Stabilization of high energy cathode-electrolyte interface is required to meet the criteria for the power source and stable cycling performance in Li-ion batteries. [1] The undesired reactions at the interface could be minimized by introducing redox-inactive ions on the surface of active materials without affecting original properties. [2] To demonstrate the roles of passivating layers more effectively, high energy nanocrystals were introduced due to its high surface area that can induce access of charges with electrolytes, accelerating chemical degradation at the interface. [3] A synthetic method based on colloidal chemistry was employed to grow a thin shell enriched in Al³⁺ in the same reaction environment where the particles were grown in dispersible form, ensuring effective coverage of all surfaces. The resultant core-shell nanocrystal consists of active lithium transition metal oxides as a core and enriched Al³⁺ shells as a passivating layers to suppress the unfavorable reaction on the surface. Careful post-synthetic annealing was used to produce the final heterostructures and tailor the specific chemistry of the shells. The modified nanocrystals improved capacity retentions in various conditions, such as elevated temperature and high applying potentials compared to the bare counterpart where a shell is not presented, strongly suggesting a role of protective layers. The chemical identity and specific structural information of the bulk and passivation layers were mainly characterized by a combination of solid state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and X-ray absorption spectroscopy (XAS).

Reference

1. Lee, K. T.; Jeong, S.; Cho, J. Acc. Chem. Res, 2013, 46, 1161-1170.
2. Kim, C.; Phillips, P. J.; Xu, L. P.; Dong, A. G.; Buonsanti, R.; Klie, R. F.; Cabana, J. Chem. Mater, 2015, 27, 394-399.
3. Bruce, P. G.; Scrosati, B.; Tarascon, J. M. Angew. Chem. Int. Ed, 2008, 47, 2930-2946.