Operando microimaging of crystal structure and orientation in all components of all-solid-state-batteries

Solid-state batteries can outperform conventional lithium-ion batteries in terms of energy density and safety, yet their widespread commercialisation remains hindered by challenges in ionic conductivity, interfacial resistance, and manufacturing. A comprehensive understanding of interactions between the electrodes, the electrolyte, and the packaging during battery operation is crucial. Still, it remains overlooked due to the lack of characterisation methods to measure these components simultaneously. Here, we perform a holistic investigation of a compact all-solid-state battery using operando synchrotron 2D X-ray micro-diffraction imaging. We image in real time and simultaneously the lattice parameters and crystal orientation of the dense LiCoO₂ positive electrode material, the Ti current collector and the electrodeposited Li metal at the negative electrode. We reveal that the reaction mechanism of LiCoO₂ depends on the crystal orientation, and that, in dense electrodes as opposed to porous ones, the delithiation is limited by the formation of a Li-rich insulating interface. Li metal is found to form large crystals whose orientation and number change during plating/stripping: from a heteroepitaxial growth on the Ti current collector at the beginning of charge to a random orientation distribution after 3 µm of Li is plated. These results demonstrate the power of X-ray diffraction imaging to link reaction mechanism and grain orientation in multiple battery components during non-equilibrium processes.