Solid-State Synthesis and Electrochemical Electrode Reactions Investigated by In Situ X-Ray Diffraction

<i>In situ</i> diffraction studies can capture transient crystalline phases forming during chemical reactions. Whether the reaction is a chemical solid-state synthesis, or an electrochemical intercalation process within typical layered compounds used as battery electrodes, proper sample environments can nowadays be developed to perform <i>in situ </i>diffraction experiments. Furthermore, <i>operando</i> studies, in the case of batteries, can be used to capture the materials' evolution during the realistic functioning of the device.<br/>In both cases, the time-resolved nature of the experiments allows to obtain a greatly increased amount of information. For example, in the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase [1]. To rationalize that, the competition between thermodynamics and kinetics occurring during the process need to be investigated in real time. Fully determining the reaction pathway potentially is a key requirement to achieve the rational synthesis of target materials [2, 3]. In this presentation, recent examples from our work applying <i>in situ</i> synchrotron XRD to understand the synthesis of relevant industrial compounds such as LiNiO₂[4] and LiCoO₂ (2022, unpublished) will be reported and compared. The use of neutrons as possible probes with Li sensitivity for such reactions will also be demonstrated.<br/>In addition, a recent example of the use of <i>in situ</i> (and <i>operando</i>) XRD to the LiNi_1-yMn_yO₂ (y = 0, 0.05, 0.1, 0.17, 0.25) series of positive electrode materials will be reported [5], where we have ensured a fair comparison of the samples by obtaining an equal amount of delithiation of all samples during charge. We found in particular a significantly decreasing anisotropy (difference in the variations of the <i>a</i> and <i>c</i> unit cell parameters) in the crystallographic lattice change of the materials with increasing y, signifying that Mn-containing compounds yield lower mechanical strain to the cathode composites.<br/><br/>References:<br/>[1] M. Aykol et al., <i>Science Advances</i>,<b> 2018,</b> 4 (4), 148.<br/>[2] Z. Jiang et al., <i>Journal of Materials Chemistry C,</i> <b>2017</b>, 5 (23), 5709-5717.<br/>[3] M. Bianchini, J. Wang et al., <i>Nature Materials</i>. <b>2020</b>, 19 (10), 1088-1095.<br/>[4] M. Bianchini et al., <i>Journal of Materials Chemistry A</i>, <b>2020</b>, 8(4), 1808-1820.<br/>[5] D. Goonetilleke et al. <i>Journal of Materials Chemistry C,</i> <b>2022, </b>https://doi.org/10.1021/acs.jpcc.2c04946