Historically, in situ NPD has seen comparatively fewer applications to Li-ion battery research relative to in situ X-ray or synchrotron diffraction (see Ref. Brant et al. [177] for further details regarding in situ X-ray-based studies). This is due to a variety of factors, including the inherent complexities of the measurement tech­nique, sample requirements, and the number of neutron diffractometers available for such experiments. However, in recent years neutron diffractometers and research trends have overcome the perceived difficulty of such complex experiments.

Unlike conventional neutron measurements where, in most cases, only the material under study is in the beam, with in situ methods, everything comprising the device can be in the beam, and thus contribute to the observed signal. For dif­fraction, H can be particularly problematic in the analysis of batteries [178] as the separator (e. g. polyethylene), electrolyte solutions, and the binder are often H-rich. Adding further to the background signal is the liquid or paste-like electrolyte. Therefore, attention has been devoted to custom-made cells for in situ neutron diffraction studies.

Commercial batteries are often produced with minimal quantities of electrolyte to maximise lifetime and avoid the issue of electrolyte leakage. Additionally, the electrodes are often coated on both sides of current collectors, and the overall of quantity of electrodes is significantly larger than that achieved in custom-made batteries. Furthermore, these batteries can be cycled at relatively high rates and are used in “real-world” applications. These considerations can outweigh the detri­mental contribution to the background that H-containing components make and yield significant information on the evolution of electrode structure.

As the challenges in battery design and construction are investigated, we also look toward the best instruments for this task by considering the neutron flux, detector, and acquisition time.