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X-ray nanodiffraction maps crystal distortions during lithium extraction

• Improving the durability of rechargeable batteries requires understanding how their materials change during operation. • At beamline ID01, nano-focused X-ray diffraction was used to map structural distortions inside single-crystal lithium manganese nickel oxide cathodes. • The results show how lattice imperfections in cathode material contribute to degradation, indicating that controlling them is critical for improving long-term battery performance.

The challenge

Lithium-ion batteries (LIBs) power many everyday appliances and electric vehicles and are critical for storing intermittent renewable energy from solar and wind. However, battery materials inevitably degrade, leading to capacity loss. Improving battery durability therefore requires a detailed understanding of material properties and degradation processes across multiple length scales during operation. The ESRF offers a unique suite of multiscale characterisation tools for this purpose (Figure 61).

The experiment

This study examined an LMNO (LiMn₁.₅Ni₀.₅O₄) cathode, a high-voltage material prone to manganese loss during cycling [1,2]. As LMNO consists of micrometre- sized crystals, degradation mechanisms were probed within individual particles using nano-diffraction X-ray imaging at beamline ID01 (Figure 61b). Operando X-ray diffraction was performed during battery charging using a specialised electrochemical cell with X-ray–transparent windows to capture structural changes accompanying lithium extraction.

Noticeable structural distortions in the crystal caused by a lattice mismatch between regions with higher and lower Li-ion concentrations were observed (Figure 62). Similar nano-diffraction measurements of particles after several hundreds of charge/discharge cycles revealed much more severe distortions of the lattice in some particles, implying that the observed effect accumulates over continuous charging cycles. However, diffraction measurements of the cathode on a bigger scale (several hundreds of micrometres, as shown in Figure 61a) revealed that degradation across particles is highly heterogeneous, with only a subset of particles affected – a fact that highlights the importance of crystal quality in the synthesis of battery cathode materials.

Fig 61: Schematic diagram of two main techniques allowing for multiscale investigations of cathode materials. a) During multi-crystal X-ray diffraction, a relatively large X-ray beam illuminates a number of crystals from the powder, enabling diffraction signals to be

gathered for all of them on the detector. b) For the scanning X-ray diffraction microscopy experiment, the X-ray beam is focused to a much smaller size than the studied particles itself, allowing the scanning of that particle and gathering local diffraction information

from different points on the crystal. c) Scanning electron microscope image of the studied LMNO (LiMn1.5Ni0.5O4) sample.