The safety of lithium-ion batteries is a recurring topic. How safe are they in your view?
 

Schopferer: Lithium-ion batteries have become significantly safer over the past years supported by increasingly stringent regulatory requirements. A prime example is the propagation time in electric vehicles.
China’s updated standard GB 38031-2025 has significantly tightened safety regulations for EV batteries. Even after a severe internal defect such as a cell short circuit, batteries must neither catch fire nor explode—for at least 120 minutes. This is a 24-fold increase of the time limit compared to the old standard, ensuring there is sufficient time for occupant evacuation and emergency response—even in difficult rescue or accident scenarios. The new standard also mandates numerous new tests, such as the thermal propagation test. This test evaluates thermal runaway across an entire battery pack, requiring the entire system to withstand the conditions.

Schaufelberger: Manufacturers have made substantial progress in recent years to make batteries safer. This includes, for example, improved separators between the cells, fire-retardant materials, smart electronics with early shut down capabilities, and more robust casings and cooling systems
 

Safety requirements have increased for manufacturers across various industries. What are the current challenges?
 

Schopferer: Strict safety requirements are a concern for all manufacturers, especially since they sometimes conflict with other performance goals. In the automotive sector, for example, OEMs want batteries that are not only safer but also more powerful to extend driving range. Higher range typically requires higher energy density- which initially conflicts with safety and demands innovative development approaches.

In aviation, electric flight—or hybrid-electric flight—is gaining importance. Here, a significant increase in energy density, and thus, reduction in battery weight, is the decisive factor.

In the defense sector, lithium-ion batteries could be of interest for powering onboard systems. However, a prerequisite here as well is that the amount of energy increases. Only this can ensure that the onboard systems can operate autonomously over a long period of time. At the same time, the vehicles are exposed to very high risks, which place entirely different demands on battery safety.

What contribution does EMI’s research make?
 

Schaufelberger: We don’t focus on standard testing—like lifecycle tests or behavior in hot or cold conditions. For us, it gets interesting when we enter the abuse range—such as during a crash or thermal runaway event. For model development, we need to understand the processes well enough to develop physics-based simulation models. Given the diverse range of multi-physical processes, this is a particular challenge. That is why we are currently focusing on two aspects that we consider: mechanically induced short circuits and heat transfer during thermal runaway.

Schopferer: In our catapult facility, we conduct impact and crush tests on charged batteries at speeds of up to 60 kilometers per hour. Using mechanical damage tests, such as the nail penetration test, we deliberately damage cells. This allows us to determine when and why overheating or propagation occurs.

Using high-speed X-ray imaging, we visualize the internal processes—in real time. This allows us to determine whether a cell enters a dangerous thermal runaway, ignites, or explodes, and whether the built-in safety mechanisms function. This data and these insights help our partners continuously improve their products. Ideally, we are involved early in the development process.

Lithium-ion batteries currently still dominate the market. Are there alternatives?
 

Schopferer: Battery technologies are evolving rapidly. Sodium-ion batteries are on the verge of a broad market launch. They will likely offer cost advantages due to the easier availability of raw materials. Additionally, they are more environmentally friendly and sustainable, as they contain no lithium or cobalt. Their disadvantage compared to lithium-ion batteries is their lower energy density. Nevertheless, they are of interest for certain applications such as stationary storage or micromobility.

However, new technologies also require new safety standards. In a study conducted with the European Synchrotron Radiation Facility (ESRF) and the Federal Institute for Materials Research and Testing (BAM), we have shown that established safety mechanisms are not automatically transferable to new technologies. They must be adapted to the new battery types.

Schaufelberger: Solid-state batteries are also of high interest. They promise higher energy densities, longer lifespans, and high safety, but they still present many challenges.

What are those challenges?
 

Schaufelberger: The production of high-quality electrodes with optimal material combinations, high cycle stability, and the scaling of the production process from laboratory to series production are challenging. For meaningful safety assessments, at least pre-series cells are required.

What recommendations can you give manufacturers to help them prepare for the future?
 

Schaufelberger: Manufacturers need to gain an even better understanding of safety-relevant processes—from short-circuit initiation to heat transfer via gas and particle flows. This foundation can then be used to build predictive simulation models, which can help shorten development times.

Schopferer: They should definitely review their testing methods and ensure they meet the new requirements. The challenges in battery safety are significant, but they can be overcome with the right preparation.