering thermal runaway than their liquid-electrolyte counterparts, but when they do fail, the consequences can be far more severe, largely because of the substantial reactive potential locked up in their lithium-metal anodes. Current regulatory testing frameworks, designed for conventional lithium-ion technologies, often fail to detect these unique hazard profiles, highlighting the urgent need for a shift in focus toward comprehensive system-level safety assessment rather than isolated cell-level performance. New standardisation efforts, such as the upcoming Chinese GB/T standards and the joint US-Canadian UL 2285 and UL 2286 initiatives, are critical to bridging this gap by establishing technology-neutral, adaptive safety protocols that can evolve alongside these disruptive materials. Ultimately, proactive collaboration between regulators, academics, and manufacturers to refine these standards is essential to mitigate uncontrolled risks and ensure the safe, reliable industrialisation of next-generation energy storage.