Probing chemical heterogeneity of Li-ion batteries by in operando high energy X-ray diffraction radiography

Uniformity of the crystal structure of battery electrodes inside a commercial prismatic Li-ion battery (LiCoO$_2$|C) with a nominal capacity of 1200 mAh were examined by diffraction of a monochromatic photon beam (60 keV). Selected structural parameters related to lithium concentrations in the positive and negative electrodes were determined averaging over cell thickness on a 1 × 1 mm$^2$ grid, thus resembling an experimental radiography technique with a pixel size of 1 mm$^2$, where the diffraction signal is used instead of attenuation of the photon beam. Non-uniformities in a prismatic Li-ion battery were unambiguously revealed by remarkable differences of the diffraction signals and systematic deviations of structural properties at different scan positions. Observed lithium heterogeneities at nominal state-of-charge (SOC) = 100% state are attributed to SOC deviations caused by the current distribution inside the examined prismatic cell