Position‐ and Discharged Capacity‐Dependent Composition of Li _{2‐ <i>X</i>} O ₂ within Cathode Layer of Lithium–Oxygen Battery Probed by Position‐Selective X‐Ray Diffraction Computed Tomography

Using a nondestructive synchrotron‐based position‐selective X‐ray diffraction computed tomography (XRD‐CT), position and discharged capacity dependences of the composition of the discharge products (Li‐deficient Li 2 O 2 ; Li 2‐ x O 2 ) within the cathode of the lithium–oxygen battery (LOB) was investigated. As the discharge reaction proceeded, the discharge product, Li 2‐ x O 2 (Li‐deficient Li 2 O 2 ), was formed and grew not from the lithium anode side where lithium ions are supplied through the separator, but from the gas diffusion layer (GDL) side where oxygen is introduced. Furthermore, the value of x , representing the lithium deficiency in Li 2‐ x O 2 , decreased from the GDL side and eventually reached zero, indicating the formation of stoichiometric Li 2 O 2 . These results revealed that the discharge reaction proceeds preferentially from the GDL side rather than the lithium anode side.