In Situ Investigation of Lattice Oxygen Loss from Preferentially Faceted Electrodeposited LiCoO₂ via Scanning Electrochemical Microscopy

Abstract

Lattice oxygen loss from transition metal oxide cathodes in Li-ion batteries (LiBs) is a key factor responsible in their gradual capacity decline over time. Understanding and mitigating this phenomenon is crucial for the development of next-generation LiBs. The effect of various parameters on lattice oxygen loss, such as cathode chemical composition, has been studied extensively. However, there is a lack of experimental investigation into the lattice oxygen stability across different crystallographic facets within the same cathode composition. Here, we employed in situ scanning electrochemical microscopy (SECM) to investigate oxygen evolution from preferentially faceted, electrodeposited LiCoO2 cathodes. Samples predominantly exposing the (003) basal planes and the (101), (102), (110) fast Li-ion diffusing facets exhibited oxygen evolution at potentials exceeding 3.5 V vs Li+/Li. Finite element simulations helped quantify the flux of oxygen evolution on the first charge cycle to 33±5 pmol/cm2s for the basal plane and 37±9 pmol/cm2s for the faceted samples at potentials above 4 V based on single spot measurements. However, spatially resolved measurements showed that faceted samples exhibited significant heterogeneity in their oxygen evolution, reaching twofold values compared to the basal plane samples at potentials beyond 4.5 V.