Control of Chemical Structure in Core–Shell Nanocrystals for the Stabilization of Battery Electrode/Electrolyte Interfaces

Undesired reactions at electrode/electrolyte interfaces impose challenges in the durability of Li-ion battery. Traditional strategies of interfacial stabilization involve coating with inactive oxide films on aggregated powders of active cathode oxides. Despite generating gains in electrode performance, the lack of control of film growth of existing methods limits the ability to design its chemical structure and enhance functionality. The complexity of these coated materials also complicates efforts to define the specific chemical and structural features that determine function. Core–shell heterostructures at the nanocrystal level offer opportunities for precise control of chemistry and homogeneity. This ability is demonstrated with the compositional and structural tailoring of passivating layers based on Al 3+, grown conformally onto LiCoO 2 nanoplates, using thermal treatments. They result in heterostructures from core–shell (LiCoO 2 nanoplates@2 nm aluminum oxide) to LiCo 1– x Al x O 2 gradient structures composed by an Al-rich outer layer on a Co-rich core. While all samples presented improvements in electrochemical performance compared to the bare material, the LiCo 1– x Al x O 2 gradient heterostructure presented the greatest advantage compared to pure aluminum oxide shells. The presence of a high Al/Co ratio at the surface, combined with the structural epitaxy and presence of Li throughout the particle, was considered to be critical to the best electrode properties and electrode/electrolyte interface stabilization. This work advances our ability to build complex heterostructures that both offer engineering solutions and create novel fundamental insight into the origins of battery durability.