The protective coating
of the electrode materials is a known source
of improvement of the cycling performances in battery devices. In
the case of the LiMn2O4cathodes, the coating
with a thin alumina layer has been proven to show performance efficiency.
However, the precise mechanism of its effect on the performance improvement
of the electrodes is still not clear. In this work we investigate
alumina-coating-induced effects on the structural dynamics of the
active materials in correlation to the modified solid electrolyte
interface dynamics. The local structures of coated and uncoated samples
at different galvanostatic points are studied by both soft X-ray absorption
measurements at the Mn L-edges and O K-edge (in total electron yield
mode) and hard X-ray absorption at the Mn K-edge (in transmission
mode). The different probing depths of the employed techniques allowed
us to study the structural dynamics both at the surface and within
the bulk of the active material. We demonstrate that the coating successfully
hinders the Mn3+disproportionation and, hence, the degradation
of the active material. Side products (layered Li2MnO3and MnO) and changes in the local crystal symmetry with formation
of Li2Mn2O4are observed in uncoated
electrodes. The role of alumina coating on the stability of the passivation
layer and its consequent effect on the structural stability of the
bulk active materials is discussed.