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Operando X-rays reveal multi- scale degradation during battery overcharge

• Battery degradation involves processes occurring simultaneously from the atomic to the macroscopic scale. • At beamline BM02, gas analysis was combined with wide-angle and small-angle X-ray scattering to track structural transitions and gas release during battery overcharge. • The results connect gas evolution to structural and nanoscale changes, advancing understanding of failure mechanisms in energy-storage systems.

The challenge

Understanding degradation mechanisms in batteries is essential for extending battery lifetime and reducing the environmental impact associated with their production and recycling. However, battery degradation is complex: it is dynamic, occurs over multiple length scales, and involves the formation of gaseous, solvated, and solid species. To deepen understanding of these mechanisms, correlated operando multiscale characterisation is required. Conventional approaches typically study gas evolution, atomic structure changes, or nanoscale morphology independently, often using different operando cells and techniques. Such methods hinder direct data correlation, as measurements are not performed under identical conditions. To overcome this limitation, an integrated characterisation platform was developed, integrating multiple probes capable of simultaneous measurements [1].

Fig. 59: Correlative OEMS-WAXS-SAXS experimental setup. A gas analysis line is

connected to the pouch cell, which is raster- scanned across a micron-sized X-ray beam at the BM02 beamline. Crystal structure (WAXS)

and nanostructure (SAXS) data are recorded using two sequential detectors.

High-energy-density lithium-nickel-oxide (LiNiO2) positive electrodes and graphite-silicon negative electrodes are key materials for electric vehicle batteries, but present significant safety risks during overcharge. Overcharging causes oxygen release, gas evolution, and structural degradation that can lead to thermal runaway and fire [2]. Understanding these interconnected processes is essential to improving both performance and safety. This study combined simultaneous gas analysis with structural and morphological characterisation during the overcharge of a LiNiO2/graphite-silicon (GrSi) battery to understand how these phenomena are interconnected.

The experiment

An integrated correlative characterisation platform was developed by combining online electrochemical mass spectrometry (OEMS) with synchrotron wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) mapping at beamline BM02 (Figure 59) [3]. A custom-designed LiNiO2/graphite-silicon pouch cell enabled simultaneous gas analysis and X-ray measurements during electrochemical cycling. The cell was continuously raster-scanned using a focused X-ray beam, producing correlated maps of crystal structure (WAXS), nanostructure (SAXS), and gas evolution every six minutes.