Turbocharging solid-state battery research: real-time insights unlocked by new sample cell

Solid-state battery research has just been turbocharged by the development of the first sample cell that unlocks the unique real-time insights of operando neutron diffraction at the ILL. This major advancement is the result of a collaborative effort between the ILL and LEPMI laboratory in Grenoble within the framework of the OpInSolid project funded by the French National Research Agency (ANR).

The EU’s commitment to net-zero emissions by 2050 places batteries centre stage – from powering electric mobility to supporting the large-scale integration of intermittent renewable energy. As battery demand soars, so too does the need for research to deliver next-generation solutions that combine high performance, reliability and durability, with sustainability, safety and affordability. While lithium-ion technology has dominated the battery landscape for the past two decades, the next major breakthrough is expected to come from replacing conventional liquid electrolytes with solid-state alternatives. Solid-state batteries have the potential to deliver a step-change in electrochemical performance, offering enhanced safety, higher energy density (allowing the storage of more energy per unit volume or weight), faster charging and longer lifespan.

Neutron techniques are a powerful tool to advance understanding in this rapidly growing field. “When lithium-ion batteries fail, it’s often because lithium ions have got lost somewhere as they migrate through the electrolyte between the negative and positive electrodes during charging or discharging,” explains Ove Korjus, research scientist at LEPMI¹. Neutrons’ particular sensitivity to lithium enables direct visualisation and quantification of these ions. When applied under operando conditions, these techniques unlock the ability to monitor batteries in real-time during operation, revealing crucial insights that might otherwise be missed due to the delay between the event and later ex situ analysis.

Neutron and synchrotron techniques offer complementarity insights into solid-state batteries. While neutrons are particularly effective at detecting lithium and distinguishing between elements close in the periodic table – such as nickel, manganese and cobalt in the electrode material – the advantage shifts when it comes to flux. “The much lower flux at neutron compared to synchrotron facilities means significantly more sample material is required,” explains Korjus. “At the ESRF², just 1 mg of electrode is sufficient, whereas 200 mg was needed at the ILL, despite it being the world’s most intense continuous neutron source! We would have liked to increase the sample mass even further, but the electrodes must be kept as thin as possible to preserve electrolyte ionic conductivity.”

Given the limited sample mass, it was critical that the sample cell required to house the solid-state battery during operando neutron diffraction be as transparent to neutrons as possible, contributing minimally to the resulting collected data. This challenge was addressed by using a titanium-zirconium alloy, which also met the requirement for electrical conductivity. “Though the sample mass was limited with respect to neutrons, it represents a relatively thick electrode for solid-state batteries,” explains Claire Villevieille, CNRS research director at LEPMI and coordinator of the OpInSolid project. “So, the next challenge was to cycle a multi-layer solid-state cell with high electrode loading while achieving electrochemical performance comparable to that of typical laboratory-scale cells.” Further design considerations included maintaining effective separation of the positive and negative electrodes to prevent short-circuiting, integrating an internal pressure application system to support repeated charge/discharge cycles and ensuring airtightness of the cell.